Wireline Works Tech-Bulletins

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Technical Bulletins

Technical Bulletin Number – 001

"Quality You Can Pull On..."

Calculating Cable Length by Measuring Conductor Resistance L1 R1 T1 r

= = = =

Length of new cable installed on the Drum in feet (ft). Total resistance of center conductor of installed cable in Ohms (Ω) Temperature of cable when R1 is measured in degrees Fahrenheit (°F) Resistance of this cable per foot at 65°F. This factor should be calculated and recorded in the cable log book.

To convert from metres to feet: 1 foot = 0.3048 metres To convert from Celsius to Fahrenheit: T°F = (T°C x 1.8) + 32 r

= (R1 / L1) x [(302.5) / (234.5 + T1)]

Example: L1 = 25,500 Feet R1 = 265.4 Ω T1 = 75°F r = (R1 / L1) x [(302.5) / (234.5 + T1)] r = 0.01017 Ω/ft This value of “r”, should be recorded in the Cable Log Book. As sections of cable are cut off, the remaining length, “L”, of cable on the drum can be calculated using the recorded value of “r”, the Resistance “R” of the centre conductor of the remaining length, and the Temperature, “T” of the remaining length of cable. L

= (R / r) x [(302.5) / (234.5 + T)]

Example: r = 0.01017245 (Ω/ft) R = 195.4 Ω T = 92°F L = (R / r) x [(302.5) / (234.5 + T)] L = 17796.7 The length of the cable is now 17,796 feet. To obtain the best results, it is recommended to use a Fluke or equal quality 4 or 5 digit 1% type Ohmmeter with good leads. It is Important to use the same Ohmmeter to establish the value of “r” and later measurements of “R”.

05/2005

Technical Bulletin Number – 002

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Locating Electrical Leaks (Part One) Electrical leaks, or the break down of the insulation of the conductor, are typically caused by one of the following reasons: • Physical Damage: The cable, jumped the sheave wheel, over-run in the hole, drum crush, kick back from a large gun, cut-in while spooling cable, or other accidental mechanical damage. • Excessive Temperature: Operating the cable at bottom hole temperatures in excess of the maximum temperature rating of the cable. High tensions at maximum temperature. • Excessive Tension: Repeated tensions over 60% of rated breaking strength or a little as one pull in excess of 75% of rated strength of the cable. • Manufacturing Defects: Inner armor coverage less than 97%, Non uniform spacing of inner armor wires, eccentricity in conductor insulation, Crossed inner armor wires, Tape lap joints or string filler knots in multi-conductor cable. There are basically three different types of electrical leaks: • “Dead short”: The resistance , or leak, is less than 100 Ohms. • Hi resistance: The leak is as high as 20 Meg-Ohms. • Intermittent leak: This is the worst type as the leak at times disappears. • Wet leak: Any of the above 3 types of leaks can have moisture present which can complicate the location of the leak. Moisture in the leak can generate a small voltage between the copper conductor and the zinc of the armor wire, which will give misleading resistance measurements. The fastest way of locating an electrical leak is to “burn it out” with a high voltage, high current source* and in doing this you dry the leak and reduce it to a “ dead short”. There are several methods of easily locating a “ dead short”. When it is known that the cable has been abused in some way, tension or temperature, then burning out the leak is the best procedures. If, however you have a fairly new cable and a factory defect is suspected, the burn out method should not be used as it completely destroys the area around the leak and the exact cause of the leak can not be determined. There are methods of locating leaks within a few inches without first burning out the leak as will be covered in later technical bulletins. Part-1, Method for locating a “dead short” leak. A dead short leak, as described above, is when the copper conductor is in direct contact with the armor or the resistance between the conductor and armor is less than 100 ohms. The only instrument required is an accurate digital ohmmeter that reads to at least 0.1 Ohm. Before any leak location process is started be sure that both ends of the cable conductor are completely disconnected from any tools , collector, etc. and clean! After both ends of the conductor are cleaned, using the digital Ohmmeter, measure and record, the following resistances. • R: Total conductor resistance, end to end, Ohms. • Rt: Resistance between conductor & armor measured at the Truck end, Ohms. • Rw: Resistance between conductor & armor measured at the whip end, Ohms. • L: The total length of the cable, feet. To be sure your problem can be classified as a “dead short”, make the following calculation: ((Rw + Rt) - R) < 300 Ohms If the this calculation is greater than 300 Ohms, you do not have a “dead short” and you should use another method of locating the leak, (Part 2 & 3), or “burn out” the leak to obtain a more direct short. If the above calculation results with a value less than 300 Ohms then the leak location can be calculated as follows: • Lw: Distance of the leak from the whip end of the cable, feet. • Lt: Distance of the leak from the truck end of the cable, feet. Lw = [ R + Rw – Rt ] x [ L / 2R ] Lt = [ R + Rt – Rw ] x [ L / 2R ] Example: Cable length: L R Rw Rt

= = = =

20,500 feet 220.5 Ohms 165.0 Ohms 325.5 Ohms

Leak Location: Lw = [ 220.5 + 165.0 – 325.5 ] x [ 20,500 / 2x220.5 ] = 2,789 feet from whip end Lt = [ 220.5 + 325.5 – 165.0 ] x [ 20,500 / 2x220.5 ] = 17,711 feet from truck end Methods for locating high resistance electrical leaks and eliminating the effects of a wet leak will be covered in later Technical Bulletins.

05/2005

Technical Bulletin Number – 003

"Quality You Can Pull On..."

Locating Electrical Leaks (Part Two): Leak Locator Bridge The most common locations of cable electrical leaks are: 1. Within 1000 feet of the whip end due to physical damage. 2. A drum crush, two or three layers down on the drum. 3. Failure at the “dog knot” where the drum end of cable passes through the flange. 4. Damage on the bed layer due to installation problems. The simple leak locator bridge is one of the fastest methods of locating the approximate location of a leak. This is important as it will quickly indicate whether the leak can be cut off the whip end or the cable will need to be strung up and pulled down to a location on the drum. The simple leak bridge circuit, shown below, can locate leaks within about +/200 feet if the leak is less than 10,000 Ohms. More sophisticated leak bridges can locate a leak as high as 1 MegOhm to an accuracy of +/- 50 feet.

• Check and adjust the ZERO on the meter with the small screw on the meter face. • Plug one test lead into the RED “WHIP” socket and clip this lead to the WHIP end of the cable. • Plug one test lead into the BLACK “TRUCK” socket and clip this lead to the TRUCK end of the cable, • Plug one test lead into the GREEN “ARMOR” socket and clip this lead to the cable ARMOR. • Rotate knob “A” to read 50. • Connect the AC power cord and turn power ON. Operation: • With the power on, the meter needle should deflect off of zero. • If a very small or no deflection occurs, starting with button “1” hold down and observe the deflection of the meter. • If the meter deflects to the left, WHIP, rotate knob “A” counter clockwise, until the meter reads zero. • If the meter deflects to the right, TRUCK, rotate knob “A” clockwise, until the meter reads zero. • Hold down button “2” until the meter again reads zero. Repeat this with button “3” held down. • Record the final dial reading, 0.252 in the example shown below.

Remember before any type of leak location procedure is started be sure that both ends of the cable are completely free and clean. When the Micro-ammeter reads zero, the percentage indicated on the potentiometer will be the same as the percentage of the cable length to the leak. Just how this works can be further understood by referring to the set up and operation of a prototype leak locator instrument. The leak bridge shown here is available from CSR in Rosenberg, Texas. Web site: www.csrusa.net Operating Instructions Leak Locator Bridge

Leak Location Multiply the dial reading, 0.252 by the length of the cable. For example with a cable length of 20,000 feet, the leak is located at: 0.252 X 20000 = 5040 feet from WHIP end

Setup: • Check that both ends of the cable are free, clean and NOT connected to anything. • Turn power switch OFF.

Accuracy • This type of instrument will only locate a leak to within +/200 feet. • For maximum accuracy: 1. Burn out the leak to the lowest resistance possible 2. Be sure all test leads fit firmly in sockets 3. The lengths of the WHIP & TRUCK test leads must be equal. 4. The test leads should be as short as possible • Check for a “ wet leak”. This is done by measuring the resistance of the leak with an Ohm meter and then reversing the leads of the Ohm meter and see if the leak resistance is the same. If the leak resistance is the same you are ok. If there is a significant difference between the two readings, you need to dry out the leak with a “burn out box”. 05/2005

Technical Bulletin Number – 004

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Precise Method for Locating Electrical Leaks The most common method of locating electrical leaks in a wire-line is to “burn out” the leak until the conductor is shorted to the armor and then use a digital ohmmeter to determine an approximate location of the leak. This is a quick and easy method of finding a leak; but, there is a disadvantage. When burning out the leak, it can melt the copper, plastic and sometimes burns the inner armor wires. If this occurs it can be impossible to determine the cause of the original leak. If it is important to determine exactly what caused the leak or if the high voltage equipment is not available to burn out the leak, then a alternate leak locating procedure is required. This procedure will locate leaks that are as high as 10 Meg-Ohms and locate the leaks within +/-1 inch. To use this method, the following shop conditions must exist: • The shop is setup to reel the cable from a metal pay off or truck drum to a metal take up shop drum. • The pay off frame is electrically insulated from the take up stand. • A POWER SOURCE, such as a 6 or 12 volt car battery or a battery charger is available, with leads long enough to connect the power between the pay off and take up stands. • A collector is mounted on the pay off, truck, drum and is called TRUCK DRUM. • A DC voltmeter that will indicate plus and minus voltages and has 200mv sensitivity and 10 Meg Ohms input impedance is required. • A set of well insulated test leads to reach between the meter, the collector on TRUCK DRUM and one test lead, fixed with a copper hook, to reach the cable.

(Pay-off)

(Take-up)

1. If the meter indicates a POSITIVE voltage, the leak is towards the SHOP DRUM. 2. If the meter indicates a NEGATIVE voltage, the leak is towards the TRUCK DRUM. Setup Procedure • String the cable between the pay off, truck, and shop drums. Going around a sheave wheel is ok as long as this sheave wheel is electrically insulated from both pay off and take up drums. • Connect the leaking conductor to the collector on TRUCK DRUM.

• Be sure the insulation on the conductor is clean. • The other end of the leaking conductor, on the SHOP DRUM, must be free and clean. • Turn the meter on, set it at the lowest dc voltage range, 200 mv. • Connect the Meter NEGATIVE, long test lead to the collector, mounted on the TRUCK DRUM. • The test lead with the copper hook is connected to the Meter POSITIVE, and the copper hook is hung on the cable between the pay off and take up. • Connect the POSITIVE lead of the POWER SOURCE to the frame of TRUCK DRUM. • Connect the NEGATIVE lead of the POWER SOURCE to the frame of SHOP DRUM. • DO NOT CONNECT THE POWER SOURCE DIRECTLY TO THE CABLE ARMOR, ONLY TO THE FRAME. The power source can arc when connected and burn an armor wire. Leak Location • With all of the connections made in accordance to the SETUP PROCEDURE listed above, place the copper hook from the meter positive in contact with the cable armor. • The meter will indicate a positive voltage if the leak is on the SHOP DRUM • The meter will indicate a negative voltage if the leak is on the TRUCK DRUM. • The cable is then spooled in a direction to move the leak off of the drum it is located on. • The copper hook, connected to the meter positive terminal, is held in contact with the cable armor as it is being spooled. • When the leak comes off the drum, the meter voltage reading will start to decrease. • When the meter reads zero, the leak is located directly under the copper hook location. • If the meter voltage changes polarity, you have passed the leak. Connection Summary • TRUCK DRUM has the collector • Connect leaking conductor to the collector • Connect NEGATIVE METER lead to the Collector TRUCK • Connect the test lead with the copper hook to the METER POSITIVE • Connect POSITIVE power source to frame of TRUCK DRUM. • Connect NEGATIVE power source to frame of SHOP DRUM Miscellaneous • Be sure the plastic insulation is CLEAN on both ends. • The pay off and take up stands must not be connected mechanically. • Do not connect the power source leads directly to the cable armor. This connection can spark when connected, burning cable armor. 05/2005

Technical Bulletin Number – 005

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Problems in Locating Electrical Leaks Bulletins 002, 003, 004 have described three methods of locating electrical leaks in electro- mechanical cable. There are four problems which when encountered increase the difficulty in locating the leaks. 1. Wet Leaks: An electrical leak occurs when there is a rupture in the plastic insulation surrounding the copper conductor. Sometimes there is direct contact between the copper and the armor wires, (dead short), other times there is burnt plastic from the break down process that leaves a carbon trail between the copper and armor, and in other cases there is moisture in the cable between the copper and armor forming a “wet leak”. The armor wires are covered with a Zinc coating. Zinc is above and Copper is below Hydrogen in the electromotive series of metals, so when they are in a conductive medium, such as salt water, there will be a voltage generated between them. In the case of Zinc and Copper the voltage is about 0.83 volts. If you would like to run a little physics experiment, simply clip a short piece of armor wire to the negative lead of a digital voltmeter and the positive lead to a piece of copper wire and place them in a glass of salt water. The meter will indicate a voltage in the range of 0.83 volts. This voltage in a leak can significantly distort the location of the leak. To determine if you have a wet leak, first measure the resistance of the leak and then reverse the leads of the ohmmeter. If you have a wet leak there will be a significant difference between the 2 resistance measurements. The wet leak can be dried out by repeated application of voltage from a Hi-pot or a “ burn out box”. If you are not equipped to burn out the leak, then using the resistance method, (Technical Bulletin 002), calculate the distance to the leak, Lw, and then reverse the polarity of the Ohmmeter and again calculate the distance to the leak Lw’. Take the average of these two values, (Lw +Lw’)/2 and this will be the correct location. Some leak locator bridges have a polarity switch built in to obtain the values of Lw and Lw’. Again the correct location will be the average of the two readings. If a reversing switch is not included, then swap the TRUCK and WHIP connections to get the value of Lw’. Again the correct location will be the average of the two values. 2. Very High Resistance Leaks: are leaks of greater than 10 Meg Ohms and require the repeated application of Hi-pot voltages of several thousand volts. Once the leak is less than one Meg Ohm, the burn out box can be used to reduce the leak to several hundred or less Ohms. As mentioned in previous Bulletins, the “ burn out box” is a DC power supply with an adjustable output up to 600 or 800 volts with a current capacity of 1 to 3 amps. This type of power supply is LETHAL, so must be used very cautiously!!! 3. Multiple Leaks: There is no straight forward way of locating multiple leaks. Generally when multiple leaks occur they are all fairly close together. The best approach is to use any of the described leak locating methods and cut the cable and check both pieces of cable using the same locating methods and cut again. After all the cutting, be sure to Hi-pot both lengths of cable, to ensure they are clear of leaks before they are spliced back together. 4. Intermittent Leaks: are leaks that are not always present. These type of leaks typically are noticed during a job, and later when the cable is brought to the cable shop, the cable tests clear. If the leak does not appear when the cable is tested at 1,000 VDC, then to get the leak to reappear the cable is spooled back and forth in a number of ways while watching the ohmmeter to see when the leak occurs. Some shops pass the cable around a capstan, through a post former or around several sheave wheels. Spooling is done at very low and then at very high tensions. Once the leak reappears the spooling is stopped and the leak is located using one of the standard methods.

05/2005

Technical Bulletin Number – 006

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Increase in Cable Resistance with Wellbore Depth The temperature of the earth increases with depth. The rate of temperature increase can vary from 10 to 25 degrees Fahrenheit for each one thousand feet increase in depth. With the increase in temperature there is an increase in the resistance of copper conductors. The resistance of copper, in fact, will double at a temperature of 370°F. This higher conductor resistance will directly increase the attenuation of signals and increase the power requirements to operate down hole tools. The plot shown below shows the overall increase in conductor resistance as a tool is lowered in the hole. For this example the total conductor resistance of a 25,000 foot Dakota Cable, type 7K-464-FTD, is shown as the tool is lowered in a 20,000 foot well with bottom hole temperatures of 500°F and 300°F.

Conductor Resistance at Depth (Ohms)

Conductor Resistance Versus Depth 400

500°F

350

300

300°F

250

200 0

5

10

15

20

Depth – 1,000s of Feet

Graph is based on the following formula Ts + 234.5 + R=r

(L - d)

(234.5 + Ts)

d (Tb - Ts) Hd 2

+d

(234.5 + 68)

(234.5 + 68)

For the above graph the following values were used R = Total conductor resistance – Ohms. r = Resistance per 1000 feet at 68°F, (20°C) – Ohms/Mft, (9.8Ohms/Mft). L = Total length of cable – Mft., (25Mft). d = Depth of cable in bore hole – Mft. Hd = Hole depth to bottom – Mft., (20Mft). Ts = Temperature at the surface – degrees F, (75°F). Tb = Bottom hole temperature – degrees F, (300°F & 500°F). To convert from metres to feet: 1 foot = 0.3048 metres To convert from Celsius to Fahrenheit: T°F = ( T°C x 1.8 ) + 32

12/2005

Technical Bulletin Number – 007

"Quality You Can Pull On..."

Stuck Point Location When a cable becomes stuck and will not move at the recommended maximum allowable tension, then the first step in deciding what action to take is to determine where the cable is stuck. In cased hole work it is most commonly, but not always, the tool that is stuck. In open hole operations, there is always the problem of the cable becoming key-seated in the bore hole wall. In any situation it is best to make a quick check of the depth to the stuck point before deciding on the best action to take. The quick procedure for locating the approximate depth of the stuck point, (Ds) is as follows: • • • • • • •

Pull on cable to remove all slack and put the cable under strain. Note and record the indicated depth from the measuring device, (D1). Note and record the tension in the cable. Increase the tension exactly 1000 pounds (4.44 kN) & record the indicated depth, (D2). Calculate the depth of the stuck point: Ds = (D1 - D2) / K (1000 feet). K is the stretch coefficient of the cable, which is listed in the Wireline Works Catalogue, ft/Kft/Klbs. To convert from metres to feet: 1 foot = 0.3048 metres

Nominal Values of Cable Stretch Coefficients: Cable K

OD-Inches ft / Kft / Klbs

3/16 3.0

7/32 2.2

1/4 1.9

9/32 1.6

5/16 1.2

3/8 1.0

7/16 0.70

15/32 0.77

0.49 0.60

Example Cable type-Dakota 1-R-322-FAH, 5/16” Mono-cable ; K = 1.2 Cable becomes stuck at an indicate depth of, D1 = 16500 ft. With the cable under strain the line tension is = 3,300 lbs. The tension is then increased to 4,300lbs and the indicated depth is D2= 16480 ft. Ds = (D1 - D2)/K = (16500-16480) / 1.2 ( 1000 ft) = 16,600 feet In this example the stuck point depth is close to the indicated tool depth, so it is the tool that has become stuck.

Depth Corrections If a more accurate stuck point is important, then the following factors can be considered: • The stretch, ( D2-D1) when measured at the truck includes the stretch in the cable from the truck to the well head. A more accurate method of measuring the stretch is to mark the cable at the well head an then measure the stretch when the tension is increased. • If the rig-up distance is known, it can be subtracted from the calculated depth based on measurements of stretch at the truck. • For well seasoned cables the stretch coefficient should be reduced by 5%. • In very deep hot holes the effective value of K can increase by 10%. • If there are reasons not to increase the tension by 1000 lbs, then just increase the tension by 500 pounds and then take the value of Ds. calculated using the above formula.

05/2005

Technical Bulletin Number – 008

"Quality You Can Pull On..."

Cable Breaking Strength New and properly maintained Dakota cables have been designed and manufactured to have a breaking strength that you can depended on. This bulletin will discuss these cables and how field operating conditions effect breaking strength. A later bulletin will discuss the mechanical failure or reduced breaking strength of cable due to effects such as fatigue, acid, H2S, corrosion and wear.

result from allowing the cable to “free fall” into the hole and coming out of the hole at speeds that cause excessive high tensions; improper sheave grove size or sheave alignment can also contribute to loosening the outer armor. When the outer armor has become loose it is important to have a cable shop “ normalize” and post-form the cable to tighten the outer armor and restore its normal breaking strength.

The breaking strength of cable, listed in the Wireline Works catalog, is the guaranteed minimum strength at which the cable will break when the ends of the cable are prevented from rotating. When a cable is loaded, with no rotation allowed, the outer armor wires are stressed slightly more than the inner armor wires. For this reason when a cable breaks with ends fixed, the outer armor wires will always break first and the inner armor wires stretch out before they break.

Dakota cables are designed to exceed the catalog breaking strength. All incoming armor wire has certified tensile strength. In addition Wireline Works routinely tests the wire and finished cables to verify the strength.

Oilfield cables are constructed with two layers of contrahelically applied armor wires. Under load each layer of wires develop torque. The torque developed by the inner armor is in opposition to the torque of the outer armor. The torque developed by each layer of armor wires is determined primarily by the total area of steel in each layer and the distance of the wires from the cable center. The outer armor wires are always further from the cable center than the inner armor and for practical reasons the outer armor layer has a greater area of steel. The outer armor layer, therefore, develops much greater torque than the than the inner armor layer. This imbalance in torque can be partially but not completely offset by adjusting the lay angles of the inner and outer armor wires. If a cable under load is free to rotate, such as a cable hanging in a vertical cased hole, the dominant torque of the outer armor wires will cause the cable to rotate in such a direction as to unwind the outer armor and reduce its stress. As the outer armor wires unwind, the inner armor wires are forced to wind tighter and this increases the stress in the inner armor. If allowed, this unwinding will continue until the torque between the layers is equal and when this occurs the stress in the inner armor is much higher than in the outer armor. When a cable is free to rotate or is forced to unwind by improper operating conditions the breaking strength is significantly reduced and when it does break, the inner armor will break first. and then the outer armor wires will stretch out before they break. In normal operations, with proper tensions going in and out of the well, the lower portion of the cable, if free to rotate will unwind in proportion to the tension but due to friction in the borehole, there is less unwinding near the surface, so the cable breaking strength at the surface is close to “ ends fixed” strength. The breaking strength will be reduced further by field operations that force the cable to unwind. This includes: trying to control pressure with a tight pack-off instead of using more flow tubes; wide cable tension variations that

05/2005

Calculating Cable Breaking Strength EXAMPLE - Dakota Cable type 1-R-322-PH ( units-- inches, square inches, psi, pounds, degrees) D = 0.322 - Cable diameter do=0.0445 - Outer armor wire diameter Do= D - do = 0.2775 - Pitch diameter outer armor layer di = 0.0445 - Inner armor wire diameter Di = Do - do - di = 0.1885 - Pitch diameter inner armor layer Dc= Di - di = 0.144 - Effective core diameter after compression Ni = 12 - Number of inner armor wires No= 18 - Number of outer armor wires Ai = Ni(π/4)di2 = 0.018663 - Total cross sectional area of all inner armor wires Ao= N0(π/4)do2 = 0.027995 - Total cross sectional area of all outer armor wires Li = 1.50 - Inner armor lay distance Lo= 2.50 - Outer armor lay distance sinαi = πDi / [ (πDi )2 + ( Li )2 ]1/2 = 0.3672 sinαo = πDo / [ (πDo )2 + ( Lo )2 ]1/2 = 0.3293 cosαi = Li / [ (πDi )2 + ( Li )2 ]1/2 = 0.9301 cosαo = Lo / [ (πDo )2 + ( Lo )2 ]1/2 = 0.9442 αi = 21.54 - Inner armor lay angle

αo = 19.22 - Outer armor lay angle P = 0.33 - Poisson’s ratio for plastic S = 270,000 - Wire tensile strength

Breaking Strength - Ends Fixed σF = [ cos2 αi - P(Dc / Di )sin2 αi] / [ cos2αo - P(Dc / Do)sin2 αo ] =0.9521 - armor stress ratio, ends fixed BF = S[ σF ( Aicos αi ) + ( Ao Cos αo ) ] BF = 11,370 - Calculated minimum BF = 11,200 - Catalog minimum Breaking Strength - Free Rotation σR = [ AiDisinαi ] / [ AoDosinαo] = 0.50496 - armor stress ratio, ends free BR = S[ ( Aicos αi ) + σR ( Ao Cos αo ) ] BR = 8,120 - Calculated minimum BR = 7,900 - Catalog minimum

Technical Bulletin Number – 009

"Quality You Can Pull On..."

Drum Crush The term “drum crush” refers to a cable electrical failures that occur as a result of the cable being crushed, smashed or distorted to such an extent that the armor wires press and distort the plastic insulation and in some cases cut through the insulation and contact the conductor. It is possible to have the conductor insulation distorted to such an extent that it affects the signal transmission characteristics of the cable with out an actual electrical short. These failures are caused by cables at high tension being spooled over cable spooled at abnormally low tension, cable installed with an incorrect tension profile or cable that is operated in a manner to cause excessive rotation. For these reasons a more correct term for this type of failure would be “Cable Crush Failure, ( CCF)”. CCF, never occurs on the whip end of the cable. Typically the failures are found at a minimum of 4 or 5 layers down and more commonly deeper than that. Failures can and often do occur in layers of cable that have never or not recently been off the drum. An important characteristic of CCF is that the failure frequently does not occur immediately. For a failure to occur the plastic insulation must cold flow under pressure and this can be a slow process. A CCF condition in some cases may have been setup several jobs, days or even weeks before the actual failure does occur. It is this time lag that makes it difficult to always identify the actual cause of the failure. Factors that can contribute to CCF include: 1. Poor drum cable entry hole. 2. Irregular drum core. 3. Spreading of drum flanges. 4. Incorrect tension profile on initial cable installation. 5. Single break cable installation. 6. Loss of normal cable tension in field operations. 7. Excessive cable rotation. 8. Low or non uniform cable inner armor coverage. A further explanation of these failures: 1. A rough or bad angle of the cable entry hole in the drum can result in a CCF from the pressure of all the wraps on the drum. This is a special case and is easily identified. 2. Irregularities in the diameter of the drum core results in irregularities in the spooling pattern which causes pressure points on the cable and distorts its shape. When the cable shape is distorted, it generates gaps in the inner armor permitting easier cold flow of the plastic. 3. When the drum flanges spread there is as much as half of the diameter of the cable on each side of the top layer then there is a situation where the cable can cut in. When this occurs, the cable shape is distorted resulting in easier plastic cold flow. 4. There is no “one size fits all” when it comes to installing a cable on the drum. The correct tension profile that should be used depends on the type of cable, the cable length and expected depth of operations. In general after the bed layer is established the spooling tension is increased each layer for 3 or 4 more layers up to a tension of about 1/3 of the cable breaking strength. This tension is maintained for half the cable length after which the tension is reduced each successive layer. This is just a very general rule and experienced cable service men in each area know how to adjust these tensions for best spooling. If too much installation tension is used in shallow hole areas, then the cable will not spool properly at the low tensions in shallow operations. If the installation tension is too low, when installing a cable to be used in deep hole operations, then the problem is more serious as CCF can result. When the installation tension is low, and the spooling tension coming out of the hole is high it can result in a CCF. The failure will typically occur several layers down on the drum and at a cable cross over between wraps or at the flange where the cable moves from one layer to the next. 5. When a cable is spooled on a drum the cable must move over one diameter distance for each wrap. If this move is accomplished at one point in the wrap it is called a single break spooling. All qualified cable spoolers now use the double break spooling method, which moves the cable half a cable diameter midway around each wrap. The single break results in a more sever distortion of the cable armor making it more susceptible to a CCF by over laying layers. 6. One frequent causes of a CCF resulting from field operations is re-spooling cable back on the drum after loss of normal cable tension. A common cause of loss of cable tension is over running the hole bottom. When this occurs it results in several wraps of the cable going back on the drum at low tension, followed by the high tension of cable when pulled off of TD. This problem has become more frequent because of deviated holes, where it is necessary to approach TD very 05/2005

Continued on next page

Technical Bulletin Number – 009ii

"Quality You Can Pull On..." slowly to avoid over run. The cable can also loose normal tension when any restriction is encountered going in the hole. When this over run occurs the cable will start back on the drum at lower tension than the subsequent layers. If this tension differential is too great, it sets up a condition for a CCF. As explained above this failure is usually not immediate and therefore if a cable has been over run it might be saved by bringing it to a cable shop and have a normal tension profile reestablished or by operating the cable in a deeper hole very soon after the previous problem. Any other situation that causes a loss of normal spooling tension coming out of the hole, such as clamping off the cable to correct a spooling problem or clamping off at a side entry sub, can also lead to a CCF. There are some radical operating conditions where the friction in the hole and tool are such that a wide variation of the in and out tension can not be avoid. In these cases special powered sheave or capstans must be used to reduce the tension differential and to avoid cable crush. 7. One factor in the ability of a cable to withstand cable crush is the “hoop strength” of the armor wires. This is greatly reduced when the outer armor unwinds and becomes loose. If the end of the cable is free to rotate then the outer armor will try to unwind in proportion to the tension on the cable. This is the most frequent cause of failures in pressure cable. a. The cable should never be spooled out of the hole at a speed greater than a speed that results in a tension greater than 125% of the static tension at that depth. Higher tensions result in excessive unwinding of the outer armor. Further, going into the hole the speed should never be less than that speed that maintains a tension greater than 75% of static tension. Failure to follow these rules will cause the cable to progressively unwind the outer armor setting up a condition for CCF. When cables are operated outside these limits, the cable should be brought into a cable service center for normalizing, (tightening the outer armor), and post forming. when the outer armor becomes loose. Examining the whip end of the cable, if you can easily move the outer armor with your finger nail or a small screw driver, then it is time for service. b. Coming out of the hole the cable unwinds and going back in the hole the cable attempts to tighten back up. If a spring centralizer is used going into the hole a swivel head must be used to avoid sever unwinding of the outer armor. c. The amount a cable unwinds under free conditions, depends not only on the tension in the cable but also the friction between the armor layers. For this reason seasoned cables with mud and corrosion products between the armor layers will rotate less and are less subject to CCF. New cables, however rotate very easily and new cable used in high pressure wells, with grease in flow tubes, must be carefully checked for loose outer armor. It would be good practice to have a new pressure cable brought to a service center to have the armor tighten after the first 20 or 30 operations and thereafter when the outer armor becomes loose. d. Alloy cables used in sour gas operations, represent a special problem. The alloy armor does not rust or produce corrosion byproducts and these cables are normally used with high pressure grease in the flow tubes, so these cables rotate more freely throughout the life of the cables. These cables MUST be brought into the cable shop regularly for normalizing and post-forming. Good practice for these alloy cables would be to have the armor tightened every 20 operations throughout the life of the cable. e. Cables can be forced to unwind when pulled through a tight packer, dragging on any fixed object, run over a sheave wheel that does not have the proper grove or the sheave and truck are not properly aligned. Any forced unwinding of the cable further reduces its resistance to CCF. f. Dakota cables are manufactured with a special, patent pending, compound called TCI, (torque, compression inhibitor), that is placed between the armor layers. The material results in new cables that have sufficient friction between the armor layers that a new Dakota Cable will closely act like a seasoned cable and will rotate 50% less than a typical new cable under similar conditions. 8. In the manufacture of Dakota cables careful attention is paid to the inner armor coverage. Coverage is how completely the surrounding inner armor wires cover the plastic core. This coverage is maintained between 98% and 99%. This range of coverage provides the maximum protection to the core to withstand CCF and still provides the necessary gaps to allow the cable to bend. It is also important that the inner armor wires are spaced evenly around the core. At Wireline Works the inner armor spacing is carefully controlled and inner armor wires are pressed into the core so that this spacing is maintained through the final armoring operation. When a CCF occurs the inner armor coverage should be checked to determine if it was a contributing factor. The inner armor coverage should be checked on a new section of cable as once the cable shape is distorted the coverage can not be judged. The cost of cable and more importantly the cost of a cable failure on a job are so great, that the cost of bringing a cable to a service center to have the armor tightened and the proper tension profile reestablished, is minor by comparison. When ever a cable has encountered any of the conditions described above where a CCF could result, get your truck to a service center before there is a failure.

05/2005

Technical Bulletin Number – 010

"Quality You Can Pull On..."

New Cable – Care & Treatment To get the maximum trouble free service from a cable, it very important to give special consideration to how a new cable is treated on its first few runs in the field. During the manufacturing of a cable the tension is only a few hundred pounds, the cable is passed from one reel to another so no rotation is possible and the temperature is always moderate. In field operations the cable is under very high tension, is free to rotate, and subjected to very high temperatures. In field operations the higher tensions and temperature cause several important changes in the cable: • When a new cable is first lowered in a well, the tension on the cable generates a torque and the cable end needs to rotate to relieve this torque. If the end is carrying a tool that can easily rotate the cable will spin out hundreds of turns to relieve this initial torque and become “normalized”. The amount of rotation depends on depth, tension and type of cable. • During manufacturing, the inner armor wires are partially embedded into the plastic core by means of pinch rollers or pre-form rollers. With the high tensions in field operations the armor wires exert an increased radial pressure on the core causing further embedment in the core resulting in a reduction in diameter. Higher down hole temperatures soften the plastic which will cause this diameter reduction to occur more rapidly. When the inner armor wires are “fully embedded”, the diameter of the cable will stabilize, which normally occurs in 20 or 30 operations. In the case of monocables the diameter reduction is only a few thousandths but unless the cable is allowed to rotate it will result in loose outer armor wires which can accumulate into a “bird cage”. • When the effective core diameter is reduced due to embedment, the armor wires wrap around this smaller diameter, resulting in an increase in cable length. • Cable can also be forced to excessively unwind as a result of using a hydraulic pack-off to control pressure, not enough clearance in flow tubes, poor truck and sheave alignment or an incorrect sheave groove. Cables forced to unwind have a reduced breaking strength, are more susceptible to drum crush and loose outer armor wires that can be ”milked” into a “bird cage”. A typical new cable is more susceptible to all of the problems associated with cable torque and rotation as there is minimal friction between the inner and outer armor wires. After a number of field operations the spaces between the armor wires become filled with mud and corrosion byproducts which increases the friction between the armor layers reducing the problem caused by forced cable rotation. • During the manufacture of DAKOTA cables a special material called TCI is applied on the inner armor layer to fill the interstitial spaces between the inner and outer armor wires. This compound not only controls the fluid and gas passage between armor layers but by the inclusion of sharp particles the friction between the armor layers is significantly increased, reducing cable rotation. A new DAKOTA cable with TCI will act more like a seasoned cable. Based on the above explanations, here are a few DO’s and DON’T’s that should be observed when breaking in a NEW cable: DO: • Run in and out of the well at half the normal speed. • Run .004” clearance in flow tubes. • Use sheave wheels with the proper grove size. DON’T: • Run tools that restrict cable rotation. • Run in deviated holes. • Apply any pressure with a hydraulic packer.

05/2005

Technical Bulletin Number – 011

"Quality You Can Pull On..."

Alternate method of leak location It should be noted that no single method of leak detection is fool-proof. Therefore it is highly recommended that more than one technique be used to provide confidence in the location of the leak.

• Measure the voltage between the armor and the conductor at the Collector end, Vc. Measure on cable ground Whip End Vc Collector End

The method described below is quick, easy and will locate a low resistance leak within +/-50 feet. This is usually close enough for service and repair. To use this method accurately, you will require a digital multi-meter (DMM) with a 4+ digit display and an input impedance of 10 Meg-Ohms or greater. Most quality DMM's meet these requirements but there are some lower quality DMM's with only a 3 digit display and a 1 Meg-Ohm input resistance.

The procedure is as follows: • Disconnect the leaking conductor from the collector and connect a 6 or 12 volt car battery between the conductor at the whip end and collector end. • Measure the battery voltage, at the cable ends, Vb, not at the battery terminals. * Whip End Battery Leads Collector End

+

Vb

–

Battery DMM *Measure at cable ends on the conductor

–

• Measure the voltage between armor and the conductor at the whip end, Vw. Whip End

Vw Collector End

To get started the total length of the cable, L, must be known. (See Tech Bulletin - 001). This method for locating the leak assumes the entire length of cable is on the truck drum.

+ Battery

+

–

Battery

Measure on cable ground

If all measurements have been done carefully, and the leak is "stable" the following formulae will validate: Vc + Vw = Vb. If this checks out, or is close, then you can have confidence in the procedure. The location of the leak from the whip end, Lw, is: Lw = L(Vw / Vb) Example: L = 18,000 feet Vb = 12.635 volts, measured at the cable ends Vw = 2.456 Vc = 10.179 CHECK: Vw + Vc = 2.456 + 10.179 = 12.635 = Vb Lw = L(Vw / Vb) = 18,000( 2.456 / 12.635) = 3,498 Ft. The leak is located +/- 50 feet from 3,498 feet from whip end.

05/2005

Technical Bulletin Number – 012

"Quality You Can Pull On..."

Breaking Strength The breaking strength of any Dakota cable can be found on both the Cable Specification Sheet and in the Catalogue. These can either be found on the website www.wirelineworks.com or call your Wireline Works Representative to send you physical copies. These values of breaking strength are theoretical values assuming the cable is in new physical condition, and the cable is pulled straight without rotating. Dakota cables are regularly tested to verify that the breaking strength exceeds the catalogue values. There are many factors which can effect the breaking strength of a cable after it has been in the field which include: • • • • • •

•

•

Physical wear on the cable which reduces the diameter of the outer armor wires; hence, reducing the breaking strength of the cable Corrosion of the cable will reduce the effective diameter of both the inner and outer armor wires and again reduce the breaking strength H2S exposure can embrittle the steel and drastically reduce its breaking strength, as it bends over the sheave wheel. CO2 exposure will also cause accelerated corrosion Excessive rotation of the cable, caused by improper operating tensions or hydraulic packers can reduce the breaking strength by as much as 30% Splices if done properly can withstand loads over 90% of the cables breaking strength. However they loose much of their strength if put into compression (spudding), and tend to deteriorate quickly when run over sheaves frequently. Shims used in splicing need to be inspected regularly for wear. Fatigue of armor wires occurs when the cable is “yo-yoed” at high tension. When it is necessary to “yo-yo” a cable, then at every 10 or 20 cycles the upper sheave wheel or truck should be moved so that a fresh section of cable is passing under the measuring head and over the sheave wheels. Physical Damage such as kinks, armor scratches, dents, etc. to the cable can result in a much reduced breaking strength

Operating Strength of a cable is expressed as the percent of ends fixed breaking strength (BS) of the cable. For GIPS cables Wireline Works recommends an Operating Strength of 60% of the breaking strength. Sour service cables should not normally be operated over 50% of there breaking strength. The cable will operate an unlimited number of tension cycles to its Operating Strength without permanent damage to the cable. When the cable is stressed to above the operating strength, there may be permanent irreversible damage. Above the recommended operating strength there can be plastic forced out of the gaps in the inner armor resulting in less electrical insulation between the conductor and armor. There may also be additional elongation of the cable and when tension is released “Z” kinks may begin to form in the copper conductor. If these high tensions are repeated it will lead to electrical failure.

05/2005

Technical Bulletin Number – 013

"Quality You Can Pull On..."

Hydrogen Sulfide – Standard Cables Hydrogen Sulfide (H2S), is lethal to breath, very corrosive, and it can embrittle the standard GIPS (Galvanized Improved Plow Steel) armor wire used on oilfield electro-mechanical cables. When water is present and galvanized steel armor wires come in contact with H2S there is a chemical reaction. The first and fastest reaction is with the Zinc resulting in the formation of Zinc Sulfide, which is black, in addition to the release of nascent or atomic Hydrogen (H). The second and on going reaction is with Iron forming Iron Sulfide and again atomic Hydrogen The more stable state of Hydrogen is H2. However the reaction we are discussing results in a large percentage of atomic hydrogen which is extremely small. The molecules are so small they can diffuse and accumulate within the crystal structure of steel. As the accumulation continues the atomic Hydrogen seeks a more stable state and combines with another H forming H2, which is twice as large as H. In this larger state it does not diffuse back out of the structure as easily as it went in. This packing of Hydrogen in the steel crystal structure generates an internal stress and in time can lead to micro stress cracks in the steel. Even before there is advanced stress cracking, the accumulation of Hydrogen in the steel crystals results in the crystals elements being unable to move internally, causing the steel to become extremely brittle. A strand of GIPS wire exposed to sufficient Hydrogen Sulfide can result in the steel wire breaking like a glass rod when bent. After the Zinc has been used up in the chemical reaction the H2S continues to react with the Iron. This action can takes place faster in the presence of water. If the well fluid is mostly oil, then the reaction of dissolved H2S on the cable is slower but there are no safe or unsafe standards. The presence of CO2 where there is water present results in the formation of Carbonic acid. This acid environment seems to accelerate the action of H2S on iron, but again the published data is not complete enough for any standard guidelines to be complete. Another catalyst occurs when the carbonic acid etches the steel surface providing additional surface area exposed to the effects of H2S. Field experience has shown that when CO2 and H2S are both present in bore hole fluids that include water, the embrittlement of steel is much faster and more severe. In addition to CO2, the well pressure, temperature and the total time of exposure, are factors that can radically effect the degree of embrittlement. The National Association of Corrosion Engineers has published a guide line for the use of GIPS in wells containing H2S: “Maximum H2S in ppm for GIPS = (50.000 / Well pressure, psi)“ Example: Well pressure = 1000 psi , GIPS can be used with H2S concentrations up to 50 ppm. The above guidelines are very general and what is safe depends on a number of other factors. The nature of H2S embrittlement is that up to a point the embrittlement is reversible without permanent damage to the cable. Over time the H2 will diffuse out of the wires and the cable will return to normal. If a standard cable has been exposed to H2S and has successfully come out of the hole, you need to make a quick check of the armor wire by bending a wire around a rod (2 to 3 times the wire diameter) 5 complete wraps. Unwrap the wire, if it does not break then it is likely there has been no permanent damage by micro fracture, and the cable can be saved. The H2 in the cable armor will ultimately diffuse out of the armor. If a wire breaks in this wrap test but there were no outer armor wires broken coming out of the hole, then it is best to let the cable sit for a few days to allow the H2 to diffuse out of the wires. Do not use this cable in an H2S well again until it has made several trips in normal wells and the wrap test has passed. Although not recommended, if you are considering running a standard, plow steel, cable in a well containing H2S, then here are several pointers: • Run an older cable, less Zinc. • Use plenty of the pressure control grease, Liquid “O” Ring 4-I, ( or equal). • Use the National Association of Corrosion Engineers guide lines, for allowable H2S. • Use larger diameter sheave wheels • No hydraulic pack off pressure . • Use more flow tubes with greater clearance, 0.004” • Get in and out of the hole as quickly as possible, within correct operating speeds. If your operating conditions do not fall within these guidelines, then an alloy cable should be used. H2S and alloy armored, MP35 & stainless steel, cables will be covered in another technical bulletin. 05/2005

Technical Bulletin Number – 014

"Quality You Can Pull On..."

Voltage and Current Ratings Voltage Voltage ratings are determined by the thickness of primary plastic insulation. The published dielectric strength for FEP and PTFE are as high as 500 & 350 volts/mil under ideal laboratory conditions. The Voltage Rating used for oil field cables is a conservative 50 Volts DC /mil of insulation As an example, Dakota Cable 1-R-224-PH has 24.5 mil’s of insulation. At 50 Volts / mil this would indicate a rating of 1,250 Volts DC. The actual catalog rating is rounded off at 1,200VDC. The sixty cycle AC RMS voltage rating of a cable is less than the DC rating. The peak voltage of the sine wave AC voltage is 1.4 times the RMS value, so this would make the AC voltage rating of the Dakota Cable 1-R-224-PH only 700VAC. With AC voltages there is always the threat of corona discharge that can deteriorate the plastic insulation. A complete treatment of corona problems is very complex and includes effects of temperature, pressure, conductor size, frequency as well as insulation thickness. A simplified conservative formula, ( NTIS), for calculating the volts per mil for the onset of corona for this cable is: E =0. 868 / d[ log(D / d)] Where: E – Volts / mil for the onset of corona d – diameter of conductor – inches D – Diameter over insulation – inches E =0. 868 / 0.059[log(0.108 / 0.059)] = 56 Volts / mil, is where corona could start to be a problem. By rating Dakota Cables at 50 Volts / mil, corona should never be a problem. Current The maximum current in a cable is determined by the allowable voltage drop and the heat generated by the current in the cable that is on the drum. Unless the maximum current is on continuously for several hours, the maximum current will normally be limited by the maximum voltage. Using a 25,000 ft. 1-R-224-FTH cable as an example, the maximum allowable current can be calculated using the values of resistance and voltage rating listed in the catalog. • Ld = cable length on drum (kft); • Lh = cable length in bore hole (kft); • The conductor resistance, of the cable on the drum is: (4.0 x Ld) Ohms (from Wireline Works Catalogue) • The armor of the cable on the drum has no resistance as it is all shorted on its self and the drum. • The conductor resistance, of the cable in the hole is (4.0 x Lh) Ohms . • The armor resistance, Ohms, of cable in the hole is (4.4 x Lh) Ohms (from Wireline Works Catalogue)

08/2005

Example #1: Length of cable in the hole is 20,000 feet; therefore, Lh = 20; Length of cable on the drum is 5,000 feet; therefore, Ld = 5; The Voltage required at the tool Vb = 700; The cable voltage rating Vmax= 1200, (from Wireline Works Catalogue) • Total cable loop resistance, Rc = (4.0 x 5) + (4.0 x 20) + (4.4 x 20) = 188 Ohms • Total allowable Voltage drop, Vd = Vmax – Vb = 1200 – 700 = 500 Volts • Current = Voltage /Resistance • Maximum current that can be supplied is Imax = Vd / Rc = 500 / 188 = 2.6 amps. Now consider the heating effect of the cable on the drum. Power = (Current)2 x Resistance = Current x Current x Resistance Power (watts) dissipated in drum cable, Pd = (Imax x Imax) x (4.0 x Ld) = (2.6 x 2.6) x (4.0 x 5) = 135 Watts. In this example the heat from 135 watts, a typical light bulb, dissipated in the 500 pounds of cable on the drum plus the steel drum will have little effect on the cable temperature. Example #2: Lh =5; Ld = 20; Vb = 700; Vmax = 1200; Calculate Imax Rc = (4.0 x 20) + (4.0 x 5) + (4.4 x 5) = 122 Ohms Vd = 1200 – 700 = 500 Volts Imax = 500 / 122 = 4.1 amps Now consider the heating effect of the cable on the drum Pd = (Imax x Imax) x Rd Rd = 4.0 x Ld Pd = (4.1 x 4.1) x (4.0 x 20) = (16.8 x 80) = 1,344 watts. This is nearly 10 times the wattage of the other example but still not a serious problem for short periods. 1,344 Watts is about the power of a kitchen “hot plate”. It would take a very long time to heat up a 2,000 pound cable on the drum plus a steel drum with a kitchen hot plate. This example does however, illustrate that the problem of maximum current becomes more serious when most of the cable is on the drum. There are too many variables to calculate the maximum allowable time limit, including: ambient temperature, layers of cable on the drum, air circulation, spooling tensions, etc. Experience has indicated that cable on the drum can tolerate, without damage, 1/10 watt per foot for periods of 24 hours. In this example that would be 1,250 watts.

Technical Bulletin Number – 015

"Quality You Can Pull On..."

15/15 Versus 12/18 Armor Packages for 7/32” Cables Choosing between a 15 X 15 and 12 X 18 armor package on 7/32” cables is always a topic of discussion among operators. The electrical characteristics of both type cables is essentially the same. The finished diameter, weight and rated breaking strength of both constructions are the same. There are, however, several factors that influence the choice for general operations with cables using standard galvanized steel (GIPS), armor wires and there are other special factors in the choice for cables using Alloy armor wires. This technical bulletin outlines factors affecting which 7/32" cables to choose when selecting from GIPS or Alloy armor wires with either 12 inner and 18 outer armor wires or 15 inner and 15 outer armor wires. These factors have been reported by some wireline operators and are presented to assist you in your decision making. Please note that your operational practices and environment must be considered in making any decision, and that your own experience may vary from that reported by these wireline operators.

Armor Specifications

Comparing 7/32” Standard GIPS

Comparing 7/32” Alloy, Stainless & MP35

15 X15 Construction • Larger outer armor wires wear longer. • Larger outer wires are stiffer and therefore easier to thread through flow tubes. • Larger outer wires do not become “crossed over” as easily during re-heading. • Smaller inner wires will corrode to brittleness faster, reducing cable life. • The larger Torque Factor means this type of cable, especially when new, will try to unwind more , which can result in loose outer armor wires. • The outer armor of the 15 X 15 construction will require more frequent trips to a service center for “normalization” and post forming, to tighten the outer armor. 12 X 18 Construction • Larger inner armor wires will not corrode and become brittle as fast. • The smaller Torque Factor means the cable will not unwind as easily, so the outer armor will stay tight longer, requiring less service. • The outer and inner armor wires are the same diameter making a better head termination.

09/2005

Armor Package Cable Diameter - inches Diameter – Inner Wires – inches

12 inner X 18 outer

15 inner X 15 outer

0.224 +.005/-.002

0.224 +.005/-.002

0.0310

0.0245

Diameter – Outer Wires – inches

0.0310

0.0358

Steel Area Inner – inches square

0.009056

0.007070

Steel Area Outer – inches square

0.013585

0.015098

Total Steel Area – inches square

0.022641

0.022168

5,600

5,600

2.2

3.2

Rated Breaking Strength – pounds Torque Factor**

** Torque Factor = (Area of outer armor)( Pitch diameter of outer armor) / ( Area of inner armor)( Pitch diameter of inner armor).

The very high costs of alloy cables and their resistance to corrosion makes the decision on the best armor package different. The primary consideration is on obtaining maximum cable life. With these armor materials the cost of the frequent cable service is small compared to the cost of the cables. 15 X 15 Construction • Larger outer armor wires will wear longer. • Alloy wires do not corrode, so smaller inner armor wires are not a problem. • With no corrosion of the armor wires, the normal corrosion products, that inhibit cable rotation, are not present between the armor wires, so the cable under load will unwind more, loosening the outer armor. • This cable construction, with a high torque factor and low rotational resistance, requires frequent trips to the service center to have the outer armor tightened and post formed. 12 X 18 Construction • The lower torque factor means this construction will unwind less than the 15X15 construction and will require less frequent service. • The same diameter armor wires make a better head termination. • This construction would be favored for use in extremely remote locations where cable service is not readily available.

Technical Bulletin Number – 016

"Quality You Can Pull On..."

Length Stability: Compound Pre-StressingTM The cable length is the primary method of determining the depth of a tool in open hole operations. In using either magnetic marks or measuring wheels, accurate depth measurements depend on known stretch characteristics of the cable. There are two types of cable stretch; elastic and inelastic. Elastic stretch is an elongation of the cable that is directly proportional to the tension applied and when tension is removed the cable returns to its original length. This is a characteristic of a “seasoned” cable. Since elastic elongation or stretch is proportional to tension, the elastic stretch can be calculated from the measured tension on the cable. Inelastic stretch is a permanent elongation of a cable that occurs when sufficient tension is applied to a new cable and the cable remains elongated after the tension is removed. In the manufacture of new cables when the inner armor is applied to the core there are voids between the underside of the inner armor and the core, figure 1. After adequate tension is applied to the cable the inner armor will embed into the plastic core material, figure 2. When the inner armor wires are fully embed, essentially all inelastic stretch will have occurred and the cable is “seasoned”. A seasoned cable will have predictable elastic stretch characteristics as long as it is not subjected to tensions over 60% of rated breaking strength. With full embedment there is also a permanent change in the effective cable core diameter. In manufacturing a cable the amount of this diameter change is important, so that after full embedment has occurred, the finished cable, will have the correct outside diameter. The desired final effective diameter, Dc, of the core is easily calculated: • Dc = D – 2do – 2 di D = required finished cable diameter • do & di = outer and inner armor wire diameters The initial diameter of the core required for full embedment can be closely approximated by: • Dc’ = [ (Dc+di)^2 – (N/2Cos Ai )(di)^2]^1/2 N = number of inner armor wires • Ai = lay angle of inner armor wires Using the Dakota slammer cable type 7-Y-484 as an example, the required finished effective core diameter is: • Dc = 0.484” – 2 X 0.0670” – 2 X 0.0535” = 0.243”

(patent pending)

If the original length of the cable, L is 25,000 feet then the increase of the inner armor length, li is: • li = ( 25,000 )(0.0044) = 110 feet The outer armor in contact with the inner armor layer experiences the same reduction in diameter but this is a smaller fraction of its original diameter, so the elongation, lo, of the outer armor is less than the inner armor: • lo = L[(Dc’-Dc)/( Dc+2di +do)]X[Tan Ao]^2 = L[(0.008)/(0.243+2*0.0535+0.067)](Tan 19)^2 =L[ 0.0023] • lo = (25,000)(0.0023) = 58 feet. It is conventional cable manufacturing practice to embed the inner armor in the core to “season” it by subjecting the finished cable to a prestressing operation. This operation typically applies a tension of about 1/3 of the cable rated breaking strength as it passes between two capstans. The tension in the cable is lost as it leaves the final capstan and goes on the shipping reel. If the tension in this standard prestressing operation has embedded the inner armor in the core, then when the tension is removed, the inner armor, now wound around a smaller core, would like to be longer than the outer armor as the above calculations demonstrate. Because of the friction between the inner and outer layers the outer armor can not shrink back over the inner armor . Since the shorter outer armor has much greater strength, it will push back on the inner armor, which will reduce the pressure on the core. The nature of plastics is that they have a memory and though the prestressing operation may have initially fully embedded the inner armor into the plastic core, when the inner armor pressure is reduced the core will start to recover its original shape. When this occurs, the cable is not fully seasoned and will have excessive inelastic stretch. Wireline Works Inc. has a proprietary cable seasoning process known as “Compound Pre-StressingTM (patent pending). With this procedure the inner armor, core assembly is first pre-stressed with sufficient tension to fully embed the inner armor wires into the core. After pre-stressing the inner armor, the outer armor is then applied to the already embedded and elongated inner armor. This permits the outer armor to add rather than reduce the pressure on the core ensuring a fully seasoned cable.

To allow for full embedment the initial core diameter required is: • Dc’ = [ (0.243” + 0.0535”)^2 –(16 / 2Cos22 )( 0.0535”)^2]^1/2 = 0.251” • Dc’- Dc = 0.251 - 0.008” is the core compression. This shows that the diameter of a newly assembled cable of this type will decrease 8 thousandths of a inch when the inner armor is fully embedded in the core. Since the inner armor wires are helically wrapped around this smaller effective core diameter the length of the embedded inner armor layer will be longer. This increase in length, li, can be calculated : • li = L[ (Dc’- Dc ) /( Dc + di)] X [ Tan Ai]^2 = L[ 0.008 / (0.243 + 0.0535)] X [Tan22]^2 = L[0.0044]

02/2006

Figure 1

Figure 2

Dc Voids

Dc

Technical Bulletin Number – 017

"Quality You Can Pull On..."

Armor Coverage Armor coverage is a very important property of electromechanical wireline cables. Proper design and armor coverage permits cables to operate under tough operating conditions of high temperatures and high tensile loads. The term “armor coverage” refers to how close the armor wires are together. If a layer of armor wires were to have 100% coverage, it would mean that all of the armor wires in that layer were touching their adjacent wires. There are a number of very important reasons why the armor coverage of both the inner and outer armor layers must be carefully controlled. If the coverage on either layer were 100%, the cable would be so stiff it would not be able to bend around a sheave wheel without forcing one of the wires out of the layer, creating a high wire. If the armor coverage is too low a premature electrical short could result under high temperature and high load conditions. The range and requirements for the coverage of the inner and outer armor layers is quite different. To calculate coverage there are at least 4 good formulas. In the case of oil field electro mechanical cables (wirelines), there is little difference in the calculated coverage values using any of these formulas. The formula that has been accepted by the major oil field service companies and Wireline Works is: di

% Ci =

π

(Dc - 2 do - di) Sin[ Ni ] Cos [αi]

% Co =

Ci Co di do Ni No αi αo Dc

= = = = = = = = =

do π

(Dc - do) Sin[ Ni ] Cos [αo]

x100

x100

Percent coverage of the inner armor layers Percent coverage of the outer armor layers Diameter of the individual inner armor wires Diameter of the individual outer armor wires The number of wires in the inner armor layers The number of wires in the outer armor layers the lay angle of the inner armor wires the lay angle of the outer armor wires Finished cable outside diameter

Inner Armor Coverage acceptable range: 97.5% to 99.5%, ideal is 98.5%. The importance of keeping the inner armor coverage as high as possible is to contain the plastic insulation covering the conductor. During cable manufacturing the equal spacing between the inner armor wires is carefully controlled and the inner armor wires are partially embedded in the plastic insulation to preserve this equal spacing. This equal spacing is important to spread the coverage equally between each wire thus minimizing the gap at any one location.

06/2006

A cable under load generates a pressure on the core and if the inner armor wires are not close enough (low coverage %), the plastic insulation can be squeezed out between the armor wires. With an inner armor coverage over 98% cables can operate under rated operating conditions of temperature and tension without the plastic insulation being squeezed out in the gap between the inner armor wires. When a cable is subjected to high downhole temperatures and excessive tension some plastic insulation may be forced out between the inner armor wires, even when the armor coverage is in an acceptable range. Excessive operating conditions, stuck tools, and pulling out of the weak point can often create this phenomena. In these cases it is good operational practice to cut back on the cable end to be assured of full electrical insulation. Outer Armor Coverage acceptable range: 96.5% to 98.5%, ideal is 97.5%. The importance of allowing a lower coverage on the outer armor is to give the cable sufficient flexibility to wrap around standard sheave wheels. On cables used in high pressure operations it is important to keep the outer armor coverage on the high side to better control pressure in the flow tubes. The outer armor being applied over the inner armor can not be embedded to control spacing. For this reason, new cables when they are first spooled may cause the outer armor wires to shift around resulting in what appears to be an excessively wide gap. This is perfectly normal. When a new cable has a dark protective grease applied, this grease will collect in this wider gap giving an appearance that the cable is “gappy”. After a few runs in the hole the outer armor will equalize the gap between the adjacent armor wires and the appearance of a “gappy” cable will disappear. Sample inner armor coverage calculation: Wireline Works 1-R-288-TH Ci =

di π

(Dc - 2 do - di) Sin[ Ni ] Cos [αi]

di = 0.0405; do = 0.040; Dc = 0.288; Ni = 12; αi =

π 180

19.5

Ci = 99.1%

(100);

Technical Bulletin Number – 018

"Quality You Can Pull On..."

Minimizing Cable Torque During Cable Design

The torque in the cable is the difference between the torque in the outer armor, Qo, and the inner armor, Qi, The factors that determine the torque in each layer are: Qo ≥

Do No do2 to Sin [αo] 2

Qi ≥

Di 2

To off set the dominant outer armor torque, the lay angle of the inner armor is increased. From cable design we know there is an angle of maximum torque for the inner armor. This is because the portion of cable tension carried by the inner armor decreases as the inner armor lay angle is increased. Therefore; even though the larger lay angle will result in increasing the component of tension that generates torque, if the tension is decreased excessively, the torque will also decrease. The result is an angle of maximum torque for the inner armor, which in turn is the angle that results in the minimum cable torque. ( Q =Qo-Qi ). The minimum torque angle for a cable with a 12/18 armor package is about 25 to 26 degrees. Again in cable design there are compromises to be made. As the lay angle of the inner armor is increased to reduce cable net torque, it also reduces the breaking strength. The best compromise between breaking strength and cable torque is an inner armor lay angle of 23 degrees. Cable Torque, inch-pounds/pound

All electromechanical Wireline cables that are used in oil well service operations are designed with two layers of armor wires around a core of insulated conductors. By design, wireline cables develop torque when subjected to load. The inner layer of armor wires is normally wrapped around the core in a right hand direction while the outer layer of armor wires are wrapped over the inner armor wires in a left hand direction. By wrapping the layers in opposite directions the torque from the inner armor opposes the torque from the outer armor. The result is that the net torque in the cable is the difference between the torque generated by each armor layer. In theory it is possible to design a cable in which the torque generated by each layer is exactly equal, resulting in a cable that has no torque under load and therefore would not rotate under load but there are a number of reasons that this is not a practical design for oilfield service operations. To better understand the impact of cable torque see Technical Bulletin “Wireline Torque”.

Ni di2 ti Sin [αi]

Di = the pitch diameter of each inner layer Do = Is the pitch diameter of each outer layer Ni = Is the number of wires in each inner layer No = Is the number of wires in each outer layer di = Is the diameter of the wires in each inner layer do = Is the diameter of the wires in each outer layer αi = Is the lay angle of each inner layer αo = Is the lay angle of each outer layer ti = Is the wire tension in each inner layer to = Is the wire tension in each outer layer

0.017

0.0165

0.016

0.0155

0.015 15

20

25 Inner Armor Lay Angle α ia

The full calculation of cable torque, qcc, for the Wireline Works cable 1-R-322 looks like this: qcc = (cd – 2 dia – 2 doa) pr sin2 (α oa)

(cd – doa) doa2 noa sin (α oa)

Looking at the picture of a standard cable type with 12 inner and 18 outer armor wires and the factors that determine the torque in each layer , the outer armor torque will be greater than the inner armor torque because:

dia2 (cd – dia – 2 doa) nia sin (α ia) cos2 (α ia) –

2 nia cos (α ia) cos2 (α ia) –

cos2 (α oa) –

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cd = 0.322 noa = 18

–

(cd – 2 dia – 2 doa) pr sin2 (α ia) cd – dia – 2 doa

cd – dia – 2 doa

dia2 +

(cd – 2 dia – 2 doa) pr sin2 (α oa)

dia = 0.0445 aia = 23

qcc = 0.0151162

cd – doa

(cd – 2 dia – 2 doa) pr sin2 (α ia)

doa2 noa cos (α oa) cos2 (α oa) –

These 3 factors give the dominate torque to the outer armor layer. When designing a cable the torque can be minimized by adjusting the lay angles of each layer. To decrease the torque generated by the outer armor wires the lay angle of the outer armor is reduced to as small of an angle that does not compromise the spooling characteristics of the cable . This angle in most cases is 19 degrees. Experience has shown that when the lay angle is less than 19 degrees the outer armor wires are easily crossed if the cable gets slack during operations.

35

The actual computation of cable torque under load is a complicated problem as when the angles of inner and outer armor are changed, the tension carried by each layer and the torque are changing.

The net torque in the cable, Qc= Qo – Qi

• Do > Di the outer armor is always over the inner armor • No > Ni in any cable with equal diameter armor wires • do = di With the standard 12 / 18 armor package

30

cd – doa

doa = 0.0445 aoa = 19

nia = 12 pr = 0.47

inch-pounds of torque / pound of tension

At a working tension of 5000 pounds, the cable torque, Qc would be: Qc = 75.6 inch pounds of torque

Technical Bulletin Number – 019

"Quality You Can Pull On..."

Wireline Torque Electromechanical Wireline Cables are designed and manufactured to minimize the inherent torque in the cable, see Technical Bulletin “Minimizing Cable Torque during Design". However, all cables inherently have some torque and will develop a need to rotate relative to the tension applied during operations. This is generally not a problem as long as the cable is allowed to rotate freely. In today’s complex oilfield there are a lot of variables that affect and restrict cable rotation. If the cable is not allowed to rotate in proportion to tension, torque build up will begin to occur in certain areas of the cable depending on what is restricting it from rotating properly. For example, the packoff will restrict the cable from rotating and the cable will accumulate torque as the cable passes through pack-off. This results in torque build up and loose outer armor. Cable rotation can be restricted and torque imbalance may occur from the following operations: • Deviated or crooked well bores. • Going in and out too fast and not observing the 80/120 tension rule, (see Technical Bulletin #9). • Pulling out of a well at high speeds that result in excessive tension. • Centralized and decentralizing tools. • Heavy and viscous drilling mud and completion fluids affect the tension of the cable. • Grease heads or pack-offs used to wipe or control pressure. • Pulling out of a rope socket under high load conditions. • Low fluid bypass conditions. Field experience has shown that almost always loose outer armor is caused from the torque imbalance resulting from improper running conditions. During the seasoning or breaking in period for new cables there will generally be some areas in the cable that become loose. These areas do not cause problems under everyday use; however, it would be good insurance to normalize (tighten loose areas) a standard GIPS cable after 20 to 30 runs. This would tighten any loose outer armor that may have occurred due to the core embedment of a new cable.

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If a cable has been run into a well bore with any condition that may prevent free rotation or cause torque imbalance, the cable will need attention to keep it from failing. The standard approach is to normalize the cable to be sure the outer armor is tight. If you feel or see your cable trying to curl up while laying on the ground during rig ups it has excessive torque. Running the cable in this condition will risk breaking, or getting a strand cross-over which can cause the cable to strand at deeper depths. Remember every bird cage you see is caused by getting too much slack in one location of the cable. It is a good idea to rehead, when possible, with inner armor strands on the cables that are using grease heads because they are lubricated and can torque up relatively easily. Lack of tension means low rotation is required, and high tensions means a lot of rotations required to prevent torque build up. If you come out of a well with very high tension and torque in the cable, the next time you go into a well with very little tension, there will be a lot of torque in the cable wanting to be released. Armor separation, high strands, or bird caging are not the only issues to worry about with torque build up, you may also experience early pullouts, cable breaks, and excessive compression on the conductor which can short out the cable. The more you understand the affects of torque the better off you are in preventing cable failures and/or well site disasters. The torque generated at maximum working load for standard cables has been calculated as follows: TYPE LOAD

Z-224

R-224

R-288

R-322

R-380 R-425

(pounds)

3360

3360

6000

6720

8600 11700

55.5

40.7

93.5

116.7

176.5

TORQUE (Inch-pounds)

268.3

Technical Bulletin Number – 020

"Quality You Can Pull On..."

Cable Rotation By design, wireline cables develop torque when subjected to load, see Technical Bulletin “Minimizing Cable Torque During Cable design”. The load on the wireline cable is a result of the weight of the tool, the weight of the cable and any dynamic friction due to running conditions. If the tool end of the cable is free to rotate, the cable will try to rotate to reduce this torque. All cables used in oil field service operations are built with the torque of the outer armor dominant over the opposing torque of the inner armor. To balance the torque the cable will unwind in a direction to loosen the outer armor, which will tighten the inner armor. If the cable is free to rotate, this unwinding or rotation will continue until the torque in the inner armor equals the torque of the outer armor. The number of revolutions, Nf (per 1000 ft per 1000 lb), that the end of the cable will make to equalize the torque can be calculated as follows: Nf = 48 x 106 (cd – doa) (– cd + dia + 2 doa) dia2 (cd – 2 (dia + doa)) nia pr sin3 (α ia) + dia2 (– cd + dia + 2 doa) nia cos2 (α ia) sin (α ia) + doa2 noa sin (α oa) (cd – doa) cos2 (α oa) + (2 (dia + doa) – cd) pr sin2 (α oa) dia2 doa2) nia noa π2 ym ((doa – cd) cos (α ia) sin (α oa) – (cd – dia – 2 doa) cos (α oa) sin (α ia)) 1 (cd – dia – 2 doa) (cd – doa)2 sin(2 α oa) cos2 (α ia) + 2 sin(α ia) ((cd – doa) (– cd + dia + 2 doa)2 cos2 (α oa) + – cd3 + (4 dia + 6 doa) cd2 – 5 dia2 cd + 8 doa3) pr sin2 (α oa) cos (α ia) + pr – cd (cd2 – 4 doa cd + doa (4 dia + 5 doa) cos (α oa) sin (α oa) sin2 (α ia) + dia cd2 + doa2 (dia + doa) sin (2 α oa) sin2 (α ia) + dia3 + 5 doa dia2 + 8 doa (doa – cd) dia – 6 cd doa2 sin (2 α ia) sin2 (α oa)

Example of Cable Rotation with Tool End Free to Rotate Using Wireline Works Cable # 1-R-322 as an example: Cd=0.322, doa=0.0445, dia=0.0445, noa=18, nia=12, αoa =19.22, αia=21.54, pr*=0.47** *pr = Poisson Ratio **Testing has shown that 0.47 is the best value for EM cables

Nf = 17.2 revolutions / 1000 ft / 1000 pounds tension. With 10,000 feet of new 1-R-322-PH cable lowered into a straight dry hole, with a 500 lb tool, the total revolutions, N, the cable would make to equalize torque would be: Cable weight lb / kft = 188 ; Average tension due to cable = 188 X 10 / 2 = 940 lb Effective tension is 940 + 500=1440=1.44 klb; Nf x 1.44 x 10 = 17.2 x 1.44 x 10 = 247 revolutions There are very few straight, dry holes but this calculation indicates the amount of rotation a new cable will try to make to equalize the torque. With fluid in the hole the tension would

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increase with cable speed coming out of the hole resulting in additional unwinding revolutions.

Standard Wireline Works Cable Rotation Nf– Number of Revolutions per 1000 feet per 1000 pound tension cable end free to rotate TYPE Z-224 Nf 83

R-224 48

R-288 22

R-322 17

R-380 10

R-425 7

The above calculations represent the possible rotation of a typical new cable. As a cable becomes “seasoned “ it will rotate less with tension changes. A “seasoned” cable is one in which the outer armor wires have dug into the Zinc of the inner armor wires and mud plus corrosion by products have collected between the armor layers add to the friction between layers reducing the amount of cable rotation. The amount of this initial new cable rotation has been reduced in Wireline Works cables by including a material called TCI (Torque Compression Inhibitor) Technical Bulletin #10, between the armor layers. TCI contains materials that increase the friction between the armor layers, reducing the rotation of new cables, so new cables will perform more like “seasoned” cables. Cables armored with alloy wires like MP-35 or 31MO are an extreme case in cable rotation. The reason is that the alloy armor does not have a soft Zinc coating and it does not corrode creating friction between armor layers that reduces the rotation in cables armored with galvanized wire. For these reasons alloy cables will continue to rotate in use and must be given extra care in field operations and periodically the outer armor needs to be “tightened”. In operations, keep in mind that when ever the tension on the cable changes it will try to rotate. When cable tension is increased above the static tension by frictional drag on the cable, the increase in cable torque will try to unwind the outer armor wires. Frictional drag comes from bore hole friction and tight pressure control equipment. This frictional drag increases with the speed of the cable spooling. Coming out of the hole too fast can result in excessive frictional tension on the cable forcing the cable to rotate excessively , further loosening the outer armor. Going into the hole the tension in the cable is reduced by the frictional drag and the cable will try to rotate to tighten the outer armor. Going into the hole too fast will not give the cable time to rotate to tighten the armor. Experience has shown that for standard GIPS armored cables if the tension going into the hole is not less than 80% of static tension at that depth and the tension coming out of the hole is never more than 120% of static tension, the cable armor will remain tight. This rule does not apply to alloy cables, which require special care. Cable rotation can cause the stress in the outer armor wires to be reduced, which not only leads to loose outer armor wires but also significantly reduces the cable breaking strength. The reduction in cable breaking strength with the cable free to rotate will be covered in a later Technical Bulletin. For additional effects of cable rotation and cable torque see Technical Bulletin “Wireline Torque”.

Technical Bulletin Number – 021

"Quality You Can Pull On..."

Temperature Rating of Cables The maximum temperature rating The maximum temperature rating of Wireline Works cables, as listed in the catalog, is based on the following operating conditions: • The maximum bore hole temperature is not greater than the cable rated temperature. • The cable is operated under a normal tension profile. • There are no unusual hole conditions or restrictions causing excessive tension. There are three factors that will influence the temperature rating of a cable. • The “nominal melting point” of the plastic used for insulating the conductor. • The pressure exerted by armor wires on the core by normal loads • The inner armor coverage

example DuPont Teflon- FEP-100 has a nominal melting point of 510 F . This plastic is, however, so soft, it would not be suitable as total insulation on an EM cable rated at 300 F. There are no published specifications by plastic manufactures that clearly identify their plastics as being suitable for use in oil field cables. Special engineering testing and controlled field testing are required to qualify a plastic for these cables. Core pressure When there is tension on the cable the helical shape of the armor wires results in a significant pressure or “squeezing” of the cable core. This pressure on the core, if high enough, will result in the plastic being “ squeezed” out between the gap in the adjacent inner armor wires (as shown in the picture below). This loss of plastic insulation will ultimately lead to an electrical failure.

The nominal melting point Plastics are called amorphous materials and as such do not have a specific melting point. Crystalline materials, such as metals and water, are characterized by the fact that they do have a very specific temperature at which they change from a solid state to a liquid state. Amorphous materials, like plastics, do not have a specific temperature at which they change from a solid material to a liquid state but just gradually become softer. At their melting point temperature crystalline materials continue to absorbed heat, called heat of fusion, with out changing temperature until all the material has completely changed state. The temperature will then again rise as heat is added. Amorphous materials under go different molecular bonding changes as they are heated and become softer. When these changes occur a certain amount of heat is absorbed with out a change of temperature , indicating the change in molecular structure. Arbitrary standards have been set on this heat absorption that is used to classify the “nominal melting point” of plastic materials. The arbitrary melting point ratings of plastics is no more than a guide as to whether a plastic is qualified to be used in an electro-mechanical cable at its rated melting point. For

07/2006

The pressure on the core , as a function of cable tension, can be calculated. The equation is rather complicated but evaluating it for different cables and tension will illustrate the importance of special testing to qualify the temperature rating of a plastic.

Technical Bulletin Number – 021ii

"Quality You Can Pull On..."

Core pressure is most important on the tool end of the cable where the temperature is the highest. The maximum tension in the cable at the tool end is the weak point pull out tension. The calculated core pressure, cp, at typical weak

point pull out tensions (POT), that would be used with standard cables operating at a depth of 20,000 feet and a tool weight of 300 pounds are as follows:

ARMOR

Z-224

R-224

R-258

R-288

R-322

R-380

R-425

POT-lbs

1200

1200

1600

2700

2800

3500

4600

cp-psi/lb

4.00

4.10

3.10

2.49

1.98

1.43

1.14

cp – Tool-psi

1200

1230

930

747

594

429

342

cp-at POT-psi

4800

4920

4960

6723

5544

5005

5244

These calculations show that under normal operating conditions the pressure on the core from the tool weight is 1200 psi or less. When a cable is manufactured with the correct inner armor coverage, the core plastic will not be squeezed out at these core pressures at the maximum rated temperature of the cable. If on the other hand the tool becomes stuck and it becomes necessary to pull out of the rope socket, then the resulting 5,000 psi core pressure is likely to squeeze the core plastic out between the inner armor wires if the temperature is high enough. When a tool becomes stuck in a hole at or near maximum rated cable temperature, then after pulling out of the tool ,it can be expected that there will be some plastic squeezed out and it will be necessary to cut back the cable. The inner armor coverage The term “ armor coverage” refers basically to how close the armor wires are together . If a layer of armor wires were to have 100% coverage, it would mean that all of the armor wires in that layer were touching their adjacent wires. If the coverage on either layer were 100%, the cable would be so stiff it could not be bent around a sheave wheel without forcing one of the wires out of the layer. (See Technical Bulletin 17, Armor Coverage). The inner armor coverage is the most important factor in determining the temperature rating of a cable. When there are large gaps between the armor wires the plastic is more easily squeezed out under cable tension. Two factors are carefully monitored during the manufacture of Wireline Works cables . The first is the inner armor coverage which is maintained between 98.0% to 99 % . On high temperature cables the coverage is kept above 98.5%. The other factor monitored in manufacturing is the uniformity of the spacing of the inner armor wires around the core. At Wireline Works “spider” wire spacers are use to properly space the armor

07/2006

wires as they are wrapped around the plastic core before the assembly enters the closing dye. The closing dye and following pinch rollers press the evenly spaced armor wires into the plastic core to insure they will stay evenly spaced during subsequent manufacturing operations (as shown in the picture below).

Conclusions As new plastics become available, Wireline Works evaluates them by testing them under simulated tension and temperature conditions. If these new materials perform well in these simulated tests, then a limited number of cables are manufactured using the new material and their performance closely monitored. If there are no problems with the new materials in the initial field trials, then additional cables will be put into field service for continued evaluation. By carefully choosing and testing all core plastic materials and precisely controlling the inner armor coverage and spacing, Wireline Works cables will operate at or above the maximum temperature rating for all routine operations.

Technical Bulletin Number – 022

"Quality You Can Pull On..."

Sheave Selection There is probably more material available on sheave selection than any other piece of cable equipment. By summarizing and analyzing all this data it will give the operator greater choice in judging the proper size sheave for an operation. There are two important characteristics of sheaves that must be considered. These are the sheave groove and sheave diameter. Of these two, running a cable with an improper groove shape can do more damage to a cable faster than running with the wrong diameter. Correct sheave groove shape and size is more important when running multi-conductor cable, as the core is easily deformed and the thin conductor insulation can be damaged more easily.

Sheave Groove • The groove of a new sheave should have a diameter 5% greater than the cable diameter. • Cables should not be run over sheaves if the sheave groove diameter is 10% greater than the cable diameter. • The sheave groove should be machined to support from 135 to 150 degrees of the cable diameter. • Sheaves should NEVER be used on 2 different diameter cables

Dc

Ds 135° to 150°

Sheave Diameter There are two rules of thumb that are published in cable literature that indicate the minimum sheave diameter that should be used for operating a cable up to its rated Maximum Working Load. The first rule states that the minimum sheave diameter, SD, should be 60 times the cable diameter, D, and the second rule states that the minimum sheave diameter should be 400 times the outer armor wire diameter, d. Wireline Works Cable Type

1-R-100 1-R-125 1-S-185 1-S-207 1-Z-224 1-R-224 1-R-258 1-R-288 1-R-322 1-R-380 1-R-425 7-Y-380 7-Y-428 7-K-464 7-Y-474 7-Y-484

09/2006

Cable Diameter D - inches

Cable Diameter D - inches

Outer Wire Diameter d - inches

1/10 1/8 3/16 13/64 7/32 7/32 1/4 9/32 5/16 3/8 7/16 3/8 7/16 15/32 Slammer Slammer

0.101 0.125 0.185 0.207 0.224 0.224 0.258 0.288 0.322 0.380 0.425 0.378 0.428 0.464 0.474 0.484

0.014 0.0175 0.0358 0.0390 0.0358 0.0310 0.0358 0.0400 0.0445 0.0525 0.0585 0.0525 0.0585 0.0495 0.0655 0.0670

Sheave Sheave Diameter Diameter SD= SD= 60 x D - inc. 400 x d - in

6.1 7.5 11.1 12.4 13.5 13.5 15.5 17.3 19.3 22.8 25.5 22.7 25.7 27.8 28.5 29.0

5.6 7.0 14.3 15.6 14.3 12.4 14.3 16.0 17.8 21.0 23.4 21.0 23.4 19.8 26.2 26.8

In addition to the two rules listed above there is a formula commonly used to determine the safe minimum sheave diameter for different working loads. This can be useful in shallow operations where the maximum tensions, Tmax, are low and therefore the cable can be operated on smaller diameter sheaves without damage to the cable or reduction of cable life. This formula for minimum Sheave Diameter, SD, is: N= Number of outer armor wires, d = diameter of outer armor wires - inches. BS = Cable breaking strength - Klbs, Tmax = Maximum operating tension – Klbs SD = [ 80(Tmax / BS) + 20 ][ d(N/2.8 + 1)]; - in ( Sheave Diameter ) For example: Wireline Works Cable type: 1-R-322 operating with the maximum tension, never over 3.0 Klb BS = 11.2 Klb ; Tmax = 3.0 Klbs ; d = 0.0445; N = 18 SD = [ 80(3.0 / 11.2) + 20 ][ 0.0445(18 / 2.8 + 1) ] = [ 41.6 ][ 0.0445(7.43) ] = 13.75 in

Operating under low tensions conditions, the minimum recommended sheave diameter, using this formula, for a 1-R-322 cable would be 14” compared to an 18” sheave diameter for operating at maximum rated loads. When a cable, under load, is bent around a sheave the armor wires experience a bending stress in addition to the stress from the load. The smaller the sheave diameter, the higher the bending stress. It is this combined stress that is the main factor in establishing the minimum sheave diameter. When this combined stress exceeds the yield strength of the wire it will result in loose outer armor wires. When this combined stress exceeds the tensile strength of the wire, the wire and possibly the cable will break. Using the above recommended or larger sheave sizes will avoid such failures.

Sheave Alignment It is important that proper sheave alignment is attained during well site set up. When the sheaves are not properly aligned, the cable will attempt to “crawl” up the sides of the sheave wheel grooves. This action can result not only in distorting the sheave grooves but can also introduce additional torque in the cable. The materials used in the construction of sheaves has changed over the years. The most popular sheaves are now the “Composite Sheaves”. These composite sheaves have become standard with most major service companies. These sheaves have the wheels and guards manufactured from synthetic materials, which has resulted in a 40% reduction in the weight. When manufactured, these sheaves have the correct groove size and shape to properly support the cable. In use however the composite sheave groove can be quickly damaged from poor sheave alignment.

Cable with Splices In running cables with complete splices it is extremely important that the sheaves have the proper groove shape to support the cable. Spliced cables should always be run using the largest sheave size available with the proper groove shape.