IADC Fishing

ROTARY DRILLING SERIES Unit I:

The Rig and Its Maintenance

Lesson I: Lesson 2: Lesson 3: Lesson 4: Lesson 5: Lesson 6: Lesson r Lesson 8: Lesson 9: Lesson 10:

The Rotary Rig and Its Components The Bit Drill String and Drill Collars Rotary, Kelly, Swivel, Tongs, and Top Drive The Blocks and Drilling Line The Drawworks and the Compound Drilling Fluids, Mud Pumps, and Conditioning Equipment Diesel Engines and Electric Power The Auxiliaries Safety on the Rig

Unit II: Normal Drilling Operations Lesson I: Lesson 2: Lesson r Lesson 4: Lesson 5:

Unit III:

Nonroutine Operations

Lesson I: Lesson 2: Lesson 3:

Unit IV: Unit V:

Making Hole Drilling Fluids Drilling a Straight Hole Casing and Cementing Testing and Completing

Controlled Directional Drilling Open-Hole Fishing Blowout Prevention

Man Management and Rig Management Offshore Technology

Lesson I: Lesson 2: Lesson 3: Lesson 4: Lesson 5: Lesson 6: Lesson r Lesson 8: Lesson 9: Lesson 10:

Wind, Waves, and Weather Spread Mooring Systems Buoyancy, Stability, and Trim Jacking Systems and Rig Moving Procedures Diving and Equipment Vessel Inspection and Maintenance Helicopter Safety and Survival Procedures Orientation for Offshore Crane Operations Life Offshore Marine Riser Systems and Subsea Blowout Preventers

ROTARY DRILLING

OPEN-HOLE FISHING Unit III • Lesson 2 Third Edition

Edited by Jean Trimble Pietrobono Published by

PETROLEUM EXTENSION SERVICE Division of Continuing Education The University of Texas at Austin Austin, Texas

in cooperation with ~ ~

INTERNATIONAL ASSOCIATION OF DRILLING CONTRACTORS Houston, Texas 1988

PREFACE

This second lesson in Unit III of the Rotary Drilling Series introduces the reader to the tools and techniques of open-hole fishing. The lesson covers the major causes of fishing jobs; basic steps in fishing out a twistoff, stuck pipe, wireline, or junk lost in the hole; and the economics of fishing. Research for this third edition of Open-Hole Fishing was done by David J. Morris of the Petroleum Extension Service staff. Gore Kemp, Vice President of PETCO Fishing and Rental Tools, reviewed the text and illustrations. His generous contribution of time and expertise to ensure the accuracy of this publication is greatly appreciated. Thanks also are extended to Michael C. Brown of Bowen Tools, Inc., Derrel D. Webb of Houston Engineers, Inc., T. J. LeFebvre of NL Industries, Inc., and Ron Baker of Petroleum Extension Service.

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pressure, chances are that the pipe is wall stuck. Prompt action, such as immediately rotating the drill string, may dislodge wall-stuck pipe that cannot be pulled free. Oil spotting (pumping a slug of oil-based fluid down the drill stem and up the annulus to the stuck point) may break the mud seal. If these actions do not free the pipe, a ~ fishing job may become necessary. Using spiral drill collars and heavyweight drill pipe, each joint of which has a large external upset in its center, can help prevent wall sticking.

. I ! I - - - IMPERMEABLE FORMATION

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PERMEABLE FORMATION

IMPERMEABLE FORMATION

Offshore Sheared Pipe

DIFFERENTIAL PRESSURE

-r---\--===:::::--------MUD LIQUIDS

MUD CAKE-~

FIGURE

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WALL-STUCK PIPE

Differential sticking. Many fishing jobs are caused by drill pipe or collars becoming differentially stuck, or wall stuck (fig. 10). Wall sticking commonly occurs in a permeable, low-pressure formation where the hydr~static pressure of the drilling mud forces mud liquids into the formation and causes a buildup of mud solids known as mud cake or filter cake. The pressure of mud in the annulus presses the pipe against the mud cake lining the hole. This pressure may be strong enough to support the entire drill string. The longer the drill string remains motionless, the more likely it will become wall stuck and the harder it will be to free. Excessive hydrostatic pressure may be responsible, but only a fairly small overbalance, or pressure differential, from wellbore to formation is necessary for wall sticking to occur. The more solids that are in the mud, the thicker the mud cake ""ill be-and the tighter the pipe will be stuck. If the pipe becomes stuck while motionless in a clean, well-conditioned hole and circulation can be stopped and then resumed at the original

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When a floating offshore drilling rig must quickly leave the well site because of unexpected rough weather or other hazards, standard procedure is to close the subsea blowout preventer pipe rams and sever the drill string. The sheared pipe still attached to the drill string must later be retrieved, using special fishing procedures, before normal drilling operations can continue. In effect, shearing the drill string intentionally creates a fishing job, but for the purpose of preventing a blowout.

Junk in the Hole Smaller fish, or junk, lost in the hole may include1. bit cones, bearings, or other parts lost when

a bit breaks; 2. broken reamer or stabilizer parts; 3. metal fragments lost in a twistoff; 4. metal fragments produced by milling the top of a fish to aid in its retrieval; 5. naturally occurring pieces of hard, crystalline, or abrasive minerals such as iron pyrite; 6. tong pins, wrenches, or other items that fall into the hole because of rig equipment failure or by accident; 7. equipment such as packers, core barrels, and drill stem test (DST) tools that become lodged downhole; and 8. wireline tools and parted wireline.

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Preparing for a Fishing Job When it becomes necessary to fish drilling equipment out of an uncased hole, the experienced operator finds out as much as possible about the situation before taking action. Among the questions he may attempt to answer are the following:

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What is to be fished out of the hole? Is the fish stuck, or is it resting freely? If stuck, what is causing it to stick? What is the condition of the hole? What are the size and condition of the fish? Could fishing tools be run inside the fish, or must they be run outside it? 7. Could other tools be run through the fishing assembly that is to be used? 8. Are there at least two ways to get loose from the fish if it cannot be freed?

In a fishing job involving the drill stri operator can often ascertain whether or lost drill pipe is stuck in the hole by deter what happened just before it was lo~ instance, if the bit was on bottom and ( and if there was no sudden, unexplained i of torque or decrease in rotary speed bef drill string broke, the most likely explan the occurrence of a twistoff, and the pip( bably not stuck. If, however, the pi] motionless in the hole or if it was being r, lowered but not rotated, it is probably either mechanically or differentially. The operator must determine, as accur possible, the depth at which the top of a off drill string can be found. The upper of the string is measured as it is remOVl the hole. If the bit was on bottom when' string broke, or if the drill string becarr off bottom, the length of the upper par same as the measured depth of the top of (fig. 11). B

A 4,000 FT

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2,000 FT -OF PIPE SET BACK AFTER BREAK

OF PIPE SET BACK

5,000 FT 10,000 FT

6,000 FT

1

3,000 FT

1 FIGURE

11.

FINDING THE DEPTH OF THE TOP OF THE FISH IF (A) THE BIT WAS ON BOTTOM WHEN THE DRILL STRING BR

THE DRILL STRING BECAME STUCK OFF BOTTOM

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FIGURE

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16.

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DITCH MAGNET (COURTESY OF BOWEN TOOLS,

INC.)

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mud pit to capture most cuttings from the milling operation (fig. 16). Removal of cuttings reduces wear on mud pumps and other equipment. Once the top of the fish has been milled fairly smooth, the operator makes up afishing string. A typical fishing string consists of, from bottom to top, an overshot, a bumper sub, a hydraulic jar, and a jar accelerator made up on drill pipe (fig. 17). To calculate how much pipe and how many collars he needs to reach the fish, the operator must consider.the made-up length of the fishing tool assembly, as well as the distance the fish must travel inside the assembly before it can be firmly caught. A typical circulating and releasing overshot consists of three outside parts: a top sub, a bowl, and a guide (fig. 18). The top sub connects the overshot to the fishing string. The bowl may be fitted with different types of equipment to grasp the fish and different guides to help center the fish beneath the tool. The overshot must have an external diameter that allows proper clearance in the hole, and the grapples must be close to the size of the fish. If the diameter of the fish is close to the maximum catch size for the overshot, a spiral grapple is used (fig. 19). If tlH' fish diameter is well below the maximum catch size, a basket grapple assembly is installed (fig. 20). A basket grapple assembly maul' up with a mill control packer can be used to dress the top of a mildly distorted or burred fish so that it can be caught firmly by the grapples. Both tYVes of packers seal around the

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- -17 ACCELERATOR ?!!-:.!

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FIGURE

17.

SIMPLF: FISHING ASSEMBLY

TOP SUB

BOWL

FIGURE 19. OVERSHOT HAVING SPIRAL GRAPPLE (COURTESY OF BOWEN TOOLS, INC.)

GUIDE

FIGURE

18.

OVERSHOT (COURTESY OF BOWEN TOOLS, INC.)

fish, allowing drilling fluid to be pumped down to clean out the bottom of the hole. The operator runs the fishing string to within a few feet of the top of the fish. He starts circulation to clean cuttings and settlings off the top of the fish and to clean out mud cake that may have accumulated inside the overshot. He then lowers the fishing string slowly to touch the top of the fish and establish its exact depth. When the fish has been tagged, hook load decreases; the position is marked on the kelly. The string is

FIGuRE 20. OVERSHOT HAVING BASKET GRAI'PLF: (COURTESY OF BOWEi'. TOOLS, INC.)

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Before being run in, the knuckle joint is manually forced off center to make sure the lip on the wallhook opening faces about 90° away from the angle of the knuckle joint so that it will touch the fish. Spacer washers between the top sub and the knuckle joint are used to face the opening correctly. The knuckle joint is kicked off by running in a restriction plug and establishing circulation. However, good practice is to run the tool in with the restriction plug in place, because the pipe could become wall stuck in the time it takes the plug to drop to the knuckle joint. The joint is kept straight by running it in without circulation; it is then kicked off in the washout by starting the pumps. With the knuckle joint bent, the fishing string is rotated slowly to make a sweep around the cavity. If it does not touch the fish, the string is then lowered a few more feet and again rotated. When the wall hook tags the fish, the string torques up and the knuckle joint tends to straighten. The string is slowly raised; when the fish slips into the wall-hook opening, torque is released suddenly. The overshot can then be lowered to engage the fish, and the fish can be removed from the hole.

cuttings without rotation. If circulation cannot be fully established and the fish cannot be pulled, the fish is almost certainly stuck mechanically in the hole. Jarring. The situation described calls for the use of a hydraulic jar and a J'ar accelerator (figs. 25 and 26). The weight of the drill collars is

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.Fishing for Stuck Pipe As mentioned earlier, there are two main ways that pipe can become stuck in the hole: mechanical sticking by solid materials and differential sticking by fluid pressure. Keyseating is a special type of mechanical sticking that happens when the pipe becomes stuck during a trip. Although differential sticking is the most common reason for stuck pipe, fishing techniques are somewhat limited for recovering differentially stuck, or wall-stuck, pipe. Emphasis is therefore placed on preventing wall sticking from the start. : l

Freeing Mechanically Stuck Pipe After a fish has been caught in the overshot, the usual procedure is to circulate out the settled

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FIGURE

25.

HYDRAULIC JAR

or liquid in the jar accelerator, snaps the jar's piston and the drill collars upward. The mandrel knocker strikes the knocker sub with great force, jarring the stuck fish upward. Weight is again applied to the string to recock the jar for another blow. Jarring is continued until the fish is free and circulation can be restored. Finding the stuck point. If jarring does not free the fish, the operator must determine at what point in the hole the fish is stuck. The most reliable way to do this is to use a free-point indicator (fig. 27). This device, consisting of a tool

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26.

JAR ACCELERATOR

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put to bear on the fish to cock the hydraulic jar. A moderate pull is then taken to stretch the fishing string, compressing an inert gas or liquid in the jar accelerator above the drill collars. At the same time, oil in the hydraulic jar begins to seep between a piston and a cylinder. The cylinder restricts the first few inches of travel, but once the piston is pulled past the restricted length of the cylinder, there is little restraint. The stretch in the drill string, aided by the compressed gas

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into the hole on drill pipe and run to within 10 feet of the top of the fish. Circulation is established, and the washover pipe is lowered slowly over a joint or two of the fish left standing as a guide. Once it is determined that the washover pipe is going over the fish, rotation and washing over can begin. The washover string is rotated at 30 to 50 rpm, depending on how tightly the fish is stuck. Rotation and circulation are stopped every 20 to 30 feet to check for torque buildup and friction in the washover string. If torque becomes too great, it may be necessary to come out of the hole and remove part of the washover pipe. In a crooked hole, the top of the fish may be lying under a bend; the shortened washover pipe can conform more easily to the curvature of the hole (fig. 32). When the entire washover pipe has washed over the fish, the fish is engaged. An upward I

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pull on the fishing string indicates whether the rest of the string below the washover pipe is free and can be pulled. If it is not free, a string shot is run down inside the drill string and fish to within a joint or two of the bottom of the washover pipe. Left-hand torque is applied, the string shot is detonated, the freed pipe backed off, and the fish brought to the surface and stripped out of the washover pipe. Stripping the fish out of the washover pipe can be a long, hard job. The drill pipe and part of the fishing string are pulled, broken out, and set back until the washover pipe is in the rotary table and the slips are set around it. A split-slip holder, or bowl, is screwed into the threads in the top of the washover pipe, and split slips are set around the fish to hold it. The backed-off fish is stripped out of the washover pipe with the elevators. Finally, the washover pipe can be pulled, if necessary, to change the rotary shoe. To retrieve the remaining stuck fish, the washover pipe is again returned to bottom. This sequence of operations (washover and pulling) is repeated until all of the fish is retrieved. The last section of the fish is stripped out until the bit is pulled up near the bottom of the washover pipe. If the bit is too large to pass through, the fish and washover pipe must be pulled, suspended, and broken out together, a complicated and laborious procedure: double stripping 500 feet of washover pipe takes about 4Ifz hours. If the fish is stuck off bottom, a 'waslwver backoff connector may be added to the washover string (fig. 33). A washover back-off connector is made up in a length of washover pipe to engage the top of the fish after the washover pipe has washed over and freed part or all of it. The washover back-off connector is stabbed down the uppermost joint of washover pipe until the threads on the connector tool (sub) mate with the washover pipe threads.

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FIGURE 32. EFFECT OF SHORTENING WASHOVER PIPE IN A CROOKED HOLE

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Drilling out. Sometimes after backing off above the stuck point and pulling the freed section, the inside bore of the fish still in the hole becomes plugged by settlings or cavings, making it impossible to run a free-point indicator and

OVERRIDING ~--CLUTCH ~\",,"" _ _

FISHING STEM PISTON

";'--FISHING STEM

FIGURE

34.

FISH PLUGGED WITH CUTTINGS OR CAVINGS

FIGL"RE

35.

DnILLOl:T TOOL

OO,l¥---S PRING

WASHOVER SAFETY JOINT

WASHPIPE CONNECTOR - -..

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RACK-OFF CONNECTOR

string shot (fig. 34). Should this happen, a drillout tool can be used to reopen the fish (fig. 35). The drillout tool is run to the top of the restricted tish and made UlJ on it.

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A special hex kelly tipped with a junk mill is run in on wireline and inserted through a selfaligning bushing built into the kelly drive. Rotating the fishing string causes the kelly and mill to also rotate. Pump pressure forces the mill into the fish and washes out the cuttings. When the kel1y has drilied all the way down, drilling fluid exits through the side opening, or tattletale, causing pump pressure to drop. If more debris must be removed, the kelly is retrieved by wireline, and a short length, or pup )oint, of drill pipe is made up between the kelly and mill. This assembly is run back into the tool, and milling is resumed until the debris is removed. Finally, the mill and kelly are again retrieved by wireline, leaving the outer case of the drillout tool attached to the fish. The rest of the fish is then removed using standard back-off procedures.

Cutting pipe. Backing off at a tool joint is usually preferable to cutting pipe because it leaves a clean tool joint box in good condition "looking up" - that is, facing uphole - so that it can be easily screwed into or engaged by the fishing string. However, hole obstructions or pipe damage may make it impossible to back off at a connection. If the fish cannot be pulled or jarred loose, cutting the pipe between tool joints may be the only way to retrieve it. Both outside and inside cutters are available for this job. If a fishing tool must be run that will not allow a free-point indicator and string shot for a normal backoff to pass, a mechanical or hydraulic outside cutter may be run on the bottom of a washover pipe string far enough to get below the obstruction (fig. 36). After the cutter has been lowered over the fish to the desired depth, it is raised until slips, pawls, or (as in fig. 36) spring dogs engage a tool joint. If the cutter is mechanical, the driller takes a strain on the fishing string, causing the knives to move into cutting position. The tool is rotated slowly under strain until the pipe has been cut in two. A hydraulic cutter uses pump pressure to energize the piston and move the knives into cutting position. The washover pipe, cutter, and plugged part of the fish are then pulled from the hole.

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