SCSSV

Assembly, Installation, and Testing SCSSV

Subsurface safety valve (SSSV) are installed in the wellbore of hydrocarbon producing wells to shut off the production flow to the surface in case of an emergency.

Design, installation, and operation of SSSV will be divided into assembly, installation, and subsurface tseting. The installation instruction of control line will be included.

I. Assembly/ Workshop testing

To complete servicing of SCSSV (Surface Controlled Sub-Surface Safety Valve), the following test should be carried out : 

Cycle the valve 4 or 5 times by alternately pressurising and depressurising the valve through the hydraulic inlet port. Observe the closure time and compare the opening pressure with the manufacturer's specifications.



Pressurise the control line port to the maximum test pressure.

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Check in each case that the valve moves to the fully open position when it is operated into the open position.

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Pressure test (to test pressure rating of valve) the SCSSV from below, after installation in a test fixture/landing nipple.

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Pressure test should be conducted with hydraulic fluid rather than water to avoid corrosion during storage/transport.

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SCSSV should be stored vertically to avoid flattening of seals (on low side) which may occur if stored horizontally.

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The SCSSV should be made up, preferably in a dedicated well services workshop into a sub-assembly prior to the well completion operation in order to facilitate rig handling. End caps should be fitted, control line exit/entry ports plugged-off and subassemblies filled with hydraulic oil before despatch to the rig site.

The test pressure should be equal to the maximum allowable pressure of the weakest link. The test consists of three parts: 1. A primary pressure holding period of not less than three minutes. 2. A reduction of the pressure to zero.

3. A secondary pressure holing period or not less than three minutes.

II. Installation of SCSSV

The procedures for installation of the valve will differ whether a tubing or wireline retrievable valve. In addition the type of lock mandrel etc. will determine specific requirements which need to be referenced in vendor or company specific manuals/documents. In all cases the control line for SCSSV will need to be run with the completion tubing.

II.1 Tubing Retrievable (TR-) SCSSV 

Function test and pressure test the TR-SCSSV at surface prior to running the completion.



Install at surface a hold open tool (HOT) to hold the TR-SCSSV in the open position throughout

the

completion

operation

(flow-tube

activated

type).

Normally, during running-in of the completion string, the control line is pressurised to monitor its integrity. However, the control line must be depressurised at a given moment in order to install the Xmas tree at which stage the TR-SCSSV will close, unless a HOT is used. 

Do not conduct a pressure test on a "TR"-type valve unless the pressure below the valve can be monitored at surface. (This precludes pressurising the tubing, closing the TR valve and bleeding-off the pressure from above).



TR-SCSSVs should not be used us a safety barrier when safeguarding a well for workover operations. Barriers in the form of positive shut-offs plugs should be used. The SCSSV is a device for safeguarding wells in emergency situations and should be used in this context only. Re-opening problems are particularly associated with ball-type valves due to the fact that the valve is designed for the ball to move down initially prior to rotating to the open position. In an unperforated or a well with a plugged tailpipe the fluid must be pressurised by this downward movement to permit valve re-opening. The re-opening operation is even more complicated when pressure exists below the closed TRSCSSV i.e. trapped pressure between a tailpipe plug and TR-SCSSV. Generally, the exact pressure during these operations is not known which further complicates the re-

opening operation. A further limiting factor is the working pressure of the control line. 

If a TR-SCSSV closure results during well completion/workover operations, the manufacturers' re-opening procedures should be strictly followed: A typical reopening instruction of an Otis 'DLS' TR-SCSSV valve is given below to illustrate such as procedure

Re-opening an otis type DLS with pressure below the valve

1.

Pressure up the tubing string until there is an indication that the valve is being pumped-through. (If the well is plugged below the TR-SCSSV indication of pump-through may not be noticeable, resulting in an even higher, pressure below the valve).

2.

Apply control line pressure to re-open the valve.

3.

Control line pressure must not exceed 4000 psi above tubing pressure and/or 2000 psi above the working pressure of the valve. Care should also be exercised so as not to exceed the Xmas tree rating.

4.

The pressure rating of the control line may be the limiting factor during this reopening operation.

5.

Due to the importance of recognising WHEN the valve is pumped off-seat, the use of a small capacity pump and continuous recorder is considered mandatory. A wireline run may be conducted to ensure the valve is open, care should be taken not to run/jar into a closed valve.

Notes :

In general the following points should be considered 

Always use HOT during completion workover when using TR-SCSSVs.



Do not use TR-SCSSVs as a barrier when tubing is plugged below.

II.2 Wireline retrievable (WL-) SCSSV Prior to installation in the well the following checks should be made: 

Cycle the valve using a hydraulic hand pump connected to the hydraulic inlet port. Check that the valve fully opens and closes.



Ensure that the mandrel and SCSSV packing stacks are undamaged and not bunched.

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Check the dimensions and condition of the mandrel lock pin carefully. Note that the mandrel lock pin dimensions are critical, due to the small overall dimensions (0.38 in.long 0.187 in.diameter). Any undersized or rounded-off lock pin shoulders could prevent locking of the fishing neck to the packing mandrel.

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Check the alignment of the lock pin with the slot in the 'expander sleeve' to ensure that the fishing neck will be locked when the mandrel is completely closed.

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•Ensure that the indicator snapring is in the correct position.

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•Tighten the prong firmly to the core of the running tool.

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•Install a running tool on the SCSSV as per vendor procedures after applying hydraulic pressure to the SCSSV hydraulic inlet port to open the valve before insertion of the running prong. Bleed off the hydraulic pressure slowly so that the valve contacts the prong gently, thus preventing damage to both prong and valve.



Ensure that the hydraulic control fluid using during workshop/surface testing is identical to that used in sub-surface operations, furthermore check that this fluid is uncontaminated with other fluids (e.g. water) and is free of solids. Check that the hydraulic system in the valve is completely fluid filled.

Notes : Some Operating Companies choose to run the SCSSV with the prong detached from the running tool, this, of course, requires an additional wireline run to retrieve the prong; but this has the advantage that should a misrun occur with the SCSSV not being properly installed in the landing nipple, resulting in no hydraulic control of the safety valve, the prong prevents the ball or flapper from closing and makes retrieval of the SCSSV a standard operation. This practice is not recommended by some manufactures and could lead to damage of the valve. However, this type of prong could prove useful during the retrieval of SCSSVs.

Running Wireline Retrievable SCSSV 1. Set zero on the depth indicator accurately so that the no-go or locator keys on the SCSSV are opposite the zero reference point on the wellhead. Ensure that the brokenout upper lubricator is lowered adjacent to the made-up position of the lower lubricator section, secured to the Xmas tree, before making this zero adjustment on the depth indicator. 2. Normally an SCSSV installation run is preceded by a recovery run. It is therefore recommended to accurately record the wireline depth of the SCSSV before its removal from the well. 3. Flush the control line with the correct hydraulic fluid during running-in operations. 4. Check the hanging weight of the tool string some 5 to 10 ft above the SCSSV landing nipple; continue pumping control line fluid and lower the SCSSV assembly into the nipple. Jar down gently, by hand if required, until a pressure increase is observed on the control line manifold. Stop pumping, mark the wireline at surface with a suitable marker 5. Jar down to shear the top shear pin and lock the SCSSV assembly in the landing nipple. 6. Check the distance required to accomplish full locking using the wireline marker as a reference point. 7. Apply tension to the wireline, 200 lb* overpull (*minimum value, higher overpulls are recommended if the wire size and strength permit.) 8. Jar up lightly by hand two or three times, followed by a 200 lb* overpull. 9. Jar up to release the running tool from the SCSSV assembly. 10. Recover the wireline tool string, taking care not to set down the tool string during the recovery operation. Check the indicating lock feature, snap ring and shear pin for full locking of the mandrel.

III. Sub Surface Testing of the SCSSV

III.1 Directly following SCSSV installation

Following SCSSV installation :

1.

Close the SCSSV by depressurising the control line, note the time required for returns to cease and record the time on the SCSSV record chart. Also note the volume of returns from the control lone.

2.

Depressurise the tubing above the SCSSV in four or five stages to zero or a predetermined pressure and observe for pressure integrity of the valve according to API RP 14 B (refer Section 13). During each stage check for leaks.

3.

Equalise the pressure across the closed valve, preferably using pressure from another well, and re-open the SCSSV by hydraulically pressurising the control line.

4.

Bring the well into production, allowing sufficient time for stabilisation of the flow (stable tubing head pressure/temperature) before conducting the SCSSV closure test under flowing conditions.

5.

Bleed off the control line pressure to zero. Note the time elapsed after triggering the control line pressure until a reduction in tubing head pressure is observed (Valve closure time). Record this information.

6.

When the tubing head pressure has decreased to a predetermined pressure, closein the wellhead flow-wing valve and observe for SCSSV integrity according to API RP 14 B.

7.

Re-open the valve after equalisation and observe the hydraulic pressure required to achieve this. (i.e. pressure required to initiate valve opening and that required to operate the valve from closed to open position).

8.

Note the control line operating pressure under flowing conditions.

3.2 Routine Testing of the SCSSV The frequency of the routine testing of the SCSSV is based on valve performance in each operating area. Generally a valve in a new field will be tested more frequently than in an established area or field where a reliable valve performance indication has been established over the years. Obviously a valve should be cycled from time to time in order to avoid 'freezing' of the valve in the open position, which is the mode in which the valve is normally maintained when installed downhole. This fact should be borne in mind when establishing the interval of time between tests. Comparison of the data received will assist in determining the condition of the valve and estimation of the optimum period of time before valve reservicing, in the case of the WL-SCSSV, is required.

Once the Frequency of testing of SCSSVs has been established for a particular field/well, the interval of time between tests should be reviewed periodically. This test frequency review is considered necessary due to changing well conditions (increase in water cut, wax formation, change in gas composition, etc.) which could adversely affect valve performance. Legislation may influence the frequency of in-situ testing.

This is recommended routine test procedure : 1. Close in the well using the flow-wing valve. 2. Depressurise the control line pressure 3. .Conduct a pressure test across the shut SCSSV by bleeding off the pressure above the valve to zero. 4. Re-open the SCSSV after equalisation, preferably by pressurising with another well and return the well to production.

Record the test data The following data should be accurately measured and recorded during routine SCSSV testing: 1. Minimum control line pressure - well flowing. 2. Pressure test data, SCSSV shut (well closed-in on flow-wing). Test procedure according to API RP 14B. 3. Control line pressure to re-open the SCSSV after equalisation. 4. After return of the well to production and stable conditions have been established record accurately the tubing head pressure and flow rate. Check the control line pressure and adjust it, if required. (Thermal effects could increase the control line pressure considerably).

The maximum pressure build-up allowed during SCSSV tests, both on installation and routinely, should be calculated according to the formula published in API RP 14B.

IV. Control Lines 1/4in OD continuous steel tubing is generally standard for control lines, available in carbon steel, stainless steel and copper-nickel based alloys. The lines can be encapsulated in various jackets and supplied in dual form with/without a stress cable. The mechanical strength of the reflected material needs to be appropriate for the conditions during installation.

Prior to running the control line in a completion, it should be thoroughly flushed with clean control fluid and pressure tested. During running, a nominal pressure should be maintained on the control line and it should be kept under tension. The control line should be securely clamped at each tubing connection to both protect the line and retain it against the tubing. Hydraulic tensioning machines are available to assist in running the control line.

Control line or cable protectors that straddle the collar reduce the number of protectors required and give protection to the control line where they are most susceptible to damage.

'Swagelok' connections are commonly found to connect control lines, following gives the correct procedure for make up of these connections.

4.1 Installation Instructions Swagelok tube fittings come completely assembled, finger-tight. They are ready for immediate use. Disassembly before use can result in dirt or foreign material entering the fitting causing leaks. Swagelok tube fittings are installed in three easy steps: 

Step 1: Insert the tube into the Swagelok tube fitting. Ensure that the tubing rests firmly on the shoulder of the fitting and that the nut is finger-tight.

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Step 2: Before tightening the swagelok nut, scribe the nut at the 6.00 o'clock position.

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Step 3: While holding the fitting body steady with a back-up wrench or vice turn the nut one-and -one-quarter turns*. (Watching the scribe mark, make one complete revolution and continue to the 9.00 o' clock position.

4.2 Swagelok inspection gauge The Swagelok inspection gauge is a device to determine when most fittings have been properly tightened. It is designed to assist personnel in checking an installation. It is not a necessary part of the Swagelok installation.

If the gauge fits between the Swagelok nut and the body hex of the fitting, it indicates that the fitting has not been sufficiently tightened.