Subsurface safety valves (SSSVs) are installed in the wellbore of hydrocarbon producing wells to shut off the production flow to the surface in case of an emergency. The importance of the correct installation of these valves to ensure well production flow is shut in during an emergency can not be over emphasised.
Improvements in valve design and reliability are of no avail if the valves are not correctly locked in the landing nipples (wire line run) and correctly function tested once installed. This article reviews the installation and testing procedures in order to prevent failure of the SSSV to operate as required. Reference should also be made to AP1 RP 14 B, Recommended practice for design, installation and operation of SSSV systems.
1. Workshop testing/assembly
Following complete redressing and servicing of surface controlled sub-surface safety valves (SCSSVs) in dedicated workshops, the following test/checks 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.
- Check in each case that the valve moves to the fully open position when it is operated into the open position.
- Pressure test (to test pressure rating of valve) the SCSSV from below, after installation in a test fixture/landing nipple.
- Pressure test should be conducted with hydraulic fluid rather than water to avoid corrosion during storage/transport.
- SCSSV should be stored vertically to avoid flattening of seals (on low side) which may occur if stored horizontally.
- 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 sub-assemblies filled with hydraulic oil before despatch to the rig site.
The recommended procedure for preparation of sub-assemblies is as follows:
- Physically check all tubing accessories, clean threads with solvent, thoroughly dry threads and inspect for damage.
- Ensure that two sets of each sub-assembly are available for back-up purposes, depending on equipment criticality.
- Functionally test all items of equipment with moving parts, e.g. open and close sliding sleeves.
- Make-up sub-assemblies as specified in vendor literature. Ensure that the correct thread compound is used and the correct make up torques are adhered to.
Where it is specified that joints should be made up with pipe locking compound (those below packer), the compound should be applied sparingly to pin ends only: after make up any excess needs to be cleaned off before it dries.
- Drift all sub-assemblies, from box end to pin end, with the appropriate API tubing drift, paying particular attention to items with moving parts (sleeves), as these can be squeezed during make up, thereby preventing/restricting movement.
Separate drift runs should be made-down to and through no-go nipples. Connections made-up with pipe locking compound should not be drifted until the compound has hardened.
- Carry out an API pressure test in each sub-assembly to the required pressure. Observation during the test should include every connection, and not just the pressure gauge, to ensure that minute leaks do not go undetected.
The test pressure should be equal to the maximum allowable pressure of the weakest link. The test consists of three parts:
- A primary pressure holding period of not less than three minutes.
- A reduction of the pressure to zero.
- A secondary pressure holing period or not less than three minutes.
The most important thing is to check for external leaks of connection and swivels.
- ·Accurately measure each sub-assembly and note:
-the position of such items as sliding sleeves;
-the serial numbers of the accessories;
-for gas lift valves and dummies, number each valve so that its exact location in the string is known.
It is recommended that accurate drawings are made of each sub-assembly for retention in the well files.
- Replace cleaned pin and box end protectors.
- Examine assemblies for tong damage. Dress out any damage, using files. If damage is excessive, a new sub-assembly should be made-up. Special care is required for CRA materials.
- Should the tubing/sub-assemblies have been internally coated with such compounds as Corban or Petrolite a check should be made for excessively thick deposits which could cause wireline problems later.
- All tubing and sub-assemblies should be box up/pin down unless specified otherwise.
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