Sub-surface safety valves (SSSV)

2.  Installation of SCSSV

The procedures for installation of the valve will differ whether a tubing or wireline retrievable valve as discussed below. 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 SCSSVs will need to be run with the completion tubing.

The sub-assemblies including SCSSV should preferably be made up at the base workshop, as discussed above. However, on site it is recommended to re-perform the majority of the above checks. Reference should be made to API spec 4A Appendix F which describes the recommended procedure for field pressure testing. As proper testing facilities are not usually available on-site, appreciate safety precautions need to be ensured.

2.1 Tubing Retrievable (TR-) SCSSVs

  • 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 TR-SCSSV 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 re-opening 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 re-opening 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.

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.

2.2 Wireline retrievable (WL-) SCSSVs

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.

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.

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.

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

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

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.

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 WR 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 broken-out 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.

The distance from when the inlet hydraulic port is straddled by the packing sets to the SCSSV hold-up depth is known. Continue jarring down gently until this known distance has been traversed by the SCSSV assembly.

5.Pump the control line to working pressure, shut off the air supply to the pump and observe for pressure integrity of the control line.

6.Jar down to shear the top shear pin and lock the SCSSV assembly in the landing nipple. 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.


#2 Michael L Schield 2017-01-27 18:09
I would like to know about the retrieval tool used to pull the plug from the tr SC sssv . How it works and also how it is assembled?
#1 Chris Newton 2015-06-04 13:54
Completion Question.
Water depth 400 meters / 1312 ft. Completion string run and set. What do you people recommend as the two best barriers having in place prior to unlatching & pulling the BOP in preparation to running a Vertical subsea tree, not a Horizontal tree.
Thank you.
Regards, Chris Newton