Capillary tubing is hung from an adapter just below the wellhead to provide surface control of the new wireline-retrievable safety valve insert.

Subsurface safety valves are critical to safe operation of oil and gas wells offshore and onshore in areas with high hydrogen sulfide levels.

Typically, these valves are controlled from the surface through a small- diameter hydraulic line that runs up the annulus behind the production tubing. If this line is compromised (e.g., by storm damage, a lifetime of bending and rubbing, corrosion, or plugging), the valve becomes inoperable.

Repairing the control line is usually not an option, so operators have been forced to choose between performing an expensive workover or installing inflexible and unreliable velocity valves or storm chokes that limit production and require expensive maintenance operations.

A new option allows for insertion of a wireline-retrievable safety valve that is controlled from surface by a through-tubing control line, thereby restoring the well economically to normal operations.

Losing control

Surface-controlled subsurface safety valves (SCSSVs) are an integral part of the safety and environmental system of any offshore well and are typically required in offshore wells and areas with high hydrogen sulfide levels.

Primary (tubing-retrievable) SCSSVs are installed as part of the production string and designed to stop flow in the event of a catastrophic failure. Regulated under API 14a, they must be able to convert to a hydraulic nipple so that a wireline-retrievable insert valve can replace the primary valve in case of malfunction.

SCSSVs are held open by positive hydraulic pressure through a control line, typically a 1?4-in. tube that runs from the valve to the surface control system in the annulus between the production tubing and the casing/liner. An emergency shutdown depressurizes the control line, so the valve reverts to its fail-safe closed position. Re-pressurizing the line opens the valve.

If the integrity of the control line is compromised in any way, loss of surface control of the SCSSV is likely. In this case, the operator has four options to restore control:
1. Pull the completion and replace the control line. This option is typically cost-prohibitive.
2. Apply a control line vacuum. This option occasionally works to dislodge a plug.
3. Inject control line sealants. These are sometimes effective for minor leaks, but the result is temporary.
4. Install a velocity valve or storm choke. In the Gulf of Mexico (GoM), the US Minerals Management Service (MMS) reluctantly grants variances to oil and gas operators who request permits to install storm chokes on wells that have lost control line integrity.

The differential pressure or rate at which a velocity valve closes is controlled by setting a mechanical spring or charging a gas chamber within the valve. When the differential pressure across the valve exceeds the force of the mechanical spring or gas chamber, it closes, shutting in the well. To reopen the valve, the pressure differential across the closed valve must be eliminated. Since these devices do not provide surface control, a well intervention is required.

Velocity valves can close unintentionally due to a change in well flow characteristics or can fail to close for the same reason.

If well flow is erratic, if the well undergoes fluid slugging, or if the operator wishes to increase the flow rate, a well intervention would be required to pull the valve and reset it. Intervention also is required in conjunction with mandatory MMS valve testing protocols.

Restoring control

To avoid interventions, BJ Services’ Reconnect system restores surface control and reliable operation with three key components: a modified wireline-retrievable SCSSV (Figure 1), a replacement control line, and a wellhead adapter.

Normally, to convert a damaged tubing-retrievable SCSSV to a hydraulic nipple that can accommodate a new wireline-retrievable SCSSV, a lock-out tool is run on wireline to permanently lock open the valve, and then a communication tool is run to penetrate the hydraulics connected to the control line in the annulus. The wireline insert valve then functions like the original device.

If the hydraulic control system is damaged, however, a different solution is needed. The reconnect system SCSSV
is similar to a standard wireline insert valve except that it has no external hydraulic port. Instead, its upper extension tube is modified to accommodate an internal polish-bore receptacle (PBR) that communicates hydraulically with the valve.

The PBR receives a stinger that is deployed and landed as the bottom piece of the replacement control line, which is a string of capillary tubing. While running in the hole, the stinger and capillary tube are positively isolated by a spring-energized sheath that covers the stinger’s hydraulic ports until it is positively engaged in the PBR.

At the wellhead, the conventional SCSSV control line terminates at the production tree, either penetrating through the tubing hanger or exiting between two seals on the outside diameter of the hanger. In the reconnect system, an adapter spool is installed between the tubing head adapter and the lower master valve (or tree, in the case of single-block trees). The spool adds only 111?4 in. to the height of the wellhead assembly and enables control line termination with system integrity and full functionality of all tree components.

The spool, manufactured to API 6a standards, incorporates a test port, a hydraulic fluid injection port, and an integral needle valve. A mandrel inside the spool flange engages the tubing hanger’s original backpressure valve (BPV) threads to provide a primary seal. External seals straddle the injection port location, providing communication from the hydraulic fluid injection port to the capillary tubing hanger locked inside the mandrel. The mandrel is deployed with the same rods and lubricator that are used to introduce a BPV for tree isolation. An additional BPV thread profile is added to the top of the mandrel for use in routine tree maintenance operations.

The capillary hanger is designed to land inside the mandrel and snap-lock into position. The hanger has two exterior seals that straddle the chemical inlet port. Production flows through a kidney-shaped cavity within the capillary hanger.

Most importantly, all components are landed below the lowest master valve, and the added backpressure threads can be used to obtain a second barrier, allowing full MMS compliance for upper tree maintenance or replacement.

Field experience

A mature well in the GoM developed an SCSSV control line leak. Injecting sealants did not repair the leak. The operator considered installing a velocity valve but the well was scheduled for a plug-and-abandonment operation for one zone and perforation of a new zone. Adjusting and re-adjusting a velocity valve for the new zone was expected to be time-consuming and expensive because of the well’s remote location. The reconnect system was seen as a more economical choice.

The system was installed in August 2008 and tested to ensure compliance with MMS regulations. The operator now has the flexibility to vary the well’s production rate without the intervention required to pull the velocity valve and adjust the differential pressure settings.

In addition, the operator has been able to perform mandatory testing of the downhole safety valve without the added cost of a liftboat previously required due to the small platform’s limited crane capacity and deck space. For this functionality alone, the system paid for itself after one test.