The primary purpose of surface-controlled subsurface safety valves (SCSSV) is to limit flow during catastrophic events. Reliability is critical, but in practice not always delivered.
While some downhole equipment remains static throughout the life of a completion, safety valves are routinely opened, closed, and tested to ensure reliability. A study by the Norwegian research institute SINTEF identified failure of the control fluid communication system as the primary cause of safety valve failures.1
Age and general wear and tear can also lead the flapper to fail or become stuck or even closed, halting production. The unscheduled workover that follows may also require installation of an insert safety valve with restrictive internal diameters (ID).
Following the malfunction of a SCSSV on a producing well in the Gulf of Mexico, Coretrax was called in for remedial action. With no control of the flapper valve and no way of hydraulically or mechanically forcing it to stay open, the company deployed its Tubing ReLineWL straddle. Unlike conventional straddles, the ReLineWL’s slim 4-in. outside diameter allows it to bypass various ID restrictions, in this case collapsed casing above the valve, to reach the flapper valve.
A dummy run was successfully performed with a 4-in. washpipe before the caliper logs, slickline runs, and e-line gauge runs with the wireless casing collar locator were deployed. A purpose-built WirePatch was also modified to run on the coil tubing, pass through the restriction, and set across the faulty SCSSV.
The wireline-run patch, with a setting pressure of 3,800 psi (262 bar) and operated from a light intervention vessel, creates a large ID to optimize access to the wellbore. The aims are to negate integrity issues caused by water, gas and sand shut off, and to avoid corrosion isolation, collar leaks and perforation shut off, thereby allowing a maximum production conduit to the surface.
For the malfunctioning SCCSV the patch, once in position at a depth of 8,675 ft (2,644 m), was expanded to 3.35-in. to allow the previously inoperable safety valve to be permanently opened. This resulted in full well access, facilitating removal of the upper completion and saving significant rig-time, compared to a traditional milling approach. The operator was then able to continue with workover operations as planned.
The one-trip, rigless system can deliver a 700% greater flow area compared with traditional straddles, allowing a patch to be installed without creating a restriction. It also dispenses with the need to install and manage a new completion.
The tool, with a high expansion ratio of 75%, is designed for stackability so that a longer, integrated straddle can be deployed, without losing ID. This in turn opens access below should well intervention be required at a later date. The system can also be configured to smart completion products such as autonomous inflow devices to enhance production by selectively eliminating gas and water production.
Expandable technology, in use since the 1990s, can reduce the overall cost of wells and support infrastructure by adapting and enhancing the basic design of liner hangers, packers and thru-tubing straddles. Demand is growing in North America, the North Sea, and Norway in particular, where operators are looking to improve recovery and revenue from mature fields.
Reference
1. “Reliability of Surface Controlled Subsurface Safely Valves - Phase IV,” Foundation for Scientific and Industrial Research, Norwegian Institute of Technology, Report No. STF75 R91038, 1992.
