Shock Absorber for Use With Barrier Valves in Lubricator Applications
Authors: Sloan James , Andrews Thad 
Published: May 2016

Bottomhole assemblies (BHAs) are becoming much longer to carry equipment to the bottom of the hole. In many instances, these BHAs can be many hundreds of feet in length and may need to be passed into a live well. Under traditional conditions, a top-side lubricator is used and mounted directly to the wellhead to contain well pressure as tools are run into the hole. However, with today's longer-length BHAs, it becomes impossible to provide a lubricator with enough length to place on top of the wellhead to run tools.

To overcome this challenge, operators are beginning to use downhole lubricator valves so that longer BHAs can be deployed. This intervention technique works well, but has introduced a new challenge. What if the very long and heavy tool string is dropped or becomes loose and falls when running or pulling? Can a closed lubricator valve withstand this kind of impact? The equipment solution to these questions is a device called a shock absorber, which is mounted to the bottom of the BHA.

This paper discusses a shock-absorbing device that can be used to protect a lubricator barrier valve from damage in the event a BHA is dropped. It is operated automatically upon impact with the barrier valve and minimizes or eliminates any induced shock through the lubricator valve closure mechanism. If a BHA is dropped onto the lubricator valve, the BHA may be retrieved and the shock-absorbing device may be reset. Design considerations for a shock-absorbing device for use with BHAs to protect a lubricator barrier valve are covered. Test results will demonstrate the capabilities of this device with respect to a given load and drop velocity in protecting a lubricator barrier valve from damage.

Background

Operators are always challenged to perform well intervention faster and more safely. With the rising cost of rig time coupled with a highly emphasized HS&E culture, there has never been a greater need to deliver faster, safer well intervention. One strategy operators have used over the years to achieve this goal is to use the top portion of the completion as a downhole lubricator section. This completion technique offers operators the flexibility of assembling long strings of perforating guns, logging tools, and other downhole tools in an underbalanced well condition.

Conventional intervention techniques employ the use a surface lubricator system. When equipment is run downhole, a pressure-containing system (i.e. lubricator) is required to stage the assembling and running of the required intervention tools. Due to height restrictions and safety considerations, the length of tool assemblies is restricted. To overcome this limitation, multiple wireline or coiled tubing trips are required to perform the total scope of the scheduled intervention. Since the surface operations are exposed to live well conditions, the use of heavy kill fluids may also be required to balance the wellhead pressures.

To entertain the use of a downhole lubricator system, operators and service companies needed to identify equipment to serve as a barrier to the completion. The first natural choice of existing equipment was the downhole safety valve. The safety valve already was surface-controlled via hydraulic control lines which allowed the well to be shut in or opened remotely. This option was attractive, but would not be acceptable because only one barrier would be in place during intervention. Most operators require two barriers in place at all times. To overcome the redundant barrier design philosophy, early downhole lubricator systems have used tandem safety valves installed one on top of the other. This equipment arrangement has been used successfully; however, it does involve a few key drawbacks.