As exploration continues to venture into more challenging environments, service companies have had to increase their scope of capabilities to meet the challenges brought about by the new environments into which the oil and gas industry has ventured. One of these areas has been the deepwater subsea arena. This paper will focus on one of the slickline innovations ? an extended-stroke electro mechanical device ? that enables performance of deepwater subsea well interventions more cost-effectively than other service alternatives.
Today's needs to provide deepwater subsea well servicing has created many new challenges for the industry. For example, pulling a deepwater subsea wellhead or crown plug can require an extreme pulling force. The difficulties experienced can be compounded by conditions that occur when the plug has been in place for extended periods of time as well as the more demanding deepwater conditions, such as high differential forces and settlement on top of the plug that contribute to the need for the higher pulling forces. These conditions often exceed the capabilities of conventional slickline services.
An option that has met other challenges in difficult scenarios is a slickline-deployed electro-mechanical device that produces a high linear pulling force directly at the wellhead plug without jarring. This tool does not require explosives or hydrostatic setting tools because it is operated by batteries. Since first being introduced, the electro-mechanical device has undergone several changes that have increased its capabilities and functionality. For example, it has recently been configured for pulling subsea wellhead plugs.
This paper will present a case history that details the first use of the 'extended stroke' electro mechanical device in the Gulf of Mexico in which it was capable of pulling plugs at a water depth of 5,339 feet. Using the electro-mechanical device with slickline instead of coiled-tubing resulted in a substantial savings in both the cost of deployment and rig time.
Well servicing of subsea wells can be expensive when intervention is required. When servicing subsea wells, one of the first tasks required is to pull the subsea crown plugs in the wellhead. Conventional slickline services have limited pulling force due to the finite strength limits of the wire. Deepwater and debris above wellhead plugs compound the required pulling force due to the hydrostatic pressure that creates a differential across the plugs. The hydrostatic pressure associated with the fluid in the riser creates a large pressure differential across the wellhead plugs created by the sealing cross sectional area. These forces are well the tensile strength limit of above slickline wire.
A subsea wellhead plug requires a steady pull along the entire length of the seal bore as it is withdrawn. Using mechanical or hydraulic jars to simplify the delivered force, conventional slickline is limited to creating extremely high but short-duration impact loads. Brief impact loads are not suitable for unseating subsea wellhead plugs because they have a tendency to reseat after each impact load and are forced back on seat by hydrostatic pressure from above. Thus, conventional slickline jarring may not effectively retrieve the plug from the wellhead.
When conventional slickline service is not capable of pulling a subsea wellhead plug, coiled tubing service methods may be used. Using coiled tubing services to pull subsea wellhead plugs can compromise the job economically because of deployment time, rig-up time, and tripping time.