Case History: Extended-Stroke Downhole Power Unit Successfully Pulls Subsea Wellhead Plugs
Abstract: 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 devicethat enables performance of deepwater subsea well interventions more cost-effectively than other service al… Show more
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Cited by 7 publications
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Today's need 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 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. As exploration continues to venture into more challenging environments, service companies have had to increase the scope of capabilities of their equipment to meet the challenges brought about by the new environments that require capability for tools to pull high tensile loads. The deepwater subsea arena has been particularly challenging, and this paper will focus on a slickline innovation ? an extended-stroke electro mechanical device ? that can provide deepwater subsea well interventions more cost-effectively than other service alternatives. The tool is a slickline-deployed electro-mechanical device that is operated by batteries rather than explosives or hydrostatic pressurized tools and can produce a high linear pulling force. 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 three case histories that discuss 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 as well as several subsequent case histories. Using the slickline electro-mechanical device rather than coiled-tubing resulted in substantial savings in both the cost of deployment and rig time. Introduction Subsea well intervention can be costly when one considers that the first task often required is to pull the subsea crown plugs in the wellhead. The hydrostatic pressure associated with the fluid in the riser creates the large pressure differential across the wellhead plugs that seal the cross sectional area. Conventional slickline services have limited constant pulling force due to the finite strength limits of the wire. Deepwater and debris above wellhead plugs often compound the required pulling force because of the additional hydrostatic pressure across the plugs. These forces are well above the tensile-strength limit of slickline wire. A subsea wellhead plug requires a steady pull along the entire length of the seal bore as it is withdrawn. Conventional slickline is limited to creating extremely high but short-duration impact loads; however, 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. Therefore, using mechanical or hydraulic jars to simplify the delivered force does 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. However, the cost of the service can be compromised significantly because of the additional deployment time, rig up time, and additional tripping time required. Since slickline is usually considered to be the most economical method for well intervention, the need for a system that could pull subsea well head plugs using slickline became more apparent.
Today's need 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 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. As exploration continues to venture into more challenging environments, service companies have had to increase the scope of capabilities of their equipment to meet the challenges brought about by the new environments that require capability for tools to pull high tensile loads. The deepwater subsea arena has been particularly challenging, and this paper will focus on a slickline innovation ? an extended-stroke electro mechanical device ? that can provide deepwater subsea well interventions more cost-effectively than other service alternatives. The tool is a slickline-deployed electro-mechanical device that is operated by batteries rather than explosives or hydrostatic pressurized tools and can produce a high linear pulling force. 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 three case histories that discuss 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 as well as several subsequent case histories. Using the slickline electro-mechanical device rather than coiled-tubing resulted in substantial savings in both the cost of deployment and rig time. Introduction Subsea well intervention can be costly when one considers that the first task often required is to pull the subsea crown plugs in the wellhead. The hydrostatic pressure associated with the fluid in the riser creates the large pressure differential across the wellhead plugs that seal the cross sectional area. Conventional slickline services have limited constant pulling force due to the finite strength limits of the wire. Deepwater and debris above wellhead plugs often compound the required pulling force because of the additional hydrostatic pressure across the plugs. These forces are well above the tensile-strength limit of slickline wire. A subsea wellhead plug requires a steady pull along the entire length of the seal bore as it is withdrawn. Conventional slickline is limited to creating extremely high but short-duration impact loads; however, 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. Therefore, using mechanical or hydraulic jars to simplify the delivered force does 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. However, the cost of the service can be compromised significantly because of the additional deployment time, rig up time, and additional tripping time required. Since slickline is usually considered to be the most economical method for well intervention, the need for a system that could pull subsea well head plugs using slickline became more apparent.
A new generation electro-mechanical downhole power unit for setting and retrieving packers, bridge plugs, whipstocks, subsea tree plugs, and other downhole devices has been recently developed and deployed. The new Downhole Power Unit - Intelligent, DPU-I® is designed to operate at high temperatures and extremely high pressures (400°F, 30K psi) and to provide up to 100K lbf setting force. The high force for either setting or retrieving downhole devices is independent of hydrostatic pressure and provides an alternative to jointed pipe or coiled tubing interventions, which were previously required to obtain high setting forces. New to the industry is the ability to monitor the downhole line tension, stroke length, setting force, the rate at which the force is being applied during the setting operation, and force at which the DPU-I detaches from the downhole device in real time at the wellsite or remotely by means of global satellite communications. This new functionality enables well completions experts to remotely monitor the setting or retrieval operations 24 hours per day, seven days per week. It also provides a record of the setting operation for risk mitigation, and for developing and improving best practices. This new downhole power unit conforms to our digital workflows used to model, measure, and optimize customer assets. The slow controlled setting operation enables the slips or other anchoring mechanisms in the device to be set and to fully engage the casing/tubing and for the elastomer sealing elements to conform to the casing or tubing ID. This function is extremely critical in highly deviated well conditions and when using casing or tubing with high Rockwell hardness. Unlike setting devices that use explosives, military or governmental escorts are not required. In addition, single lift heli-operations can be used. This tool does not require radio silence operations, and there is no nonproductive time associated with tool re-dressing between runs. Tool sizes are available for well intervention in 2 3/8 in. tubing through 13 3/8 in. casing and can be tractor-conveyed in high angle or horizontal wells. Introduction Traditionally, the method of choice for setting packers, bridge plugs, and similar wellbore devices consisted of conveying an electrically-activated explosive-charge setting tool to the required depth on electric line and activating the explosive train (deflagration) by applying voltage or current to the e-line. Although this explosively activated setting tool has been used in the industry for many decades, it has many limitations and safety issues:Requires explosive activation • Requires special explosive transport and rig/well site explosive storageRequires radio and telecommunication silence on the rig during operationsRequires personnel trained to use explosivesSetting force decreases with increasing hydrostatic pressureSetting force is rapidly applied over a few seconds, which may not be sufficient time for slips and elastomers to conform and engage in the casing/tubing.High temperature operations can be more difficult to perform reliablyNeed to re-dress between runs
Traditionally, when wells in extreme environments required service, slickline, which had always been considered as the most cost-effective service option, was unable to provide the services because the available slickline tool options could not maintain integrity in the extreme well environments now being explored and developed. To address the requirements of the new scope of conditions in extreme environments, new methods that would meet a greater scope of needs were developed. The innovations include prejob wire-tension-modeling software and a state-of-the-art timed-release tool that provides successful intervention in difficult scenarios that normally could not have been considered as slickline candidates. This paper will discuss these developments and how they have enabled slickline to be a more cost-efficient alternative for the operations that had to be performed by other service options when intervention was required in extreme depths or in or highly deviated wells. A tool that can be timed to release the wire from the tool string at the rope socket without surface intervention has been developed to reduce the risks associated with stuck strings and dropping of conventional wire cutters. In addition, pre-job wire-tension modeling software is now available. How the newly developed slickline techniques can be used to mitigate the risks associated with the challenges created by the extremely deep and highly deviated wells will be discussed along with the enhanced cost efficiency and safety provided by these innovations. Implementation of the smart-release tool into the tool string will also be discussed.
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