Subsea completions have been on the rise in recent years due to the economics, extreme environments, the use of infrastructures (subsea tiebacks), and migration to water depths in excess of 1300-feet. In this paper, subsea slickline operations are performed on three cluster wells situated beneath the operator's semi-submersible floating production unit in Vietnam's offshore Dai Hung field. The services were needed for reservoir management, including installation and retrieval of memory gauges, performance of logging surveys, and to manipulate sliding sleeves that had been installed with the ultimate purpose of optimizing hydrocarbon recovery. A subsea wireline unit (capable of deploying slickline and electric line) was chosen to provide the services. This unit was selected because of its cost efficiency and capability to perform a fishing job without impacting platform space and weight restrictions on the floating production unit as would have been imposed by use of a drilling riser. This paper will provide the case history of these services, which were unique in that these were the first diverless subsea slickline jobs performed solely with remote-operated vehicle (ROV) support for manipulation or assistance. Slickline provided an effective solution for the operator's service requirement within the specified criteria. Because of the versatility of newly developed advanced systems, slickline equipment was able to meet the restrictions of weight and size on platforms to provide a more efficient alternative for services that traditionally require rig mobilization.
As a result of the success of this operation, the operator is planning other subsea slickline services that will be performed without a drilling or jack-up rig.
With the present economic climate of the oil-and-gas industry, the significant costs normally associated with heavy workover and drilling facilities have strengthened the need to find other ways to enhance cost efficiency in subsea workover scenarios. To support this trend, innovative methods that have expanded the scope of operations that can be performed on subsea wells without a drilling rig have now been introduced. As an example, plug and abandonment operations can be performed with subsea wireline intervention units and other coiled tubing and wireline intervention techniques rather than with a tensioned riser from an anchored drilling vessel or a jack-up rig. With the new methods, the deployment system for wireline and coiled tubing does not require special system modification—any standard wireline or coiled tubing unit can be used. These techniques will be discussed more fully in the paper.
