Planning for Successful Rig Assist HP/HT Cleanout Operations

Abstract

This paper describes the equipment and techniques that were used for a high-pressure, high-temperature (HPHT) cleanout operation carried out on the Shearwater platform in the UK central North Sea with the support of a jackup drilling unit. The project involved intervention in three wells over a period of 9 months. The wells had been shut in for some time following production of reservoir solids. A hydraulic workover unit (HWU) was selected to clean out the production tubing to allow isolation barriers to be installed. In rig-assist mode, the HWU deploys pipe against surface pressure with the rig providing pipe-handling support. The paper details the planning and pre-engineering work that preceded offshore operations. Detailed planning and risk assessment were also required during operations because well conditions changed. Some equipment problems required a review of planned operations, and during an annual process plant shutdown, onshore tests were carried out before mobilization for the second phase of the intervention project. Modifications were required to the HWU to withstand the high buckling loads associated with snubbing against high pressure. Additionally, special downhole tooling was required to accommodate extreme well conditions. The paper discusses the development work involved and the subsequent performance of the equipment. Operating performance statistics and key lessons learned during the project are presented. Introduction The Shearwater field is located in the central North Sea in Block 22/30b, approximately 138 miles east of Aberdeen (Fig. 1). The field was discovered in 1988 and developed with dual platform facilities. The development consisted of a process, utilities, and quarters (PUQ) platform linked to a wellhead platform (WHP) by an 80-m (262-ft) bridge (Fig. 2). The platforms are installed in 90 m (297 ft) of water.