A Case Study in the Design and Execution of Subsea Production Development Wells in the Captain Field

Abstract

This technical paper outlines the challenges presented and solutions chosen to allow execution of the well construction design for the Captain Area ‘B’ subsea development. It is intended to give an overview of how a blend of proven and emerging technologies can be applied to develop such fields in innovative ways in order to meet performance metrics. Introduction The Captain Field is located in Block 13/22a in the UK sector of the North Sea, approximately 130 km north east of Aberdeen, in a water depth of 369 ft. Due to the high viscosity and low temperature of Captain oil, long, horizontal wells are required to effectively drain the reservoirs (Fig. 3). Although the field was discovered in 1977, it was not until 1995 that appropriate technology was available and development approval was received. The field is being developed as a phased installation of two drilling centres tied back to a centrally located floating production, storage and offloading vessel (FPSO) by ChevronTexaco and its partner, Korea Captain Company Limited (KCCL), which has 15% equity. The first phase of development consisted of the FPSO and wellhead protection platform (WPP) at the Area ‘A’ drilling centre, 1.5 km west of the FPSO. The second phase of development is termed the Captain Area ‘B’ Expansion. This includes a subsea development, some 2.2 km east of the FPSO, to access reserves in the Eastern and ‘gas-cap’ part of the field, called Area ‘B’. The process throughput has also been increased by the addition of a bridge-linked platform (BLP) to the WPP (see Fig. 1 for the field layout and Fig. 2 for Captain field map which highlights areas ‘A’ and ‘B’). Nine subsea production wells have been drilled from the UTM to date. Drilling operations commenced in Sept 2000 and are due to finish in April 2003. The rig has also worked for other ChevronTexaco assets during this period. In order to meet economic metrics it was necessary for the Captain Expansion to be a subsea development with long drain sections through the unconsolidated sandstone reservoir. Hydraulic submersible pumps (HSP), with an integral bypass system, were also required as they brought good gas handling characteristics and removed some of the disadvantages associated with subsea electric submersible pumps (Ref. 1 and 2). As a result, while completions have been among the most challenging, through effective risk management of the solutions, they are among the most successful to date in the North Sea for ChevronTexaco. A key milestone in this process was the successful field trial of a prototype HSP on platform well 13/22a-C13 and is outlined in detail in ref. 1. The background information on the geological aspects and the production drivers will outline the requirements for technical solutions such as extended reach drilling (ERD), associated long sand control completions and state-of-the-art subsea equipment. The impact this had on rig selection and modification will also be explained. The performance metrics for the first nine subsea production wells are testimony to the equipment, design and execution associated with this development. Geological Setting and Structure The Captain Field is a large (1000 million barrels STOIIP (Stock Tank Oil Initially In Place), shallow (–2,800 ft true vertical depth, subsea - TVDSS), heavy oil accumulation. The major reservoirs comprise thin, poorly consolidated, turbiditic sandstones spread over a large, 53 Km2 area (Fig. 2). Salient reservoir properties are summarized in Table 1, below.