Subsea Tree Installation, Lessons Learned on a West Africa Development

Abstract

Abstract A Subsea Production Development Project was undertaken in West Africa. The Development is a subsea production project in 1200 ft of water. Twenty-eight subsea Horizontal Trees (HT) were installed from 1999 through 2002 in four drill centers over several campaigns. A remaining five trees are scheduled for future installation. A project was undertaken to review and analyze the field service reports for each of these installations. The scope of this review included the subsea tree, tubing hanger, crown plug, internal tree cap, and debris cap. Ancillary operations such as wear bushing retrieval, bop test tool, straddle sleeve, and bore protector were also included. Other subsea equipment and interfaces were not subject to this analysis in order to maintain focus on the tree itself. The review of this data had several purposes:To compare the equipment and activity performances against related variables such as rig, personnel, well condition, and environmental conditions.For benchmarking, to establish mean and standard deviations of installation times and other key variable data such as landing loads, pull-out forces, etc.A critical review of the installation procedures against the actual field reports to look for "hidden factories" and other undocumented activities. Based on this review, the procedures were revised to both optimize the process, and ensure the required performance data is recorded.To establish a standard electronic format for the future collection of field tree installation data. This on-line database will be used to maintain baseline performance statistics, identify equipment performance trends, and formally address field failures for complete resolution. The field data will be back-loaded into this existing WELS (Well Electronic Log System) database, and all future tree installations will use this format. This paper will document the results of the West Africa installation data analysis, including:Presenting the installation data in chart and graph format.Drawing conclusions about the equipment performance and effectiveness of the procedures.Making recommendations as to the requirements for a tree installation data collection system. Introduction Project and Field Description The field, discovered May 1997, is located in West Africa in about 1200 ft of water. The operator for and on behalf of joint venture partners decided to develop the first of three phases as a fast-track early production system. First oil was in December 1999, 30 months after discovery and 15 months after contract awards. Refer to Figure 1 for an illustration of the full field development. The field is a full subsea development with a local FPSO host. The nature of the field dictated multiple drill centers and pressure maintenance on the natural drive reservoirs. The subsea architecture is a traditional cluster system with discrete wells surrounding central manifolds at each of the three major drill centers. Another key aspect of this development was the desire to maintain a Zero-flare environment for the produced gas.