Summary
Brine displacements were one of several areas of focus in a continuous process to optimize completion methodology in Amerada Hess's Ceiba project wells, located in deepwater offshore Equatorial Guinea. The time between making up the cleaning string and laying it down, after displacement and filtration operations are completed, can exceed two days and cost U.S.$500,000. It is imperative that wellbore-cleaning operations are performed efficiently and correctly the first time. Amerada Hess and its brine suppliers, working together in a joint task force, have taken specific steps to minimize the time required for displacement and filtration operations.
Introduction
The Ceiba field in deepwater Equatorial Guinea was discovered in mid-1999 by Triton Energy Ltd., now Amerada Hess. To date, 20 wells have been completed, and three wells have been recompleted. Ongoing development of the field still continues at this time. Five of the wells were completed as openhole gravel-packed producers. The others were cased-hole producers or injectors. The initial average pore pressure in the field was 8.7lbm/gal, and the majority of wells in the field were completed in a 9.0 to9.2-lbm/gal CaCl2 brine. This fluid was selected because of its minimal damage effect during core tests and its ready availability at stock points in the west Africa operating area. All wells were drilled through the pay interval by use of mineral-oil-based mud.
The Ceiba field lies in approximately 800 m of water. The wells flow through individual subsea flowlines for 8 to 11 km to a floating-production, storage, and offloading unit that was positioned to receive first oil in the late fall of 2000.1 The semisubmersible Sedco 700 has been on location in the field since the spring of 2000 and has drilled the majority, and completed all, of the Ceiba development wells.
As part of a continuing improvement program used throughout the development of Ceiba, a critical review of brine-displacement practices was performed to optimize this process. A review of cased-hole completions by the taskforce indicated room for improvement in our displacement process and chemical usage. At the time the task force was formed, the average displacement took 25or more hours, with up to 4,000 bbl of completion brine discarded because of poor quality and filtration problems. This paper examines the stages of mud-to-brine displacement used in the cased-hole completions of the Ceiba deepwater development and demonstrates how these stages were adjusted in their relationship to one another to make a more efficient displacement. Data are presented to show simplification of procedures, improved mud-solids removal, shorter filtration time, reduced loss of brine, and shorter rig timeover the course of the development. These modifications and changes had a major impact on time and cleaning efficiency. Please note, Ceiba openhole-completion displacements are not addressed in this paper.
