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 whenthe cleaning string is made up and when it is laid down after displacement and filtration operations are completed can exceed two days and cost $500,000. Itis 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.
The Ceiba field in deepwater Equatorial Guinea was discovered in mid 1999 by Triton Energy Ltd., now Amerada Hess. To date, twenty 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 remainder were cased-hole producers or injectors. The initial average pore pressure in the field was 8.7 lb/gal, and the majority of wells in the field were completed in a 9.0-lb/gal to 9.2-lb/galCaCl2 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 using mineral oil based mud.
The Ceiba field lies in approximately 800 meters of water. The wells flow through individual subsea flowlines for eight to eleven kilometers to an FPSOthat was positioned to receive first oil in the late fall of 2000.1The semi-submersible Sedco 700 has been on location in the field since the spring of 2000 and has drilled a 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 in order to optimize this process. A review of cased-hole completions by the taskforce indicated room for improvement in our displacement process and chemical utilization. At the time the task force was formed, the average displacement took 25 or more hours with up to 4000 bbl of completion brine discarded due to 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 is presented to show simplification of procedures, improved mud solids removal, shorter filtration time, reduced loss of brine and shorter rig time over the course of the development. These modifications and changes had a major impact on time and cleaning efficiency. Ceiba openhole completion displacements are not addressed in this paper.
The displacement stage of a completion is considered to commence with the makeup of the casing clean out string consisting of a bit, casing scrapers and brushes, magnets and junk baskets, riser brush and riser jetting tool. The stage ends when these tools are pulled from the hole and laid aside. In between these events, fluid already in the hole is replaced by seawater followed by completion brine. Several intermediate operations are usually required to affect the successful replacement of mud or seawater with brine. These include 1) conditioning the mud or circulating the hole; 2) short-tripping the drillpipe to scrape the casing wall or to pick up or lay down a tool;3) jetting the blowout preventer (BOP) stack and wellhead to remove pockets of mud, cuttings or scale debris; 4) pumping a series of displacement spacers around the wellbore; 5) rotating and reciprocating the drill pipe while pumping to facilitate mud or scale removal and 6) filtering the completion fluid to the desired level of clarity (+/- 20 NTU's).