Sintered bauxite is the primary proppant used during deepwater Gulf of Mexico (GOM) operations because of its high strength and conductivity. However, the use of bauxite proppant presents operational issues for coiled tubing (CT) resulting from its high specific gravity (approximately 3.6). This paper describes the planning and execution of a heavy post-fracturing proppant cleanout operation using CT in the operator's Tahiti field in the US GOM.
During completion operations on a subsea well, access to the well was provided by a dynamically positioned drillship. After installing the lower completion in the well using drillpipe, a proppant-laden stimulation treatment was pumped. During this process, an early screenout was encountered, and approximately 171,300-lbm proppant remained in the drillpipe that was unable to be reversed out. A CT unit was rigged up in a tension-lift frame that suspended the drillpipe string, allowing for a motion-compensated window to rig up the CT injector head and pressure- control equipment. A 1.75-in. outer diameter (OD) CT string was used to clean out the wellbore to 24,215 ft by circulating brine down the CT string and up and out of the drillpipe through a flow cross.
Preexisting contingency planning proved invaluable for efficient cleanout operations by providing the physical assets necessary to perform a successful operation as well as a framework for the engineering and procedures required. The drillstring was effectively cleaned of proppant to 24,215 ft. Once the well was deemed clean, kill-weight fluid was circulated into the well to allow for further well intervention operations and the eventual return to completion operations.
This case study illustrates the importance of contingency planning to help minimize overall operation costs. The large-scale and challenging well conditions of this unique project led to valuable lessons learned that can be used to optimize performance during future cleanout and drillship operations.