Economic and Operational Benefits of Drill-Through Completion Technologies

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper OTC 17405, "Economic and Operational Benefits of Drill-Through Completion Technologies," by M. Matusek, S. Stjernstrom, and D. Theiss, Cooper Cameron Corp., prepared for the 2005 Offshore Technology Conference, Houston, 2–5 May. The drill-through completion concept revolves around the principle that substantial cost savings can be realized by installing the subsea horizontal tree before running the blowout preventer (BOP) stack, thus eliminating one BOP stack round trip. Drilling operations are performed through the subsea horizontal tree. Additional cost savings can be achieved in a batch-drilling and -completion program by reducing the number of required rig moves and BOP-stack trips. Introduction Interest in drill-through systems has increased in recent years as oil companies search for ways to reduce installation and workover costs associated with deepwater drilling and completions. As water depth increases, time required to deploy equipment to the seabed and the day rate of a rig capable of operating in deeper waters increase. As a result, the value of reducing deployment trips and improving operations reliability increases. The horizontal subsea tree has had a large influence on the way completion and workover operations are conducted. Drill-through technology allows some or all of the drilling operations to be conducted through the tree—providing numerous opportunities to save time and money, particularly in deepwater operations. Benefits The conventional approach to drilling and completing wells involves two round trips of the BOP stack. The drill-through approach to drilling allows the horizontal tree to be installed on top of the wellhead high-pressure housing before running the BOP stack, so that all drilling operations are performed through the tree. The tree is capable of drifting all of the drill bits, casing hangers, seal assemblies, and associated running/test tools required during the drilling and wellhead-installation process. This drilling and completion method requires only a single BOP-stack trip. By eliminating one of the round-trip BOP-stack deployments, substantial cost savings can be achieved. For a rig operating in 6,000 to 8,000 ft of water, deployment of the BOP-stack and drilling-riser system is estimated to require 4 to 5 rig days. Another 8 to 12 hours are required to test the BOP-stack connections, functions, and control system once it is landed. BOP-stack retrieval is estimated to require 3 days of rig time. With the cost for deepwater rigs estimated to be U.S. $180,000 to $240,000 per day, the estimated cost to make one BOP-stack and riser-system round trip is U.S. $1,300,000 to $2,000,000. This cost may be significantly higher if poor weather conditions delay operations.