Drilling-Fluids Planning and Execution for a World-Record Ultradeepwater Well

Abstract

This article, written by Assistant Technology Editor Karen Bybee, contains highlights of paper SPE 92587, “Drilling Fluids Planning and Execution for a World Record Water Depth Well,” by J. Dieffenbaugher, SPE, and R. Dupre, SPE, Chevron Corp., and G. Authement, SPE, G. Mullen, SPE, Y. Gonzalez, SPE, and P.B. Tanche-Larsen, Baker Hughes Drilling Fluids, prepared for the 2005 SPE/IADC Drilling Conference, Amsterdam, 23–25 February. Drilling-fluids planning plays a major role in reducing the likelihood of drilling problems in ultradeep waters. Because deepwater drilling is expensive, proper drilling-fluid selection requires careful planning. Common deepwater challenges include hydrate suppression, shallow water flows, equivalent-circulating-density (ECD) management, lost circulation, and viscosity profiles. The full-length paper discusses the planning and execution of a drilling-fluids program for a world-record ultradeepwater well in 10,011 ft of water in the Gulf of Mexico (GOM) Alaminos Canyon Block 951. The well was drilled to a total depth of 22,695 ft by use of an advanced synthetic-based mud (SBM) that met all GOM compliance requirements. Introduction Since the mid-1990s, operators have explored and developed fields in ever-increasing water depths. The industry has identified techniques and developed new technology that allows them to drill wells safely and successfully in water depths greater than 10,000 ft. Because of the presence of young sedimentary deposits, many of these wells have an extremely narrow margin between the pore pressure and reservoir fracture pressure. The deeper the operator can set the initial casing string, the greater the likelihood of drilling success. Use of a riserless drilling technique has been instrumental in extending casing depths in deepwater and ultradeepwater environments. This technique played an important role in the success of this challenging ultradeepwater project, because the initial upper section was extended to obtain required leakoff tests (LOTs) at the 22- and 17⅞-in. casing shoes. The unmatched combination of technical performance and environmental compliance of synthetic-based drilling fluids has made them the preferred fluids for deepwater drilling in the GOM. On the basis of an overall analysis of this project, the operator selected a proprietary synthetic drilling fluid for drilling the well from the 18×22-in. section to total depth (TD). This decision was based primarily on the presence of highly reactive shales in the deepwater formations and the previous performance of the drilling fluid in offset wells. Several important factors must be considered in the deepwater environment. Most important is the effect of temperature and pressure on the fluid system. As water depth increases, temperature decreases and pressure at the seabed increases. A typical temperature curve for the GOM indicates an average seabed temperature lower than 40°F at water depths greater than 4,000 ft. This cooling, combined with increased pressure, influences drilling-fluid design. Because of the chemical composition of the GOM-compliant synthetic-based fluids, the cooling will increase the viscosity of a base fluid, resulting in an increase in the overall drilling-fluid viscosity.