Abstract
Technology Update To compete successfully in the global energy market, exploration and production companies must operate efficiently, economically, and safely in increasingly difficult environments. Subsalt applications, unstable coal and shale layers, tar zones, depleted zones, and formations with variable flows and pressures are among the problems routinely encountered that must be overcome. In these problem zones, nonproductive time (NPT) of 30% in drilling operations has become commonplace in many areas, with 45% reported in some wells. Wellbore instability appears to be the main cause of NPT. Some operators report that it accounts for more than 40% of their NPT and approximately 25% of drilling costs in difficult wells. NPT related to wellbore stability in these applications ranges from several hours to several weeks in just one section, and costs run from thousands to millions of dollars. Other causes of NPT in these wells include narrow drilling margins and lost circulation. In many situations, operators must compromise ideal well placement to avoid troublesome formations, leaving millions of barrels of oil in the ground. Baker Hughes recently developed the SureTrak steerable drilling liner (SDL), the industry’s first SDL system that has been used to drill, evaluate, and place a liner to total depth (TD) in complex, 3D directional wells in a single run (Fig. 1). The advent of SDL technology mitigates the risk of drilling through problem zones or formations and creates opportunities to maximize reservoir potential by reaching reservoirs that were previously unreachable. The SDL system was recently used in an innovative openhole patch application that saved drilling time and significantly increased oil recovery in a problematic North Sea well. Technology Evolution The concept of drilling with a string of casing rather than conventional drillpipe has existed since Reuben Baker’s original 1907 patent for a casing shoe used in cable tool drilling. In its most basic form, casing is driven into soft formations by circulating and rotating. The addition of basic cutting structures on the casing shoe facilitates the procedure. It also allows harder formations to be drilled and enables the shoe to be drilled out conventionally afterward so that drilling can continue. Various casing drilling technologies and approaches have been used throughout the decades; in general, the main goal was to reduce drilling time by combining the casing and drilling into a single operation. As the need arose for more power to the bit in high-torque operations, a system was developed with the motor installed inside the casing. However, only minimal steering was possible with this system, which led to the emergence of steerable casing while drilling (CWD).
Published Version
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