Casing During Drilling With Rotary-Steerable Technology in the Stag Field—Offshore Australia

Abstract

Summary Originally discovered in 1993, the Stag oil field, located on the Northwest shelf of Western Australia, has produced more than 58 million bbl since production began in 1998 (Goodacre et al. 2000). The field is shallow (680 m subsea), encompassing highly unconsolidated and highly permeable sandstone. Reservoir depletion, unconsolidated rock, water breakthrough, and sand production have created conditions under which infill-drilling campaigns have become increasingly problematic in the Stag field in recent years. There have been numerous papers documenting the history of the Stag field (McDiarmid et al. 2001; Muecke et al. 2002; Wibawa et al. 2008). On three recent infill wells, the intermediate 12¼-in. intervals were drilled and cased with casing-while-drilling (CWD) technology with a rotary-steerable system (RSS). This was used to navigate wellbore congestion, to drill designer well paths to avoid "incoherencies" [a seismic attribute that is mappable and correlates with drilling problems (Chima et al. 2012)], to land the horizontal section, and then to drill horizontal tangent sections out to the initial reservoir penetration (liner point). The CWD applications progressed from a "new technology" trial to a stretch reach and performance goal, to finally successfully being used as a key enabling technology to drill a well that might otherwise be undrillable because of instability issues. The directional CWD 12¼-in.-hole intervals were drilled from just below the 13-⅜in. surface casing to the 9⅝-in.-casing point, building from 25° inclination to horizontal and holding thereafter. This program (the first applications of this type in Australia) resulted in two consecutive world-record runs. The result is that CWD is a viable enabling technology that will be used to drill future Stag infill wells and should be considered as a viable alternative on other drilling projects. This paper will discuss the identification of the technology application, planning, implementation, results, and lessons learned. This paper will end with a notional conversation regarding CWD becoming a mainstream method.