Originally discovered in 1993, the Stag Oil Field, located on the Northwest Shelf of Western Australia, has produced over 58 MMbbls since production began in 19987. The Field is a shallow (680m SS), highly unconsolidated, highly permeable sandstone. Reservoir depletion, unconsolidated rock, water breakthrough and sand production have created conditions where infill drilling campaigns have become increasingly problematic in the Stag field in recent years. Numerous papers have documented the history of the Stag Field's colorful past12-13, 23.
On three recent infill wells the intermediate 12 ¼?? intervals were drilled and cased using Casing while Drilling (CwD) technology using a rotary steerable system. This was used to navigate wellbore congestion, drill designer wellpaths to avoid "incoherencies?? (a seismic attribute that is mappable and correlates with drilling problems5), land the horizontal section and then 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 a key enabling technology to drill a well that might otherwise be undrillable due to instability issues.
The directional CwD 12 ¼?? hole intervals were drilled from just below the 13 3/8?? surface casing to the 9 5/8?? casing point, building from 25 degrees 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 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.