Abstract
The Danau-Bubut gas field was discovered in 1969 with the Danau-1 (DA-1) well. This discovery came between two major gas and oil field discoveries in Brunei; South West Ampa in 1963 and Champion in 1970. In light of economic conditions and technical challenges posed by Danau-Bubut at the time, field development was deferred. Over the subsequent three and a half decades the area was intermittently explored with limited success due primarily to poor quality log data upon which to base further action. In 2007 the company returned to re-explore the area with its sixth well. The well's success in 2007 led to two further appraisal wells in 2008–09. Equipped with new technology, extensive log, core, reservoir fluid, and well test information were acquired to more accurately describe the reservoirs and their contents. This paper will discuss several findings to date in context of subsurface uncertainty in tight gas sands and briefly overview future development plans.
To successfully develop tight gas sands often requires more reservoir data than conventional reservoirs (Holditch 2006). The Danau-Bubut field is no exception. The reservoirs were deposited in a lower shore-face environment and thinly bedded, very fine grained sands are interpreted as storm events. Bioturbation is abundant in most shales and present in some sands. Rich in clays, the general reservoir quality degrades with depth due to compaction. Permeability ranges from 0.01mD to 1mD in reservoirs with 8% to 12% porosity with rare occurrences of thin interbedded high permeability sands. The structure is faulted into five main blocks and several smaller blocks. The use of seismic is largely limited to structure and major fault definition. The key to improved understanding of in place volumes was extensive logging, formation pressure tests and samples, coring, and subsequent well testing.
The last well drilled in the appraisal campaign finished operations in early 2009 and individually drill stem tested four different zones. The uppermost zone was stimulated with a hydraulic fracture. Results from each of the four zones and treatment were surprising. Three zones were capable of producing over 10 MMscf/day each and one zone was non-commercial. Detailed results from this appraisal well will be presented and discussed. Nonetheless, significant uncertainty remains and as a result, field development will be phased to accommodate future outcomes.
The Danau-Bubut field is an example of opportunity that presents a different risk profile than normal and is unlike any other field currently operated in this company's portfolio. Understanding how to bring offshore tight gas volumes to market with Danau-Bubut will enable unlocking other similar offshore potential in Brunei.