ROBERTSON, LAURA, DAVE WEBBY, and KEITH RUSSELL
Cairn Energy plc, Edinburgh, Scotland, UK

Abstract: The Sangu Field (Bangladesh Offshore): Technical Challenges During The Appraisal Phase Of A Fast Tracked Gas Development

The Sangu Field was discovered by exploration wildcat Sangu-1 in February 1996 and subsequently appraised by five wells in 1997 and early 1998. Production started in June 1998.

The technical challenges encountered during the simultaneous appraisal and development were considerable. The sedimentological and stratigraphic complexity of the field, made even more problematic by the presence of severely overpressured layers and a "gas chimney" at the crest of the structure resulted in a high level of geological uncertainty and drilling risk.

The difficult acquisition of cores and wireline logs meant that the problems of evaluating the lithologically complex and extremely finely laminated reservoir units was solved through advanced petrophysical interpretation and carefully planned and focused coring and logging programmes. As the sands are rich in mica and feldspar, alternative methods for estimating the Vshale and Net/Gross were considered including the use of NMR logs.

The frequent channelling in the shallower sections, associated with seismic opacity and lack of log character of some of the reservoir sands made correlation between wells difficult. Given the poor results of biostratigraphic analysis, alternative stratigraphic tools were applied, with mixed results.

The appraisal of Sangu resulted in an increase of P50 reserves of 33%; this result was made possible by integration of drilling, geological and engineering data which were evaluated in real time.

The Sangu Field developed from a "new venture" in a remote area to a producing asset in a record time of two years from discovery.

AAPG Search and Discovery Article #90928©1999 AAPG Annual Convention, San Antonio, Texas