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ABSTRACT: "Classic clastics" - has high-tech. 3D improved imaging of stratigraphic traps found with 'traditional' techniques? Yvonne 'B' Field, Sunda Basin, Java Sea

Wight, Andrew W. R.1, Syafri Syafar1, Ariane Kartika1, Chris Oglesby2
(1) YPF Maxus Southeast Sumatra BV, Jakarta, Indonesia 
(2) Independent Consultant to Maxus Southeast Sumatra BV

During a mature exploration phase, concentrated on a search for stratigraphic traps, Yvonne 'B' field, in Talang Akar Fm. sandstones, was discovered by IIAPCO in 1983. Originally estimated from structural closure to be uneconomic, it was later put on production and the current GUR of 16 MMBO shows this stratigraphic trap to be a significant accumulation.

Discovery was by a combination of 2D isochron and structural mapping which revealed mutually perpendicular structural culminations. Their correspondence with isopach thickening suggested differential draping over stacked, nearshore marine sandstone bodies; this led to a six-well exploration programme. Discovery well Yvonne-18 encountered a 10 ft. oil-bearing sandstone; two other oil wells and three dry holes gave 50% success rate. The fining-upward reservoirs are fluvial point bars, meandering obliquely across an east-plunging structural nose, and stratigraphically trapped updip.

The less successful development phase illustrated the difficulty in imaging channel thalwegs. To remedy this, a 3D survey was shot in 1990, but neither amplitudes nor isochrons could define the thalwegs. Worse still, structural mapping showed an unclosed nose, with no obvious exploration well location: conceivably a large field could possibly have been overlooked, even with 3D!

Thus 3D was not the panacea for development. Recently, however, technology has struck back with other attributes beginning to show channels. Although technology will surely accelerate our understanding of the reservoir, this stratigraphic discovery was made with traditional geologic interpretation and, last but not least, pure drilling.

Wight, Andrew W. R., Syafri Syafar, Ariane Kartika, Chris Oglesby

AAPG Search and Discovery Article #90913©2000 AAPG International Conference and Exhibition, Bali, Indonesia