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The AAPG/Datapages Combined Publications Database

Indonesian Petroleum Association

Abstract


16th Annual Convention Proceedings (Volume 1), 1987
Pages 191-214

Exploration of the North Seribu Area, Northwest Java Sea

Roberto Fainstein

Abstract

In 1986 the NF-1 exploratory well was completed as a significant oil discovery. This well, which is located at the northwest corner of the PERTAMINA-ARII acreage in the Java Sea, tested over 3,000 BOPD from deltaic sands of the Oligocene Talang Akar Formation. The well was drilled downthrown to the North Seribu Fault, on a structural top deltaic Talang Akar closure similar to the nearby Karmila Field. The upper deltaic sand reservoir, which are prolific producers in the Karmila Field, were all water-bearing in the NF-1 well. Producing reservoirs were encountered, however, in the lower section near the basement.

The ensuing vertical seismic profiling did not correlate with the available seismic data over the reservoir zone and did not tie the previously interpreted basement. Therefore, to facilitate basement mapping, a seismic reprocessing study was undertaken with the aim of improving basement definition. New processing parameters were obtained through the analysis of signal/noise ratios on common depth point (CDP) stacks with distinct ranges of offsets. Stacks of the far traces enhanced the basement reflection whereas stacks of the near traces were contaminated with multiples and reverberations. Offset weighting of the far traces with respect to the near traces therefore enhanced the basement signature. This procedure, together with an appropriate definition of the seismic wavelet and optimum stacking velocities for dip and strike lines, made it possible to obtain seismic sections with considerably improved basement definition. A basement map was produced from these data.

The basement map revealed the existence of a basement ridge in which the anticlinal culmination is offset by a left-lateral oblique slip fault. Two oil traps are now more clearly defined. The NF trap is a basal sand wedge onlapping onto the North-Seribu Fault. The NG trap which is defined by four-way dip closures of upper deltaic sand horizons and by basal sand bodies pinching-out against basement fault blocks.


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