--> ABSTRACT: Geological Model of Shallow Marine Clastic Reservoirs in a Wrench-Faulted Province: St. Joseph Field, Offshore Sabah, Northwest Borneo, by H. D. Johnson, J. W. Chapman, and J. Ranggon; #91030 (2010)

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Geological Model of Shallow Marine Clastic Reservoirs in a Wrench-Faulted Province: St. Joseph Field, Offshore Sabah, Northwest Borneo

H. D. Johnson, J. W. Chapman, J. Ranggon

The St. Joseph field is situated along a major wrench-fault zone in offshore Sabah (the Bunbury-St. Joseph-Bambazon "ridge") that divides the field into several structural areas. The most prospective of these is the structurally simple northwest flank (about 6 km long and 1 km wide) that dips uniformly to the northwest (about 15°-20°) in a basinward direction away from the crestal wrench-fault zone. The main hydrocarbon-bearing interval comprises a 1,350-ft long oil column, which is contained within a highly heterogeneous sequence of late Miocene shallow marine sandstones and shales.

The main geologic uncertainties of the northwest flank concern lateral variations in sand development, shale-layer continuity, and reservoir quality. They have a major impact on reservoir recovery mechanisms, pressure-maintenance schemes, and on field development strategy. Therefore, a reservoir geologic model was developed that incorporates sedimentologic studies, well-log facies analysis, reservoir mapping, and detailed structural interpretation (using a full reservoir core and three-dimensional seismic data).

These studies demonstrate that depositional processes and tectonic setting had a major impact in controlling the thickness, quality, and distribution of the sandstone reservoirs. Features that had a particularly significant impact on hydrocarbon distribution, reservoir modeling and field development are: (1) a storm-dominated shelf-sand depositional system, (2) rapid vertical and lateral switches in sand supply, (3) a tectonically unstable, narrow (about 5-15 km wide) shelf, and (4) shelf-edge slumping (slump scars).

AAPG Search and Discovery Article #91030©1988 AAPG Annual Convention, Houston, Texas, 20-23 March 1988.