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NESTER, DOUGLAS C., Landmark/Concurrent Solutions, no location given

ABSTRACT: Use of Sequence Stratigraphy to Determine Tectonic and Depositional History and to Predict Reservoir Character

Sequence stratigraphy played a crucial role in unraveling the tectonic and depositional history of a frontier back-arc basin offshore Korea. A total of five wells drilled into this basin penetrated over 2500 meters of Miocene lowstand sediments. Two of these wells tested hydrocarbons that were found within individual sands with thicknesses less than five meters. A detailed sequence stratigraphic evaluation of this basin was performed using biostratigraphy, well stratal patterns and nearly 2500 km of 2D seismic.

This interpretation documented initial extension of this basin began some 17.5 million years ago. First compression occurred approximately 10.5 million years ago, and a wrenching episode began as recent as 4.3 million years ago and is continuing today. The tectonic and stratigraphic interpretation was integrated with the geochemical analysis to identify the more promising exploration areas within this basin. Structural mapping of the sequence boundaries identified numerous faulted anticlines, some having apparent direct hydrocarbon indicators on the seismic. Statistical analysis of the petrophysical parameters for sands in the existing five wells identified three distinct reservoir types that correspond to deposits within prograding complexes, slope fans and basin floor fans. When mer ed with the sequence interpretation, these reservoir characteristics provided the basis for volumetric estimates and risk analysis.

The sequence stratigraphic methodology provides the means to integrate the disparate datasets of geology, seismic, petrophysic, engineering and geochemical information. As a result of this methodology, four consecutive gas discoveries have been drilled. Each discovery contained multiple pay intervals and closely matched the predicted reservoir character.

AAPG Search and Discovery Article #90988©1993 AAPG/SVG International Congress and Exhibition, Caracas, Venezuela, March 14-17, 1993.