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

Abstract

Sequence stratigraphy was used to determine the tectonic and depositional history of a frontier back-arc basin offshore in Korea. A total of five wells drilled into this basin penetrated over 2500 meters of Miocene lowstand sediments. Two of these wells tested hydrocarbons were found in sands less than five meters thick. A detailed sequence stratigraphic evaluation of this basin was performed using biostratigraphy, well strata patterns and nearly 2500 km of 2D seismic data. Initial extension of this basin began some 17.5 million years ago and a wrenching episode began 4.3 million years ago continues today. The tectonic and stratigraphic interpretations were integrated with geochemical analyses to identify the more promising exploration areas within this basin. Structural mapping of the sequence boundaries identified numerous faulted anticlines, some indicating the presence of hydrocarbons. 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 integrated with the sequence interpretations, these reservoir characteristics provided the basis for volumetric estimates and risk analysis. Sequence stratigraphy methods provide a technique for integrating the disparate datasets of geology, seismic, petrophysic, engineering and geochemical information.more » Use of this technique led to four consecutive gas discoveries. Each discovery contained multiple pay intervals and closely matched the predictions of reservoir characteristics.« less