A RELATIONSHIP OF OVERPRESSURE, DIAGENESIS AND HYDROCARBON ACCUMULATION, EAST BALINGIAN BASIN, OFFSHORE SARAWAK - MALAYSIA

摘要

This paper describes the integration of data from well discoveries in the East Balingian Basin, Offshore Sarawak - Malaysia. It attempts to contribute to an understanding of overpressure and clastic diagenesis which it is hoped can be used to guide exploration in an inverted basin with coastal plain to shoreface depositional environments.In the East Balingian Basin, the target reservoirs are categorized according to three generic depth intervals; shallow, intermediate and deep. With few exceptions, most shallow reservoirs are normally pressured. The majority of intermediate depth reservoirs retain a degree of overpressure and their vertical hydrocarbon column can be nearly double that of shallow hydrocarbon bearing normally pressured reservoirs. The deeper reservoirs of the East Balingian are generally highly overpressured and of low quality even where they are hydrocarbon bearing.Overpressure retention can be related to the degree of erosion on a structure by shallow post inversion unconformity surfaces and local faults. In the East Balingian Basin, most shallow reservoirs are of excellent reservoir quality and are normally pressured. The poor quality of the deep overpressured reservoirs is due to the development of quartz overgrowths and ferroan dolomite which occlude porosity and permeability. These diagenetic minerals appear to have locked the sand framework such that little or no porosity permeability restoration occurred during inversion uplift. The same mechanism may in part be responsible for the retention of overpressure. These observations are being used to guide exploration efforts in the East Balingian Basin. The better understanding of two of the main petroleum system components; overpressure retention (Trap) and diagenesis(Reservoir) evolved during the drilling of 11 new oil and gas discoveries in the East Balingian from Quarter 4 2004 to Quarter 4 2006.