ABSTRACT: Source Rock and Hydrocarbon Geochemistry, Offshore N.W. Sabah, Malaysia
WOODROOF, PETER B., British Gas Malaysia S.A., and ANDREW D. CARR, British Gas Plc., Research and Technology Division, London
A subsurface geochemical study has been undertaken on sediment and hydrocarbon samples from wells in the northern part of the North West Sabah Basin, Malaysia. The objective of this study was firstly to identify source rock intervals and hydrocarbon families, and secondly to attempt a correlation of oils and source rocks.
Three potential source rock zones, each spanning both marine and terrestrial environments, have been identified through biomarker analysis. Terrestrial kerogens dominate all these environments. Biomarker variations are small between marine and terrestrial sediments
of each zone, while the larger zonal differences represent biostratigraphy.
The most important source rock zone occurs within the Middle Miocene. This zone has generated significant quantities of oil from source rocks deposited in both marine and terrestrial environments. It is often thicker than 5,000 ft (1,500 m) and it gains from quantity what it lacks in quality. Vitrinite reflectance data and basin modeling indicate that large areas of this zone entered the peak oil window in the last 10 million years.
The remaining two source rock zones span the Upper Miocene, but are rarely buried sufficiently deeply to allow significant oil generation and expulsion. However, minor oil associated with early mature gas has been correlated with the deeper of these zones.
Significant quantities of oil derived from the Middle Miocene have accumulated in Upper Miocene as well as Middle Miocene reservoirs. For the Upper Miocene accumulations, vertical migration via faults and fractures is proposed as a charging mechanism. These accumulations typically overlie deeply buried, highly tectonized and overpressure Middle Miocene sediments.
AAPG Search and Discovery Article #91015©1992 AAPG International Conference, Sydney, N.S.W., Australia, August 2-5, 1992 (2009)