Basin Modeling Study of Deepwater Block R (DWR) Offshore Sabah and Its Correlation with Surface Geochemical Analyses

Abstract

Abstract Significant oil and gas discoveries found at the southern production hub of offshore deepwater Sabah proved the existence of a working petroleum system in the area. DWR, which is located on trend with the Gumusut/Kakap and Limbayong oil and gas discoveries, remains under-explored with a number of attractive prospects to be tested in the block. To further evaluate the prospectivity of the block, JX Nippon conducted Genesis 1D thermal maturation investigations at selected pseudo-well locations, and a Trinity 2.5D basin modeling study to better understand the timing of hydrocarbon maturation, expulsion and migration in relation to the timing of trap formation. Taking into considerations the unproven source rock interval(s) and limited seismic coverage for the block, preliminary results of the basin modeling study suggest there is sufficient hydrocarbon charge for the prospects in DWR, most of which is generated from the modeled "Pseudo-Brown" source rock interval. The HC migration models suggest accumulations in the area tend to be oil-rich for the deeper Kinarut objective level due to larger structural reliefs and slow HC leakage (over geological time), whereby gas is being leaked preferentially and progressively to shallower levels leaving behind the oil columns. Consequently, the shallower Kamunsu and Pink targets, where present are likely to be condensate- and gas-rich, respectively. The gas leakage model has also been observed in nearby discoveries, notably Murphy's Kikeh and Shell's Gumusut-Kakap oil fields. In 2013, a surface macro-geochemical study within DWR was also conducted. The preliminary results of basin modeling study integrated with the occurrence of hydrocarbon seepages based on the outcomes of surface geochemical analyses show some positive indications. C10+ gas chromatogram and biomarker investigations at selected sampling locations suggest the presence of thermogenic hydrocarbon generation with pockmarks and mud volcanoes on seabed indicating potential leakage of hydrocarbons to surface. Overall the Trinity model suggests a favorable timing of HC generation and migration, mostly post-structuration with surface geochemical study indicating a presently active petroleum system in the block.