History of hydrocarbon generation in the Tembungo field, offshore northwest Sabah

Abstract

The Tembungo field in the Sabah Basin produces oil from upper Miocene turbidite reservoirs. The oils, possessing low sulphur and wax contents and API gravities of 38-40°, were derived from marginal marine source rocks subject to significant land plant input. The history of hydrocarbon generation in the Tembungo area including burial, fluid pressure and fluid-flow, thermal history, hydrocarbon generation and migration has been studied using a two-dimensional finite difference basin modelling approach. Backstripping exercises suggest that high sedimentation rates occurred during middle to late Miocene. The Tembungo structure itself began to grow in late Miocene (7.2 Ma), with an accelerated growth rate in early Pliocene. A constant basement heat flow of 55 m Wm-2 was determined for the area. The faults are known to be sealing, with very low associated permeabilities. The presence of barrier faults contributed to the development of overpressure in the area. The contribution of hydrocarbon generation to the overpressure is considered less significant. Maturity reconstruction based on kinetic models indicates that hydrocarbon generation began approximately 9.0 Ma and oil began to be trapped in the Tembungo structure in late Miocene to early Pliocene. These oils were most likely sourced from middle Miocene sediments. Sensitivity analysis of transient state versus steady state pressure calibration reveals different histories of hydrocarbon generation and migration.