Complex geothermal gradients and their implications, deepwater Sabah, Malaysia

Abstract

Seabed heat flow measurements together with values estimated from the position of the base of the gas hydrate stability zone mapped from 3D seismic data from a deepwater study area in Block X approximately 100 km offshore Sabah, Malaysia, are discussed. The data show a variable and high geothermal gradient that is consistent with the regional trend of 6-9°C/100m. Rising plumes of warm fluid and locally remobilised mud are abundant and are interpreted to be responsible for the high values, locally creating zones of very high gradients in excess of 20°C/100m above the plumes. In contrast, initial interpretation of data from the Block X exploration wells show geothermal gradients greater than the regional average (5.08 to 5.66°C/100m compared to 4.43°C/100m) but still significantly lower than the shallow values. Reinterpretation of the deep geothermal gradient well data suggests that the regional gradient fits these data if the influence of the warm fluid plumes on the shallow section is taken into account. The resultant gradient is no longer a simple linear function but a complex curve that varies depending upon the offset of a well from the areas of anomalous warming in the shallow section. A lower geothermal gradient at reservoir depth, as suggested by this study, could have important implications for hydrocarbon maturation and generation, as well as for equipment selection for well operations.