Subsurface temperature from seismic reflections: Application to the post-breakup sequence offshore Namibia

Abstract

Accurate estimations of present-day subsurface temperatures are of critical importance to the energy industry, in particular with regard to geothermal energy and petroleum exploration. In frontier basins, the subsurface temperature regime can give an indication of the hydrocarbon potential of source horizons. The L€ uderitz Basin, offshore Namibia, is a frontier deep-water basin located on a volcanic passive margin. With only two wells drilled in the area, there are limited downhole temperature data available with which to constrain the hydrocarbon window of key source rock intervals. However, high-quality seismic data are available and, by applying the reflection seismic thermometry (RST) process, provide a remote sensing alternative to direct temperature measurements at high spatial resolution. Using seismic reflection and velocity data, first, the identification of a gas hydrate bottom-simulating reflector is used to derive a shallow heat flow proxy (averaging 64 mW m À2 ). Deriving subsurface thermal conductivity from velocity data using an empirical relationship, a prediction for subsurface temperature can be made through forward modeling. Results indicate that average temperatures at the base of the Aptian Kudu Shale interval are 134 C, placing the source in the gas-generative window within the study area. This case study demonstrates the power of RST to generate indicative subsurface temperature results in frontier exploration basins, thereby reducing uncertainty over source rock maturity prior to drilling.