Integrated seismic-electromagnetic workflow for sub-basalt exploration in northwest Saudi Arabia

Abstract

A project involving magnetotellurics, shallow EM and gravity acquisition was carried out in northwest Saudi Arabia to improve the imaging of a basalt-covered section of the Al Jawf graben where seismic is particularly noisy. The Al Jawf graben extends from Jordan to Saudi Arabia. Mesozoic and Paleozoic sections contained within the structure have the potential to host multiple oil reservoirs. The lack of reliable seismic data in this area motivated the use of a multi-geophysics exploration approach. Electromagnetic (EM) techniques were identified as the optimal complementary geophysical data set. In fact, the EM signal propagates through the resistive basalt cover with minimal attenuation, providing information about the underlying conductive sedimentary section. A combination of active-source time-domain EM (TDEM) and broadband magnetotelluric (MT) techniques imaged the base of the shallow basalt cover and its internal variations as well as larger-scale faults that control the graben structure. Integration of the broadband EM and gravity data with seismic was achieved through simultaneous joint inversion (SJI) to derive an integrated velocity model that was subsequently used to reprocess the seismic data in the time and depth domains. Seismic reprocessing resulted in a substantial improvement in the seismic imaging of deep structures predicted by the structural model but not imaged by the previous seismic processing.