Gary McNeice

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

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. Integrati...

Exploration beyond seismic: The role of electromagnetics and gravity gradiometry in deep water subsalt plays of the Red Sea

ABSTRACTThe Red Sea is characterized by thick salt sequences representing a seal for potential hydrocarbon accumulations within Tertiary formations deposited over deep basement structures. The Red Sea “salt” is characterized by halite concentrations embedded in layered evaporite sequences composed of evaporite and clastic lithologies. Salt complicates seismic exploration efforts in the Red Sea by generating vertical and lateral velocity variations that are difficult to estimate by seismic methods alone. In these conditions, the exploration challenges of independently imaging the subsalt section and provide enhanced velocity model building capabilities were addressed by a multigeophysics strategy involving marine electromagnetics (magnetotellurics and controlled source electromagnetics [CSEM]) and gravity gradiometry surveys colocated with wide azimuth seismic. Three-dimensional inversion of MT and CSEM is performed first with minimal a priori constraints and then by including variable amounts of interpret...