Illuminating and optimising a three-dimensional model of an oil shale seam and its volume distribution using the transient electromagnetic induction method, central part of Jordan
J.S. Abu Rajab and E. Al Tarazi
Journal name: Geophysical Prospecting
Issue: Vol 66, No 3, March 2018 pp. 603 - 625
Info: Article, PDF ( 13.17Mb )
The oil shale exploration program in Jordan is undertaking great activity in the domain of applied geophysical methods to evaluate bitumen-bearing rock. In the study area, the bituminous marl or oil shale exhibits a rock type dominated by lithofacies layers composed of chalky limestone, marls, clayey marls, and phosphatic marls. The study aims to present enhancements for oil shale seam detection using progressive interpretation from a one-dimensional inversion to a three-dimensional modelling and inversion of ground-based transient electromagnetic data at an area of stressed geological layers. The geophysical survey combined 58 transient electromagnetic sites to produce geoelectrical structures at different depth slices, and cross sections were used to characterise the horizon of the most likely sites for mining oil shale. The results show valuable information on the thickness of the oil shale seam at 3.7 m, which is correlated to the geoelectrical layer between 2- and 4 ms transient time delays, and at depths ranging between 85 and 105 m. The 300 m penetrated depth of the transient electromagnetic soundings allows the resolution of the main geological units at narrow resistivity contrast and the distinction of the main geological structures that constrain the detection of the oil shale seam. This geoelectrical layer at different depth slices illustrates a localised oil shale setting and can be spatially correlated with an area bounded by fold and fault systems. Also, three-dimensional modelling and inversion for synthetic and experimental data are introduced at the faulted area. The results show the limitations of oil shale imaging at a depth exceeding 130 m, which depends on the near-surface resistivity layer, the low resistivity contrast of the main lithological units, and the degree of geological detail achieved at a suitable model’s misfit value.