3. EM/GPR Imaging Technologies
Integration of Surface Geophysical Methods for Fracture Detection in Crystalline Bedrocks of Southwestern Nigeria
Adepelumi Adekunle Abraham(1), Myeong-Jong Yi(2), Jung-Ho Kim(2) and Jeong-Sul Son(2)
(1) Department of Geology, Obafemi Awolowo University, Nigeria. (2) Korea Institute of Geoscience and Mineral Resources, Korea.
Abstract
The application of electrical imaging and very-low-frequency (VLF) electromagnetics for delineating basement fracture zones was investigated. It was shown how incorporating a priori information in numerical modeling would facilitate locating fractured zones within a basement rock more precisely. To this end, a direct current (DC) dipole-dipole resistivity and VLF modeling and inversion were carried out to evaluate the efficacy of the methods in detecting low resistivity fracture zone in a typical crystalline basement rock environment. These studies were necessary because most wells drilled in such an environment usually have low yields. Results of the numerical experiment indicate that fractures, covered by moderate overburden and having high depth extent, and thickness comparable to their depth of burial, produce good responses resulting in high-resolution resistivity images. Lower resolution resistivity images were obtained as the thickness of the overburden increases. Also, the model investigations indicate that width of the fracture zone plays a major role in controlling image resolution. Conclusions from the synthetic modeling were confirmed by gathering resistivity and VLF data across a suspected fault in a hard rock terrain of southwestern Nigeria. The results from the field data are in general agreement with the numerical modeling experiments.
Last modified: Thu Apr 27 20:32:16 2006