Evaluation of Fractured Basement Complex Rock Porosity by Azimuthal Cross-Square Vertical Electrical Soundings

Abstract

This paper gave an overview on the use of Azimuthal Cross-Square direct-current resistivity sounding as complementary geophysical technique to Schlumberger vertical electrical sounding in characterizing fractured geologic systems. Previously, Schlumberger vertical electrical sounding was used to collect data. Interpretation of the generated data revealed the stratigraphic setting and identified anomalous feature at the downstream section of Tiga Dam, Northwestern Nigeria. The feature was large in size, appeared deep down and at an angle to the extended tip of the locality surface manifested fractures and increase in size on approaching the core of the dam. These prompted the use of Azimuthal Cross-Square Array direct-current resistivity soundings about eight strategically selected points in order to characterize the fractures and the anomalous feature. Some of the parameters deduced were depth of fracturing (76.00m – 126.02m), anisotropy (1.02 – 1.43), fracture swarthiness and secondary porosity (0.01 – 0.28). Specifically the anomalous body has porosity ranging from 0.16 to 0.28.

Keyword: Anomalous, Azimuthal, Foliation, Porosity and Swarthiness.