Integrated Geophysical, Geological and Hydrogeological Studies for Correlating and Characterizing Hydraulic Anisotropy in Fractured Shale Aquifer

B.I. Odoh and F. Ogala
Geology and Exploration Geophysics, Ebonyi State University, Abakaliki, NIGERIA

The study area spans about 177km2 and covers the entire Abakaliki urban and environs. The objectives of the research were to locate fractures and estimate their orientations, determine the coefficient of anisotropy of fractured shale, quantify the fracture porosity, estimate the specific surface area of fractures, and determine if the fractures extend to recharge zones. This work integrates geophysical, geological and hydrogeological studies to characterize fractured shale hydraulic anisotropy in Abakaliki shale. The fracture parameters obtained from geological field measurements are in good agreement with those obtained from azimuthal resistivity measurements and the direction of flow of groundwater obtained from hydraulic head contouring and visualization. The integrated result show that the dominant fracture strike is NW-SE where NE-SW is the recessive fracture strike. The fractures are more prominent at the depth of 28.3m where 75% of the fractures are trending NW-SE (mainly 1350 azimuth). The analysis of the resistivity data indicates that the fracture porosity within the study area range from 0.002 to 0.03 and that the coefficient of anisotropy range from 1.15 to 1.55. The values of specific surface area vary from 188.2 to 14.1µs/cm. Fractured rock with relatively high fracture porosity, and relatively high coefficient of anisotropy are likely to have better groundwater yield and more vulnerable to contaminant transport. The dominant fracture system strikes almost perpendicular to the bedding plane. Groundwater flow in the area is along the strike of the fractures. The field measurements made were used to generate the three-classic models of fracturing in the area. Equations for estimation of hydraulic conductivity, flow direction have been derived by a modification of Darcy’s law.

AAPG Search and Discovery Article #90078©2008 AAPG Annual Convention, San Antonio, Texas