Petrophysical Characteristics of Rocks in Girei Local Government Area of Adamawa State, N.E. Nigeria.

Abstract

Petrophysical measurements namely; electrical resistivity, density, porosity, electrical resistivity anisotropy and water saturation were performed on fourteen representative surface rock samples from Girei, part of the Yola arm of the Upper Benue trough, NE Nigeria. The purpose was to provide information required for determining the electrical conductivity mechanism of these rocks. This will further aid in the interpretation of down hole, ground and air-borne electromagnetic surveys. The two electrode method was used in the resistivity measurements while density and porosity were measured following Olhoeft and Johnson, 1990 and Scromeda and Connell, 2001 techniques. Results obtained showed that the dry bulk density, ñd, were in the range of 1.86 to 2.23g/cm3 with an average of 2.08±0.03g/cm3, wet density, ñw ranged from 2.11 to 2.55g/cm3 with an average of 2.23± 0.03 g/cm3 and particle or grain density ñg ranged from 2.47 to 2.81g/cm3 having an average of 2.59±0.03 . Porosity, Ô values were in the range of 0.12-0.28 with a mean value of 0.20±0.01. Results of the electrical resistivity of the saturated rock samples gave values of 7.485 to 10.690 x 103 m with an average of 8.160 ± 0.229 x 103 m. Investigation of the relationship of porosity and water saturation showed a direct proportionality with saturation increasing with increasing porosity. The preferred orientation of the water wet pores results in low electrical anisotropy values from 1.2:1 to 1.7:1.

Key words: Electrical resistivity, Density, Porosity, Anisotropy, Petrophysical.