A PERCOLATION STUDY OF WETTABILITY EFFECT ON THE ELECTRICAL-PROPERTIES OF RESERVOIR ROCKS

Measurements of the electrical resistivity of oil reservoirs are commo nly used to estimate other properties of reservoirs, such as porosity and hydrocarbon reserves. However, the interpretation of the measureme nts is based on empirical correlations, because the underlying mechani sms that control the electrical properties of oil bearing rocks have n ot been well understood. In this paper, we employ percolation concepts to investigate the effect of wettability on the electrical conductivi ty of a reservoir formation. A three-dimensional simple cubic network is used to represent an ideal reservoir formation, for which the effec t of the wettability can be isolated from the others. The phase distri bution in the network is analyzed for different flow processes, and th e conductivity is then estimated using a power law approximation of th e percolation quantities. The proposed conceptual model predicts the g eneric behavior of reservoir resistivities of different wettabilities. It demonstrates that the resistivity index depends on saturation hist ory and wettability. For strongly oil-wet systems, significant hystere sis is expected, while there is little hysteresis for strongly water-w et systems, and some hysteresis is also expected for intermediate wet systems. One of the interesting results from this study is that for in termediate wet systems, Archie's saturation exponent is between 1.9 an d 3.0.