Resistivity Index and Capillary Pressure Measurements Under Reservoir Conditions Using Crude Oil

Abstract

ABSTRACT Experimental data of resistivity index and oil-brine capillary pressure on sandstone and carbonate rock samples from 4 reservoirs are reported. Laboratory equipment using actual fluids at reservoir conditions has been developed. The capillary drainage was achieved with the porous-plate method and fluid saturation along the core was checked for uniformity by conductivity measurements with a four-electrode system. For each rock sample, the resistivity index and capillary pressures were measured first with refined oil and then with crude oil. In addition, wettability indices were determined using Amott's tests. The resistivity/water-saturation law is well fitted by Archie's law except for vuggy carbonates. In this case, the resistivity/water-saturation plot consisted in two straight line segments in log-log coordinates. The Archie's n-exponent values obtained with crude oil were different than those determined with refined oil except in one case. The n-value increases as the rock becomes more oil-wet. The maximum increase of n-value, from 1.68 to 2.19, was observed for one carbonate, initally neutral and becoming oil-wet during drainage with the crude oil.