THE EFFECT OF WETTABILITY ON ARCHIE SATURATION EXPONENT FOR LIBYAN NUBIAN SANDSTONE RESERVOIRS

Abstract

The estimation of oil initially in place is an important issue and since the saturation exponent is the most important factor in determining the hydrocarbon/water saturations from the electrical resistivity measured on core plugs or from wireline logs using the Archie equation, the value of saturation exponent should be determined accurately.

Laboratory measurements methods were undertaken on core samples selected from three different fields (S, T, and U) from the Nubian Sandstone Formation of the central graben reservoir in Libya. The experimental data includes porosity, permeability, and wettability. This includes determining the saturation exponent (n) in the laboratory at two stages. The first stage was before wettability measurements were conducted on the samples, and the second stage was after the wettability measurements in order to find any effect on the saturation exponent.

Changes were also observed in the saturation exponent (n) and water saturation (S_w) before and after wettability measurement. Samples with an oil-wet tendency have higher irreducible brine saturation and higher Archie saturation exponent values than samples with a uniform water-wet surface. A significant change in slope (saturation exponent, n) between resistivity index and water saturation after wettability measurement was observed.