A DIRECT METHOD FOR SIMULTANEOUSLY DETERMINING POSITIVE AND NEGATIVE CAPILLARY-PRESSURE CURVES IN RESERVOIR ROCK

Two methods, under development and evaluation, are described that dire ctly measure fluid saturation in centrifuged sample plugs to produce c apillary pressure curves. The fluids, which define the two methods, co nsist of (1) liquid hydrocarbon/D2O and (2) frozen hydrocarbon/H2O, wi th the imaged fluid being liquid hydrocarbon in (1) and H2O in (2). Ca pillary pressure at any position in the plug was calculated from the s peed, distance of the free water level from the rotor, and density of the fluids. The capillary pressure curve was made by plotting the meas ured saturation against pressure at all locations along the centrifuga l axis in the plug. By positioning the free water level along the heig ht of the plug, both negative and positive portions of the capillary p ressure curve were measured from one centrifuge run. Primary drainage, primary imbibition and secondary drainage capillary pressures were ob tained. Examples of initial efforts to obtain capillary pressure curve s obtained by the two methods are presented. (C) 1998 Elsevier Science B.V. All rights reserved.