A direct method for simultaneously determining positive and negative capillary pressure curves in reservoir rock

Two methods, under development and evaluation, are described that directly measure fluid saturation in centrifuged sample plugs to produce capillary pressure curves. The fluids, which define the two methods, consist of (1) liquid hydrocarbon/D2O and (2) frozen hydrocarbon/H2O, with the imaged fluid being liquid hydrocarbon in (1) and H2O in (2). Capillary pressure at any position in the plug was calculated from the speed, distance of the free water level from the rotor, and density of the fluids. The capillary pressure curve was made by plotting the measured saturation against pressure at all locations along the centrifugal axis in the plug. By positioning the free water level along the height of the plug, both negative and positive portions of the capillary pressure curve were measured from one centrifuge run. Primary drainage, primary imbibition and secondary drainage capillary pressures were obtained. Examples of initial efforts to obtain capillary pressure curves obtained by the two methods are presented.