Determination of saturation functions

The end effects in tight core samples contain valuable information about the saturation functions, that may allow determination of the saturation functions for a broad saturation interval. A complex five-step core flooding scheme using an oil-brine fluid system provides the fluid distributions and pressure drop data necessary for the calculation. An NMR technique is used for fluid distribution determiantion. A non-magnetic coreholder connected to a mobile flooding unit allows NMR measurement at selected times during the flooding scheme. The core flooding scheme comprises a primary drainage experiment, a reversed flow experiment creating an internal spontaneous imbibition, a forced imbibition experiment and a threshold pressure determination. The saturation functions are determined by a least squares technique. The procedure also allows estimation of sample wettability, and of the scanning parameter for capillary hysteresis. The procedure is demonstrated on chalk samples from the North Sea. The procedure is superior to the centrifuge and mercury injection methods respectively by eliminating errors from end effects and using reservoir relevant fluids. Contrary to the centrifuge and mercury injection methods, the new procedure has no problems with damage to the pore structure of the samples. The procedure is superior to the porous plate methods in being faster. Finally, the new method also determines the relative permeability functions for the sample