Capillary pressure hysteresis behavior of three sandstones measured with a multistep outflow-inflow apparatus

Many phenomena of practical importance, such as water movement in soils and the recovery of oil and gas from subterranean reservoirs, involve capillary pressure hysteresis in natural porous materials. Experimental capillary pressure-saturation relationships provide important information on pore systems and multiphase displacements. Data, at various levels of detail, are available for strongly wetted soils and sphere packs, but very few detailed hysteresis data have been reported for consolidated porous media, such as rocks, at equivalent wetting conditions. A new porous plate apparatus and procedure have been used to give extensive capillary pressure hysteresis relationships within a few days, a significant improvement on previous methods. Air-brine data are presented for three types of consolidated sandstones. Rate of outflow and inflow were recorded for each data point. Imbibition scanning curves have been obtained starting from the primary and secondary drainage curves. Drainage scanning curves that branch from imbibition curves starting at different levels of initial water saturation have also been measured. The data met a stringent test of quality in that all hysteresis loops exhibited closure as predicted by theory and as usually reported for unconsolidated media. The overall form of the hysteresis curves is related to fluid distributions, percolation effects, and trapping. Initial wetting phase (WP) saturation versus residual nonwetting phase (NWP) relationships provide detailed information on the extent of trapping for imbibition starting at different initial saturations, a parameter of particular interest in carbon dioxide sequestration. Features of the dynamic outflow-inflow data provided indication of the differences in flow rates for drainage and imbibition.