On the Pressure Response During Unsteady State Fluid Displacement Experiments

The pressure response observed during the unsteady state displacement is a critical factor in determining the steady value and contains valuable characteristics about the rock permeability and capillary pressure. Our objective is to elucidate the mechanism of the unsteady state displcment and its impact on the pressure reponse. We tried to match the experimentally-measured pressure profile using both numerical simulation and analytical solutions. Promising results are observed when the capillary pressure is considered. The results clarify that this response is not a function of gas compressibility or viscous fingering, but is directly linked to the ratio of liquid fractional flow to liquid relative permeability as a function of saturation. The relative permeability exponents have a direct role to play in this regard. This work highlights the inacpaibility observed in a reservoir simulator to capture the pressure signature. This brings into question the ability of such simulators to provide reliable data when it comes to model the displacement processes at the core-scale.