Gas-Phase Relative Permeability Characterization on Tight-Gas Samples

Relative permeability to formation fluids is an essential input into reservoir characterization, dynamic modeling, and production prediction. In this work, a method combining evaporation and unsteady-state pressure-falloff technique is developed to measure gas-phase relative permeability on tight-gas cores for both drainage and imbibition cycles. Toluene is used to mimic formation water and its saturation is varied by evaporation and determined by mass balance. Nitrogen gas is used to imitate the hydrocarbon fluid, and the gas effective permeability at certain toluene saturations is measured by the pressure-falloff technique. The method greatly reduces the measurement duration, and provides a relatively simple and effective way to characterize the gas-phase relative permeability for tight-gas cores. It has been applied on similar to 30 tight-gas cores from various fields. Results show that the gas relative permeabilities follow the Corey model with a Corey exponent of similar to 2 for the drainage cycle and similar to 3 for the imbibition cycle. The assumptions are studied by both numerical modeling and separate experiments.