Gas-cap effects in pressure-transient response of naturally fractured reservoirs

This paper presents a theoretical framework of gas-cap effects in naturally fractured reservoirs. General pressure solutions are derived for both pseudosteady-state and unsteady-state matrix-fracture interporosity flow. Deviation from the fracture or fracture-matrix response occurs as the gas-cap effect is felt. Anomalous slope changes during the transition period depend entirely on the contrast between the fracture anisotropy parameter, lambda(1), and matrix-fracture interporosity parameter, lambda, and between the total gas-cap storage capacitance (1 - omega(1)) and oil-zone matrix storage (1 - omega). A composite double-porosity response is observed for omega(1) less than or equal to omega(1c), and 1.0 less than or equal to(1)/lambda less than or equal to 1000. A triple-porosity response is observed for omega(1) greater than or equal to omega(1c), and 140 < omega lambda(J)/lambda < 1.0E05.