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 pseudo-steady 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, depends entirely on the contrast between the fracture anisotropy parameter λ₁ and matrix-fracture interporosity parameter λ, and between the total gap cap storage capacitance ω-1$/ and oil zone matrix storage ω. A composite double porosity response is observed for ω-1$/ ≤ ω-1c$/ and 1.0 ≤ λ₁/λ ≤ 100.0. A triple porosity response is observed for ω-1$/ > ω-1c$/ and 140 < ωλ₁/λ ≤ 1.0E05.