Empirical Modeling of Gravity Drainage in Fractured Porous Media

Gravity drainage is considered to be the main mechanism in primary oil production from naturally fractured reservoirs, but mathematical models to adequately predict the oil recovery and flux rate between the matrix and fracture network under gravity drainage are rarely described in the literature. To address this lacuna, gas-oil contact movement and oil recovery rates in a thin glass-bead-packed simulator were measured, allowing for the capture of information, about the matrix-fracture fluid-transfer process. A two-dimensional mathematical model was developed to numerically simulate the process under the same conditions as the experiments, and then empirical models were proposed for oil production in such fractured systems because the final liquid recovery Was found to be correlated to dimensionless groups, such as the Bond number. The empirical model approach was then extended to predict the matrix-fracture liquid-transfer rate during the-free-fall gravity drainage process. On the basis of experimental data and empirical correlations, the matrix-fracture liquid flux rate appears to be proportional to the liquid level difference in the matrix and fracture. These correlations were tested against numerical simulation results and actual field data of oil production by free-fall gravity drainage. The empirical models have been judged to perform acceptably in the prediction of the oil production and fluid-transfer rate in the oil-gas gravity drainage cases studied.