عنوان مقاله [English]
The gravitational drainage of oil in gas-invaded zone is identified as the major production mechanism in carbonate reservoirs. Oil is kept in a matrix block surrounded by gas and then subject to two distinct and opposing forces. Due to the difference between oil and gas densities, gravitational forces tend to expel oil through the lower part of the block, while oil-rock adhesive force acts to peneterate within the rock. Drainage arises when “gravitational” and “capillary” forces coincide. In this study, the mathematical modelling of gravitational drainage in naturally fractured reservoir is presented which involve capillary, gravitational, and infiltration processes. A simple approach was proposed to simulate gas-oil gravity drainage process in fractured porous media using an appropriate fracture capillary pressure. The permeability value is approximated by the location of fracture in the stack block. The capillary pressure in horizontal fracture is related to height of fracture in stack block to gas-oil interface. Numerical simulation results revealed good agreement with experimental data. This study revealed that capillary continuity and fracture transmissibility are the most important factors in oil recovery by gravitational drinage mechanism.