Fractured reservoirs simulation is one of the most important challenges in the oil and gas industry. These reservoirs contain significant amounts of world’s oil and gas reserves. Basically, the development of Iranian’s simulators is a major part of its economy that based on oil production, and it avoids to exit of large amounts of currency each year by purchasing external simulators and training users. In addition, in some cases external simulators can not even simulate the carbonate fractured reservoirs.The mass transfer mechanism between the matrix and the fracture is very important ,because permeability of the matrix is often low. Molecular diffiusion in Fractured reservoirs, can affect the gas injection efficiency in oil reservoirs or storage of natural gas. By modeling the diffiusion mechanism in the fractured reservoirs, we can have an accurate prediction of Enhanced oil recovery of reservoirs. The convection and diffiusion of mass transfer in fractured reservoirs were modeled and tested using dual permeability method. In the present project, three-dimensional and three-phase fractured reservoirs are simulator using dual permeability and compositional models. . Also, the governing equations are completely implicit and solved simultaneously. In this simulator, answers that obtained near the critical point are more stable and more accurate and increase the effect of the mass transfer. The error of the results are low, comparing to analytical solutions. The effect of parameters such temperature and pressure was investigated on the molecular diffusion mechanism. Also, the effects of reservoir rock properties such as permeability and porosity were investigated on molecular diffusion. Considering the molecular diffusion, the amount of oil produced from the reservoir has increased, as well as in the gas injection method to increase the recovery of 5 percent more oil. Keywords: Compositional Modeling, Dual Permeability, Fractured Reservoirs, Finite Difference Method, Shape Factor, Transfer Function, Molecular Diffiusion.
