عنوان مقاله [English]
Due to more than one hundred years of oil and gas extraction, most reservoirs, especially those with high ermeability, are gradually running out. Hence, the tendency is towards utilization of reservoirs with low permeability. Also, after continuous extraction of hydrocarbon products, natural reservoir pressure is reduced, cracks are losed nd he roduction of the reservoir is reduced. It is, therefore, necessary to undertake additional methods in order to enhance the capacity of such reservoirs; hydraulic fracturing is such a method, which is popularly applied to 50% of oil and 70% of gas wells in North America.In hydraulic fracturing, the fluid with pressure more than the in-situ stress of the region is injected into the place of the well that had been isolated by packers. When the fluid pressure exceeds the in-situ stress, hydraulic fracturing will occur.
One numerical method recently developed for simulation of hydraulic fracturing is the extended finite element method (XFEM). In this method, the nodes surrounding the cracks are enriched through special functions. Accordingly, for
such nodes, the degrees of freedom are increased, which results in greater displacement around each crack. In this research, a XFEM code was developed to simulate the hydraulic fracturing problem.The code provides three interaction processes: (I) Mechanical deformation due to fluid pressure on the crack, (II) Fluid flow in the crack and (III) Crack propagation due to fluid motion.
The results of numerical analysis by the provided code, which is examined on a classic hydraulic fracturing problem, exhibit decreasing fluid pressure and increasing crack openings at the borehole well, as the crack length progresses. These results are in line with the results obtained by the KGD analytical solution. Also, it was observed that the width of the crack opening should be increased to enhance the exploitation of hydrocarbon products. In order to reach this goal, the fluid viscosity and/or injection rate of the fluid should be increased.