A novel method for calculating polymer adsorption in fractures through a dual porosity model

Abstract

AbstractIncreasing demand for energy and limited capacity of available resources of fossil fuels have drawn attention to enhanced oil recovery for maximum use of the available resources. Among different enhanced recovery methods, polymer injection maintains the advantages of water flooding, including the simplicity of this technique, while eliminating some of its drawbacks such as high mobility of the injected water. Therefore, mechanisms involved in the flow of polymer in the reservoirs need to be well understood and modeled. An important phenomenon affecting the flow of polymer in the oil reservoirs is polymer adsorption on reservoir rock. In fractured reservoirs, the polymer is adsorbed both in the matrix and the fracture. Miscalculation of the amount of adsorbed polymer results in the miscalculation of the fracture permeability on one hand, and concentration of dissolved polymer on the other. This, in turn, leads to over- or under-estimation of polymer injection performance in fractured reservoirs. An important tool for simulating fractured reservoirs is dual-porosity models. The models, however, may not correctly estimate polymer adsorption in fractures. This is attributable to the assumptions used in the dual-porosity model and the nature of adsorption. The present study attempts to improve the way this phenomenon is modeled by dual-porosity models. A new parameter called “pseudo-density” is defined here to replace the density of the fracture cells in the dual-porosity model for polymer adsorption. Then, a hypothetical reservoir is simulated using this new parameter, and the results of the two simulations, one with density and the other with pseudo-density, are compared in terms of three parameters, including the polymer adsorbed in the reservoir, the polymer dissolved in the aqueous phase, and the polymer produced in the reservoir. The results show that using pseudo-density instead of rock density decreases the required polymer amount to reach the maximum polymer concentration. Consequently, polymer solution viscosity and permeability reduction are increased. Furthermore, it results in increasing the polymer production compared to the conventional dual-porosity models.