Application of Pore Scale Network Modeling Technology for Waterflooding Oil Recovery Evaluation in Different Wettability Conditions

Abstract In oilfield development, waterflooding is normally characterized as an economical and efficient process, which leads to a considerable residual oil saturation. Wettability, being one of fundamental petrophysical properties which reflects interactions between reservoir rock surfaces and fluids during waterflooding, is an essential parameter in reservoir evaluation and simulation, and its effect on waterflooding oil recovery has often been a research hotspot. In this paper, the effect of wettability on waterflooding oil recovery is studied based on a pore scale network model which is a statistical structure of pores and throats extracted from porous media to conduct fluid flow simulation and characterize various physical and chemical effects. A new method combining micro-CT scanning and rate-controlled mercury injection experiment is applied to obtain pore structure data and to improve the representativeness of pore scale network. Multiphase fluid distribution and transportation in pores and throats are simulated by assuming quasi-static flow in pore scale network where both viscous force and capillary force are comparable. A special pore scale network simulation workflow is established, which is capable of simulating two intrusive simulation processes corresponding to oilsaturating with irreducible water and waterflooding, respectively. Wettability is applied in pore scale network model by randomly distributing contact angles onto pores and throats. Based on a series of numerical simulation experiments, it can be summarized that neutral wet condition always corresponds to higher oil recovery than water and oil wet conditions in the waterflooding process, which is consistent with adequate experimental results when preferential wet for one phase fluid is mild. However, simulation results from pore network show that the difference between oil recoveries of water and oil wet conditions doesn't remain constant, which indicates that effect of wettability should be linked with pore structure characteristic when assessing the oil recovery performance. On this basis, characterization of its effect on oil recovery through pore scale network modeling forms an important component of waterflooding development and research for new EOR methods.