Numerical simulation method for multiphase and multicomponent flow in ultra-low permeability and tight oil reservoirs based on discrete fracture model

Numerical simulation technologies faces new challenges from the development of ultra-low permeability and tight oil reservoirs by large-scale fracturing and water/chemical injection for enhanced recovery. A discrete fracture model is used to characterize the complex fracture network; on this basis, a multiphase and multicomponent flow mathematical model has been established when considering reservoir stress sensitivity and nonlinear flow characteristics, and coupling the machanisms of the surfactants/salts adsorption and diffusion effects and their impacts on capillary pressure, relative permeability curves, and osmotic pressure variations. The explicit characterization of fractures is achieved using an adaptive grid refinement method, and the mode is solved by the finite volume method. The simulation results of the "vertical well injection with fractured horizontal well production" test model are consistent with the results from commercial software. The multiphase and multicomponent flow model established based on the discrete fracture model can successfully simulate the development of ultra-low permeability and tight oil reservoirs under the influence of complex fracture networks. The results show that when the matrix and fractures exhibit high stress sensitivity, a significant drop in reservoir pressure will lead to a substantial decline in well productivity. The development of ultra-low permeability and tight oil reservoirs has to consider the nonlinear flow characteristics of reservoirs, so as to accurately evaluate the development range and well productivity. To appropriately reduce the oil-water interfacial tension through surfactant addition can improve the energy-enhanced imbibition efficiency. The osmotic pressure effect induced by low salinity can improve the energy-enhanced imbibition to a certain extent, whereas the incremental oil recovery is limited.