Pore scale simulation of liquid and gas two-phase flow based on digital core technology

Two-phase flow in two digital cores is simulated by the color-gradient lattice Boltzmann method. This model can be applied to two-phase flow with high-density ratio (on order of 1000). The first digital core is an artificial sandstone core, and its three-dimensional gray model is obtained by Micro-CT scanning. The gray scale images are segmented into discrete phases (solid particles and pore space) by the Otsu algorithm. The second one is a digital core of shale, which is reconstructed using Markov Chain Monte Carlo method with segmented SEM scanning image as input. The wettability of solid wall and relative permeability of a cylindrical tube are simulated to verify the model. In the simulations of liquid and gas two phase flow in digital cores, density ratios of 100, 200, 500 and 1000 between liquid and gas are chosen. Based on the gas distribution in the digital core at different times, it is found that the fingering phenomenon is more salient at high density ratio. With the density ratio increasing, the displacement efficiency decreases. Besides, due to numerous small pores in the shale, the displacement efficiency is over 20% less than that in the artificial sandstone and the difference is even about 30% when density ratio is greater than 500. As the density ratio increases, the gas saturation decreases in big pores, and even reaches zero in some small pores or big pores with small throats. Residual liquid mainly distributes in the small pores and the edge of big pores due to the wettability of liquid. Liquid recovery can be enhanced effectively by decreasing its viscosity.