Volume 66

Microscopic pore-throat utilization characteristics of water flooding/Nâ‚‚/COâ‚‚ in tight oil reservoirs Yuhao Xiong, Linsong Cheng, Renyi Cao

Abstract

Newly proven tight reservoirs show increasingly poor physical properties, insufficient natural energy, and small pore throats. As a result, waterflooding often faces the problem of “difficult injection and poor production”, making the switch of displacement media urgent for oilfield sites. This study couples the Navier-Stokes (N-S) equations and level-set equations to build a mathematical model of microscale two-phase flow. Using this model, it simulates the entire process of water, Nâ‚‚, and COâ‚‚ flooding and reveals the mechanism behind differences in pore-throat utilization characteristics of different injected media. Results indicate: Water has low injectivity and cannot enter small-medium pore throats with high seepage resistance, with its displacement front advancing slowest and microscale oil displacement efficiency lowest. Nâ‚‚ flooding has higher injectivity but suffers severe gas channeling, leading to low efficiency. COâ‚‚ flooding eases gas channeling, and crude oil in small-medium pores can be displaced via dissolution, diffusion, viscosity reduction, and interfacial tension lowering, achieving the highest efficiency. Based on the microscale pore-throat simulation via the level set method, this study provides theoretical guidance for developing tight oil reservoirs by switching displacement media.

Keywords Tight oil reservoirs, Level set method, Displacement characteristics, PoreA-throat activation, Medium optimization