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| Investigation of two-phase flow mechanism at pore scale using the phase field method |
| LIU Xianshan1, 2, SUN Meng1, CAO Yiting1, YANG Wenyuan1, DAI Yuhang1, CHEN Shunshun1, LIU Xinqian1 |
| (1. School of Civil Engineering, Chongqing University, Chongqing 400045, China; 2. State Key Laboratory of Safety and Resilience of Civil Engineering in Mountain Area, Chongqing 400045, China) |
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Abstract Regarding the extraction of unconventional shale oil, in-depth investigations of two-phase flow patterns are crucial for describing residual oil content, displacement efficiency, and ultimate recovery. Using a pore-scale rock as a case study, a two-phase flow model has been developed based on phase-field theory and the Navier-Stokes equations to simulate the water-oil two-phase flow process, influenced by pore-throat size and structural wettability under specified flow velocities. The results indicate that variations in pore-throat size inversely correlate with the advancement of the leading-edge positions of the water-oil two-phase interfaces on both sides. It is observed that dominant flow channels form within the pores, with internal flow velocity being inversely proportional to pore size. Moreover, the pressure difference distribution in small-pore-throat structures is considerably greater, while the average pressure change at the inlet gradually diminishes and stabilizes. The stabilization times for both average inlet pressure and leading-edge position are consistent. As the pore-throat size decreases, displacement efficiency within the pores progressively increases, although it deviates from stable displacement. Additionally, variations in pore structure wettability result in the advancement speed of the leading-edge positions being directly proportional to contact angle size, and the central two-phase interface exhibits irregular capillary fingering characteristics; however, final displacement saturation is inversely proportional to contact angle size. Furthermore, the initial pore pressure distribution is uniform, and the pressure gradient at the two-phase interface increases as wettability weakens, particularly with the average pressure change at the inlet gradually diminishing and stabilizing. The advancement speed of the displacement front increases with larger contact angle sizes, and displacement within the pores is significantly influenced by capillary effects, especially for a wetting angle of 30°, leading to an extensive displacement range of the two-phase interface that affects fingering on both sides. These investigations elucidate the water-oil flow mechanism during unconventional shale oil reservoir extraction, providing a scientific basis for optimizing efficient development strategies.
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2026, Vol. 45 
