Hypergravity experimental study on immiscible fluid-fluid displacement in micromodels

Hypergravity offers transformative potential for enhanced oil recovery (EOR) and CO2 sequestration by mimicking subsurface geostress and pressure conditions, facilitating the study of large-scale physical phenomena like fluid migration and sediment compaction within reduced experimental timeframes and scales. In CO2 sequestration, hypergravity shortens Ostwald ripening, facilitates bubble coalescence, and intensifies gas-solid mass transfer. While the dynamic process of two-phase flow under hypergravity remains insufficiently explored. Hence, a hypergravity microfluidic observation system (HMOS) was developed to investigate the aforementioned process. Seven sets of water-oil displacement experiments were conducted on two chips (channel depths of 160 mu m and 30 mu m) under 0 g, 1 g, and 50 g conditions, with capillary numbers (Ca) ranging from 9.55 x 10(-6) to 9.05 x 10(-5) (typical of the viscous fingering regime) and Bond numbers (Bo) ranging from -0.69 to 0. The results demonstrate that hypergravity (50 g) dragged down the bulk of the dense defending phase, reducing the local pressure gradient at the fluid-fluid interface, and thereby inhibited the upward advancement of the invading phase. In a wide flow channel (576 mu m in Chip 1, Bo = -0.69), hypergravity overwhelmed viscous forces, accelerated the dense defending phase downward, even pinched off the invading phase (snap-off), and thus reduced displacement efficiency (S-nw) to 26.9 % (compared to 55.5 % at 1 g); while in a narrow flow channel (80 mu m in Chip 2, Bo = -0.0133), the effects of hypergravity and viscous forces were comparable, resulting in enhanced lateral spreading of the invading phase, and thus drastically improved S-nw up to 60.9 % (compared to 29.6 % at 1 g). Meanwhile, hypergravity has a secondary influence on the displacement morphology, as evidenced by the fact that the slope of fluid-fluid interface length (l(nw)) to invading phase saturation (S-nw) were constricted to narrow ranges (23.04 similar to 29.12 for Chip 1, and 50.46 similar to 64.96 for Chip 2). These findings shed lights on the immiscible fluid-fluid displacement efficiency and morphology under hypergravity, providing insights on applying hypergravity field on meter level models to simulate large-scale and long-duration physical phenomena encountered in deep-earth oil recovery.