Abstract
The fractured-vuggy carbonate reservoir possesses the characteristics of a highly discrete distribution of fractures and vugs, a wide scale range, and the coexistence of free flow and porous flow. However, it also exhibits a high degree of filling media in vugs, including chemical sedimentation, carried fillings and collapsed fillings, which poses challenges for studying the mechanism of enhanced oil recovery (EOR) in filled fracture-vug reservoirs. In this paper, 3D printing technology is utilized to construct heterogeneous, filled models. With a multiphase flow visualization platform, displacement experiments of different injection-production methods, including water injection, gas injection and the co-injection of water and gas, are conducted to elucidate the mechanisms of EOR. It is found that the lower is the gas injection rate or the higher is the water injection rate, the higher is the recovery factor for a horizontal filled vug. For a vertical filled vug, gravity exerts a greater influence on the gas swept area, but inertial forces dominate fluid flow when the water injection log Ca exceeds −2.68. In addition, in a displacement experiment of a simultaneous injection of gas and water, the gas-water mixing zone appears until log Ca ≥ −4.38 (gas) and log Ca ≥ −2.68 (water). Then, the synergistic gas-water effect displaces the oil phase in the filled medium with a higher recovery rate. Therefore, the displacement of gas and water co-injection is preferred over sequential injections, and the injection velocity of gas and water should be compatible. • 3D printing technology is utilized to construct heterogeneously-filled vug media. • Displacement experiments of different injection-production methods are conducted to investigate mechanisms of EOR. • The gas-water mixing zone appears when log Ca ≥ −4.38 (gas) plus log Ca ≥ −2.68 (water). • The synergistic gas-water effect displaces the oil phase in the filled medium with a higher recovery rate. • The co-injection of gas-water is preferred, and the velocity of gas and water should be compatible.
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