Simulation Study of Large-Slope Well Leakage in Carbonate Fracture-Cave Reservoirs

According to the characteristics of carbonate fracture-cave reservoirs, the conditions and window for gravity displacement between fracture-cave reservoirs and wellbores are analyzed, and the characteristics of large-slope wells are analyzed. The numerical simulation method is used to simulate and analyze the occurrence process of gravity displacement gas invasion in vertical wells and large-slope wells, and the evolution process of velocity field and gas-liquid interface during gravity displacement is studied. The results show that the inclination angle of micro-cracks, medium cracks, wide cracks and extra-wide cracks has relatively little effect on the leakage rate, but the leakage rate increases with the decrease of the angle between the fracture and the upward return direction of the drilling fluid. (<5 m3/h) is usually drilled in the middle fracture or wide fracture development formation, high leakage rate (5–20 m3/h) is usually drilled in the extra-wide fracture development formation, high leakage rate (20–40 m3/h) is usually drilled in fault zone or small karst cave (50–500 mm), extremely high leakage rate (>40 m3/h) is usually drilled in medium or large caves (> 500 mm); The displacement of drilling fluid has little effect on the leakage rate of micro-cracks and medium cracks, but has a significant effect on wide cracks, extra-wide cracks and caves, and the increased displacement will lead to a significant increase in the leakage rate of these types of fractures.