Liquid bridge properties and fractured parameters interaction during gravity drainage process in fractured reservoirs

In fractured reservoirs under the gravity drainage, the oil transfer between the matrix blocks is affected by mechanisms such as capillary continuity or re-imbibition. The connection between adjacent matrix blocks is formed through either fluid bridges, or physical contact due to the roughness of the fracture wall surface. Hence, the study of liquid bridges and investigating how they may change in terms of volume and shape in the process of oil and gas movement is of particular importance. In particular, the study of the critical amount of fracture aperture for the formation of the liquid bridge, its shape and stability, and the fracture capillary pressure due to the presence of the liquid bridge, is still a necessary task. This study aims to address these for liquid bridges formed through gravity drainage by analyzing the simulation results.The simulation results in COMSOL shows that the shape of the liquid bridge can be either nodoid, catenoid, and Unduloid and the capillary pressure due to the liquid bridge can be positive or negative values depending on the fracture properties If the fracture aperture is larger than a critical value (۱.۷ mm in this study) or the volume of fluid inside the fracture is less than the threshold value (here ۱ microliter), the capillary pressure becomes negative. We also observed that the fracture capillary pressure function is saturation dependent and its form is similar to the matrix capillary pressure curve. However, its magnitude is significantly lower than the matrix capillary pressure. This means that in the presence of liquid bridge with flow across the matrix blocks and perpendicular to the fracture a different capillary pressure is expected.Moreover, the effective parameters in the formation and stability of the liquid bridge, and their effects on the shape and properties of the liquid bridge has been investigated through a series of sensitivity analysis. Unlike the volume of fluid between two surfaces which has a large impact on the parameters of the liquid bridge (i.e., throat radius) The effect of wettability is negligible and it has visible effects only in the case of fractures with large openings. The results of this study help us to understand to how and when the fracture capillary pressure values must be taken into account in fracture reservoir simulations.