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 matrix blocks is affected by mechanisms such as capillary continuity or re-imbibition. 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 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 or the volume of fluid inside the fracture is less than the threshold value, 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. The effective parameters in the formation and stability of the liquid bridge have been investigated through a series of sensitivity analysis. Unlike the volume of fluid which has a large impact on the liquid bridge (i.e., throat radius), the effect of wettability is negligible and it has visible effects only in the case of large fractures. The results of this study help us to understand how and when the fracture capillary pressure values must be taken into account in the fracture reservoir simulations.