An insight into the formation of liquid bridge and its role on fracture capillary pressure during gravity drainage in fractured porous media

Abstract

AbstractThe formation of liquid bridges can maintain capillary continuity between matrix blocks during gas/oil gravity drainage in fractured reservoirs. A travelling oil drop draining into a fracture either forms a liquid bridge or breaks into detached drops. However, the different characteristics of a travelling drop during its elongation and required conditions for transformation into a liquid bridge are not well described in the published literature. In this work, a one‐dimensional model based on slender‐drop theory is employed that holds gravity, viscosity, and surface tension forces but ignores inertia. This model, together with Young‐Laplace equation, gives the fracture capillary pressure. Then, the effect of liquid influx rate, viscosity, surface tension, density difference, contact angle, and contact radius on the shape, critical (or maximum) volume, and length of travelling liquid drops is analyzed and compared with the results in the absence of flow (ie, pendant drops). Critical length is shown to be an increasing function of both liquid viscosity and the influx rate, but the effect of surface tension and density is somewhat case dependent. Furthermore, it is found that if fracture aperture is equal to or less than the critical length of a drop, the formed liquid bridge would be stable. Also, fracture capillary pressure is shown to be remarkable in thin fractures (apertures of less than 50 μm) with embedded liquid bridge. On the other hand, the suspended oil drops, even when reaching critical length, cannot provide considerable capillary pressure.