Analysis of Liquid Bridge Characteristics in a Horizontal Fracture: Critical Fracture Aperture and Fracture Capillary Pressure

The liquid bridge is considered a good means to maintain capillary continuity between overlying matrix blocks if its stability in fractures is preserved. Despite several studies focusing on the liquid bridge in different environments, little attention is paid to dig through a single liquid bridge between thin sections of minerals found in fractured reservoirs. In this study, a set of experiments was conducted to investigate liquid bridge stability and surface profile for different values of liquid volume and surface wettability conditions. It is found that critical fracture aperture is linearly proportional to the contact angle and to the third root of liquid volume, which is depicted by a newly developed expression. An accurate method for computation of capillary pressure of liquid bridge (known as fracture capillary pressure) from the experimentally determined interface profiles, based on the numerical solution of the Young-Laplace equation, is proposed. Following the Plateau sequence, both nodoid and unduloid shape bridges are observed with an increase in fracture aperture, corresponding to positive and negative fracture capillary pressure, respectively. It is interesting to note that instability of liquid bridges occurs at small negative values of capillary force where some attraction force exists between fracture faces. By applying a 1D mathematical model of liquid dripping, a modified expression for the prediction of critical fracture aperture is proposed, including fluid and flow-related parameters. The findings of this study help to better incorporate the role of liquid bridge and corresponding fracture capillary pressure in capillary continuity in fractured porous media.