Fracture capillary pressure plays a major role in many aspects of fluid flow in fractured rocks, including physical interpretation, mathematical modeling, and simulation of various mechanisms. The 2D microfluidic devices are a ubiquitous tool to study the multiphase behavior of fractures. However, these devices still suffer from two essential limitations: 1) narrow-etched depth of the middle fracture, producing an undesirable effect on the fracture capillary pressure and 2) undesired deformation of the liquid bridge curvature. In this work, a novel technique is developed for fabricating microfluidic devices where the 2D domain is attached to a 3D open medium that is realistic enough to capture the essential physics underlying the mechanisms of multiphase flow and liquid bridge evolution in fractures. The developed “3D fracture-2D matrix” microfluidic device is utilized to study the mechanism of gas gravity drainage in fractured rocks and evaluate the available models that describe the fracture capillary pressure. The reasonable agreement between experimental results and theoretical calculations reveal that the Young-Laplace equation can be used as a framework for the fracture capillary pressure. This result is in contrast with the previous experimental results in the literature that rejected the validity of the Young-Laplace equation for evaluating fracture capillary pressure. Furthermore, the capillary bridge description is a key parameter in evaluating the fracture capillary pressure and estimating the recovery profile of matrix blocks through the capillary continuity phenomenon. The visual analysis shows that the circle approximation can describe the shape of the bridge and the dynamic bridge curvature is almost constant during the fracture desaturation under the gravity drainage mechanism. These findings can improve our understanding of fracture capillary pressure models that not only affect the ultimate recovery but also are required to design enhanced oil recovery in fractured reservoirs.

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