Abstract
Summary Gas–oil gravity drainage that takes place in the gas-invaded zone of fractured reservoirs is the main production mechanism of gas-cap drive fractured reservoirs as well as fractured reservoirs subjected to gas injection. Interaction of neighboring matrix blocks through reinfiltration and capillary continuity effects controls the efficiency of gravity drainage. Existence of capillary continuity between adjacent matrix block is likely to increase the ultimate recovery significantly. Liquid bridge formed in fractures has a significant role in maintaining the capillary continuity between two neighboring matrix blocks. The degree of capillary continuity is proportional to capillary pressure in the fracture due to the presence of formed liquid bridge. Only a handful of studies have focused on the subject of liquid bridge in fractures and related capillary pressure. The main contribution is to develop a numerical procedure to predict liquid bridge characteristics (e.g. its shape, its stability and its capillary pressure). Accurate determination of gas-liquid interface profile of liquid bridge is crucial to predict fracture capillary pressure precisely. To this end, numerical solution of Young-Laplace equation in the absence and in the presence of gravitational effects is found and the obtained results are verified by the experimental data. Computation of fracture capillary pressure as a function of liquid bridge volume for different contact angles revealed that the fracture capillary pressure-liquid saturation curve has a shape similar to that of a matrix. Therefore, the capillary pressure of porous media can be applied directly for fractures considering proper modifications. Furthermore, the stability of liquid bridge has been investigated using the concept of critical fracture aperture. Critical fracture aperture is defined as the maximum fracture aperture that a liquid bridge with specific volume can exist. Finally, an empirical relation has been developed that correlates the critical fracture aperture to both the liquid bridge volume and the contact angle. Results of this study emphasize the importance of capillary continuity created by liquid bridges and therefore, incorporation of liquid bridges in the study of gas-oil gravity drainage will lead to more realistic performance prediction of fractured porous media.
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