Capillary Continuity in Fractured Oil Reservoirs

In well fractured carbonate reservoirs the gas/oil gravity drainage from the gas-invaded zone is the dominating oil producing process. when the gravitational forces exceed the capillary forces, the matrix blocks, which are surrounded by gas, will release their oil. the results of our experimental works reveal that, depending on the interfacial tension, spreading coefficient, rock wettability, and surface roughness, there is a critical fracture aperture size, t_fc. rock wettability, surface roughness and spreading coefficient play their rules in formation of oil droplets, while the maximum size of the droplet is controlled by the amount of surface tension. when the fracture aperture is more than tfc, the continuity is via solid compressed spacers and/or oil film around them, which atactual reservoir conditions may be considered as non-effective capillary continuity. whereas for the case that the fracture aperture is less than its critical value, the capillary continuity is mainly through liquid bridges, which due to their high transmissibility will result in an effective capillary continuity between blocks. two new definitions for horizontal fracture capillary pressure based on the type of capillary continuity have been presented. the laplace formula and pressure difference between the fracture gas and the matrix oil may be used for the calculation of fracture capillary pressure for non-effective and effective continuity, respectively.