To investigate the characteristics of fractures and surrounding region induced by the hydraulic fracturing, a new method to visualize hydraulically induced fractures in the laboratory experiment was developed. For this purpose, a thermosetting acrylic resin, methyl methacrylate, mixed with a fluorescent paint was used as the fracturing fluid. The resin was able to fix within the specimen by heating just after the fracturing experiment, and then cut sections of the specimen were observed under ultraviolet light irradiation. In this way, it is expected that the hydraulically induced fractures and the surrounding regions will be detected because the induced fractures filled with the resin should emit light, while the other parts will not.
As a result, the hydraulically induced fractures, which were filled and fixed with the resin, are successfully observed in the shale specimens. The configuration of bi-wing fractures extended from the injection hole along the maximum stress direction is clearly observed under the uniaxial compressive condition. Detailed microscopic observations show that the main fractures are tortuous and are accompanied by many thinner ramified fractures. Additionally, fractured regions where the resin penetrates significantly are observed around the main fractures. These induced fractures and fractured regions are considered to be the stimulated region in which permeability is improved.
