1 Hubei Cooperative Innovation Center of Unconventional Oil and Gas, Yangtze University, Wuhan 430100, China
2 Petroleum Engineering College of Yangtze University, Wuhan 430100, China
3 Mechanical Engineering College of Yangtze University, Jingzhou 434023, China
The application of conventional hydraulic fracture treatment is not ideal in coalbed methane reservoirs, which influences the industry development in China, thus, the present technique should be improved. From two aspects of net pressure and stress sensibility of permeability, it is analyzed and considered that permeability around hydraulic fractures is damaged severely, so this is the main flaw of conventional hydraulic fracturing in CBM. It is proposed to shear natural fractures by fracturing treatment, which are plentiful in coalbed methane reservoirs, and the mechanical condition to generate sheared fractures is presented, in the meanwhile, it is verified that the permeability of sheared fractures is much larger than coal matrix permeability. When the angle between natural and hydraulic fractures is small in coalbed methane reservoirs, the natural fractures will shear easily at low net pressure, so network fractures can be formed. In comparison with conventional hydraulic fracturing, this new methodology can make natural fractures shear at low net pressure to form transverse network fractures, hence, the stimulated reservoir volume is larger, and damage to coal permeability is avoided. This new technique is advantageous in both stimulated reservoir volume and permeability improvement, and it is more adaptable for coalbed methane reservoirs, thus, it has a wide application prospect and significant value.
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