Meikuang Anquan (Dec 2021)
Comparative study on permeability enhancement effect of separate-layer fracturing and multi-layers comprehensive fracturing in coal seam group
Abstract
In this paper, a gas roadway with multiple coal seams in southwest China is taken as the test site, and the separate-layer hydraulic fracturing and multilayers comprehensive hydraulic fracturing are carried out. This paper analyzes the whole process of coal seam fracturing development, discusses the influence of water injection volume in coal seam on subsequent drilling construction, and obtains the distribution law of gas content and water content of coal seam after fracturing, and the gas drainage effect. And the fracturing influence ranges of the two fracturing methods are obtained. The results show that the hydraulic fracturing in coal seam composes of five stages: stress accumulation, fracture initiation, fracture propagation, multiple fracture initiation and propagation, and fracture propagation completion. Compared with the multilayers comprehensive hydraulic fracturing, the average pressure of separate-layer hydraulic fracturing is slightly higher, but the total water injection volume is significantly less. The gas content and water content of coal seam after separate-layer hydraulic fracturing are lower and higher than those of comprehensive fracturing technology, respectively; and the initial gas drainage concentration of coal seam is also higher. In addition, the average gas drainage concentration of single hole and drilling field are 54.1% and 43%, increased by 14.9% and 9% compared with comprehensive fracturing technology. And the effective fracturing influence radius of separate-layer fracturing and multilayers comprehensive fracturing reaches about 50 m and 40 m, respectively. This indicates that the separate-layer hydraulic fracturing technology can significantly improve the effective influence range and effect of seam permeability improvement in coal seam group. Moreover, the separate-layer hydraulic fracturing technology can reduce the water injection volume in coal seam, decreasing the bad phenomena in the subsequent drilling construction of gas drainage borehole, such as sticking drilling.
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