| Coal rock reservoir with low porosity and low permeability reservoir characteristics, often do not have natural capacity.Hydraulic fracturing is the efficient way of CBM development.Due to the unique permeability characteristics,cleat features,mineral and rock mechanics characteristics,the meachanism of hydraulic fracturing is different from conventional reservoir.The fracture propagation of CBM is different from the conventional reservoir,tight sandstone and shale reservoir.The research on CBM fracture propagation is not thorough.So,it’s necessary to counduct furture research on the problem.In this paper, based on fluid mechanics, mechanics of fracture mechanics and seepage mechanics knowledge, considering coal seam hole deep characteristics, mineral characteristics, cleat systems, analysis summarized the coal seam fracturing fracture morphology, and equivalent rock mechanics parameter model was established, using complex function method to calculate the complex stress intensity factor of crack of coal seam, and optimizing the compound crack propagation criterion. A kind of hydraulic fracture and natural fracture intersection criterion was established.The mechanism of hydraulic fracture and natural fracture intersection was conducted in-depth research. based on research a two-dimensional crack propagation model of coal seam was established to analyze the influence of construction parameters,formation parameters, and the natural fracture on coal seam fracture morphology.Based on the above theoretical research, the coal seam fracture propagation law has great difference with conventional and unconventional reservoir.Fracture morphology is greatly effected by operation parameters, formation parameters and natural fracture parameters. Thus,this study further has certain guiding significance on CBM well fracturing operation optimization. |
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