Coal Fracturing Expansion Finite Element Study

China has abundant coal resources and the potential for CBM development is huge.However,China's CBM development technology is not yet mature and many problems need to be resolved.Unlike conventional oil and natural gas resources,CBM reservoirs are characterized by low porosity,low permeability,and low pressure,resulting in the inability of CBM development to use conventional development methods.At present,fracturing technology is a feasible method for increasing production and stabilizing CBM production.However,due to the special rock mechanics characteristics of coal,coal seam fracturing is different from general hydraulic fracturing methods.This paper analyzes the characteristics of coal seam hydraulic fracturing.Introduced and discussed the extended finite element and its advantages.Through the basic rock mechanics experiments,the basic mechanical parameters of coal and rock in the seven-element mine area in China were obtained.According to the heterogeneity and anisotropy characteristics of coal and rock,as well as the advantages and disadvantages of various hypothetical models,it is concluded that the hypothetical model of the orthotropic orthotropicity is more applicable to coal and rock.The theoretical knowledge of fluid-structure interaction and crack propagation criterion is briefly introduced.An extended finite element analysis model for coal-rock fractures was established.By analyzing the different fracturing fluid displacement,viscosity and different coal rock tensile strength on the impact of fracturing.Coal seam fracturing was studied by simulating different tensile strengths and reflecting different damages.Based on basic theoretical knowledge and numerical simulation studies,it was concluded that the increase in tensile strength increases the crack width appropriately and the seam pressure increases slightly.In addition,the effect of displacement on cracks is greater than the effect of viscosity and tensile strength on cracks.The micro-crack in the coal seam can be regarded as a kind of damage,and this damage makes the strength of the coal seam low.This paper observes that the Poisson's ratio of the elastic modulus increases at the same time.The numerical simulation results show that the effect of the Poisson's ratio change on the length and width of the crack is less than the effect of the change of the elastic modulus on the length and width of the crack.The conclusions of this paper provide guidance for follow-up fracturing design,and also provide new ideas and methods for follow-up researchers to study coal seam fracturing.