Optimization Of Hydraulic Fracturing Parameters For Horizontal Wells In Different Coal Reservoir Types

Horizontal section hydraulic fracturing of CBM technology has become one of the most important means for increasing production of coalbed methane because of its large single well control area and pressure relief range.However,due to the differences in the coal-forming environment and the tectonic movements in the later stages of coal formation,the characteristics of China's coal reservoirs have obvious diversity,and there are great differences in the fracturing effects of reservoirs in different regions.In order to maximally improve the effectiveness of the horizontal well fracturing,this paper systematically analyzes the influence of various geological factors on the hydraulic fracturing from the three aspects of surrounding rock characteristics,coal reservoir characteristics,andstress characteristics and divides them into actual conditions.Six typical reservoir types are listed as the main research object of this paper.Based on theories of elasticity and rock mechanics,a mathematical model for establishing the state of comprehensive stress at the ends of hydraulic fractures was established,and then criteria for the intersection of hydraulic fractures and natural fractures was established,and Finally,the law of the hydraulic fracture propagation under different reservoir types was obtained: Under the condition of low stress difference,two groups of natural fractures and a group of natural fractures developed with high crossing angles will produce complex extensions.Hydraulic fractures are easily deflected along the natural fracture surface at low cross-angles,and hydraulic fractures easily pass through natural fractures at high stress angles and high cross angles.The accuracy of theoretical analysis was verified by comparing the literature with other people's experimental results.On this basis,according to the conditions of the complex extension,the distribution law of induced stress of hydraulic fractures under the two-stage fracturing and alternate fracturing methods was simulated by RFPA2D-Flow software.The results show that the alternative fracturing method can change the type of reservoir in the middle section and change the extension law of the fracture,and then combine the extension characteristics of hydraulic fractures under different reservoir types,and determine the principle of fracturing optimization for different reservoir types.Taking the Daning block as an example,the staged fracturing parameters of LP2 well in this block were optimized,and then combined with the capacity calculation model to calculate the production capacity under optimized conditions and actual fracturing conditions.The calculation results show that optimizing the parameters of the well in combination with the type of reservoir can increase the productivity of the well.The research results can provide reference for the optimization of the parameters of hydraulic fracturing in horizontal wells under different reservoir types.