| In order to improve resource utilization,hydraulic fracturing based permeability enhancement technology is widely used for resource extraction in deep low permeability coal seams.Its advantages of safety,environmental protection,and convenient construction have been recognized in the industry.In recent years,the optimization of hydraulic fracturing parameters through numerical simulation to solve the technical problems such as high ground stress,high gas pressure,and low permeability of coal seams commonly existing in the exploitation of deep low permeability coal seam resources has become the main trend to study and improve the permeability enhancement effect of hydraulic fracturing.This study starts from the perspective of porous media theory and uses the extended finite element method to establish a two-dimensional homogeneous hydraulic fracturing numerical model.The purpose is to study and analyze the main factors that affect the development of artificial fractures under different geological properties of coal and rock layers,explore the development laws of fractures,and develop on-site test plans.Combining numerical simulation and on-site test results,the fracturing parameters that affect the development radius of hydraulic fracturing fractures were determined.The results indicate that:1)The angle between the maximum principal stress and the crack has a significant impact on the range of fracturing radius.Based on the theory of hydraulic fracturing crack development,when the crack is parallel to the direction of the maximum principal stress,the longest crack length can be developed within the same time;When the angle between the crack and the maximum principal stress gradually increases to 90°,the length of the crack that can develop gradually decreases to the shortest within the same time.On the other hand,when the crack length increases to near the maximum length,the crack length hardly increases with time,and the crack width will significantly increase.2)The angle between vertical crustal stress and fracture has a great influence on the range of fracturing radius.When fractures develop in coal strata,the greater the angle between vertical crustal stress and fractures,the more difficult it is to deflect the direction of fracture development;The smaller the included angle is,the faster the fracture will develop along the vertical crustal stress direction and penetrate the coal bed,leading to"Pressure Relief".3)The impact of different fracturing fluid flow rates on the final fracturing radius is relatively small.When the injection flow rate changes within the range of 0.001 m3·s-1 to0.050 m3·s-1,the injection amount decreases and the direction of fracture development will approach the direction of maximum principal stress;With the increase of liquid injection,the direction of fracture development will be close to the vertical crustal stress direction.Figure[58]Table[15]Reference[84]... |
