| The upper Permian is mainly developed in the coal seams of eastern yunnan,and the upper Permian has the geological characteristics of "two more,three higher and two larger",such as many types of coal structure,many layers of coal,high gas content,high resource abundance,high reservoir pressure,large amount of resources and great change of permeability.According to the geological conditions of coal measures strata in the study area,this article adopts the numerical simulation software of ABAQUS and Laochang area more close layer of coal seam hydraulic fracturing fracture development characteristics,analyzed the geological and engineering factors on the coal seam and more layers fracturing effect,put forward the suitable for the study area more coal layer fracturing advice,providing theoretical basis for combined layer fracturing operation.The Young's modulus E of coal in Laochang area is 1.11 GPa ?9.22 GPa,the Poisson's ratio? is 0.23?0.40,and the tensile strength is 0.60 MPa?1.71 MPa.The in-situ stress characteristics of coal seams buried within 167.77 m?1043.72 m in Laochang area are as follows: The minimum horizontal principal stress is 3.80 MPa?21.44 MPa,the maximum horizontal principal stress is4.65 MPa?32.73 MPa,and the vertical principal stress is 4.53 MPa?28.18 MPa.The horizontal principal stress of the coal reservoir is positively correlated with the burial depth.The lithology of the roof and floor of the main coal seam in Laochang area is mainly argillaceous siltstone,silty mudstone and mudstone.Translated with Based on finite element method,in ABAQUS software,the use of cohesion in the model simulation Cohesive unit consisting of the Cohesive layer cracks,using the software comes with crack fracture and the extension of the standard,use the existence of pipe flow unit simulation wellbore,the establishment of a vertical well fracturing coal seams more threedimensional numerical model,implements the seepage stress damage coupling,The initiation and extension of multiple fractures can be simulated accurately.In this paper,the effects of Young's modulus and tensile strength of coal rock,Young's modulus and tensile strength of coal rock interlayer rock,construction displacement and fracturing fluid viscosity,horizontal in-situ stress difference and horizontal in-situ stress difference between layers on the formation of multi-seam hydraulic fracturing fractures and reservoir fracturing fluid distribution are simulated.The paper has obtained the following main results: 1)the closer the mechanical properties of coal and rock in the fractured interval are,the more uniform the fracturing fluid distribution is;The smaller the Young's modulus or the greater the tensile strength of the coal reservoir,the less the flow distribution.The large Young's modulus difference or small tensile strength difference between adjacent layers of coal and rock are conducive to the longitudinal extension of fractures,so as to achieve multi-reservoir fracturing.2)The research indicates that increasing the construction displacement or fracturing fluid viscosity is beneficial to the extension and propagation of fractures,but the change of fracture morphology is limited when increasing to a certain value.3)Horizontal in-situ stress difference is related to the distribution of fracturing fluid between reservoirs.Minimization of horizontal stress difference in interbed is the key to the success of multi-seam combined fracturing.Appropriate stress difference between layers can not only make fractures connect other reservoirs,but also restrict the height of fractures,so as to realize the comprehensive transformation of multiple coal seams. |
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