Experimental And Numerical Study On Fracture Conductivity Of Secondary Fracturing Of Coal Bed Methane

China has a large amount of coalbed methane resources,and coalbed fracturing is the core and key to the development and utilization of coalbed methane.the hydraulic fracturing supporting fracture conductivity is the key factor affecting the coalbed methane production.Hydraulic fracturing technology is an important technology to improve the productivity of coalbed methane and the efficiency of exploration and development.Hydraulic fracturing conductivity is the key factor to determine coalbed methane productivity.In the process of coal seam gas fracturing,proppant is easy to embed.At the same time,brittle coal seam is fragile,due to the role of high pressure fluid of fracturing process,a large number of pulverized coal particles will be produced,which leads to reduction of conductivity,or even invalidating fracturing.Therefore,it is necessary to study the influencing factors and control mechanism of the secondary fracture diversion capacity in the case of more and more coalbed gas fields carrying out secondary reconstruction.It is of great significance to open a new fracture with high conductivity,improve the efficiency of coal seam reconstruction,formulate a reasonable secondary fracturing scheme,and realize the secondary stimulation development of coal bed methane.Hydraulic fracturing technology is an important technology to improve the productivity of coalbed methane and the efficiency of exploration and development.Hydraulic fracturing conductivity is the key factor to determine coalbed methane productivity.In the process of coal seam gas fracturing,proppant is easy to embed.At the same time,brittle coal seam is fragile,due to the role of high pressure fluid of fracturing process,a large number of pulverized coal particles will be produced,which leads to reduction of conductivity,or even invalidating fracturing.Therefore,it is necessary to study the influencing factors and control mechanism of the secondary fracture diversion capacity in the case of more and more coalbed gas fields carrying out secondary reconstruction.It is of great significance to open a new fracture with high conductivity,improve the efficiency of coal seam reconstruction,formulate a reasonable secondary fracturing scheme,and realize the secondary stimulation development of coal bed methane.In this paper,the experimental and Numerical Simulation Research on the conductivity of coal and rock is carried out.Firstly,the confining pressure of 8Mpa is applied according to the actual well depth(≥600m),and the triaxial compression experiment is carried out.The relevant parameters of rock Young’s modulus and Poisson’s ratio are obtained for numerical calculation.Then,FCES-100 fracture conductivity meter is used to test the short-term and long-term conductivity of coal rock,and the influence of different closure pressure,sand concentration and proppant particle size on the conductivity of coal rock hydraulic fracture is tested.The results show that the smaller the closing pressure,the greater the sand concentration,the larger the proppant particle size,the smaller the proppant embedment and the greater the conductivity.At the same time,based on the theory of space geometry,the model of capillary tube bundle and the diamond distribution model of proppant,the calculation model of fracture conductivity considering the influence of embedment and pulverized coal particles is established.Compared with the experimental data of conductivity,the results are in good agreement.It is found that when the sand laying concentration is greater than 5kg/m~2,the increase of sand laying concentration can significantly improve the conductivity.With the increase of closing pressure,the influence of large proppant particle size on the improvement of conductivity decreases gradually.At the same time,with the increase of the closing pressure,the larger the particle content and the smaller the particle size,the greater the damage conductivity.The research results provide theoretical and technical basis for the design and construction of coal seam secondary fracturing.