Study On Fracture Formation Mechanism Of Low Permeability Coal Seam With Multiple Crack Fracturing

For the development of CBM now,Hydraulic fracturing as a relatively mature technology has been applied to engineering practice.Under the influence of principal stress aspects,Most of existing hydraulic fracturing technology can only product a series of single direction main cracks.How to product more and more complicated fractures has been the key.In essence,changing the fracturing region principal stress distribution can change the extension of hydraulic fracture direction accordingly.Rich natural fractures in coal reservoir system and the formation of multiple fracturing puts forward a train of thought.Starting from the development and extension of hydraulic fracturing,this paper investigated and studied the low permeability of coal reservoir characteristics in China.It carried out the research from the following several aspects:This paper Carried out numerical implementation under the condition of different principal stress of hydraulic fracturing and Observed the fracture morphology and acoustic emission.Through the physical image to intuitively understand the process of Cracks in initiation,development and well versed in the ultimate state.Results showed that the maximum principal stress control the development direction of crack.Crack and reservoir pressure had a linear relation with the principal stress ratio.Some synchronous fracturing simulations with two different location wells and simple well-bore network under different principal stress ratio were made,The results showed that under the influence of inter-well stress disturbance,the hydraulic fracture extension had a opposite trend ? Multiple cracks can be made based on this principle.Crack pressure was also less because of the influence of the stress interfere between Wells.To simulate different approximation of hydraulic fracture and natural fracture intersection through the preset Angle of natural fracture.The results showed that under the condition of middle approaching Angle,hydraulic fractures can easily extend according to the natural fracture extension section of distance,so as to change the direction of crack.In high Angle and low approximation horn,hydraulic fractures usually directly cross the natural fractures and then continue extending according to the direction of the original...