Research On Optimization And Transformation Of Hydraulic Fracture Network In Coal Reservoirs Based On The Influence Of Natural Fracture Distributio

As an efficient and clean unconventional natural gas,CBM is considered to be an ideal alternative to conventional oil and gas energy.The study of the fracture initiation and expansion patterns of the fracture network for hydraulic fracturing of naturally fractured coal reservoirs is a key scientific issue involved in the process of coalbed methane extraction.In this paper,coal rocks of the Longtan Formation in Panxian County,Liupanshui,were studied by XRD,SEM,conventional mechanical tests,insitu logging and numerical simulations.The fracture expansion pattern and damage process of hydraulic fracturing in coal rocks under different natural fracture distribution and different injection parameters were investigated.The main conclusions and insights are as follows.(1)The mineralogical composition and internal pore and fissure structure of the coal rocks in the Panxian area of Liupanshui were elucidated,and the coal rocks in the study area were generally in the low maturity stage.(2)The distance from the natural fracture to the injection hole and the different initial water pressures have a significant effect on the seam network expansion and damage pattern in the coal reservoir.When the distance is close,the hydraulic fractures tend to pass through the natural fractures to form new seepage channels;the damage pattern basically becomes more complex as the distance and initial water pressure increase.(3)Shot hole parameters,natural fracture angle and number have a significant effect on the expansion and damage pattern of the seam network in coal reservoirs.When the natural fractures are at high angles,the seam network expansion pattern is more complex and the complexity of the seam network increases with the number of natural fractures,and the expansion rate of the hydraulic fractures increases with the shot hole length.(4)Wellbore displacements have a large effect on fracture initiation in hydraulic fracturing of coal reservoirs,with hydraulic fracture initiation being inhibited at closer distances and the inhibition disappearing when the distance reaches a certain threshold.The threshold size increases with increasing initial hydraulic pressure.