Study On Hydraulic Fracturing In Low Permeability Reservoir By Numerical Simulation

Due to years of high-pressure water injection development,the injection-production ratio is high,the injection-production pressure difference is large,and the pressure between injection-production Wells is serious,the natural fractures in the low permeability fractured reservoir are in the open state,and the uneven distribution of natural fractures increases the heterogeneity of the reservoir.When an infill or adjustment well is deployed in the field,the injection well is usually shut down or the well is opened to relieve pressure,resulting in a rapid drop in formation pressure.In this state,due to the heterogeneity and low permeability of low permeability fractured reservoir,there are great differences in the range of effect in different directions,formation pressure system disorder,there is a local high pressure area,drilling under such conditions,easy to occur oil and gas water flooding,kick,pipe out,well leakage and other safety accidents.In view of the above problems,firstly,through the investigation of the structural characteristics,sedimentary characteristics,reservoir physical properties and reservoir natural fracture characteristics of the target block,this paper establishes the reservoir fracture distribution model of the target block by using petrel simulation software.Second,considering the effective stress equation theory of permeability and the stress sensitivity of permeability of low-permeability argillaceous sandstone matrix,the relationship between reservoir rock matrix permeability and formation pressure is obtained.Thirdly,according to the mechanical conditions of natural fracture opening and closing,the relationship between permeability and formation pressure under the condition of fracture closing is established.Fourthly,COMSOL finite element software is used to simulate and analyze the variation law of formation pressure under the condition of well shut in and pressure relief in the target block.The results show that the opening and closing state of natural fractures has a great influence on the permeability of low-permeability fractured reservoirs;The natural fractures near the injection well are open and the distal natural fractures are closed.During pressure relief,the natural fractures near the injection well are closed rapidly,reducing the reservoir permeability,resulting in the formation of a high-pressure area near the well belt of the injection well;Therefore,for the formation pressure prediction of low-permeability fractured reservoir,the influence caused by the opening and closing state of natural fractures should be considered.The research content of this paper can provide a basic basis for the formulation of drilling shut-in scheme,reduce the drilling construction risk of this kind of reservoir and improve the cementing quality.