Study On Coupling Effects Of Natural Fractures And Hydraulic Fractures In Water Injection Process In Ultra-Low Permeability Reservoirs

In order to ensure good productivity and long stable production time for ultra-low permeability reservoirs,hydraulic fracturing and water injection methods are adopted.The coupling relationship between artificial fractures and natural fractures during hydraulic fracturing and water injection plays a decisive role in production.If the fracture intersects the complex fracture network,it will increase the production of oil well and increase the recovery rate.If the fracture is connected and the dominant channel is formed,the oil well will be flooded and discarded.Therefore,it is of practical significance to study the coupling relationship between natural fractures and artificial fractures in ultra-low permeability reservoirs during water injection.This paper focuses on the distribution of stress field of reservoir rock;the fracture mode and fracture pressure calculation formula of rock with consideration of induced stress interference;fracture coupling criterion,and simulation of water injection fracture extension by ABAQUS finite element numerical simulation software.It could provide reference for efficient water injection development.The main study are as follows:Firstly,the distribution model of the stress field of the open hole completion is established by considering the stress,the inner pressure of the wellbore and the stress of the injection fluid;and the distribution model of the stress field of the perforation completion is established by combining the stress concentration of the perforation channel;and the maximum shear stress,vertical stress and the maximum circumferential stress are obtained from the model.The area of stress provides a basis for optimization of fracturing parameters.Secondly,with consideration of the influence of induced stress,the calculation model of fracture pressure of reservoir rock is established,and the fracture pressure under different rock conditions is obtained by numerical solution of the model,which provides the basis for the study of the fracture coupling criterion.In addition,through the stress relationship on the fracture surface,the model and criterion of the intersection of artificial fractures and natural fractures are established and the discriminant method is simple and practical.Finally,by using the ABAQUS finite element numerical simulation software,through the contrast analysis of injection and recovery parameters of injection production well network,the optimization scheme of injection production well network parameters is obtained to avoid the formation of the dominant channel and improve the recovery of the ultra-low permeability reservoir.Through the trend and tendency of natural fractures,combined with the intersecting criteria and fracture pressure of reservoir rock,network fractures can be formed during water injection and hydraulic fracturing,and construction suggestions for the forming of dominant channels can be avoided.The research results have certain guiding significance for the efficient development of ultra-low permeability reservoirs.