Study On The Influence Factors Of Hydraulic Fracture Propagation In Fracture-cave Carbonate Reservoir

The carbonate reservoirs in the Tahe oilfield are mainly fracture-cave reservoirs,of which the caves are the main reservoir space for oil and gas,and the fractures are the main seepage channels that communicate the wellbore and the cave.Currently,most wells in this area need to be stimulated by hydraulic fracturing or acid fracturing to obtain production.However,natural fractures,caves and faults in fracture-cave reservoirs have a significant impact on the propagation of hydraulic fractures compared to the homogeneous reservoirs.Based on this,this paper mainly studied the propagation law of hydraulic fractures in carbonate reservoirs and analyzed the influence of different factors on hydraulic fracture propagation.This paper established a numerical model of hydraulic fracturing based on the finite element method and pore elasticity theory,and verified the rationality of the model by comparing the calculation results of two-dimensional KGD model with the calculation results of ABAQUS software.In terms of the influence of natural fractures,this paper studied the interaction between hydraulic fractures and natural fractures by using the method of cohesive elements.The numerical results show that the interaction between the two is mainly affected by the approach angle of natural fracture,horizontal stress difference and natural fracture cement strength.The larger the value of these factors,the more likely the hydraulic fracture will cross through the natural fracture.Based on the extended finite element method,this paper studied the propagation law of hydraulic fracture in homogeneous formation,and analyzed the effects of perforation angle,horizontal stress difference and fracturing fluid displacement on the propagation law.On this basis,the propagation law of hydraulic fracture in cave-containing formation is studied.The numerical results show that the cave has a certain repulsion effect on the hydraulic fracture,and the hydraulic fracture will deflect around it.The degree of deflection is mainly affected by the wellborn position,the horizontal stress difference,the internal pressure of cave and the fracturing fluid displacement.Through the true triaxial hydraulic fracturing simulation experiment,this paper studied the effect of fault-krast in carbonate reservoir on the hydraulic fracture propagation.According to the experimental results,the hydraulic fracture is more likely to communicate faults than communicate caves.By placing strain gauges in the experimental samples,the changes of horizontal stresses in different regions during the fracturing process were measured,and the trend of stress change and the law of stress variation were obtained through statistical analysis.Based on this,the optimization proposal for the acid fracturing scheme of Tahe oilfield was put forward.The research in this paper provides some theoretical support for the exploitation of Tahe oilfield,and has referential significance for the effective development of fracture-cave carbonate reservoirs.