Numerical Study Of Hydraulic Fractures Propagation For Horizontal Well

As one of the current core and hotspot technologies for oil and gas exploration and development,the horizontal well multistages fracturing is largely promoting the course of development for low permeable petroleum resources.Post-fracture geometry is a general concern of field fracturing engineers,since it largely determines the efficiency of stimulated production.Furtherly,to predict the geometry of hydraulic fractures is of great significance.During horizontal well fracturing,the induced stress of each cluster will interact with each other to disturb local stress field.It,together with the influence from geological and engineering parameters,leads to an extremely complex controlling mechanism of multi-fractures propogation.Consequently,the propogation mechanism and geometry prediction of hydraulic fractures need some further studies.Based on this background,this thesis centres on numerical simulation of fracture propogation during multistage hydraulic fracturing.The following works are conducted:(1)Based on literature review and the advantages and disadvantages of the existed numerical simulation schemes for hydraulic fracturing,the extended finite element method(XFEM)was selected in the thesis.Besides,the handling methods of various associate special units were summarized allowing XFEM to simulate hydraulic fracturing.(2)Mathematical models simulating fractures propogation were established combining with the theory of linear elasticity and fracture mechanics based on plane strain assumption;besides,associating with the above established models and fluid-solid coupling,a program being able to simulate horizontal well fracturing is coded to solve hydraulic fractures'propogation.(3)The models and coded simulation program is first being validated and then used to simulate and analyze the multi-fracture propogation.Results show that:a).The lateral fractures propogates with a mutual repulsion phenomenon,while the middle fracture is comparably smaller in terms of width and length because of the inducing effect;b).Volumn of fracturing fluid,rock's elastic modulus and in situ stresses difference are positive parameters while visicosity of fracturing fluid remains negative one in relation to fractures' length;c).The Poisson's ratio of formation rock does not have significant influence over fracture's length.(4)As for three-cluster fracturing,simulation shows that the greater each of visicosity of fracturing fluid,pumping rate,rock's Young's modulus and rock's Poisson's ratio is,the greater the turing angles of lateral fractures will be;The greater cluster space or in situ stresses difference is,the smaller the turing angles of lateral fractures will be.This study furtherly discusses the rules for multifractures propogation and reveals its controlling mechanism.It can be used for hydraulic fracturing analysis.