Study On The Propagation Law Of Hydraulic Fractures In The Interbedded Sand And Mudstone Of The Fifth Member Of The Xuwu Member In Western Sichuan

Hydraulic fracturing is one of the primary technologies used to reservoir production enhancement,but the complexity of fracture propagation has largely plagued the design of fracturing program.There are many factors dominating the extension of hydraulic fracture,and the propagation path would be more complicated especially encountering the geological discontinuities such as interbedded interface.It is very important to understand the fracture propagation law in layered information for the effective development this formation.In this paper,finite element numerical simulation method was use to study the hydraulic fracture propagation law in Xu5 sand and mud interbedded information in western Sichuan basin,the results had an important referecen role on the stimulation development of Xu5 foramtion.Based on geological characteristics of X5,a seepage-stress-damage coupled finite element model was builit to study the dynamic propagation process in sandstone and mud interbedded formation.A Cohesive pore pressure element(CPPE)was used to simulate the initiation and propagation of hydraulic fracture based on damage mechanics.Geological parameters and operation parameters are coupled each other in the hydraulic fraturing process,which determine the propagation behavior of hydraulic fracture in layered formation.The influences of stress difference,Young’s modulus,tensile strength,injection rate and fracturing fluid viscosity on hydraulic fracture geometry and induced stress were studied in this paper.Meanwhile,a plastic damage constitutive model of natural fracture was established to analyse the impacts of nature fractures on hydraulic fracture geometry in layered formation.Simulation results showed that the hydraulic fracture geometry is mainly“(?)”shaped and"I"shaped in Xu5 sand-mud interbedded formation.Limted to poor physical properties,geological conditions and operation conditions,the hydraulic fracture geometry in sand-mud interbedded tight gas reservoir is not a complex network system like shale gas but a local stimulated reservoir volume near hydraulic fracture.The simulation results showed that it was not easy for hydraulic fracture initiating and propagating along sand-mud interface under the condition of high stress difference and high approach angle.However,it was prone to occur shear slippage in layered formation under the situation of small vertical stress difference of sandstone and mud,large Young’s modulus of sandstone,small tensile strength difference of sandstone and mud,large injection rate and small fracturing fluid viscosity.The induced stress near hydraulic fracture is determined by rock deformation and pore pressure.The shear slippage along interface resulted in increasing of rock deformation,so,there was a sudden increase of induced stress near sand-mud interface.The research results have largely promoted the study of interaction mechanism of hydraulic fracture and interface.What’s more,it can provide a significant scientific guidance to the development of tight gas.