Dynamic Simulation Of Stimulated Reservoir Volume(SRV) During Hydraulic Fracturing In Horizontal Shale Gas Well

Based on the shale gas reservoir development experience and practice,multi-stage multi-cluster hydraulic fracturing in horizontal well is the pivotal technology for commercial exploitation of shale gas,and has undertaken in most of the shale gas fields in the world wide.According to the hydraulic fracturing theoretical researches,there is a strong positive correlation between shale gas production of fractured horizontal wells and stimulated reservoir volume(SRV).Hence,it is necessary to estimating the SRV for fracturing design and evaluation in shale gas reservoir.Currently,the SRV estimation methods can be divided into two categories:direct-monitor methods and numerical simulation methods.The direct-monitor methods,which include micro-seismic monitoring,tilt-meter measuring,electromagnetic imaging,etc.,were applied widely in the preliminary stage of shale gas reservoir exploitation.However,as the further development of shale gas industry,the high cost and complex procedures undermine the potential application of direct-monitor methods.Therefore,establishing a numerical simulation method for SRV estimation,which is economical,reliable,and repeatable,have become a research hotspots in shale gas reservoir fracturing field.During the multi-stage multi-cluster hydraulic fracturing in horizontal shale gas well,multiple hydraulic fractures initiate from different perforation clusters and propagate simultaneously.The formation rock deforms as hydraulic fractures propagate,resulting in formation stress field change;meanwhile,a large amount of fracturing fluid leakoff from hydraulic fractures surface into reservoir,leading to reservoir pressure field rise and formation temperature field decrease.Consequently,the change of formation stress field will veer the propagate direction of hydraulic fractures propagate,beside,the variation of formation stress field,reservoir pressure field and temperature field will conspire to activate massive natural fractures surrounding hydraulic fractures,forming a high-permeability fractures network.And then,this fractures network will facilitate fracturing fluid leakoff,which in turn aggravates the reservoir physical field above.The SRV expands continually under this positive feedback mechanism.According to the formation mechanism of SRV during hydraulic fracturing in horizontal shale gas well,this paper established the natural fractures model,hydraulic fractures propagation model,formation stress field model,reservoir pressure field model,and formation temperature field model respectively,based on rock mechanics,fracture mechanics,elastic mechanics,fluid mechanics,seepage mechanics,and thermodynamics.By integrating these models above,we proposed a dynamic simulation method of SRV during hydraulic fracturing in horizontal shale gas well.This method fully reflects the physical mechanism of SRV expanding process,making its simulation result more accurate and reliable for field application,it not only can simulate the hydraulic fractures propagation behavior and SRV expansion process,but also can calculate the dynamic change of formation stress field,reservoir pressure field,formation temperature field,natural fractures failure,and reservoir permeability field during shale gas fracturing.The dynamic simulation method of SRV during hydraulic fracturing in horizontal shale gas well has been applied practically in the Jiaoshiba block of Fuling shale gas field in southwest China.It simulated and evaluated all the hydraulic fracturing stages in X-2HF horizontal well,and compared the simulation results with on-site micro-seismic monitoring data to validate our numerical simulation method.Finally,it investigated the influence of primary geological conditions(stress contrast,Young’s modulus,Poisson’s ratio,initial reservoir pressure,natural fracture approaching angle,natural fracture dip angle,natural fracture density,natural fracture tensile strength,natural fracture cohesion,natural fracture friction coefficient,and initial formation temperature)and engineering parameters(pump rate,fracturing fluid volume,fracturing fluid viscosity,perforation cluster number,and perforation cluster spacing)on SRV during shale fracturing,and provided several relevant suggestions for shale gas fracturing design and optimization based on the conclusions of sensitivity analysis.This research proposed a reliable,accurate,economical dynamic simulation method of SRV during hydraulic fracturing in horizontal shale gas well,it could contribute to improving the fundamental theory of shale gas fracturing,motivating the shale fracturing technology,reducing the irrationality and blindness in shale fracturing design,promoting the post-fracturing evaluation method development,enhancing the shale fracturing performance and efficiency.Therefore,this paper provides profound significance of theoretical guidance and field application for the sustainable development of unconventional natural gas industry in China.