| With the increasing demand for unconventional oil and gas resources,the geological environment in the process of exploitation is more severe.The interaction between the mechanical properties of rock strata and wellbore structure makes the near well area prone to structural damage during drilling,completion and production,which affects the recovery of unconventional resources such as oil and gas.In view of the key mechanical problems of nearwellbore formation breakdown and hydraulic fracture propagation under complex geological conditions,the following works are carried out by means of theoretical analysis and numerical simulation:(1)Based on elastic mechanics and complex function theory,an analytical model of nearwellbore stress distribution in open hole is established for anisotropic formation,and the influence of elastic anisotropy on near-wellbore stress distribution in different drilling directions is quantitatively analyzed;for perforation completion mode,a parameterized finite element model is established using Python language to predict the formation fracturing pressure.(2)Based on the pipe flow model and the cohesive force model of flow deformation coupling,a numerical model of near well hydraulic fracture propagation in anisotropic formation is established.The effects of material azimuth and elastic modulus anisotropy on the initiation and extension of hydraulic fracture are studied,and the possible causes of near well multiple fractures are discussed.Based on the theory of induced stress field,a three-dimensional numerical model of multi fracture dynamic propagation is established to solve the problem of stress interference between multiple fractures.The change of stress field in the process of fracture propagation is analyzed,and the effect of fracture spacing on stress reversal is emphatically studied.(3)Considering the influence of natural fractures on the formation of complex fracture network,firstly,the fracture intersection criterion based on stress discrimination is established for frictional natural fractures,and the influence of horizontal principal stress difference,approach angle,interface friction coefficient and net pressure in fractures on whether hydraulic fractures pass through or not is studied;secondly,the fracture energy parameters are used to characterize the cemented natural fractures,and a two-dimensional fracture model is established The effects of in-situ stress,approach angle,cementation strength ratio,injection rate and fluid viscosity on the extension mechanism of hydraulic fractures after encountering natural fractures are analyzed. |
