Full Three Dimension Hydraulic Fracture Propagation Characteristics Research On Sand/Shale Interface

This article is in view of the poor thin oil reservoir hydraulic fracture during the processof hydraulic fracturing in sand/shale understanding unclear interface extension featurescarried out this problem, this problem belongs to the state of fluid-structure interaction, thehydraulic fracture in sand/shale elastic interface extension characteristics research.Based on the experimental study and theoretical analysis, the method of using digitalspeckle techniques, observed the crack propagation in the process of the changing law ofstrain and displacement of the interface, find sand/shale interface produced by asymmetricshear strain is the main cause of crack extension to, using strain coordination hypothesis andintensity equivalent hypothesis, established the description of sand/shale interface sheardamage plasticity constitutive model, and into the full three dimension hydraulic fracturemechanics model, the formation of the sand/shale interface of full three dimension hydraulicfracture numerical simulation model of oil Wells in daqing oilfield site related validation ofthe computation.The submodel analysis technology, on the basis of interface crack propagation process,the change rule of maximum principal stress analysis in the process of crack propagation, theinterface of asymmetric shear strain is the major cause of crack extension to, the inconformity with the digital speckle experimental results, and proved the correctness of theinterface model.Through the process of hydraulic fracture extension analysis found that the change ruleof fluid within the raphe crack parallel to the first formation on the length direction ofmaximum principal stress direction extension, form water for cracks, seam pressuredistribution is controlled by the dimensions of the cracks. The analysis results show that thecrack is penetrating interlayer, minimum in-situ stress difference depends on the sand/shalereservoir, formation stress state, formation and mechanical properties, fluid property andfracturing operation parameters. Through theoretical analysis and field application evaluation,in view of the geological conditions of daqing oil field, puts forward the interface basic shadecondition of packer, is the development of poor thin reservoir provides strong theoreticalsupport, has solved the key problem in thin reservoir effective development.