Study on the propagation law of hydraulic fractures by cyclic injection in glutenite
As an emerging hydraulic fracturing technology,cyclic injection has a promising application in glutenite reservoirs.Based on the true triaxial hydraulic fracturing system,the hydraulic fracturing experiments by continuous and cyclic injection are carried out under different stress conditions.By comparing the propagation characteristics,the propagation law of hydraulic fractures in glutenite under cyclic injection is clarified.The results show that the fracture propagation in glutenite is mainly controlled by two factors,including the stress difference and the structural characteristics,and the fracturing effect in glutenite can be improved significantly by cyclic injection.Under continuous injection,with the decrease of stress difference,the main controlling factor of fracture propagation will be changed from stress difference to gravel and natural fractures,and the glutenite will tend to produce scattered multiple fractures.There are limitations in enhancing the fracturing effect by pre-breakdown cyclic injection.Only under low stress difference(6 MPa),the breakdown pressure of glutenite can be decreased by 19％.By applying cyclic load to the fracture surface,the non-uniform deformation of the glutenite will be promoted by post-breakdown cyclic injection,and the influence of glutenite structure on the fracture propagation will be strengthened,thus the formation of multi-branch fractures will be promoted as well.At the same time,the limit of in-situ stress conditions can be broken by post-breakdown cyclic injection,the multi-fracture propagation in glutenite can still be formed under the condition of high stress difference(10 MPa).
rock mechanicsglutenitehydraulic fracturingcyclic injectionfracture propagation
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