Investigation Of Fractures Propagation Of Hydraulic Fracturing In Shale With Defects

Bedding defects,as a macroscopic weak surface widely present in shale reservoirs,have significant differences in their mechanical properties and distribution,which have a significant impact on the complexity of hydraulic fracture networks.Therefore,it is of great practical significance for efficient exploitation of shale gas to explore the propagation law of hydraulic fractures in shale containing bedding defects and the interaction law of hydraulic fractures and bedding defects.This article explores the influence of bedding defects on hydraulic fractures under different levels and vertical stress differences by designing hydraulic fracturing experiments under uniaxial and triaxial loading conditions,as well as competition and expansion experiments for hydraulic fractures in uniaxial and dual wellbore wells.On the basis of parameter measurement experiments,establish a hydraulic fracturing model for shale containing bedding and multiple types of bedding defects.By exploring the influence of the mechanical properties of bedding defects on the expansion of hydraulic fractures,based on this research law,in-depth research is conducted on the development law of shale hydraulic fractures under the combination of multiple types of bedding defects.The results indicate that:(1)The expansion of hydraulic cracks under different loads is greatly affected by the maximum principal stress,and there is a critical value in the vertical stress difference between 10MPa-15 MPa,which can serve as a sign of whether hydraulic cracks can pass through bedding joints.Under uniaxial loading,the crack morphology is single and it is difficult to open the bedding;Under triaxial loading,due to the influence of horizontal stress difference,the lateral expansion situation is complex and it is easy to form a complex seam network.Under uniaxial and triaxial loading conditions,three types of responses occur when hydraulic cracks intersect with bedding cracks.There are a total of 8 types of interaction between hydraulic cracks and bedding defects.(2)The presence of bedding cracks can suppress the complexity of hydraulic crack competition and expansion.(3)When the bedding angle is around 60 °,more bedding defects can be communicated,and the fracturing effect is the best.The strength of bedding bonding affects the complexity of the joint mesh.The strength of bedding bonding can affect the mode of failure.The injection flow rate,injection method,and fracturing fluid viscosity all affect the effectiveness of hydraulic fracturing in communicating bedding defects.The initiation pressure of cracks is positively correlated with the bedding angle,bedding bonding strength,fracturing fluid viscosity,and injection flow rate.(4)The use of a low to high injection flow rate approach can effectively promote the passage of hydraulic fractures through bedding defects.(5)When hydraulic cracks open the bedding plane,if the bedding angle is large,the initial damage is mainly shear failure;The bedding angle is small,and the initial damage is mainly tensile failure.The process of opening the bedding surface is mainly tensile failure.When the bedding bonding strength weakens,the proportion of shear failure increases,but overall,tensile failure is the main damage.(6)When both bedding and bedding fractures exist inside shale reservoirs,the extension rate of hydraulic fractures along bedding fractures is higher than that of bedding fractures;Under the same conditions,hydraulic cracks are more likely to pass through bedding defects with higher strength.The greater the strength ratio of bedding defects,the more significant the effect of crack penetration at strong bedding defects on the crack penetration effect at weak bedding defects.The failure modes under different strength ratios of bedding defects also differ significantly.The higher the strength ratio,the higher the proportion of internal crack tensile failure.The magnitude of hydraulic fracture initiation pressure is determined by the bedding defect with the lowest bonding strength.This paper has 83 figures,8 tables,and 83 references.