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Study On Physical And Mechanical Anisotropy Of Shale And Failure Characteristics In Tension-Shear State

Posted on:2017-05-18Degree:MasterType:Thesis
Country:ChinaCandidate:Z YangFull Text:PDF
GTID:2272330485958253Subject:Geological Resources and Geological Engineering
Abstract/Summary:PDF Full Text Request
As for shale, it is common to see complex mineral composition, natural fracture development, mud development and layered structure that lead to high heterogeneity and anisotropy of shale, and all that above greatly affect the production capacity of shale gas. Therefore, it is necessary to conduct some physical and mechanical experiments to study the anisotropic characteristics of shale, and more intuitive experimental methods to obtain the mechanical properties and fracture characteristics of the bedding plane.In this paper, the shale specimen were subjected to ultrasonic test, Brazilian split crack and uniaxial compressive mechanical test, to study the physical and mechanical anisotropic properties of shale with different bedding angles, where bedding angle was defined as the angle between the normal line of bedding face and the axis of the sample. Then, it analyzed the dynamic and static elastic parameters changes with the angle of bedding, and fitted the variation of dynamic elastic parameters, tensile strength and compressive strength with bedding angle. Finally, it calculated the anisotropy material parameters of shale through the transformation formula. It gets the conclusion that with the bedding angle increases, the longitudinal wave velocity, shear wave velocity and dynamic elastic modulus and dynamic shear modulus increases, the change trend is consistent, the variation of the bulk modulus and Poisson’s ratio shows a "M" type, there are two process of first increases and then decreases, the minimum point comes to be the point of bedding angle 45°. Tensile strength was decreased with the stratification angle, the elastic modulus and fracture complexity of the surface were increased with the angle, but the uniaxial compressive strength showed a decreased first and then increased which is the same as "U" and it takes a minimum value at 60°To study the mechanical characteristics of the bedding surface, tensile-shear and compression-shear experiments were conducted on shale samples with 0° and 90° mainly focused on the fracture characteristics under the condition of tensile-shear force of. As a result, it established all region rupture characteristic curve in tensile-shear region. The results show that the specimen with bedding angle 0° is very unstable and easy to destroy under tension-shear stress condition, but the 90° samples which were better. According to the curves, tensile strength and shear strength were less than other value got by traditional fracture criterion, this illustrates that the former rock rupture characteristics are not precise for the tensile shear should stress condition.After tensile-shear experiments, the method of 3D laser scanning and scanning electron microscopy (SEM) were used to study the fracture surface characteristics of shale, it has studied the failure mode from the macroscopic perspective and the fracture mechanism from the micro perspective. It mainly draws conclusions as follows:a variety of factors led the rupture of the shale sample under tensile shear stress, as a result surface morphology is complex, and the failure mainly occurs in the cement, especially serious weathering and poor cementation parts, matrix particles usually act as a role of induction and traction in the crack propagation process.
Keywords/Search Tags:Shale, Anisotropy, Tensile shear, Fracture surface characteristics, Fracture mechanism
PDF Full Text Request
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