APPLICATION OF X-RAY DIFFRACTION RESIDUAL STRESS TESTING TECHNOLOGY IN PRESENT STRESS STATE ANALYSIS OF FIBROUS CALCITE VEIN

The fibrous calcite vein is widely developed in the organic-rich shale, but the understanding of its mechanical genetic mechanism is controversial. In order to obtain the present stress state of the fibrous calcite vein directly, this paper takes the fibrous calcite vein developed in the organic-rich shale from lower Es3 to upper Es4 of Jiyang depression as the research object, quantitatively obtains the present stress type and size by the X-ray diffraction residual stress testing technology, and establishes the stress mathematical model of the shear fracture of the calcite vein. The mechanical origin of fracture line in the calcite vein is determined and the influence of pore fluid pressure on the development of the calcite vein is analyzed. The results show that the vertical effective stress of the fibrous calcite vein is 59 MPa, the horizontal effective stress is 16 MPa, and it is in the state of three-dimensional compression space stress. The effective stress model and the shear fracture discriminant on any section determine that the calcite vein appears conjugate shear fracture, the fracture line is polyline or curve, the theoretical fracture angle is 45° or 28°, which are consistent with the actual measurements from thin sections but also affected by the polished direction of the thin section. The pore fluid pressure causes the normal stress to decrease while the shear stress remains unchanged, which affects the fracture mode of the shale rock skeleton or calcite vein. X-ray diffraction residual stress testing technology has good practical effect in determining the present effective stress in rock and mineral.