3D displacement discontinuity analysis of in-situ stress perturbation near a weak faul

Abstract

A numerical investigation utilizing the 3D displacement discontinuity method is performed to examine the stress perturbations and induced displacements near a weak fault with arbitrary orientations and dip, assuming zero shear stress and normal displacement. The in-situ stress field near the fault is taken as known and varied with depth. The modelling is constructed based on indirect boundary integral equations. In this work, the fault plane is first modelled as a rectangular plane with negligible thickness between the adjacent surfaces. The fault plane is then divided into numerous rectangular boundary elements with imposed shear singularities on the surface, which is normal to the fault plane to simulate a traction-free scenario. The numerical results of the total induced stresses and displacements are then compared to the existing solutions of a penny-shaped crack for validation purpose. With validated results, the paper moves on to the discussion of various factors that have impacts on the induced stress and displacements, including: aspect ratio which is defined by strike over dip; orientation of the strike on the horizontal ground surface; as well as dip. The boundary integration method with modification is also used to model an elliptical distribution of singularities with inner, corner, and edge elements to accommodate more complex shape of a discontinuity; small differences are observed.

Genetic Mechanism of Lower-Order Faults in Shale Formations in Rift Basins

“…According to the boundary stress conditions and node equilibrium conditions, establish and solve the equations with node displacement as the unknown quantity and the overall stiffness matrix as the coefficient. The interpolation function is used to obtain the displacement on each node, and then, the stress and strain values in each element are calculated [27][28][29][30][31][32].…”

Development or absence of conjugate fractures in low-permeability sandstones

“…The orientation of fractures is indicative for determining the migration and accumulation of oil and gas in different geological periods and is a prerequisite for accurately predicting the current fracture opening pressure, effective opening, permeability and other parameters (Zeng et al, 2008a;Liu et al, 2021;Li et al, 2022). The Coulomb law of Mohr's failure theory predicts that the angle between conjugate failure planes is a constant, which is independent of the magnitude of the stress difference in rock failure, and that the maximum principal stress divides the angle equally (Muehlberger, 1961;Palchik, 2006;Li et al, 2019Li et al, ,2022Chai and Yin, 2021;Wood, 2022). Experimental results show that the angle actually decreases with decreasing confining pressure (Muehlberger, 1961).…”

Unreliable determination of in situ stress orientation by cross multipole array acoustic logging in fractured shale reservoirs

“…[1][2][3][4][5][6] After nearly a century of development, a variety of comprehensive methods can be used to determine the stress state in reservoirs. [7][8][9][10] Stress evaluation has become an indispensable basic method for reservoir engineering [4][5][6] ; oil, gas, and coal exploration 8,[11][12][13][14][15] ; and oil and gas engineering design, drilling, and completion. [16][17][18][19] Stress evaluation also has important applications in the development of well pattern deployment, 4,6,20 prediction of reservoir fractures, [21][22][23][24] wellbore stability, 4,19,25 hydraulic fracturing, [26][27][28][29] and sand control in oil and water wells.…”

“…Careful screening and diagnosis are needed in studies of the direction of in situ stress 1–6 . After nearly a century of development, a variety of comprehensive methods can be used to determine the stress state in reservoirs 7–10 . Stress evaluation has become an indispensable basic method for reservoir engineering 4–6 ; oil, gas, and coal exploration 8,11–15 ; and oil and gas engineering design, drilling, and completion 16–19 .…”