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.

Geothermal energy is one of the most stable and clean solutions to replace the traditional fossil fuel energy resource. The South Meager geothermal prospect, located in southwestern British Columbia, contains large geothermal energy resources due to recent volcanic activities. The in-situ stress state in the prospective area that influences the characteristics of fractures, thus affecting productivity, remains unknown. In this paper, we present a preliminary analysis of in-situ stress induced by gravitational load at Mount Meager, with tectonics considered. The in-situ stress model was constructed with 3D displacement discontinuity method based on the site-specific topography. The 3D model reveals that the impact of topography is more prominent in shallow and deep regions, while the impact of tectonics is prominent in an intermediate depth range. With the implementation of inferred tectonic stress state, normal faulting regime takes place at shallow depth (<800 m); at the intermediate depth (800–1600 m), the transition of faulting regime from normal to strike-slip and then to thrust occurs; at deeper depth (>1800 m), the fault type becomes normal again. The orientations of major and minor induced horizontal stresses transition from varying with local topography to perfectly aligned with the orientations of major and minor horizontal tectonic stresses at NWN-SES 330° and NEE-SWW 60°, respectively, as depth increases.

Wellbore integrity in a gas hydrate bearing formation during drilling and production is a great challenge in the energy industry since a complex thermal-hydraulic-mechanical interaction with decomposed solid hydrate process is involved. A wellbore temperature increase and/or depressurization process may induce additional stresses and thermal and fluid flows, which may trigger wellbore instability, sand production, and undesired fracturing. Production-related wellbore integrity issues such as solid production during wellbore depressurization or heating are also widely observed and studied. To understand the thermal-hydraulic-mechanical behavior with hydrate decomposition (THMD) process and to simulate the THM responses of hydrate gas bearing sediments to wellbore pressure and temperature variations under a given in-situ stress regime during drilling and production, a fully coupled THMD model is presented in this paper. The conceptual THMD model with simplified semi-analytical solutions for the induced stress, pore pressure, and temperature at the wellbore and inside the formation is discussed. A linear Mohr-Coulomb criterion is utilized to define the onset of the wellbore instability or plastic yielding when sand production defined by effective plastic strain (EPS) is considered with a cohesion dependent on hydrate saturation. Numerical method with Laplace transformation is used to solve the transformed homogeneous PDE. We conclude that thermally- and hydration-induced stresses will affect wellbore integrity during hydrate gas production due to wellbore pressure reduction and temperature increase. Unlike the stress perturbation in the conventional gas reservoir, critical temperature and pressure for the equilibrium phase change must be surpassed to induce additional incremental stresses due to the hydrate decomposition. Additional fluid mass and energy transfer may take place with induced temperature and pore pressure because of the hydrate decomposition/recomposition. In addition, the hydrate saturation changes due to the typical drilling strategy applied may reduce the hydrate formation significantly, which will affect the design of production pressure control and management. Thus, pressure optimization is crucial for both maximum production and wellbore integrity.