Shale formations have laminated structures which result in significant differences in mechanical properties along the orientations parallel to and perpendicular to laminations (bedding planes). These differences lead to anisotropic horizontal stresses. Failure to consider the effect of anisotropic behavior of shale can have severe consequences for drilling. In rocks with anisotropic mechanical properties and strength, there is a high risk of wellbore instability while building deviation angle from vertical sections. Conventional wellbore stability analysis approaches do not consider material anisotropy and laminated nature of shales, which can result in underestimated stresses leading to incorrect safe trajectory or mud-weights.Shale formations in the Horn River Basin (HRB) are strongly anisotropic with anisotropic ratios varying from 1.2 to 3.5. In this paper, the authors demonstrate the importance of considering anisotropy in estimation of in-situ stresses and wellbore stability analysis. Two field case study examples are presented to underscore the consequences of neglecting anisotropy in wellbore stability analysis.
Ensuring long-term containment of CO2 is critical for a safe geological storage of carbon. Although Carbon Capture and Storage (CCS) is feasible in depleted hydrocarbon fields, it can pose significant risk to safety and the environment if its containment is not ensured. An integrated geomechanics workflow to evaluate caprock integrity is presented in this paper. This approach integrates reservoir simulation which typically computes variation in formation pressure and temperature with geomechanical simulation which models variation in stresses. Coupling between these two simulation modules is done iteratively until an equilibrium state between formation pressure and stress is achieved within a given tolerance. The efficiency of this approach is demonstrated through a case study of a proposed carbon storage site in Canada where an injection rate of 600 tonne/day for 25 years is planned.
In 2014, more than 30,000 wells will be drilled in different unconventional plays across the US. As drilling density increases, chances are these new wells will be located in the vicinity of a producing unit. When the new well is being completed, the pressure depletion around the producing well affects the principal stress regime, creating low stress compartments that attract the majority of the slurry injected. This condition has been studied in the past for vertical wells and results confirmed that the asymmetric propagation of the fracture wings leaves vast sections of the reservoir un-stimulated affecting well performance. This study uses a dataset from the Williston basin to evaluate the impact of this condition in modern horizontal completions. Pore pressure maps from single well models are used to build a multi-well geomechanical model, a numerical fracture simulator is used to understand fracture geometry and quantify wing asymmetry and a multi-well production model is created to estimate the impact in ultimate recovery. Finally, this paper concludes with a series of recommendations regarding completion design and production strategy that can reduce the severity of fracture asymmetry and increase EUR.
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