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Numerical Assessment of the Maximum Operating Pressure for SAGD Projects by Considering the Intrinsic Shale Anisotropy
This paper investigates the effect of anisotropic behavior of caprock shales on the caprock failure
pressure in SAGD projects. Shales and mudstones exhibit strong anisotropy at the micro and macro
scales. However, the anisotropic behavior has been neglected in the existing published works on
this subject. This paper focuses on the effect of the intrinsic anisotropy of shales on caprock
integrity. The Maximum Operating Pressure (MOP) is calculated from the failure pressure using
an appropriate safety factor.
In this paper, a coupled hydro-thermo-mechanical model was developed for the assessment of
caprock integrity in thermal operations. A transversely isotropic constitutive model in the elastic
range was combined with an anisotropic failure criterion to capture the intrinsic anisotropy of the
cap shale. The coupled tool was validated against field data (mainly the surface heave) and
employed in a study to determine the effect of shale anisotropic behavior on the pressure associated
with caprock breach.
Results display the effect of shale anisotropy on caprock response in terms of deformations,
stresses and failure pressure. The assumption of isotropic shale behavior in caprock integrity
assessment for a case study resulted in the overestimation of the failure pressure by about 7%.
Existing numerical models for evaluating the integrity of caprocks during thermal operations
employ isotropic constitutive laws. These models are believed to be deficient in capturing strongly
anisotropic response of shales and mudstones. The research described in this paper incorporated
elasto-plastic shale anisotropy in the caprock failure analysis model for the first time. This study
demonstrates the importance of capturing shale anisotropy in the accurate prediction of caprock
breach pressure in SAGD projects.
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- Article (Draft / Submitted)