Numerical Assessment of the Maximum Operating Pressure for SAGD Projects by Considering the Intrinsic Shale Anisotropy

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  • 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)
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    Attribution-NonCommercial 4.0 International