Numerical Assessment of Caprock Integrity in SAGD Operations Considering Mechanical Anisotropic Behavior of Shale Layers

• Author / Creator

  Rahmati, Ehsan

• There has been an increasing awareness of the importance of caprock integrity during Steam Assisted Gravity Drainage (SAGD) operations. However, mathematical tools that have been developed for caprock integrity studies have not incorporated an important characteristic of cap shales, which is the anisotropic behavior of the shales. This study focuses on the numerical assessment of the Maximum Operating Pressure (MOP) in SAGD projects accounting for the anisotropic behavior of cap shales. This research demonstrates the importance of capturing shale anisotropy and considering the effect of Natural Fractures (NFs) in the accurate prediction of MOP for SAGD projects. A coupled hydro-thermo-mechanical model was developed to assess the MOP of SAGD projects. A constitutive model was incorporated and verified to consider the effect of NFs and intrinsic anisotropy of the caprock shale. The coupled numerical tool was validated against field data and utilized to determine the MOP for a SAGD operation. Also, the numerical model was utilized in a series of simulations to investigate the effects of sensitivity of the results to several characteristics of the NFs and intrinsic anisotropy. Results of the coupled tool show that neglecting NFs and intrinsic anisotropy can result in MOP overestimation. The MOP was found to be highly sensitive to the fracture density, direction, and height. For the case study, results displayed horizontal fractures had minor effect on the MOP while fractures with the dip angle between 25° to 65° had a significantly lower MOP and could not be neglected. Furthermore, results showed that neglecting the intrinsic anisotropy of caprock shales resulted in an overestimation of the MOP by 7% for the case study. This research incorporated the intrinsic and structural shale anisotropy in the caprock failure analysis model for the first time. Existing numerical models for evaluating the integrity of caprocks during SAGD operations employ isotropic constitutive laws. These models are believed to be deficient in capturing strongly intrinsic and structural anisotropic response of shales and mudstones, which have been well documented in applications other than SAGD studies. The isotropy assumption for the cap shale in caprock integrity analysis can lead to the overestimation of the MOP in SAGD operations. Results of this research can be of significant benefit to avoid choosing high MOPs which could lead to caprock failure in SAGD operations.

• Subjects / Keywords

  • Caprock integrity
  • Shale anisotropy
  • Natural fracture
  • SAGD

• Graduation date

  Spring 2016

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/R3804XQ7T

• License

  This thesis is made available by the University of Alberta Libraries with permission of the copyright owner solely for non-commercial purposes. This thesis, or any portion thereof, may not otherwise be copied or reproduced without the written consent of the copyright owner, except to the extent permitted by Canadian copyright law.