Hydro-Geomechanical Characterization of Inclined Heterolithic Stratification (IHS)

• Author / Creator

  Khademi, Masoud

• A sizeable portion of the Athabasca oil sand reservoir is classified as Inclined Heterolithic Stratification (IHS). IHS is a particular type of lithosome that is comprised of two alternating lithologies which are fluvially-dominated sand beds and brackish tidally-influenced mud beds. However, due to the significant heterogeneity of IHS and the minimal experimental studies performed on it, its hydro-geomechanical properties are relatively unknown. The main objectives of this study are investigating the geomechanical constitutive behavior of IHS and linking its geological and mechanical characteristics to their hydraulic behavior to estimate the permeability evolution of IHS during a Steam Assisted Gravity Drainage (SAGD) operation. To that end, a detailed methodology for reconstitution of analog IHS specimens was developed, and a microscopic comparative study was conducted between analog and in situ IHS samples. The SAGD-induced stress paths were experimentally simulated by running isotropic cyclic consolidation and drained triaxial shearing tests on analog IHS samples. Both series of experiments were performed in conjunction with permeability tests at different strain levels, flow rates, and stress states. Additionally, an analog sample with bioturbation was tested to examine the hydro-geomechanical effects of bioturbation. Furthermore, the hydro-mechanical characteristics of analog IHS were compared with its constituent layers (sand and mud). Finally, a geomechanical model was developed to numerically simulate the behavior of sand-dominated IHS with FLAC3DTM version 6.

  The microscopic study showed that the layers’ integration and grain size distribution are similar in analog and in situ IHS specimens. The results also revealed that the geomechanical properties of IHS, such as shear strength, bulk compressibility, Young’s modulus, and dilation angle, are stress state dependent. In other words, elevating the effective confining stress could significantly increase the strength and elastic modulus of a sample, while decreasing the compressibility and dilation angle. In contrast, the friction angle and Poisson’s ratio are not very sensitive to changes in the isotropic confining stress. An important finding of this study is that the effect of an IHS sample’s volume change on permeability is contingent on the stress state and stress path. Volume change during isotropic unloading-reloading resulted in permeability increases, and sample dilation during compression shearing resulted in permeability decreases, especially at high effective confining stresses. Moreover, the tests revealed that the existence of bioturbation dramatically improves permeability of IHS in comparison to equivalent non-bioturbated specimens but has negligible effects on its mechanical properties, which remain similar to non-bioturbated specimens. The results also showed that bioturbation has minimal impact on permeability changes during shearing. Lastly, experimental correlations were developed for each of the parameters mentioned above.

  The numerical study performed in this thesis showed that the geomechanical model applied in the FLAC3DTM simulation can be a representative model for sand-dominated IHS. This numerical model used the Plastic Hardening constitutive model, with two separate sets of parameters for sand and mud layers. The required parameters for this geomechanical model were obtained through a series of triaxial tests on sand and mud specimens. For the first time, specialized experimental protocols have been developed that guide the infrastructure and processes required to reconstitute analog IHS specimens and conduct geomechanical testing on them. This study also delivered fundamental constitutive data to better understand the geomechanical behavior of the IHS reservoir and its permeability evolution during the in situ recovery processes. Such data can be used to capture the reservoir behavior and increase the efficiency of SAGD operations in IHS reservoirs.

• Subjects / Keywords

  • Inclined Heterolithic Stratification (IHS)
  • Permeability
  • Constitutive Behavior
  • Triaxial cell
  • SAGD

• Graduation date

  Spring 2020

• Type of Item

  Thesis

• Degree

  Doctor of Philosophy

• DOI

  https://doi.org/10.7939/r3-kzh4-6w40

• License

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