Influences of Layered Heterogeneity on Poroelastic Behavior of Geothermal Reservoirs

Ganiyat Shodunke, Junle Jiang, & Segun S. Bodunde

Submitted February 27, 2025, SCEC Contribution #12629

Geothermal reservoir deformation can be induced by pore pressure changes resulting from the interaction between circulating fluids and rocks, with deformation rates of up to tens of centimeters per year. Elastic deformation models often ignore or simplify structural heterogeneity that may control fluid-rock interactions, potentially biasing subsurface inference from surface data. Here, we investigate the impacts of depth variations of rock physical properties (porosity, permeability, confining rock thickness, and compaction) and elastic properties (Young’s modulus and Poisson’s ratio) on the magnitude, rate, and spatiotemporal pattern of poroelastic deformation and pore pressure in geothermal fields. We design three-dimensional finite-element models to explore a single-well geothermal production scenario with a constant rate in homogeneous half-space or multi-layered geologic settings. The cases of layered heterogeneity involve (1) caprock-reservoir systems with varying permeability and caprock thickness, (2) compaction-induced porosity variations following Athy’s law, and (3) depth-dependent profiles for Young’s modulus. Even in homogeneous models, decreased porosity or permeability causes increased rates of displacement and pore pressure at the early transient or later steady stages, respectively, with different expansion rates of surface deformation patterns. In contrast, reduced elastic moduli amplify surface displacement but have negligible effect on pore pressure. Our results show significant and different influences of layered heterogeneity on poroelastic deformation and pore pressure. In the presence of a less permeable or thicker caprock, ground deformation and pore pressure are more amplified than those in the compaction scenario, with deformation dimensions depending on overall permeability. In comparison, depth variations in elastic moduli generally incur larger deformation, with either more expanded or compact deformation possible. These findings can improve our understanding and prediction of the hydromechanical behavior of complex reservoir structures within geothermal fields.

Key Words
Creep and deformation; Elasticity and anelasticity; Permeability and porosity; Numerical modeling; Geomechanics; Hydrothermal systems

Citation
Shodunke, G., Jiang, J., & Bodunde, S. S. (2025). Influences of Layered Heterogeneity on Poroelastic Behavior of Geothermal Reservoirs. Geophysical Journal International, (submitted).

Related Projects & Working Groups
Stress and Deformation Over Time (SDOT)