Validated thermo-hydro-mechanical modeling framework for CO₂ storage in chalk reservoirs: A case study from the Harald East field

The injection of CO₂ into depleted hydrocarbon fields or aquifers involves a complex interplay of coupled physical and chemical processes. In chalk reservoirs, this complexity is further amplified by the highly deformable nature of chalk, necessitating the application of thermo-hydro-mechanical (THM) modeling. Such modeling is critical for understanding and quantifying potential risks, including the development of hazardous leakage pathways. This study evaluates the reliability and validation of reservoir models for CO₂ injection in chalk formations using geomechanically informed calibration. The Harald East field, a depleted gas reservoir with significantly reduced average pressure due to extensive production, is used as a case study. An in-house "two-way" coupling framework between flow and geomechanical models was employed to simulate induced deformations and in situ stress variations resulting from gas production. These simulations were validated against production data, platform subsidence, and seismic measurements during the production period. Once the model's reliability was established, coupled simulations were performed for cold and hot CO₂ injection scenarios, followed by a post-injection period, to evaluate their effects on reservoir stability and long-term CO₂ plume propagation. The results demonstrate the reliability of a two-way coupled geomechanical and reservoir simulation framework for CO₂ storage in chalk reservoirs. The coupled THM simulations effectively capture critical interactions between fluid flow, thermal processes, and geomechanics required for geological CO₂ storage assessment.