Hydro-Mechanical-Chemical Modelling of CO₂ storage in a North Sea hydrocarbon chalk reservoir

This paper describes the effect of CO₂ injection into one of the depleted North Sea hydrocarbon chalk reservoirs considering coupled Hydro-Mechanical-Chemical processes. Literature data suggest that supercritical CO₂ may alter chalk's geomechanical properties, such as yield stress and bulk modulus, making it necessary to assess the hydro-mechanical-chemical response of the near wellbore and reservoir intervals, caprock, and more importantly, potential issues with well integrity. By considering different physics and reservoir properties, here we evaluate the ultimate CO₂ storage capacity for highly deformable chalk. To that aim, a wrapper is developed in Ocean Petrel that utilizes the Eclipse reservoir and Visage geomechanics simulators to capture the induced alteration of the mechanical and petrophysical properties of chalk caused by supercritical CO₂. The Hydro-Mechanical-Chemical model is built using a detailed history-matched reservoir model based on more than 20 years of hydrocarbon production data to estimate the CO₂ storage capacity of the depleted Harald East chalk field in the Danish North Sea. The results reveal that changing the geomechanical properties by CO₂ injection causes pore volume and permeability change around the injection well, which influences CO₂ injectivity.