Optimising supercritical CO2 saturation and reservoir conditions for geological energy storage with transcritical carbon dioxide systems

Abstract

The CO₂-based Electrothermal Energy and Geological Storage (CEEGS) system integrates energy storage with CO₂ sequestration by storing excess renewable energy as supercritical CO₂, which is back-produced for power generation. This study investigates reservoir (porosity, permeability, relative permeability, heterogeneity, anisotropy) and operational (injection rates, shut-in periods) parameters to maximise CO₂ saturation near the wellbore and minimise water co-production, critical for the energy storage capacity and operation of the surface transcritical CO₂ power cycles. Using CMG-STARS and CMOST-AI, we conducted a sensitivity analysis across injection rates (5–100 kg/s), porosity (0.05–0.25), permeability (10–1000 mD), and heterogeneity (C.V. 0.1–1.5). Results show that injection rates of 30–40 kg/s, porosity of 0.05–0.15, and low heterogeneity (C.V. <0.25) achieve gas saturation up o 76 % with water production below 0.1 kg/s. Shut-in periods should not exceed 3 months to limit saturation losses. These findings provide a robust framework for optimising the CEEGS site selection and operation definition, ensuring supercritical CO₂ back production with adequate characteristics for efficient energy storage and operation.