Thermo-Hydro-Mechanical Modeling of CO2 Injection in Multilayer Reservoirs

Abstract CCUS-EOR technology, as a core application of Carbon Capture, Utilization and Storage (CCUS), serves dual purposes of enhancing oil recovery and enabling geological sequestration of CO2. The multilayer CO2 injection into heterogeneous reservoirs technology achieves balanced displacement control by injecting tailored CO2 volumes into layers with heterogeneous permeability, thereby enabling precise regulation of reservoir dynamics. Field monitoring data indicate multiple wellbore integrity risks during CO2 injection operations, including engineering challenges such as packer failure. This study develops a coupled wellbore-reservoir model to analyze fluid flow, heat transfer, and mechanics during CO2 injection in a multilayer reservoir. The effects of injection parameters on wellbore flow behavior and the mechanical responses of completion wellbore are systematically investigated. Model validation against field measurements and commercial software benchmarks demonstrated a relative average error of less than 5% in predicting pressure and temperature distributions. When CO2 reaches the target injection zone, the reduction in flow rate prolongs the heat exchange duration between the fluid and reservoir, thereby enhancing the heating rate. The constraining effect of the packer induces an abrupt variation in the axial force of the tubing at its installation location. Wellhead injection pressure is primarily governed by injection gas composition and temperature. Reducing CO2 purity from 100% to 80% necessitates approximately 5 MPa additional pressure compensation at the wellhead. Injection rate critically influences the wellbore temperature profile through modulation of CO2 flow velocity. Namely, increasing injection flow rate from 5×104 to 17×104 m3/d will lead to 12 °C bottomhole temperature differential. Injection temperature affects tubing axial stress, where a 60 °C injection temperature increment (0–60 °C) results in a 103% elevation in axial stress at the wellhead. The proposed framework provides a robust quantitative tool for evaluating injection pressure requirements and wellbore mechanical responses under variable injection parameters, offering a decision-support foundation for optimizing multilayer CO2 injection processes in CO2 -EOR applications.