Fully Coupled Thermal-Hydro-Mechanical Model for ScCO2 Storage in Shale Gas Reservoirs
Authors: Tian Jianwei , Zeng Jie , Sun Yingfeng 
Published: August 2024

ABSTRACT:
This study explores the potential of using supercritical CO2 (ScCO2) injection for carbon sequestration in shale gas reservoirs, focusing on the impact of structural heterogeneities on CO2 storage. This investigation presents a fully coupled thermo-hydro-mechanical (THM) analysis of ScCO2 injection in such reservoirs, aiming to unravel the complexities imposed by multiscale structural heterogeneities on the process of ScCO2 sequestration, encompassing the intricate shale matrix and the discrete fracture network. The model incorporates a fractal-based paradigm for accurately delineating shale matrix porosity and the evolution of pore diameters, which are instrumental in refining the permeability model within these geologically complex structures. The model considers the unique properties of ScCO2 and uses the Navier-Cauchy equation to simulate the mechanical behavior of shale formations during ScCO2injection. A thorough sensitivity analysis assesses the influence of various factors, such as injection pressure, temperature and principal stresses, on the process's efficiency. Our findings aim to improve carbon capture and storage (CCS) techniques, contributing to NetZero goals by optimizing ScCO2 sequestration in unconventional reservoirs.

1. INTRODUCTION
The global commitment to achieving net-zero emissions is a cornerstone in the fight against climate change, necessitating innovative strategies to capture and store carbon dioxide (CO2) effectively (Alcalde et al., 2018). CO2 storage, particularly in geological formations, emerges as a pivotal solution to mitigate atmospheric CO2 levels. Among various geological formations, shale reservoirs offer unique advantages for CO2 storage. Their abundant organic content and low permeability make them potential candidates for secure and long-term CO2 sequestration. Moreover, the injection of supercritical CO2 (ScCO2) into shale formations not only facilitates storage but also enhances gas recovery, thereby presenting a dual benefit of mitigating climate change while improving energy resource utilization (Iddphonce et al., 2020).
The complexity of subsurface environments, especially in shale reservoirs, demands sophisticated numerical models to accurately simulate CO2 storage processes. These models encompass various physical and chemical interactions through multiphysics coupling, addressing the thermal (T), hydraulic (H), and mechanical (M) responses of the reservoir to CO2 injection (Gaus et al., 2008). Recent studies have highlighted the significance of such THM coupled models in predicting the behavior of CO2 within shale formations, considering aspects like CO2 plume migration, pressure build-up, and the potential for inducing seismic events (Cheng et al., 2023; Gholami et al., 2021). For instance, Zhang et al. (2016) and Lei et al. (2015) have made substantial contributions by developing models that integrate these multiphysics aspects, offering insights into the optimal strategies for CO2 injection and storage in subsurface rock formations.