Investigation of creep and transport mechanisms of CO2 fracturing within natural gas hydrates

Natural gas hydrates (NGH) are considered as a potential energy resource in the future because of its dramatic energy reserves. NGH formation owns the characteristic of viscoelasticity, to some extent behaves both like liquid and solid. Not considering the viscoelastic properties of NGH can lead to inaccurate prediction of related characteristics. In 2020, horizontal-well drilling technology is adopted to improve the stimulation performance of NGH reservoirs in the Shenhu area of China. This indicates that it is possible to apply hydraulic fracturing or CO2 fracturing in the reservoir reconstruction of NGH. CO2 fracturing can generate more fracture networks and connect micro fractures. Additionally, CO2 can be stored geologically and integrated with injection, production, and storage. This study provides a relatively detailed demonstration of the formation and basic mechanical properties of NGH. Then, a comprehensive overview of potential NGH production enhancement methods is conducted. Finally, an evaluation method for dual conductivity considering creep effect is proposed, and the results show that the creep effect of NGH can reduce the conductivity of fractures and matrices. Thus, it is of great importance to investigate the viscoelastic properties of NGH formation, for the long-term prediction of the geo-mechanical response to gas extraction.