Systematic Review and Perspectives of Methane (CH₄) Classifications and Production Methods from CH₄ Hydrate Reservoirs

Abstract

Methane (CH 4 ) hydrates represent a promising yet intricate future energy source. Challenges in sustainable offshore extraction, such as fine sand production, CH 4 hydrate reformation, water production, and a possible increase in the bottom well pressure due to sand formation, highlight the need for ongoing research. This study provides a systematic review of CH 4 hydrate classification, evaluating its deposit composition, formation, stability, and extraction potential through various experimental, simulations, and field trial tests and highlighting the factors impairing their effectiveness. Critical factors, such as the kinetic behavior of CH 4 hydrate formation, the impact of geological structures on CH 4 migration and accumulation, and the environmental and technical challenges, are illustrated. The effects of sediment specific and sediment modification at varied temperatures, pressures, and salinity for developing efficient methods for CH 4 recovery from hydrate reserves and optimizing conditions for hydrate storage and transport technologies are also presented. The unique characteristics of Class 1, Class 2, Class 3, and Class 4 CH 4 hydrate reservoirs along with production methods, production factors like the injection rate, temperature, and pressure drop, as well as reservoir parameters such as the permeability, porosity, and surface area are revealed to influence gas production significantly. It is revealed that depressurization is widely recognized across all class types for its effectiveness due to the low economic cost and feasibility of implementation, particularly highlighted in Class 1 and Class 3 reservoirs, where it facilitates the dissociation of CH 4 hydrates for CH 4 recovery, indicating potential extraction rates of up to 75% over two decades. Thermal stimulation and CO 2 swapping also stand out, especially for Class 1 reservoirs, as viable methods contribute to CH 4 extraction by directly heating the reservoir to destabilize hydrates or injecting CO 2 to replace CH 4 in the hydrate structure, simultaneously sequestering CO 2 . Class 2 reservoirs, characterized by low permeability, often require combining depressurization with thermal methods or innovative approaches like CO 2 injection to enhance CH 4 extraction efficiency, indicating potential extraction rates of up to 87.80%. Furthermore, hydraulic fracturing emerges as essential for Class 3 reservoirs by improving the permeability and facilitating gas flow, indicating potential extraction rates of up to 80.60%, thus enhancing CH 4 extraction. Additionally, this review emphasizes the current challenges and suggests potential interventions. The concise synthesis of findings, encompassing both experimental evidence and simulation deductions, as presented in this review, will enhance comprehension regarding screening, designing, and formulating CH 4 extraction strategies.