Distinct gas production characteristics from laboratory-synthesized Class I, II, and III hydrate reservoirs: A novel thermally-segmented rotatable approach

Abstract

Natural gas hydrate in Class I reservoirs holds significant commercial potential, as demonstrated by production trials in the South China Sea. However, experimental studies have focused largely on Class III systems, with Class I/II reservoirs remaining underrepresented due to the difficulties in simulating the geothermal gradient and interlayer interactions. This study investigates depressurization performance across all three classes using a novel 360° rotatable reactor with segmented temperature control, enabling precise simulation of reservoir conditions. Results reveal: (i) Class I shows two-stage gas production, with 50% from early free gas enabling rapid depressurization, followed by dissociated gas dominance. They achieve 38.4%–78.3% higher cumulative production and superior gas-to-water ratios due to efficient energy use. (ii) The free gas layer in Class I accelerates pressure and heat transfer. Class II’s water layer provides sensible heat but causes water blocking, impairing heat flow. Class III exhibits rapid initial dissociation but a quick decline without fluid support. (iii) Low temperature, low hydrate saturation, and high production pressure collectively reduce efficiency by increasing flow resistance, limiting gas supply, and reducing dissociation drive. Over-depressurization risks hydrate reformation and ice blockage. This work bridges experimental gaps for Class I/II reservoirs, offering key insights for optimizing recovery.

Keywords

Natural gas hydrate / Class I, II, and III reservoirs / Rotatable reactor / Depressurization / Gas production characteristics / Sensitivity analysis

CRediT authorship contribution statement

Hongyu Ye: Writing – review & editing, Writing – original draft, Methodology, Formal analysis, Data curation. Jie Li: Methodology, Investigation, Data curation. Yuanxin Yao: Visualization, Validation, Methodology. Daoyi Chen: Resources, Project administration. Jun Duan: Visualization, Validation. Xuezhen Wu: Supervision. Dayong Li: Supervision. Mucong Zi: Writing – review & editing, Writing – original draft, Supervision, Funding acquisition, Conceptualization.

Declaration of Competing Interest

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Acknowledgement

This study has been partially funded by Shenzhen Science and Technology Program (No. JCYJ20240813112038050), the National Natural Science Foundation of China (No. 52404059), the Economy, Trade and Information Commission of Shenzhen Municipality, China (No. HYCYPT20140507010002), and the Key Program of Marine Economy Development (Six Marine Industries) Special Foundation of the Department of Natural Resources of Guangdong Province, China (No. GDOE[2021]55).

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