Co-production of gas hydrates, shallow gas, and deep gas in the Qiongdongnan Basin: A pathway to commercial production

The commercial recovery of gas hydrate (GH) remains challenging due to low production rates and high operational costs. This study explores the feasibility of three-gas co-production (TGCP) as a viable method for enhancing gas production's efficiency and economic viability by integrating the exploitation of GH, shallow gas, and deep gas simultaneously. Using field data from Site W8 in the Qiongdongnan Basin, South China Sea, as a geological model, we conducted experimental trials and comprehensive numerical simulations to assess the long-term performance of TGCP. Results demonstrated that TGCP substantially improves gas production compared to individual/joint recovery strategies, surpassing the commercial production threshold of 200,000 m3/day for the first time in this region. In the early stages of production, deep gas compensates for the limited contribution from GH decomposition, while in later stages, decomposed gas from GH supports production as deep gas declines. Compared with traditional deep gas exploitation, the TGCP can extend the deep gas development cycle. Sensitivity analysis revealed that reducing bottom hole pressure promotes gas hydrate decomposition, while higher permeability (∼100 mD) and extended production periods further enhance output. We also developed an economic evaluation framework incorporating the gas-water ratio (RGW), energy return on investment (EROI), and profit time. The analysis showed that TGCP maximizes RGW and EROI while extending profitability, especially under lower BHP conditions. It was confirmed that the TGCP model's potential to significantly boost GH recovery rates and provide valuable insights into its future commercial applications in hydrate-rich regions such as the South China Sea. Our findings offer a promising pathway toward commercializing GH exploitation through TGCP.