Abstract

There have been at least 29 groups of estimates on the global natural gas hydrate (NGH) resource since 1973, varying greatly with up to 10,000 times and showing a decreasing trend with time. For the South China Sea (SCS), 35 groups of estimations were conducted on NGH resource potential since 2000, while these estimates kept almost the same with time, varying between 60 and 90 billion tons of oil equivalent (toe). What are the key factors controlling the variation trend? What are the implications of these variations for the NGH development in the world and the SCS? By analyzing the investigation characteristics of NGH resources in the world, this study divided the evaluation process into six stages and confirmed four essential factors for controlling the variations of estimates. Results indicated that the reduction trend reflects an improved understanding of the NGH formation mechanism and advancement in the resource evaluation methods, and promoted more objective evaluation results. Furthermore, the analysis process and improved evaluation method was applied to evaluate the NGH resources in the SCS, showing the similar decreasing trend of NGH resources with time. By utilizing the decreasing trend model, the predicted recoverable resources in the world and the SCS are (205–500) × 1012m3 and (0.8–6.5) × 1012m3, respectively, accounting for 20% of the total conventional oil and gas resources. Recoverable NGH resource in the SCS is only about 4%–6% of the previous estimates of 60–90 billion toe. If extracted completely, it only can support the sustainable development of China for 7 years at the current annual consumption level of oil and gas. NGH cannot be the main energy resource in future due to its low resource potential and lack of advantages in recovery.