Abstract

Natural gas hydrate (NGH) has attracted much attention as a new alternative energy globally. However, evaluations of global NGH resources in the past few decades have casted a decreasing trend, where the estimate as of today is less than one ten-thousandth of the estimate forty years ago. The NGH researches in China started relatively late, but achievements have been made in the South China Sea (SCS) in the past two decades. Thirty-five studies had been carried out to evaluate NGH resource, and results showed a flat trend, ranging from 60 to 90 billion tons of oil equivalent, which was 2–3 times of the evaluation results of technical recoverable oil and gas resources in the SCS. The big difference is that the previous 35 group of NGH resource evaluations for the SCS only refers to the prospective gas resource with low grade level and high uncertainty, which cannot be used to guide exploration or researches on development strategies. Based on the analogy with the genetic mechanism of conventional oil and gas resources, this study adopts the newly proposed genetic method and geological analogy method to evaluate the NGH resource. Results show that the conventional oil and gas resources are 346.29 × 108 t, the volume of NGH and free dynamic field are 25.19 × 104 km3 and (2.05–2.48) × 106 km3, and the total amount of in-situ NGH resources in the SCS is about (4.47–6.02) × 1012 m3. It is considered that the resource of hydrate should not exceed that of conventional oil and gas, so it is 30 times lower than the previous estimate. This study provides a more reliable geological basis for further NGH exploration and development.