New method proposed for offshore gas hydrate production

A team of researchers from China and Singapore has proposed an innovative method for the commercial exploitation of natural gas hydrates (NGHs) from offshore reservoirs, leveraging geothermal energy and depressurization techniques. Their findings, published in Engineering, offer a potential pathway to enhance the efficiency and economic viability of NGH extraction.

The study, led by Baojiang Sun from the China University of Petroleum (East China) and Praveen Linga from the National University of Singapore, introduces a novel loop well structure designed to effectively utilize geothermal energy from deep reservoirs. This method combines depressurization with geothermal coupling to improve gas production rates and reduce costs. The researchers argue that this approach could significantly boost NGH production, making it a more feasible option for commercial exploitation.

Traditional methods for NGH extraction, such as depressurization and heat injection, face limitations due to low energy utilization efficiency and limited extraction ranges. The proposed method addresses these challenges by integrating a loop well system that extracts geothermal energy from deep formations and injects it into the hydrate reservoir. This system includes a heat-extraction well, a heat-injection well, and a production well, all connected to form a closed loop for efficient heat transfer.

The researchers developed a comprehensive model to analyze the fluid flow, heat transfer, and hydrate decomposition processes involved in this method. Their simulations, based on geological conditions in the Shenhu area of the South China Sea, indicate that the proposed method can increase gas production by approximately 73% compared to conventional depressurization techniques. Moreover, the economic analysis suggests that the cost of methane exploitation could be reduced to as low as 0.46 USD per cubic meter, with further reductions possible under optimal conditions.

The study highlights the importance of geothermal energy in enhancing NGH dissociation. When the temperature of the fluids from the geothermal layer exceeds 62 °C, the heat is primarily absorbed by the rock matrix of the hydrate formation, rather than directly promoting NGH dissociation. This threshold temperature is crucial in optimizing the extraction process, as higher temperatures do not necessarily lead to significant increases in gas production.

The researchers also examined the impact of different injection flow rates on the efficiency of the loop well system. They found that while higher flow rates result in lower fluid temperatures entering the hydrate reservoir, the differences in gas production rates are relatively minor. This suggests that excessively high injection temperatures are not necessary for effective hydrate decomposition.

Furthermore, the study explores the commercialization potential of the proposed method. The results indicate that the unit cost of produced natural gas decreases with increasing porosity and hydrate saturation. For example, with a porosity of 0.55 and a hydrate saturation of 0.51, the unit cost could be reduced to about 0.14 USD per cubic meter, making it a potentially viable option for commercial development.

The research concludes that the proposed dual horizontal well method, combining geothermal energy and depressurization, offers significant advantages over existing techniques. While further reductions in drilling and operational costs are needed to make NGH exploitation economically feasible, the study provides valuable insights into optimizing the extraction process and maximizing gas production efficiency.

This innovative approach could pave the way for more efficient and cost-effective NGH extraction, contributing to the development of cleaner energy sources in the future.

The paper “A Potential Commercialization Method for Gas Production from Off-Shore Hydrate Reservoirs,” is authored by Baojiang Sun, Jinsheng Sun, Youqiang Liao, Miao Dong, Jie Zhong, Praveen Linga. Full text of the open access paper: https://doi.org/10.1016/j.eng.2025.04.016. For more information about Engineering, visit the website at https://www.sciencedirect.com/journal/engineering.