In the quest to unlock the potential of oil shale, a team of researchers led by Yijian Zeng from the State Key Laboratory of Deep Earth Exploration and Imaging at Jilin University has made significant strides. Their work, published in the journal *Meitian dizhi yu kantan* (which translates to *Geotectonica and Metallogeny*), offers a promising approach to enhance the efficiency and economic viability of oil shale extraction through autothermic pyrolysis in situ conversion (ATS).
Oil shale, a sedimentary rock rich in organic material called kerogen, has long been considered a viable alternative to conventional oil reserves. However, the extraction process has historically been energy-intensive and costly. Zeng and his team have tackled this challenge head-on, focusing on the configuration of well groups and the optimization of injection-production process parameters to improve the overall efficiency of ATS.
The study employed numerical simulations to evaluate the performance of three vertical well group configurations: one injection well and one production well (1I1P), one injection well surrounded by four production wells (1I4P), and one injection well surrounded by six production wells (1I6P). The results were compelling. “Considering drilling costs, ATS under the 1I4P configuration showed the highest comprehensive efficiency,” Zeng explained. This configuration not only optimized the utilization of stratigraphic conditions but also enhanced the synergistic mechanisms between well group configuration and energy efficiency.
The research delved into the intricacies of the thermal excitation phase and the autothermic reaction control stage. During the thermal excitation phase, a gas injection rate of 400 m³/h for preheating was found to be optimal, balancing energy efficiency with consistent temperature and duration. In the autothermic reaction control stage, the team discovered that a gas injection rate of less than 200 m³/h failed to initiate the autothermic pyrolysis reaction, while an excessive rate exceeding 1000 m³/h interrupted the reaction process. “Within the effective injection rate range, a gas injection rate of 400 m³/h yielded the optimal energy return ratio,” Zeng noted.
The study also explored the impact of well spacing on the performance of the 1I4P well pattern. It was found that a 25-meter spacing between the injection and production wells yielded high comprehensive energy efficiency. This configuration allowed for the effective development of strata with a low oil content of 4%, achieving an ideal energy ratio.
The implications of this research for the energy sector are profound. Through joint optimization of well spacing and gas injection parameters, the development of field-scale oil shale through ATS yielded a peak energy return ratio of 8.85 after 3.7 years and a cumulative oil production of 10,519.5 tons over four years. Moreover, ATS exhibited high economic viability in terms of average operating cost per barrel while contributing to the preservation of a considerable amount of available residual heat.
“This research provides a theoretical basis for well group configuration design and an economic assessment framework for the industrial application of in situ conversion of oil shale,” Zeng stated. The findings offer a roadmap for enhancing the efficiency and economic viability of oil shale extraction, potentially reshaping the energy landscape.
As the world seeks sustainable and cost-effective energy solutions, the work of Yijian Zeng and his team at Jilin University represents a significant step forward. Their research not only advances our understanding of oil shale extraction but also paves the way for future developments in the field, offering hope for a more energy-efficient and economically viable future.