Modern societies are still very much dependent on oil and gas resources for their smooth functioning. However, natural oil and gas resources are limited and non-renewable. In order to keep up with the growing demand for hydrocarbons, a secure alternate sources of natural oil and gas needs to be discovered. Fortunately, a massive and mostly untapped reserve of oil and gas does exist.

Oil shale is a flaky sedimentary rock with high organic content. When low-maturity oil shale is heated for extended periods of time, its organic molecules break down via pyrolysis and transform into lighter and more useful oil and gas. This forms the basis of a strategy known as in situ upgrading (ISU), whereby heating wells are drilled and laid out directly into the shale layer to provide the necessary heat for pyrolysis. The hydrocarbons produced on site are then extracted through a separate production well. While the process is technically feasible, there is, however, no agreement on whether it is economically feasible as well.

On-site oil shale heating as an economically feasible source of hydrocarbons. Source: Earth Science FrontiersOn-site oil shale heating as an economically feasible source of hydrocarbons. Source: Earth Science Frontiers

To address this knowledge gap, a research team from Northeast Petroleum University, China, and China University of Petroleum in East China recently conducted a study on ISU technology. Led by Dr. Li Wenbiao from Northeast Petroleum University, the team analyzed the economic feasibility of ISU from the perspective of the energy consumption ratio (ECR). ECR is a measure of how much of the energy provided to the heating wells is used for pyrolysis in relation to the energy lost to heat diffusion and absorption into minerals, water and surrounding rock.

The team reportedly used a geological model to look into the factors that affect ECR the most. The model accounted for the heating well design and layout, heating technology and shale composition, among other parameters and variables.

The results indicate that appropriate spacing between the heating and production wells is crucial to improve the efficiency of ISU. The team also determined the minimum total organic content in the oil shale that leads to acceptable ECR values. Moreover, they also compared and contrasted new heating methods to increase the efficiency of ISU beyond the conventional approach using heating wires. "One important way to increase the efficiency of ISU is to explore alternative heating technologies, such as convection and electromagnetic heating," explained Dr. Wenbiao.

Overall, the team hopes that the findings of their study would help pave the way for an economically viable ISU technology. "We want our results to promote the application of ISU technology for optimized oil shale exploitation," said Dr. Wenbiao

The study, Economic feasibility and efficiency enhancement approaches for in situ upgrading of low-maturity organic-rich shale from an energy consumption ratio perspective, appears in the journal Earth Science Frontiers.

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