Advances and Prospects of Supercritical CO₂ for Shale Gas Extraction and Geological Sequestration in Gas Shale Reservoirs

Abstract

The advancements in hydraulic fracturing and horizontal drilling techniques have substantially facilitated the large-scale extraction of natural gas from shale gas reservoirs. However, the use of fracking water poses several potential drawbacks including the contamination of groundwater, surface water, and soil, as well as risks to air quality. Due to the unique physical properties of supercritical CO2, shale gas exploitation using this method has been considered a promising technology that can not only improve gas recovery but can also enable CO2 geological storage. This paper clarifies the gas adsorption mechanism in shale formations, including the factors influencing the adsorption of CH4, the differences between CH4 and CO2 adsorption, and various adsorption models. We show that shale inherently exhibits a preference for CO2 adsorption over CH4. Then, the supercritical CO2 fracturing mechanism, including the shale fracking pressure and the factors influencing CO2 fracturing, is analyzed. The mechanisms of CO2 extraction in shale gas and the key factors influencing CO2 geological storage are discussed. The main challenges and future prospects regarding the use of supercritical CO2 for shale gas recovery and geological sequestration in gas shale reservoirs are finally summarized. A more detailed understanding is required to evaluate the efficiency of shale gas recovery and CO2 geological sequestration in shale formations using supercritical CO2. This work provides a basis and serves as a reference for future research investigating the mechanisms of shale gas exploitation using supercritical CO2, as well as the limitations and advantages of CO2 geological sequestration in unconventional shale gas reservoirs.

Combined Analytic Hierarchy Process and Weighted Interval Method Models for the Geological Evaluation of CO2 Storage in Coal Goaf

“…Stable roadway spaces can be stored in artificially reconstructed storage tanks with a supercritical storage capacity. The burial depth of coal in China is generally 500-1000 m. The feasibility of CO 2 storage in the goaf of medium and shallow coal mining is a topic of concern for Chinese geologists [14,[20][21][22][23]33]. A pilot experiment for CO 2 storage was conducted in the Southern Shanxi Formation of the Qinshui Basin in Shanxi Province (buried at depths of 472.34~478.70 m), with an injection of 192.8 tons of liquid CO 2 .…”

“…A pilot experiment for CO 2 storage was conducted in the Southern Shanxi Formation of the Qinshui Basin in Shanxi Province (buried at depths of 472.34~478.70 m), with an injection of 192.8 tons of liquid CO 2 . The storage effect was satisfactory [14,33]. Wang et al [21] studied the occurrence conditions of natural CO 2 in the Yaojie mining area of Gansu Province (<400 m) and concluded that it is feasible to store CO 2 in coal goaf.…”

“…CO 2 is injected through pipelines into strata with specific geological conditions and at specific depths. Geological environments such as old oil and gas fields, difficult-to-exploit coal seams, and deep groundwater layers are often used for CO 2 storage [14]. Geological storage is considered to be a more effective method for the long-term storage of CO 2 because of site feasibility and economic aspects, among other issues.…”