Greenhouse Gas Emissions during Oil Shale Crushing and Its Main Controlling Factors: A Contrast Study of Oil Shale in Yaojie and Fushun Areas, China

Abstract

Geological bodies are important sources of greenhouse gas (GHG) emissions. Organic-rich oil shale in sedimentary basins is a good gas source rock, the GHG in which will be released into the atmosphere during crushing to affect climate change. Quantitative calculations of GHG emissions during oil shale crushing were carried out on oil shales from the Yaojie (YJ) and Fushun (FS) mining areas in China. Organic geochemistry, X-ray diffraction, and pore structure analysis experiments, as well as the relationship between storage time and GHG emissions, were analyzed to investigate the main controlling factors of GHG release in different types of oil shales. The results showed that the CH 4 and CO 2 released from the YJ oil shale were 0.002−0.145 mL/g and 0.011−0.054 mL/g, respectively; the CH 4 and CO 2 released from the FS oil shale were 0.0001−0.0008 mL/g and 0.002−0.045 mL/g, respectively. Residual CH 4 release was closely related to total organic carbon (TOC) and maturity: the CH 4 released from the organic-rich and mature YJ oil shale was much higher than that of the FS oil shale, which is relatively organic-lean and immature. The control factors of the released CO 2 vary in different regions: CO 2 released from the YJ oil shale was somewhat affected by the TOC, while that released from the FS oil shale was mainly controlled by carbonate minerals and their contributing pores. The results of pore structure and organic maceral analyses indicated that both organic and inorganic pores of the YJ oil shale are occupied by asphaltenes, forming a key gas preservation mechanism of residual CH 4 and CO 2 as solutes dissolved in asphaltenes. In addition, CO 2 has a greater absorptive capacity than CH 4 and is therefore more difficult to release during the same crushing time. As oil shale is stored for longer periods, residual CH 4 will be preferentially released to the atmosphere, while residual CO 2 will be released in large quantities during crushing.