“…The burial depth of the Longmaxi Formation in the Weirong area ranges from approximately 3000–3500 m. The thickness of the organic-rich shale of S 1 l 1 ranges from 80 to 90 m, which is the focus of shale gas exploration. Exploration and drilling results suggest that the Longmaxi Formation in the Weirong block is generally subject to a high pressure, and the pore fluid pressure coefficient varies between ~ 1.94 and 2.05 28 , which provides suitable conditions for shale gas preservation but also causes great difficulties in fracturing development of shale gas. Figure 1 ( a ) Location of the Weirong area in the Sichuan Basin (modified after Nie et al 29 ); ( b ) Sampling well location in the Weirong block (modified after Xiong 30 ); ( c ) Stratigraphic information of the Longmaxi Formation (modified after Xu et al 31 ).…”
Gas-bearing property evaluation and main controlling factor analysis have remained a concern in shale gas research. The application of principal component analysis, an important mathematical statistical method, in gas-bearing property evaluation and main controlling factor analysis of the Longmaxi shale in the Weirong area, Sichuan Basin, was examined. The Longmaxi shale exhibits high heterogeneity, manifested in the organic matter abundance, mineral composition, and pore structure. Seven geological factors, including the temperature, pressure, TOC content, clay content, brittle mineral content, pore volume, and specific surface area (SSA), were selected in principal component analysis. Four principal components with geological significance, such as mineral composition, formation condition, pore structure, and organic matter abundance, were extracted through principal component analysis, and further constituted a comprehensive factor. Shale gas-bearing properties were evaluated according to the score of the comprehensive factor. The Longmaxi shale could be identified as exhibiting good, medium, and poor gas-bearing properties based on the comprehensive factor scores of these samples. According to each geological factor’s contribution to the comprehensive factor, combined with geological analysis, it could be considered that gas-bearing properties are primarily controlled by pore volume, SSA, and clay content, followed by TOC content, brittle mineral content, temperature and pressure.
“…The burial depth of the Longmaxi Formation in the Weirong area ranges from approximately 3000–3500 m. The thickness of the organic-rich shale of S 1 l 1 ranges from 80 to 90 m, which is the focus of shale gas exploration. Exploration and drilling results suggest that the Longmaxi Formation in the Weirong block is generally subject to a high pressure, and the pore fluid pressure coefficient varies between ~ 1.94 and 2.05 28 , which provides suitable conditions for shale gas preservation but also causes great difficulties in fracturing development of shale gas. Figure 1 ( a ) Location of the Weirong area in the Sichuan Basin (modified after Nie et al 29 ); ( b ) Sampling well location in the Weirong block (modified after Xiong 30 ); ( c ) Stratigraphic information of the Longmaxi Formation (modified after Xu et al 31 ).…”
Gas-bearing property evaluation and main controlling factor analysis have remained a concern in shale gas research. The application of principal component analysis, an important mathematical statistical method, in gas-bearing property evaluation and main controlling factor analysis of the Longmaxi shale in the Weirong area, Sichuan Basin, was examined. The Longmaxi shale exhibits high heterogeneity, manifested in the organic matter abundance, mineral composition, and pore structure. Seven geological factors, including the temperature, pressure, TOC content, clay content, brittle mineral content, pore volume, and specific surface area (SSA), were selected in principal component analysis. Four principal components with geological significance, such as mineral composition, formation condition, pore structure, and organic matter abundance, were extracted through principal component analysis, and further constituted a comprehensive factor. Shale gas-bearing properties were evaluated according to the score of the comprehensive factor. The Longmaxi shale could be identified as exhibiting good, medium, and poor gas-bearing properties based on the comprehensive factor scores of these samples. According to each geological factor’s contribution to the comprehensive factor, combined with geological analysis, it could be considered that gas-bearing properties are primarily controlled by pore volume, SSA, and clay content, followed by TOC content, brittle mineral content, temperature and pressure.
“…Many references stated the key elements resulting in the difference of estimated environmental impact between the two countries. The geological conditions in China are much more complicated (Teng and Liu, 2013;Chen et al, 2017;Ma et al, 2021). China's shale basins are different from the ones in the United States, which located in harsh terrains and mountainous (Yu et al, 2013).…”
People have higher expectations for shale gas exploitation. However, the promotion of large-scale shale gas exploitation does not seem to be as good as it seems, since the extraction technology - hydraulic fracturing - harms the environment, which causes cognitive biases. This paper reviews studies that estimate the environmental and economic influence of the fracturing process in the U.S. and China to help people better understand the shale gas exploitation. It summarizes the methodological issues and results of main projections. There are shared problems in evaluating the influence of shale gas development due to limited identification methods, data sources and advancing exploitation technologies. Little research values the environmental influence of shale gas development in social benefit or economic benefit. Though varies significantly across various plays and parameter compared with conventional gases, previous researches indicate that water use for shale gas development will not affect the local water supply vastly, and the ultimate influence relies on the water management method. Moreover, compared with conventional natural gas and other energy resources, freshwater consumption about shale gas exploration is decreasing with the progress of exploration technology, while its life-cycle GHG emissions are greater in the long term.
“…Although commercial shale flows have been found in different blocks in the southern Sichuan Basin, due to differences in sedimentation and structure, different blocks and different shale gas wells in the same block have shale gas and single-well gas production (Ma et al, 2021). These large differences seriously restrict the next stage of shale gas development in this area.…”
To investigate the geological characteristics and exploration potential of shale gas in the southern Sichuan Basin, we analyze the coupling relationship between the hydrocarbon generation and storage conditions of the Longmaxi Formation and discuss the preservation conditions from the lateral and vertical migration mechanisms of shale gas. According to the results, the organic-rich shale at the bottom was formed in a strongly euxinic and anoxic reducing environment, the oxygen content increased in the upper water body in which the Longmaxi Formation was deposited, and the water body became oxidized. The organic matter type in the shale is dominantly type I kerogen and a small amount of type II1 kerogen. The organic matter content is more than 3.0% and is in the high-to postmature stage. The enrichment of siliceous organisms increases the organic matter and enhances the brittleness of shale, resulting in “superior hydrocarbons and a favorable reservoir”. Pyrolysis of organic matter promotes the formation of organic matter pores and dissolution pores, resulting in a coupled “source-reservoir” accumulation control system. The high vertical formation pressure guarantees the sealing of shale and restrains the lateral escape of shale gas. The high-angle intersection of the highly filled fractures and the current crustal stress can effectively enhance the fracture sealing and inhibit the vertical escape of shale gas, forming a three-dimensional effective closure. Hence, the area featuring a short tectonic uplift time, small amplitudes, large-scale underdeveloped fractures, and a high formation pressure coefficient is a favorable area for shale gas exploration, according to the analysis of three-dimensional preservation conditions.
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