Mineralogy and geochemical investigation of Cambrian and Ordovician–Silurian shales in South China: Implication for potential environment pollutions

Abstract

Rapid expansion of shale gas development in China raises environmental and human health concerns. Several studies present related information on these concerns in the United States and Canada, yet they are few in China at present. This paper presents a series of original and published mineralogical and trace elements data from two gas shales (Niutitang shale and Longmaxi shale) considered as producing gas shale in China. Mineralogical and geochemical data surveyed can be applied to evaluate the potential environment pollutions during shale weathering and hydraulic fracturing. After compilations of the mineralogical and trace elements data, we can conclude that (a) there is generally more pyrite compared with carbonate for Niutitang shales, indicating that Niutitang shales are more prone to generate the hydrogen ions than Longmaxi shales; (b) many of the environmental hazardous trace elements considered here show an association with organic matter and/or pyrite, indicating that these trace elements are prone to mobilize and release during shale weathering and hydraulic fracturing; (c) some environmental hazardous elements like As, Ni, and Ba that have extremely high concentrations in some regions as compared with the screening limits for soil and drinking water should attract more attention; and (d) clay-rich shale with abundant organic matter may be the most favourable shale gas reservoir for the Niutitang shale, especially for those shales in Lower Yangtze region. Moreover, more mineralogical and geochemical data will be required for a comprehensive environmental impacts assessment. KEYWORDS environmental and human impacts, mineralogy, pyrite oxidization, shale, South China, trace elements

The Lithofacies of Pandua Formation Shale in the Andowia Area, North Konawe, Southeast Sulawesi and Its potential as Petroleum source rock

“…The presence of the pyrite mineral commonly used as an indicator to indicate the reducing conditions [9]. These show that the high preservation of organic material in this research was deposited in anoxic/ euxinic conditions [9]. The result indicates that environmental conditions of deposition strongly influence the preservation of organic material.…”

“…This shows that shale with the presence of pyrite, zircon, and chlorite mineral association positively correlates to the abundance of organic material. The presence of the pyrite mineral commonly used as an indicator to indicate the reducing conditions [9]. These show that the high preservation of organic material in this research was deposited in anoxic/ euxinic conditions [9].…”

Investigation of the Enrichment and Accumulation of Normal Pressure Shale Gas in Anchang Syncline Outside of Sichuan Basin

“…Imaging log about these rocks shows that the high conductivity fractures are not developed in the rocks of Xintan Formation, but there are many high resistivity fractures and horizontal bedding. The breakthrough pressure of rocks in Xintan Formation is about 5.9 MPa, indicating good sealing conditions in general (Zhang et al, 2018;Xie et al, 2019). The porosity of the limestones in the Silurian Shiniulan Formation is between 0.3 and 3.9%, and the permeability ranges from 0.001 to 2.1mD.…”

Potential Impacts of Shale Gas Development on Inorganic Groundwater Chemistry: Implications for Environmental Baseline Assessment in Shallow Aquifers

“…Shales are primarily composed of clay minerals (i.e., illite, mixed-layer illite/smectite, smectite, kaolinite, chlorite) and quartz and can contain significant proportions of other minerals such as feldspars (i.e., K-feldspars, plagioclase), micas (i.e., biotite, muscovite), and carbonate minerals (i.e., calcite, dolomite, siderite, ankerite). ,,,, Formed under reducing conditions, black shales contain abundant organic matter (>2% total organic carbon) and sulfide minerals, primarily pyrite. ,, Black shales are commonly enriched in trace elements that are primarily associated with sulfide minerals and to a lesser degree with organic matter and clay minerals. ,,, In particular, black shales are often enriched in trace metals and metalloids such as As, Cd, Co, Cr, Cu, Mn, Mo, Ni, Pb, Sb, U, V, and Zn ,,− and may contain significant contents of naturally occurring radioactive material (NORM). ,,, The high levels of radioactivity result from the natural abundance of U-238 and Th-232 and their decay products including isotopes of Ra, Po, Rn, and Pb in many organic-rich shale formations. , It is noteworthy that black shales can host sulfide ore deposits that usually contain very high contents of trace metals and metalloids. , As a result of water–rock interactions, elevated concentrations of trace metals/metalloids have been reported in shallow groundwater associated with organic-rich shale occurrences. ,− However, the concentrations of a number of trace metals/metalloids and NORMs were likely limited by sequestration in Fe–Mn oxyhydroxides and clay minerals in shallow oxidizing groundwater and by sulfide mineral and organic matter stability in reducing groundwater. , …”