Depositional environment and hydrothermal controls on organic matter enrichment in the lower Cambrian Niutitang shale, southern China

Abstract

The purpose of this research was to examine paleoenvironments, hydrothermal activity, and seawater restriction of the lower Cambrian Niutitang Formation shale gas reservoir in the eastern Xuefeng Uplift and to determine factors affecting organic matter (OM) enrichment. In the studied borehole (X1) in western Hunan Province, the Niutitang Formation can be subdivided into the Niu1, Niu2, and Niu3 members based on geological and geochemical features, including trace element enrichment, lithology and fossil content. Total organic carbon (TOC) values of the Niutitang Formation are variable, averaging 1.5 wt.% in the Niu1 Member, 12.7 wt.% in the Niu2 Member, and 5.1 wt.% in the Niu3 Member. Paleoclimatic changes were responsible for changes in biota, which impacted patterns of OM enrichment. Climate proxies (Chemical Index of Alteration (CIA)), and productivity proxies (Babio, Cu/Al, and Ni/Al) consistently indicate higher paleoproductivity in the Niu2 Member. The Niu1 and Niu2 members were possibly affected by hydrothermal events, whereas hydrothermal activity was absent during deposition of the Niu3 Member.Hydrothermal activity may not only provide nutrients and silica but alsoenhance the reducing condition of the water column. In addition, hydrothermal events may have possibly influenced biological survival in the different environments, which in turn increased their reproduction within the early Cambrian ocean and affected OM production. Redox proxies (MoEF and UEF) imply that the Niu1, Niu2, and Niu3 members were deposited in suboxic, euxinic, and ferruginous environments, respectively. Redox conditions, strongly restricted water environments, and

Characterization of an Angstrom-Scale Pore Structure in Organic-Rich Shales by Using Low-Pressure CO2 Adsorption and Multifractal Theory and Its Role in CH4/CO2 Gas Storage

“…Consequently, the microscopic images and XRD analysis yielded a consistent result of high TOC and pyrite contents in our samples. This phenomenon is closely associated with an anoxic sedimentary environment, upwelling events, and hydrothermal activity in the early Cambrian Niutitang Formation. , …”

“…A total of 14 fresh shale core samples were collected from the lowermost Cambrian Niutitang Formation in the newly drilled shale gas wells TX1 and TM1 located in the Cengong block (Figure ). The Cengong shale gas block is a residual syncline in northern Guizhou Province, South China, and the geological setting has been introduced in great detail elsewhere. − The Niutitang Formation, one of the most organic-matter-rich shale units in China, was formed in the deep-water environment of marine facies, , and the Niutitang shale is considered a shale gas exploration and development target in South China.…”

“…This phenomenon is closely associated with an anoxic sedimentary environment, upwelling events, and hydrothermal activity in the early Cambrian Niutitang Formation. 52,53 3. OM pores are a type of intraparticle pore and located within OM.…”

Depositional Environment Variation and Organic Matter Accumulation Mechanism of Marine–Continental Transitional Shale in the Upper Permian Longtan Formation, Sichuan Basin, SW China

“…The discussion on organic matter enrichment mechanisms currently exists in two main aspects, namely, paleoproductivity and preservation conditions . Preservation conditions emphasize the effect of anoxic environments during organic matter preservation, while paleoproductivity theory suggests that high paleoproductivity is required to produce abundant organic matter, which consumes oxygen and creates an anoxic environment . To illustrate the organic matter enrichment mechanism, we selected proxies that characterize paleoclimate and paleoweathering conditions (CIA and C values), redox environments (Mo and Corg/ P value), terrigenous debris influx (Al), and primary productivity (Cu) and analyzed the relationship between each parameter and TOC to reveal the organic matter enrichment mechanism of the P l shales.…”

Experimental Investigation of the Impacts of Fracturing Fluid on the Evolution of Fluid Composition and Shale Characteristics: A Case Study of the Niutitang Shale in Hunan Province, South China

“…The achievements made in the analysis of pores and mineral composition in shale reservoirs [6,[11][12][13] revealed the favorable pore systems for shale gas storage and a high brittleness that favors fracturing. More recently, wells targeting the Niutitang shale in the western Hubei province have already shown industrial gas flow [14].…”