Lithofacies and cyclicity of the Lower Cambrian Niutitang shale in the Mayang Basin of western Hunan, South China

et al. 2018

Minerals

A suite of shale samples from the Lower Cambrian Niutitang Formation in northwestern Hunan Province, China, were investigated to better understand the pore structure and fractal characteristics of marine shale. Organic geochemistry, mineralogy by X-ray diffraction, porosity, permeability, mercury intrusion and nitrogen adsorption and methane adsorption experiments were conducted for each sample. Fractal dimension D was obtained from the nitrogen adsorption data using the fractal Frenkel-Halsey-Hill (FHH) model. The relationships between total organic carbon (TOC) content, mineral compositions, pore structure parameters and fractal dimension are discussed, along with the contributions of fractal dimension to shale gas reservoir evaluation. Analysis of the results showed that Niutitang shale samples featured high TOC content (2.51% on average), high thermal maturity (3.0% on average), low permeability and complex pore structures, which are highly fractal. TOC content and mineral compositions are two major factors affecting pore structure but they have different impacts on the fractal dimension. Shale samples with higher TOC content had a larger specific surface area (SSA), pore volume (PV) and fractal dimension, which enhanced the heterogeneity of the pore structure. Quartz content had a relatively weak influence on shale pore structure, whereas SSA, PV and fractal dimension decreased with increasing clay mineral content. Shale with a higher clay content weakened pore structure heterogeneity. The permeability and Langmuir volume of methane adsorption were affected by fractal dimension. Shale samples with higher fractal dimension had higher adsorption capacity but lower permeability, which is favorable for shale gas adsorption but adverse to shale gas seepage and diffusion.

Section: Introductionmentioning

confidence: 99%

Pore Structure and Fractal Characteristics of Niutitang Shale from China

Tang

et al. 2018

Minerals

“…The study area is in Northwest Hunan, which is situated on the southeast margin of the Yangtze Platform, spanning two secondary tectonic units, bounded by the Baojing-Cili fault zone, southeast of which is the Jiangnan-Xuefeng nappe uplift zone, and to northwest is located the west Xiang-Exi fold zone (Figure 2B, Yang et al, 2016;Xi et al, 2019). The study area is located in the Sangzhi-Shimen syncline.…”

Section: Longmaxi Shale In the Hunan Areamentioning

confidence: 99%

Influence of the Duration of Tectonic Evolution on Organic Matter Pore Structure and Gas Enrichment in Marine Shale: A Case Study of the Lower Silurian Longmaxi Shale in Southern China

et al. 2022

Front. Earth Sci.

The exploration and development of the shale in the Lower Silurian Longmaxi Formation in the Chongqing area has shown that gas production here is commercially viable. In contrast, the Longmaxi Formation shale in Hunan shows that gas production is not commercial. Why is there such a difference between the Chongqing and Hunan areas for the same formation. A mount of previous studies showed that gas is stored primarily in the organic matter (OM) pores in shale. This study has investigated the Longmaxi shale from two well locations in Chongqing and Hunan in order to understand whether differences in pore structure are the cause of the difference in commerciality in the two areas. The formation burial histories were established, analyzing samples for mineral composition, total organic carbon (TOC) content, thermal maturity (Ro), and OM pore structures. The results show that the Longmaxi shale in Chongqing and Hunan has similar TOC content and Ro. The average TOC content is above 3.0% for samples from both areas, and the thermal maturity was all between 2.4 and 2.9%. OM pores of the Longmaxi shale in Chongqing are abundant in number and relatively large sized, with mostly circular and oval shapes. In contrast, the number and size of the OM pores in the Longmaxi shale in Hunan are small, and the shape is irregular. OM pore structure of the Longmaxi shale in Chongqing is therefore favorable for preservation of gas. The poor pore structure of the Longmaxi shale in Hunan is not conducive to gas preservation. The OM pore structure difference of the Longmaxi shale in Chongqing and Hunan is determined by the formation burial history. The Longmaxi shale in the Chongqing area experienced rapid burial in the Early Jurassic and rapid uplift in the Late Cretaceous. The Longmaxi Formation in Hunan experienced rapid burial in the Early Triassic and rapid uplift in the Early Jurassic. The long evolution time (100 Ma) of the Longmaxi shale in Chongqing produced a large amount of gas supply and enough storage space (OM pores) for the gas occurrence, which makes the amount of gas be preserved in geological history. The short evolution time (50 Ma) of the Longmaxi shale in Hunan produced insufficient gas supply and not enough OM pores in reservoir, which leads to gas loss in geological history, resulting in low gas content. Therefore, to evaluate the potential of shale gas, the evolution time of organic matter must be considered. In other words, the time interval between rapid subsidence and uplift of formation during geological history must be considered.

“…Currently, the accumulation characteristics of organic matter with the geochemical method for Niutitang Formation shale in China mainly focus in south of Yangtze platform (Liu et al 2015(Liu et al , 2016Xia et al 2015;Wu et al 2017;Zhou et al 2017Zhou et al , 2019Li et al , 2019Zhang et al 2018;Ma et al 2019;Awan et al 2020). The lithofacies of Niutitang Formation shale in South China could be divided into five types, including organic matter-rich siliceous shale, silty-siliceous shale, argillaceous shale, calcareous shale and silty-siliceous mixed shale (Yang et al 2016;Wu et al 2017).…”

Section: Introductionmentioning

confidence: 99%

The accumulation model of organic matters for the Niutitang Formation shale and its control on the pore structure: a case study from Northern Guizhou

Gao

J Petrol Explor Prod Technol

et al. 2022

Shale gas reservoir is a fine-grained sedimentary rock with component of clastic particles and organic matters, and the accumulation of the organic matters would determine the effective development of shale gas. The paleoclimate, detrital influx, redox of the water and paleoproductivity are effective geochemical indicators that could help to find the favorable shale gas reservoir stratum. In this study, the shale samples collected from Niutitang Formation (Northern Guizhou, China) were launched the measurements of the content of major elements and trace elements, and the characteristics of geochemical indicators were analyzed, which can be used to discuss the accumulation model of organic matters. Besides, the pore structure of shale sample controlled by the enrichment of organic matters is also discussed. The paleoclimate is dominant cold and dry, and it changes to warm and humid at the later Niutitang period, and the detrital influx also increased at the later Niutitang period; the water environment of Niutitang Formation shale presents as reductive, and the paleoproductivity of the Niutitang Formation shale is commonly high. The enrichment of organic matters in the Niutitang Formation is dominantly controlled by the redox of the water, while the hydrothermal activity and the paleoproductivity lead to the difference enrichment of organic matters in the Niutitang Formation shale. The accumulation model of organic matters also influences the characteristics of pore structure from the Niutitang Formation shale, and the pore structure could be divided into two types. The shale with high content of organic matters also features high content of quartz and pyrite, and these minerals contribute to the preservation of pore space in the shale, while that of the clay minerals is contrary. The high content of organic matters and preferable pore characteristics indicate the Niutitang Formation favors the development of shale gas, especially that for the lower Niutitang Formation.