scholarly journals Controls of Distinct Mineral Compositions on Pore Structure in Over-Mature Shales: A Case Study of Lower Cambrian Niutitang Shales in South China

Minerals ◽  
2021 ◽  
Vol 11 (1) ◽  
pp. 51
Author(s):  
Xing Niu ◽  
Detian Yan ◽  
Mingyi Hu ◽  
Zixuan Liu ◽  
Xiaosong Wei ◽  
...  
Keyword(s):  
Organic Matter ◽  
Pore Structure ◽  
Clay Minerals ◽  
Mineral Composition ◽  
South China ◽  
Lower Cambrian ◽  
Great Influence ◽  
Rock Composition ◽  
Niutitang Formation ◽  
Siliceous Shale

Investigating the impacts of rock composition on pore structure is of great significance to understand shale gas occurrence and gas accumulation mechanism. Shale samples from over-mature Niutitang formation of Lower Cambrian in south China were measured by X-ray diffraction (XRD), field emission scanning electron microscopy (FE-SEM), low pressure N2 and CO2 adsorption to elucidate the controls of distinct mineral composition on pore development. Two distinct lithofacies, namely siliceous shale and argillaceous shale, were ascertained based on their mineral composition. Due to the variability of mineral composition in different lithofacies, pore structure characteristics are not uniform. Pores in siliceous shales are dominated by interparticle pores and organic matter (OM) pores, among which the interparticle pores are mainly developed between authigenic quartz. Furthermore, most of these interparticle pores and cleavage-sheet intraparticle pores within clay minerals are usually filled by amorphous organic matter that is host to OM pores. Due to the lack of rigid minerals, argillaceous shale was cemented densely, resulting in few interparticle pores, while cleavage-sheet intraparticle pores within clay minerals are common. Comparing siliceous shales with argillaceous shales, specific surface areas and pore volumes are higher on the former than on the latter. The content of total organic carbon (TOC) and authigenic quartz have a great influence on micropore structures, but less on mesopore structure for siliceous shales. The rigid framework structure formed by authigenic quartz is believed to be able to prevent primary interparticle pores from mechanical compaction and facilitate the formation of organic matter-associated pores. In terms of argillaceous shales, due to the lack of authigenic quartz, interparticle pores were rarely developed and its pore structure is mainly controlled by illite content.

scholarly journals Constraints on the Organic Matter Accumulation of Lower Cambrian Niutitang Shales in the Middle Yangtze Region, South China

Lithosphere ◽  
2021 ◽  
Vol 2021 (Special 1) ◽  
Author(s):  
Xing Niu ◽  
Yini Liu ◽  
Detian Yan ◽  
Mingyi Hu ◽  
Zixuan Liu ◽  
...  
Keyword(s):  
Organic Matter ◽  
Sea Level ◽  
South China ◽  
Primary Productivity ◽  
Lower Cambrian ◽  
Hydrothermal Activity ◽  
Oxic Condition ◽  
Organic Matter Accumulation ◽  
Niutitang Formation ◽  
And Sea Level

Abstract The lower Cambrian Niutitang shales, as one of target intervals with the greatest potential for shale gas exploration and development, have attracted much attention. Nevertheless, the organic matter enrichment mechanisms of the lower Cambrian Niutitang shales need further study, especially in the hydrothermal active zone. In this study, samples from ND1 well in western Hubei Province, middle Yangtze region, South China, were investigated for the controlling factors of organic matter accumulation of Lower Cambrian Niutitang shales by detailed petrographic, mineralogic, and geochemical proxies. The results show that hydrothermal activity and sea level fluctuation controlled the redox conditions and paleoproductivity of seawater and ultimately controlled the organic matter accumulation of Niutitang formation. In the Niu-1 member, the intense hydrothermal events lead to a suboxic to anoxic environment, which is conducive to the organic matter preservation. However, low sea level strengthens the restriction of water mass and reduced nutrient upwelling into the shelf, leading to decreased marine primary productivity, which was ultimately responsible for depleted organic matter accumulation in the Niu-1 member. In the Niu-2 member, the anoxic-euxinic environment and high paleoproductivity, driven by continuous hydrothermal activity and rising sea level, were the main factors controlling the enrichment of organic matter. In the Niu-3 member, the dysoxic to oxic condition plus low primary productivity, caused by the disappearance of hydrothermal activities and sea-level fall, resulted in the unfavorable organic matter accumulation. The results of this paper enrich the model of organic matter enrichment in the lower Cambrian black shale in the middle Yangtze region.

scholarly journals Pore Structure and Fractal Characteristics of Organic-Rich Lacustrine Shales of the Kongdian Formation, Cangdong Sag, Bohai Bay Basin

2021 ◽  
Vol 9 ◽  
Author(s):  
Shouxu Pan ◽  
Ming Zha ◽  
Changhai Gao ◽  
Jiangxiu Qu ◽  
Xiujian Ding
Keyword(s):  
Organic Matter ◽  
Specific Surface ◽  
Pore Structure ◽  
Surface Area ◽  
Clay Minerals ◽  
Mineral Composition ◽  
Fractal Dimensions ◽  
Nitrogen Adsorption ◽  
Thermal Maturity ◽  
Pore Types

In order to examine the pore structure and reveal the fractal geometric nature of shales, a series of laboratory experiments were conducted on lacustrine shale samples cored from the Kongdian Formation. Based on the low temperature nitrogen adsorption, fluorescent thin section and field emission scanning electronic microscope, a comprehensive pore structure classification and evaluation were conducted on shale samples. Fractal dimensions D1 and D2 (with relative pressure of 0–0.45 and 0.45–1.00, respectively) were obtained from the nitrogen adsorption data using the fractal Frenkel-Halsey-Hill (FHH) method. With additional means of X-ray diffraction analysis, total organic carbon content analysis and thermal maturity analysis, the relationships between pore structure parameters, fractal dimensions, TOC content and mineral composition are presented and discussed in this paper. The results show that interparticle pores and microfractures are predominant, whereas organic matter pores are rarely found. The pore morphology is primarily featured with wide-open ends and slit-shaped structures. In terms of pore scale, mesopores and macropores are predominant. The value of fractal dimension D1 representing small pores ranges from 2.0173 to 2.4642 with an average of 2.1735. The value of D2 which represents large pores ranges from 2.3616 to 2.5981 with an average of 2.4960. These low numbers are an indication of few pore types and relatively low heterogeneity. In addition, smaller D1 values reveal that large pores have more complicated spatial structures than smaller ones. The results of correlation analysis show that: 1) D2 is correlated positively with specific surface area but negatively with average pore diameter; 2) D1 and D2 literally show no obvious relationship with mineral composition, TOC content or vitrinite reflectance (Ro); 3) both total Barrett-Joyner-Halenda (BJH) volume and specific surface area show a positive relationship with dolomite content and a negative relationship with felsic minerals content. These results demonstrate that the pore types are relatively few and dominated by mesopores, and the content of brittle minerals such as dolomite and felsic minerals control the pore structure development whilst organic matter and clay minerals have less influence due to low thermal maturity and abundance of clay minerals.

scholarly journals Reservoir characteristics and controlling factor of shale gas in Lower Cambrian Niutitang Formation, South China

2018 ◽  
Vol 3 (3) ◽  
pp. 210-220 ◽  
Author(s):  
Pengfei Wang ◽  
Zhenxue Jiang ◽  
Bo Han ◽  
Peng Lv ◽  
Can Jin ◽  
...  
Keyword(s):  
South China ◽  
Shale Gas ◽  
Lower Cambrian ◽  
Controlling Factor ◽  
Reservoir Characteristics ◽  
Niutitang Formation

scholarly journals Characteristics of Pore Structure and Gas Content of the Lower Paleozoic Shale from the Upper Yangtze Plate, South China

Energies ◽  
2021 ◽  
Vol 14 (22) ◽  
pp. 7603
Author(s):  
Xiaoyan Zou ◽  
Xianqing Li ◽  
Jizhen Zhang ◽  
Huantong Li ◽  
Man Guo ◽  
...  
Keyword(s):  
Organic Matter ◽  
Pore Structure ◽  
Shale Gas ◽  
Lower Cambrian ◽  
Gas Content ◽  
Lower Paleozoic ◽  
Lower Silurian ◽  
Surface Areas ◽  
Specific Surface Areas ◽  
Yangtze Plate

This study is predominantly about the differences in shale pore structure and the controlling factors of shale gas content between Lower Silurian and Lower Cambrian from the upper Yangtze plate, which are of great significance to the occurrence mechanism of shale gas. The field emission scanning electron microscopy combined with Particles (Pores) and Cracks Analysis System software, CO2/N2 adsorption and the high-pressure mercury injection porosimetry, and methane adsorption were used to investigate characteristics of overall shale pore structure and organic matter pore, heterogeneity and gas content of the Lower Paleozoic in southern Sichuan Basin and northern Guizhou province from the upper Yangtze plate. Results show that porosity and the development of organic matter pores of the Lower Silurian are better than that of the Lower Cambrian, and there are four main types of pore, including interparticle pore, intraparticle pore, organic matter pore and micro-fracture. The micropores of the Lower Cambrian shale provide major pore volume and specific surface areas. In the Lower Silurian shale, there are mesopores besides micropores. Fractal dimensions representing pore structure complexity and heterogeneity gradually increase with the increase in pore volume and specific surface areas. There is a significant positive linear relationship between total organic carbon content and micropores volume and specific surface areas of the Lower Paleozoic shale, and the correlation of the Lower Silurian is more obvious than that of the Lower Cambrian. The plane porosity of organic matter increases with the increase in total organic carbon when it is less than 5%. The plane porosity of organic matter pores is positively correlated with clay minerals content and negatively correlated with brittle minerals content. The adsorption gas content of Lower Silurian and Lower Cambrian shale are 1.51–3.86 m3/t (average, 2.31 m3/t) and 0.35–2.38 m3/t (average, 1.36 m3/t). Total organic carbon, clay minerals and porosity are the main controlling factors for the differences in shale gas content between Lower Cambrian and Lower Silurian from the upper Yangtze plate. Probability entropy and organic matter plane porosity of the Lower Silurian are higher than those of Lower Cambrian shale, but form factor and roundness is smaller.

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