Study on the Pore Structure and Fractal Characteristics of Different Lithofacies of Wufeng–Longmaxi Formation Shale in Southern Sichuan Basin, China

Qian, Chao; Li, Xizhe; Shen, Weijun; Zhang, Qing; Guo, Wei; Hu, Yong; Cui, Yue; Jia, Yuze

doi:10.1021/acsomega.1c06913

Cited by 17 publications

(21 citation statements)

References 52 publications

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“…The relationship between shale composition and pore volumes shows that mesopore volumes had a moderate-strong positive correlation with TOC and carbonate content, while a moderate-weak negative correlation with quartz and clay content and macropore volumes had a moderate positive correlation with quartz content (Han et al, 2018). Both NMR and nitrogen adsorption show that organic pores are the main source of mesopores, which is consistent with previous studies proven by both qualitative and quantitative methods, such as N 2 gas adsorption and FE-SEM images (Yang et al, 2016;Han et al, 2018;He et al, 2021;Qian et al, 2022). Frontiers in Earth Science frontiersin.org…”

Section: Pore Type and Psd In Black Shalesupporting

confidence: 89%

Qualitative–quantitative multiscale pore characteristics of black shale from the Upper Ordovician and Lower Silurian black shale in the Southern Sichuan Basin, China

et al. 2022

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Accurate investigation of shale pores is critical to the assessment of shale-gas reservoir properties. Qualitative and quantitative methods have been commonly conducted in shale pore studies. In this study, we take the black shale from the Upper Ordovician and Lower Silurian black shale in the Southern Sichuan Basin as an example. Both qualitative and quantitative methods were used to study the pores at multiple scales, and we discuss the effectiveness of shale pore detection by multiple methods. The following results were obtained: 1) The black shale is composed of quartz, feldsaper, calcite, dolomite and clay minerals in the study area, and its average TOC and porosity are 2.19 and 2.12%, respectively. 2) The CT results show that the pore size of macropores (pore size >0.5 μm) mainly ranges from 2 to 16 μm. Nitrogen adsorption analysis shows that organic-rich shale has abundant organic matter pores with narrow necks and wide bodies. The pores of organic-poor shale are mainly composed of mineral-associated pores with narrow slit shapes. The NMR results show that with increasing TOC, the left peak T2 relaxation times move leftwards, meaning that organic matter pores have a larger pore size than matrix pores at the mesopore scale. 3) CT data identify lamellation fractures and bed-cutting fractures, and their development is controlled by mineral type and content, TOC and laminae density. 4) The determination of segmentation thresholds in CT and transverse surface relaxivity in NMR seriously affects the accuracy of the results.

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Section: Pore Type and Psd In Black Shalesupporting

confidence: 89%

Qualitative–quantitative multiscale pore characteristics of black shale from the Upper Ordovician and Lower Silurian black shale in the Southern Sichuan Basin, China

et al. 2022

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“…For Longmaxi Formation shales, the pore volume mainly comes from a large number of OM nanopores as well as inorganic mineral interpores and intrapores, where the micropores mainly contribute from the OM pores. The results of previous studies demonstrate that the micropore volume has a high correlation with the micropore surface area. ,,, In the present study, higher pore volume tended to indicate higher surface area, which could provide more oxygen-containing functional groups for adsorption, resulting in higher monolayer adsorption q 1 . At high Rh, both hydrophilic and hydrophobic pores take place capillary coalescence, forming large clusters of water molecules in the pore space, resulting in higher water adsorption.…”

Section: Resultssupporting

confidence: 58%

“…Ji et al observed that TOC can increase pore heterogeneity and the specific surface area, thereby producing a better positive correlation with the fractal dimension . Qian et al think that OM pores well developed in organic-rich siliceous shales provided more PV and SSA, and more complicated pore boundary of organic-rich shale . However, the shale samples from the Longmaxi Formation in this study have a high degree of OM maturity and have reached a late stage of over maturity.…”

Section: Resultsmentioning

confidence: 99%

“…Recently, an increasing number of scholars have been employing the water vapor isothermal adsorption methods to study the water-bearing capacity of shales, such as Marcellus, Shanxi Formation, and Wufeng-Longmaxi Formation Shale, and a series of results have also been obtained. − It is believed that the adsorption behavior of water vapor in shale is affected by the clay minerals, brittle minerals, organic matter content, pore structure characteristics, mineral surface wettability, environmental conditions (adsorption temperature, relative pressure), and other factors. ,,− Because shale mainly consists of inorganic minerals and organic matter (OM), the water distribution characteristics in the different components is significant. Water molecules are believed to mainly reside in the pores of inorganic minerals, especially clay minerals that are usually negatively charged and can strongly interact with water molecules (e.g., highly negatively charged montmorillonite). ,,,, Water molecules can form a water film on the surface of clay-rich shale, which is strongly adsorbed on the inner and outer surface by electrostatic forces and hydrogen bonds. ,, For the OM pore, hydrocarbons are primarily found in the kerogen pores, and the interior of kerogen pores have almost no water molecules. , However, some scholars disagree that the oxygen-containing functional groups within OM have certain hydrophilic properties. ,,− Furthermore, the internal pore structure characteristics of shale are important factors for measuring and evaluating the quality of shale reservoirs, including storage capacity and fracturability. − WVA describes the relationship between the activity of water molecules and the saturation of water content on the surface and inside of a solid material at the constant pressure and temperature . It has been shown that the pore diameters of shale have multiscale characteristics, and the pore structure parameters at the micron to nanometer scale also affect the interaction mechanism between water and matrix rock.…”

Section: Introductionmentioning

confidence: 99%

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A Modified Dent-Fractal Mathematical Model to Investigate the Water Vapor Adsorption on Nanopore Structure Heterogeneity from the Longmaxi Shale, Sichuan Basin, China

Liang,

Jiang,

Han

et al. 2023

Energy Fuels

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The study of water vapor adsorption (WVA) isotherms on shales is crucial to comprehend the adsorption− desorption behavior and deposit mechanism of water in shale pore systems. To systematically investigate the relationship between fractal dimension and WVA in shale reservoirs, a new Dent-fractal (DF) model was developed and the ability of different adsorption models to match with WVA experimental data was evaluated. The role of shale pore structure heterogeneity controlling the amount of WVA is also discussed. The results indicate that WVA on shale involves the monolayer−multilayer adsorption and capillary condensation. On the one hand, the GAB and Dent and DF models were found to be the best models for fitting and predicting WVA isotherms in Longmaxi shale. On the other hand, the DLP and DS models had the worst fitting qualities for WVA adsorption data. The pore structure of micropores has a more significant effect on WVA adsorption than that of meso-macropores. The larger surface and pore volume of micropores can provide more adsorption sites and space, which is favorable for WVA. In low-Rh conditions, the higher surface area, the pore surface complexity rises, resulting in higher water vapor monolayer adsorption. Under high-Rh conditions, for shale reservoirs with a highly heterogeneous pore structure, the relationship between the heterogeneous pore structure of the shale and the amount of water adsorbed in multiple layers is not obvious due to the formation of clusters of water molecules.

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“…Therefore, the OM-hosted pore is positively correlated with the gas content, which proves that the OM pores control the gas content (Figures 12C,D). Many studies have been conducted on the relationship between OM abundance and mineral content in deep marine shale (Li et al, 2022;Qian et al, 2022). It is generally agreed that clay minerals have a negative correlation with TOC, whereas brittle minerals have a positive correlation.…”

Section: Discussionmentioning

confidence: 99%

New insights into the evaluation criteria for high-quality deep marine shale gas reservoirs in the Longmaxi formation: Evidence from organic matter pore development characteristics

Zhu

Meng²,

Pan³

et al. 2023

Front. Ecol. Evol.

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Porosity, total organic carbon content, brittle mineral content, and gas content are now the primary references for classifying and evaluating marine shale gas reservoirs in China. Is there a more effective and appropriate reservoir classification scheme for deep marine shale? The Longmaxi Formation in Luzhou, southern Sichuan Basin, China, is the main object of study. Quantitative analysis and modeling using data from field emission scanning electron microscopy, nitrogen adsorption, and logging were used to characterize organic matter (OM) pore multi-scale development and reveal the relationship between OM pore and the high-quality reservoirs. Microscopic and macroscopic indications from OM pores show that a large number of OM pores were developed in high-quality reservoirs. OM surface porosity occupancy of the high-quality reservoir in the Luzhou area was more than 60%. OM porosity occupancy was more than 50%. The nitrogen adsorption–desorption hysteresis loops demonstrate the development of bottleneck and wedge-shaped OM pores. Characterization of multi-scale pore structure by box dimension, pore volume and specific surface area. It is found that the key to the formation of high-quality reservoirs was the massive development of OM mesopores in siliceous shale and the relatively homogeneity structure, which was conducive to the enrichment and migration of shale gas. Furthermore, the improved model decreased the relative error in predicting the OM porosity by about 32.5%. The use of OM porosity occupancy for high-quality reservoir classification was better, and the results were consistent with geological understanding. OM porosity occupancy showed that the area from Lunanxi to Luzhou to Rongchang to Jiangjin was the key exploration area for high-quality reservoirs in southern Sichuan. This study is expected to provide a new idea for OM pore modeling analysis and deep marine shale gas reservoir classification.

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Study on the Pore Structure and Fractal Characteristics of Different Lithofacies of Wufeng–Longmaxi Formation Shale in Southern Sichuan Basin, China

Cited by 17 publications

References 52 publications

Qualitative–quantitative multiscale pore characteristics of black shale from the Upper Ordovician and Lower Silurian black shale in the Southern Sichuan Basin, China

Qualitative–quantitative multiscale pore characteristics of black shale from the Upper Ordovician and Lower Silurian black shale in the Southern Sichuan Basin, China

A Modified Dent-Fractal Mathematical Model to Investigate the Water Vapor Adsorption on Nanopore Structure Heterogeneity from the Longmaxi Shale, Sichuan Basin, China

New insights into the evaluation criteria for high-quality deep marine shale gas reservoirs in the Longmaxi formation: Evidence from organic matter pore development characteristics

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