Mineral composition and seal condition implicated in pore structure development of organic-rich Longmaxi shales, Sichuan Basin, China

Zhao, Jianhua; Jin, Zhijun; Hu, Qinhong; Liu, Keyu; Jin, Zhenkui; Hu, Zhao; Nie, Haikuan; Du, Wei; Yan, Caina; Wang, Ruyue

doi:10.1016/j.marpetgeo.2018.09.009

Cited by 47 publications

(38 citation statements)

References 41 publications

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“…Yang and Aplin [51] also observed that no apparent correlation between the clay content and specific surface area in the Horn River Group shale in Canada. Some studies have even documented that a slightly negative correlation between the specific surface area and total clay mineral content of some marine shale [52,53]. Chalmers and Bustin [54] attributed these insignificant or negative relationships to the fact that the clay-associated pores are usually mesopores and macropores, which only contribute very limited pore volume and specific surface area.…”

Section: Geological Controls On Pore Structure In Shale Samples From ...mentioning

confidence: 99%

Pore Structure in Shale Tested by Low Pressure N2 Adsorption Experiments: Mechanism, Geological Control and Application

et al. 2022

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The N2 adsorption experiment is one of the most important methods for characterizing the pore structure of shale, as it covers the major pore size range present in such sediments. The goal of this work is to better understand both the mechanisms and application of low-pressure nitrogen adsorption experiments in pore structure characterization. To achieve this, the N2 adsorption molecular simulation method, low-pressure N2 adsorption experiments, total organic carbon (TOC) analysis, X-ray diffraction (XRD) analysis, scanning electron microscopy (SEM), and a total of 196 shale samples from the Wufeng–Longmaxi formations in the Sichuan basin have been employed in this study. Based on the analytical data and the simulations, two parameters, the connectivity index and the large pore volume index, are proposed. These parameters are defined as the connectivity of the pore system and the volume of large nanopores (>10 nm) respectively, and they are calculated based on the N2 adsorption and desorption isotherms. The experimental results showed that TOC content and clay minerals are the key factors controlling surface area and pore volume. However, in different shale wells and different substrata (divided based on graptolite zonation), the relative influences of TOC content and clay minerals on pore structure differ. In three of the six wells, TOC content is the key factor controlling surface area and pore volume. In contrast, clay minerals in samples from the W202 well are the key factors controlling pore volume, and with an increase in the clay mineral content, the pore volume increases linearly. When the carbonate content exceeds 50%, the pore volume decreases with an increase in carbonate content, and this may be because in the diagenetic process, carbonate cement fills the pores. It is also found that with increasing TOC content the connectivity index increases and SEM images also illustrate that organic pores have better connectivity. Furthermore, the connectivity index increases as quartz content increases. The large pore volume index increases with quartz content from 0 to 40% and decreases as quartz increases from 40% to 100%. By comparing the pore structure of shale in the same substrata of different shale gas wells, it was found that tectonic location significantly affects the surface area and pore volume of shale samples. The shale samples from wells that are located in broad tectonic zones, far from large-scale faults and overpressure zones, have larger pore volumes and surface areas. On the contrary, the shale samples from shale gas wells that are located in the anticline region with strong tectonic extrusion zones or near large-scale faults have relatively low pore volumes and surface areas. By employing large numbers of shale samples and analyzing N2 adsorption mechanism in shale, this study has expanded the application of N2 adsorption experiment in shale and clarifies the effects of sedimentary factors and tectonic factors on pore structure.

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Section: Geological Controls On Pore Structure In Shale Samples From ...mentioning

confidence: 99%

Pore Structure in Shale Tested by Low Pressure N2 Adsorption Experiments: Mechanism, Geological Control and Application

et al. 2022

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“…The samples in this study were collected from the Southern Sichuan Basin and the Ordos Basin in China (Gao & Hu, 2018). The shale reservoirs in the Sichuan Basin are the marine shale of the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation, mainly distributed in southeastern Sichuan Province and Chongqing (Tang et al, 2019;Wang et al, 2017;Xinhua & Jun, 2018;Zhao et al, 2018). The shale reservoir in the Ordos Basin is the Chang 7 and Chang 9 sections of the Yanchang Formation of the Triassic Strata, mainly distributed in the northern part of Shanxi Province (Gao & Hu, 2018;Xiong et al, 2016).…”

Section: Samples Informationmentioning

confidence: 99%

“…The TOC of the shales was measured with a Leco CS230 Carbon-Sulfur analyzer after the samples were treated by hydrochloric acid to remove the carbonate (Zhao et al, 2018). The error is 0.5%.…”

Section: Samples Informationmentioning

confidence: 99%

Effect of Clay and Organic Matter Content on the Shear Slip Properties of Shale

Wang

et al. 2019

JGR Solid Earth

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Shale gas reservoirs contain a large number of natural fractures. When shear slip occurs during hydraulic fracturing, it will increase reservoir permeability and improve the reservoir stimulation performance. Because shale contains a large amount of clay and organic matter, its shear slip behavior differs from that of other rocks. In this study, the shear behavior of different shale blocks is experimentally studied, and the proportion of clay and organic matter in the shale dominates the shear slip behavior. Specifically, the friction coefficient and shear strength decrease with the increasing content of clay and organic matter. A microscopic support model was developed to describe the different shear slip behaviors for different contents of clay and organic matter. When the clay and organic matter content is lower than a critical threshold (~35%), shale is microscopically grain supported and brittle shear occurs and the material is prone to shear dilation. When this content is greater than a critical content (~43%), the microscopic structure is a matrix‐supported fabric and plastic shear occurs, which is prone to shear contraction. Shale with contents between these two critical thresholds has a mixed‐support fabric, which is a transition type between brittle and plastic shear. If the proportion of clay and organic matter is less than ~35%, the natural fracture tends to dilate and retain a certain degree of opening after shearing, improving stimulation performance. When the proportion is more than ~43%, shear contraction occurs on the natural fracture surface, which is not conductive and cannot increase reservoir permeability.

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“…Shale pore structure distinctions are essentially affected by mineral composition, organic matter type, organic carbon content, thermal evolution degree, preservation conditions, and other factors. The degree of thermal evolution has the most pronounced effect [7,[23][24][25][26]. As the degree of thermal evolution, organic carbon content, and clay mineral content rise, the number of microscopic pores, the specific surface area, and pore volume increase [16,27,28].…”

Section: Introductionmentioning

confidence: 99%

Differential Reservoir-Forming Mechanisms of the Lower Paleozoic Wufeng-Longmaxi and Niutitang Marine Gas Shales in Northern Guizhou Province, SW China: Theories and Models

Yang

et al. 2022

Energies

Self Cite

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Fine dissection of microscopic pore structure variations between the Niutitang Formation and the Wufeng-Longmaxi Formation will help to improve the understanding of the underlying geological theory of shale gas in northern Guizhou Province. The stratigraphic, geochemical, physical, and tectonic properties of the two formations vary greatly, resulting in differential development of the microscopic pore structure among reservoirs and, as a result, major variances in gas concentration. To explore the mechanism of differential pore evolution, experimental techniques and instruments such as gas adsorption, liquid intrusion, SEM, XRD, and organic geochemical tests were utilized. The results indicate that the Wufeng-Longmaxi Formation is in a high-maturity stage, while the Niutitang Formation is in an over-mature stage. The latter has a higher TOC content. Both petrographic phases are siliceous shale petrographic phases, and the former has more developed dissolution pores with better pore volume, throat radius, and macropore pore diameters than the latter, as well as organic matter pores, intergranular pores, and microfracture structural parameters, whereas the specific surface area is the opposite. The differences in reservoir pore formation between the two formations were analyzed, and the results showed that the petrographic type, thermal evolution, and tectonic preservation conditions were the primary controlling elements of differential shale gas reservoir formation. A differential reservoir-forming model of the Wufeng-Longmaxi Formation and the Niutitang Formation was constructed, providing a geological and theoretical basis for shale gas geological exploration in northern Guizhou Province.

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Mineral composition and seal condition implicated in pore structure development of organic-rich Longmaxi shales, Sichuan Basin, China

Cited by 47 publications

References 41 publications

Pore Structure in Shale Tested by Low Pressure N2 Adsorption Experiments: Mechanism, Geological Control and Application

Pore Structure in Shale Tested by Low Pressure N2 Adsorption Experiments: Mechanism, Geological Control and Application

Effect of Clay and Organic Matter Content on the Shear Slip Properties of Shale

Differential Reservoir-Forming Mechanisms of the Lower Paleozoic Wufeng-Longmaxi and Niutitang Marine Gas Shales in Northern Guizhou Province, SW China: Theories and Models

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