Quartz types, silica sources and their implications for porosity evolution and rock mechanics in the Paleozoic Longmaxi Formation shale, Sichuan Basin

Xu, Hao; Zhou, Wen; Hu, Qinhong; Yi, Tao; Jiang, Ke; Zhao, Aiwu; Lei, Zihui; Yu, Yu

doi:10.1016/j.marpetgeo.2021.105036

Cited by 49 publications

(40 citation statements)

References 40 publications

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“…However, the genetic origin of the quartz would play different roles in pore types and pore evolution. Many studies have been done to identify quartz of biogenic origin by crystalline morphology, luminescence, grain size, and geochemical proxies and to clarify its impact on the pore development (Milliken et al, 2016;LU et al, 2018;Xu et al, 2021). These studies showed that biogenic silica formed the opal framework in the early stage and then transformed into a stiff quartz crystal in the later stage resulting in a tight structure.…”

Section: Contribution Of Different Pore Types To Connectivitymentioning

confidence: 99%

Pore Connectivity Characterization Using Coupled Wood’s Metal Intrusion and High-Resolution Imaging: A Case of the Silurian Longmaxi Shales From the Sichuan Basin, China

Liu

Fan

et al. 2021

Front. Earth Sci.

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Pore connectivity is crucial for shale gas production. However, the three-dimensional (3D) characteristics and distribution of pore networks and, more fundamentally, the underlying role of different pore types on pore connectivity in shales are inadequately understood. By comparing the 3D pore connectivity derived from direct microstructural imaging of pores filled with Wood’s metal at a pressure corresponding to the finest accessible pore throat in the resolution ranges that may be achieved by X-ray micro-CT and SEM, it is possible to evaluate pore connectivity of different types of shales. The pore connectivity of three shales including a mixed mudstone, siliceous shale, and argillaceous shale from the Silurian Longmaxi Formations is investigated via combined broad ion beam (BIB) polishing, and SEM and X-ray micro-CT imaging after Wood’s metal injection at a pressure up to 380 MPa. The three shales show significant differences in pore connectivity. The mixed mudstone shows excellent pore connectivity in the matrix; the siliceous shale shows an overall poor connectivity with only a small amount of OM (organic matter) pores immediately adjacent to microfractures displaying interconnectivity, while the pores in the argillaceous shale, dominated by plate-like clay pores, are largely not interconnected.

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Section: Contribution Of Different Pore Types To Connectivitymentioning

confidence: 99%

Pore Connectivity Characterization Using Coupled Wood’s Metal Intrusion and High-Resolution Imaging: A Case of the Silurian Longmaxi Shales From the Sichuan Basin, China

Liu

Fan

et al. 2021

Front. Earth Sci.

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“…Tectonically, the Sichuan Basin starts from the Hunan-Guizhou and Hubei fold belt in the east, the Longmenshan Fault-fold belt in the west, the Micangshan-Dabashan fold belt in the north, and the Emeishan and Liangshan fold belt in the south (Z. J. Jin, Nie, Liu, Zhao, & Jiang, 2018;Nie et al, 2017;Nie et al, 2020;Sun et al, 2019;Xu et al, 2021;R. Yang, He, et al, 2016).…”

Section: Tectonic Evolution Of the Sichuan Basinmentioning

confidence: 99%

“…Different mineral compositions are important factors controlling pore types and porosity development of shale reservoirs (Nie et al, 2020). Brittleness minerals, especially siliceous minerals, because of their high hardness and strong compaction resistance, can provide a large number of intergranular pores to form a hard granular framework to avoid the compaction of primary pores, which can support and protect the pores of deeply buried shale to a certain extent and provide space for methane injection (Guo et al, 2021;Sun et al, 2019;Xu et al, 2021). As quartz has a positive correlation with TOC (Figure 7), so does the quartz content with porosity (Figure 12b).…”

Section: Influence Of Sedimentary Structures On Storage and Adsorption Capacitymentioning

confidence: 99%

Constraints of sedimentary structures on key parameters of shale gas reservoirs: A case study of the Wufeng and Longmaxi formations of the Ordovician‐Silurian transition in Luzhou area, Sichuan Basin, southwestern China

et al. 2021

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There are various sedimentary structures developed in the black shales of the Upper Ordovician Wufeng Formation and the Lower Silurian Longmaxi Formation in Luzhou area, southern Sichuan Basin, southwestern China. In order to evaluate the controlling effects of sedimentary structures on the key parameters of shale reservoir properties, collected classification of sedimentary structures, scanning electron microscope observation, analysis of shale fabric and porosity characteristics, lowpressure nitrogen adsorption, methane isothermal adsorption, and conventional triaxial compression test were carried out based on shale samples from Wells A-H1, B-H1, C-H1 and D-H1 in the study area. The sedimentary structures recorded in these shales are categorized into five types: homogeneous bedding, weak horizontal bedding, strong horizontal bedding, discontinuous ripple bedding, and gravel-bearing massive bedding. In general, the palaeo-hydrodynamics and oxygen content of water columns were weak when homogeneous bedding shale was deposited. The organic matter is the most abundant and the total organic carbon content is up to 4.01% on average. The average quartz content is 43.5%, and the brittleness index is the highest. The porosity and adsorption capacity were the highest, with an average of 4.57% and 79.5 scf/ton, respectively. Combined with its mechanical properties of low Poisson's ratio and high Young's modulus, homogeneous bedding sedimentary structure is associated with the shale units possessing the highest organic matter abundance, the strongest reservoir property, and the best fracability, which is the priority target for exploration and development of the Wufeng to lower Longmaxi Formation in the Sichuan Basin, southwestern China.

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“…Therefore, it is very important to clarify the origin of quartz for reservoir brittleness evaluation, gas bearing evaluation, and development potential evaluation of shale (Dong and Harris, 2020;Qiu et al, 2020). With the vigorous development of shale gas in the world, many scholars focus their aims on the origin of quartz in shale (Milliken et al, 2012;Milliken et al, 2016;Li et al, 2019;Joseph et al, 2020;Xu et al, 2021). Milliken et al (2016) classified quartz in Barnett shale into extrabasin clastic quartz, intrabasin clastic quartz, and authigenic quartz.…”

Section: Introductionmentioning

confidence: 99%

“…The organisms generally refer to diatoms, radiolarians, and sponge spicules (Boggs, 2006;Day-Stirrat et al, 2010;Joseph et al, 2020;Guan et al, 2021). At present, it is found that biogenic silica in shale is not only related to the enrichment of organic matter (Dong et al, 2019;Khan et al, 2019;Li et al, 2019) but also can promote the mechanical properties and pore preservation of shale reservoir (Yang et al, 2018;Dong et al, 2019;Dong and Harris, 2020;Qiu et al, 2020;Xu et al, 2021), so it is very urgent to study the origin of silica for shale gas exploration and development.…”

Section: Introductionmentioning

confidence: 99%

The Origin of Silica of Marine Shale in the Upper Ordovician Wulalike Formation, Northwestern Ordos Basin, North China

Zhang

Huang

et al. 2021

Front. Earth Sci.

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The shale of the Wulalike Formation developed in the northwestern Ordos Basin is considered to be an effective marine hydrocarbon source rock. One of the key factors for successful shale gas exploration in the Wufeng–Longmaxi Formation in the Sichuan Basin is the high content of biogenic silica. However, few people have studied the siliceous origin of the Wulalike shale. In this study, we used petrographic observation and element geochemistry to analyze the origin of silica in the Wulalike shale. The results show that the siliceous minerals are not affected by hydrothermal silica and mainly consist of biogenic and detrital silica. A large number of siliceous organisms, such as sponge spicules, radiolarians, and algae, are found under the microscope. It has been demonstrated that total organic carbon has a positive correlation with biogenic silica and a negative correlation with detrital silica, and biogenic silica is one of the effective indicators of paleoproductivity. Therefore, the enrichment of organic matter may be related to paleoproductivity. Through the calculation of element logging data in well A, it is found that biogenic silica is mainly distributed in the bottom of the Wulalike Formation, and the content of biogenic silica decreases, while the content of detrital silica increases upward of the Wulalike Formation. Biogenic silica mainly exists in the form of microcrystalline quartz, which can form an interconnected rigid framework to improve the hardness and brittleness of shale. Meanwhile, biogenic microcrystalline quartz can protect organic pores from mechanical compaction. Therefore, it may be easier to fracture the shale gas at the bottom of the Wulalike Formation in well A.

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Quartz types, silica sources and their implications for porosity evolution and rock mechanics in the Paleozoic Longmaxi Formation shale, Sichuan Basin

Cited by 49 publications

References 40 publications

Pore Connectivity Characterization Using Coupled Wood’s Metal Intrusion and High-Resolution Imaging: A Case of the Silurian Longmaxi Shales From the Sichuan Basin, China

Pore Connectivity Characterization Using Coupled Wood’s Metal Intrusion and High-Resolution Imaging: A Case of the Silurian Longmaxi Shales From the Sichuan Basin, China

Constraints of sedimentary structures on key parameters of shale gas reservoirs: A case study of the Wufeng and Longmaxi formations of the Ordovician‐Silurian transition in Luzhou area, Sichuan Basin, southwestern China

The Origin of Silica of Marine Shale in the Upper Ordovician Wulalike Formation, Northwestern Ordos Basin, North China

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