Grain assemblages and diagenesis in organic-rich mudrocks, Upper Pennsylvanian Cline shale (Wolfcamp D), Midland Basin, Texas

Peng, Junwen; Milliken, Kitty L.; Fu, Qilong; Janson, Xavier; Hamlin, H. Scott

doi:10.1306/03022018240

Cited by 32 publications

(16 citation statements)

References 41 publications

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“…It is worth noting that SEM and SEM‐based CL petrographic analyses are time‐consuming and impractical to perform with the large quantity of samples required in industrial exploration. Some major and trace elements, such as nickel, are recognized as a proxy for palaeoproductivity (Tribovillard et al ., ) and exhibit a well‐correlated, direct relationship with biosiliceous allochems and reservoir properties (for example, TOC, porosity, permeability and brittleness) in the Cline Shale (Peng et al ., ). Portable and field‐deployable EDS XRF‐based elemental analysis from cores, outcrops or cuttings in the field is a rapid and cost‐effective way to discriminate favourable unconventional‐play sweet spots for the Cline Shale and other shale systems in industrial unconventional exploration.…”

Section: Discussionmentioning

confidence: 97%

“…All samples in this study have reached a thermal maturity (about 1·0% R o ; Table ) at which some degree of smectite illitization through the precipitation of mixed‐layer illite–smectite may have occurred (Hower et al ., ). The XRD data from previous research document the presence of illite–smectite mixed layers for the same samples used in this study (Peng et al ., in press). However, the precise mechanism and reaction condition for smectite illitization remains poorly understood.…”

Section: Discussionmentioning

confidence: 99%

“…X‐ray diffraction, TOC and Gas Research Institute (GRI) crushed‐rock porosity data collection for these same samples was conducted by Firewheel Energy, LLC of Salt Lake City, Utah, and compiled from Peng et al . (in press) (Table ). The XRD analysis was conducted using a Bruker D8 ADVANCE powder X‐ray diffractometer using copper‐spectrum radiation (40 kV, 100 mA) from a long line focus tube, a graphite monochromator in the diffracted beamline, and a vacuum device to minimize absorption of the X‐rays by air.…”

Section: Sampling and Methodsmentioning

confidence: 99%

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Quartz types in the Upper Pennsylvanian organic‐rich Cline Shale (Wolfcamp D), Midland Basin, Texas: Implications for silica diagenesis, porosity evolution and rock mechanical properties

Peng

Milliken

2020

Sedimentology

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Associate Editor -Catherine Reid ABSTRACTThe origin and form of quartz in mudrocks has significant implications for interpretation of depositional environments, diagenetic pathways, mechanisms of porosity reduction and rock mechanical-property evolution. Quartz types in the Upper Pennsylvanian Cline Shale, Midland Basin, Texas, were examined using a combination of field-emission scanning electron microscopy-based energy-dispersive spectroscopy elemental mapping (to determine mineralogy) and scanning electron microscopy-based cathodoluminescence imaging (to determine quartz types) with the goal of elucidating a high-resolution imaging protocol at the micrometre scale for shale petrology. Also, the unconfined compressive rock strength of shale samples with contrasting proportions of different quartz types was measured using Equotip Bambino analyses. The results suggest that extrabasinal detrital quartz, which accounts for an average of 26 vol.% of the rock in all analyzed samples, is the dominant form of quartz in the Cline Shale. The intergranular clay-size microquartz, which accounts for an average of 10 vol.% of the rock in all analyzed samples, is the dominant form of authigenic quartz. Dissolved radiolarians and sponge spicules are likely sources of silica for clay-size microquartz and other authigenic quartz showing pale-mauve to dark greyish cathodoluminescence colour. Some authigenic quartz in the form of intragranular pore filling and mollusc skeletal replacement displays bright-reddish cathodoluminescence colour, which may be associated with silica released at a different time in the rock's diagenetic history, such as during smectite illitization. Porosity reduction in the Cline Shale predominantly resulted from compaction because of extremely low intergranular volume and the general lack of early cementation. Quartz form significantly impacts rock mechanical properties in the Cline Shale: widely distributed intergranular clay-size microquartz cement is a major factor controlling rock strength. This correlation also applies to other mudrock successions of various geological ages, tectonic histories and lithologies.

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Section: Discussionmentioning

confidence: 97%

Section: Discussionmentioning

confidence: 99%

Section: Sampling and Methodsmentioning

confidence: 99%

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Quartz types in the Upper Pennsylvanian organic‐rich Cline Shale (Wolfcamp D), Midland Basin, Texas: Implications for silica diagenesis, porosity evolution and rock mechanical properties

Peng

Milliken

2020

Sedimentology

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“…Microscopically, the sealing character and sealing capacity were attributable to systematic differences in shale texture and fabric. ,, The sedimentary structure, mineral compositions, and arrangements, as well as the diagenesis process of mud shales, can directly influence the porosity, permeability, pore throat, and pore connectivity of the caprocks, thereby affect the sealing performance of the mud shale. ,− Fine-grained, parallel microstratification and high clay minerals content can improve the sealing capacity of mud shale. − , For the roof in the LM2 and LM3 members, the argillaceous shale and silty shale developed multilayers of centimeter-scale muddy bands and silty bands (Figure a,b), the well-developed laminar fabrics appear to enhance the sealing capacity…”

Section: Discussionmentioning

confidence: 99%

Sealing Mechanism of the Roof and Floor for the Wufeng-Longmaxi Shale Gas in the Southern Sichuan Basin

et al. 2020

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Exploration activities revealed that high-efficient sealings of the roof and floor for the Wufeng-Longmaxi (WF-LM) gas-bearing shales were the indispensable conditions for shale gas preservation and enrichment in the Sichuan Basin. However, little attention has been paid to their sealing mechanism and sealing model. In this paper, systematic core samplings (Ning-A and YY-B) and a series of supporting experiments (geochemical and rock components analysis, physical properties measurements, pore structure characterization, and sealing capacity tests) were carried out for further analyses and discussion. Results show that the roof and floor have four-level vertical sealing capacities for the WF-LM shale gas, where the direct roof is the argillaceous shale and silty shale of the LM1–2 and LM1–3 members (the middle and upper members of the first part of the Longmaxi Formation) and the floor is the nodular limestone of the Linxiang Formation (LX Fm.). Heterogeneous lithofacies and steady thickness of the roof and floor lead to strong lithologic sealing capacities. The roof and floor are characterized by higher density and water saturation, lower porosity and permeability, lower pore volumes, and poor pore connectivity, resulting in developing larger capillary pressure at the interface and thereby forming strong petrophysical sealing capacities. Based on the sealing model, the great sealing capacities are attributed to the well-developed laminar fabrics, lower TOC content, less (organic matter) OM-related pores, and the compacted clay mineral fragments reoriented into lamellar ones, as well as the unconnected clay-related interparticle pores in the roof shales and high breakthrough pressure in the floor. This study will provide guidance for evaluating the preservation condition and sweet spot prospecting of shale gas exploration in the Sichuan Basin.

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“…The pore network evolution is jointly affected by the depositional environment, diagenetic events, and OM thermal maturation. ,,− …”

Section: Controlling Factors On Pore Developmentmentioning

confidence: 99%

Advances in Microscopic Pore Structure Characterization of Fine-Grained Mudrocks

Wang

Cheng

2023

Energy Fuels

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The microscopic structure of the pore system in fine-grained mudrocks provides spaces for hydrocarbon percolation, migration, and occurrence. It exhibits strong heterogeneity due to the intimate mingling of organic matter (OM) and inorganic minerals and the intricate architecture of the internal network and dynamic changes along the diagenetic pathway and OM thermal maturation. The present review critically summarizes the advances in structure characterization, geological controlling factors, and heterogeneity of the pore system in mudrocks. The pore system in mudrocks can be divided into micro-, meso-, and macropores by diameters, OM-hosted, interparticles, and intraparticle pores by origin and distribution and connected and nonconnected pores according to whether they are connected. The commonly used pore structure characterization techniques can be classified into three categories: i.e., imaging, fluid invasion, and ray-related techniques. Their principles, experimental conditions, applicability, required sample sizes, detectable pore types and diameter ranges, advantages, and disadvantages have been comparatively summarized. To obtain more precise and comprehensive structural properties, multiple techniques are highly recommended to validate and complement each other. The depositional environment, diagenetic events, and OM thermal maturation jointly control the formation and evolution of the pore system. Differences in provenance and depositional background affect primary grain assemblages and thus changes in physical properties during burial depth. Diagenetic transformations mainly change the morphology and structure of mineral-related pores, while OM thermal maturation mainly controls that of OM-hosted pores. Furthermore, the pore structure of mudrocks generally shows strong heterogeneity, which can be effectively assessed by a point-counting porosity quantification and multifractal theory. Finally, we propose the challenges and prospects of microscopic pore structure characterization of mudrocks. More attention needs to be paid to quantifying OM-hosted and mineral-related pore volume fractions, effectively distinguishing connected and nonconnected pores, and comprehensively quantifying the coupled effect of diagenesis and hydrocarbon generation on pore network evolution. In conclusion, the most important aspect of this review is to summarize modern characterization methods and geological controls on pore structure development and propose prospects for unconventional reservoir characterization, with the hope of providing the ultimate knowledge to researchers engaged in unconventional shale oil and gas resources.

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Grain assemblages and diagenesis in organic-rich mudrocks, Upper Pennsylvanian Cline shale (Wolfcamp D), Midland Basin, Texas

Cited by 32 publications

References 41 publications

Quartz types in the Upper Pennsylvanian organic‐rich Cline Shale (Wolfcamp D), Midland Basin, Texas: Implications for silica diagenesis, porosity evolution and rock mechanical properties

Quartz types in the Upper Pennsylvanian organic‐rich Cline Shale (Wolfcamp D), Midland Basin, Texas: Implications for silica diagenesis, porosity evolution and rock mechanical properties

Sealing Mechanism of the Roof and Floor for the Wufeng-Longmaxi Shale Gas in the Southern Sichuan Basin

Advances in Microscopic Pore Structure Characterization of Fine-Grained Mudrocks

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