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Minerals
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Characterisation of Mudrocks: Textures and Mineralogy
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Characterisation of Mudrocks: Textures and Mineralogy

A special issue of Minerals (ISSN 2075-163X). This special issue belongs to the section "Mineral Deposits".

Deadline for manuscript submissions: closed (20 May 2020) | Viewed by 26035

Special Issue Editor

Dr. Jim Buckman

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Guest Editor
Institute of GeoEnergy Engineering, School of Energy Geoscience Infrastructure and Society, Heriot-Watt University, Riccarton, Edinburgh, Scotland EH14 4AS, UK
Interests: mudrocks; diagenesis; 3D modelling; scanning electron microscopy: X-Ray tomography; wettability; biomineralization
Special Issues, Collections and Topics in MDPI journals

Special Issue Information

Dear Colleagues,

Mudrocks are a volumetrically important part of many sedimentary basins, both in the present day and across geological time. Although often considered to be somewhat simple, or even of little research interest, recent research has indicated that mudrocks are highly heterogeneous in terms of texture and mineralogy at the micron to decimetre scale. Mudrocks are economically significant as seals for oil, gas, water, CO2 and H storage, as source rocks for unconventional oil and gas plays and an important engineering material in their own right. Characterisation of mudrocks in terms of texture and mineralogy is, therefore, important in determining variation in porosity, permeability and structural rigidity as well as the environment of deposition and diagenetic history. Techniques used in characterising mudrocks include, amongst others, scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-Ray tomography (XRT), neutron microscopy/diffraction, X-Ray fluorescence (XRF) and X-Ray diffraction (XRD).

Research papers, and review articles, on all aspects related to mudrock characterisation in the context of texture and mineralogy, at a variety of scales, are welcome, including articles on novel techniques under development as well as pertinent case studies, covering all areas where mudrocks play a significant role.

Dr. Jim Buckman
Guest Editor

Manuscript Submission Information

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Keywords

  • Mudrock microstructure
  • Mineralogy
  • Diagenesis
  • Structural rigidity
  • Environment of deposition
  • CO2 and H storage
  • Unconventional reservoirs

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Published Papers (8 papers)

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Editorial

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4 pages, 156 KiB  
Editorial
Editorial for Special Issue “Characterisation of Mudrocks: Textures and Mineralogy”
by Jim Buckman
Minerals 2021, 11(9), 1000; https://doi.org/10.3390/min11091000 - 14 Sep 2021
Viewed by 1401
Abstract
Mudrocks are a volumetrically important part of many sedimentary basins, both in the present day and across geological time [...] Full article
(This article belongs to the Special Issue Characterisation of Mudrocks: Textures and Mineralogy)

Research

Jump to: Editorial

17 pages, 5693 KiB  
Article
Mudrocks Lithofacies Characteristics and North-South Hydrocarbon Generation Difference of the Shahejie Formation in the Dongpu Sag
by Yuanfeng Li, Xiang Zeng, Jingong Cai, Xinyu Wang, Xiaoshui Mu and Yunxian Zhang
Minerals 2021, 11(5), 535; https://doi.org/10.3390/min11050535 - 19 May 2021
Cited by 6 | Viewed by 2238
Abstract
Lacustrine mudrocks are composed of minerals and organic matter (OM). The origin and preservation of OM are two controlling factors of the hydrocarbon generation capacity of mudrocks. It is a key method in source rock research to study the deposition process from the [...] Read more.
Lacustrine mudrocks are composed of minerals and organic matter (OM). The origin and preservation of OM are two controlling factors of the hydrocarbon generation capacity of mudrocks. It is a key method in source rock research to study the deposition process from the view of the OM and sedimentary environment. Following this idea, the reason for the discrepancy in hydrocarbon production between the northern and the southern part of Dongpu Sag is analyzed and discussed. The lacustrine mudrocks of the Shahejie Formation in Dongpu Sag are sampled and analyzed for information about mineralogy, microstructure, elemental geochemistry, and OM characteristics. The mudrocks are then divided into three lithofacies: silt-rich massive mudstone, homogeneous massive mudstone, and laminated mudstone. Each lithofacies shows distinct characteristics, and the hydrocarbon generation ability of them increases in sequence. Further discussion that the differences in hydrocarbon generation are caused by the sedimentary environment. The water depth, salinity, and reducibility of the sedimentary environments of these three lithofacies increase in sequence, as well. The correlation analysis indicates that it is the environment that controls the origin, accumulation, and preservation of OM in each lithofacies and then causes the great differences in hydrocarbon generation capacity. In Dongpu Sag, the proportion of laminated mudstone is much higher in the northern part, which leads to greater oil/gas production than the southern part. In research of source rocks, both the lithofacies characteristics and the sedimentary environments that control the characteristics should be studied. Full article
(This article belongs to the Special Issue Characterisation of Mudrocks: Textures and Mineralogy)
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23 pages, 8187 KiB  
Article
Sedimentation of the Kimmeridge Clay Formation in the Cleveland Basin (Yorkshire, UK)
by Elizabeth Atar, Andrew C. Aplin, Violaine Lamoureux-Var, Christian März and Thomas Wagner
Minerals 2020, 10(11), 977; https://doi.org/10.3390/min10110977 - 2 Nov 2020
Cited by 4 | Viewed by 3885
Abstract
Fine-grained sedimentary successions contain the most detailed record of past environmental conditions. High-resolution analyses of these successions yield important insights into sedimentary composition and depositional processes and are, therefore, required to contextualise and interpret geochemical data which are commonly used as palaeoclimate proxies. [...] Read more.
Fine-grained sedimentary successions contain the most detailed record of past environmental conditions. High-resolution analyses of these successions yield important insights into sedimentary composition and depositional processes and are, therefore, required to contextualise and interpret geochemical data which are commonly used as palaeoclimate proxies. The Kimmeridge Clay Formation (KCF) is a 500 m-thick mudstone succession deposited throughout the North Sea in the Late Jurassic and records environmental conditions through this time. Here, we present petrographic analyses (on 36 thin sections) on a 50 m section of a KCF core from the Cleveland Basin (Yorkshire, UK) to investigate controls on sedimentation in this region during the Tithonian, Late Jurassic. Facies descriptions demonstrate that deposition took place in a hydrodynamically variable environment in which the sediment origins, sediment dispersal mechanisms, and redox conditions fluctuated on the scale of thousands of years. Petrographic analyses show that the sediment comprises marine (algal macerals, calcareous fossils), detrital (quartz, clay, feldspar), and diagenetic (dolomite and authigenic kaolinite) components and that several sediment dispersal mechanisms influenced deposition and facilitated both the supply and preservation of terrestrial and marine organic material. This work provides a framework for the interpretation of geochemical palaeoclimate proxies and reinforces the importance of looking at the rock when interpreting whole-rock geochemical data. Full article
(This article belongs to the Special Issue Characterisation of Mudrocks: Textures and Mineralogy)
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38 pages, 8995 KiB  
Article
Lower Cretaceous Rodby and Palaeocene Lista Shales: Characterisation and Comparison of Top-Seal Mudstones at Two Planned CCS Sites, Offshore UK
by Richard H. Worden, Michael J. Allen, Daniel R. Faulkner, James E. P. Utley, Clare E. Bond, Juan Alcalde, Niklas Heinemann, R. Stuart Haszeldine, Eric Mackay and Saeed Ghanbari
Minerals 2020, 10(8), 691; https://doi.org/10.3390/min10080691 - 3 Aug 2020
Cited by 22 | Viewed by 5924
Abstract
Petroleum-rich basins at a mature stage of exploration and production offer many opportunities for large-scale Carbon Capture and Storage (CCS) since oil and gas were demonstrably contained by low-permeability top-sealing rocks, such as shales. For CCS to work, there must be effectively no [...] Read more.
Petroleum-rich basins at a mature stage of exploration and production offer many opportunities for large-scale Carbon Capture and Storage (CCS) since oil and gas were demonstrably contained by low-permeability top-sealing rocks, such as shales. For CCS to work, there must be effectively no leakage from the injection site, so the nature of the top-seal is an important aspect for consideration when appraising prospective CCS opportunities. The Lower Cretaceous Rodby Shale and the Palaeocene Lista Shale have acted as seals to oil and gas accumulations (e.g., the Atlantic and Balmoral fields) and may now play a critical role in sealing the Acorn and East Mey subsurface carbon storage sites. The characteristics of these important shales have been little addressed in the hydrocarbon extraction phase, with an understandable focus on reservoir properties and their influence on resource recovery rates. Here, we assess the characteristics of the Rodby and Lista Shales using wireline logs, geomechanical tests, special core analysis (mercury intrusion) and mineralogical and petrographic techniques, with the aim of highlighting key properties that identify them as suitable top-seals. The two shales, defined using the relative gamma log values (or Vshale), have similar mean pore throat radius (approximately 18 nm), splitting tensile strength (approximately 2.5 MPa) and anisotropic values of splitting tensile strength, but they display significant differences in terms of wireline log character, porosity and mineralogy. The Lower Cretaceous Rodby Shale has a mean porosity of approximately 14 %, a mean permeability of 263 nD (2.58 × 10−19 m2), and is calcite rich and has clay minerals that are relatively rich in non-radioactive phases such as kaolinite. The Palaeocene Lista Shale has a mean porosity of approximately 16% a mean permeability of 225 nD (2.21 × 10−19 m2), and is calcite free, but contains abundant quartz silt and is dominated by smectite. The 2% difference in porosity does not seem to equate to a significant difference in permeability. Elastic properties derived from wireline log data show that Young’s modulus, material stiffness, is very low (5 GPa) for the most shale (clay mineral)-rich Rodby intervals, with Young’s modulus increasing as shale content decreases and as cementation (e.g., calcite) increases. Our work has shown that Young’s modulus, which can be used to inform the likeliness of tensile failure, may be predictable based on routine gamma, density and compressive sonic logs in the majority of wells where the less common shear logs were not collected. The predictability of Young’s modulus from routine well log data could form a valuable element of CCS-site top-seal appraisals. This study has shown that the Rodby and Lista Shales represent good top-seals to the Acorn and East Mey CCS sites and they can hold CO2 column heights of approximately 380 m. The calcite-rich Rodby Shale may be susceptible to localised carbonate dissolution and increasing porosity and permeability but decreasing tendency to develop fracture permeability in the presence of injected CO2, as brittle calcite dissolves. In contrast, the calcite-free, locally quartz-rich, Lista Shale will be geochemically inert to injected CO2 but retain its innate tendency to develop fracture permeability (where quartz rich) in the presence of injected CO2. Full article
(This article belongs to the Special Issue Characterisation of Mudrocks: Textures and Mineralogy)
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17 pages, 7626 KiB  
Article
The Secret ‘After Life’ of Foraminifera: Big Things Out of Small
by Jim Buckman, Carol Mahoney, Christian März and Thomas Wagner
Minerals 2020, 10(6), 550; https://doi.org/10.3390/min10060550 - 18 Jun 2020
Cited by 2 | Viewed by 3106
Abstract
Calcareous and siliceous microorganisms are common components of mudrocks, and can be important in terms of stratigraphy and environmental interpretation. In addition, such microorganisms can have a significant ‘after life’, through post-mortem alteration, and represent a potential source of additional information about the [...] Read more.
Calcareous and siliceous microorganisms are common components of mudrocks, and can be important in terms of stratigraphy and environmental interpretation. In addition, such microorganisms can have a significant ‘after life’, through post-mortem alteration, and represent a potential source of additional information about the diagenetic and deformation history of the rock unit. Some examples of the latter are illustrated in this study from foraminifera within a Cretaceous black shale of Colombia. This includes foraminifera tests acting as understudied repositories of authigenic calcite cement, and of elements such as Ba, Zn, Fe and S through the formation of baryte, sphalerite and iron sulphides (pyrite, marcasite). Such repositories, within the body chambers of foraminiferal tests, can provide important windows into the diagenetic processes within mudstones. If calcite cement is not recognised or separated from biogenic calcite, the depositional calcite budget can be easily overestimated, skewing the application of mudrock classification schemes, and affecting environmental interpretation including that of productivity. The elements Ba, Zn and Fe (often in ratio with Al) are commonly utilised as geochemical proxies of environmental parameters (productivity, bottom water redox conditions, etc.). Therefore, the presence of significant amounts of baryte, sphalerite and pyrite-marcasite (within foraminifera) should be noted and their origins (source and timing) investigated based on their spatial relationships before making environmental deductions based on geochemical analysis alone. Additionally, commonly observed marginal shell damage of many of the observed foraminifera is reported. We interpret this damage, for the first time, as an indicator of lateral dissolution, brought about by horizontal foreshortening during orogenesis. This is also supported by the occurrence of microscale anastomosing horizontal to inclined baryte-filled fractures within the mudstone matrix. Full article
(This article belongs to the Special Issue Characterisation of Mudrocks: Textures and Mineralogy)
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19 pages, 9735 KiB  
Article
Unusual Components Within a Fine-Grained Contourite Deposit: Significance for Interpretation of Provenance and the Contourite Budget
by Shereef Bankole, Jim Buckman and Dorrik Stow
Minerals 2020, 10(6), 488; https://doi.org/10.3390/min10060488 - 27 May 2020
Cited by 7 | Viewed by 2525
Abstract
Deep-water contourite muds are an important component of many continental margin systems and are currently the focus of much interest amongst deep-water researchers. One outstanding gap in our knowledge of these systems is to understand and quantify a contourite budget, both at the [...] Read more.
Deep-water contourite muds are an important component of many continental margin systems and are currently the focus of much interest amongst deep-water researchers. One outstanding gap in our knowledge of these systems is to understand and quantify a contourite budget, both at the small (facies) scale and at the larger drift scale. A second problem concerns the establishing of robust criteria for discriminating between contourites and associated deepwater facies—turbidites and hemipelagites. This paper contributes to these topics by detailed examination of sediment composition, with a particular focus on potentially diagnostic components, within contourites and hemipelagites from the same depositional basin. Samples were selected from Pliocene to Quaternary muddy contourites from the Gulf of Cadiz (IODP 339) and examined by scanning electron microscopy. The presence of tunicate spicules, micro-bored shell fragments, and a particular species of coccolithophore, Braarudosphaera biglowii, all indicate derivation from shallow waters and hence lateral off-shelf supply. In contrast, micro-mudclasts and fragmented bioclasts are indicative of alongslope transport in bottom currents. A normal planktic component of the contourite muds shows a significant vertical input from pelagic settling. Such diagnostic components can also help in the discrimination between contourites, turbidites and hemipelagites. Full article
(This article belongs to the Special Issue Characterisation of Mudrocks: Textures and Mineralogy)
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16 pages, 7626 KiB  
Article
Fine-Scale Heterogeneity of Pyrite and Organics within Mudrocks: Scanning Electron Microscopy and Image Analysis at the Large Scale
by Jim Buckman, Anabel Aboussou, Onoriode Esegbue, Thomas Wagner and Gabriele Gambacorta
Minerals 2020, 10(4), 354; https://doi.org/10.3390/min10040354 - 16 Apr 2020
Cited by 5 | Viewed by 2792
Abstract
Mudrocks are highly heterogeneous in terms of both composition and fabric, with heterogeneities occurring at the submicron to centimetre plus scale. Such heterogeneities are relatively easy to visualise at the micron-scale through the use of modern scanning electron microscopy (SEM) techniques, but due [...] Read more.
Mudrocks are highly heterogeneous in terms of both composition and fabric, with heterogeneities occurring at the submicron to centimetre plus scale. Such heterogeneities are relatively easy to visualise at the micron-scale through the use of modern scanning electron microscopy (SEM) techniques, but due to their inherent fine grain size, can be difficult to place within the greater context of the mudrock as a whole, or to visualise variation when viewed at a centimetre scale. The utilisation of SEM to collect automated high-resolution backscattered (BSE) images (tiles) over whole, polished thin-sections presents a potential large data bank on compositional and fabric changes that can be further processed using simple image analysis techniques to extract data on compositional variation. This can then be plotted graphically in 2D as colour contoured distribution maps to illustrate any observed variability. This method enables the easy visualisation of micron-scale heterogeneity present in mudrock, which are here illustrated and discussed for pyrite and organic content at the larger (thin-section) centimetre scale. This does not require the use of other techniques such as energy dispersive x-ray (EDX) mapping to identify phases present, but instead utilizes BSE images that may already have been collected for textural fabric studies. The technique can also be applied to other phases in mudrocks, such as carbonates and silicates, as well as porosity. Data can also be extracted and used in a similar fashion to bulk compositional analytical techniques such as inductively coupled plasma-atomic emission microscopy (ICP-AES) and carbon, nitrogen and sulphur (CNS) analysis, for average organic carbon and percentage pyrite. Full article
(This article belongs to the Special Issue Characterisation of Mudrocks: Textures and Mineralogy)
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27 pages, 14211 KiB  
Article
Characteristics of Organic Matter Particles and Organic Pores of Shale Gas Reservoirs: A Case Study of Longmaxi-Wufeng Shale, Eastern Sichuan Basin
by Guochang Wang, Shengxiang Long, Yongmin Peng and Yiwen Ju
Minerals 2020, 10(2), 137; https://doi.org/10.3390/min10020137 - 6 Feb 2020
Cited by 10 | Viewed by 3225
Abstract
Heterogeneity of organic matter (OM), including size, type, and organic pores within OM, is being recognized along with increasing study using SEM images. Especially, the contribution of organic pores to the entire pore system should be better understood to aid in the evaluation [...] Read more.
Heterogeneity of organic matter (OM), including size, type, and organic pores within OM, is being recognized along with increasing study using SEM images. Especially, the contribution of organic pores to the entire pore system should be better understood to aid in the evaluation of shale reservoirs. This research observed and quantitatively analyzed over 500 SEM images of 19 core samples from Longmaxi-Wufeng Shale in the eastern Sichuan Basin to summarize the features of OM particles and OM-hosted pores and their evolution during burial. The features of organic pores as well as the embedded minerals within OM particles enables to recognize four different type of OM particles. The organic pore features of each type of OM particles were quantitatively described using parameters such as pore size distribution (PSD), pore geometry, and organic porosity. The PSD of weakly or undeformed porous pyrobitumen indicates that the large organic pores (usually 200 nm to 1 um) is less common than small pores but the major contributor to organic porosity. The organic porosity of OM particles covers a large range of 1–35%, indicating a high heterogeneity among OM particles. Based on analysis of 81 OM particles, the average of organic porosity of the five samples were calculated and ranges from 3% to 12%. In addition, samples from well JY1 have higher organic porosity than JY8. These results helped to reveal how significant the organic pores are for shale gas reservoirs. In addition to presenting many examples of OM particles, this research should significantly improve the understanding of type and evolution of OM particles and contribution of OM-hosted pores to the entire pore system of high to over mature shale. Full article
(This article belongs to the Special Issue Characterisation of Mudrocks: Textures and Mineralogy)
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