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Volume 31 Issue 6
Dec.  2020
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Kouqi Liu, Natalia Zakharova, Thomas Gentzis, Adedoyin Adeyilola, Humberto Carvajal-Ortiz, Hallie Fowler. Microstructure Characterization of a Biogenic Shale Gas Formation—Insights from the Antrim Shale, Michigan Basin. Journal of Earth Science, 2020, 31(6): 1229-1240. doi: 10.1007/s12583-020-1344-4
Citation: Kouqi Liu, Natalia Zakharova, Thomas Gentzis, Adedoyin Adeyilola, Humberto Carvajal-Ortiz, Hallie Fowler. Microstructure Characterization of a Biogenic Shale Gas Formation—Insights from the Antrim Shale, Michigan Basin. Journal of Earth Science, 2020, 31(6): 1229-1240. doi: 10.1007/s12583-020-1344-4

Microstructure Characterization of a Biogenic Shale Gas Formation—Insights from the Antrim Shale, Michigan Basin

doi: 10.1007/s12583-020-1344-4
More Information
  • Biogenic gas shales, predominantly microbial in origin, form an important class of organic-rich shale reservoirs with a significant economic potential. Yet large gaps remain in the understanding of their gas generation, storage, and transport mechanisms, as previous studies have been largely focused on mature thermogenic shale reservoirs. In this study, the pore structure of 18 Antrim Shale samples was characterized using gas adsorption (CO2 and N2). The results show that most of the Antrim Shale samples are rich in organic matter content (0.58 wt.% to 14.15 wt.%), with highest values found in the Lachine and Norwood members. Samples from the Paxton Member, characterized by lower organic content, have smaller micropore surface area and micropore volume but larger meso-macro pore surface area and volume. The deconvolution results of the pore size distribution from the N2 adsorption indicate that all of the tested Antrim Shale samples have similar pore groups. Organic matter in the Antrim Shale hosts micro pores instead of meso-macro pores, while clay minerals host both micro and meso-macro pores. Mineral-related pores play a primary role in the total porosity. The biogenic Antrim Shale, therefore, has different pore structures from other well-studied thermogenic gas shales worldwide.
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  • Chalmers, G.R., Bustin, R.M., Power, I.M., 2012. Characterization of Gas Shale Pore Systems by Porosimetry, Pycnometry, Surface Area, and Field Emission Scanning Electron Microscopy/Transmission Electron Microscopy Image Analyses:Examples from the Barnett, Woodford, Haynesville, Marcellus, and Doig Units. AAPG Bulletin, 96(6):1099-1119. https://doi.org/10.1306/10171111052 doi:  10.1306/10171111052
    Chen, J., Xiao, X. M., 2014. Evolution of Nanoporosity in Organic-Rich Shales during Thermal Maturation. Fuel, 129:173-181. https://doi.org/10.1016/j.fuel.2014.03.058 doi:  10.1016/j.fuel.2014.03.058
    Clarkson, C. R., Solano, N., Bustin, R. M., et al., 2013. Pore Structure Characterization of North American Shale Gas Reservoirs Using USANS/SANS, Gas Adsorption, and Mercury Intrusion. Fuel, 103:606-616. https://doi.org/10.1016/j.fuel.2012.06.119 doi:  10.1016/j.fuel.2012.06.119
    Colosimo, F., Thomas, R., Lloyd, J. R., et al., 2016. Biogenic Methane in Shale Gas and Coal Bed Methane:A Review of Current Knowledge and Gaps. International Journal of Coal Geology, 165:106-120. https://doi.org/10.1016/j.coal.2016.08.011 doi:  10.1016/j.coal.2016.08.011
    Currie, B. J., 2016. Stratigraphy of the Upper Devonian-Lower Mississippian Michigan Basin: Review and Revision with an Emphasis on the Ellsworth Petroleum System: [Dissertation]. Geological and Environmental Sciences, Western Michigan University, Kalamazoo
    Curtis, J. B., 2002. Fractured Shale-Gas Systems. AAPG Bulletin, 86(11):1921-1938 http://www.nrcresearchpress.com/servlet/linkout?suffix=refg13/ref13&dbid=16&doi=10.1139%2Fcjes-2014-0188&key=10.1306%2F61EEDDBE-173E-11D7-8645000102C1865D
    Do, D. D., Do, H. D., 2003. Pore Characterization of Carbonaceous Materials by DFT and GCMC Simulations:A Review. Adsorption Science & Technology, 21(5):389-423. https://doi.org/10.1260/026361703769645753 doi:  10.1260/026361703769645753
    Garrido, J., Linares-Solano, A., Martin-Martinez, J. M., et al., 1987. Use of Nitrogen vs. Carbon Dioxide in the Characterization of Activated Carbons. Langmuir, 3(1):76-81. https://doi.org/10.1021/la00073a013 doi:  10.1021/la00073a013
    Groen, J. C., Peffer, L. A. A., Pérez-Ramı́rez, J., 2003. Pore Size Determination in Modified Micro-and Mesoporous Materials. Pitfalls and Limitations in Gas Adsorption Data Analysis. Microporous and Mesoporous Materials, 60(1/2/3):1-17. https://doi.org/10.1016/s1387-1811(03)00339-1 doi:  10.1016/s1387-1811(03)00339-1
    Hill, R. J., Tang, Y. C., Kaplan, I. R., 2003. Insights into Oil Cracking Based on Laboratory Experiments. Organic Geochemistry, 34(12):1651-1672. https://doi.org/10.1016/s0146-6380(03)00173-6 doi:  10.1016/s0146-6380(03)00173-6
    Hopkins, C. W., Frantz, J. H. Jr, Hill, D. G., et al., 1995. Estimating Fracture Geometry in the Naturally Fractured Antrim Shale. In: SPE Annual Technical Conference and Exhibition. SPE Annual Technical Conference and Exhibition, Society of Petroleum Engineers, Oct. 22-25, Dallas, Texas
    Jarvie, D. M., Claxton, B. L., Henk, F., et al., 2001. Oil and Shale Gas from the Barnett Shale, Ft. Worth Basin, Texas. Talk Presented at the AAPG National Convention, Jun. 3-6, 2001, Denver, CO
    Jarvie, D. M., Hill, R. J., Ruble, T. E., et al., 2007. Unconventional Shale-Gas Systems:The Mississippian Barnett Shale of North-Central Texas as One Model for Thermogenic Shale-Gas Assessment. AAPG Bulletin, 91(4):475-499. https://doi.org/10.1306/12190606068 doi:  10.1306/12190606068
    Ji, L. M., Su, L., Wu, Y. D., et al., 2017. Pore Evolution in Hydrocarbon-Generation Simulation of Organic Matter-Rich Muddy Shale. Petroleum Research, 2(2):146-155. https://doi.org/10.1016/j.ptlrs.2017.07.002 doi:  10.1016/j.ptlrs.2017.07.002
    Jia, B., Tsau, J. S., Barati, R., 2019. A Review of the Current Progress of CO2 Injection EOR and Carbon Storage in Shale Oil Reservoirs. Fuel, 236:404-427. https://doi.org/10.1016/j.fuel.2018.08.103 doi:  10.1016/j.fuel.2018.08.103
    Ko, L. T., Ruppel, S. C., Loucks, R. G., et al., 2018. Pore-Types and Pore-Network Evolution in Upper Devonian-Lower Mississippian Woodford and Mississippian Barnett Mudstones:Insights from Laboratory Thermal Maturation and Organic Petrology. International Journal of Coal Geology, 190:3-28. https://doi.org/10.1016/j.coal.2017.10.001 doi:  10.1016/j.coal.2017.10.001
    Krüger, M., van Berk, W., Arning, E. T., et al., 2014. The Biogenic Methane Potential of European Gas Shale Analogues:Results from Incubation Experiments and Thermodynamic Modelling. International Journal of Coal Geology, 136:59-74. https://doi.org/10.1016/j.coal.2014.09.012 doi:  10.1016/j.coal.2014.09.012
    Li, J. Q., Zhang, P. F., Lu, S. F., et al., 2019. Scale-Dependent Nature of Porosity and Pore Size Distribution in Lacustrine Shales:An Investigation by BIB-SEM and X-Ray CT Methods. Journal of Earth Science, 30(4):823-833. https://doi.org/10.1007/s12583-018-0835-z doi:  10.1007/s12583-018-0835-z
    Liu, B., Song, Y., Zhu, K., et al., 2020. Mineralogy and Element Geochemistry of Salinized Lacustrine Organic-Rich Shale in the Middle Permian Santanghu Basin:Implications for Paleoenvironment, Provenance, Tectonic Setting and Shale Oil Potential. Marine and Petroleum Geology, 120:104569. https://doi.org/10.1016/j.marpetgeo.2020.104569 doi:  10.1016/j.marpetgeo.2020.104569
    Liu, K. Q., Ostadhassan, M., Gentzis, T., et al., 2018. Characterization of Geochemical Properties and Microstructures of the Bakken Shale in North Dakota. International Journal of Coal Geology, 190:84-98. https://doi.org/10.1016/j.coal.2017.08.006 doi:  10.1016/j.coal.2017.08.006
    Liu, K. Q., Ostadhassan, M., Zhou, J., et al., 2017. Nanoscale Pore Structure Characterization of the Bakken Shale in the USA. Fuel, 209:567-578. https://doi.org/10.1016/j.fuel.2017.08.034 doi:  10.1016/j.fuel.2017.08.034
    Liu, K. Q., Wang, L., Ostadhassan, M., et al., 2019. Nanopore Structure Comparison between Shale Oil and Shale Gas:Examples from the Bakken and Longmaxi Formations. Petroleum Science, 16(1):77-93. https://doi.org/10.1007/s12182-018-0277-3 doi:  10.1007/s12182-018-0277-3
    Loucks, R. G., Reed, R. M., Ruppel, S. C., et al., 2012. Spectrum of Pore Types and Networks in Mudrocks and a Descriptive Classification for Matrix-Related Mudrock Pores. AAPG Bulletin, 96(6):1071-1098. https://doi.org/10.1306/08171111061 doi:  10.1306/08171111061
    Ma, Y. Z., Holditch, S., 2015. Unconventional Oil and Gas Resources Handbook: Evaluation and Development. Gulf Professional Publishing
    Manger, K. C., Oliver, S. J. P., Curtis, J. B., et al., 1991. Geologic Influences on the Location and Production of Antrim Shale Gas, Michigan Basin. Low Permeability Reservoirs Symposium, Society of Petroleum Engineers, Apr. 15-17, Denver, Colorado. SPE 21854
    Martini, A. M., Walter, L. M., Ku, T. C. W., et al., 2003. Microbial Production and Modification of Gases in Sedimentary Basins:A Geochemical Case Study from a Devonian Shale Gas Play, Michigan Basin. AAPG Bulletin, 87(8):1355-1375. https://doi.org/10.1306/031903200184 doi:  10.1306/031903200184
    Pfeifer, P., Wu, Y. J., Cole, M. W., et al., 1989. Multilayer Adsorption on a Fractally Rough Surface. Physical Review Letters, 62(17):1997-2000. https://doi.org/10.1103/physrevlett.62.1997 doi:  10.1103/physrevlett.62.1997
    Rebata-Landa, V., Santamarina, J. C., 2006. Mechanical Limits to Microbial Activity in Deep Sediments. Geochemistry, Geophysics, Geosystems, 7(11). https://doi.org/10.1029/2006gc001355 doi:  10.1029/2006gc001355
    Reeves, S. R., Cox, D. O., Smith, M. B., et al., 1993. Stimulation Technology in the Antrim Shale. In: SPE Gas Technology Symposium. SPE Gas Technology Symposium, Society of Petroleum Engineers, Jun. 28-30, Calgary, Alberta
    Rice, D. D., 1993. Biogenic Gas: Controls, Habitats, and Resource Potential. United States Geological Survey, Professional Paper. 1570
    Rouquerol, J., Avnir, D., Fairbridge, C. W., et al., 1994. Recommendations for the Characterization of Porous Solids (Technical Report). Pure and Applied Chemistry, 66(8):1739-1758. https://doi.org/10.1351/pac199466081739 doi:  10.1351/pac199466081739
    Sahouli, B., Blacher, S., Brouers, F., 1997. Applicability of the Fractal FHH Equation. Langmuir, 13(16):4391-4394. https://doi.org/10.1021/la962119k doi:  10.1021/la962119k
    Schulz, H. M., Biermann, S., van Berk, W., et al., 2015. From Shale Oil to Biogenic Shale Gas:Retracing Organic-Inorganic Interactions in the Alum Shale (Furongian-Lower Ordovician) in Southern Sweden. AAPG Bulletin, 99(5):927-956. https://doi.org/10.1306/10221414014 doi:  10.1306/10221414014
    Strąpoć, D., Mastalerz, M., Dawson, K., et al., 2011. Biogeochemistry of Microbial Coal-Bed Methane. Annual Review of Earth and Planetary Sciences, 39(1):617-656. https://doi.org/10.1146/annurev-earth-040610-133343 doi:  10.1146/annurev-earth-040610-133343
    Stolper, D. A., Martini, A. M., Clog, M., et al., 2015. Distinguishing and Understanding Thermogenic and Biogenic Sources of Methane Using Multiply Substituted Isotopologues. Geochimica et Cosmochimica Acta, 161:219-247. https://doi.org/10.1016/j.gca.2015.04.015 doi:  10.1016/j.gca.2015.04.015
    Wang, Y., Liu, L. F., Zheng, S. S., et al., 2019. Full-Scale Pore Structure and Its Controlling Factors of the Wufeng-Longmaxi Shale, Southern Sichuan Basin, China:Implications for Pore Evolution of Highly Overmature Marine Shale. Journal of Natural Gas Science and Engineering, 67:134-146. https://doi.org/10.1016/j.jngse.2019.04.020 doi:  10.1016/j.jngse.2019.04.020
    Wuchter, C., Banning, E., Mincer, T. J., et al., 2013. Microbial Diversity and Methanogenic Activity of Antrim Shale Formation Waters from Recently Fractured Wells. Frontiers in Microbiology, 4:367. https://doi.org/10.3389/fmicb.2013.00367 doi:  10.3389/fmicb.2013.00367
    Yang, R., He, S., Yi, J. Z., et al., 2016. Nano-Scale Pore Structure and Fractal Dimension of Organic-Rich Wufeng-Longmaxi Shale from Jiaoshiba Area, Sichuan Basin:Investigations Using FE-SEM, Gas Adsorption and Helium Pycnometry. Marine and Petroleum Geology, 70:27-45. https://doi.org/10.1016/j.marpetgeo.2015.11.019 doi:  10.1016/j.marpetgeo.2015.11.019
    Zhang, Q., Liu, R. H., Pang, Z. L., et al., 2016. Characterization of Microscopic Pore Structures in Lower Silurian Black Shale(S1l), Southeastern Chongqing, China. Marine and Petroleum Geology, 71:250-259. https://doi.org/10.1016/j.marpetgeo.2015.12.015 doi:  10.1016/j.marpetgeo.2015.12.015
    Zhou, W. D., Xie, S. Y., Bao, Z. Y., et al., 2019. Chemical Compositions and Distribution Characteristics of Cements in Longmaxi Formation Shales, Southwest China. Journal of Earth Science, 30(5):879-892. https://doi.org/10.1007/s12583-019-1013-7 doi:  10.1007/s12583-019-1013-7
    Zoback, M. D., Kohli, A. H., 2019. Unconventional Reservoir Geomechanics. Cambridge University Press, Cambridge
    Zuo, J. X., Peng, S. C., Qi, Y. P., et al., 2018. Carbon-Isotope Excursions Recorded in the Cambrian System, South China:Implications for Mass Extinctions and Sea-Level Fluctuations. Journal of Earth Science, 29(3):479-491. https://doi.org/10.1007/s12583-017-0963-x doi:  10.1007/s12583-017-0963-x
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Microstructure Characterization of a Biogenic Shale Gas Formation—Insights from the Antrim Shale, Michigan Basin

doi: 10.1007/s12583-020-1344-4

Abstract: Biogenic gas shales, predominantly microbial in origin, form an important class of organic-rich shale reservoirs with a significant economic potential. Yet large gaps remain in the understanding of their gas generation, storage, and transport mechanisms, as previous studies have been largely focused on mature thermogenic shale reservoirs. In this study, the pore structure of 18 Antrim Shale samples was characterized using gas adsorption (CO2 and N2). The results show that most of the Antrim Shale samples are rich in organic matter content (0.58 wt.% to 14.15 wt.%), with highest values found in the Lachine and Norwood members. Samples from the Paxton Member, characterized by lower organic content, have smaller micropore surface area and micropore volume but larger meso-macro pore surface area and volume. The deconvolution results of the pore size distribution from the N2 adsorption indicate that all of the tested Antrim Shale samples have similar pore groups. Organic matter in the Antrim Shale hosts micro pores instead of meso-macro pores, while clay minerals host both micro and meso-macro pores. Mineral-related pores play a primary role in the total porosity. The biogenic Antrim Shale, therefore, has different pore structures from other well-studied thermogenic gas shales worldwide.

Kouqi Liu, Natalia Zakharova, Thomas Gentzis, Adedoyin Adeyilola, Humberto Carvajal-Ortiz, Hallie Fowler. Microstructure Characterization of a Biogenic Shale Gas Formation—Insights from the Antrim Shale, Michigan Basin. Journal of Earth Science, 2020, 31(6): 1229-1240. doi: 10.1007/s12583-020-1344-4
Citation: Kouqi Liu, Natalia Zakharova, Thomas Gentzis, Adedoyin Adeyilola, Humberto Carvajal-Ortiz, Hallie Fowler. Microstructure Characterization of a Biogenic Shale Gas Formation—Insights from the Antrim Shale, Michigan Basin. Journal of Earth Science, 2020, 31(6): 1229-1240. doi: 10.1007/s12583-020-1344-4
  • The recent boom in hydrocarbon production from unconventional reservoirs has led to significant advances in understanding of the microstructure and petrophysical properties of organic-rich shales. However, most of the shale gas formations being developed and extensively studied in the United States are thermogenic systems, such as Bakken Shale (in the Williston Basin), Barnett Shale (in the Fort Worth Basin), Marcellus Shale (in the Appalachian Basin), and Woodford Shale (in the Arkoma Basin) (Jia et al., 2019; Liu et al., 2019; Zoback and Kohli, 2019; Ma and Holditch, 2015). In China, the thermogenic shale gas reservoirs such as Longmaxi Shale (Zhou et al., 2019) and Niutitang Shale (Li et al., 2019; Zuo et al., 2018) are also deeply studied. Hydrocarbons in the thermogenic systems are generated from thermal cracking of kerogen during burial, with increasing maturation at higher temperatures (Liu et al., 2020). In contrast, biogenic gas shale formations occur at shallower depths, where methane is produced by a consortium of bacteria and methanogenic archaea through breaking down and biodegradation of organic matter (Colosimo et al., 2016). Immature biogenic gas shales, which are estimated to comprise more than 20% of the world's gas resources (Martini et al., 2003; Rice, 1993), remain poorly understood. Pore structure, in particular, plays a very important role in biogenic shales. In addition to the gas storage and transport, it also determines the amount of surface area available for microbial colonization, and controls the supply of nutrients and the ability of microbes to migrate within the formation (Krüger et al., 2014; Rebata-Landa and Santamarina, 2006). Thus, quantifying the distribution of pore sizes and describing pore morphology in biogenic gas shales is essential for understanding a wide range of processes related to gas generation and storage mechanisms.

    The Upper-Devonian Antrim Shale in the Michigan Basin is one of the few biogenic and mixed-origin gas plays in the United States (Curtis, 2002; Manger et al., 1991). The Antrim Shale consists of finely laminated, silty, pyritic, black shales interbedded with gray and green shales and carbonate units (Martini et al., 2003). The formation is subdivided into four members based on the differences in mineralogy and organic content (Fig. 1). The black-shale Norwood and Lachine members have the highest TOC and are main production targets, while the gray to black Paxton and Upper Antrim members have lower TOC and higher carbonate content (Martini et al., 2003; Curtis, 2002). Previous studies of the Antrim Shale primarily have been focused on the hydrogeochemistry and the history of methanogenesis (e.g., Schulz et al., 2015; Stolper et al., 2015; Krüger et al., 2014; Wuchter et al., 2013), as well as on understanding overall production trends and fracture distribution in the Antrim Formation (e.g., Curtis, 2002; Hopkins et al., 1995; Manger et al., 1991). The pore structures of the Antrim Shale are still poorly understood.

    Figure 1.  The Antrim Shale Formation, Michigan Basin. (a) Isopach map of the Lower Antrim, which includes the Norwood, Paxton and Lachine members, showing the location of the sampled core well (adopted from Currie, 2016). (b) Gamma-ray (GR) well log from the Krocker 1-17 well, with marked boundaries between individual members of the Antrim Shale. Higher GR values correspond to black organic-rich shales (the Norwood and Lachine members).

    In this study, we selected 18 samples from the three lower members of the Antrim Shale and performed pore structure analysis using gas adsorption experiments. This research aims at answering the following two questions: (1) what are the characteristics of the pore structures of the Antrim Shale? (2) What is the difference between the pore structures of the biogenic Antrim Shale and other known thermogenic gas shales?

  • In order to study the pore structures of the Antrim Shale, 18 core samples (8 samples from the Lachine Member, 5 samples from the Paxton Member and 5 samples from the Norwood Member) were selected from a deep drill hole (Krocker 1-17) near the center of the basin (Fig. 1). The samples were selected within the thickest part of the Antrim Shale to target intervals of known mineral composition characterized using the X-ray diffraction (XRD) method at the Michigan Geological Repository for Research and Education (MGRRE) in Kalamazoo, MI. Samples were crushed into powder and loaded into the X-ray diffractometer. The relative mineral percentages were estimated by calculating the curve of the major peaks of each mineral.

  • The instrument utilized was a Rock-Eval 6 Turbo unit (RE6) at the facilities of the Core Laboratories in Houston, TX. The Shale Play® pyrolysis method was used for this study. This method was developed by the IFP Rock-Eval methods to characterize tight, fractured, and hybrid shale plays as well as shale oil systems. The temperature program of this method has been explained in Liu et al. (2018). Briefly, the initial temperature was set at 100 ℃ and then increased immediately to 200 ℃ at 25 ℃/min. The temperature was held isothermal at 200 ℃ for 3 min to complete the thermal extraction of the lightest hydrocarbon fraction (Sh0). From 200 ℃, the temperature was further increased to 350 ℃ at 25 ℃/min, staying there for 3 min for the thermal extraction of the medium/heavy hydrocarbon fraction (Sh1). The temperature was then increased from 350 to 650 ℃ at 25 ℃/min to achieve thermal cracking of the NSO (nitrogen, sulfur and oxygen) or kerogen fraction (Sh2). It should be noted that the sum of Sh0 and Sh1 is equivalent to the S1 of the Basic/ Bulk-Rock method of IFP and the Sh2 is equivalent to the S2 parameter of the same method. Total organic carbon (TOC) content was determined by pyrolysis.

  • Prior to gas adsorption, all samples were crushed into powder with a size less than 250 µm (60 mesh). The powdered samples were degassed for at least 10 h at 105 ℃ to remove the moisture and volatiles. The N2 adsorption and CO2 adsorption were performed at the temperature of 77 K (-196 ℃) and 273 K (0 ℃), respectively. Due to the working temperature and the kinetics difference of the N2 and CO2 molecules, N2 adsorption is applied for the meso-macro pore characterization (pores > 2 nm) while the CO2 adsorption is employed for the microspore characterization (pores < 2 nm) (Garrido et al., 1987). The gas adsorption volume of N2 adsorption experiments was measured over the relative equilibrium adsorption pressure (p/p0) range of 0.01–0.99, while the gas adsorption volume of CO2 adsorption experiments was measured over the relative equilibrium adsorption pressure (p/p0) range of 0.001–0.03. The instrument used for the gas adsorption was the Micromeritics® Tristar Ⅱ apparatus. The pore size distribution of the shale samples using the N2 and CO2 adsorption was calculated by using the density functional theory (Do and Do, 2003).

  • SEM images were obtained using an FEI Quanta model 250 field emission SEM on uncoated, freshly broken (rough), and argon ion-milled (smoothed) surfaces prepared with a Leica EM TIC 020 argon ion mill. Secondary electron and backscattered electron images were obtained at low electron beam energy (10–15 keV) operating in a high-pressure vacuum chamber environment at 59–62 Pa (0.000 9 psi).

  • According to XRD data, clay minerals and quartz are the two main components of all three lower members of the Antrim Shale (Table 1). The average content of clays and quartz for the 18 samples are 58.8 wt.% and 29.3 wt.%, respectively. Compared to samples from the Lachine and Norwood members, samples from the Paxton Member have a larger amount of calcite and a smaller average amount of clay minerals. Samples from the Norwood Member have a higher average content of quartz and a lower average content of pyrite than samples from the Lachine Member. Rock-Eval pyrolysis results indicate that the TOC of the samples in the Lachine and Norwood members is greater than in the Paxton Member (Table 2). These results agree with previous studies, which shows that the Lachine and Norwood members are more organic-rich and are the main target zone for gas production (Reeves et al., 1993). The Tmax values of these shale samples range from 426 to 443 ℃, indicating that the Antrim Shale is in the immature to early oil window (Jarvie et al., 2001). However, the three lowest Tmax values (426–428 ℃) are unreliable. They were obtained in samples 9–11 from the Paxton Member, which has the lowest TOC content as well as the lowest combined Sh0 and Sh1 (indicative of in-situ and sorbed hydrocarbons) and also the lowest Sh2 (indicative of the remaining hydrocarbon generation potential) values. As a result of the very low Sh2 values of these three samples, the corresponding Tmax values are considered to be unreliable and do not reflect the level of thermal maturity of the Paxton Member in this drill hole. The Paxton Member is considered to be a reservoir rather than a source rock in this location.

    Samples Depth (ft) Members Minerals (wt.%)
    Quartz Plagioclase K feldspar Calcite Dolomite Pyrite Clay
    1 3 260.8 Lachine 25 2 1 0 7 3 62
    2 3 270.9 27 2 1 0 2 3 65
    3 3 277.5 25 0 0 0 5 20 50
    4 3 297.2 29 2 0 0 3 1 65
    5 3 310.3 28 1 1 0 5 5 60
    6 3 320.3 26 2 1 0 1 5 65
    7 3 340.3 29 2 1 0 2 6 60
    8 3 350.3 25 1 0 5 7 5 57
    9 3 360.4 Paxton 25 1 1 5 8 2 58
    10 3 371.2 27 1 2 2 2 3 63
    11 3 379.3 30 1 1 21 3 1 43
    12 3 389.7 31 1 1 5 2 2 58
    13 3 399.5 40 1 1 5 4 2 47
    14 3 410.5 Norwood 32 1 1 0 0 3 63
    15 3 420.8 41 1 1 0 1 1 55
    16 3 430.7 26 1 1 2 1 4 65
    17 3 441.1 35 0 2 2 1 4 56
    18 3 451.3 27 1 1 1 1 2 67

    Table 1.  Mineral composition of Antrim Shale samples, data courtesy of the Michigan Geological Repository for Research and Education (MGRRE)

    Samples Depth (ft) TOC
    (wt.%)
    Sh0
    (mg HC/g)
    Sh1
    (mg HC/g)
    Sh2
    (mg HC/g)
    Tmax
    (℃)
    1 3 260.8 7.61 2.61 4.36 31.97 440
    2 3 270.9 4.43 1.42 3.54 14.35 437
    3 3 277.5 7.42 2.59 4.38 26.74 439
    4 3 297.2 1.84 0.33 1.81 5.37 426
    5 3 310.3 8.83 2.69 3.81 36.83 441
    6 3 320.3 8.76 2.67 3.94 31.43 438
    7 3 340.3 9.00 2.13 3.23 51.31 445
    8 3 350.3 1.43 0.23 1.13 3.74 431
    9 3 360.4 0.58 0.15 0.97 1.91 426
    10 3 371.2 0.59 0.13 0.73 1.55 428
    11 3 379.3 0.23 0.07 0.26 0.60 426
    12 3 389.7 1.50 0.42 1.89 5.36 435
    13 3 399.5 2.26 0.61 2.16 9.00 439
    14 3 410.5 14.15 3.76 4.53 69.11 439
    15 3 420.8 10.80 2.92 4.09 44.48 442
    16 3 430.7 1.88 0.34 2.19 6.89 432
    17 3 441.1 12.00 3.49 4.60 39.54 443
    18 3 451.3 7.49 2.10 3.44 23.78 442

    Table 2.  Selected geochemical parameters of the Antrim Shale samples

  • The CO2 adsorption isotherms of the Antrim Shale samples from the three different members show the same increasing trend as the relative pressure increases (Fig. 2). Under the same relative pressure, the adsorption quantity exhibits some variability between the samples from each member, indicating that the microstructure of these samples is not the same. Table 3 summarizes the micropore structure information of the Antrim Shale samples. The average micropore surface area and the micropore volume of the samples from the Paxton Member are the smallest among all the samples. The samples from the Norwood Member have the largest average micropore surface area (10.483 64 m2/g) and micropore volume (0.003 26 cm3/g).

    Figure 2.  CO2 adsorption isotherms of the Antrim Shale samples (note different vertical scale on the graphs). (a) Lachine Member; (b) Paxton Member; (c) Norwood Member.

    Samples Depth (ft) Members Micropore information
    Micropore area (m2/g) Micropore volume (cm3/g)
    1 3 260.8 Lachine 6.787 23 0.002 11
    2 3 270.9 6.504 05 0.002 07
    3 3 277.5 8.498 81 0.002 70
    4 3 297.2 4.837 48 0.001 49
    5 3 310.3 9.254 33 0.002 82
    6 3 320.3 10.077 13 0.003 13
    7 3 340.3 7.664 15 0.002 43
    8 3 350.3 5.630 57 0.001 70
    9 3 360.4 Paxton 5.520 68 0.001 70
    10 3 371.2 6.256 98 0.001 94
    11 3 379.3 3.234 46 0.000 99
    12 3 389.7 4.377 55 0.001 40
    13 3 399.5 5.073 31 0.001 60
    14 3 410.5 Norwood 16.084 05 0.004 93
    15 3 420.8 9.976 97 0.003 11
    16 3 430.7 5.262 55 0.001 78
    17 3 441.1 11.790 40 0.003 58
    18 3 451.3 9.304 23 0.002 92

    Table 3.  Summary of the micropore structures of the Antrim Shale

    We further analyzed the pore size distribution of these samples based on CO2 adsorption. Figure 3 shows that most of the micropores are within the pore size from 3 to 9 Å. The pore size distribution of the Antrim Shale samples shows multimodal characteristics. The largest peak corresponds to the pore size between 8 and 9 Å. For the pore size under 6 Å, the samples from the Lachine, Paxton, and Norwood members show similar two peaks: one peak between 4 and 5 Å and the other peak between 5 and 6 Å. For the pore sizes larger than 6 Å, the pore size distribution of different samples has a greater variability.

    Figure 3.  The pore size distribution of the Antrim Shale samples from CO2 adsorption. (a) Lachine Member; (b) Paxton Member; (c) Norwood Member.

  • The nitrogen adsorption isotherm of all the samples analyzed also exhibits a positive trend of increasing adsorption volume with the increasing relative pressure (Fig. 4). At the beginning of the desorption process, the desorption isotherm is above the adsorption isotherm. As the relative pressure decreases further (less than 0.5), the desorption isotherm overlaps with the adsorption isotherm due to the tensile effect (Groen et al., 2003). The sudden disappearance of the hysteresis can indicate the presence of small pores less than 4 nm in the Antrim Shale samples, which has been shown from the CO2 adsorption results (Fig. 3). According to the recommendations by the International Union of Pure and Applied Chemistry (IUPAC), the shape of the N2 adsorption and desorption isotherms indicates that the pores in the Antrim Shale samples are mainly slit pores. The hysteresis for the Antrim Shale samples in this study is likely due to capillary condensation. In the open-ended pore (e.g., slit pores), the adsorption isotherm is not in thermodynamic equilibrium, while the desorption isotherm is in the thermodynamic equilibration stage (Rouquerol et al., 1994). The delayed condensation could thus form the hysteresis observed in the Antrim Shale samples.

    Figure 4.  Examples of the N2 adsorption isotherms of the Antrim Shale samples. (a) Lachine Member; (b) Paxton Member; (c) Norwood Member.

    Table 4 summarizes the pore structures of the Antrim Shale samples including the BET surface area, the mesopore volume (pores with size 2–50 nm) and the macropore volume (pores with size larger than 50 nm) (Rouquerol et al., 1994). Samples from the Paxton Member have a larger average surface area (9.08 m2/g), mesopore volume (0.027 cm3/g) and macropore volume (0.014 cm3/g) than samples from the Lachine and Norwood members. Samples from the Lachine Member have a larger average surface area (8.63 m2/g) and mesopore volume (0.021 cm3/g) than samples from the Norwood Member. The macropore volume of the samples from the Lachine Member is very close to that of the Norwood Member samples.

    Samples Depth (ft) Members BET (m2/g) Mesopore (cm3/g) Macropore volume (cm3/g)
    1 3 260.8 Lachine 7.855 5 0.018 83 0.011 04
    2 3 270.9 8.404 8 0.023 14 0.013 58
    3 3 277.5 6.214 5 0.014 61 0.009 07
    4 3 297.2 11.480 5 0.032 60 0.017 88
    5 3 310.3 7.861 7 0.015 56 0.008 56
    6 3 320.3 7.611 0 0.016 13 0.009 40
    7 3 340.3 7.312 4 0.017 49 0.009 75
    8 3 350.3 12.299 8 0.029 20 0.012 96
    Average 8.630 0 0.020 95 0.011 53
    9 3 360.4 Paxton 10.090 2 0.030 83 0.015 45
    10 3 371.2 12.218 1 0.028 09 0.009 64
    11 3 379.3 4.772 6 0.014 85 0.010 76
    12 3 389.7 8.378 2 0.027 90 0.014 90
    13 3 399.5 9.990 2 0.033 25 0.017 04
    Average 9.089 9 0.026 98 0.013 56
    14 3 410.5 Norwood 6.365 4 0.012 87 0.009 42
    15 3 420.8 7.449 3 0.016 10 0.011 63
    16 3 430.7 9.738 4 0.029 98 0.015 29
    17 3 441.1 7.076 5 0.015 01 0.008 98
    18 3 451.3 7.588 7 0.019 03 0.011 98
    Average 7.643 7 0.018 60 0.011 46

    Table 4.  Summary of the pore structures from N2 adsorption

    The pore size distribution of the Antrim Shale samples from N2 adsorption has a multimodal shape, with a number of similar peaks, e.g., the peak around 30 Å (Fig. 5). In order to investigate the pore structures in a greater detail, we deconvolved the pore size distribution into several different pore groups using the method fully explained in Liu et al. (2017). To summarize, the pores in the shale samples are composed of different pore groups and the pore size distribution of each pore group fit the Gaussian distribution. As such, the whole pore size distribution of the shale samples can be regarded as the combination of several Gaussian distributions. The mathematical equations for the deconvolution are as follows

    Figure 5.  The pore size distribution of the Antrim Shale samples from N2 adsorption. (a) Lachine Member; (b) Paxton Member; (c) Norwood Member.

    where J is the number of the groups, J=1, … n; UJ and SJ are the mean value and the standard deviation of pore size distributions of the Jth group; fJ is the fraction of the Jth pore group of the total pores. The unknowns {fJ, UJ, SJ} can be derived by minimizing the difference between the data from the weighted model-phase probability distribution function (PDF) and the experimental PDF

    In the above equation, Px (xi) is the measured value of the normalized frequency of the pore size xi and m is the number of the intervals (bins). Equation 4 is used to guarantee that the different pore groups have sufficient contrast.

    Figure 6 shows that the pore size distribution of Sample 1 can be deconvolved into 5 different pore groups, a combination of which fits the experimental pore size distribution very well. Using the same method, we deconvolved the pore size distributions of all 18 samples. Table 5 shows that all of the Antrim Shale samples are composed of 5 pore groups, and some of these pore groups are the same in different samples. The pore groups with a mean value of around 30 Å (group 1), 50 Å (group 2) and 90 Å (group 3) exist in all the Antrim Shale samples analyzed. The mean pore size of group 4 and group 5 are different for different samples. Samples from the Paxton Member have a larger pore volume of small pores (group 1 and group 2) compared to the samples from the Lachine and Norwood members.

    Figure 6.  The deconvolution result of the pore size distribution of Sample 1.

    No. Group 1 Group 2 Group 3 Group 4 Group 5 Fitting coefficients
    W (Å) Area (cm3/g) W (Å) Area (cm3/g) W (Å) Area (cm3/g) W (Å) Area (cm3/g) W (Å) Area (cm3/g)
    1 32.018 2.348 51.357 17.144 89.454 2.397 116.788 26.565 305.211 18.985 0.988 3
    2 32.048 3.687 51.168 23.170 89.908 2.585 115.054 32.586 303.599 23.013 0.992 7
    3 31.441 3.759 50.188 17.174 89.516 1.631 105.317 19.070 276.312 16.110 0.993 6
    4 32.359 5.119 51.665 32.490 89.619 3.507 112.124 46.263 288.337 33.182 0.992 0
    5 31.674 2.632 51.004 14.583 89.248 2.105 114.446 20.206 298.263 15.690 0.991 8
    6 31.835 3.695 50.338 18.711 89.660 2.052 113.894 21.302 307.044 16.376 0.990 2
    7 31.974 3.895 50.536 21.275 89.764 2.268 109.749 24.610 291.005 16.946 0.992 7
    8 34.802 10.156 50.478 42.250 89.536 3.694 102.636 42.296 258.285 26.142 0.996 3
    9 33.029 12.349 47.468 32.689 78.904 21.608 136.333 34.082 326.738 24.453 0.997 0
    10 32.696 9.148 50.420 31.841 89.660 2.862 102.494 38.234 250.957 29.218 0.993 6
    11 35.563 2.988 51.404 14.009 88.838 2.420 126.853 19.906 350.994 14.488 0.990 2
    12 31.901 4.105 52.119 28.880 90.698 3.870 115.398 41.392 309.101 26.183 0.994 7
    13 31.798 5.363 52.048 34.793 90.845 4.723 117.598 50.012 316.957 29.437 0.995 4
    14 32.026 2.480 50.315 14.045 89.105 1.672 111.995 16.247 299.226 14.314 0.989 9
    15 31.974 2.236 50.957 15.494 89.640 2.360 120.670 20.708 333.580 17.400 0.987 5
    16 32.322 2.901 52.626 24.452 90.053 2.914 114.104 40.923 305.985 33.057 0.987 4
    17 32.085 1.818 51.039 13.879 89.269 1.938 112.150 19.938 296.551 16.559 0.991 9
    18 32.137 3.637 50.455 20.511 89.888 2.314 113.789 26.459 312.896 19.176 0.992 8

    Table 5.  Summary of the deconvolution results of the N2 adsorption

    In order to quantify the complexity of the pore structures of the Antrim Shale, we applied the fractal theory to describe the pore structures. FHH (Frenkel-Halsey-Hill) model was applied in this study using the following equation (Pfeifer et al., 1989)

    where V is the total volume of the adsorption, p is the equilibrium pressure, p0 is the saturated vapour pressure of the adsorption, and D is the fractal dimension. C is the constant which can be derived from curve fitting. If linear correlation exists between the ln(ln(1/(p/p0)) and lnV, then the pore structure has the fractal behaviour and the fractal dimension D can be calculated based on the slope of the linear part. D should be between 2 and 3.

    Figure 7 shows the fractal analysis of the adsorption isotherm of Sample 1. The curve can be fitted with two linear segments: D1 and D2. D1 likely reflects the monolayer-multilayer adsorption in which the dominant force is van der Waals, while D2 shows the capillary condensation regime with the surface tension being the dominant force (Sahouli et al., 1997). The analysis results in Table 6 show that D1 is smaller than D2, indicating that the pore surface is less complicated than the pore volume. The average D1 values of samples from the Lachine and Norwood members are larger than the samples from Paxton Member, indicating that the samples from the Lachine and Norwood members have more complicated pore surface.

    Figure 7.  Fractal dimension analysis of Sample 1.

    Samples Depth (ft) Members D1 D1 fitting coefficient D2 D2 fitting coefficient
    1 3 260.8 Lachine 2.450 5 0.999 2 2.639 9 0.983 1
    2 3 270.9 2.416 7 0.999 2 2.650 9 0.984 7
    3 3 277.5 2.403 9 0.999 5 2.674 2 0.983 7
    4 3 297.2 2.419 5 0.999 3 2.644 8 0.990 2
    5 3 310.3 2.451 5 0.999 4 2.655 1 0.990 0
    6 3 320.3 2.431 9 0.999 4 2.656 5 0.987 2
    7 3 340.3 2.408 4 0.999 5 2.679 5 0.977 9
    8 3 350.3 2.398 6 0.999 3 2.731 7 0.981 2
    9 3 360.4 Paxton 2.387 7 0.999 0 2.682 2 0.987 2
    10 3 371.2 2.419 1 0.998 8 2.683 4 0.986 1
    11 3 379.3 2.409 4 0.998 2 2.614 1 0.986 6
    12 3 389.7 2.389 5 0.999 4 2.633 3 0.985 8
    13 3 399.5 2.394 6 0.999 8 2.634 5 0.990 5
    14 3 410.5 Norwood 2.455 0.999 7 2.653 7 0.992 4
    15 3 420.8 2.441 8 0.999 7 2.618 8 0.991 5
    16 3 430.7 2.414 6 0.999 3 2.587 7 0.988 9
    17 3 441.1 2.450 2 0.999 6 2.648 2 0.987 5
    18 3 451.3 2.412 3 0.999 6 2.649 6 0.983 1

    Table 6.  Summary of the fractal dimension of the Antrim Shale samples

  • A comparison of mineral composition, organic matter properties and pore structures of the Antrim Shale indicates that TOC is positively correlated with the micropore surface area (Fig. 8a), but is negatively correlated with the meso-macro pore surface area (Fig. 8c). Thus, the organic matter in the Antrim Shale mainly hosts micro pores instead of meso-macro pores. Positive correlations exist between the amounts of clay minerals and the micropore surface area (Fig. 8b) and meso-macro pore area (Fig. 8d), indicating that both micropores and meso-macro pores exist in the clay minerals. The SEM images of the samples confirm that the organic matter (telalginite; Fig. 9a) is non-porous, while slit pores exist in the clay minerals (Fig. 9b).

    Figure 8.  Correlations between pore structures and rock composition. (a) Micropore surface vs. organic matter; (b) micropore surface vs. clay content; (c) meso-macro pore surface vs. organic matter; (d) meso-macro pore surface vs. clay content.

    Figure 9.  SEM images of the pores structures of the Antrim Shale. (a) Non-porous organic matter; (b) slit clay pore.

  • This section discusses some differences between the pore structures of a low-maturity biogenetic gas shale (Antrim Shale) and a few well-known thermogenic gas shales, such as the Barnett, Marcellus, Woodford, and Haynesville shales. The micropore volume from the CO2 adsorption of the Antrim Shale samples ranges from 0.001 to 0.005 cm3/g. Clarkson et al. (2013) showed that the CO2 pore volume of thermogenic gas shales ranged from 0.001 4 to 0.004 cm3/g, which is very similar to the micro pore volume of the Antrim Shale. The BET surface area of their samples was between 2 to 17 m2/g, and the N2 pore volume from 0.004 to 0.05 cm3/g. In our study, the surface area of the Antrim Shale ranges from 4.77 to 12.30 m2/g and the N2 pore volume 0.022 to 0.050 cm3/g. All these indicate that the pore volume and the pore surface area of the Antrim Shale samples are very similar to the pore structures of other thermogenetic gas shales. However, the pore size distribution of the Antrim Shale and the other thermogenic gas shales shows a few noticeable differences. Clarkson et al. (2013) found the largest peak pore size from nitrogen adsorption to be around 10 nm, which agrees with the results of Chalmers et al. (2012). Wang et al. (2019) also analyzed the pore structures of the Wufeng-Longmaxi Shale (a typical thermogenic gas shale in China) and found that the peak of the pore size distribution is smaller than 10 nm. Zhang et al. (2016) analyzed the pore structures of the Lower Silurian black shale and found that the major pores from the N2 adsorption are smaller than 10 nm. However, in the Antrim Shale, one can observe the presence of a major peak with the pore size around 30 Å (Table 5). Compared with the pores in thermogenic gas shales, the Antrim Shale hosts many larger-sized pores.

    For thermogenic gas shale formations, TOC has a primary impact on pore structures. Loucks et al. (2012) divided the pore structures of the shale gas systems into three different pore types. Two pore types are related to the minerals, such as the minerals intraparticle and interparticle pores, and the third pore type is related to organic matter pores. By using an image analysis method, Chalmers et al. (2012) studied several different thermogenic gas shale plays in the USA (Barnett, Woodford, and Marcellus) and found that networks of mesopores are connected to larger macropores within the kerogen aggregates. Yang et al. (2016) studied the pore structures of the Longmaxi Formation and found that the surface area and pore volume increase with the increasing TOC based on N2 adsorption. Zhang et al. (2016) studied the pore structures of the Lower Silurian black shale and also found positive correlations between pore volumes/pore surface with TOC content. However, for the Antrim Shale in this study, we found that the organic matter does not contribute a lot to the meso-macro pore volume. The differences in the pore structures between thermogenic gas shales and biogenic shales can be due to maturity differences between the two different gas shale types. In shales that are immature or in the early oil window, the major pores are hosted by minerals (Ko et al., 2018). In typical thermogenic shales, during thermal conversion of kerogen to oil, an increase in porosity is usually observed as a result of decomposition of convertible organic carbon to hydrocarbons and carbonaceous residue. This net porosity gain has an impact on gas storage capacity (Jarvie et al., 2007). When thermal maturity increases to the gas window, methane generated from the secondary cracking of oil to thermogenic gas contributes to the creation of pores (Chen and Xiao, 2014; Hill et al., 2003). For thermogenic shale, from the late oil window to the gas window, due to a high formation temperature, the volume of the gas or oil will expand much more than the kerogen and the minerals, which helps to create some meso-macro pores. Ji et al. (2017) applied the SEM method to understand the pore structure changes of the shale using the pyrolysis method and found obvious changes in the organic matter. As the temperature increases from 350 to 450 ℃ (gas window), the pore size of the organic matter increases. The pores in the organic matter are dominated by abudant meso-macro pores. For the biogenic gas generation, at the beginning, the complex organic matter can be decomposed into long chain aliphatics, aromatics and heteroatoms due to the exoenzymatic hydrolysis, fragmentation, activation, and dissolution. Subsequently, the decomposed molecules solubilize and initiate methanogenesis (Strąpoć et al., 2011). The organic matter pores change during this process. However, the low biogenic gas generation temperature and the slow gas generation rate (Krüger et al., 2014) indicate that the change of the pore structures related to organic matter during the biogenic gas generation process is very small. This is the reason we could not see the meso-macro pores in the organic matter in the Antrim Shale. It is the mineral- related pores that play the primary role in the total pore structure, which suggests that biogenic shale gas formations, such as the Antrim Shale, have different pore structures from well-known mature thermogenic gas shales around the world.

  • In this study, the pore structures of a selected number of samples taken from three members of the Antrim Shale were analyzed through gas adsorption methods. The following preliminary conclusions are drawn.

    (1) Clay and quartz are the two major minerals in the Antrim Shale, but the Paxton Member has a carbonate component as well. The average TOC of the samples in the Lachine and Norwood members is 6.17 wt.% and 9.26 wt.%, respectively, which is greater than in the Paxton Member (1.03 wt.%).

    (2) The micro pore size distribution (from CO2 adsorption) and the meso-macro pore size distribution (from N2 adsorption) show a multimodal pattern. The micro pores in the Antrim Shale are mainly in the range from 3 to 9 Å. Compared to the samples from the Lachine and Norwood members, the Paxton Member has smaller average micro pore volume and micro pore surface area but larger meso-macro pore surface area and meso-macro pore volume. The deconvolution results from the pore size distribution from N2 adsorption shows that the pores in the Antrim Shale have a number of similar pore groups. Based on the fractal analysis of N2 adsorption volume, samples from the Lachine and Norwood members have a more complicated pore surface than samples from the Paxton Member.

    (3) The organic matter in the Antrim Shale hosts micro pores instead of meso-macro pores. Clay minerals host both micro pores and meso-macro pores. Mineral-related pores contribute most to the total pore structures. The pore structure in the Antrim Shale is therefore very different from that observed in a number of well-studied thermogenic gas shales.

  • The authors gratefully acknowledge the Michigan Geological Repository for Research and Education (MGRRE), and in particular, Dr. William B. Harrison Ⅲ, Linda Harrison, and Jennifer Trout, for assistance with core access, description, and sampling, as well as access to XRD data. The authors also thank the reviewers and the editors for their constructive comments and valuable suggestions. The final publication is available at Springer via https://doi.org/10.1007/s12583-020-1344-4.

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