Structure and Evolution of Clay-Organic Nanocomposites in Three Leading Shales in China

Abstract

Organic matter (OM) in shales occurs as nanometer-sized intercalations with clay minerals that are termed as clay-organic nanocomposites; however, the OM occurrence in nanocomposites at different stages of maturation is still unclear, and the co-evolution process of OM and clay under burial is not well understood. To reveal the variation of OM occurrence and clarify the relationship between petroleum generation of OM & transformation of clay minerals in nanocomposites as a function of maturity, this study investigates the structure and clay-OM association in 44 samples from three leading shales at different maturity stages from two basins in China. A total of 15 samples of lacustrine shale from upper Triassic Yanchang Formation, 15 samples of marine shale from Lower Silurian Longmaxi Formation, and 14 samples of marine shale from Lower Cambrian Niutitang Formation were analyzed based on organic geochemistry, X-ray diffraction (XRD), and field emission-scan electron microscopy (FE-SEM), focused ion beam (FIB) sample preparation and consequent high resolution-transmission electron microscopy (HR-TEM) observations combined with energy dispersive spectroscopy (EDS). The results from this study show that most shale samples are organic-rich, and these three shales represent thermal evolutionary process from oil-window mature to overmature in a sequence of Triassic Yanchang, Silurian Longmaxi, and Cambrian Niutitang formations. Thorough observations indicate that sub-parallel bands of clays and intermingling of detrital minerals (such as quartz) dominate the nanocomposites in the Yanchang samples. While for Longmaxi and Niutitang shales, abundant nanopores and pyrite nanoparticles are observed in nanocomposites with features of layered distributions of OM and clay minerals. The structural investigation of nanocomposites shows that organic carbon between multi-layers dominates the OM occurrence in nanocomposites, which significantly extends the traditional opinion of OM-clay association. At an oil-window mature stage, the fluctuational interlayer spacing and a certain intensity of the carbon peak observed in the EDS spectra for corresponding clays provide a visual evidence of the organic molecules accessing the monolayer spaces of smectite. With the evolutional process of nanocomposites in shale and petroleum generation of OM & mineral transformation (illitization of smectite) running in parallel, it is inferred that the organic molecules migrate from monolayer spaces as gaseous hydrocarbons are generated, and eventually form stable clay-organic nanocomposites at an overmature stage. The results presented here will contribute to an improved understanding of diagenesis and organic-inorganic interactions in OM-rich shales.

Keywords

organic matter / shale / clay-organic nanocomposites / structure / hydrocarbons

References

Aplin A C, Bishop A N, Clayton C J, . A Lamina-Scale Geochemical and Sedimentological Study of Sediments from the Peru Margin (Site 680, ODP Leg 112). Geological Society, London, Special Publications, 1992, 64(1): 131-149.

Aplin A C, MacQuaker J H S. Mudstone Diversity: Origin and Implications for Source, Seal, and Reservoir Properties in Petroleum Systems. AAPG Bulletin, 2011, 95(12): 2031-2059.

Berthonneau J, Grauby O, Abuhaikal M, . Evolution of Organo-Clay Composites with Respect to Thermal Maturity in Type II Organic-Rich Source Rocks. Geochimica et Cosmochimica Acta, 2016, 195: 68-83.

Bu H L, Yuan P, Liu H, . Effects of Complexation between Organic Matter (OM) and Clay Mineral on OM Pyrolysis. Geochimica et Cosmochimica Acta, 2017, 212: 1-15.

Cai J G, Bao Y J, Yang S Y, . Research on Preservation and Enrichment Mechanisms of Organic Matter in Muddy Sediment and Mudstone. Science in China Series D: Earth Sciences, 2007, 50(5): 765-775.

Cai J G, Song M S, Lu L F, . Organo-Clay Complexes in Source Rocks—A Natural Material for Hydrocarbon Generation. Marine Geology & Quaternary Geology, 2013, 33(3): 123-131. in Chinese with English Abstract)

Cai J G, Zhu X J, Zhang J Q, . Heterogeneities of Organic Matter and Its Occurrence Forms in Mudrocks: Evidence from Comparisons of Palynofacies. Marine and Petroleum Geology, 2020, 111: 21-32.

Cao H Y, Zhu C Q, Qiu N S. Thermal Evolution of Lower Silurian Longmaxi Formation in the Eastern Sichuan Basin. Journal of Earth Sciences and Environment, 2015, 37(6): 22-32. (in Chinese with English Abstract)

Chen G J, Yen M C, Wang J M, . Layered Inorganic/Enzyme Nanohybrids with Selectivity and Structural Stability upon Interacting with Biomolecules. Bioconjugate Chemistry, 2008, 19(1): 138-144.

Chen S B, Zuo Z X, Zhu Y M, . Applicability of the Testing Method for the Maturity of Organic Matter in Shale Gas Reservoirs. Natural Gas Geoscience, 2015, 26(3): 564-574. (in Chinese with English Abstract)

Curtis M E, Cardott B J, Sondergeld C H, . Development of Organic Porosity in the Woodford Shale with Increasing Thermal Maturity. International Journal of Coal Geology, 2012, 103: 26-31.

Dai J X, Li J, Luo X, . Stable Carbon Isotope Compositions and Source Rock Geochemistry of the Giant Gas Accumulations in the Ordos Basin, China. Organic Geochemistry, 2005, 36(12): 1617-1635.

Day-Stirrat R J, Loucks R G, Milliken K L, . Phyllosilicate Orientation Demonstrates Early Timing of Compactional Stabilization in Calcite-Cemented Concretions in the Barnett Shale (Late Mississippian), Fort Worth Basin, Texas (USA). Sedimentary Geology, 2008, 208(1): 27-35. 2

Dong D Z, Wang Y M, Li X J, . Breakthrough and Prospect of Shale Gas Exploration and Development in China. Natural Gas Industry, 2016, 36(1): 19-32. (in Chinese with English Abstract)

Du J Z, Cai J G, Lei T Z, . Diversified Roles of Mineral Transformation in Controlling Hydrocarbon Generation Process, Mechanism, and Pattern. Geoscience Frontiers, 2021, 12(2): 725-736.

Duan Y, Wang C Y, Zheng C Y, . Geochemical Study of Crude Oils from the Xifeng Oilfield of the Ordos Basin, China. Journal of Asian Earth Sciences, 2008, 31(4): 341-356. 5/6

Fu H J, Yan D T, Yao C P, . Pore Structure and Multi-Scale Fractal Characteristics of Adsorbed Pores in Marine Shale: A Case Study of the Lower Silurian Longmaxi Shale in the Sichuan Basin, China. Journal of Earth Science, 2022, 33(5): 1278-1290.

General Administration of Quality Supervision, Inspection and Quarantine of the People’s Republic of China Determination of Total Organic Carbon in Sedimentary Rock: GB/T 19145-2003, 2003, Beijing: Standard Press of China (in Chinese)

Gu Y T, Li X X, Wan Q, . On the Different Characteristics of Organic Pores in Shale and Their Influencing Factors: Taking Typical Marine, Continental and Transitional Facies Reservoirs in China as Examples. Acta Sedimentologica Sinica, 2021, 39(4): 794-810. (in Chinese with English Abstract)

Gu Y T, Li X X, Wan Q, . The Differential Evolution of Nanopores in Discrete OM and Organic-Clay Composites for Shale: Insights from Stress Manipulation. Arabian Journal of Geosciences, 2021, 14(7): 554

Guo H J, Jia W, Peng P A, . The Composition and Its Impact on the Methane Sorption of Lacustrine Shales from the Upper Triassic Yanchang Formation, Ordos Basin, China. Marine and Petroleum Geology, 2014, 57: 509-520.

Hower J, Eslinger E V, Hower M E, . Mechanism of Burial Metamorphism of Argillaceous Sediment: 1. Mineralogical and Chemical Evidence. Geological Society of America Bulletin, 1976, 87(5): 725-737.

Jia W, Segal E, Kornemandel D, . Polyaniline-DBSA/Organophilic Clay Nanocomposites: Synthesis and Characterization. Synthetic Metals, 2002, 128(1): 115-120.

Jiang Z. Pore Structure and Gas Bearing Property of Typical Marine and Continental Shale Reservoirs in China, 2018, Beijing: Scientific Press (in Chinese with English Abstract)

Jiang Q, Zhu C, Qiu N, . Paleo-Heat Flow and Thermal Evolution of the Lower Cambrian Qiongzhusi Shale in the Southern Sichuan Basin, SW China. Natural Gas Geoscience, 2015, 26(8): 1563-1570. (in Chinese with English Abstract)

Kelemen S R, Fang H L. Maturity Trends in Raman Spectra from Kerogen and Coal. Energy & Fuels, 2001, 15(3): 653-658.

Kennedy M J, Droser M, Mayer L M, . Late Precambrian Oxygenation: Inception of the Clay Mineral Factory. Science, 2006, 311(5766): 1446-1449.

Kennedy M J, Löhr S C, Fraser S A, . Direct Evidence for Organic Carbon Preservation as Clay-Organic Nanocomposites in a Devonian Black Shale: From Deposition to Diagenesis. Earth and Planetary Science Letters, 2014, 388 59-70.

Kennedy M J, Pevear D R, Hill R J. Mineral Surface Control of Organic Carbon in Black Shale. Science, 2002, 295: 657-660.

Kennedy M J, Wagner T. Clay Mineral Continental Amplifier for Marine Carbon Sequestration in a Greenhouse Ocean. Proceedings of the National Academy of Sciences of the United States of America, 2011, 108(24): 9776-9781.

Lagaly G. Principles of Flow of Kaolin and Bentonite Dispersions. Applied Clay Science, 1989, 4(2): 105-123.

Lanson B, Sakharov B A, Claret F, . Diagenetic Smectite-to-Illite Transition in Clay-Rich Sediments: a Reappraisal of X-Ray Diffraction Results Using the Multi-Specimen Method. American Journal of Science, 2009, 309(6): 476-516.

Li S Y, He H P, Tao Q, . Kaolinization of 2: 1 Type Clay Minerals with Different Swelling Properties. American Mineralogist, 2020, 105(5): 687-696.

Liu A Q, Tang D J, Shi X Y, . Growth Mechanisms and Environmental Implications of Carbonate Concretions from the ∼1.4 Ga Xiamaling Formation, North China. Journal of Palaeogeography, 2019, 8(1): 1-16.

Liu D, Xiao X, Tian H, . Sample Maturation Calculated Using Raman Spectroscopic Parameters for Solid Organics: Methodology and Geological Applications. Chinse Science Bulletin, 2012, 58(11): 1285-1298. in Chinese)

Liu S G, Deng B, Zhong Y, . Unique Geological Features of Burial and Superimposition of the Lower Paleozoic Shale Gas across the Sichuan Basin and Its Periphery. Earth Science Frontiers, 2016, 23(1): 11-28. (in Chinese with English Abstract)

Liu Z X, Xu L L, Wen Y R, . Accumulation Characteristics and Comprehensive Evaluation of Shale Gas in Cambrian Niutitang Formation, Hubei. Earth Science, 2022, 47(5): 1586-1603. (in Chinese with English Abstract)

Loucks R G, Reed R M, Ruppel S C, . Morphology, Genesis, and Distribution of Nanometer-Scale Pores in Siliceous Mudstones of the Mississippian Barnett Shale. Journal of Sedimentary Research, 2009, 79(12): 848-861.

Lu L F, Cai J G, Liu W H, . Occurrence and Thermostability of Absorbed Organic Matter on Clay Minerals in Mudstones and Muddy Sediments. Oil & Gas Geology, 2013, 34(1): 16-26. (in Chinese with English Abstract)

Metwally Y M, Chesnokov E M. Clay Mineral Transformation as a Major Source for Authigenic Quartz in Thermo-Mature Gas Shale. Applied Clay Science, 2012, 55: 138-150.

Meunier A, Velde B. Solid Solutions in I/S Mixed-Layer Minerals and Illite. American Mineralogist, 1989, 74(9): 1106-1112. 10

Milliken K L, Rudnicki M, Awwiller D N, . Organic Matter-Hosted Pore System, Marcellus Formation (Devonian), Pennsylvania. AAPG Bulletin, 2013, 97(2): 177-200.

National Energy Administration Analysis Method for Clay Minerals and Ordinary Non-Clay Minerals in Sedimentary Rocks by the X-ray Diffraction: SY/T 5163-2010, 2010, Beijing: Petroleum Industry Press (in Chinese)

O’Brien N R. Fabric of Kaolinite and Illite Floccules. Clays and Clay Minerals, 1971, 19(6): 353-359.

Rahman H M, Kennedy M, Löhr S, . The Influence of Shale Depositional Fabric on the Kinetics of Hydrocarbon Generation through Control of Mineral Surface Contact Area on Clay Catalysis. Geochimica et Cosmochimica Acta, 2018, 220: 429-448.

Schoenherr J, Littke R, Urai J L, . Polyphase Thermal Evolution in the Infra-Cambrian Ara Group (South Oman Salt Basin) as Deduced by Maturity of Solid Reservoir Bitumen. Organic Geochemistry, 2007, 38(8): 1293-1318.

Song D J, Tuo J C, Wang Y T, . Research Advances on Characteristics of Nanopore Structure of Organic-Rich Shales. Acta Sedimentologica Sinica, 2019, 37(6): 1309-1324. (in Chinese with English Abstract)

Sposito G, Skipper N T, Sutton R, . Surface Geochemistry of the Clay Minerals. Proceedings of the National Academy of Sciences of the United States of America, 1999, 96(7): 3358-3364.

Środoń J. Bergaya F, Theng B K G, Lagaly G. Chapter 12.2 Identification and Quantitative Analysis of Clay Minerals. Developments in Clay Science. Developments in Clay Science, 2006, Amsterdam: Elsevier, 765-787

Theng B K G, Churchman G J, Newman R H. The Occurrence of Interlayer Clay-Organic Complexes in Two New Zealand Soils. Soil Science, 1986, 142(5): 262-266.

Tosca N J, Johnston D T, Mushegian A, . Clay Mineralogy, Organic Carbon Burial, and Redox Evolution in Proterozoic Oceans. Geochimica et Cosmochimica Acta, 2010, 74(5): 1579-1592.

Tuschel D. Raman Spectroscopy of Oil Shale. Spectroscopy, 2013, 28(3): 20-28

Wang P F, Jiang Z, Chen L, . Pore Structure Characterization for the Longmaxi and Niutitang Shales in the Upper Yangtze Platform, South China: Evidence from Focused Ion Beam-He Ion Microscopy, Nano-Computerized Tomography and Gas Adsorption Analysis. Marine and Petroleum Geology, 2016, 77: 1323-1337.

Wang X Z, Gao S L, Gao C. Geological Features of Mesozoic Lacustrine Shale Gas in South of Ordos Basin, NW China. Petroleum Exploration and Development, 2014, 41(3): 326-337.

Wang Y F, Zhai G Y, Liu G H, . Geological Characteristics of Shale Gas in Different Strata of Marine Facies in South China. Journal of Earth Science, 2021, 32(4): 725-741.

Wang Z M, Jiang Y Q, Fu Y H, . Characterization of Pore Structure and Heterogeneity of Shale Reservoir from Wufeng Formation-Sublayers Long-11 in Western Chongqing Based on Nuclear Magnetic Resonance. Earth Science, 2022, 47(2): 490-504. (in Chinese with English Abstract)

Xu M. Studies on the Complexation and Stability of Clay Minerals and Organic Matter, 2013, Nanjing: Nanjing University (in Chinese with English Abstract)

Yang H, Niu X B, Xu L M, . Exploration Potential of Shale Oil in Chang7 Member, Upper Triassic Yanchang Formation, Ordos Basin, NW China. Petroleum Exploration and Development, 2016, 43(4): 560-569.

Yang Y, Lei T Z, Xing L T, . Oil Generation Abilities of Chemically Bound Organic Matter in Different Types of Organic Clay Complexes. Petroleum Geology & Experiment, 2015, 37(4): 487-493. (in Chinese with English Abstract)

Yariv S, Cross H. Clay-Organic Complexes and Interaction, 2002, New York: Marcel Dekker

Yuan P. Unique Structure and Surface-Interface Reactivity of Nanostructured Minerals. Earth Science, 2018, 43(5): 1384-1407. (in Chinese with English Abstract)

Zhao J H, Jin Z J, Jin Z K, . Lithofacies Types and Sedimentary Environment of Shale in Wufeng-Longmaxi Formation, Sichuan Basin. Acta Petrolei Sinica, 2016, 37(5): 572-586. (in Chinese with English Abstract)

Zhu H J, Ju Y W, Huang C, . Microcosmic Gas Adsorption Mechanism on Clay-Organic Nanocomposites in a Marine Shale. Energy, 2020, 197: 117256

Zhu X J, Cai J G, Liu W X, . Occurrence of Stable and Mobile Organic Matter in the Clay-Sized Fraction of Shale: Significance for Petroleum Geology and Carbon Cycle. International Journal of Coal Geology, 2016, 160 1-10. 161

Zhu X J, Cai J G, Wang G L, . Role of Organo-Clay Composites in Hydrocarbon Generation of Shale. International Journal of Coal Geology, 2018, 192: 83-90.