Maturity Assessment of the Lower Cambrian and Sinian Shales Using Multiple Technical Approaches

Abstract

The Lower Cambrian Niutitang and Sinian Doushantuo shales are the most important and widespread source rocks and target layers in South China. Reliable data of the thermal maturity of organic matter (OM) is widely used to assess hydrocarbon generation and is a key property used in determining the viability and hydrocarbon potential of these new shales. Nevertheless, traditional thermal maturity indicators are no longer suited to the vitrinite-lack marine shales. This study aims to combine high throughput Raman and infrared spectroscopy analysis to confirm and validate the thermal maturity in comparison with the bitumen reflectance (R _b). Raman parameters such as the differences between the positions of the two bands (V _G-V _D) are strong parameters for calculating the thermal maturity in a large vitrinite reflectance (R _o) ranging from 1.60% to 3.80%. The infrared spectroscopy analysis indicates that the aromatic C-C bands and CH₂/CH₃ aliphatic groups both are closely correlated with thermal maturity. The calculated R _o results from Raman and infrared spectroscopy are in strong coincidence with the R _b. The relationships between Rb and pore volumes/surface areas (calculated from N₂ adsorption) indicate that the sample with R _b of 3.40% has the lowest pore volumes and surface areas. Focused ion beam scanning electron microscopy (FIB-SEM) observations of OM pores indicate that R _o of approximately 3.60% may be an upper limit for OM porosity development. Obviously, kerogen Raman and infrared spectroscopy can indicate methods for reducing the risk in assessing maturity with practical, low-cost accurate results. Exploration of shale gas in the high maturity (>3.40%–3.60%) region carries huge risks.

Keywords

thermal maturity / marine shale / kerogen / raman spectroscopy / infrared spectroscopy

References

[1] Abarghani A, Ostadhassan M, Gentzis T, . Correlating Rock-Eval™ Tmax with Bitumen Reflectance from Organic Petrology in the Bakken Formation. International Journal of Coal Geology, 2019, 205: 87-104.

[2] Akiyama M, Nakashima S, Jin C. FT-IR Microspectroscopy Analysis of Kerogen. Researches in Organic Geochemistry, 1992, 8: 17-19.

[3] Bai B J, Elgmati M, Zhang H, . Rock Characterization of Fayetteville Shale Gas Plays. Fuel, 2013, 105: 645-652.

[4] Beyssac O, Goffé B, Chopin C, . Raman Spectra of Carbonaceous Material in Metasediments: A New Geothermometer. Journal of Metamorphic Geology, 2002, 20(9): 859-871.

[5] Bray E E, Evans D E. Hydrocarbons in Non-Reservoir-Rock Source Beds. AAPG Bulletin, 1965, 49(3): 248-257

[6] Cao T T, Song Z G, Wang S B, . A Comparative Study of the Specific Surface Area and Pore Structure of Different Shales and their Kerogens. Science China Earth Sciences, 2015, 58(4): 510-522.

[7] Chalmers G R L, Bustin R M. A Multidisciplinary Approach in Determining the Maceral (Kerogen Type) and Mineralogical Composition of Upper Cretaceous Eagle Ford Formation: Impact on Pore Development and Pore Size Distribution. International Journal of Coal Geology, 2017, 171: 93-110.

[8] Chen X, Zhang G, Hu Y. Deposit Environment of the Ediacaran Doushantuo Formation in Yichang Area, Western Hubei Province, China and Its Geological Significance for Shale Gas. Geology and Mineral Resources of South China, 2016, 32(2): 106-116. (in Chinese with English Abstract)

[9] Cloutis E A. Spectral Reflectance Properties of Hydrocarbons: Remote-Sensing Implications. Science, 1989, 245(4914): 165-168.

[10] Correia, M., 1971. Diagenesis of Sporopollenin and Other Comparable Organic Substances: Application to Hydrocarbon Research. Proceedings of a Symposium Held at the Geology Department, Imperial College, September 23–25, London

[11] Craddock P R, le Doan T V, Bake K, . Evolution of Kerogen and Bitumen during Thermal Maturation via Semi-Open Pyrolysis Investigated by Infrared Spectroscopy. Energy & Fuels, 2015, 29(4): 2197-2210.

[12] Craddock P R, Prange M D, Pomerantz A E. Kerogen Thermal Maturity and Content of Organic-Rich Mudrocks Determined Using Stochastic Linear Regression Models Applied to Diffuse Reflectance IR Fourier Transform Spectroscopy (DRIFTS). Organic Geochemistry, 2017, 110: 122-133.

[13] Curtis J B. Fractured Shale-Gas Systems. American Association of Petroleum Geologists Bulletin, 2002, 86: 1921-1938.

[14] 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.

[15] Curtis, M. E., Sondergeld, C. H., Rai, C. S., 2013. Investigation of the Microstructure of Shales in the Oil Window. In: Unconventional Resources Technology Conference, August 12–14, Denver

[16] Dai J X, Zou C N, Liao S M, . Geochemistry of the Extremely High Thermal Maturity Longmaxi Shale Gas, Southern Sichuan Basin. Organic Geochemistry, 2014, 74: 3-12.

[17] Fan J, Li C, Hou X. The International Chronostratigraphic Chart. Journal of Stratigraphy, 2018, 42(4): 365-370. (in Chinese with English Abstract)

[18] Feng G, Chen S. Relationship between the Reflectance of Bitumen and Vitrinite in Rock. Natural Gas Industry, 1988, 8(3): 20-25. (in Chinese with English Abstract)

[19] Ferralis N, Matys E D, Knoll A H, . Rapid, Direct and Non-Destructive Assessment of Fossil Organic Matter via MicroRaman Spectroscopy. Carbon, 2016, 108: 440-449.

[20] Fishman, N., Guthrie, J. M., Honarpour, M., 2013. The Stratigraphic Distribution of Hydrocarbon Storage and Its Effect on Producible Hydrocarbons in the Eagle Ford Formation, South Texas. In: URTec1579007 Unconventional Resources Technology Conference, August 12–14, Denver

[21] Ganz H H, Kalkreuth W. IR Classification of Kerogen Type, Thermal Maturation, Hydrocarbon Potential and Lithological Characteristics. Journal of Southeast Asian Earth Sciences, 1991, 5(1/2/3/4): 19-28.

[22] Gonçalves P A, Mendonça Filho J G, da Silva F S, . Solid Bitumen Occurrences in the Arruda Sub-Basin (Lusitanian Basin, Portugal): Petrographic Features. International Journal of Coal Geology, 2015, 131: 239-249.

[23] Gregg S J, Sing K S W. Adsorption, Surface Area and Porosity, 1982, London: Academic Press

[24] Grobe A, Urai J L, Littke R, . Hydrocarbon Generation and Migration under a Large Overthrust: The Carbonate Platform under the Semail Ophiolite, Jebel Akhdar, Oman. International Journal of Coal Geology, 2016, 168: 3-19.

[25] Ground Water Protection Council, 2009. Modern Shale Gas Development in the United States: A Primer. (2012-3-19). https://www.energy.gov/sites/prod/files/2013/03/f0/ShaleGasPrimer_Online_4-2009.pdf

[26] Guedes A, Valentim B, Prieto A C, . Raman Spectroscopy of Coal Macerals and Fluidized Bed Char Morphotypes. Fuel, 2012, 97: 443-449.

[27] Guo T L, Zhang H R. Formation and Enrichment Mode of Jiaoshiba Shale Gas Field, Sichuan Basin. Petroleum Exploration and Development, 2014, 41(1): 31-40.

[28] Han Y J, Horsfield B, Wirth R, . Oil Retention and Porosity Evolution in Organic-Rich Shales. AAPG Bulletin, 2017, 101(6): 807-827.

[29] Hill D G, Nelson C R. Gas Productive Fractured Shales—An Overview and Update. Gas TIPS, 2000, 6(2): 4-13

[30] Hinrichs R, Brown M T, Vasconcellos M A Z, . Simple Procedure for an Estimation of the Coal Rank Using Micro-Raman Spectroscopy. International Journal of Coal Geology, 2014, 136: 52-58.

[31] Hou Y G, Liang Y Q, He S, . Distribution and Thermal Maturity of Devonian Carbonate Reservoir Solid Bitumen in Desheng Area of Guizhong Depression, South China. Geofluids, 2017, 2017(6): 1-15.

[32] Hu K, Liu Y J, Willeins R W T. Raman Spectral Studies of Sedimentary Organic Matter. Acta Sedimentologica Sinica, 1993, 11(3): 64-71. (in Chinese with English Abstract)

[33] Jacob H. Classification, Structure, Genesis and Practical Importance of Natural Solid Oil Bitumen (“Migrabitumen”). International Journal of Coal Geology, 1989, 11(1): 65-79.

[34] Jennings D S, Antia J. Petrographic Characterization of the Eagle Ford Shale, South Texas: Mineralogy, Common Constituents, and Distribution of Nanometerscale Pore Types. In: Camp, W., Diaz, E., Wawak, B., eds., Electron Microscopy of Shale Hydrocarbon Reservoirs. American Association of Petroleum Geologists Memoir, 2013, 102: 101-113.

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

[36] Khatibi S, Ostadhassan M, Tuschel D, . Evaluating Molecular Evolution of Kerogen by Raman Spectroscopy: Correlation with Optical Microscopy and Rock-Eval Pyrolysis. Energies, 2018, 11(6): 1406

[37] Labus M, Lempart M. Studies of Polish Paleozoic Shale Rocks Using FTIR and TG/DSC Methods. Journal of Petroleum Science and Engineering, 2018, 161: 311-318.

[38] Liu D H, Xiao X M, Tian H, . Sample Maturation Calculated Using Raman Spectroscopic Parameters for Solid Organics: Methodology and Geological Applications. Chinese Science Bulletin, 2013, 58(11): 1285-1298.

[39] Liu Y, Yin C, Gao L, . Advances in the Study of Sedimentary Facies of the Sinian Candidate Stratotype in the Eastern Areas of the Three Gorges, Hubei. Geological Review, 2003, 49(2): 187-194. (in Chinese with English Abstract)

[40] Liu Z X, Yan D T, Niu X. Insights into Pore Structure and Fractal Characteristics of the Lower Cambrian Niutitang Formation Shale on the Yangtze Platform, South China. Journal of Earth Science, 2020, 31(1): 169-180.

[41] Löhr S C, Baruch E T, Hall P A, . Is Organic Pore Development in Gas Shales Influenced by the Primary Porosity and Structure of Thermally Immature Organic Matter?. Organic Geochemistry, 2015, 87 119-132.

[42] Lomando A J. The Influence of Solid Reservoir Bitumen on Reservoir Quality (1). AAPG Bulletin, 1992, 76: 1137-1152.

[43] 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.

[44] Lünsdorf N K. Raman Spectroscopy of Dispersed Vitrinite—Methodical Aspects and Correlation with Reflectance. International Journal of Coal Geology, 2016, 153: 75-86.

[45] Lupoi J S, Fritz L P, Hackley P C, . Quantitative Evaluation of Vitrinite Reflectance and Atomic O/C in Coal Using Raman Spectroscopy and Multivariate Analysis. Fuel, 2018, 230: 1-8.

[46] Mastalerz M, Drobniak A, Stankiewicz A B. Origin, Properties, and Implications of Solid Bitumen in Source-Rock Reservoirs: A Review. International Journal of Coal Geology, 2018, 195: 14-36.

[47] Mastalerz M, Schimmelmann A, Drobniak A, . Porosity of Devonian and Mississippian New Albany Shale across a Maturation Gradient: Insights from Organic Petrology, Gas Adsorption, and Mercury Intrusion. AAPG Bulletin, 2013, 97(10): 1621-1643.

[48] Milliken K L, Ko L T, Pommer M, . Sem Petrography of Eastern Mediterranean Sapropels: Analogue Data for Assessing Organic Matter in Oil and Gas Shales. Journal of Sedimentary Research, 2014, 84(11): 961-974.

[49] National Energy Administration Method of Determining Microscopically the Reflectance of Vitrinite in Sedimentary [SY/T 5124-2012], 2012, Beijing: Petroleum Industry Press

[50] Peng N, He S, Hao F, . The Pore Structure and Difference between Wufeng and Longmaxi Shales in Pengshui Area, Southeastern Sichuan. Earth Science, 2017, 42(7): 1134-1146. (in Chinese with English Abstract)

[51] Pommer M, Milliken K. Pore Types and Pore-Size Distributions across Thermal Maturity, Eagle Ford Formation, Southern Texas. AAPG Bulletin, 2015, 99(9): 1713-1744.

[52] Quirico E, Rouzaud J N, Bonal L, . Maturation Grade of Coals as Revealed by Raman Spectroscopy: Progress and Problems. Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2005, 61(10): 2368-2377.

[53] Reed R M, Loucks R G, Ruppel S C. Comment on “Formation of Nanoporous Pyrobitumen Residues during Maturation of the Barnett Shale (Fort Worth Basin)” by Bernard et al. (2012). International Journal of Coal Geology, 2014, 127: 111-113.

[54] Schiffbauer J D, Wallace A F, Hunter J L Jr., . Thermally-Induced Structural and Chemical Alteration of Organic-Walled Microfossils: An Experimental Approach to Understanding Fossil Preservation in Metasediments. Geobiology, 2012, 10(5): 402-423.

[55] Schito A, Romano C, Corrado S, . Diagenetic Thermal Evolution of Organic Matter by Raman Spectroscopy. Organic Geochemistry, 2017, 106: 57-67.

[56] Schmidt Mumm A, İnan S. Microscale Organic Maturity Determination of Graptolites Using Raman Spectroscopy. International Journal of Coal Geology, 2016, 162: 96-107.

[57] Staplin F L. Sedimentary Organic Matter, Organic Metamorphism, and Oil and Gas Occurrence. Bulletin of Canadian Petroleum Geology, 1969, 17(1): 47-66

[58] Stasiuk L D. The Origin of Pyrobitumens in Upper Devonian Leduc Formation Gas Reservoirs, Alberta, Canada: An Optical and EDS Study of Oil to Gas Transformation. Marine and Petroleum Geology, 1997, 14(7/8): 915-929.

[59] Tissot B P, Pelet R, Ungerer P. Thermal History of Sedimentary Basins, Maturation Indices, and Kinetics of Oil and Gas Generation. AAPG Bulletin, 1987, 71(12): 1445-1466

[60] Vandenbroucke M, Largeau C. Kerogen Origin, Evolution and Structure. Organic Geochemistry, 2007, 38(5): 719-833.

[61] Varma A K, Mishra D K, Samad S K, . Geochemical and Organo-Petrographic Characterization for Hydrocarbon Generation from Barakar Formation in Auranga Basin, India. International Journal of Coal Geology, 2018, 186: 97-114.

[62] Wang M, Xiao X, Wei Q, . Thermal Maturation of Solid Bitumen in Shale as Revealed by Raman Spectroscopy. Natural Gas Geoscience, 2015, 26(9): 1712-1718. (in Chinese with English Abstract)

[63] Wang R Y, Ding W L, Zhang Y Q, . Analysis of Developmental Characteristics and Dominant Factors of Fractures in Lower Cambrian Marine Shale Reservoirs: A Case Study of Niutitang Formation in Cen’gong Block, Southern China. Journal of Petroleum Science and Engineering, 2016, 138: 31-49.

[64] Wang Y. An Overview on the Maturation Indicators of Organic Matter. Science Paper Online, 2009, 2(9): 900-911. (in Chinese with English Abstract)

[65] Washburn K E, Birdwell J E, Foster M, . Detailed Description of Oil Shale Organic and Mineralogical Heterogeneity via Fourier Transform Infrared Microscopy. Energy & Fuels, 2015, 29(7): 4264-4271.

[66] Wei L, Wang Y Z, Mastalerz M. Comparative Optical Properties of Macerals and Statistical Evaluation of Mis-Identification of Vitrinite and Solid Bitumen from Early Mature Middle Devonian-Lower Mississippian New Albany Shale: Implications for Thermal Maturity Assessment. International Journal of Coal Geology, 2016, 168: 222-236.

[67] Wei S L, He S, Pan Z J, . Models of Shale Gas Storage Capacity during Burial and Uplift: Application to Wufeng-Longmaxi Shales in the Fuling Shale Gas Field. Marine and Petroleum Geology, 2019, 109: 233-244.

[68] Wilkins R W T, Boudou R, Sherwood N, . Thermal Maturity Evaluation from Inertinites by Raman Spectroscopy: The ‘RaMM’ Technique. International Journal of Coal Geology, 2014, 128/129: 143-152.

[69] Wilkins R W T, Wang M, Gan H J, . A RaMM Study of Thermal Maturity of Dispersed Organic Matter in Marine Source Rocks. International Journal of Coal Geology, 2015, 150–151: 252-264.

[70] Wilkins R W T, Wilmshurst J R, Russell N J, . Fluorescence Alteration and the Suppression of Vitrinite Reflectance. Organic Geochemistry, 1992, 18(5): 629-640.

[71] Wu S T, Zhu R K, Cui J G, . Characteristics of Lacustrine Shale Porosity Evolution, Triassic Chang 7 Member, Ordos Basin, NW China. Petroleum Exploration and Development, 2015, 42(2): 185-195.

[72] Wu Z R, He S, Han Y J, . Effect of Organic Matter Type and Maturity on Organic Matter Pore Formation of Transitional Facies Shales: A Case Study on Upper Permian Longtan and Dalong Shales in Middle Yangtze Region, China. Journal of Earth Science, 2020, 31(2): 368-384.

[73] Xu X, Sun W, Wang S, . Maturity Evaluation of Marine Shale in the Lower Paleozoic in South China. Earth Science, 2019, 44(11): 3717-3724. (in Chinese with English Abstract)

[74] Yang R, Hao F, He S, . Experimental Investigations on the Geometry and Connectivity of Pore Space in Organic-Rich Wufeng and Longmaxi Shales. Marine and Petroleum Geology, 2017, 84: 225-242.

[75] Yang R, He S, Yi J Z, . 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, 2016, 70: 27-45.

[76] Yang R, Hu Q H, He S, . Wettability and Connectivity of Overmature Shales in the Fuling Gas Field, Sichuan Basin (China). AAPG Bulletin, 2019, 103(3): 653-689.

[77] Yang W, He S, Iglauer S, . Porosity Characteristics of Different Lithofacies in Marine Shale: A Case Study of Neoproterozoic Sinian Doushantuo Formation in Yichang Area, China. Journal of Petroleum Science and Engineering, 2020, 187: 106856

[78] Yang W, He S, Zhai G Y, . Pore Characteristics of the Lower Sinian Doushantuo Shale in the Mid-Yangtze Yichang Area of China: Insights into a Distinct Shale Gas Reservoir in the Neoproterozoic Formation. Journal of Natural Gas Science and Engineering, 2020, 73 103085

[79] Yang W, He S, Zhai G, . Shale-Gas Accumulation and Pore Structure Characteristics in the Lower Cambrian Niutitang Shales, Cen-Gong Block, South China. Australian Journal of Earth Sciences, 2019, 66(2): 289-303.

[80] Zargari S, Canter K L, Prasad M. Porosity Evolution in Oil-Prone Source Rocks. Fuel, 2015, 153 110-117.

[81] Zeng Y S, Wu C D. Raman and Infrared Spectroscopic Study of Kerogen Treated at Elevated Temperatures and Pressures. Fuel, 2007, 86(7/8): 1192-1200.

[82] Zhang B, Yan D T, Drawarh H J, . Formation Mechanism and Numerical Model of Quartz in Fine-Grained Organic-Rich Shales: A Case Study of Wufeng and Longmaxi Formations in Western Hubei Province, South China. Journal of Earth Science, 2020, 31(2): 354-367.

[83] Zhang M, Peng S, Zhang L, . New Recognition of Carbonate nodules Genesis in Sinian Doushantuo Formation in Zigui Area and Its Geological Implication. Earth Science, 2016, 41(12): 1977-1994. (in Chinese with English Abstract)

[84] Zhang C, Xia X, Yang Y, . Raman Spectrum Characteristics of Organic Matter in Silurian Longmaxi Formation Shale of Well Anye-1 and Its Geological Significance. Rock and Mineral Analysis, 2019, 38(1): 26-34. (in Chinese with English Abstract)

[85] Zhou Q, Xiao X M, Pan L, . The Relationship between Micro-Raman Spectral Parameters and Reflectance of Solid Bitumen. International Journal of Coal Geology, 2014, 121: 19-25.

[86] Zou C N, Yang Z, Zhang G S, . Conventional and Unconventional Petroleum “Orderly Accumulation”: Concept and Practical Significance. Petroleum Exploration and Development, 2014, 41(1): 14-30.