Microstructural characterisation of organic matter pores in coal-measure shale

Abstract

To gain the insight into the nature of organic matter (OM) micro-nanometer pores and fractal features of coal-measure shale from the OM macromolecular evolution perspective, 28 Taiyuan formation shale samples are collected from Qinshui Basin and characterized with Rock-eval, Field emission scanning electron microscope (FE-SEM), low-pressure N₂ gas adsorption (Lp-N₂GA) and Fourier transform infrared spectroscopy (FTIR). The results show that OM is in the high-over mature stage. Pore size ranges from 5.7 to 26.7 nm and pores less than 4 nm are dominant. Two pore fractal dimensions D₁ and D₂ are obtained from Lp-N₂GA with the Frenkel-Halsey-Hill method, which are in the range of 2.272-2.617 and 2.561-2.799, respectively. A series of FTIR structure parameters are obtained by peak fitting the FTIR spectra to describe the microstructure of OM molecules, such as length of aliphatic chain, degree of aromatic carbon condensation and hydrocarbon generation potential. Micro-nanometer OM-related pores in FE-SEM images can be classified as OM hydrocarbon-generating pores, OM structure pores, OM intergranular pores and micro- cracks, with the first being most developed. Both hydrocarbon-generation and condensation of aromatic nucleus have positive effects on D₁ . Hydrocarbon-generation is more effective for the development of micropores, while the condensation of aromatic nucleus is more conducive for the development of mesopores (<10 nm). The higher the total organic carbon content, and the more the micropores and mesopores (<10 nm) develop, the higher the value of D₁ .

Cited as: Li, K., Kong, S., Xia, P., Wang, X. Microstructural characterisation of organic matter pores in coal-measure shale. Advances in Geo-Energy Research, 2020, 4(4): 372-391, doi: 10.46690/ager.2020.04.04

References

Abouelresh, M.O. An integrated characterization of the porosity in Qusaiba Shale, Saudi Arabia. J. Pet. Sci. Eng. 2017, 149: 75-87.

Bhargava, S., Awaja, F., Subasinghe, N. Characterisation of some Australian oil shale using thermal, X-ray and IR techniques. Fuel 2005, 84(6): 707-715.

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). Org. Geochem. 2017, 110: 122-133.

Curtis, M.E., Sondergeld, C.H., Ambrose, R.J., et al. Mi-crostructural investigation of gas shales in two and three dimensions using nanometer-scale resolution imaging. AAPG Bull. 2012, 96(4): 665-677.

Fleury, M., Romero-Sarmiento, M. Characterization of shales using T1-T2 NMR maps. J. Pet. Sci. Eng. 2016, 137: 55-62.

Dong, D.Z., Guan, Q.Z., Wang, S.F., et al. Shale gas in China: Reality and dream. Energy Explor. Exploit. 2015, 33(3): 397-418.

Gao, Z.Y., Fan, Y.P., Xuan, Q.X., et al. A review of shale pore structure evolution characteristics with increasing thermal maturities. Adv. Geo-Energy Res. 2020, 4(3): 247-259.

Gou, Q.Y., Xu, S., Hao F., et al. Full-scale pores and micro-fractures characterization using FE-SEM, gas adsorption, nano-CT and micro-CT: A case study of the Silurian Longmaxi Formation shale in the Fuling area, Sichuan Basin, China. Fuel 2019, 253: 167-179.

Gu, X., Cole, D.R., Rother, G., et al. Pores in Marcellus Shale: A neutron scattering and FIB-SEM study. Energy Fuels 2015, 29(3): 1295-1308.

Ibarra, J. Muñoz, E., Moliner, R. FTIR study of the evolution of coal structure during the coalification process. Org. Geochem. 1996, 24: 725-735.

Jaroniec, M., Avnir, D., An isotherm equation for adsorption on fractal surfaces of heterogeneous porous materials. Langmuir 1989, 5: 1431-1433.

Jarvie, D.M., Hill, R.J., Ruble, T.E., et al. Unconventional shale-gas systems: The mississippian barnett shale of north-central texas as one model for thermogenic shale-gas assessment. AAPG Bull. 2007, 91(4): 475-499.

Ji, W.M., Song, Y., Jiang, Z.X., et al. Fractal characteristics of nano-pores in the Lower Silurian Longmaxi shales from the Upper Yangtze Platform, south China. Mar. Pet. Geol. 2016, 78: 88-98.

John, M. Hunt. Petroleum Geochemistry and Geology, Second Edition. New York, USA, W. H. Freeman, 1996.

Ko, L.T., Loucks, R.G., Milliken, K.L., et al. Controls on pore types and pore-size distribution in the Upper Triassic Yanchang Formation, Ordos Basin, China: Implications for pore-evolution models of lacustrine mudrocks. Interpretation 2017, 5(2): 127-148.

Kong, S.Q., Huang, X., Li, K.J., et al. Adsorption/desorption isotherms of CH4 and C2H6 on typical shale samples. Fuel 2019, 255: 115632.

Li, K.J., Chen, G., Li, W., et al. Characterization of marine-terrigenous transitional Taiyuan formation shale reservoirs in Hedong coal field, China. Adv. Geo-Energy Res. 2018, 2(1): 72-85.

Li, K.J., Zeng, F.G., Cai, J.C., et al. Fractal characteristics of pores in Taiyuan formation shale from Hedong coal field, China. Fractals 2018a, 26(2): 1840006.

Li, K.J., Zeng, F.G., Sheng, G.L., et al. Investigation of fractal characteristics of taiyuan formation coal-shale from southern qinshui basin, china, by nitrogen adsorption and desorption analysis. J. Porous Media 2018b, 21(10): 929-951.

Li, X.H., Gao, Z.Y., Fang, S.Y., et al. Fractal characterization of nanopore structure in shale, tight sandstone and mudstone from the ordos basin of china using nitrogen adsorption. Energies 2019, 12(4): 583.

Li, X., Zeng, F.G., Wang, W., et al. FTIR characterization of structural evolution in low-middle rank coals. Journal of China Coal Society 2015, 40(32): 2900-2908. (in Chinese)

Lis, G.P., Mastalerz, M., Schimmelmann, A., et al. FTIR absorption indices for thermal maturity in comparison with vitrinite reflectance R0 in type-II kerogens from Devonian black shales. Org. Geochem. 2005, 36(11): 1533-1552.

Liu, X.F., Nie, B.S., Wang, W.X., et al. The use of AFM in quantitative analysis of pore characteristics in coal and coal-bearing shale. Mar. Pet. Geol. 2019, 105: 331-337.

Loucks, R.G., Reed, R.M., Ruppel, S.C., et al. Morphology, genesis, and distribution of nanometer-scale pores in siliceous mudstones of the Mississippian Barnett Shale. J. Sediment. Res. 2009, 79(12): 848-861.

Pfeiferper, P., Avnir, D. Chemistry nonintegral dimensions between two and three. J. Chem. Phys. 1983, 79: 3369-3558.

Rouquerol, J., Avnir, D., Fairbridge, C.W., et al. Recommendations for the characterization of porous solids (Technical Report). Pure Appl. Chem. 1994, 66(8): 1739-1758.

Shao, X.H., Pang, X.Q., Li, Q.W., et al. Pore structure and fractal characteristics of organic-rich shales: A case study of the lower Silurian Longmaxi shales in the Sichuan Basin, SW China. Mar. Pet. Geol. 2017, 80: 192-202.

Sheng, G.L., Su, Y.L., Wang, W.D. New fractal approach for describing induced fracture porosity/permeability/compressibility in stimulated uncoonventional reservoirrs. J. Pet. Sci. Eng. 2019, 179: 855-866.

Slatt, R.M., O”Brien, N.R. Pore types in the barnett and woodford gas shales: Contribution to understanding gas storage and migration pathways in fine-grained rocks. AAPG Bull. 2011, 95: 2017-2030.

Sun, M.D., Yu, B.S., Hu, Q.H., et al. Nanoscale pore characteristics of the lower cambrian niutitang formation shale: A case study from Well Yuke #1 in the Southeast of Chongqing, China. Int. J. Coal Geol. 2016, 154-155: 16-29.

Wang, S.Q. Shale gas exploration and appraisal in China: Problems and discussion. Natural Gas Industry 2013, 33(12): 13-29. (in Chinese)

Wang, S.Y., Tang, Y.G., Schobert, H.H., et al. FTIR and 13C NMR investigation of coal component of late permian coals from Southern China. Energy Fuels 2011, 25(12): 5672-5677.

Wood, D.A., Hazra, B. Pyrolysis S2-peak characteristics of raniganj shales (India) reflect complex combinations of kerogen kinetics and other processes related to different levels of thermal maturity. Adv. Geo-Energy Res. 2018, 2(4): 343-368.

Yang, F., Ning, Z.F., Liu, H.Q. Fractal characteristics of shales from a shale gas reservoir in the Sichuan Basin, China. Fuel 2014, 115: 378-384.

Yang, F., Ning, Z.F., Wang, Q., et al. Pore structure characteristics of lower Silurian shales in the southern Sichuan Basin, China: Insights to pore development and gas storage mechanism. Int. J. Coal Geol. 2016, 156: 12-24.

Yang, R., He, S., Yi, J.Z., et al. 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. Mar. Pet. Geol. 2016, 70: 27-45.

Zhang, J.C., Fan, T.L., Li, J., et al. Characterization of the Lower Cambrian Shale in the northwestern Guizhou province, south China: Implications for shale-gas potential. Energy Fuels 2015, 29(10): 6383-6393.

Zhang, Q., Liu, R.H., Pang, Z.L., et al. Characterization of microscopic pore structures in Lower Silurian black shale (S1l), southeastern Chongqing, China. Mar. Pet. Geol. 2016, 71: 250-259.

Zhou, L., Kang, Z.H. Fractal characterization of pores in shales using NMR: A case study from the Lower Cambrian Niutitang Formation in the Middle Yangtze Platform, Southwest China. J. Nat. Gas Sci. Eng. 2016, 35: 860-872.

Zou, C.N., Dong, D.Z., Wang, Y.M., et al. Shale gas in China: Characteristics, challenges and prospects (II). Pet. Explor. Dev. 2016, 43(2): 182-196.

Zou, C.N., Yang, Z., Huang, S.P., et al. Resource types, formation, distribution and prospects of coal-measure gas. Pet. Explor. Dev. 2019, 46(3): 451-462.