Abstract
The pore structure and fractal characteristics of the Lower Cambrian marine organic-rich shale in southern China were comprehensively studied using low-pressure adsorption and organic geochemical experiments, X-ray diffraction, petrophysical property tests, and scanning electron microscope observations. The results indicate that the total organic carbon (TOC) content of the study shale varies between 0.45% and 8.50%, with an average value of 3.97%. The adsorption isotherm of the shale samples belongs to type IV, and slit-type pores are the predominant pore type in these shales. The shale has a Brunner–Emmet–Teller specific surface area ranging from 1.83 to , a pore volume ranging from 0.00398 to , and an average pore diameter ranging from 3.61 to 15.19 nm. Organic matter pores (OMPs) are the main contributors to the specific surface area and the pore volume. The organic matter is closely symbiotic with the epigenetic quartz. We have obtained two fractal dimensions ( and ) of the shale using the Frenkel-Halsey-Hill method. It was found that is suitable for the quantitative characterizing of the pore structure of nanopores inside the shale due to its good correlation with the TOC content and pore structure parameters. When the TOC content of the shale exceeds 4%, the main pore type inside the shale is OMP and the value mainly reflects the fractal characteristics of OMP. Moreover, we analyzed the seepage characteristics of different types of pores. It was found that the parallel plate-like pores and the slit-type pores are more favorable for fluid seepage than the ink bottle-like pores. The shale with and type pore structures should be the key exploration targets for the target shale in the study area.
References
- 2015, Characterization and analysis of porosity and porestructures: Reviews in Mineralogy and Geochemistry, 80,
161–164 . , - 1940, On a theory of the van der Waals adsorption of gases: Journal of the American Chemical Society, 62,
1723–1732 . , - 2012, Sweet spots in shale gas and liquids plays: Prediction of fluid composition and reservoir pressure: Search and Discovery Article, 40936,
12–15 . , - 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,
1099–1119 .AABUD20149–1423 , - 2019, Charging of Carboniferous volcanic reservoirs in eastern Chepaizi Uplift, Junggar Basin (NW China) constrained by oil geochemistry and fluid inclusion: AAPG Bulletin, 103,
1–14 , doi:10.1306/12171818041 .AABUD20149–1423 , - 2013, Pore structure characterization of North American shale gas reservoirs using USANS/SANS, gas adsorption, and mercury intrusion: Fuel, 103,
606–616 , doi:10.1016/j.fuel.2012.06.119 . , - 1998, Kerogen conversion in fractured shale petroleum systems: AAPG Bulletin, 82,
5–7 .AABUD20149–1423 , - 2002, Fractured shale-gas system: AAPG Bulletin, 86,
1921–1938 .AABUD20149–1423 , - 2019, Geochronology and geochemistry of Permo-Triassic sandstones in eastern Jilin Province (NE China): Implications for final closure of the Paleo-Asian Ocean: Geoscience Frontiers, 10,
685–706 . , - 1982, Adsorption, surface area and porosity, 2nd ed.: Academic Press. ,
- 2019, Source analysis of quartz from the upper Ordovician and lower Silurian black shale and its effects on shale gas reservoir in the Southern Sichuan Basin and its periphery, China: Geological Journal, 54,
439–449 . , - 2016, The lithofacies and reservoir characteristics of the upper Ordovician and lower Silurian black shale in the southern Sichuan Basin and its periphery, China: Marine and Petroleum Geology, 75,
181–191 , doi:10.1016/j.marpetgeo.2016.04.014 . , - 2018, Pore characteristics of distinct thermally mature shales: Influence of particle size on low-pressure CO2 and N2 adsorption: Energy and Fuels, 32,
8175–8186 . , - 1985, Disperse solid bitumens as an indicator for migration and maturity in prospecting for oil and gas: Erdol und Kohle Erdgas Petrochemie, 38,
364–366 . , - 2007, Comparative life-cycle air emissions of coal, domestic natural gas, LNG, and SNG for electricity generation: Environmental Science and Technology, 41,
6290–6296 . , - 2007, Unconventional shale-gas systems: The Mississippian Barnett shale of north-central Texas as one model for thermogenic shale-gas assessment: AAPG Bulletin, 91,
475–499 .AABUD20149–1423 , - 2008, Coalbed- and shale-gas reservoirs: Journal of Petroleum Technology, 60,
92–99 , doi:10.2118/103514-JPT . , - 2013, Characteristics of pore permeability of highly metamorphic bone coal (in Chinese with English abstract): Coal Geology and Exploration, 41,
9–13 . , - 2018, Characteristics of in-situ stress state and prediction of the permeability in the upper Permian coalbed methane reservoir, western Guizhou region, SW China: Journal of Petroleum Science and Engineering, 165,
199–211 , doi:10.1016/j.petrol.2018.02.037 . , - 2015, Fractal analysis of tight gas sandstones using high-pressure mercury intrusion techniques: Journal of Natural Gas Science and Engineering, 24,
185–196 , doi:10.1016/j.jngse.2015.03.027 . , - 2017b, Deep burial diagenesis and reservoir quality evolution of high-temperature, high-pressure sandstones: Examples from lower Cretaceous Bashijiqike Formation in Keshen area, Kuqa depression, Tarim basin of China: AAPG Bulletin, 101,
829–862 .AABUD20149–1423 , - 2016, Insight into the pore structure of tight sandstones using NMR and HPMI measurements: Energy and Fuels, 30,
10200–10214 . , - 2017a, Fracture detection in oil-based drilling mud using a combination of borehole image and sonic logs: Marine and Petroleum Geology, 84,
195–214 , doi:10.1016/j.marpetgeo.2017.03.035 . , - 2018b, Review of diagenetic facies in tight sandstones: Diagenesis, diagenetic minerals, and prediction via well logs: Earth-Science Reviews, 185,
234–258 , doi:10.1016/j.earscirev.2018.06.009 . , - 2018a, A review on pore structure characterization in tight sandstones: Earth-Science Reviews, 177,
436–457 , doi:10.1016/j.earscirev.2017.12.003 . , - 2017, Quantitative impact of diagenesis on reservoir quality of the Triassic Chang 6 tight oil sandstones, Zhenjing area, Ordos Basin, China: Marine and Petroleum Geology, 86,
1014–1028 . , - 2015, Investigation of pore structure and fractal characteristics of organic-rich Yanchang formation shale in central China by nitrogen adsorption/desorption analysis: Journal of Natural Gas Science and Engineering, 22,
62–72 , doi:10.1016/j.jngse.2014.11.020 . , - 2018, Diagenetic constraints on the heterogeneity of tight sandstone reservoirs: A case study on the upper Triassic Xujiahe Formation in the Sichuan Basin, southwest China: Marine and Petroleum Geology, 92,
650–669 , doi:10.1016/j.marpetgeo.2017.11.027 . , - 2017, Depositional environment, sequence stratigraphy and sedimentary mineralization mechanism in the coalbed- and oil shale-bearing succession: A case from the Paleogene Huangxian Basin of China: Journal of Petroleum Science and Engineering, 148,
32–51 , doi:10.1016/j.petrol.2016.09.028 . , - 1977, The fractal geometry of Nature: Freeman. ,
- 2013, Organic matter-hosted pore system, Marcellus Formation (Devonian), Pennsylvania: AAPG Bulletin, 97,
177–200 , doi:10.1306/07231212048 .AABUD20149–1423 , - 2016, Characteristics and origin of amygdale and crack fillers in volcanic rock of late Carboniferous in Santanghu basin, Xinjiang: Acta Petroleum Sinica, 32,
1901–1913 . , - 2013, Exploration potential of shale gas in Cen’gong block, southeastern Guizhou province (in Chinese with English abstract): Oil Gas Geology, 34,
274–280 . , - 2018, Factors impacting on oil retention in lacustrine shale: Permian Lucaogou Formation in Jimusaer Depression, Junggar Basin: Journal of Petroleum Science and Engineering, 163,
79–90 , doi:10.1016/j.petrol.2017.12.080 . , - 2019, Mesozoic-Cenozoic denudation and thermal history in the central uplift of the South Yellow Sea basin and the implications for hydrocarbon systems: Constraints from the CSDP-2 borehole: Marine and Petroleum Geology, 99,
355–369 , doi:10.1016/j.marpetgeo.2018.10.027 . , - 1993, Guide for the application of biological markets: Prentice-Hall. ,
- 1983, Chemistry nonintegral dimensions between two and three: The Journal of Chemical Physics, 79,
3369–3558 . , - 2004, An investigation of fractal characteristics of mesoporous carbon electrodes with various pore structures: Electrochimica Acta, 49,
4171–4180 . , - 2002, Adsorption isotherms of fractal surfaces: Colloids and Surfaces A: Physicochemical and Engineering Aspects, 206,
401–407 , doi:10.1016/S0927-7757(02)00063-8 . , - 2014, Late triassic tuff intervals in the Ordos basin, Central China: Their epositional, petrographic, geochemical characteristics and regional implications: Journal of Asian Earth Sciences, 80,
148–160 , doi:10.1016/j.jseaes.2013.11.004 . , - 1996, SY/T 5336-1996, method of core routine analysis (in Chinese): Petroleum Industry Press. ,
- 2007, Shale gas potential of the lower Jurassic Grdondale Member, northeastern British Columbia: Bulletin of Canadian Petroleum Geology, 55,
51–75 . , - 2009, The importance of shale composition and pore structure upon gas storage potential of shale gas reservoirs: Marine and Petroleum Geology, 26,
916–927 , doi:10.1016/j.marpetgeo.2008.06.004 . , - 2019, Quantitative evaluation model of tight sandstone reservoirs based on statistical methods — A case study of the triassic Chang 8 tight sandstones, Zhenjing area, Ordos Basin, China: Journal of Petroleum Science and Engineering, 173,
601–616 , doi:10.1016/j.petrol.2018.10.035 . , - 1985, Reporting physisorption data for gas/solid systems with special reference to the determination of surface area and porosity: Pure and Applied Chemistry, 57,
603–619 .MPEGD8 0264-8172 , - 2015, Experimental investigation of thermal maturation on shale reservoir properties from hydrous pyrolysis of Chang 7 shale, Ordos Basin: Marine and Petroleum Geology, 64,
165–172 , doi:10.1016/j.marpetgeo.2015.02.046 . , - 2015, Pore characterization of organic-rich lower Cambrian shales in Qiannan Depression of Guizhou province, Southwestern China, Ordos Basin: Marine and Petroleum Geology, 62,
28–43 , doi:10.1016/j.marpetgeo.2015.01.004 . , - 1996, Elastic anisotropy of source rocks: Implications for hydrocarbon generation and primary migration: AAPG Bulletin, 80,
531–544 .AABUD20149–1423 , - 2017, In-situ disposal of CO2: Liquid and supercritical CO2 permeability in coal at multiple down-hole stress conditions: Journal of CO2 Utilization, 17,
235–242 . , - 2013b, Permeability of sub-critical carbon dioxide in naturally fractured India bituminous coal at a down-hole stress conditions: Engineering Geology, 167,
148–156 , doi:10.1016/j.enggeo.2013.10.007 . , - 2013a, CO2 permeability of Indian bituminous coals: Implications for carbon sequestration: International Journal of Coal Geology, 105,
36–47 , doi:10.1016/j.coal.2012.11.003 . , - 2015, Influence of sorption time in CO2-ECBM process in Indian coals using coupled numerical simulation: Fuel, 139,
51–58 , doi:10.1016/j.fuel.2014.08.009 . , - 1996, SY/T 6210-1996, quantitative analysis of total contents of clay minerals and common non-clay minerals in sedimentary rocks by X-ray diffraction (in Chinese): Petroleum Industry Press. ,
- 2016b, Effects of gas diffusion from fractures to coal matrix on the evolution of coal strains: Experimental observations: International Journal of Coal Geology, 162,
74–84 , doi:10.1016/j.coal.2016.05.012 . , - 2016a, Hydrocarbon generation characteristics, reserving performance and preservation conditions of continental coal measure shale gas: A case study of mid-Jurassic shale gas in the Yan’an Formation, Ordos Basin: Journal of Petroleum Science and Engineering, 145,
609–628 , doi:10.1016/j.petrol.2016.06.031 . , - 2017a, Impact of diagenesis on reservoir quality and heterogeneity of the Upper Triassic Chang 8 tight oil sandstones in the Zhenjing area, Ordos Basin, China: Marine and Petroleum Geology, 83,
84–96 , doi:10.1016/j.marpetgeo.2017.03.008 . , - 2017b, Quantitative analyses of porosity evolution in tight grainstones: A case study of the Triassic Feixianguan formation in the Jiannan gas field, Sichuan Basin, China: Marine and Petroleum Geology, 86,
259–267 , doi:10.1016/j.marpetgeo.2017.05.021 . , - 2005, SY/T 5118-2005, Determination of bitumen from rocks by chloroform extraction: Petroleum and Gas Standards. ,
- 2019, Petrogenesis of early cretaceous andesite dykes in the Sulu orogenic belt, eastern China: Mineralogy and Petrology, 113,
77–97 , doi:10.1007/s00710-018-0636-1 . , - 2015, Micro-structure evaluation of gas reservoir based on fractal theory (in Chinese with English abstract): Natural Gas Geoscience, 26,
754–759 . , - 2014, Influence of Soxhlet-extractable bitumen and oil on porosity in thermally maturing organic-rich shales: International Journal of Coal Geology, 132,
38–50 , doi:10.1016/j.coal.2014.08.003 . , - 1995, SY/T 6154-1995, Determination for rock specific surface area and pore size distribution — Static nitrogen absorption volumetric method (in Chinese): Chinese Standard. ,
- 2006, Contrast of nitrogen adsorption method and mercury intrusion method in analysis of shale pore size distribution (in Chinese with English abstract): Natural Gas Industry, 26,
100–102 . , - 2003, GB/T 19145-2003, Determination of total organic carbon in sedimentary rock: Standards Press of China. ,
- 1979, Adsorption and condensation: The surface and pore of solid (in Chinese): Science Press. ,
- 2014, Fractal characteristics of shales from a shale gas reservoir in the Sichuan Basin, China: Fuel, 115,
378–384 , doi:10.1016/j.fuel.2013.07.040 . , - 2017, Climatic and tectonic controls of lacustrine hyperpycnite origination in the late triassic Ordos Basin, Central China: Implications for unconventional petroleum development: AAPG Bulletin, 101,
95–117 .AABUD20149–1423 , - 2008, Fractal characterization of adsorption-pores of coals from North China: An investigation on CH4 adsorption capacity of coals: International Journal of Coal Geology, 73,
27–42 , doi:10.1016/j.coal.2007.07.003 . , - 2019, Evaluation indexes of coalbed methane accumulation in the strong deformed strike-slip fault zone considering tectonics and fractures: A 3D geomechanical simulation study: Geological Magazine, 156,
1052–1068 , doi:10.1017/S0016756818000456 . , - 2016, Shale uniaxial compressive failure property and the affecting factors of UCS (in Chinese with English abstract): Earth Science Frontiers, 23,
75–95 . , - 2018c, Numerical simulation of the in situ stress in a high-rank coal reservoir and its effect on coal-bed methane well productivity: Interpretation, 6, no. 2,
T271–T281 , doi:10.1190/INT-2017-0183.1 . , - 2018b, New method for assessing microfracture stress sensitivity in tight sandstone reservoirs based on acoustic experiments: International Journal of Geomechanics, 18,
1–16 . , - 2019b, Developmental characteristics and distribution law of fractures in a tight sandstone reservoir in a low-amplitude tectonic zone, eastern Ordos Basin, China: Geological Journal, 54,
1–9 , doi:10.1002/gj.v54.1 . , - 2019a, In situ stress heterogeneity in a highly developed strike-slip fault zone and its effect on the distribution of tight gases: A 3D finite element simulation study: Marine and Petroleum Geology, 81,
1–17 . , - 2018a, Strain energy density distribution of a tight gas sandstone reservoir in a low-amplitude tectonic zone and its effect on gas well productivity: A 3D FEM study: Journal of Petroleum Science and Engineering, 170,
89–104 , doi:10.1016/j.petrol.2018.06.057 . , - 2010, Characteristics of high gamma ray reservoir of Yanchang formation in Ordos Basin: Chinese Journal of Geophysics, 53,
205–213 . , - 2017, Lithology-dependent minimum horizontal stress and in-situ stress estimate: Tectonophysics, 703,
1–8 . , - 2019, Nuclear magnetic resonance experiment analysis of tight gas sandstone reservoir: Fresenius Environmental Bulletin, 24,
1–7 . , - 2018, Micropore heterogeneity of marine shale reservoirs and its quantitative characterization: Journal of China University of Mining and Technology, 47,
1–12 . , - 2012, Tight gas sandstone reservoir in China: Characteristics and recognition criteria: Journal of Petroleum Science and Engineering, 88–89,
82–91 . ,