Quantitative description of shale pore structure using image analysis and determination of controls on shape, size and orientation complexity

  • Gaoyuan Yan
  • Chongtao Wei
  • Yu Song
  • Jinhui Luo
  • Junjian Zhang
Original Paper


Pore structure characteristics are important aspects of shale reservoirs. Shale samples were collected from the Taiyuan and Shanxi Formations from the WX-1 well in the Qinshui basin, Shanxi, China. Pore morphology was analyzed using argon ion polishing scanning electron microscopy (Ar-SEM) and focused ion beam scanning electron microscopy (FIB-SEM). Subsequently, the structural pore features in the images were quantitatively characterized using the pores (Particles) and cracks analysis system (PCAS) method. The results show that the sample pores are primarily organic pores, intergranular pores, and intragranular pores, and the pore sizes are concentrated at less than 100 nm. In addition, the following rules are determined: first, with the pixel accuracy (PA) increase on the same pore, the pore edge becomes smooth, the degree of pore orientations (DPO) improves, and the apparent pore structure complexity (APSC) decreases. In addition, when the pore edge roughness increases and the DPO decreases, this effect becomes larger to change PA. Second, when the pore shape tends to be “round,” the edge becomes smooth, and APSC decreases; when the pore tends to be “narrow,” the edge becomes rough, and the APSC increases. Third, with the increase of depth, the pore size and DPO first increase and then decrease, and the APSC decreases gradually; with the increase of maturity, the pore size first decreases and then increases. Conversely, the APSC first increases and then decreases when the turning point occurs in the high-mature to over-mature stages of the transition, and the DPO improves.


Qinshui basin Apparent pore structure complexity Form factor Fractal dimension Probability entropy 



We thank associate professor Chun Liu for providing PCAS. This work is supported by the 13th Five-year Plan for large-scale oil and gas fields and coalbed methane development (No. 2016ZX05044002-003), the coal fundamental science and technology key projects in Shanxi, China (No. MQ 2014), the Scientific Research Foundation of Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, Ministry of Education (China University of Mining and Technology) (No. 2016-008), and surface well placement optimization via the topology analysis of well spatial form (41402291).


  1. Bai B, Elgmati M, Zhang H, Wei M (2013) Rock characterization of Fayetteville shale gas plays. Fuel 105:645–652. CrossRefGoogle Scholar
  2. Bernard S, Wirth R, Schreiber A, Schulz H, Horsfield B (2012) Formation of nanoporous pyrobitumen residues during maturation of the Barnett Shale (Fort Worth sBasin). Int J Coal Geol 103:3–11. CrossRefGoogle Scholar
  3. Bu H, Ju Y, Tan J, Wang G, Li X (2015) Fractal characteristics of pores in non-marine shales from the Huainan coalfield, eastern China. J Nat Gas Sci Eng 24:166–177. CrossRefGoogle Scholar
  4. Chalmers GRL, Bustin RM (2007) The organic matter distribution and methane capacity of the Lower Cretaceous strata of Northeastern British Columbia, Canada. Int J Coal Geol 70(1-3):223–239. CrossRefGoogle Scholar
  5. Chen J, Xiao X (2014) Evolution of nanoporosity in organic-rich shales during thermal maturation. Fuel 129:173–181. CrossRefGoogle Scholar
  6. Chen YY, Zou CN, Maria M, Zhu R k, Bai B, Yang Z (2015) Porosity and fractal characteristics of shale across a maturation gradient. Nat Gas Geosci 26:1646–1656.
  7. Chen Q, Kang Y, You L, Yang P, Zhang X, Cheng Q (2017) Change in composition and pore structure of Longmaxi black shale during oxidative dissolution. Int J Coal Geol 172:95–111. CrossRefGoogle Scholar
  8. Curtis JB (2002) Fractured shale gas system. AAPG Bull 86:1921–1938.
  9. Curtis ME, Cardott BJ, Sondergeld CH, Rai CS (2012) Development of organic porosity in the Woodford Shale with increasing thermal maturity. Int J Coal Geol 103:26–31. CrossRefGoogle Scholar
  10. Dathe A, Eins S, Niemeyer J, Gerold G (2001) The surface fractal dimension of the soil–pore interface as measured by image analysis. Geoderma 103(1-2):203–229. CrossRefGoogle Scholar
  11. Deng H, Hu X, Li HA, Luo B, Wang W (2016) Improved pore-structure characterization in shale formations with FESEM technique. J Nat Gas Sci Eng 35:309–319. CrossRefGoogle Scholar
  12. Fishman NS, Hackley PC, Lowers HA, Hill RJ, Egenhoff SO, Eberl DD, Blum AE (2012) The nature of porosity in organic-rich mudstones of the Upper Jurassic Kimmeridge Clay Formation, North Sea, offshore United Kingdom. Int J Coal Geol 103:32–50. CrossRefGoogle Scholar
  13. Fu CQ, Zhu YM, Chen SB (2016) Pore structure and fractal features of Hetang formation shale in western Zhejiang. J China Univ Min Tecnol 45:77–86.
  14. Gensterblum Y, Ghanizadeh A, Cuss RJ, Amann-Hildenbrand A, Krooss BM, Clarkson CR, Harrington JF, Zoback MD (2015) Gas transport and storage capacity in shale gas reservoirs—a review. Part A: transport processes. J Unconv Oil Gas Resour 12:87–122. CrossRefGoogle Scholar
  15. Hu J, Tang S, Zhang S (2016) Investigation of pore structure and fractal characteristics of the Lower Silurian Longmaxi shales in western Hunan and Hubei Provinces in China. J Nat Gas Sci Eng 28:522–535. CrossRefGoogle Scholar
  16. Javadpour F, Fisher D, Unsworth M (2007) Nanoscale gas flow in shale gas sediments. J Can Pet Technol 46:55–61.
  17. Jiao K, Yao S, Liu C, Gao Y, Wu H, Li M, Tang Z (2014) The characterization and quantitative analysis of nanopores in unconventional gas reservoirs utilizing FESEM–FIB and image processing: an example from the lower Silurian Longmaxi Shale, upper Yangtze region, China. Int J Coal Geol 128-129:1–11. CrossRefGoogle Scholar
  18. Jin L, Mathur R, Rother G, Cole D, Bazilevskaya E (2013) Evolution of porosity and geochemistry in Marcellus Formation black shale during weathering. Chem Geol 356:50–63. CrossRefGoogle Scholar
  19. Karasu B, Sezer A, Sezer G, Ramyar K, Ktepe AG (2008) Image analysis of sulfate attack on hardened cement paste. Mater Des 29:224–231.
  20. Klaver J, Desbois G, Urai JL, Littke R (2012) BIB-SEM study of the pore space morphology in early mature Posidonia Shale from the Hils area, Germany. Int J Coal Geol 103:12–25. CrossRefGoogle Scholar
  21. Klaver J, Desbois G, Littke R, Urai JL (2016) BIB-SEM pore characterization of mature and post mature Posidonia Shale samples from the Hils area, Germany. Int J Coal Geol 158:78–89. CrossRefGoogle Scholar
  22. Liang M, Wang Z, Gao L, Li C, Li H (2017) Evolution of pore structure in gas shale related to structural deformation. Fuel 197:310–319. CrossRefGoogle Scholar
  23. Liu K, Ostadhassan M (2017a) Multi-scale fractal analysis of pores in shale rocks. J Appl Geophys 140:1–10. CrossRefGoogle Scholar
  24. Liu K, Ostadhassan M (2017b) Quantification of the microstructures of Bakken shale reservoirs using multi-fractal and lacunarity analysis. J Nat Gas Sci Eng 39:62–71. CrossRefGoogle Scholar
  25. Liu C, Shi B, Zhou J, Tang C (2011) Quantification and characterization of microporosity by image processing, geometric measurement and statistical methods: application on SEM images of clay materials. Appl Clay Sci 54(1):97–106. CrossRefGoogle Scholar
  26. Liu C, Tang CS, Shi B, Suo WB (2013) Automatic quantification of crack patterns by image processing. Comput Geosci 57:77–80. CrossRefGoogle Scholar
  27. Liu X, Xiong J, Liang L (2015) Investigation of pore structure and fractal characteristics of organic-rich Yanchang formation shale in central China by nitrogen adsorption/desorption analysis. J Nat Gas Sci Eng 22:62–72. CrossRefGoogle Scholar
  28. Loucks RG, Reed RM (2014) Scanning-electron-microscope petrographic evidence for distinguishing organic matter pores associated with depositional organic matter versus migrated organic matter in mudrocks. GCAGS J 3:51–60.Google Scholar
  29. Loucks RG, Reed RM, Ruppel SC, Jarvie DM (2009) Morphology, genesis, and distribution of nanometer-scale pores in siliceous mudstones of the Mississippian Barnett Shale. J Sediment Res 79(12):848–861. CrossRefGoogle Scholar
  30. Loucks RG, Reed RM, Ruppel SC, Hammes U (2012) Spectrum of pore types and networks in mudrocks and a descriptive classification for matrix-related mudrock pores. AAPG Bull 96(6):1071–1098. CrossRefGoogle Scholar
  31. Lubelli B, de Winter DAM, Post JA, van Hees RPJ, Drury MR (2013) Cryo-FIB–SEM and MIP study of porosity and pore size distribution of bentonite and kaolin at different moisture contents. Appl Clay Sci 80-81:358–365. CrossRefGoogle Scholar
  32. Mares TE, Radliński AP, Moore TA, Cookson D, Thiyagarajan P, Ilavsky J, Klepp J (2009) Assessing the potential for CO2 adsorption in a subbituminous coal, Huntly Coalfield, New Zealand, using small angle scattering techniques. Int J Coal Geol 77(1-2):54–68. CrossRefGoogle Scholar
  33. Qin Y, Zhang DM, Fu XH, Lin DY, Ye JP, Xu ZB (1999) A discussion on correlation of modern tectonic stress field to physical properties of coal reservoirs in Central and Southern Qinshui Basin. Geol Rev 45:576–583.
  34. Qin Y, Shen J, Wang BW, Yang S, Zhao L (2012) Accumulation effects and coupling relationship of deep coalbed methane. Acta Pet Sin 33: 48–54.
  35. Qu XR, Zhu YM, Zhang QH (2017) Reservoir characteristics and co-exploration and concurrent production analysis of unconventional natural gases in transitional facies coal measures: taking Yushe-Wuxiang Block as an example. J Xi’an Shiyou Univ (Nat Sci Ed) 32:1–8.
  36. Radlinski AP, Mastalerz M, Hinde AL, Hainbuchner M, Rauch H, Baron M, Lin JS, Fan L, Thiyagarajan P (2004) Application of SAXS and SANS in evaluation of porosity, pore size distribution and surface area of coal. Int J Coal Geol 59(3–4):245–271. CrossRefGoogle Scholar
  37. Romero-Sarmiento M, Rouzaud J, Bernard S, Deldicque D, Thomas M, Littke R (2014) Evolution of Barnett Shale organic carbon structure and nanostructure with increasing maturation. Org Geochem 71:7–16. CrossRefGoogle Scholar
  38. Saif T, Lin Q, Bijeljic B, Blunt MJ (2017) Microstructural imaging and characterization of oil shale before and after pyrolysis. Fuel 197:562–574. CrossRefGoogle Scholar
  39. Shao LY, Xiao ZH, He ZP, Liu YF, Shang LJ, Zhang PF (2006) Palaeogeography and coal accumulation for measures of the Carboniferous-Permian in Qinshui Basin, Southeastern Shanxi Province. J Palaeogeogr 8:43–52.
  40. Song L, Carr T (2016) Nano-scale pore structure evolution of Middle Devonian organic-rich Black Shale through thermal maturation. AAPG Annual Convention and Exhibition, Calgary, Canada Alberta, June 19-22, 2016.Google Scholar
  41. Soroushian P, Elzafraney M (2005) Morphological operations, planar mathematical formulations, and stereological interpretations for automated image analysis of concrete microstructure. Cem Concr Compos 27(7-8):823–833. CrossRefGoogle Scholar
  42. Strąpoć D, Mastalerz M, Schimmelmann A, Drobniak A, Hasenmueller NR (2010) Geochemical constraints on the origin and volume of gas in the New Albany Shale (Devonian–Mississippian), eastern Illinois Basin. AAPG Bull 94(11):1713–1740. CrossRefGoogle Scholar
  43. Sun L, Tuo J, Zhang M, Wu C, Wang Z, Zheng Y (2015a) Formation and development of the pore structure in Chang 7 member oil-shale from Ordos Basin during organic matter evolution induced by hydrous pyrolysis. Fuel 158:549–557. CrossRefGoogle Scholar
  44. Sun W, Feng Y, Jiang C, Chu W (2015b) Fractal characterization and methane adsorption features of coal particles taken from shallow and deep coalmine layers. Fuel 155:7–13. CrossRefGoogle Scholar
  45. Sun M, Yu B, Hu Q, Chen S, Xia W, Ye R (2016) 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 154-155:16–29. CrossRefGoogle Scholar
  46. Takashimizu Y, Iiyoshi M (2016) New parameter of roundness R: circularity corrected by aspect ratio. Prog Earth Planet Sci 3:1–16.
  47. Tang HP, Wang JZ, Zhu JL, Ao QB, Wang JY (2012) Fractal dimension of pore-structure of porous metal materials made by stainless steel powder. Powder Technol 217:383–387. CrossRefGoogle Scholar
  48. Tang X, Zhang J, Jin Z, Xiong J, Lin L, Yu Y, Han S (2015) Experimental investigation of thermal maturation on shale reservoir properties from hydrous pyrolysis of Chang 7 shale, Ordos Basin. Mar Pet Geol 64:165–172. CrossRefGoogle Scholar
  49. Wang BY, Hu B, Bai JP, Yang LC (2015a) Coal-accumulating environments of the Upper Carboniferous-Lower Permian Taiyuan Formation in Southeastern Qinshui Basin, Shanxi Province. J Palaeogeogr 17:677–688.
  50. Wang M, Xue H, Tian S, Wilkins RWT, Wang Z (2015b) Fractal characteristics of Upper Cretaceous lacustrine shale from the Songliao Basin, NE China. Mar Pet Geol 67:144–153. CrossRefGoogle Scholar
  51. Yang F, Ning Z, Liu H (2014) Fractal characteristics of shales from a shale gas reservoir in the Sichuan Basin, China. Fuel 115:378–384. CrossRefGoogle Scholar
  52. Yang R, He S, Yi J, Hu Q (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. Mar Pet Geol 70:27–45. CrossRefGoogle Scholar
  53. Yang R, He S, Hu Q, Sun M, Hu D, Yi J (2017) Applying SANS technique to characterize nano-scale pore structure of Longmaxi shale, Sichuan Basin (China). Fuel 197:91–99. CrossRefGoogle Scholar
  54. Zeng Q, Luo M, Pang X, Li L, Li K (2013) Surface fractal dimension: an indicator to characterize the microstructure of cement-based porous materials. Appl Surf Sci 282:302–307. CrossRefGoogle Scholar
  55. Zhang P, Lu S, Li J, Xue H, Li W, Zhang P (2017) Characterization of shale pore system: a case study of Paleogene Xin’gouzui Formation in the Jianghan basin, China. Mar Pet Geol 79:321–334. CrossRefGoogle Scholar

Copyright information

© Saudi Society for Geosciences 2018

Authors and Affiliations

  • Gaoyuan Yan
    • 1
    • 2
  • Chongtao Wei
    • 1
    • 2
  • Yu Song
    • 1
    • 2
  • Jinhui Luo
    • 1
    • 2
  • Junjian Zhang
    • 1
    • 2
  1. 1.Key Laboratory of Coalbed Methane Resources and Reservoir Formation Process, Ministry of EducationChina University of Mining and TechnologyXuzhouChina
  2. 2.School of Resources and GeosciencesChina University of Mining and TechnologyXuzhouChina

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