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International Journal of Fracture

, Volume 185, Issue 1–2, pp 187–194 | Cite as

Oil-Gas Transformation Induced Subcritical Crack Propagation and Coalescence in Petroleum Source Rocks

  • Z. Q. Fan
  • Z.-H. Jin
  • S. E. Johnson
Letters in Fracture and Micromechanics

Abstract

The present work describes a multi-physics model to investigate subcritical propagation of initially oil-filled, sub-horizontal collinear microcracks driven by the excess pressure induced by the conversion of oil to gas in a petroleum source rock under continuous burial. The crack propagation distance, propagation duration, crack coalescence and excess pressure in the crack are determined using a finite difference scheme that couples linear elastic fracture mechanics, oil-gas transformation kinetics and an equation of state for the gas. The numerical results for a shale source rock with typical properties show that when the crack spacing parameter b/a0 is greater than 3, where a0 is the half crack length and b the half distance between the crack centers, the cracks do not coalesce, and the duration of gas-driven crack propagation is governed by the transformation kinetics because the oil-gas conversion rate is much slower than the subcritical crack propagation rate. The collinear cracks coalesce for smaller crack spacing and the crack propagation duration may reduce significantly due to crack interactions. The multi-physics model presented in this work together with our previous model for crack propagation during the conversion of solid kerogen to oil indicates that self-propagating microcracks resulting from the buildup of excess fluid pressure during hydrocarbon generation may serve as effective pathways for primary migration of hydrocarbons.

Keywords

collinear cracks subcritical growth gas migration oil-gas conversion overpressure 

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References

  1. Atkinson B.K. (1984) Subcritical crack growth in geological materials. Journal of Geophysical Research 89: 4077–4144CrossRefGoogle Scholar
  2. Barker C. (1990) Calculated volume and pressure changes during the thermal cracking of oil to gas in reservoirs. AAPG Bulletin 74: 1254–1261Google Scholar
  3. Berg R.R., Gangi A.F. (1999) Primary migration by oil-generation microfracturing in low-permeability source rocks: application to the Austin Chalk, Texas. AAPG Bulletin 83: 727–756Google Scholar
  4. Capuano R.M. (1993) Evidence of fluid flow in microcracks in geopressured shales. AAPG Bulletin 77: 1303–1314Google Scholar
  5. Comer J.B., Hinch H.H. (1987) Recognizing and quantifying expulsion of oil from the Woodford Formation and age-equivalent rocks in Oklahoma and Arkansas. AAPG Bulletin 71: 844–858Google Scholar
  6. Duan, Z. H., Moller, N., Weare, J. N. (1992). An equation of state for the CH_4-CO_2-H_20 system: I. Pure systems from 0 to 1000°C and 0 to 8000 bar. Geochimica Et Cosmochimica Acta 56, 2605–2617.Google Scholar
  7. Fan Z. Q., Jin Z.-H., Johnson S. E. (2010) Subcritical propagation of an oil-filled penny-shaped crack during kerogen–oil conversion. Geophysical Journal International 182: 1141–1147CrossRefGoogle Scholar
  8. Fan Z. Q., Jin Z.-H., Johnson S. E. (2012) Modelling petroleum migration through microcrack propagation in transversely isotropic source rocks. Geophysical Journal International 190: 179–187CrossRefGoogle Scholar
  9. Fan Z. Q., Jin Z.-H., Johnson S. E. (2012) Gas-driven subcritical crack propagation during the conversion of oil to gas. Petroleum Geoscience 18: 191–199CrossRefGoogle Scholar
  10. Hunt J.M. (1979) Petroleum geochemistry and geology. Freeman, San FranciscoGoogle Scholar
  11. Jin, Z.-H., Johnson, S.E., Fan, Z.Q. (2010). Subcritical propagation and coalescence of oil-filled cracks: getting the oil out of low-permeability source rocks. Geophysical Research Letters 37, L01305.Google Scholar
  12. Lash G.G., Engelder T. (2005) An analysis of horizontal microcracking during catagenesis: an example from the Catskill delta complex. AAPG Bulletin 89: 1433–1449CrossRefGoogle Scholar
  13. Littke R., Baker D. R., Leythaeuser D. (1988) Microscopic and sedimentologic evidence for the generation and migration of hydrocarbons in Toarcian source rocks of different maturities. Organic Geochemistry 13: 549–559CrossRefGoogle Scholar
  14. Marquez X.M., Mountjoy E.W. (1996) Microcracks due to overpressure caused by thermal cracking in well-sealed Upper Devonian reservoirs, deep Alberta basin. AAPG Bulletin 80: 570–588Google Scholar
  15. Meissner, F. F. (1978). Petroleum geology of the Bakken Formation, Williston basin, North Dakota and Montana: Williston Basin Symposium, Montana Geological Society, 24th Annual Conference, 207–227.Google Scholar
  16. Momper, J. A. (1978). Oil migration limitations suggested by geological and geochemical considerations. AAPG Short Course Notes Series 8: B1–B60Google Scholar
  17. Pepper A. S., Dodd, T. A. (1995). Simple kinetic models of petroleum formation. Part II: oil-gas cracking. Marine and Petroleum Geology 12, 321–340.Google Scholar
  18. Schmidt, R. A. (1977). Fracture mechanics of oil shale-unconfined fracture toughness, stress corrosion cracking, and tension test results, 18th U.S. Symposium on Rock Mechanics: Golden, Colorado, Colorado School of Mines, 2A2-1–2A2-6.Google Scholar
  19. Sneddon I. N., Srivastav R. P. (1965) The stress in the vicinity of an infinite row of collinear cracks in an elastic body. Proceedings of the Royal Society of Edinburgh A 67: 39–49Google Scholar
  20. Talukdar, S., Gallango O., Vallejos C., Ruggiero A. (1987). Observations on the primary migration of oil in the La Luna source rocks of the Maracaibo Basin, Venezuela, in Doligez B., (Ed.), Migration of hydrocarbons in sedimentary basins, Editions Technip, Paris, 59–78.Google Scholar
  21. Tissot B.P., Welte D.H. (1984) Petroleum formation and occurrence, A New Approach to Oil and Gas Exploration. Springer, BerlinCrossRefGoogle Scholar

Copyright information

© Springer Science+Business Media Dordrecht 2013

Authors and Affiliations

  1. 1.Department of Mechanical EngineeringUniversity of MaineOronoUSA
  2. 2.School of Earth and Climate SciencesUniversity of MaineOronoUSA

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