Hydraulic fracturing under high temperature and pressure conditions with micro CT applications: Geothermal energy from hot dry rocks

W. G. P. Kumari, P. G. Ranjith, M. S. A. Perera, X. Li, L. H. Li, B. K. Chen, B. L. Avanthi Isaka, V. R. S. De Silva

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Hydraulic fracturing has been widely employed to enhance the permeability of tight geological formations including deep geothermal reservoirs. However, due to the complex in-situ stresses, high-temperature conditions and heterogeneity of the formations, hydraulic fracturing under deep geothermal conditions is poorly understood to date. The aim of the current study is, therefore, to investigate the effect of reservoir depth, temperature, and sample heterogeneity during hydraulic fracturing and the influences of rock micro-structure on fracture propagation. A series of hydraulic fracturing experiments was conducted on two Australian granite types under a wide range of confining pressures from 0 to 60 MPa and temperatures from room temperature to 300 °C simulating different geothermal environments. The corresponding micro-structural effects on the rock matrix were investigated employing high-resolution CT imaging using the IMBL facility of the Australian Synchrotron. According to the results, the breakdown pressure of reservoir rock linearly increases with reservoir depth (confining pressure). However, with increasing temperature breakdown pressure linearly decreases. This corresponds to the linear reduction of tensile strength measured by high-temperature Brazilian tensile tests. In addition, CT images showed that the injection of cold water into hot rock can result in a porous zone with porosity ranging from 2 to 3% close to the wellbore due to thermally-induced inter- and intra-crystalline cracks. In this condition, fluid leak-off is high and the measured fracture aperture of the main hydraulic fracture is relatively small. Further, fracture propagation paths and apertures are mainly controlled by the stress state and the heterogeneity of the rock matrix. It was found that fractures tend to propagate along preferential paths, mainly along grain boundaries and in large quartz and biotite minerals (grain size > 0.3 mm) and minerals with pre-existing micro-cracks.

Original languageEnglish
Pages (from-to)138-154
Number of pages17
JournalFuel
Volume230
DOIs
Publication statusPublished - 15 Oct 2018

Keywords

  • Breakdown pressure
  • CT scanning
  • Geothermal
  • Granite
  • High temperature
  • Hydraulic fracturing
  • Micro-scale

Cite this

Kumari, W. G. P. ; Ranjith, P. G. ; Perera, M. S. A. ; Li, X. ; Li, L. H. ; Chen, B. K. ; Isaka, B. L. Avanthi ; De Silva, V. R. S. / Hydraulic fracturing under high temperature and pressure conditions with micro CT applications : Geothermal energy from hot dry rocks. In: Fuel. 2018 ; Vol. 230. pp. 138-154.
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title = "Hydraulic fracturing under high temperature and pressure conditions with micro CT applications: Geothermal energy from hot dry rocks",
abstract = "Hydraulic fracturing has been widely employed to enhance the permeability of tight geological formations including deep geothermal reservoirs. However, due to the complex in-situ stresses, high-temperature conditions and heterogeneity of the formations, hydraulic fracturing under deep geothermal conditions is poorly understood to date. The aim of the current study is, therefore, to investigate the effect of reservoir depth, temperature, and sample heterogeneity during hydraulic fracturing and the influences of rock micro-structure on fracture propagation. A series of hydraulic fracturing experiments was conducted on two Australian granite types under a wide range of confining pressures from 0 to 60 MPa and temperatures from room temperature to 300 °C simulating different geothermal environments. The corresponding micro-structural effects on the rock matrix were investigated employing high-resolution CT imaging using the IMBL facility of the Australian Synchrotron. According to the results, the breakdown pressure of reservoir rock linearly increases with reservoir depth (confining pressure). However, with increasing temperature breakdown pressure linearly decreases. This corresponds to the linear reduction of tensile strength measured by high-temperature Brazilian tensile tests. In addition, CT images showed that the injection of cold water into hot rock can result in a porous zone with porosity ranging from 2 to 3{\%} close to the wellbore due to thermally-induced inter- and intra-crystalline cracks. In this condition, fluid leak-off is high and the measured fracture aperture of the main hydraulic fracture is relatively small. Further, fracture propagation paths and apertures are mainly controlled by the stress state and the heterogeneity of the rock matrix. It was found that fractures tend to propagate along preferential paths, mainly along grain boundaries and in large quartz and biotite minerals (grain size > 0.3 mm) and minerals with pre-existing micro-cracks.",
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author = "Kumari, {W. G. P.} and Ranjith, {P. G.} and Perera, {M. S. A.} and X. Li and Li, {L. H.} and Chen, {B. K.} and Isaka, {B. L. Avanthi} and {De Silva}, {V. R. S.}",
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Hydraulic fracturing under high temperature and pressure conditions with micro CT applications : Geothermal energy from hot dry rocks. / Kumari, W. G. P.; Ranjith, P. G.; Perera, M. S. A.; Li, X.; Li, L. H.; Chen, B. K.; Isaka, B. L. Avanthi; De Silva, V. R. S.

In: Fuel, Vol. 230, 15.10.2018, p. 138-154.

Research output: Contribution to journalArticleResearchpeer-review

TY - JOUR

T1 - Hydraulic fracturing under high temperature and pressure conditions with micro CT applications

T2 - Geothermal energy from hot dry rocks

AU - Kumari, W. G. P.

AU - Ranjith, P. G.

AU - Perera, M. S. A.

AU - Li, X.

AU - Li, L. H.

AU - Chen, B. K.

AU - Isaka, B. L. Avanthi

AU - De Silva, V. R. S.

PY - 2018/10/15

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