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© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.
© Author(s) 2020. This work is distributed under
the Creative Commons Attribution 4.0 License.

  20 May 2020

20 May 2020

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This preprint is currently under review for the journal SE.

Measuring hydraulic fracture apertures: a comparison of methods

Chaojie Cheng1,2, Sina Hale3, Harald Milsch1, and Philipp Blum3 Chaojie Cheng et al.
  • 1GFZ German Research Centre for Geosciences, Section 4.8 Geoenergy, Telegrafenberg, 14473 Potsdam, Germany
  • 2University of Potsdam, Institute for Geosciences, Karl-Liebknecht-Str. 24–25, 14476 Potsdam, Germany
  • 3Karlsruhe Institute of Technology (KIT), Institute of Applied Geosciences (AGW), Adenauerring 20b, 76131 Karlsruhe, Germany

Abstract. Hydraulic fracture apertures predominantly control fluid transport in fractured rock masses. Hence, the objective of the current study is to investigate and compare three different laboratory scale methods to determine hydraulic apertures in fractured (Fontainebleau and Flechtinger) sandstone samples with negligible matrix permeability. Direct measurements were performed by using a flow-through apparatus and a transient-airflow permeameter. In addition, a microscope camera permitted to measure the mechanical fracture apertures from which the corresponding hydraulic apertures were indirectly derived by applying various empirical correlations. Single fractures in the sample cores were generated artificially either by axial splitting or by a saw cut resulting in hydraulic apertures that ranged between 8 μm and 66 μm. The transient-airflow permeameter shows accurate values in comparison to the flow-through derived results, in particular when repeated measurements along the full fracture width are performed. In this case, the derived hydraulic fracture apertures are in an excellent quantitative agreement. When hydraulic apertures are calculated indirectly from optically determined mechanical apertures using empirical equations, aperture differences between samples are merely reproduced qualitatively. Variations in hydraulic apertures as observed between methods are almost certainly related to differences in sampled fracture volume. Overall, using direct flow-through measurements as a reference, this study demonstrates the applicability of mobile methods to determine hydraulic fracture apertures at both the laboratory and outcrop scales.

Chaojie Cheng et al.

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Chaojie Cheng et al.

Chaojie Cheng et al.


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Latest update: 20 Sep 2020
Publications Copernicus
Short summary
Fluids (like water or gases) within the Earth's crust often flow and interact with rock through fractures. The efficiency how these fluids may flow through this void space is controlled by the width of the fracture(s). In this study, three different physical methods to measure fracture widths were applied and compared and their predictive accuracy was evaluated. As a result, the mobile methods tested may well be applied in the field in case a number of limitations and requirements are observed.
Fluids (like water or gases) within the Earth's crust often flow and interact with rock through...