Measuring hydraulic fracture apertures: a comparison of methods
<p>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) sandsto...
| Main Authors: | , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2020-12-01
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| Series: | Solid Earth |
| Online Access: | https://se.copernicus.org/articles/11/2411/2020/se-11-2411-2020.pdf |
| Summary: | <p>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 measuring 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 and 66 <span class="inline-formula">µ</span>m.
Hydraulic apertures, accurately determined by the flow-through apparatus,
are used to compare results obtained by the other methods. The
transient-airflow permeameter delivers accurate values, particularly when
repeated measurements along the full fracture width are performed. In this
case, the derived mean hydraulic fracture apertures are in excellent
quantitative agreement. When hydraulic apertures are calculated indirectly
from optically determined mechanical apertures using empirical equations,
they show larger variations that are difficult to compare with the
flow-through-derived results. 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 portable methods to
determine hydraulic fracture apertures at both the laboratory and outcrop
scales.</p> |
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| ISSN: | 1869-9510 1869-9529 |