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| Titel |
Understanding the mechanical and acoustical characteristics of sand
aggregates compacting under triaxial conditions |
| VerfasserIn |
Suzanne Hangx, Nicolas Brantut |
| Konferenz |
EGU General Assembly 2016
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| Medientyp |
Artikel
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| Sprache |
en
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 18 (2016) |
| Datensatznummer |
250130031
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| Publikation (Nr.) |
 EGU/EGU2016-10218.pdf |
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| Zusammenfassung |
| Mechanisms such as grain rearrangement, coupled with elastic deformation, grain breakage,
grain rearrangement, grain rotation, and intergranular sliding, play a key role in determining
porosity and permeability reduction during burial of clastic sediments. Similarly, in poorly
consolidated, highly porous sands and sandstones, grain rotation, intergranular sliding, grain
failure, and pore collapse often lead to significant reduction in porosity through the
development of compaction bands, with the reduced porosity and permeability of such bands
producing natural barriers to flow within reservoir rocks. Such time-independent compaction
processes operating in highly porous water- and hydrocarbon-bearing clastic reservoirs can
exert important controls on production-related reservoir deformation, subsidence, and
induced seismicity.
We performed triaxial compression experiments on sand aggregates consisting of
well-rounded Ottawa sand (d = 300-400 μm; φ = 36.1-36.4%) at room temperature, to
systematically investigate the effect of confining pressure (Pceff = 5-100 MPa), strain rate
(10−6-10−4 s−1) and chemical environment (decane vs. water; Pf = 5 MPa) on compaction.
For a limited number of experiments grain size distribution (d = 180-500 μm) and
grain shape (subangular Beaujean sand; d = 180-300 μm) were varied to study their
effect. Acoustic emission statistics and location, combined with microstructural and
grain size analysis, were used to verify the operating microphysical compaction
mechanisms.
All tests showed significant pre-compaction during the initial hydrostatic (set-up) phase,
with quasi-elastic loading behaviour accompanied by permanent deformation during the
differential loading stage. This permanent volumetric strain involved elastic grain contact
distortion, particle rearrangement, and grain failure. From the acoustic data and grain size
analysis, it was evident that at low confining pressure grain rearrangement controlled
compaction, with grain failure being present but occurring to a relatively limited extent.
Acoustic emission localization showed that failure was focussed along a broad shear plane.
At higher confining pressure pervasive grain failure clearly accommodated compaction,
though no strain localization was observed and failure appeared to be through cataclastic
flow. Chemical environment, i.e. chemically inert decane vs. water as a pore fluid,
had no significant effect on compaction in the strain rate range tested. Grain size
distribution or grain shape also appeared to not affect the observed mechanical
behaviour. Our results can be used to better understand the compaction behaviour of
poorly consolidated sandstones. Future research will focus on understanding the
effect of cementation on strain localization in deforming artificial Ottawa sandstone. |
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