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| Titel |
The effects of supercritical carbon dioxide on the frictional behavior of simulated anhydrite fault gouge |
| VerfasserIn |
Anne Pluymakers, Jon Samuelson, Chris Spiers |
| Konferenz |
EGU General Assembly 2013
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 15 (2013) |
| Datensatznummer |
250082205
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| Zusammenfassung |
| One option for mitigating climate change is to store anthropogenic CO2 in subsurface
reservoirs, particularly in depleted oil and gas fields. Reactivation of fault zones within and
adjacent to potential reservoirs can lead to (micro)seismicity and to leakage of CO2 due to
enhanced permeability. To avoid these consequences, careful evaluation of the frictional
properties of such faults is necessary. Both worldwide and in the Netherlands, anhydrite is a
common caprock to many potential CO2 storage sites. It is therefore likely that
reservoir-bounding faults at such sites will contain anhydrite fault gouge. Against this
background we investigated the effects of the presence of CO2 on the frictional strength and
on the rate and state dependent properties of simulated anhydrite fault gouge under dry and
wet conditions.
Intact anhydrite core material, from the base of the Dutch Zechstein Group, was
powdered and sieved to a grain size of < 50μm to simulate fault gouge. Experiments were
conducted using a direct shear set-up placed in a triaxial testing machine, employing a 1mm
thick gouge layer. A range of temperatures (80 - 150Ë C) and sliding velocities
(0.2-10μms-1) was studied, at a fixed effective normal stress of 25MPa. The gouge was
pressurized with dry supercritical CO2, and with CO2-saturated water. In both cases, the CO2
pressure was 15MPa.
The results of the experiments on dry gouge pressurized with CO2 show a friction
coefficient (μ) of ~0.65 at 80Ë C, decreasing to 0.55 at 150Ë C. Wet anhydrite fault
gouge pressurized with CO2 was slightly weaker at 80Ë C, with μ=0.6 and a slight
decrease in strength with increasing temperature, reaching 0.55 at 150Ë C. Dry
CO2 saturated samples showed a transition from predominantly velocity neutral
frictional behavior at temperatures of 80 and 100Ë C to mixed behavior at the higher
temperatures. Above 100Ë C, the dry CO2 saturated material shows velocity weakening
(occasionally accompanied by stick-slip behavior) at low strains, and velocity strengthening
behavior at high strains. In contrast, all wet experiments pressurized with CO2 show
velocity neutral to velocity strengthening behavior over the entire temperature range
studied.
Since faults are expected to be water saturated under normal CO2 storage conditions,
our results imply that the presence of CO2 is unlikely to significantly increase the
(micro)seismic potential of anhydrite-filled faults under typical storage site conditions.
To avoid fault reactivation during the injection phase it is useful to note that our
results imply a slight decrease in the strength of faults containing anhydrite gouge at
the in-situ temperatures (80-120Ë C) compared with room temperature values. |
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