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Buoyancy Effects on Upward Brine Displacement Caused by CO2 Injection
Language
English
Status
Published
JCR Journal
JCR Journal
Title of the book
Issue/vol(year)
2/87(2011)
ISSN
0169-3913
Electronic ISSN
1573-1634
Publisher
Springer Science+Business Media B.V.
Pages (printed)
525-540
Issued date
2011
Keywords
Abstract
Upward displacement of brine from deep reservoirs driven by pressure increases
resulting fromCO2 injection for geologic carbon sequestrationmay occur through improperly
sealed abandoned wells, through permeable faults, or through permeable channels between
pinch-outs of shale formations. The concern about upward brine flow is that, upon intrusion
into aquifers containing groundwater resources, the brinemay degrade groundwater. Because
both salinity and temperature increase with depth in sedimentary basins, upward displacement
of brine involves lifting fluid that is saline but also warm into shallower regions that contain
fresher, cooler water. We have carried out dynamic simulations using TOUGH2/EOS7 of
upward displacement of warm, salty water into cooler, fresher aquifers in a highly idealized
two-dimensional model consisting of a vertical conduit (representing a well or permeable
fault) connecting a deep and a shallow reservoir. Our simulations show that for small pressure
increases and/or high-salinity-gradient cases, brine is pushed up the conduit to a new
static steady-state equilibrium. On the other hand, if the pressure rise is large enough that
brine is pushed up the conduit and into the overlying upper aquifer, flow may be sustained
if the dense brine is allowed to spread laterally. In this scenario, dense brine only contacts
the lower-most region of the upper aquifer. In a hypothetical case in which strong cooling
of the dense brine occurs in the upper reservoir, the brine becomes sufficiently dense that it
flows back down into the deeper reservoir from where it came. The brine then heats again
in the lower aquifer and moves back up the conduit to repeat the cycle. Parameter studies
delineate steady-state (static) and oscillatory solutions and reveal the character and period of
oscillatory solutions. Such oscillatory solutions aremostly a curiosity rather than an expected
natural phenomenon because in nature the geothermal gradient prevents the cooling in the
upper aquifer that occurs in the model. The expected effect of upward brine displacement is either establishment of a new hydrostatic equilibrium or sustained upward flux into
the bottom-most region of the upper aquifer.
resulting fromCO2 injection for geologic carbon sequestrationmay occur through improperly
sealed abandoned wells, through permeable faults, or through permeable channels between
pinch-outs of shale formations. The concern about upward brine flow is that, upon intrusion
into aquifers containing groundwater resources, the brinemay degrade groundwater. Because
both salinity and temperature increase with depth in sedimentary basins, upward displacement
of brine involves lifting fluid that is saline but also warm into shallower regions that contain
fresher, cooler water. We have carried out dynamic simulations using TOUGH2/EOS7 of
upward displacement of warm, salty water into cooler, fresher aquifers in a highly idealized
two-dimensional model consisting of a vertical conduit (representing a well or permeable
fault) connecting a deep and a shallow reservoir. Our simulations show that for small pressure
increases and/or high-salinity-gradient cases, brine is pushed up the conduit to a new
static steady-state equilibrium. On the other hand, if the pressure rise is large enough that
brine is pushed up the conduit and into the overlying upper aquifer, flow may be sustained
if the dense brine is allowed to spread laterally. In this scenario, dense brine only contacts
the lower-most region of the upper aquifer. In a hypothetical case in which strong cooling
of the dense brine occurs in the upper reservoir, the brine becomes sufficiently dense that it
flows back down into the deeper reservoir from where it came. The brine then heats again
in the lower aquifer and moves back up the conduit to repeat the cycle. Parameter studies
delineate steady-state (static) and oscillatory solutions and reveal the character and period of
oscillatory solutions. Such oscillatory solutions aremostly a curiosity rather than an expected
natural phenomenon because in nature the geothermal gradient prevents the cooling in the
upper aquifer that occurs in the model. The expected effect of upward brine displacement is either establishment of a new hydrostatic equilibrium or sustained upward flux into
the bottom-most region of the upper aquifer.
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