Crisman Annual Report 2009 - Harold Vance Department of ...

Aquifer Management for CO 2
Sequestration
Objectives
Among various possible solutions to mitigate the
increasing concentration of “greenhouse gases” in
the atmosphere, geological sequestration seems the
most attractive and promising one. This research
explores carbon dioxide sequestration in deep saline
aquifers, and will study issues related to aquifer
pressurization, monitoring, and risk mitigation using
a numerical reservoir simulator that models the
multiphase flow physics of CO 2
process using the
Peng-Robinson equation of state (EOS).
Approach
Simulations clearly indicated that bulk CO 2
injection
into a single well could rarely inject the volume of
CO 2
produced by the power plant in a typical aquifer,
and that multiple wells would be required. In an
array of injection wells, the aquifer volume allotted
to each injection well is limited by interference with
other injection wells. Therefore, modeling of CO 2
injection must consider a closed outer boundary,
and bulk injection in a closed system will pressurize
the aquifer. Simulations confirm this conclusion.
An analytical model developed for this study extends
a previously published one for an open aquifer to
a closed aquifer. A spreadsheet model provides
similar results to detailed simulation in a fraction of
the time, enabling systematic determination of the
aquifer volume and the number of wells required to
sequester the target amount of CO 2
. Results indicate
that, depending on the aquifer properties, the
sequestration operation would require thousands of
square miles of aquifer area or hundreds of wells or
both. In either case, the aquifer must be pressurized,
and CO 2
would accumulate at the top of the aquifer,
leading to an unacceptable risk of leakage.
Over 30 years of simulations on injection have
demonstrated the value of regular pressure falloff
monitoring of CO 2
injection wells. Falloff responses
provide ongoing indications of the dry zone and
two-phase zone radii over time and quantification
of the zone mobility values. For the case studied,
these responses also provided reasonable estimates
for the ongoing average aquifer pressure used
for material balance analysis. In turn, analysis
of average pressure over time can indicate if the
behavior is that of an open or closed aquifer and an
estimation of the aquifer size. Alternatively, average
pressure over time can signal the presence of an leak
and provide an estimation of how much fluid may
be leaking from the aquifer and whether the leak is
predominantly CO 2
or brine. These results suggest
that bulk CO 2
injection is neither economically nor
environmentally acceptable.
To avoid pressurization and to reduce the number
of wells required to sequester the CO 2
, brine should
be produced from the aquifer as a volume equal to
that of the injected CO 2
. This approach addresses
the pressurization risk, but not the problem of CO 2
accumulating at the top of the aquifer.
Significance
An engineered system is proposed to both
avoid aquifer pressurization and accelerate CO 2
dissolution and trapping. This system would position
a horizontal brine injection well above and parallel
to a horizontal CO 2
injection well with the brine
production wells drilled parallel to the CO 2
injection
well at a specified lateral spacing. Simulations show
that this configuration prevents CO 2
accumulation at
the top of the aquifer during injection, where 90% of
the CO 2
is permanently dissolved or trapped during
injection after 50 years, including the 30 years of
injection. This approach would greatly reduce the
risk of CO 2
leakage both during and forever after
injection.
CRISMAN INSTITUTE
Project Information
4.1.8 Aquifer Management for CO 2
Sequestration
Related Publications
Anchliya, A.: 2009. Aquifer Management for CO 2
Sequestration. MS thesis. Texas A&M U., College Station,
Texas.
Anchliya, A., Ehlig-Economides, C.A. Aquifer Management
to Accelerate CO 2
Dissolution and Trapping. Paper
SPE 126688, presented at the 2009 SPE International
Conference on CO 2
Capture, Storage, and Utilization, San
Diego, California, 2-4 November.
Contacts
Christine Ehlig-Economides
979.458.0797
c.economides@pe.tamu.edu
Abhishek Anchliya
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Crisman Annual Report 2009