Monitoring groundwater flow and chemical and isotopic composition at a demonstration site for carbon dioxide storage in a depleted natural gas reservoir
Highlights
► The CO2CRC injected >65,000 tonnes of CO2-rich gas in a depleted gas reservoir. ► Groundwater levels and composition were monitored for about 5 years in two aquifers. ► Most hydrochemical parameters were statistically similar before and after injection. ► Where water composition did change, trends are not consistent with a CO2 addition. ► Groundwater quality was not measurably affected by the CO2 storage experiment.
Introduction
Sequestration of atmospheric CO2 in geological formations is recognised as one of several key methods able to reduce greenhouse gas emissions to combat climate change (e.g., Pacala and Socolow, 2004, Oelkers and Cole, 2008). Injection of fluids, including CO2, in subsurface strata has a long history, for instance for Enhanced Oil Recovery (EOR) and/or for CO2 storage, e.g., at Sleipner in the Norwegian sector of the North Sea (Korbøl and Kaddour, 1995), or at Weyburn in western Canada (Wilson and Monea, 2004).
To permanently store CO2 in geological formations requires (1) a porous and permeable injection unit, (2) an overlying sealing unit, and (3) mechanisms to lock in the CO2 (e.g., structural/stratigraphic, residual, solubility, and mineral trapping) (Holloway, 2001, IPCC, 2005, Benson and Cole, 2008). If CO2 leaks up from an intended storage unit, it could potentially reach overlying aquifers where it would interact with the groundwater and change its chemical properties; thus groundwater monitoring is important not only to establish baseline conditions but also to demonstrate whether these conditions have changed over time or not, and why.
In the Cooperative Research Centre for Greenhouse Gas Technologies (CO2CRC) Otway project, 65,445 tonnes of a CO2:CH4 (∼75:21 mol%) gas mixture were injected into a depleted natural gas reservoir, the Waarre C unit, at ∼2 km depth between March 2008 and August 2009 (for more details, see Underschultz et al., 2011, Jenkins et al., 2012). The gas originated from the nearby Buttress 1 well (Fig. 1), and was injected into the purpose-drilled CRC 1 well. In the Waarre C unit, the injected CO2 moved up-gradient into the structural trap (that previously held the natural gas produced at Naylor 1 well; see Fig. 1) as demonstrated by geochemical (e.g., Boreham et al., 2011) and geophysical (e.g., Jenkins et al., 2012) verification techniques. Assurance monitoring was established well before injection started in order to demonstrate the ongoing integrity of the environment through the absence of injected CO2 in the overlying aquifers, soils, or the atmosphere (Sharma et al., 2007, Hennig et al., 2008). Both verification and monitoring activities at the Otway site have been described in Jenkins et al. (2012). Groundwater monitoring at over 20 bores (see below) within a 10 km radius around injection well CRC 1 started in June 2006 and continued until March 2011 at a roughly 6-monthly interval (annual monitoring is expected to continue for some time thereafter).
As this is the first C storage demonstration project in Australia, this study presents in some detail a methodology for groundwater monitoring that can be applied elsewhere in the country. Importantly, baseline conditions were able to be established by monitoring groundwater levels and composition for nearly 2 years before injection started. Groundwater monitoring is not intended to be a detection method for potential leaks of CO2 by itself, as there is only a very small probability that any groundwater bore would intersect a plume of CO2 mixing into the aquifers. Thus, the most fundamental goal of groundwater monitoring in a C storage context is to be able to demonstrate that no changes in the physical and chemical conditions of the aquifers have resulted from these activities, including the drilling, pressure changes and storage of CO2.
The aims of this paper are thus to (1) describe the groundwater monitoring program developed at the Otway site, (2) present results for several key water parameters pre-, syn- and post-injection, (3) identify the major natural processes controlling the groundwater composition here, and (4) discuss any variations observed between pre- and post-injection data in terms of significance and potential cause.
Section snippets
Study area
The Otway project is located in the onshore Otway Basin in southwestern Victoria, Australia (Fig. 1) at approximately 38.53°S and 142.81°E. The groundwater bores monitored for this study are located between the towns of Warrnambool in the west and Port Campbell in the east, and all lie within a 10 km radius of the CO2 injection well CRC 1.
Groundwater levels
Permanent water level loggers (Solinst Levelogger Gold) were installed in six pre-existing open bores where water level and temperature are measured and recorded hourly. Four of these bores are owned and maintained by the State water monitoring body, the Department of Sustainability and Environment (DSE), one is owned by a private water corporation, Wannon Water, and another one is privately owned; three of the bores tap the Port Campbell Limestone and the other three reach the Dilwyn Aquifer.
Groundwater levels
The baseline reduced water levels (RWL), i.e., relative to the Australian Height Datum (AHD), recorded prior to injection for the Port Campbell Limestone show seasonal response to rainfall (Fig. 4), however, the fluctuation in hydraulic head due to rainfall is minor relative to the regional hydraulic gradient, which ranges from 100 m inland to 20 m close to the coast (above AHD). The hydraulic head map for the aquifer in this area is consistent over time in spite of the seasonal rainfall, the
Conclusions
The Otway project is Australia’s first, and, to-date, only, CO2 storage project. Over 65,000 tonnes of CO2-rich gas were injected downdip of a depleted natural gas reservoir ∼2000 m below surface in 2008–2009. Groundwater levels have remained constant in both the shallow, unconfined the Port Campbell Limestone aquifer and the deeper, confined Dilwyn Aquifer, even though drilling, pumping and injection activities were taking place, and rainfall increased during the course of the project.
Acknowledgments
We are grateful to the Cooperative Research Centres Program and all government, academia and industry sponsors for their financial and in-kind support of the CO2CRC. Local landowners, the Victorian Department of Sustainability & Environment (DSE) and Wannon Water granted access to the bores, without which this work could not have occurred. Successive CO2CRC Community Liaison Officers Carmel Anderson, Fiona Aulsebrook and Josie McInerney helped coordinate field work, which was carried out with
References (58)
- et al.
The distribution of deuterium and oxygen-18 in dry soils: II. Experimental
J. Hydrol.
(1983) - et al.
Water–rock interactions during a CO2 injection field-test: implications on host rock dissolution and alteration effects
Chem. Geol.
(2009) - et al.
The distribution of deuterium and oxygen-18 in dry soils: I. Theory
J. Hydrol.
(1983) - et al.
Monitoring of CO2 storage in a depleted natural gas reservoir: gas geochemistry from the CO2CRC Otway project, Australia
Int. J. Greenhouse Gas Control
(2011) - et al.
Geological characterisation of the Otway project pilot site: what a difference a well makes
Energy Proc.
(2009) - et al.
Monitoring of fluid–rock interaction and CO2 storage through produced fluid sampling at the Weyburn CO2-injection enhanced oil recovery site, Saskatchewan, Canada
Appl. Geochem.
(2005) - et al.
Sleipner Vest CO2 disposal – injection of removed CO2 into the Utsira Formation
Energy Convers. Manage.
(1995) - et al.
CO2CRC Otway project – soil gas baseline and assurance monitoring 2007–2010
Energy Proc.
(2011) - et al.
CO2 storage in a depleted gas field: an overview of the CO2CRC Otway project and initial results
Int. J. Greenhouse Gas Control
(2011) - et al.
Australia’s southern margin: a product of oblique extension
Tectonophysics
(1990)
Reactive transport modeling to study changes in water chemistry induced by CO2 injection at the Frio-I brine pilot
Chem. Geol.
CO2 sequestration in deep sedimentary formations
Elements
Stable isotopes in precipitation
Tellus
Isotopes—Principles and Applications
Port Campbell reviewed: methane and champagne
Aust. Petrol. Product Explor. Assoc. J.
Storage of fossil fuel-derived carbon dioxide beneath the surface of the Earth
Annu. Rev. Energy Environ.
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