Monitoring, or observation, wells are designed for long-term monitoring, verification and accounting of a carbon storage project. Specific information about the geologic storage project, including injection rate and volume, geology, the presence of artificial penetrations, area of review, and other factors, determines the location and number of monitoring wells to be used.1National Energy Technology Laboratory. (2017). Best practices: Monitoring, verification, and accounting (MVA) for geologic storage projects. National Energy Technology Laboratory, U.S. Department of Energy. https://netl.doe.gov/sites/default/files/2018-10/BPM-MVA-2012.pdf
Wells may be shallow for near-surface monitoring, e.g., less than 100 m deep for shallow groundwater monitoring. Or, wells may extend several kilometers deep for subsurface monitoring tasks. Monitoring goals vary depending on the project and may include elements such as:
- Geochemical monitoring of near-surface groundwater with installation of shallow monitoring wells for measuring potential changes in groundwater chemistry related to CO2 injection.
- Gauges for pressure, temperature and other measurements.
- Non-conductive well casings if required electrical techniques
- Continuous collection of fluid and gas samples for chemical and tracer analyses
Monitoring wells may encounter similar problems that are common within conventional oil and gas wells, and thus, rely on tried solutions and strategies developed in the oil and gas industry.2National Energy Technology Laboratory. (2017). Best practices: Monitoring, verification, and accounting (MVA) for geologic storage projects. National Energy Technology Laboratory, U.S. Department of Energy. https://netl.doe.gov/sites/default/files/2018-10/BPM-MVA-2012.pdf
Like the design and construction of all wells, monitoring wells for a carbon storage project must be carefully thought out and planned considering the overall, long term goals of the project, specifically related to monitoring, verification and accounting throughout the life of the project. As an example, we will look at the observation, or monitoring, well designed for the Aquistore Project in Saskatchewan, Canada as compiled in a report by the Global CCS Institute.3Global CCS Institute. (2015). Aquistore, CO2 storage at the world’s first integrated CCS project. https://www.globalccsinstitute.com/archive/hub/publications/192038/aquistore-co2-storage-worlds-first-integrated-ccs-project.pdf
Observation well design for the Aquistore Project in Canada. The deep saline system targeted for the Aquistore project comprises the Deadwood and Black Island Formations at a depth of ~ 3,150 m in the well. The Ice Box Shale / Winnipeg Shale constitute the primary sealing unit. Notice that the Prairie Evaporite, higher up in the well, is considered a secondary sealing unit.4Global CCS Institute. (2015). Aquistore, CO2 storage at the world’s first integrated CCS project. https://www.globalccsinstitute.com/archive/hub/publications/192038/aquistore-co2-storage-worlds-first-integrated-ccs-project.pdf
A number of well-design elements can be seen in the diagram for the observation well. The well is designed to be built and operated with health, safety and the environment as critical motivators.
- The observation well is also designed and constructed to be CO2 resistant with CO2 resistant cement in place to a depth of 3025 meters.
- Aquistore’s observation well is heavily instrumented for CO2 monitoring.
- Permanently mounted monitoring tools and gauges are installed which will help the project track and understand the movement of CO2 in the subsurface after it has been injected.
- These down-hole techniques allow for time lapse logging to be conducted with no interruptions.
- Some of the monitoring tools being used include the fluid recovery system, pressure and temperature gauges, a fiber optic Distributed Temperature System (DTS) line, and a fiber optic Distributed Acoustic System (DAS) line.
- The fluid recovery system was installed on the well’s casing and enables geochemical monitoring of fluids within the injection formation.
- The DAS line is a new technique which is being used experimentally as an alternative to a string of geophones (receivers).
- The fluid recovery system will collect samples from the reservoir which helps track the CO2 plume and provides geochemical information.
- As with the injection well, the observation well is topped with a 34.5 MPa wellhead.
- Wireline logs were also run on the observation well.5Global CCS Institute. (2015). Aquistore, CO2 storage at the world’s first integrated CCS project. https://www.globalccsinstitute.com/archive/hub/publications/192038/aquistore-co2-storage-worlds-first-integrated-ccs-project.pdf
Image Credits: Aquistore Project and Global CCS Institute, Copyright Act 1968 (Cth), research, study and review