Near-Surface Monitoring

Near-Surface Monitoring tools enable both direct and indirect detection of CO2 above underground storage reservoirs. These tools include geochemical monitoring in the soil and vadose zone, geochemical monitoring of shallow groundwater or surface waters, surface displacement monitoring, and ecosystem stress monitoring. The purpose of these monitoring approaches is to detect near-surface manifestations of CO2 that may be leaking from geologic storage.

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MVA domains, featuring the near-surface monitoring region (click to enlarge)

Description

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Satellite image of cumulative surface deformation at the In Salah caused by CO2 injection operations. (click to enlarge)

Geochemical monitoring in the soil and vadose zone involves direct sampling of CO2 and its reaction products, as well as sampling for tracers that were injected into underground storage along with the CO2. Geochemical monitoring of groundwater involves installation of shallow monitoring wells for detecting any changes in groundwater chemistry related to CO2 injection. Such geochemical sampling techniques provide valuable direct measurements of CO2 and associated indicators, but characterizing a large area requires many individual data collection points.

Surface displacement measurements are designed to detect uplift of the land surface that may have been caused by CO2 injection within the storage formation. Ecosystem stress monitoring is aimed at mapping vegetative stress that may have resulted from elevated CO2 levels near the soil/atmosphere interface. Remote sensing data can provide highly precise surface displacement measurements and indications of vegetative stress over a large area. However, the data can be a challenge to interpret where site conditions are complex.

Research Agenda and Challenges

Research is needed to develop near-surface monitoring tools for detecting possible releases of CO2 in the vadose zone and in shallow groundwater and surface waters. Its important to note that near-surface measurements complement atmospheric measurements, because natural variations in CO2 levels in the near-surface ecosystem are minimal. Shallow groundwater monitoring is obviously important for protection of underground sources of drinking water. Techniques are needed for monitoring large areas associated with CO2 storage projects.

Pathways for near-surface monitoring research include:

  • By 2020: Develop real-time monitoring systems for measuring CO2 at the surface, in the unsaturated zone, and in shallow groundwater. Measurement of gas concentrations and biological changes at the surface and in the shallow subsurface, using geophysical methods and other approaches, are included in this research area. Techniques to measure land surface deformation that may result from CO2 movement in the subsurface are also included.

  • By 2030: Develop advanced systems for measuring near-surface manifestations of CO2 movement and release.

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Storage MVA Research Timeline for Near-Surface Monitoring (click to enlarge)

NETL-Supported Near-Surface Monitoring Research


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Columbia University’s conceptual design of a microfluidic chip for 14CO2 injection (top) and schematic design of tracer syringe system (bottom). (click to enlarge)

NETL supports projects that are addressing research challenges associated with Near-Surface Monitoring. Examples of projects supporting this key technology include: (1) development of low-cost, autonomous hardware which will detect CO2 in groundwater and automatically process data; (2) development of a network of shallow subsurface sensors to monitor statistical fluctuations of CO2 concentrations to detect any excess emissions indicating leakage from a storage site; and (3) development of a procedure for 14C tagging CO2  streams prior to injection into a geologic formation as a method for leakage detection.

The MVA webpage offers links to detailed information on projects performing research in this area.