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Task 3: Conduction of Push-Pull Tests in the Field

Push-pull tests (PPTs) will be conducted at the Cranfield site using an existing water well 70 m deep. The water table is ~18 m deep. The aquifer consists of sandy material from 60- to 80-m depth that is overlain by a confining clay layer. Packers will be used to isolate the injection zone in the aquifer (Figure 3). We will evaluate different approaches of introducing CO2 into the aquifer, i.e. CO2 gas or CO2 equilibrated with groundwater. A tracer will be used with the CO2, such as N or Ar gas for CO2 gas injection or Br for liquid injection. Different tests will be conducted by varying CO2 pressure in the injection (if CO2 gas is directly injected) or injected water (if CO2 equilibrated groundwater is injected), injection time, and injection rate to estimate variations in leakage rates with these parameters. Groundwater chemistry will be measured prior to testing and will be combined with the previous monitoring data to establish baseline chemical conditions for major and trace elements, pH, Eh, stable C and O isotopes, and Pb and Sr isotopes. During injection, the hydraulic pressure and injection amount of CO2-equilibrated water (or CO2 gas) will be monitored. After the PPT rest phase, groundwater will be extracted, field parameters (pH, EH, T, alkalinity) will be monitored, and groundwater samples will be collected at pre-specified time intervals on the basis of modeling results to record breakthrough curves for major and trace elements. Groundwater samples will be analyzed for major and trace elements and C isotopes in the laboratory. During the tests, a LICOR CO2 flux chamber will be used for measuring CO2 flux to monitor possible leakage of injected CO2 back to the surface, which would most likely occur along the borehole annulus, if it occurs at all. These data will provide information on mobilization of major and trace elements caused by CO2 injection. Carbon isotope information will provide data on how stable C isotope in injected CO2 is fractionated when CO2 reacts with water and sedimentary rocks. Strontium isotope measurements will provide information on carbonate mineral dissolution.

 
 

 




The GCCC Mission

The GCCC seeks to apply its technical and educational resources to implement geologic storage of anthropogenic carbon dioxide on an aggressive time scale with a focus in a region where large-scale reduction of atmospheric releases is needed and short term action is possible.

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