WaterRF Project: Task 3.0

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 CO2pressure in the injection (if CO₂ gas is directly injected) or injected water (if v 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.

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