GEO-SEQ

Task 1. Phase II for the Frio Brine Formation Pilot Tests

During FY2006, field testing for Phase II of the CO₂ injection test at the Frio Test Site was carried out in cooperation with the Texas Bureau of Economic Geology. The experiment was designed to answer extremely important questions not addressed during the first experiment. Specifically,

•   To what extent do gravitational forces drive upward migration of the CO₂ plume?
•   How much CO₂ becomes trapped as a residual phase?
•   How much CO₂ dissolves in the brine as it migrates upward under buoyancy forces?
•   Where does the displaced water go?

For this test, CO₂ was injected into a deeper part of the C sand than was used in the first Frio injection. After injecting a small amount of CO₂ (the volume will be determined by modeling studies), migration of the plume will be tracked for a period of up to a year or more, allowing observations of the extent to which gravitational forces drive the plume upwards and the extent to which the CO₂ remains trapped a residual phase. A combination of well logs and geophysical imaging was used to track migration of the CO₂. Fluid samples were collected to determine the extent of CO₂ dissolution in the brine. As CO₂ migration continues, fluid sampling will be used to track migration of the displaced water. In addition, as part of the test, a unique real-time cross-well seismic monitoring technique is being deployed to continually monitor movement of CO2 in the region between the two wells. This first-time deployment of such a system provides the opportunity to evaluate more fully the potential for real-time plume tracking using novel geophysical techniques.

The role of our team will be to:

• Use TOUGH2 and TOUGHREACT to interpret the data with regard to the extent of residual gas trapping, solubility trapping, and mineral trapping;
• Evaluate the effectiveness and resolution of real-time cross-well seismic imaging for mapping plume migration in real-time; and
• Evaluate the injectivity of the Frio Formation and how the presence of CO₂ enhances or degrades it.