GSA Annual Meeting in Denver, Colorado, USA - 2016

Paper No. 92-5
Presentation Time: 9:05 AM


BICKLE, Mike J.1, CHAPMAN, Hazel J.1, KAMPMAN, Niko2, BUSCH, Andreas2 and EVANS, James P.3, (1)Department of Earth Sciences, Univ of Cambridge, Downing St, Cambridge, CB2 3EQ, United Kingdom, (2)Shell Global Solutions International, Kessler Park 1, Rijswijk, 2288 GS, Netherlands, (3)Department of Geology, Utah State University, 4505 Old Main Hill, Logan, UT 84322; Dept of Geology, Utah State University, 4505 Old Main Hill, Dept Geology, Logan, UT 84322,

Natural CO2 systems provide invaluable information on the processes which control retention and potential migration pathways for anthropogenic storage of CO2 in geological formations. Natural CO2 has been leaking up fault systems for > ~ 100,000 years at Green River, Utah, now enhanced by leakage through many recently abandoned drill holes. Scientific drilling adjacent to the Little Grand Wash fault in 2012 has established the mechanisms of CO2 transport at shallower stratigraphic levels and the consequent reactions between CO2-charged brines and formation minerals. Corrosion of caprocks is restricted to a few centimetres and involved dissolution of haematite and dolomite with precipitation of pyrite and Fe-dolomites. CO2-rich brines were encountered at shallow levels and fluid samples collected at pressure in the underlying Navajo sandstone were CO2-saturated in the lower half of the formation and close to saturation in the upper half of the formation. Given the marked increase of solubility of CO2 with pressure at these depths, this requires that both CO2-saturated brines and free CO2 must be migrating up the fault zone from a CO2 source at depth. Numerical modelling illustrates how groundwater flow in the Navajo sandstone dissolves any free CO2 escaping the fault zone and buffers the flow of denser CO2-saturated brines away from the fault. It is estimated that > 80% of the CO2 reaching the level of the Navajo sandstone is removed by dissolution in the groundwater. This implies that CO2 migrating up fault systems through multiple stacked aquifers may largely be dissolved in formation fluids and not reach the surface.