Do CO2-rich Fluids Significantly Alter Fault Rocks at low Temperature Conditions? A Look at Leaking and Sealed Strands of the Little Grand Wash fault, SE Utah

P. Benjamin Luetkemeyer¹ and David L. Kirschner^2
1Department of Earth and Atmospheric Sciences, Saint Louis, Missouri, USA
²Shell International Exploration and Production, Inc., Shell Technology Center, Houston, TX, USA

This study is motivated by the idea that carbon dioxide (CO2) can be stored in various subsurface reservoirs as a means to reduce global CO2 emissions. However, the longterm effects of injecting CO2-charged fluids into the subsurface are poorly understood. The presence of faults, fractures, and fracture-filling minerals influence the overall permeability and porosity of reservoir and cap rocks, and could either enhance or inhibit the release of CO2 .

The Colorado Plateau contains a number of large CO2 reservoirs some of which leak and some of which do not. Several normal faults within the Paradox Basin (SE Utah) dissect the Green River anticline giving rise to a series of footwall reservoirs with faultdependent columns. Numerous CO2-charged springs and geysers are associated with these faults.

Geochemical data obtained from faults that have sealed and leaked CO2 are used to compare styles of fluid-rock interaction. The data come from mineralogical, elemental, and stable isotope analyses for fault rocks, host rocks, and carbonate veins collected along traverses across several strands of the Little Grand Wash (LGW) fault system. Most data come from two localities along one fault that locally sealed CO2. This fault is just tens of meters away from another normal fault that has leaked CO2-charged waters to the land surface for 100,000-200,000 years. A geochemical model is developed to illustrate how CO2-bearing fluids into a fault system can profoundly affect the overall fluid chemistry of the fault system and subsequent enhancement or degradation of fault seal integrity.

AAPG Search and Discovery Article #90181©2013 AAPG/SEG Rocky Mountain Rendezvous, University of Wyoming, Laramie, Wyoming, September 27-30, 2013