Print this pageEvaluation of Knox Group Dolostones as a Target for CO2 Storage in Western Kentucky
Much like an exploration play, defining a CO2 storage target starts with understanding the subsurface. This requires the integration of all available data, from core descriptions to seismic interpretation. Unfortunately, in the areas and reservoirs not traditionally explored for oil and gas, these data are rare to non-existent. The Cambrian-Ordovician Knox Group dolostones of western Kentucky qualify as one of these types of potential injection targets. With a database of about 25 well logs, a loose 2-D seismic grid, a few whole cores, and a few well tests, a geologic model of the Knox in western Kentucky was constructed to help understand the potential for CO2 storage in these rocks.
Initially, ideas for porosity development in the predominantly tight Knox dolostones were based on geologic models of the age-equivalent Ellenburger and Arbuckle formations. In these formations, karsting plays a dominant role. Evaluation of several Knox whole cores, however, indicated only minor epikarst zones in very low porosity intervals. Most of the porosity development is associated with large dolomite crystal-lined vugs which are interpreted to have precipitated from hydrothermal fluids. Borehole image logs also seem to point towards vugs and fractures as significant contributors to porosity.
Interpreted core and log data were integrated with 2-D seismic interpretations to produce a geocellular model which was used for flow simulation of potential CO2 injection volumes and rates within the Knox Group dolostones. Initial indications are that the Knox Group dolostones have the potential to accept the large volumes of supercritical CO2 necessary for a CO2 storage site, though a significant number of wells may be required. In order to further assess this model, the Kentucky Consortium for Carbon Sequestration will drill a well in early 2009 to test the CO2 injection capacity of the Knox Group and potential secondary targets. Further evaluation of the sealing capacity of the overlying tight carbonates and shales will also be done using whole cores taken in this test well to assess their ability to permanently contain injected supercritical CO2.
AAPG Search and Discovery Article #90090©2009 AAPG Annual Convention and Exhibition, Denver, Colorado, June 7-10, 2009