DOE OSTI2011
The Southwest Regional Partnership (SWP) on Carbon Sequestration designed and deployed a medium-scale field pilot test of geologic carbon dioxide (CO2) sequestration in the Aneth oil field. Greater Aneth oil field, Utah's largest oil producer, was discovered in 1956 and has produced over 455 million barrels of oil (72 million m3). Located in the Paradox Basin of southeastern Utah, Greater Aneth is a stratigraphic trap producing from the Pennsylvanian Paradox Formation. Because it represents an archetype oil field of the western U.S., Greater Aneth was selected as one of three geologic pilots to demonstrate combined enhanced oil recovery (EOR) and CO2 sequestration under the auspices of the SWP on Carbon Sequestration, sponsored by the U.S. Department of Energy. The pilot demonstration focuced on the western portion of the Aneth Unit as this area of the field was converted from waterflood production to CO2 EOR starting in late 2007. The Aneth Unit is in the northwestern part of the field and has produced 149 million barrels (24 million m3) of the estimated 450 million barrels (71.5 million m3) of the original oil in place - a 33% recovery rate. The large amount of remaining oil makes the Aneth Unit ideal to demonstrate both CO2 storage capacity and EOR by CO2 flooding. This report summarizes the geologic characterization research, the various field monitoring tests, and the development of a geologic model and numerical simulations conducted for the Aneth demonstration project. The Utah Geological Survey (UGS), with contributions from other Partners, evaluated how the surface and subsurface geology of the Aneth Unit demonstration site will affect sequestration operations and engineering strategies. The UGS-research for the project are summarized in Chapters 1 through 7, and includes (1) mapping the surface geology including stratigraphy, faulting, fractures, and deformation bands, (2) describing the local Jurassic and Cretaceous stratigraphy, (3) mapping the Desert Creek zone reservoir, Gothic seal, and overlying aquifers, (4) characterizing the depositional environments and diagenetic events that produced significant reservoir heterogeneity, (5) describing the geochemical, petrographic, and geomechanical properties of the seal to determine the CO2 or hydrocarbon column it could support, and (6) evaluating the production history to compare primary production from vertical and horizontal wells, and the effects of waterflood and wateralternating- gas flood programs. The field monitoring demonstrations were conducted by various Partners including New Mexico Institute of Mining and Technology, University of Utah, National Institute of Advanced Industrial Science and Technology, Japan, Los Alamos National Laboratory and Cambridge Geosciences. The monitoring tests are summarized in Chapters 8 through 12, and includes (1) interwell tracer studies during water- and CO2-flood operations to characterize tracer behavoirs in anticipation of CO2-sequestration applications, (2) CO2 soil flux monitoring to measure background levels and variance and assess the sensitivity levels for CO2 surface monitoring, (3) testing the continuous monitoring of self potential as a means to detect pressure anomalies and electrochemical reaction due to CO2 injection, (4) conducting time-lapse vertical seismic profiling to image change near a CO2 injection well, and (5) monitoring microseismicity using a downhole string of seismic receivers to detect fracture slip and deformation associated with stress changes. Finally, the geologic modeling and numerical simulation study was conducted by researcher at the University of Utah. Chapter 13 summarizes their efforts which focused on developing a site-specific geologic model for Aneth to better understand and design CO2 storage specifically tailored to oil reservoirs.