The BSCSP is conducting a large volume injection field project within Kevin (pronounced kee-vin) Dome in north-central Montana (Figure 1), with the Duperow (dolostone) Formation as the primary targeted storage reservoir. Naturally-occurring CO2 is trapped in the Duperow at the top of Kevin Dome, but large areas of the Duperow around the flanks of the dome are saline-saturated, do not contain CO2, and are available for additional CO2 storage. Over a four-year period, the project will use up to five production wells to extract one million metric tons of CO2 from the top of the dome, compress and transport the CO2 approximately six miles in a 2-inch underground pipeline, and inject it via a single injection well into the Duperow formation downgradient from the CO2 reservoir (Figure 2). Four monitoring wells will be completed into the Duperow in the vicinity of the injection well. Hydrologic, geochemical, geomechanical, and geophysical data - including comprehensive 3-D, 9-component seismic surveys of the CO2 production/injection areas, crosswell seismic surveys, and vertical seismic profiling - will be obtained and used to monitor, describe, and predict the behavior of the CO2 in the formation. After the 4-year injection period, BSCSP will continue to monitor the site for an additional two years. At that time, all commercially-viable CO2 production wells (including, perhaps, the injection well) would be transferred to a private-sector partner (Vecta Oil & Gas, Ltd.), with all other wells being properly plugged. All data will be incorporated into the BSCSP’s existing graphical information system (GIS) framework and the Big Sky Carbon Atlas as well as the U.S. 2012 Carbon Utilization and Storage Atlas. In addition, the data collection techniques and results of the study will be incorporated into DOE’s Best Practices Manuals. Information will be disseminated to the public and stakeholders throughout all phases of the project.
Description of Geology
Kevin Dome is a large, anticlinal structural culmination located along the Sweetgrass Arch in north-central Montana. The geology of Kevin Dome is well understood due to its history of oil and gas development; however, the characteristics of the Duperow Formation within the dome are less well-known because it occurs deeper and stratigraphically lower than past and current oil and gas production. The dome closure covers approximately 700 square miles at the Devonian Duperow stratigraphic level with approximately 750 feet of structural relief. Naturally occurring CO2 has been documented from several oil and gas wells that have tested the Duperow over the last 50 years, but the volume, continuity of the trapped gas, and circumstances of its entrapment have been poorly understood. Below the CO2 gas in the trapped reservoirs of the Duperow Formation within the Kevin Dome is a saline aquifer having very poor water quality (greater than 20,000 ppm of total dissolved solids). The combination of a natural trap ensuring good overlying caprock, formation compatibility with CO2, the large volume of this static trap, the poor quality of contained water, the proximity to present and future sources of anthropogenic CO2, and the similarity of this feature to other large domes suggest this geologic feature is of great regional significance for understanding carbon storage potential and capacity. Tightlycompacted layers at the top of the Duperow formation will serve as an immediate seal for the injected CO2, while the 175 feet thick, regionally-extensive Potlatch Anhydrite will provide an effective caprock for the entire Kevin Dome injection site.
Injection Site Description
The injection site is located in a rural section of Toole County, Montana (pop. ~5,267), about 8-miles east of the village of Sunburst (pop. ~375) and 8 miles south of the Canadian border. The CO2 production well site is approximately 6 miles south of the injection site, 12-miles northeast of the town of Kevin (pop. ~154) and 18 miles north of the county seat of Shelby (pop. ~3,376). The wells, compressor station, and pipelines will be located on lands owned by the State of Montana and/or lands held in fee title by private landowners; BSCSP will work closely with these owners for access. The seismic work would be performed on private, state, and U.S. government owned lands pending landowner permission or acquisition of required state and Federal permits.
Source of CO2
Large volumes of naturally occurring CO2 are trapped in the Duperow Formation, which has closure under the Kevin Dome. The BSCSP will produce this naturally occurring CO2 for large-scale injection by drilling up to five CO2 production wells into the formation beneath the top of the dome. The purity of the CO2 will be determined once the first production well is drilled. The extracted CO2 will then be transported by pipeline to the single injection well drilled into the flank of the dome, where it will be injected into the Duperow and perhaps the Souris River formations (Figure 2).
CO2 will be injected through a single wellbore, and initial data from the targeted injection zone of the Duperow suggests the interval has 12 percent porosity and greater than 50 millidarcy permeability. These values should allow for injection volumes in the range of 12 to 13 MMcf/day, or approximately 250,000 metric tons of CO2 per year, over a four-year period.
The CO2 production wells are expected to recover CO2 at a pressure and temperature of approximately 1,100 lbs. and 96°F respectively. The CO2 will then be compressed via a compressor station at the production well site and transported through a pipeline to the injection site approximately six miles to the north.
Simulation and Monitoring of CO2
The commercially available PETRA software will be used to construct the basic geological framework, augmented by geophysical interpretation of available data using Kingdom geophysical interpretation software, and then uploaded into PETREL software as a precursor to creating a basic 3-D flow model. The TOUGH series of codes developed by Lawrence Berkeley National Laboratory will be the primary means of simulating multiphase flow, CO2 transport, and geochemical reactions along the flow path, although other model types may be employed for comparison purposes. Core samples taken from the CO2 gas cap and brine-filled flank of the dome will be tested in the laboratory to determine brine chemical and rock mineral composition and provide data for initializing and calibrating the geochemical model.
The BSCSP plans to employ an extensive and novel set of monitoring technologies at the Kevin Dome site. The methods include borehole (downhole and distributed pressure and temperature sensing, cased hole logs such as pulsed neutron) and seismic methods (crosswell seismic, 3-D, 9-component surface seismic, and multi-component vertical seismic profiling), core analyses, a suite of geochemical methods, injected and natural tracer studies, atmospheric CO2 monitoring, soil gas sampling, and surface and ground water monitoring. The Kevin Dome project offers several unusual monitoring and validation opportunities due to the presence of a large natural accumulation of CO2 and the unique geophysical capabilities and expertise of the BSCSP partners. For example, Vecta Oil and Gas has developed a skill set for processing, interpretation, and integration of nine-component data to image complex stratigraphy; Lawrence Berkeley National Laboratory will employ a unique down-hole seismic source for the crosswell survey; Columbia University has extensive experience in performing experiments with 14C and other types of chemical tracers; and Idaho National Laboratory has developed a novel technique for using rare-earth element signatures as an environmental aqueous tracer to determine if formation fluids are leaking from the target reservoir into overlying formations or to measure the extent that CO2 displaced waters have migrated.