Final Report for Gulf Coast Stacked-Storage Project SECARB Phase II at Cranfield


Phase I regional geologic characterization found that in the Gulf Coast, abundant geologic sequestration targets are found in many areas. The idea of stacked storage, developed for the current (Phase II) study, included the use of multiple hydrologically isolated injection zones beneath a common surface area to produce large capacity yet minimize the monitoring infrastructure footprint and increase public acceptance. Stacked zones include the use of CO2 for enhanced oil production (EOR), which was the focus of the Phase II study. An EOR project provided an opportunity to monitor injection at a higher rate and over a more prolonged injection period than an earlier test in brine (Frio Brine Pilot). The downdip water leg of the same field was then used for Phase III to assess geologic storage capacity beyond the use of CO2 for EOR (Hovorka and others, 2010).

At the end of the regional study of options, the site selected was a four-way structural closure at a depth of 10,300 ft (3100 m) below the surface at Cranfield, Mississippi. The field produced oil, gas condensate, and methane gas from the lower Tuscaloosa Formation "D-E" sandstones during the period 1944 through 1966. The field was then pressure depleted and wells plugged and abandoned. The field was purchased by Denbury Onshore, LLC, to be flooded with large volumes of CO2 transported via pipeline from CO2 produced from a geologic accumulation at Jackson Dome, Mississippi. Project design focused on coordination of the monitoring design with Denbury's commercial plans for injection, infrastructure development, and permitting in the Phase II area on the north side of Cranfield field. Phase II provided an opportunity to test innovative monitoring approaches that may be needed in the future to document that either EOR or brine storage is performing correctly in terms of permanence of storage (Hovorka and others, 2010).

Injection started July 15, 2008, in 2 wells but increased over the study period to 16 wells over an area of several square miles. Half the wells were updip injectors at the gas-oil contact, and half were downdip injectors injecting CO2 at the oil-water contact. The monitored injection was commercial (½ million metric tons per year) scale, and was sustained over a multiyear time frame, with the end of the Phase II project defined as September 30, 2010. In the report period, 23,640 MMSCF (1,229,510 metric tons) of CO2 was stored under Phase II. Injection and monitoring continued in the Phase II area; however, these were logistically connected to ongoing Phase III injection, which was conducted on the east side of Cranfield.


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