Advantages of Gasification - Product Flexibility - Useful Byproducts
Removal of carbon dioxide (CO2) from synthesis gas (syngas) often takes place before further processing. Carbon dioxide can be removed in a variety of ways and for varying reasons. Limits on emissions are looking increasingly likely, so finding a use for produced CO2 is important. Fortunately, CO2 is valuable for use in enhanced oil recovery (EOR).
Enhanced Oil Recovery
Carbon dioxide EOR is an established technique in the United States, and the only one that has shown any growth since the 1980s. In fact, CO2 EOR now accounts for 4% of the Nation’s oil production. Carbon dioxide can be injected into oil reservoirs to decrease the viscosity of the oil, increase pressure, or otherwise facilitate the easier removal of oil from the reservoir. Carbon dioxide EOR is particularly attractive because of its effectiveness and its ability to sequester gasification-created CO2 emissions.
EOR is the use of CO2 to recover oil from typically mature fields that are at or near the end of the effective period of traditional oil extraction techniques. EOR is used when primary and secondary methods of oil extraction have ceased being productive. Primary and secondary methods typically leave two-thirds of original oil in-place (OOIP). In all, 600 billion barrels of oil have been discovered in the United States and approximately 400 billion barrels are unrecoverable by conventional methods. Half of that unrecoverable oil (200 billion barrels) lies less than 5,000 feet below the surface, and is therefore a primary target for EOR.
The Great Plains Synfuels Plant/Weyburn Project
In 2000, the Great Plains Synfuels Plant (GPSP) began selling CO2 emissions, becoming one of the first commercial facilities to sequester CO2 from a coal process (see Designs for CO2 Capture for more information). The program began in 1997, when EnCana (formerly PanCanadian Resources) sought a solution to declining production in their Weyburn Oil Fields. Dakota Gasification Company, owners of the GPSP, and EnCana made an agreement to sell CO2 for use in EOR. Through 2006, the GPSP compressed approximately 105 million standard cubic feet per day of CO2 and delivered it through a 205 mile pipeline from Beulah, North Dakota, to the Weyburn Oil Fields, located in Saskatchewan, Canada. The CO2, about 95.5% pure and very dry, is then injected into the mature fields where it has doubled the oil recovery rate of the field. In 2006, a third compressor was installed and an additional agreement was reached with Apache Canada Ltd. to supply CO2 for EOR to their nearby oilfields. The three compressors increased CO2 delivery to 160 million standard cubic feet (MMSCF; or 8,000 tonnes) per day, or almost 50% of the plants CO2 production. To date, approximately 6 million tonnes of CO2 have been sequestered and over the current expected lifetime of the program, an anticipated 20 million tons of CO2 will be stored.
This agreement benefits both parties: byproduct revenue and sequestered carbon emissions for the gasification plant and enhanced oil production for the oil field. The use of CO2 from the GPSP for EOR is predicted to allow an extra 130 million barrels of oil to be produced and enable the oilfields to be productive an additional 25 years. The Dakota Gasification Company expects to see increased net revenue beyond the $100 million initial investment in the pipeline and compressors, with some sources placing the pre-Apache Canada Ltd. agreement at between $15 and $18 million per year.1
The GPSP benefits from being in relatively close proximity (205-miles) to an area of mature oil fields (the Williston Basin, which extends from northern North Dakota and Montana into Saskatchewan and Manitoba). Relative proximity to a CO2 buyer is important, as geographical limitations, expensive piping of CO2, and safety are all key factors. Experts have speculated that the Permian Basin in Texas offers potentially good opportunities for CO2 use in EOR. In some areas, naturally occurring CO2 is being used for EOR, and its availability could affect markets for a carbon-separating gasification facility.
1. The Sinor Synthetic Fuels Report. J.E. Sinor Consultants Inc. July 2001.