Enhanced oil recovery
Producing oil from sandstone and carbonate reservoirs is not always easy, especially after many years of production. The oil can be tightly held in pore spaces, which means that a lot of oil can be left behind after natural drive mechanisms diminish. Eventually, it becomes cost prohibitive to continue pumping oil unless recovery can be enhanced.
Under the right pressure and temperature conditions CO2 acts like a liquid and can be injected through a well at the center of an oilfield, enhancing the flow of oil to surrounding wells. This practice, called Enhanced Oil Recovery, has been in use for years in America's oilfields, providing valuable oil when demand is high. The injected CO2 goes into solution in the oil in rock pore spaces, making it less sticky, and allowing for easier production.
Looking at the bigger picture.
Because of the established effectiveness of CO2 in enhanced oil recovery, oil reservoirs have the most potential to offset the costs associated with storing carbon in the Illinois Basin. To assess this potential, a Basin-wide EOR estimate was made, based on a new understanding of the original oil-in-place in the Basin, the CO2 storage resource, the assessed EOR resource, the geographic distribution of EOR potential, and the type of recovery mechanism (miscible vs. immiscible). Based on this data, it is possible that enhanced oil recovery could yield 137 to 207 million m3 (860 to 1,300 million barrels (bbl)) of oil from the Basin, while providing 140 to 440 million metric tons (154 to 485 million tons) of CO2.
With cumulative oil production for the Basin of about 0.67 billion m3 (4.2 billion bbls), nearly 1.5 billion m3 (10 billion bbl) of oil remains, primarily as unrecovered resources in known fields. To assess the recovery potential of a part of this resource and the concurrent stored CO2 volumes, geologic modeling and compositional reservoir simulation were carried out. Parts of nine fields were used to create generic geological models for the most prolific oil-bearing reservoirs in the Basin — the Aux Vases and Cypress Sandstones and the St. Genevieve Limestone. These models incorporated data from more than 1,000 total wells, 120 wells with core, over 2,000 core sample points, 12,000 field acres and 20 flow zones. Structure and isopach maps were developed deterministically from well logs, whereas porosity and permeability distributions were developed geostatistically from core analysis data for use in the reservoir simulator. Processes simulated were miscible and immiscible flooding (based on reservoir pressure and temperature), as well as continuous and water-alternating-gas CO2 injection scenarios.
For additional information and more detail see:
World Resources Institute
National Energy Technology Laboratory (NETL)
