Study establishes feasibility of near-miscible CO2 injection to recover significant percentage of residual oil in Kansas oilfields
A study by the University of Kansas Center for Research funded by the US Department of Energy (DOE) has established the feasibility of using near-miscible CO2 injection for recovering between 250 million and 500 million additional barrels of oil from Kansas oilfields. Miscibility refers to the pressure at which the CO2 and oil are completely soluble in one another or form a single phase.
Below the minimum miscibility pressure (MMP) the injected CO2 mixes with and swells the oil to reduce its viscosity, increasing its ability to flow through the reservoir more easily to the production well.
The University of Kansas team studied the possibility of near-miscible CO2 flooding for extending the life of mature oilfields in the Arbuckle Formation while simultaneously providing permanent geologic storage of carbon dioxide, a major greenhouse gas.
The project was administered through the Research Partnership to Secure Energy for America to address the technology challenges of small producers as part of the Ultra-Deepwater and Unconventional Natural Gas and Other Petroleum Resources Program (Energy Policy Act, 2005). The program is managed by the Office of Fossil Energy’s National Energy Technology Laboratory.
In the laboratory, researchers subjected core samples from the Arbuckle Formation to simulate CO2 flooding. The studies showed that more than 50% of the residual oil remaining after water-flooding could be recovered from Berea Sandstone, Baker dolomite, and Arbuckle dolomite cores at pressures below the MMP.
The investigators also conducted simulation studies which indicated that the ultimate oil recovery is highly dependent on the degree of reservoir heterogeneity. Maximum recovery efficiency can be achieved by proper design and implementation of CO2 injection, with optimization of injection pressure, injection rates, and the well pattern.
The project is now moving into a second phase of research, in which researchers will conduct a variety of tests to improve characterization of Arbuckle reservoirs. The testing will determine the nature of the flow paths and average properties in the reservoir, assess the effect of geology on process performance, calibrate a reservoir simulation model, and identify operational issues and concerns for future applications of near-miscible CO2 flooding. Future work, if funded, would include field demonstration of the methodology.
The Arbuckle Formation has produced 36% (2.2 billion barrels) of the 6.1 billion barrels of total Kansas oil produced over the past 100 years. Oil production peaked in the 1950s, tapering off to the point where today, 90% of the wells operated by more than 100 small producers pump less than five barrels per day. The Arbuckle was chosen for the DOE-sponsored project because it represents a significant resource for improved oil recovery even though miscibility with CO2 is not achievable at the operating pressures in most Arbuckle reservoirs.
Following primary oil recovery (in which oil is naturally driven from a reservoir) and secondary recovery (in which pressure is applied to force the oil from the reservoir, usually by water flooding), as much as two thirds of the original oil in place typically remains stranded in a reservoir. Additional oil can be recovered using improved oil recovery techniques that increase the mobility of the crude oil. This enhanced oil recovery (EOR) also provides a means of safe, secure long-term storage of CO2, and is a key component of carbon capture, storage and utilization research.
Near-miscible CO2 flooding may be applicable to thousands of mature oilfields in Kansas and prevent them from being abandoned prematurely. According to the Kansas Geologic Survey, more than 6,400 highly compartmentalized reservoirs exist in Kansas, though about a third of these are small fields with an average of five producing wells or less.