Hydrogen: Coal-to-Synthetic Natural Gas
What is Carbon Dioxide Enhanced Oil Recovery (CO2 EOR)?
Carbon dioxide enhanced oil recovery (CO2 EOR) is a technique used to recover oil, typically from mature fields that have ceased being productive through traditional primary and secondary recovery methods. Primary and secondary recovery methods typically leave two-thirds of the original oil in place (OOIP). To put the potential of EOR into perspective, of the total of 600 billion barrels of oil that have been discovered in the United States, approximately 400 billion barrels are unrecoverable by conventional methods. Half of that unrecoverable oil (200 billion barrels) is at reasonable depths at which EOR may be applicable.
CO2 EOR is an established technique in the United States, and is the only oil recovery technique that has shown any growth since the 1980s. In fact, CO2 EOR now accounts for 4% of the Nation's oil production. It can extend the productive life of an existing oilfield by several decades, and it can lead to recovery of millions of barrels of additional oil.
The basic principle behind CO2 EOR is the mutual solubility of crude oil and CO2 in the temperature and pressure conditions of a geologic reservoir. Given the right conditions, injected CO2 is able to dissolve and displace oil residue that is trapped in rock pores (like a solvent is able to displace grease from a dirty bicycle chain). In a typical CO2 flood operation, a pipeline delivers CO2 to the oilfield, where it is directed to injection wells. These wells are strategically placed to optimize the areal sweep of the CO2 through the reservoir. As the injected CO2 moves through pore spaces in the rock, it encounters residual crude oil. The crude oil mixes with the CO2, decreases oil viscosity, pressurizes it, and mobilizes it, forming a concentrated oil bank that is swept to producing wells. In this way, oil and gas companies are able to gain access to oil that would otherwise be left in the ground.
CO2 EOR is additionally attractive because of its effectiveness and its ability to sequester gasification-created CO2 emissions. Following CO2 EOR operations, the CO2 can remain underground in the reservoir, and is thereby prevented from entering the atmosphere.
Background on CO2 EOR
CO2 EOR was first tested in the early 1970s in West Texas. Since then, it has been utilized successfully throughout the Permian Basin of West Texas and eastern New Mexico. It is currently being used in oilfields in Kansas, Mississippi, Wyoming, Oklahoma, Colorado, Utah, Montana, Alaska, and Pennsylvania. In the United States, there are currently 13,000 CO2 EOR wells in operation that produce a total of about 245,000 barrels of oil per day. Industry experts estimate that we have the potential to produce over 40 billion barrels of additional oil from existing domestic fields using advanced CO2 EOR techniques.
Until recently, most CO2 EOR has depended on naturally-occurring underground deposits as the source of the CO2. In recent years, however, industry has begun to utilize CO2 that has been captured as a by-product of fossil fuel combustion, gasification, or other industrial processes. Because a ton of CO2 costs $30, and each ton can yield 2-3 barrels of oil, there is a strong economic incentive to re-use industrially-sourced CO2 from gasification plants, gas processing facilities, and power generation plants.
CO2 EOR represents a win-win strategy for beneficial use of industrially-sourced CO2. From an economic standpoint, CO2 EOR is a highly effective tool for re-invigorating oil production from mature fields that might otherwise be abandoned. From an environmental standpoint, it represents a practical way to recycle and utilize CO2 while reducing overall atmospheric CO2 emissions.