What is Enhanced Oil Recovery (EOR)? Over time, as oil is extracted from underground reservoirs, these reservoirs lose pressure, making it more and more difficult to extract the remaining oil in the reservoir. One way to counteract this decrease in pressure is to inject a fluid -- commonly CO2 -- into the oil reservoir to force more oil to the surface. This process, called EOR, traps much of the CO2 used for oil extraction in the underground rock. Because the CO2 remains trapped in the rock, this method has been proposed as a carbon sequestration technique.
Source: NETL CO2 EOR Primer
Does CO2 EOR represent a net sequestration of CO2?
Much of the CO2 used for EOR gets extracted from naturally occurring underground CO2 reservoirs. Using this CO2 for EOR involves extracting the CO2 from the natural source, transporting it to the oil field, and then injecting it back underground for the EOR. Given that energy (with resulting CO2 emissions) is required at each step of this process, this type of EOR does not count as net source of CO2 sequestration.
CO2 used in EOR processes, however, can also come from anthropogenic sources (like industrial facilities and power plants). In this process, a device that separates CO2 from other exhaust particles is installed on an industrial facility. There are many different techniques for separating CO2 from industrial emissions sources (see chart below and this startup that promises significant cost savings in CO2 separation). The resulting pure stream of CO2 is then transported to the EOR field for underground injection.
Without EOR, the vast majority of these anthropogenic CO2 emissions would otherwise get released into the atmosphere. If the process of capturing, transporting, and storing the CO2 from an anthropogenic source to an EOR field uses energy that emits less CO2 into the atmosphere than is stored through the EOR process, a case can be made that such EOR would be a net negative source of emissions.
But what about all of the additional oil that is brought to the surface to be burned in this process? If CO2 EOR enables oil that otherwise would not have been extracted from the ground to be released and this oil from EOR doesn't displace oil elsewhere in the world from being extracted, the net impact of EOR on CO2 emissions is likely positive.
Over the long run, determining the "additionality" and global price impacts of oil recovered through EOR will be critical for determining whether CO2 EOR provides a net negative source of emissions. Providing a mechanism for continued extraction of low-cost fossil fuels -- even if some CO2 is sequestered in the process -- is the main drawback of EOR.
How can EOR help with the commercialization of CDR approaches?
EOR has the potential to aid in the development of CDR approaches like biomass power generation with carbon capture and storage (BECCS) and direct air capture (DAC). For one, without strong carbon prices, BECCS and DAC businesses need another customer for the CO2 that their processes capture. EOR provides the best target customer: the approximately 100M tonnes of CO2 consumed in EOR globally is likely a full order of magnitude greater than all of the other CO2 consumed for other purposes worldwide (though it is difficult to get a precise estimate of total global CO2 consumption by end use...). If the oil recovered through a BECCS+EOR or DAC+EOR can also get credit for low carbon fuel production (like the Low Carbon Fuel Standard in CA), BECCS and/or DAC installations could begin to get developed, which would provide a number of benefits for the CDR industry. Such early installations would help CDR companies:
1. Learn how to inject and store CO2 with the greatest efficiency
2. Monitor and verify how long the CO2 emissions remain sequestered
3. Streamline the project development process -- getting the right permits, securing financing, etc.
4. De-risking technology and driving technology innovation to reduce costs and improve efficiency
With this learning from EOR projects under their belt, CDR companies could more easily transition to storing CO2 underground without EOR when carbon prices increase to make such standalone sequestration economically viable. And without EOR, it looks unlikely that such CDR projects will get developed at scale in the near-term.
Are there ways that we can gain the short-term benefits to CDR from EOR developments while mitigating long-term potential costs of prolonged fossil fuel dependence?
Probably. If only a small amount of EOR is enabled to come online, or if EOR permits are only given for a set time frame (say 15 to 20 years), it would be possible to gain many of the benefits to CDR listed above while hedging against the prospect of opening up billions of barrels of additional oil supply.
Bottom line: EOR has the long-term potential to increase our dependence on fossil fuels, but also has the short-term potential to help kickstart the development of several promising CDR technologies. These early benefits to the development of CDR likely outweigh the potential long run costs of EOR -- especially if EOR is regulated in a way to mitigate these potential long run costs.