The oil and gas industry is one of the global leaders in developing and deploying CO2 capture. Of the approximately 30 Mt CO2 captured today from industrial activities in large-scale carbon capture, utilisation and storage (CCUS) facilities, nearly 70% is captured from oil and gas operations. The oil and gas industry is also often in a position to make use of this captured CO2, either by selling it to industrial facilities or by injecting it into the subsurface to boost oil recovery.
This process of injecting CO2 into existing oil fields is a well-known “enhanced oil recovery” (EOR) technique: the addition of CO2 increases the overall pressure of an oil reservoir, forcing the oil towards production wells. The CO2 can also blend with the oil, improving its mobility and so allowing it to flow more easily. The IEA’s new global database of enhanced oil recovery projects shows that around 500 thousand barrels of oil are produced daily using CO2-EOR today, representing around 20% of total oil production from EOR.
In CO2-EOR, some portion of the injected CO2 remains below the ground. If the CO2 that returns to the surface is separated and reinjected to form a closed loop, this results in permanent CO2 storage. Today, between 300 kg CO2 and 600 kg CO2 is injected in EOR processes per barrel of oil produced in the United States (although this does vary between fields and across the life of projects). Given that a barrel of oil releases around 400 kg CO2 when combusted, and around 100 kg CO2 on average during the production, processing and transport of the oil, this opens up the possibility for the full lifecycle emissions intensity of oil to be neutral or even “carbon-negative”
The idea of “carbon-negative” oil is attractive. It could help reduce emissions from hard-to-decarbonise sectors such as aviation and trucks that are heavily dependent on energy-dense, liquid fuels. However, the logic of “carbon-negative oil” critically depends on the boundaries of the analysis and the origin of the CO2.
Today the majority of CO2 injected in CO2-EOR projects is produced from naturally occurring underground CO2 deposits. This may appear a somewhat ironic situation, but the reason for this is the absence of available CO2 close to oil fields. Using natural sources clearly provides no benefit in terms of the emissions intensity of the produced oil. In the United States, more than 70% of the CO2 injected today for CO2-EOR is from natural sources.
There are, however, some projects that use CO2 captured from anthropogenic sources for EOR: the Century and Petra Nova plants in Texas are two of the largest such facilities. For these, it is important to track who claims credit for the avoided CO2 emissions. A credit associated with storing CO2 underground can only be counted once: either it can reduce the emissions from the original source when it was captured or it can reduce the emissions from oil production. It cannot do both.
For example, say a capture unit is attached to a coal-fired power plant and the captured CO2 is transported to and injected in a CO2-EOR site. In this case, it is not possible for both the electricity generated to be low-carbon and for the CO2-EOR to be low-carbon. To put this another way, if a coal-fired power plant operator were to pay a CO2-EOR operator to store captured CO2, the CO2-EOR operator could not claim that the oil produced has negative emissions.
Therefore to produce “carbon-negative oil” – that is for CO2-EOR actually to reduce the stock of CO2 in the atmosphere – EOR projects would need to inject CO2 that has either come from the combustion or conversion of biomass or has been captured directly from the air.
Ensuring the integrity of CO2 storage is also important for validating the emissions reductions. There are certain steps operators can take to ensure and demonstrate the permanency of CO2 storage, including: identifying sites with suitable geology that traps CO2; avoiding abandoned wells that could create a conduit for CO2 to reach the surface (or ensuring that these are plugged); and introducing monitoring and field surveillance to detect potential leakage. These measures reduce the risk of the injected CO2 migrating back to the surface and adding to the atmospheric concentration of CO2.
One additional potential advantage of CO2-EOR is that it offers a lower-cost opportunity to deploy CCUS projects. Under the IEA’s Sustainable Development Scenario, CCUS from both power generation and industrial facilities grows to 2040, reaching nearly 2 400 Mt CO2 of total CO2 captured worldwide – 80 times more than is captured today. In CO2-EOR, the oil revenues generated reduce overall project costs and expand the amount-of CO2 stored per unit of investment. Developing a number of projects of this kind would help reduce the costs of CCUS more generally and could provide the catalyst for commercial-scale CCUS finally to take off.