EOR

About Enhanced Oil Recovery (EOR)

Utilization of Carbon Dioxide for Enhanced Oil Recovery

Today, there are more than 114 active commercial carbon dioxide injection projects involving enhanced oil recovery in the United States. Combined, they inject more than 2 billion cubic feet of carbon dioxide and produce more than 280,000 barrels of oil per day (see April 19, 2010, Oil and Gas Journal). For comparison, the total undeveloped US domestic oil resources still in the ground total more than 1 trillion barrels (160 km3), most of it remaining unrecoverable. By most estimates, enhanced oil recovery (EOR) can help to recover an additional 50-60% of the original oil in place. DOE estimates that if the EOR potential were to be fully realized, State and local treasuries would gain $280 billion in revenues from future royalties, severance taxes, and state income taxes on oil production, aside from other economic benefits. Further developing this potential would depend on the availability of commercial carbon dioxide in large volumes, which could be made possible by widespread use of carbon capture and storage.
What is Enhanced Oil Recovery?

Oil fields are found in layers of sedimentary rock. The crude oil in these rock layers was made when organic material, such as plankton and algae, deposited millions of years ago decomposed. Crude oil is a thick fluid that, like carbon dioxide, tends to migrate towards the surface. Oil fields are formed when the migrating oil is trapped by nonporous and nonpermeable layers of rock. Many oil fields have existed for millions of years. Today, people have developed sophisticated techniques for finding oil fields and producing the oil from them. When an oil field is first produced, the background pressure in the formation helps to push the oil to the surface. In the early days of oil industry, this sometimes led to the famous “gushers” seen in history books. Typically, the background pressure is great enough to help produce roughly 10% of the oil in an oil field. Once the pressure is released, new means are employed to restore pressure in the oil field and reduce the thickness or viscosity of the oil so that it can move more easily. These methods are generally referred to as Enhanced Oil Recovery or EOR. 

There are 3 major approaches used in EOR: 
  • Thermal: steam is injected to thin the oil and help it flow
  • Chemical: polymers or surfactants that behave like soap are injected to break up the oil and help release it from the rock surfaces in the pore space; and, 
  • Gas: natural gas (a by-product), nitrogen or carbon dioxide is injected to increase reservoir pressure and to help thin the oil so it can flow to the surface (Figure 1). 
The figure above illustrates how gas injection – in this case carbon dioxide – is used for EOR. Carbon dioxide and water are injected through the injection well on the left. The carbon dioxide mixes with the water forming a weak acid that helps to break down the viscosity of the oil. At the same time, the carbon dioxide-water mix restores the background pressure in the oil field, helping to push the oil towards the production well on the right. The resulting oil, carbon dioxide, and water mix is brought to the surface in a closed loop system that allows the operator to separate the carbon dioxide and water for reuse while the oil and related products are sold into the market. In this process, carbon dioxide displaces oil and some of it remains behind permanently. There is not a lot of surplus carbon dioxide available in a form that can be used for EOR so operators try to recover as much of the carbon dioxide as they can. Despite these efforts, at least about 20-30% of the injected carbon dioxide remains in the ground.
What does it mean for the MRCSP?

Industrial use of carbon dioxide for EOR could increase domestic oil production while making it more economically attractive for industry to reduce carbon dioxide emissions. Executed together and synergistically, EOR and Carbon Capture and Storage are referred to as Carbon Capture, Utilization, and Storage or CCUS. The ultimate goal of CCUS technology development is to develop viable options for reducing carbon dioxide emissions related to large point sources. The Midwest Regional Carbon Sequestration Partnership (MRCSP) region contains some of the largest historic oil-and-gas producing areas in the conterminous United States. The MRCSP estimates that potentially 8500 million metric tons of carbon dioxide could be stored within our region alone – or approximately ten years worth of emissions from our region. Using carbon dioxide for EOR could lead to the production of an additional 1.2 billion barrels of oil that would otherwise be stranded in the ground.
oil and gas field map of the MRCSP region
Existing enhanced oil recovery operations also offer opportunities to research carbon sequestration technologies while providing valuable information about optimizing the recovery of additional oil. Experienced gained will help develop more efficient ways to monitor carbon dioxide injection both to assure safety but also to make the best use of resources. MRCSP will also further refine the understanding of the oil bearing formations by continuing with its geological characterization work throughout the region.
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