Residual oil zones

A Tale of Two CO2 Opportunities

American Association of Petroleum Geologists (AAPG)
Residual oil zone (ROZ) CO2 injection manifold: The development of ROZs is estimated to increase producible oil reserves in the United States by 30-to-50 percent or more. Photo courtesy of David Vance
Residual oil zone (ROZ) CO2 injection manifold: The development of ROZs is estimated to increase producible oil reserves in the United States by 30-to-50 percent or more. Photo courtesy of David Vance

The use of injected carbon dioxide for enhanced oil recovery (EOR) is a process that was first used on Jan. 26, 1972, at the SACROC unit in Scurry County, Texas. Since then carbon dioxide-enhanced oil recovery in primary production zones has expanded across the Permian Basin in west Texas and eastern New Mexico, and to a more limited extent in Kansas, Mississippi, Wyoming, Oklahoma, Colorado, Utah, Montana, Alaska and Pennsylvania – and in other countries.

Last year it was estimated that there are 114 active carbon dioxide injection projects that inject over two billion cubic feet of carbon dioxide per year – from largely geologic sources – to produce 280,000 barrels of oil per day.

It also is estimated that 10,000 of those barrels are being produced from a type of newly recognized oil deposit that is still in the process of being characterized – and is beginning to be perceived as a significant source of future oil production: the residual oil zone, or ROZ.

The basic concept of the ROZ is a zone in which oil is not present at saturations that have historically been thought to be required for primary or secondary oil production (typically over 50 percent). Under current economic conditions, viable production can take place from ROZs with oil saturations as low as 20 percent to 25 percent.

To do this requires the injection of carbon dioxide.

Residual oil zones are associated with petroleum migration and primary production areas:

  • “Brown Fields” are ROZs located beneath existing primary production zones.
  • “Green Fields” are ROZ zones with no associated primary production.

Aside from purely commercial projects, a series of strategic projects for the development of ROZs for petroleum production and utilization/control of carbon dioxide in the United States is under way in the Permian Basin of Texas and New Mexico, with funding directly from the DOE and the Research Partnership to Secure Energy for America (RPSEA, a DOE program). These projects include the creation of a regional groundwater model to evaluate groundwater sweeping and formation of ROZs in the San Andres along the Northwest Shelf and Central Basin Platform bordering the Delaware Basin.

The field application of the results of that modeling program also is under way, and petroleum, water and gas (including flash gas) are being collected from ROZ production wells in their native state and during carbon dioxide flooding to more closely evaluate the biological/chemical/physical processes that govern the formation and location of ROZs – and the specific response of those ROZs to carbon dioxide flooding.

It currently is estimated that there are 30.7 billion barrels of ROZ oil in the Permian Basin, and that 11.9 billion barrels of that are producible using carbon dioxide EOR. Furthermore, it takes somewhere in the range of 6,000 to 20,000 cubic feet of carbon dioxide to produce a barrel of oil, with 16,000 cubic feet being the average.

Carbon dioxide as used for EOR programs is a commodity that has value and an associated cost. The specific value/cost is established in contracts between the suppliers and consumers of that carbon dioxide; as such the specific costs are often closely held and considered proprietary.

However, a useful rule of thumb is that the cost of 1,000 cubic feet of carbon dioxide is 2 percent of the cost of a barrel of oil.

When carbon dioxide is used for enhanced oil recovery, a portion is retained in each usage cycle – with ultimately 90 percent to 100 percent of it irretrievably retained, despite rigorous recovery and recycle. Those recapture efforts are driven by the fact that the carbon dioxide is a commodity, must be purchased and has significant value.

There is another word for that retained carbon dioxide: “sequestration.”

For a practical illustration, currently three billion cubic feet of carbon dioxide is handled each day in the Permian Basin. Of that, two billion cubic feet are new stocks and one billion is from recycle. The two billion cubic feet is for new projects, project expansions and what’s needed to replace that which has been retained or sequestered.

Although to date not a primary driving factor in the development of this resource, there also is a perspective regarding the control of greenhouse gas emissions.

Carbon dioxide is used as a commodity for EOR during which sequestration takes place; this is increasingly being recognized as a viable and practical means to implement greenhouse gas control as part of a profit-making commercial activity.

The DOE literally is in the process of shifting its focus on the management of carbon dioxide from carbon capture and sequestration (CCS), where the carbon dioxide is to be managed as a regulated waste, to carbon capture and utilization (CCU), where carbon dioxide has very real economic value. For example, on Oct. 21, a senior DOE official at a federal coal advisory board meeting in Washington, D.C., announced the decision to officially shift the focus from CCS to CCU.

The bottom line is that the development of ROZs is estimated to increase producible oil reserves in the United States by 30-to-50 percent or more.

In addition, the process provides a means to sequester carbon dioxide that is driven by economics, not regulation, thereby offsetting unavoidable parasitic costs associated with carbon dioxide capture.

That represents two significant opportunities for moving the hydrocarbon energy sector into a viable future.

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Division Column-DEG Jeffrey Paine

Jeffrey Paine is DEG President for 2014-15.

Division Column-DEG David Vance

David Vance is principal scientist, ARCADIS-US Inc., Midland, Texas, and is a member of the DEG CO2 Sequestration Committee.  

Division Column DEG

The Division of Environmental Geosciences (DEG), a division of AAPG, is concerned with increasing awareness of the environment and the petroleum industry and providing AAPG with a scientific voice in the public arena. Among its objectives are educating members about important environmental issues, supporting and encouraging research on the effects of exploration and production on the environment, and communicating scientific information to concerned governmental agencies.

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