Injected carbon dioxide acts as a cleaning solvent in wells, forcing out oil

BY ALAN BAILEY FOR GREENING OF OIL

Anadarko Petroleum Corp’s reinvigoration of Wyoming’s huge but aging Salt Creek oil field has become something of a poster child for what can be done to reduce the environmental impact of oil production, Craig Walters, Anadarko’s general manager for Rockies enhanced oil recovery, told Greening of Oil Feb. 9. The company has been pumping carbon dioxide into the field reservoir, using a technique known as carbon dioxide enhanced oil recovery, or EOR, to increase oil production.

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EOR is a win for the environment because it reduces the oil field’s surface footprint and keeps the CO2 underground, out of the atmosphere. And because it squeezes more oil out of the ground, extending the life of the Salt Creek field, it is a win for Anadarko and the local and U.S. economy.

To date, Anadarko has injected 181 billion cubic feet of carbon dioxide into the field as part of a project to tease more oil from the field and in the process sequester a greenhouse gas that would otherwise have to be discharged into the atmosphere. In fact, the around 125 million cubic feet of carbon dioxide that Anadarko injects into the Salt Creek field each day is roughly equivalent to the reduction in carbon emissions resulting from taking half-a-million cars out of service, Walters said.

Carbon dioxide comes from LaBarge field

Anadarko buys the carbon dioxide for its Salt Creek project as a byproduct from natural gas and helium production at ExxonMobil’s LaBarge field, some miles to the west of Casper, Wyo. LaBarge supplies carbon dioxide to a cluster of enhanced oil recovery projects in the region.

“We consider these projects to be a win-win-win,” Walters said. In addition to sequestering carbon dioxide, the implementation of carbon dioxide enhanced oil recovery at Salt Creek has boosted employment at the field from about 30 people to around 100, with an additional 100 to 200 contractors employed to work on field development. Increased oil production at the field reduces the amount of oil that the United States has to import from overseas while also boosting the state’s tax take from the field, Walters said.

“In 2009 we paid roughly $36 million of taxes to the state as a result of our increased oil production,” he said.

The purchase of carbon dioxide from LaBarge presumably also improves the economics of that field, with the subsequent effect of increasing state revenues.

And then there’s the economic stimulus that comes from Anadarko’s increased capital spending with local service providers as a consequence of the company’s multiyear project at Salt Creek.

The field has been in production for 100 years

Discovered in the early 1900s and having produced oil for about 100 years from the high desert to the north of Casper, the Salt Creek field’s production had slowed to around 4,000 barrels per day when Anadarko took over the field in 2002 by buying out field operator Howell Petroleum, Walters said. At the time of purchase the field relied on bulky wellhead pumps to draw oil from the subterranean reservoir, with a network of power lines distributing power to the pumps. Howell had also for some years been injecting water into the reservoir, to flush oil from the reservoir rock in a technique referred to as “waterflood.”

Anadarko had been seeking opportunities in the Rockies for the application of carbon dioxide enhanced recovery to flush new oil from old fields, and the company had established a screening process for selecting candidate fields in which to apply that strategy.

“Salt Creek readily floated to the top of that list,” Walters said.

Carbon dioxide infrastructure in place since the 1980s

A particular attraction at Salt Creek, in addition to the 1.7 billion barrels of oil known to still be in place in the field, was the existence of a pipeline infrastructure, mostly in place since the 1980s, for transporting carbon dioxide from LaBarge—the delivery of carbon dioxide to Salt Creek only required Anadarko to construct a spur line from that existing infrastructure.

“Anadarko in 2003 laid 125 miles of 16-inch pipeline that took it from roughly the middle part of the state—it was the terminus of ExxonMobil’s line at the time—and took that carbon dioxide up to our Salt Creek field,” Walters said.

And at the same time that Anadarko purchased Howell Petroleum, Anadarko also purchased carbon dioxide contract rights from a company called Petro Source that had a contract with ExxonMobil, he said.\

Anadarko subsequently embarked on a series of development phases to progressively implement the carbon dioxide enhanced oil recovery system across the Salt Creek field. The company is currently implementing phase seven of this program, with phases one to six already having applied the new recovery technique to 30 to 40 percent of the field, thus increasing production to about 12,000 barrels per day, Walters said.

Well pumps no longer needed

And, because the carbon dioxide now injected into the field reservoir is able to push oil from production wells without the assistance of well pumps, Anadarko has been able to remove the unsightly pumps and their associated network of landscape-marring power cables, thus reducing the surface footprint of each oil well to a simple and inconspicuous well valve and pipework structure. In fact, although the field has a central processing facility, used for separating produced oil from water and carbon dioxide, and some stations used for compressing the carbon dioxide that is passed into the field reservoir through injection wells, the field has become relatively inconspicuous.

“From a visual standpoint … it’s very hard to tell that we actually have an oilfield operation,” Walters said.

The U.S. Bureau of Land Management, the surface land owner, is especially pleased at Anadarko’s progress in tidying up the field, in territory inhabited by wildlife such as antelope and leased out to cattle ranchers.

“Anadarko has been able to clean up a lot of things and the BLM showcases it as a model project,” Walters said.

Scrubbing oil from the reservoir

But just how does carbon dioxide achieve its magic in moving additional oil from an aging field such as Salt Creek?

Although a gas at typical atmospheric pressures, carbon dioxide behaves more like a liquid at high pressure, when pumped to depth in an oilfield reservoir through injection wells, Walters explained. The liquid-like carbon dioxide mixes with residual oil in the reservoir to form a fluid that is less viscous than the oil and that can flow more easily than the oil through the pores of the reservoir rock.

The mixture of carbon dioxide and oil under pressure is a bit like scotch and water—the fluids are completely mixed, with no interface between them. And the physical properties of this fluid cocktail are such that they cause the fluid to act as a solvent, cleaning oil from the reservoir, Walters said.

“It’s no different from using soap or detergent on your hands to get dirt off,” he said. “It basically scrubs that oil (out) better than what water can do.”

The fluid that reaches the surface through the field’s production wells still contains that mixture of oil and carbon dioxide. But at surface pressures, the carbon dioxide boils off in the field’s separator facility for piping to compressor stations for re-injection into the reservoir.

Thus, carbon dioxide is continuously cycled through the field, with some remaining underground, in space previously occupied by oil and water removed from the field reservoir. Eventually, when field production ceases to be viable, all of the carbon dioxide purchased from LaBarge will remain underground, with virtually no loss of carbon dioxide at the surface, Walters said.

“It’s essentially a closed loop system,” he said

Adding 40 to 50 years to the field life

This entire process will probably add 40 to 50 years to the life of the Salt Creek field, upping the recovery of the original oil in place from 40 percent to perhaps 50 percent, Walters said.

And there are further opportunities to apply carbon dioxide enhanced oil recovery in other oil fields, where factors such as the oil viscosity, the oil temperature and the reservoir depths are appropriate for the use of the technique, Walters said. The great beauty of the technique is that it enables the production of new domestic oil from known oil resources, he said.

“That’s the great thing about these projects,” Walters said. “You know the oil is there. It’s already been discovered. You’re basically just increasing the recovery factor.”

There is also the spinoff environmental benefit of developing new oil without the need for new exploration drilling and without having to open a new oil field.

On the other hand, the competition for capital and skilled personnel in the United States is such that carbon dioxide enhanced oil recovery projects have tended to be very large.

“There are only so many people who can do it, so obviously you’re going to focus on those bigger projects first,” Walters said. “The smaller ones you’re going to catch as time goes on.”

The other major factor in this project-scale equation is the availability of carbon dioxide: A large enhanced oil recovery project can do the financial heavy lifting for the development of the required carbon dioxide distribution infrastructure, with smaller projects perhaps piggy backing off that infrastructure later.

Makes carbon dioxide sequestration feasible

But, by turning otherwise waste carbon dioxide into a commodity with commercial value, enhanced oil recovery is providing a means of making carbon capture and sequestration economically feasible.

“Enhanced oil recovery is the bridge to carbon capture and sequestration, if that’s the direction we head as a nation at some point in time,” Walters said.

And the impact on the carbon footprint of oil can be impressive.

In a typical oil field you may end up purchasing 5,000 to 8,000 cubic feet of carbon dioxide for every incremental barrel of oil that results from enhanced oil recovery, Walters said. By the time that the barrel has been ultimately consumed it will have released about 8,000 cubic feet of carbon dioxide.

“You’re basically producing green oil,” Walters said. “You’re offsetting 60 to 100 percent of the carbon dioxide that would be released by that barrel of oil.”

Links of interest

AAPG’s Explorer: CO2 puts new fizz in old field

About Anadarko Petroleum, from company Web site

American Carbon Registry: Salt Creek enhanced oil recovery project

Contact Alan Bailey at abailey@petroleumnews.com