A Tricky Tradeoff - Can Adding a Little Solvent Yield a Lot More Heavy Crude?

Abstract

Years of small-scale testing have shown that adding a small amount of a light hydrocarbon to steam can yield large gains in heavy-oil output and reduce emissions; but, no one has proven it can be done on the large scale common in the Canadian oil sands. That could change soon. Two innovative Canadian operators—Imperial Oil and Cenovus Energy—are working on commercial steam-injection installations. They have spent more than a decade developing and testing ways to add solvents such as butane to steam to increase production and ultimate recoveries. If it works on a large scale, it will allow heavy-oil producers to use significantly less steam per barrel to coax out thick crude. Lowering the steam/oil ratio (SOR)—which represents the barrels of water used to produce an added barrel of oil—could offer a profitable path to reduced emissions. “If you can improve the thermal efficiency—the steam/oil ratio—emissions go down. Also, costs go down,” said Ian Gates, an associate professor at the University of Calgary, whose research includes solvents. “It all goes in the same direction. You make more money with lower greenhouse emissions.” Based on laboratory work and field tests, the combination of heat and solvents can increase production—30% or more is often cited—though some have done better and some worse. Cenovus’ pilot program, which was run at two locations, showed it could reduce its steam/oil ratio by 25%, said Subodh Gupta, chief of technology development for the company spun off by Encana. He also said the greater efficiency could allow wide well spacing. Imperial said it sees a significant increase in the amount of oil it will ultimately be able to produce. The operator, which improved its estimated recoveries from 20% to 40% at its Cold Lake field by improved reservoir analysis, steam injection, and drilling techniques, said that solvent use plus continued improvements in those three areas “have the potential to increase recovery to more than 60%.” Despite the potential, many working on the technology express concerns about the cost of the solvent required. “There is no doubt it works, but solvent is quite expensive,” said Neil Edmunds, vice president for enhanced oil recovery at Laricina Energy, who has long been involved in solvent research and simulation work. For companies considering the idea, he said, the cost of the solvent can be “sobering.”