Using enzymes to enhance oil recovery

Biofuels are no longer the only beneficiaries of enzyme-assisted energy production. Enhanced-oil-recovery (EOR) techniques are benefiting from enzymatic treatment as well, as technology provider Jumpstart Energy Services recently explained.

Enzymes, the broad class of protein-based catalysts found in all living matter, have been used to accelerate the rate of chemical reactions in various manufacturing industries. Biofuel production has recently generated the most attention for enzymes in terms of energy production, in which the catalysts are used to accelerate the biological breakdown of cellulosic material into sugars suitable for biofuel production. The US Department of Energy recently announced a 4-year, USD33-million investment in projects aimed at improving enzyme systems for this purpose.

But the oilfield is not to be left out, and Jumpstart Energy Services is aiming at EOR techniques for application of its enzyme technologies. "We call our application enzyme-enhanced oil recovery (EEOR)," said John Gray, President and Founder of Jumpstart. "We focus on combined EOR technologies where enzymes bring benefit to existing secondary or tertiary production."

Jumpstart represents an enzyme fluid technology, sold under the trade name Greenzyme, that is a water-soluble formulation reportedly made from DNA-modified proteins extracted from oil-loving microbes in a batch fermentation process. The enzyme itself is nonliving, which provides EEOR an advantage over microbial EOR techniques that may require a detailed pretreatment involving the injection of a fermentable carbohydrate nutrient base into the reservoir. With the EEOR technique, only a dilution of the enzyme into the injection water is required. No subsequent nutrients are required either, which allows for a broader range of well treatment applications.

Greenzyme is reportedly ideally suited for sandstone, waterdrive formations with <30 API oil, >20% porosity, and >100-md permeability for single well treatments, but can have broader ranges in other applications such as waterfloods. "We've had success in fractured limestone formations as well," Gray said.

Intertek laboratory tests shed light on EEOR mechanism

In order to explain how EEOR works, Jumpstart began laboratory tests at Intertek's Westport Technology Center designed to make an initial determination of the mechanism for any downhole oil-production improvement. These tests included comparing nonenzyme-treated and enzyme-treated 26 API oil samples (a 10% concentration of Greenzyme diluted in water was used) that were both heated under pressure in order to simulate reservoir conditions.

Allan Hartman, Jumpstart's Vice President of Business Development, postulated that the enzymatic treatment may be improving oil recovery by catalyzing the breakdown of larger molecules in the oil into smaller molecules, which might improve the flow characteristics of the oil including heavy oil. A SARA (saturates, aromatics, resins, and asphaltenes) analysis supported the breakdown hypothesis in terms of the saturate content, as the enzyme-treated sample had a 5% lower saturate content than the nonenzyme sample.

Further analysis by means of high-resolution gas chromatography demonstrated that while the nonenzyme-treatment samples had clearly visible hydrocarbon peaks out to at least C₄₄ (44 carbon atoms on a molecule, typical for high-carbon content paraffins), the enzyme-treated samples presented much smaller peaks beyond C₃₀, and no visible hydrocarbon peaks past C₃₇. According to Jumpstart, the observed reduction in high-carbon-number paraffins and a corresponding reduction in the molecular size of the waxes point to a positive contribution from the enzyme.

The enzyme's contribution to oil recovery may be a multipronged approach, as further testing indicated. "We commissioned a series of viscosity and interfacial-tension tests on these samples at the same time," Hartman said. "There was a sizable drop in viscosity, from 90.3 cP to 76.1 cP, in the presence of the enzyme treatment."

Interfacial-tension tests, which provide an indirect measure of the relative miscibility between oil and water, were conducted on oil/water samples in the absence of enzyme, oil/water samples in the presence of enzyme but prior to a heating/pressure treatment, and oil/water samples in the presence of enzyme and following a heating/pressure treatment. The Intertek report showed oil/water samples alone had fairly high interfacial tensions, on the order of 20.5 mN/m. For both enzyme-treated samples, there was an order of magnitude decrease in interfacial tension. "We expected to see a reduction of interfacial tension which was confirmed by these tests," Gray said, and noted that the heating/pressure step to simulate reservoir conditions did not influence this behavior.

"This indicated to us that in addition to catalyzing the breakdown of higher molecular-weight paraffins, the enzyme also possesses some biosurfactant properties, helping to release the oil from within the formation in the form of small droplets that are carried with fluids moving to a producing well," Gray continued. "The overall effect appears to improve relative permeability and oil mobility."