A U.S. Department of Energy (DOE) project is turning stranded natural gas at marginal or low-production oilfields into fuel for distributed electric power. The breakthrough is bringing previously idle oilfields back into production and could boost domestic oil production by some 28 million b/year within the next 10 years.

Stranded gas is natural gas that is uneconomic to produce for one or more reasons: the energy, or Btu content, may be too low; the gas may be too impure to use; or the volume may be too small to warrant a pipeline connection. Noncommercial gas is sometimes produced along with oil, becoming an environmental liability. This unwanted byproduct of oil production has become a major problem in California oilfields where producers have been forced to abandon sites early.

A project managed by the Office of Fossil Energy’s National Energy Technology Laboratory (NETL) called Oil Field Flare Gas Electricity Systems (OFFGASES) is turning this waste gas into fuel for distributed generation power units at marginal well sites in California.

Oil production sites are heavy electricity consumers. According to the California Oil Producers Electric Cooperative, electricity accounts for 40-60% of the operating cost of oil production and delivery, and it represents one of the highest expenses in producing marginal oil wells. In California, equipment such as pump jacks are all run by electricity, and this power must be purchased from the utility grid.

By using microturbines to harness the stranded gas and generate low-cost electricity — usually at 20-40% of the costs of utility grid electricity — the distributed generation/OFFGASES project is increasing oil production in previously hopeless fields, making use of a fuel that was previously considered unusable and uneconomic to produce. In electrical terms, the equivalent of about 45 MW of potential electrical generation has been identified as stranded gas.

The project is conducting four field demonstrations with fuels of varying energy contents and quality. Three of the demonstrations have shown success so far.

A demonstration using high-Btu gas, which contains more than 1,600 Btu/cubic foot, boosted oil production in its three-well marginal oilfield from 10 b/d to 23 b/d. A demonstration with medium-Btu gas, which does not meet the quality requirements for commercial pipelines in California, is now producing 150 b/d in a 19-well field that had been at risk for abandonment. And a field containing “harsh” gas, which contains naturally high levels of nitrogen, carbon dioxide and hydrogen sulfide, has been brought into compliance with air emissions regulations by scrubbing hydrogen sulfide from the gas using a patented sulfur-treating system.

The fourth demonstration deals with ultralow-Btu gas, which has as little as 15 Btu/cubic foot. This gas is of such low quality that it’s not immediately flammable and therefore cannot even be flared; operators have been spiking the weak gas with purchased commercial natural gas just to flare it. As part of the NETL-funded project, operators are now using FlexEnergy’s Flex-Microturbine, a new technology that uses catalytic combustors and actually runs on 15-Btu gas. While the microturbine is working, improvements are still needed, and researchers are testing the equipment needed to turn this field into another success.

NETL demonstration partners include FlexEnergy, the Interstate Oil and Gas Compact Commission, California Oil Producers Electrical Cooperative, California Energy Commission and California South Coast Air Quality Management District.

The project was awarded under DOE’s Office of Fossil Energy’s Preferred Upstream Management Practices program, which aims to slow the decline in America’s oil production by pairing “best practices” and solutions from new technologies to an active campaign of disseminating information to domestic producers.

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