Experimenting with Gas Cycling for EOR

Researchers at Core Laboratories have conducted laboratory tests that demonstrate that, in certain cases, production from unconventional reservoirs can be increased by several percentage points.

In oil production from unconventional reservoirs, several percentage points can mean a difference of millions of dollars.

Core’s Vice President of Reservoir Description Larry Bruno said they have achieved those results in the lab and he expects the company’s clients to begin taking the technology – referred to as gas cycling or engineered gas injection – into the field.

Bruno said a typical well in an unconventional reservoir in the Permian Basin is about 9 percent of reserves.

“In the laboratory, we’ve demonstrated that we can get that into the low to mid-teens,” Bruno said.

“If a tight well is expected to produce a million barrels …a successful engineered gas cyclic injection program may yield 1.3, 1.4, 1.5 million,” he said.

In an earlier interview with Bloomberg, company CEO David Demshur said the technique could be applied for an additional investment of $1 million to $2 million. That could mean an additional 1 to 2 million barrels, he said.

Enhanced oil recovery techniques in conventional reservoirs typically involve pushing the oil from injector wells to producer wells with water or gas. In these unconventional reservoirs, the rock is just too tight, Bruno said.

Image Caption

This shows a proprietary Core Lab pressure-volume-temperture PVT cell, used to determine the properties and phase behavior of the crude oil.

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Researchers at Core Laboratories have conducted laboratory tests that demonstrate that, in certain cases, production from unconventional reservoirs can be increased by several percentage points.

In oil production from unconventional reservoirs, several percentage points can mean a difference of millions of dollars.

Core’s Vice President of Reservoir Description Larry Bruno said they have achieved those results in the lab and he expects the company’s clients to begin taking the technology – referred to as gas cycling or engineered gas injection – into the field.

Bruno said a typical well in an unconventional reservoir in the Permian Basin is about 9 percent of reserves.

“In the laboratory, we’ve demonstrated that we can get that into the low to mid-teens,” Bruno said.

“If a tight well is expected to produce a million barrels …a successful engineered gas cyclic injection program may yield 1.3, 1.4, 1.5 million,” he said.

In an earlier interview with Bloomberg, company CEO David Demshur said the technique could be applied for an additional investment of $1 million to $2 million. That could mean an additional 1 to 2 million barrels, he said.

Enhanced oil recovery techniques in conventional reservoirs typically involve pushing the oil from injector wells to producer wells with water or gas. In these unconventional reservoirs, the rock is just too tight, Bruno said.

The lab work on the reservoir fluids revealed that if the oil was exposed to certain compositions of gas, the oil would vaporize and enrich the gas. When the pressure is dropped on the enriched gas, liquids condense and are recovered. The gas can then be re-injected.

Bad Rocks, Containment and Timing

As with any new technology, there are potential challenges. Bruno said a thorough understanding of the rock and fluid properties is the essential starting point. Also, maximizing the surface area of the fracture network and the stimulated rock volume are key components.

Good reservoir rock is a limiting factor.

“You can’t make good rock out of bad rock,” Bruno said.

Containment can also be a concern.

If the formation is “leaky,” the injected gas might dissipate away from the target zone, he said.

To address this concern, Core has been engaged to deploy its proprietary tracers in the injected gas.

“We can see if the tracers show up in a different zone or well bore, outside of the targeted reservoir interval”, he said.

“A properly stimulated tight formation with effective seals above and below is favorable,” Bruno said.

If hydraulic fracturing is limited to the zone of interest, the injected gas may be contained. Alternatively, the injected gas may escape if the fractures go beyond the target zone, or through faults or other leaks.

“Containment will either be a natural strength or deficiency of the formation,” said Bruno.

Time issues also are being studied, such as how long to let the injected gas remain in place during each cycle, how many cycles are optimal, and when in the life of the well to begin the process.

“Each time we strip a little oil out, it can change the formula of the remaining oil in the rock,” he said. Researchers can adjust the recipe of the gas to achieve the best results, he said. “We have to understand how the oil will react with different compositions of injected gas.”

“We’re in the early innings with this. We’re still trying different things,” he added.

“Our role is to validate the process in the lab, getting the right engineered gas in contact (with) a specific oil. In the lab, we’ve demonstrated that we can recover incremental oil with multiple cycles,” he explained.

Traditionally, EOR efforts begin late in the life of a field.

“Maybe we don’t need to wait so long. Perhaps we can change the shape of the decline curve if we start at midlife or earlier,” Bruno said.

Eagle Ford and Beyond

Last year, Core Laboratories announced the formation of a multi-company consortium in the Eagle Ford to pursue the technology, and Core is looking forward to working in other basins.

“That’s high on our list of conversations right now,” Bruno said.

The consortium approach benefits companies who are able to view shared results he said.

“Some clients have done rudimentary field injection projects. We get feedback and that directs additional lab work,” Bruno said.

Bruno said the technology will be useful in many areas, with some horizons in the Permian already under investigation.

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