Fizzy Frack

Unconventional reservoirs provide a unique set of challenges like low permeability and very low porosity that require stimulation to be economically viable. The addition of CO₂ or nitrogen to water-based fracturing fluids energizes the system, delivering improved well productivity and other benefits.

“Besides the water savings, which can be upward of 80% per well, there are other benefits,” said Murray Reynolds, director of technical services for Ferus. “You’re sourcing much less water, and you tend to be able to pump smaller-sized fracture treatments vs. slickwater, in particular.”

According to Reynolds, CO₂ foam-based systems inherently carry proppant better into the fracture and hold it in the upper portion of the fracture, creating a better and more conductive propped fracture and resulting in better production over the life of the well. This increased flowback is due to the pumping of the CO₂ downhole into the formation as a high-density liquid.

“Once it enters the formation, as it warms, it expands into a gas. One gallon of liquid CO₂, when it warms to 89 F [31 C], starts to expand and—at standard temperature and pressure—becomes 542 gallons of gas,” he said. “The huge expansion that occurs in the reservoir helps to flow out not only load fluids that you pumped in there but also any hydrocarbon or water liquids in the reservoir.”

While the use of CO₂ and nitrogen in fracturing is a proven approach in the Western Canadian Sedimentary Basin, its acceptance in the U.S. has been delayed, possibly due to a number of perceived challenges, namely availability, cost and logistics.

“Probably the biggest drawback is availability in certain areas as transporting over long distances is costly,” Reynolds said. “Several of our Canadian CO₂ plants are located right in field locations, so the transportation is over short distances, easily done and logistically easy. In the U.S. and Canada, there are thousands of small emitting plants that could quite easily have a CO₂ recovery unit put on them.”

Reynolds noted that in developing a market, Ferus looks for local high-emitting sources like fertilizer plants or ethanol plants for gasoline as candidates for recovery units as these sources produce pure CO₂ as a byproduct.

“Another perception is cost. Yes, one barrel of CO₂ is more costly than one barrel of freshwater,” he said. “However, when you add up all the other costs associated with water such as transport, flowback of water, trucking of flowback water, and either recycling or disposal of that flowback water, then it becomes very competitive,” he said. “Of course, not all of the treatment fluid is typically CO₂. It’s usually 70% to 80% quality CO₂, so there’s a small aqueous water portion of the fluid. Certainly you’re reducing those water-related costs significantly.”

Statoil recently awarded Ferus with a service agreement to supply the CO₂ and provide transportation, logistics, storage, and onsite supervision for the Statoil test occurring later this year in the Bakken Shale. For more information about the Statoil test, be sure to check out “Energized fracturing comes to the Bakken” in this month’s cover story, or read it now at https://www.epmag.com/energized-fracturing-comes-bakken-804411