Enhanced oil recovery (EOR) is the unsung hero of CCUS

Since the mid-1970s, the oil and gas industry has used CO₂ for enhanced oil recovery (EOR) in mature reservoirs. Now, as carbon capture, utilization, and storage (CCUS) becomes a critical part of the industry's decarbonization strategy, lessons learned from EOR can help provide a path forward.

For more than four decades, Halliburton has used CO₂ in places like the Permian Basin in Texas to help its customers maximize reservoir output. In the past, engineers have used this technique to pipe naturally occurring CO₂ underground to oil fields.

In his main stage session at the Carbon Capture & Hydrogen Technology Expo, Steven Knabe, global director of Evaluation and Production for Halliburton Consulting explained the relationship between EOR and CCUS.

Expanded commercial use of CO₂ for EOR in many oil-producing regions can help provide incentives to capture CO₂.

“Moreover, using CO₂ for EOR results in a high percentage of the CO₂ remaining in the oil reservoir, effectively sequestering it over time. Once EOR is no longer economical in a field, the CO₂ can be either used for other commercial purposes or sequestered permanently in the geological formation,” said Knabe.

The presentation focused on how companies can start the process of pilot-testing EOR using CO₂ in oil fields, and demonstrated the profitable expansion of these projects, which in turn promotes increased CO₂ capture from industrial sources.

Traditional EOR helps pave the path for CCUS

Most of the drilling and cementing in the Permian Basin began in the 1950s, before CO₂ injection was employed for EOR. CO₂ is miscible with light oils at relatively low pressures, which means that even shallow reservoirs may be candidates for EOR. Two techniques are often used:

• Water alternating with gas, or WAG, is a time-honored technique for CO₂ EOR projects. WAG allows reservoir engineers to optimize each CO₂ injection and use water to reduce early CO₂ breakthroughs in projects. While corrosion is a concern, corrosion-resistant packers and fiberglass-lined tubing help mitigate CO₂'s effects so it can be recovered and not seep into groundwater.

• An even older technique, known as huff and puff, involves cyclic stimulation or forced imbibition of CO₂. Because industrial gas suppliers are accustomed to the delivery of liquid CO₂ in 25-ton tankers to well sites, operators can conduct a pilot huff and puff program to determine if CO₂ EOR is feasible before they decide on a pipeline project.

Due to EOR, operators commonly inject CO₂ in depleted shale reservoirs. CO₂ adheres to shale and displaces methane. When shale fields reach their life's end, operators have the ability to utilize CO₂ for the extraction of any methane left.

Old reservoirs, new tricks

Once shale fields are depleted of oil and/or gas and the commercial efficacy of EOR is exhausted, operators can shift the empty reservoirs to repositories for permanent CO₂ sequestration. Halliburton has pioneered technology to help enable more effective sequestration:

• Computerized reservoir simulations model underground CO₂ behavior to optimize slugs of water for WAG and huff and puff operations.
• The integration of smart completions with reservoir simulation enhances oil recovery and readies shale reservoirs for sequestration.
• Advanced completions allow operators to manage injection and production locations with valves if rapid CO₂ breakthrough occurs.
• Fiber optics enable comprehensive monitoring of CO₂ behavior in the subsurface.

Reservoir simulation holds critical importance before the initiation of a project, be it EOR or CCUS. This simulation allows for the examination of potential effects on rock-fluid interactions, types of chemicals, and changes in permeability due to impurities in the CO₂.

The ability to increase oil production profitably and effectively through EOR builds the foundation for CO₂ sequestration. As mature fields near the end of their productive lives, CO₂ injection can help maximize asset value and support decarbonization strategies.

To learn more about how Halliburton can assist with CCUS projects, visit www.halliburton.com/ccus.