Carbon dioxide ranks as one of the hottest topics going in oil and gas today.
Areas of active research include carbon capture, utilization and storage and CO2 use in enhanced recovery. Combine carbon dioxide with unconventional reservoirs, or alternative fuels, and there’s additional interest.
The subject of CO2 left a big imprint on the recent International Meeting for Applied Geoscience and Energy in Houston.
“I was pretty flabbergasted to find out there were six CO2 sessions at IMAGE. I thought, ‘Man, this thing has really taken off,’” said Scott Singleton, a geophysics consultant in Houston.
Singleton served as co-chair for the 2023 meeting’s first session on carbon dioxide, “CO2 1: Developments and Lessons Learned.” He’s also been a technical co-chair for the SPE-AAPG-SEG-sponsored CCUS annual meeting, most recently held in April.
“Some people have been pursuing this (CO2 research) for half a decade. A decade ago, no one really cared that much about this,” Singleton noted.
Two changes have occurred over time, he said. First, a concept of social responsibility involving CO2 emerged in oil and gas and other heavy industry, especially in relation to climate change issues.
“Before that happened, there was really no way to get this off the ground because of economics,” he commented.
Second, governments began to offer tax credits and other incentives for CO2 sequestration and to make funds available for CCUS research. Singleton said recent pieces of major U.S. legislation have provided a significant boost.
Blue Hydrogen Byproduct
Now, CO2 research has started to shift from theoretical issues to more practical, nitty-gritty applications.
As an example, Singleton cited an oral presentation from the session he chaired, “Blue hydrogen and CO2 enhanced geothermal energy: A concept for the transformation of hydrocarbon-based economies.”
At first, he said, attendees tried to remember what “blue hydrogen” is and started going online to look it up.
“Blue hydrogen is splitting hydrocarbons to get hydrogen, but the problem there is that CO2 is generated from splitting the hydrocarbons,” he said.
It’s one of the components of the confusing hydrogen rainbow. With blue hydrogen, natural gas is split into hydrogen and CO2 though a reforming process, and the CO2 is then captured and stored.
The presentation described a loop where captured CO2 is injected into wet reservoirs with quality seals, common in Arabia. The authors found that “stored CO2 utilized for geothermal energy extraction offers a factor-two efficiency increase over water and can provide electricity for domestic use.”
Additionally, they reported, a secondary loop can be opened with the stored CO2 used for large-scale EOR to improve recovery in depleting hydrocarbon reservoirs.
As might be predicted, the presentation “went right over most people’s heads” and elicited all sorts of questions, Singleton said.
That was a good thing, showing the audience was interested and involved. The session turned out to be one of the most well-attended and well-received at IMAGE, and Singleton thought the CO2/geothermal/EOR talk was probably the best presentation of the session.
Sequestration, Machine Learning
Some other presentations involved CO2 sequestration in depleted unconventional reservoirs. Sequestration also was addressed in the last-day workshop, “Insights and questions related to CCUS and reservoir characterization utility.”
“The workshops on Friday, one of them – an entire day’s session – was on sequestration. In that session, there were a number of papers dealing with unconventionals. I came away learning several things from that,” Singleton said.
Oladoyin Kolawole is an assistant professor in the Department of Civil and Environmental Engineering at New Jersey Institute of Technology, and director of the school’s Geomechanics for Geo-Engineering and Sustainability Lab.
In addition to Kolawole’s interest in traditional geomechanics, he has developed a “biogeomechanics” concept, which studies the mechanical responses of microbial-rock interactions.
He said “the enormous carbon sinks in shales, the existing infrastructure available in the field for injection/production wells vital to CO2 storage operations, and the ability of shales to provide seals for stored CO2 as a caprock” all make unconventional reservoirs candidates for CO2 sequestration.
But anomalously low reservoir pressure, low porosity and high reservoir heterogeneity can result in more complexity for CO2 storage after injection in shale reservoirs and also result in insufficient flow rates for CO2-EOR, he noted.
“Comprehensive, coupled hydro-chemo-mechanical assessments of target shale reservoirs prior to CO2 injection should be carried out to achieve more successful CO2 injection operations and ensure long-term stability of CO2 storage in shales,” Kolawole observed.
“Further, injecting CO2 into the host-shale reservoir prior to production in CO2-EOR may be an efficient way to establish the reservoir pressure to meet the minimum miscible pressure requirement,” he added.
In addition, the effects of CO2-brine-rock interaction pose a major challenge for CO2 storage in shales, he said.
“The injected CO2, mostly at supercritical conditions, will undergo a chemical reaction with porewater … to form carbonic acid, which studies have shown can accelerate the dissolution of minerals in shale reservoirs,” he said.
That can “promote lateral and vertical migration of CO2 in the storage reservoir, thereby defeating the objective of permanent CO2 storage,” Kolawole added.
In other CO2-related sessions, Singleton highlighted presentations involving machine learning and modeling for predicting CO2 plume evolution, part of “CO2 6: Modeling and simulation: machine learning in CCS.”
The session included the presentations “A denoising diffusion probabilistic modeling (DDPM) approach for predicting CO2 plume evolution from seismic shot gathers” and “Monitoring subsurface CO2 plumes with sequential Bayesian inference.”
“That was very interesting. For a model you have to generate the geostratigraphy. He was coming up with a number of scenarios about what actually happens. What’s going on with these plumes?” Singleton said.
“There’s some big argument about that. This now goes into chemistry, geochem,” he noted.
CO2 and CCUS research has evolved to the point where “most of us are comfortable with the technology of sequestration. I say that carefully, because most of us know the technology is going to improve,” Singleton said.
The Next Revolution?
“A lot of us read the tea leaves. A lot of us were on the ground floor when unconventionals came out of nowhere. A lot of us now see the same thing happening with CCUS,” he said.
Singleton believes CO2 will continue to be a hot topic and important focus of industry research. The trend is just starting, he thinks.
“I don’t foresee the social responsibility part decreasing. I see it increasing,” he said.
“I see it increasing because it’s becoming more acceptable to talk about climate change. And oil and gas companies are acknowledging that they are the ones producing the hydrocarbons,” he added.
Researchers who’ve been working on CO2 issues for years have grappled with two main concerns, Singleton said.
“One has been the economics. The second was the human pipeline. The human pipeline is young people going through school, and academics – a lot of whom lead the way on this – responding to the concerns of young people,” he explained.
“There’s been a lot of us stressing over this,” he said.
Today, with more money backing CO2 research and more incentives for sequestration, the economics look considerably better. And for graduating students, “a lot of people now have places to go to work,” he observed, with a promising future for CO2 specialists as the industry develops net-zero carbon plans.
“Any company that is looking out for its own well-being over the next half century or whatever – choose your own timeframe – they better darn well be looking out for their own social responsibility. That means they have to have a net-zero strategy,” Singleton said.