The 15th International Virtual Conference on Greenhouse Gas Control Technologies will take place from March 15th to 18th, 2021. GCCC will have a large presence there with researchers giving nine presentations over three days.
Time in UAE (For Full Session)
2F-Environmental Impacts & Remediation
Assuring long-term storage of captured CO2:
Once injected, CO2 does not stay in one place. CO2 storage depends on a variety of trapping mechanisms to ensure long-term storage. Once in the reservoir, CO2 interacts with the resident brine water, minerals, and other chemicals in the subsurface, determining its ultimate destination. Predicting the movement of CO2 is a crucial step in the monitoring of carbon capture and storage projects which the Gulf Coast Carbon Center (GCCC) specializes in.
The primary trapping mechanism for a CO2
storage project is the overlying nonporous caprock that restricts the vertical,
buoyant flow of CO2. A secondary trapping mechanism called residual
trapping is a major contributor to the volumes of CO2 that can be
Residual trapping can occur when two immiscible fluids flow together in porous media. The porous media is usually “wetting” to one fluid and “nonwetting” to another. Wetting is the ability of water to spread out and cover a substrate, often in water-loving or “hydrophilic” settings. Typically, water is the wetting medium and CO2 is the nonwetting. When both flow through the porous media, water surrounds the nonwetting fluid (CO2) and restricts its movement. This causes trapping at the individual rock grain level, so that CO2 does not have enough driving force to get out of the microscopic spaces between grains.
GCCC’s newest post-doctoral student, Hailun Ni,
studies two different types of residual trapping: pore-scale and mesoscale
capillary heterogeneity trapping at carbon storage sites. Mesoscale captures
rock at the millimeter scale and pore scale looks at rock within the micron
range and smaller. At the mesoscale, rock heterogeneities such as lamination
can act like tiny caprocks, restricting the flow of CO2 and trapping
it securely underneath.
Ni’s research, under the guidance of Tip Meckel, is a
unique addition to our research consortium because we have scientists working
on the pore-scale and reservoir trapping, but not in between. By constraining
the movement of CO2 at these different scales, we have a more
accurate prediction of CO2 movement in the subsurface, therefore
Before joining GCCC, Ni earned her Ph.D. from Stanford University where she studied Energy Resources Engineering under Sally Benson. On Tuesday, Ni gave a talk during the weekly GCCC staff meeting regarding her Ph.D. research.
As part of her Ph.D. research, Ni conducted coreflooding
experiments and CT imaging to characterize and quantify the impact of
small-scale heterogeneity on CO2-water capillary flow and residual
trapping with sandstone cores. During her talk titled, “Coreflooding
experiments and prediction of CO2 residual trapping,” Ni covered the
first half of her Ph.D. thesis.
Many studies have been conducted using microCT scans which do not capture the mesoscale heterogeneity of rocks, which can have a significant influence on flow. No previous studies have used real rocks to quantify the relative contribution of the two different CO2 residual trapping mechanisms for different sandstone types.
In order to find residual trapping rates, she used an experimental apparatus that injects CO2 in nine representative sandstone cores with varying petrophysical properties. For most of the cores, the flow rates of CO2 remained the same during injection throughout the experiment. The core was initially soaked with water, and the injection fluid was initially composed of half CO2 and half water. Gradually, the ratio of CO2 was increased in the injectate until it was 100 percent CO2 which was plotted as the initial CO2 saturation value. Then, the CO2 ration was decreased until the injectate was 100 percent water, which was the final value for residual saturation.
The results of the experiment help distinguish the
relative importance of the two residual trapping mechanisms. Experimental
results demonstrate that CO2 residual trapping ability decreases
with porosity and increases with the degree of heterogeneity. In order to quantify
the level of heterogeneity in a sample, Ni and colleagues also evaluated a
number of metrics that act as proxies for heterogeneity. Ni found that the two
best predictors for a sandstone core’s CO2 residual trapping ability
are porosity and the maximum standard deviation in the drainage CO2
saturation field. As stated in the paper, additional results indicate that “pore-scale
trapping mechanisms account for 46–97% of the residually trapped CO2
and the mesoscale capillary heterogeneity trapping mechanism accounts for 3–54%
of the residually trapped CO2 for the nine sandstone samples tested.”
Ni’s next steps are to ask geological questions: What
simple parameters can be used to infer more difficult parameters in order to
characterize the regional-scale geology? During the preliminary discussion, one
of our researchers suggested that cementation, minerology, and depositional
facies can derive other parameters, and could be a launching point for Ni’s
future work with the GCCC.
As for her work with the GCCC, Ni will continue to
build on the work of previous Ph.D. student Prasanna Krishnamurthy to build
sand tanks with realistic sedimentary structures and conduct
capillary-dominated, gravity-driven multiphase flow experiments with the light
transmission visualization method to study how different types of heterogeneity
affect CO2 migration and capillary heterogeneity trapping (local
capillary trapping) at a larger scale.
Each year, the Gulf Coast Carbon Center (GCCC) holds two mid-year meetings for their industrial affiliates: one in January and one in August. These meetings cover the latest developments in carbon capture and storage research completed by the center’s scientists. The most recent meeting took place on August 25 and was attended by nearly 50 representatives from the GCCC’s sponsors.
To give a different look and feel to the poster session this summer,
researchers used Prezi, an online presentation software, to create an
interactive environment in place of the usual static poster content.
During each of three time slots, grouped into three themes, researchers
gave a technical brief followed by lengthy discussion. You can read an
overview of each theme below.
Following the poster sessions, the researchers conducted a short
feedback poll to glean insights for the next sponsor meeting.
Researchers that serve as point liaisons with the various sponsor
companies will follow up after the meeting to schedule more
individualized meetings to further discuss research and future
directions to pursue. GCCC researchers are looking forward to applying
lessons learned to the next meeting.
BIGFOOT refers to GCCC research into storage that has a large
footprint. Enhanced tax credits for storage, combined with falling oil
prices and public concerns over climate change, have spurred interest in
near-term, moderate-scale storage projects on the Gulf Coast and
longer-term interest in large-scale storage hubs capable of storing
several megatons or more per year.
Work to date has demonstrated the Gulf Coast’s capacity for storing large volumes of CO2
at industrial rates, but the process of optimizing site selection for
individual projects is still an open question, particularly for
large-scale projects. BIGFOOT aims to address that gap by developing
both a Gulf Coast prospect inventory and a set of broadly applicable
characterization workflows that can reduce cost and increase confidence
in siting very large-volume storage.
During the BIGFOOT presentation, Alex Bump
gave an overview of the GCCC’s recent work on large-scale storage
projects. He shared the center’s progress on adapting petroleum
exploration workflows for carbon capture and storage (CCS) using layered
risk maps calibrated with historic gas production to predict regional
variations in storage performance of the Gulf Coast Oligocene and
Miocene sections. He also presented promising storage play concepts and
more detailed, site-specific characterizations.
Modeling and Monitoring
CO2 storage regulations require that storage operations
are rigorously monitored to provide assurance of long-term storage
integrity. To evaluate injection scenarios and estimate storage capacity
and security, an accurate understanding of the subsurface migration of
CO2 plume and its trapping mechanisms is essential. Through pore-scale studies, researchers have shown how dissolution of CO2 in brine contributes to the trapping of the advancing plume during the injection stage.
During the Modeling and Monitoring presentation, Sahar Bakhshian covered two topics: prediction of a CO2
plume migration and trapping using numerical models, and advanced
field-scale monitoring techniques. Among other models and simulations,
she presented an analytical solution to a basin-scale theoretical model
for the migration and capillary trapping of CO2 plume in a sloping aquifer during the post-injection stage.
She also reviewed the recently deployed process-based technique for soil-gas monitoring at geologic CO2
storage sites that her team is working on, and demonstrated her team’s
machine learning techniques for facilitating prediction of plume
migration and their data-driven deep learning approach for anomaly
detection in streaming environmental sensor data.
The Ecosystem theme covered outreach and networking done by the GCCC
for the energy ecosystem outside and within the field of carbon capture
and storage. During the Ecosystem presentation, Katherine Romanak covered
research and outreach relevant to the ever-changing CCS ecosystem. To
reiterate the importance of stakeholder-oriented research, Romanak
“The ecosystem includes expanding our connections with new
stakeholders such as the Gulf Coast Carbon Collaborative and the Carbon
Utilization Research Council. We also have continued our previously
successful activities, such as implementing the 4th International
Workshop on Offshore CO2 storage and continuing our
involvements with ISO standards. We are also embarking on targeted
studies, including looking at the potential for recommissioning offshore
infrastructure and providing screening of storage sites looking at
“Looking to the future, we are developing an online CCS course for
petroleum professionals who may need to retool their skills for
application in CCS industry and applying our environmental monitoring
techniques to satisfy the technically challenging requirements of the
low carbon fuel standard CCS protocol.”
GCCC’s next sponsor meeting is scheduled for January 2021.
To become a sponsor member of the Gulf Coast Carbon Center, please contact Research Program Coordinator Emily Moskal.