Carbon Capture, Utilization, and Storage
Carbon capture, utilization, and storage (CCUS) is a broad term that describes all parts of the process of gathering carbon dioxide (CO2) from either the atmosphere or industrial point sources (power plants and petroleum refineries) and using it for commercial processes (utilization) or storing it for very long periods of time underground (sequestration). Effective geologic sequestration requires a combination of porous rock types, called “reservoirs,” into which CO2 is injected, and overlying non-porous rock layers, called “seals” or “confining layers,” that trap the CO2 underground. Typical combinations used for CO2 sequestration are reservoirs of sandstone, limestone, and basalt with confining layers of mudstone or salt.
Due to its unique geology, Utah has many locations throughout the state favorable for geologic sequestration of CO2. Many of these locations are also near existing CO2 emission sources, such as power plants. Industrial facilities such as coal-fired power plants, refineries, iron reduction plants, cement plants, and other industrial facilities have hard-to-abate CO2 emissions. Adding carbon capture infrastructure to existing industrial facilities (retrofitting) and planning carbon capture operations as part of new facilities would allow for the long-term storage of CO2 underground, reducing the volume of anthropogenic CO2 released into the atmosphere.
Where does the CO2 come from?
Elemental carbon, typically in the form of CO2, can be either captured directly from the atmosphere or gathered from concentrated industrial waste streams. Industrial facilities, such as power plants, chemical plants, and iron, cement, and gas processing plants are fundamental to society and the economy; however, they produce significant CO2 emissions. These industrial facilities are considered point sources of emissions because they emit a relatively dense volume of greenhouse gas into the atmosphere at a single location. These facilities can be designed or retrofitted with carbon capture technology to gather CO2 on site and pump it into underground rock layers, where it is trapped for long periods of time, rather than allowing it to enter the atmosphere.
CO2 can also be removed from the atmosphere through direct-air-capture (DAC) technology, a flexible and scalable burgeoning technology that involves building complex machinery that removes CO2 directly from the air. Currently, this technology requires more energy to capture CO2 than re-designing or retrofitting point-source facilities.
How is CO2 stored in the ground?
Once the CO2 is captured, it can be injected into geological formations, or reservoirs, deep in the ground. These reservoir rocks are selected because they are porous, meaning they have space between the grains of the rock to enable them to hold fluids and gasses. Reservoir layers lie well below any potential drinking water aquifers and tend to hold naturally-existing saline brines (salty water). To get the CO2 into the ground it is first compressed into a supercritical fluid, which behaves like a liquid, and can be injected into the reservoir rock formation using a well like those drilled for oil and gas production. In fact, decommissioned oil and gas wells are considered for conversion into CO2 injection wells since the porous rock layers they penetrated for the extraction of petroleum also have the potential to act as CO2 reservoirs. Compressing CO2 into a supercritical fluid allows for the storage of larger quantities of CO2 per volume.
Once injected, CO2 may be permanently trapped within rock formations through a variety of mechanisms. Primarily it is held at great depth in the subsurface by the impermeable seal rock that overlies the reservoir. Further entrapment may occur as CO2 dissolves in brine, or salty water, which typically fills most deep underground rock layers. Depending on the reservoir rock type and the chemistry of the brine, the CO2 can also precipitate (or crystalize) to form carbonate minerals in the pore space of the reservoir rock formation. This process traps the CO2 as a mineral and decreases the ability of fluids to move through the reservoir in the future, increasing the capacity of the rock to further trap non-mineralized CO2. These processes are well understood because CO2 has been injected into reservoirs for Enhanced Oil Recovery (EOR) for decades. EOR refers to injecting CO2 into existing oil fields to aid in extracting residual hydrocarbons.
Because CO2 injection uses the same technology as oil and gas production, the technology and expertise from those industries can be leveraged and transferred to CCUS. The technical expertise geologists and engineers use to understand how hydrocarbons flow through the subsurface can instead be applied to assessing how CO2 moves through similar rocks.
CCUS in Utah
CCUS was proposed as early as 1977, but it has not yet been widely deployed due to lack of economic incentives. The CCUS process requires considerable energy to capture, compress, and inject CO2 into the ground and these energy costs, as well as infrastructure costs, are persistent hurdles for economically viable CCUS projects. Ongoing research to demonstrate the potential for, and feasibility of, CO2 sequestration, combined with increased tax credits will improve the viability of future projects, potentially encouraging greater participation in CCUS by the private sector (see Survey Notes, v. 55, no. 1).
The Utah Geological Survey (UGS) has been involved in CCUS projects since 2000, often partnering with the Energy & Geoscience Institute (EGI) at the University of Utah. The UGS began CCUS research as part of the Southwest Partnership (see project details) then did the research to support the Utah part of the nationwide assessment called NATCARB (see project details). The Greater Aneth oil field was the site for a demonstration of injection feasibility and enhanced oil recovery (see project details). In 2017 a detailed geologic characterization of potential CO2 storage reservoirs in saline aquifers in the northern San Rafael Swell of Emery County was completed as part of the CarbonSafe project (Survey Notes, v. 49, no. 3, see project details).
More recently, the UGS has contributed geological expertise to U.S. Department of Energy (DOE)-funded grants that assess the viability of geological CO2 sequestration in Utah. Specifically, the UGS is currently performing a statewide assessment of CCUS potential as part of a wider regional initiative called the Carbon Utilization Storage Partnership (CUSP), a DOE-funded research consortium consisting of academia, government agencies, national laboratories, and industry that was established in 2019 to accelerate onshore CCUS technology deployment in 13 western states (see project details). Another ongoing CUSP-funded project is a more detailed reservoir characterization and viability assessment of CO2 injection at Iron Mountain, near Cedar City (Survey Notes v. 54, no. 2, see project details). Moving forward, the UGS will continue to provide geologic support for feasibility and implementation projects, advance CCUS research, and aggregate and disseminate information on CCUS opportunities within Utah.
Basin Analysis and Reservoir Characterization for Geologic Carbon (CO2) Sequestration Associated with a Direct Reduced Iron Plant, Iron County, Utah
This ongoing project is a detailed reservoir characterization and geological risk assessment of a potential CO2 storage site at Iron Mountain near Cedar City.
Statewide Assessment of CO2 Storage Potential in Utah as part of the CUSP West Partnership
This ongoing project is a statewide assessment of geological CO2 storage potential as part of a wider, western US evaluation.
CarbonSAFE Rocky Mountains Phase 1: Ensuring Safe Subsurface Storage of CO2 in the Intermountain West
The UGS performed geological reservoir characterization of the Navajo Sandstone to assess CO2 sequestration potential in association with the Hunter power plant in Emery County as part of a larger collaboration. Phase 1 of this project was completed and the project was not progressed to Phase 2.
|2017 – 2019|
Aneth Oil Field, Southeastern Utah: Demonstration Site for Geologic Sequestration of Carbon Dioxide
The Aneth Test was a CO2 injection demonstration for Enhanced Oil Recovery that took place in the Greater Aneth Field on the Navajo Nation in southwest Utah as part of the SWP Phase II Field Demonstrations.
|2007 – 2009|
DOE’s Carbon Storage Atlas – Fifth Edition (NATCARB Atlas V)
As part of the Southwest Partnership the Utah Geological Survey provided inputs to the NATCARB atlas of CCUS resources in the US. While this product is now out of date it was the first attempt to assess CO2 sequestration potential in Utah at a statewide scale.
|2005 – 2015|
Reactive, Multi-phase Behavior of CO2 in Saline Aquifers Beneath the Colorado Plateau
This project investigates the probable fate of CO2 if it can be economically separated from power plant flue gases and injected beneath the Colorado Plateau.