Assessing Geologic Carbon Sequestration Opportunities in Utah

by Eugene Szymanski, PhD

Big picture perspective of the natural biogenic and geologic carbon cycles. Commercial opportunities for Carbon Capture Utilization and Sequestration (CCUS) often exist below ground within the dashed line region. Image modified from the Woods Hole Oceanographic Institution, 23 Nov. 2015 (https://www.whoi.edu/oceanus/feature/carbon-cycle/); used with permission.

As the primary component of all life on Earth, carbon (C) is all around us: in the air as carbon dioxide gas (CO₂), in plants and animals as drivers of cellular growth and respiration, including animal waste products like methane gas (CH₄), and as a building block of carbonate rocks like limestone (CaCO₃). Earth has two primary natural carbon cycles—the biogenic and geologic cycles—which use, exchange, and recycle elemental carbon over vastly different timescales. Carbon can be weathered from rocks, belched from volcanoes, integrated into living organisms of the biosphere, released into the atmosphere, soils, and oceans from decaying plant and animal material, and sequestered naturally as rocks and minerals in geological formations for thousands to millions of years.

These natural cycles have been disrupted since the start of the Industrial Revolution as significant volumes of CO₂ have been building disproportionately in the atmosphere from the combustion of fossil fuels and output from industrial processes. This is problematic because, as a greenhouse gas, CO₂ traps heat in the atmosphere which, in turn, affects global climate on geologic and human timescales. Commercial-scale carbon sequestration (a.k.a. “storage”) is billed as a primary tool for combating anthropogenic climate impacts by redirecting harmful volumes of produced carbon from the atmosphere into less impactful storage options.

The phrase Carbon Capture Utilization and Sequestration (CCUS) is typically used to describe the full range of techniques employed in the commercial carbon sector. Addressing each term individually: capture is the first step wherein elemental carbon, typically in the form of CO₂, is either captured directly from the atmosphere or concentrated from industrial waste streams; utilization can follow where the carbon, in many forms, is recycled for use in industrial processes or as feedstock for the manufacture of consumer goods like concrete, steel, and plastics; and sequestration is intended as a solution to keep produced carbon out of Earth’s atmosphere, part of a greater initiative known as transitioning to “net zero” wherein a balance is achieved between the total volume of carbon stored versus emitted into the atmosphere. CCUS helps accomplish this in four key ways:

1. it can be retrofitted to existing power and industrial plants to reduce emissions;
2. it can support rapid upscaling of low-carbon hydrogen production;
3. it can capture and store CO₂ directly from the air and bioenergy—energy that is derived from the breakdown of recently living organic materials; and
4. it is often the most cost-effective approach to curb emissions in cement, iron, steel, and chemicals manufacturing.

CCUS also complements nature-based solutions, such as afforestation, reforestation, and restoration of native plant habitats along coastlines.

Instead of being vented into the atmosphere, CO2 produced from sources like power plants can be redirected either for industrial and commercial uses like Enhanced Oil Recovery (EOR) and manufacturing or into geological storage, whether onshore or offshore. Figure modified from imagery provided by Global CCS Institute (https://www.globalccsinstitute.com/resources/ccs-image-library/).

Value Proposition

Apart from myriad environmental benefits, the economic value proposition for private sector carbon capture lies in tax incentives and carbon offset credits. Passed by the U.S. Congress in 2018, the FUTURE Act amends the Internal Revenue Code to extend and modify the tax credit for carbon dioxide sequestration and increases incentives for the capture and storage of CO₂. Specifically, Section 45Q provides a credit for every ton of captured CO₂ for secure geological storage within either enhanced oil recovery (EOR) processes or deep saline aquifers.

The University of Utah’s Energy & Geoscience Institute (EGI) has led the way on CCUS research and projects in Utah for over 20 years, often partnering with the Utah Geological Survey (UGS) to leverage geologic knowledge and share technical project tasks related to assessing the potential for geologic CO₂ sequestration in Utah. Previous CO₂ projects in Utah include a large-scale CO₂ injection demonstration for storage and EOR in the Aneth oil field of southeastern Utah and a detailed geologic characterization of potential CO₂ storage reservoirs in saline aquifers in the northern San Rafael Swell of Emery County—more information about the CarbonSafe project can be found in Survey Notes, v. 49 no. 3. Most recently, EGI and the UGS are active members of the Carbon Utilization Storage Partnership (CUSP), a U.S. Department of Energy-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.

Geological Assessment Work

The opportunity for Carbon Capture Utilization and Sequestration (CCUS)—sometimes abbreviated to CCS—depends considerably on the type of rock present in the subsurface. (A) CO2 storage can occur by injecting gas deep underground into rock strata deemed unsuitable for other purposes. Modified from imagery provided by Global CCS Institute (https://www.globalccsinstitute.com/resources/ccs-image-library/). (B) A 4-inch-wide slabbed rock core from the Covenant oil field, Sevier County, Utah. The sandstone (buff-colored) is a good reservoir rock due to its porous and often permeable grains. The mudstone (red) is a good geological seal because it has low permeability and prohibits fluid and gas from escaping upwards. The sharp color contrast indicates the boundary between the seal and reservoir rock. The five holes in the rock core are where plugs were drilled into the rock and removed for analysis. (C) and (D) are photomicrographs of Jurassic-age Navajo Sandstone (reservoir rock) from the Covenant oil field that illustrate pore space availability (blue areas) for CO2 storage between quartz grains (white areas). Images B, C, and D modified from Chidsey and others (2020) (https://doi.org/10.34191/ss-167). Note the significant difference in scale from the well (kilometers) to the core (meters) to the rock grain and pore space (millimeters).

The basic premise of sequestration is that compressed and liquified CO₂ is pumped via injection wells into underground porous rock formations (reservoirs) where it can invade pore space and either become trapped beneath impermeable strata (a.k.a. seal rock), dissolve within saline groundwater, or react with reservoir rock to form carbonate minerals, thus becoming stored for relatively long periods of time (thousands of years or more). A lot of scientific, technical, legal, and administrative work is required to rate the suitability of storage sites. Fortunately, Utah has many potentially viable geologic formations suitable as large-scale CO₂ sequestration reservoirs including, but not limited to: 1) the Leadville Limestone and Paradox Formation salts in the Paradox Basin, 2) the Mesaverde Group in the Uinta Basin and Mesozoic-age sandstone units in the south and east (e.g., the Navajo, Weber, and Entrada Sandstones), 3) the Navajo Sandstone in the northern San Rafael Swell, and 4) the Navajo Sandstone or deeper Kaibab Limestone in the southwest part of the state.

One interesting area of study is Iron County, Utah, where the UGS and EGI are performing rigorous site characterization including subsurface geological CO₂ storage viability and capacity, environmental risk assessment, and economic feasibility options. This region in Utah’s Basin and Range Province—expressed topographically as low, broad valleys punctuated by tall, north-south-oriented mountain ranges—was selected for several reasons including accessible outcroppings of key geologic strata, existing public datasets, and wells that provide strong control on subsurface geology potentially favorable for CO₂ injection.

In southwest Utah, wildcat oil and gas exploration has had very few economic successes, but those efforts demonstrated the presence of thick sequences of Paleozoic- and Mesozoic-age sandstone and limestone strata in the subsurface that could potentially store vast volumes of CO₂ gas. Several world-class reservoir/seal pairs are present in the area, providing multiple injection targets, and the absence of working petroleum systems lowers the risk of unavailable pore space and overpressure. Additionally, relatively low drilling and injection costs are anticipated since some reservoirs lie at relatively shallow depths (less than 7,000 feet) still acceptable for proper storage.

The UGS and its partners use many techniques to study the local geology. Rock collected from wells provides important ground-truth information about groundwater conditions, pressure domains, and the range of rock types. Interpretations made from 2D (two-dimensional) seismic, gravity, and magnetics data allow us to create images of the subsurface for mapping structural controls and to develop models of fracture networks that control reservoir permeability and seal rock competency.

Future Direction

Utah has a natural wealth of subsurface geologic reservoirs suitable for carbon sequestration. Utah also has several major industrial carbon emitters within the state. Because the Iron County region can be used as a geologic analogue for other sites in the Basin and Range Province, characterization work by the UGS and its partners will reduce geologic uncertainty, allow prioritization of potentially viable CO₂ sequestration sites elsewhere, and set precedents for rigorous site characterization reports, data, and products in other western states.