A Review of New Studies on Carbon Sequestration by AAPG Core Elements Editor Emphasizes Work Toward Developing Best Practices

     AAPG Core Elements editor Rasoul Sorkhabi recently wrote a review of some new carbon sequestration studies aiming to develop some best practices for sequestration. He highlighted three new studies: one on China’s first offshore CCS project, one on carbon sequestration in basalt and other mafic rocks, and one on the carbon storage potential of saline reservoirs and depleted oil & gas reservoirs in the Appalachian Basin.

 

China’s Offshore CCS Project at Enping 15-1

     Sorkhabi noted that China’s first offshore CCS project in the Enping 15-1 field injects CO2 into syn-rift Eocene and post-rift Oligocene sandstone and shale sitting atop pre-rift Cretaceous basement rocks. The rocks, which already contain CO2, are considered to be an excellent saline aquifer for CO2 sequestration. The platform is located  200 km southwest of Shenzhen and captures and processes CO2 from oilfields. The platform then injects CO2 into a “dome” geological structure at a depth of around 800 meters under the seabed and about 3 km from the platform. The CO2 is from oilfields with high CO2 content, and so is another project in which sequesters produced CO2. It is designed to store a total of more than 1.5 million tonnes of CO2. This project proves the geologic structures of the area are good CO2 saline storage reservoirs and more projects are in the works.

    Researchers in a new study in Fuel conducted “thermal-hydraulic-mechanical-chemical coupling modeling for cap rock, reservoir rock, and base rock.” They utilized Monte Carlo simulations and sensitivity analysis for 13 different parameters:

“Sensitivity analyses were made for 13 parameters, including reservoir parameters (porosity, permeability, water saturation, temperature, pressure, and compressibility) and compressibility and geomechanical parameters (stresses, Biot’s coefficient, Young’s modulus, Poisson’s ratio, cohesion, and internal friction angle).”

The results yielded geomechanical response predictions for surface uplift, which is often a result of CO2 disposal in low-permeability rocks. He notes that the research shows that:

“Permeability, Young’s modulus, vertical/horizontal stress ratio, cap cohesion, and well length have the most impact on surface uplift.”

“Permeability, reservoir cohesion, and vertical/horizontal stress ratio have the most impact on rock failure and reservoir safety.”

The researchers note that there is significant uncertainty of geomechanical responses to CO2 injection which increases safety risks.

 

In-situ Mineral Carbonation: Storing CO2 in Mafic and Ultra-Mafic Rocks

     Mafic rocks are 3igeneous rocks with high iron and magnesium content. They include:

“(1) Basaltic lava containing high concentrations of calcium and magnesium ions; (2) Mantle peridotite containing olivine, brucite, and serpentinite; and (3) Ultramafic plutons and intrusives with high magnesium and iron content.”

Project developer Stellae Energy gives the following areas as prospective for in-situ mineral carbonation:

•  Iceland – reactive basalt (e.g., CarbFix project) 

•  Washington State – continental flood basalt (e.g., Wallula project)

•  India – continental basaltic lava (e.g., Deccan traps)

•  Cyprus, Turkey and Oman – reactive peridotite intrusions (i.e., Troodos, Kizildag, and Semail ophiolites)

•  Portugal – gabbros and peridotites (e.g., Sines subvolcanic massif)

Source: Stellae Energy

      The mineral carbonation yields the following minerals: calcite, dolomite, magnesite, siderite, and ankerite. The CO2 is injected either in a supercritical state as sCO2 or dissolved in water. Applicable rock types may be onshore or offshore. Prospective offshore rocks include:

“(1) oceanic ridges containing serpentinites and peridotites composed of ferromagnesian minerals including olivine altered to serpentine and (2) oceanic igneous plateaus with high magnesium and iron content.”

     The new research shows the potential of alkaline basalts in China’s Yangtze River Basin to store carbon by chemically reacting with silicate rocks to form carbonates. Sorkhabi notes:

“They used SEM, EDS, XRD, and ICP-MS techniques to characterize the solid and liquid phases before and after the experiment. This allowed them to measure the degree of the carbonation reaction.”

The researchers utilized a closed experimental setup using synthetic formation water to test the basalt-CO2 interaction. They found that after 180 days the reaction rates stabilized. They also noted that much more CO2 was consumed under high-pressure conditions. This allowed them to develop a new calculation method to predict the CO2 storage potential of those basaltic rocks. However, they also emphasized that more research is needed to confirm their methods.

 

CO2 Storage Potential of the Appalachian Basin

     Two studies published in the journal Geoenergy Science and Engineering explored the CO2 storage potential of Appalachian Basin rocks, including the prolific gas-producing Marcellus Shale. The first study explored several different potential storage reservoirs for CO2 including deep saline formations, depleted oil & gas reservoirs, coal-bearing formations, and organic-rich shales (Utica and Marcellus). They found that the deep saline aquifers had by far the most storage potential. I made the graph below from their conclusions. It should be noted that for all types besides the saline aquifers the technically feasible storage potential is much lower, somewhere between 10 and 35% of the storage potential given below. Since shale wells are already drilled it makes them more attractive for storing CO2, but saline aquifers are by far the reservoir of choice, especially in Ohio where they are shallower in depth.

Data Source: A critical review of assessments of geological CO2 storage resources in Pennsylvania and the surrounding region. Levent Taylan Ozgur Yildirim, Qihao Qian, and John Wang. Geoenergy Science and Engineering. Volume 247, April 2025, 213732. A critical review of assessments of geological CO2 storage resources in Pennsylvania and the surrounding region - ScienceDirect

     The second study focused solely on the CO2 storage potential of Marcellus Shale. Here they came up with a higher number than study one which apparently focused on the Marcellus in Pennsylvania. They found that the CO2 storage potential was 289 gigatons of CO2 in total and up to 32 gigatons in technically accessible wells. The abstract notes that:

“In Pennsylvania, total CO2 storage resources in the Marcellus shale is 181 Gt, while the contingent CO2 storage resources is 20 Gt. Northeastern Pennsylvania has the highest CO2 storage potential in the Marcellus shale.”

Since in Pennsylvania the saline reservoirs can be very deep, the potential of the Marcellus to store carbon is important.

    

References:

 

New Studies of Geological Carbon Storage. Rasoul Sorkhabi. AAPG Core Elements. March 17, 2025.

Uncertainty analysis of geomechanical responses: China’s first offshore carbon capture and storage project. Zhiqiang Wang, Shuyang Liu, Hangyu, Qizhi Tan, Wenyue Sun, Junrong Liu, Jianchun Xu, Xiaopu Wang. Fuel. Volume 382, Part A, 15 February 2025, 133728.  Uncertainty analysis of geomechanical responses: China’s first offshore carbon capture and storage project - ScienceDirect

China's first offshore million-tonne carbon storage project (video). Tseles John. Offshore CO2. November 1, 2023. China's first offshore million-tonne carbon storage project (video)

Carbon Dioxide Sequestration with In-situ Mineral Carbonation. Stellae Energy. Carbon Dioxide Sequestration with In-situ Mineral Carbonation – Stellae Energy

Carbon Sequestration of Alkaline Olivine Basalt in the Yangtze River Basin of China: Carbonation Mechanism and CO2 Storage Potential. Xiaoqi Ye; Ziwang Yu; Yanjun Zhang; Tianfu Xu; Wentao Hong; Wei Zhang; Peiyi Yao; Shubing Zhang. Society of Petroleum Engineers. SPE J. 1–13. Paper Number: SPE-225427-PA. March 3, 2025. Carbon Sequestration of Alkaline Olivine Basalt in the Yangtze River Basin of China: Carbonation Mechanism and CO2 Storage Potential | SPE Journal | OnePetro

A critical review of assessments of geological CO2 storage resources in Pennsylvania and the surrounding region. Levent Taylan Ozgur Yildirim, Qihao Qian, and John Wang. Geoenergy Science and Engineering. Volume 247, April 2025, 213732. A critical review of assessments of geological CO2 storage resources in Pennsylvania and the surrounding region - ScienceDirect

Assessment of total and contingent CO2 storage resources in the Marcellus shale. Levent Taylan Ozgur Yildirim and John Wang. Geoenergy Science and Engineering. Volume 247, April 2025, 213669. Assessment of total and contingent CO2 storage resources in the Marcellus shale - ScienceDirect