A groundbreaking experiment completed with NETL oversight is expected to generate important insights about the behavior of faults and other seismic activity when carbon dioxide (CO₂) — a greenhouse gas — is injected into geologic formations.

Completed at the Mont Terri Underground Research Laboratory in Switzerland, the experiment involved injecting water mixed with CO₂ into a subsurface fault for approximately five hours. The injection caused a controlled CO₂-induced fault slip to determine its impact on the caprock that prevents CO₂leakage.

“The work completed in Switzerland by NETL partners at the Lawrence Berkeley National Laboratory and Rice University marked the first time a mixture of CO₂ and water was injected into a fault,” said James Gardiner, a federal project manager and a member of the NETL Carbon Transport and Storage team.

“This project is important because it will help us understand how CO₂ may affect fault activation in caprocks,” Gardiner said.

Capturing CO₂ and sequestering it in underground reservoirs is known as carbon capture and storage (CCS). NETL is developing CCS technologies as a cost-effective way to reduce emissions, address climate change and attain a net-zero U.S. carbon-emissions economy by 2050.

Carbon storage reservoirs are layers of porous rock underneath a layer of impermeable rock that acts as a seal. The caprock prevents injected CO₂ from returning to the surface or migrating to aquifers that provide drinking water.

Researchers collected several terabytes of novel geophysical field data during the injection. The data will provide significant observations about fault slip and strain related to CO₂ injection and the effect that CO₂-induced fault activation has on storage reservoir caprocks.

The project, titled “Changes in Seal Integrity Induced by CO₂ Injection and Leakage in a Hydromechanically Reactivated Fault,” is designed to assess and mitigate potential risks caused by induced seismicity, which could occur due to fault slips.

Analysis of the data generated by the injection of the CO₂-water solution will help researchers better understand fault slip processes, provide new insights into the leakage potential of complex fault zones and help the NETL Carbon Storage Program attain a rate of 99% CO₂ storage permanence.

Other insights to be attained from the experiment include an enhanced understanding about the changes in water chemistry and fault mineralogy that may occur along a potential leakage pathway. In addition, research findings will assist in the development of a new fiber optic chemical sensing system to monitor CO₂ within reservoirs and the injection wellbore.

“The project is helping us better understand important subsurface behaviors to ensure that the CO₂ we store underground remains safely and securely sequestered in the subsurface,” Gardiner said.

The experiment was conducted at a depth of approximately 1,200 feet below the surface at the Mont Terri Underground Research Laboratory. The lab’s major objectives are to investigate and analyze the hydrogeological, geochemical and rock mechanical properties of formations containing clay.

NETL is a U.S. Department of Energy national laboratory that drives innovation and delivers technological solutions for an environmentally sustainable and prosperous energy future. By leveraging its world-class talent and research facilities, NETL is ensuring affordable, abundant and reliable energy that drives a robust economy and national security, while developing technologies to manage carbon across the full life cycle, enabling environmental sustainability for all Americans.