Key Engineering Challenges for Underground Gas Storage Applications

Applying advanced technology and deep technical expertise to address unique subsurface storage complexities

As global electricity demand surges — driven by the rapid growth of data centers, electric vehicles, and evolving residential consumption patterns — underground gas storage is becoming an essential tool for balancing energy supply and demand. These storage facilities allow utilities to stockpile natural gas, which currently fuels 43% of U.S. electricity generation, and store hydrogen produced from natural formations or excess renewable energy. This capability helps providers ensure reliable energy delivery during peak periods and manage market fluctuations.

However, realizing the full potential of underground storage poses significant engineering challenges — and risks to human health and the environment when subsurface containment fails. The use of aquifers, salt caverns, and aging oil and gas wells presents formidable technical obstacles, ranging from corrosion and structural integrity issues to gas migration and regulatory compliance.

Successfully navigating these complexities requires multidisciplinary experts — from geomechanical and civil engineers to environmental scientists and data specialists — to conduct rigorous infrastructure evaluations and site-specific risk assessments. This multi-faceted approach is crucial for energy companies and facility operators seeking to enhance containment integrity, improve reliability and safety, and protect surrounding communities and ecosystems.

Where is gas stored and why?

In the U.S., underground gas storage depends on roughly 14,000 active wells, with the majority located in depleted oil and natural gas reservoirs, which account for 80% of total storage capacity (non-potable water aquifers and solution-mined salt caverns account for the other 20%). These sites are chosen for their demonstrated ability to safely contain gas under high pressure, allowing energy companies to store gas during periods of low consumption, such as summer, and release it during periods of high demand, such as winter, when heating and electricity needs spike.

Energy companies are also exploring using underground facilities to store hydrogen, following a “power-to-gas-to-power” strategy. This approach involves converting surplus electricity into hydrogen via electrolysis, storing the hydrogen underground, and then converting it back into electricity — using fuel cells or turbines — during periods of peak demand.

Each storage method — be it depleted reservoirs, aquifers, or salt caverns — presents unique geomechanical and regulatory challenges. These include managing aging infrastructure and pressure cycling in depleted reservoirs, ensuring long-term containment in aquifers, and maintaining the structural stability of salt caverns. Overcoming these challenges demands a broad range of technical expertise, sophisticated evaluation techniques, and customized design and monitoring strategies to maintain well integrity and improve operational safety.

Gas storage wells, depleted reservoirs, and multidisciplinary engineering expertise

Depleted oil and gas production formations are attractive options for underground gas storage, harnessing proven containment structures and existing infrastructure to support energy reliability and grid flexibility. As these assets age, however, corrosion, mechanical wear, and deterioration of casing or tubing systems increasingly impact their integrity, raising the risk of leaks, blowouts, and significant environmental and public health hazards when wells are adapted for gas storage.

Many underground gas storage wells in the U.S. were originally drilled in the 1950s or earlier, making thorough characterization and continuous integrity monitoring critical as they are repurposed for modern energy applications. Any compromise in well integrity can endanger nearby communities and ecosystems, highlighting the substantial risks at every stage of a storage project’s lifecycle. Exponent’s extensive experience includes root-cause investigations and client assistance in high-profile incidents such as the Grand Bayou salt cavern well leaks in Louisiana and the Aliso Canyon well leak in Southern California. Our work frequently includes custom evaluations and analyses such as the following, although each site can demand additional scopes of technical expertise.

Wellbore logging

Geomechanical and petroleum engineering experts leverage electromagnetic logging tools to measure casing thickness, detect corrosion, and identify structural weaknesses. Specialized logging tools, which collect detailed data from inside wells and subsurface formations, can provide site-specific information crucial for assessing risks and planning effective remediation strategies.

Corrosion analysis

Specialized engineers and metallurgists rigorously test materials, review historical data, and use advanced techniques like electrochemical impedance spectroscopy, scanning electron microscopy, and corrosion-rate modeling to predict future leak points and diagnose potential failure mechanisms. Hands-on field and failure analysis experience can be a key differentiator in identifying potential threats in advance.

Gas migration and environmental analysis

Multidisciplinary teams apply sophisticated technologies and methods to understand complex gas migration pathways through underground geology and differentiate gas sources where present. Isotopic analysis of this sort demands specialized expertise in advanced analytical chemistry, enabling scientists to accurately interpret isotopic signatures of gas components and trace the origin of the sampled gas, whether a storage gas, native gas, bacterial gas, or a mixture of gases.

Hydrogen-specific risk assessments

Hydrogen atoms, with their small molecular size, can diffuse into metal components, weakening bonds and making materials brittle and more susceptible to cracking under stress. Engineers can address embrittlement risks by selecting optimal pipe materials, identifying impurities and optimal supply chain sourcing, and addressing site-specific environmental factors in models of long-term material performance.

Infrastructure restoration

Experienced engineering teams recommend targeted repairs or replacement strategies, including a range of specific modifications to existing infrastructure, such as using corrosion-resistant alloys, installing enhanced cement barriers, or adding pressure and temperature monitoring systems, all customized to each site’s subsurface conditions and operational history.

Monitoring

Effective monitoring of underground gas storage facilities is vital, according to standards set by the American Petroleum Institute, The Pipeline and Hazardous Materials Safety Administration, and applicable state regulations. Expert engineering guidance can help stakeholders apply industry best practices, which include conducting regular inspections, deploying advanced leak detection systems, implementing continuous pressure monitoring, and utilizing surface deformation modeling to identify potential integrity issues, going beyond standards where recommended.

While depleted oil and gas wells provide proven containment structures for underground storage, non-potable (saline) aquifers characterized by their porous rock formations are increasingly being considered as alternative repositories for gas. Unlike depleted reservoirs, however, the geological characteristics of aquifers are often unconfirmed, presenting a distinct set of technical and regulatory challenges. Effective utilization of these formations demands thorough hydrogeological surveys, advanced modeling of subsurface flow and gas migration pathways, and rigorous testing to establish containment integrity and estimate storage capacity. Dynamic simulation models are also essential to predict gas behavior over time. As a result, aquifer assessments are inherently more complex, time-intensive, and costly than repurposing depleted wells, requiring innovative evaluation strategies to support safe, reliable, and sustainable underground gas storage.

Salt caverns and complex geomechanical assessments

Salt caverns are particularly compelling for underground storage because of salt’s natural near-impermeability and self-sealing properties. However, these advantages come with unique engineering challenges that demand careful management. Unlike porous, depleted reservoirs, salt caverns are created by solution mining within salt domes — large subterranean formations that develop as salt migrates upward through sedimentary layers. These caverns exhibit complex mechanical behavior, especially under repeated cycles of gas injection and withdrawal.

Many of the subsurface storage considerations relevant to depleted gas wells — such as robust monitoring practices and addressing hydrogen-specific challenges — are also crucial for salt caverns. Additionally, several key technical and application-specific considerations include:

Creep deformation

Salt “creeps” over time, slowly closing cavern voids and exerting stress on casing strings. Material performance models of site-specific salt samples can help predict long-term deformation and optimize storage operations.

Casing stress and integrity

High-pressure gas storage subjects well casings to significant mechanical loads. Failure to account for salt creep and pressure cycling can result in casing fracture and surface leaks, as witnessed in Louisiana’s Grand Bayou incident. Geomechanical engineers can implement continuous monitoring systems to detect early signs of deformation and address potential risks.

Cavern stability

Cavern roof and wall collapses can occur if the structure is improperly located relative to the dome edge or if pressure cycles are not carefully managed. The Napoleonville sinkhole illustrated the critical importance of stability assessments, prompting new regulations on cavern design and minimum distances from dome boundaries.

Material heterogeneity

Salt domes are geologically heterogeneous, with variable properties throughout their volume. Typically, sparse sampling complicates accurate modeling, demanding sophisticated numerical methods and conservative design assumptions. Samples of salt from a dome or a depleted gas formation are usually taken when drilling a well in the form of a cylindrical sample or core of only 6 inches in diameter. Yet a salt dome or formation can generally cover an area of miles at the surface. Thus, samples of the storage rock are miniscule in comparison to the storage space.

Regulation and permitting

The regulatory landscape for underground gas storage is evolving in response to high-profile incidents and changing energy priorities, reflecting heightened concern over the potential for explosions, hazardous chemicals contaminating groundwater and polluting air, and related risks to human health and the environment. Regulatory updates aim to address these dangers by strengthening safety measures and requiring more rigorous evaluations of well integrity and site-specific conditions.

Federal and state agencies have implemented new regulations governing well design, maximum allowable pressures, inspection frequencies, and safety barriers. For instance, California’s Geologic Energy Management Division now requires dual barriers to pressurized gas and mandates frequent reinspection of storage wells, while Louisiana enforces minimum distances between caverns and salt dome edges.

Experience and specialized expertise are essential for navigating these complex regulatory environments and needs, including:

• Regulatory review: Experienced technical experts can assist stakeholders through careful interpretation of evolving or ambiguous regulations, leveraging deep familiarity with specific regulatory bodies to offer tailored guidance.
• Risk assessments: Multidisciplinary experts help stakeholders conduct risk assessments and prepare technical reports supporting complex regulatory applications for new storage projects or modifications to existing facilities.
• Site-specific design considerations: Experts in gas production well and salt cavern assessments may, depending on site-specific conditions and other factors, recommend more frequent logging, enhanced corrosion protection, or other measures beyond minimum standards to further mitigate risk and address operational efficiency.
• Stakeholder engagement: Addressing public concerns about environmental impacts, especially with new technologies like hydrogen, requires clear communication and proactive regulatory engagement. Experienced consultants can help bridge communication between stakeholders and regulators.

Additionally, acquired technical and regulatory knowledge from natural gas and hydrogen storage heavily informs evolving opportunities, like carbon capture and sequestration (CCS) — a pivotal technology that also relies on subsurface containment. While CCS shares challenges like well integrity and geomechanical stability in reservoirs or caverns, it requires stricter controls and long-term monitoring as carbon dioxide is injected for permanent storage.

Regulations are changing quickly, with new well classes for carbon dioxide storage and increased monitoring requirements. Successful CCS projects can leverage several of the methods applied in underground gas storage projects — including rigorous integrity and corrosion evaluations, advanced modeling, and proactive regulatory coordination. Bespoke risk assessments are critical to address temperature and pressure variations, supporting the selection of customized materials and pipe designs that safeguard against potential failures, environmental hazards, and costly operational disruptions, following the same tenets to promote long-term integrity and subsurface storage safety.