Tenaska, an American energy company known for safe and environmentally responsible projects, is determining the viability of a carbon capture and sequestration (CCS) project – called Longleaf CCS Hub – in Mobile County, Alabama. Should the project move forward, the Longleaf CCS Hub will sustain and advance local and regional industries while supporting local farmers and the local economy.

As part of the initial site feasibility assessment, Tenaska will need to conduct seismic surveying that will confirm the underground geology is ideal for this type of project. We have planned this work for the upcoming summer months.

Seismic surveys create a localized vibration in a limited area to collect seismic data that will determine if the geology is suitable for carbon dioxide sequestration deep underground. While residents in close proximity (100 feet or less) may feel slight vibrations from vibroseis trucks, these surveys are safe to the public, property and roadways. Similar seismic surveys are performed to locate underground stores of oil and natural gas.

Seismic Surveying FAQs

A “vibroseis” truck will generate seismic waves, or pulses, underneath the earth’s surface. This truck is equipped with large metal plates, called pads, that send vibrations through the earth. The waves bounce off the multiple layers of rock formations underground and are recorded by geophone sensors to create accurate maps of the complex layers underground.

To collect this information, a crew drills a series of 1.5-inch-diameter holes approximately 3 inches deep and places the geophone sensors into them to detect and record imperceptible ground movement. The geophones are placed every 20 to 40 feet along a bar ditch.

Next, we create waves that travel underground. Once geophones are in place, the vibroseis truck lowers its pads and sends pulses into the ground. (For maximum safety, we also monitor the ground motion near any adjacent structures to ensure that we stay below established thresholds.)

When seismic surveys are performed, residents will see a vibroseis truck along select roadways. The truck will generate vibrations that may be felt up to 100 feet away. It’s important to note that the vibrations are less than what would be felt from a passing freight train and pose no risk to infrastructure or drain tiles.

Seismic crews will be equipped with high-visibility clothing, lighted vehicles and a flagging/signing crew to ensure other road users are aware of operations.

Safety is our top priority. The work will not proceed if there is a risk of damage to roads or private property. Once completed, there should be no sign at the surface that our crew was present.

Tenaska and its contractors will work closely with Mobile County to obtain necessary permits to conduct the surveys.

Depending on the size of the area to be mapped and the complexity of the project, seismic surveying in Mobile County will likely take about 30 days, with the seismic truck on the roads for about half of that time.

While ‘seismic’ does refer to earthquakes, the term here simply describes the process of generating small vibrations which bounce off deep rock layers and are then recorded to give an image of the subsurface.

Underground geology is an important component for siting CCS projects. Tests and surveys identify locations with porous rock overlaid by impermeable cap rock. To ensure safe, secure storage of CO2, storage areas are then pinpointed using maps, published studies, rock samples and seismic imaging data.

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