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 Hickory CCS Hub – in Warren County, Indiana. Should the project move forward, the Hickory CCS Hub will sustain and advance regional industry, 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 that the underground geology is ideal for this type of project.
Seismic surveys create 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 surveys use low-frequency sound waves that travel through solid rock and sediment layers beneath the earth’s surface to create maps of rock formations underground. This surveying is performed using sensors, called geophones, that are temporarily placed on the ground to listen to echoes from sound waves reflected from subsurface layers as shown above. Sound waves are also used in ultrasounds, though ultrasounds utilize high-frequency sound waves.
Seismic surveys determine geologic stability and map the safest locations for deep underground storage of carbon dioxide (CO2). The process is already used across a variety of industries, including water resources (such as locating groundwater), geothermal energy, oil and gas exploration and mining.
To minimize our footprint, Tenaska uses a wide range of data and remote-sensing techniques before going into the field to conduct these surveys.
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 and places the geophone sensors into them to detect and record 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 heavy vibroseis truck lowers its pads and shakes the ground. (For maximum safety, we also monitor the ground motion near any 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. It’s important to note that the vibrations are less than what would be felt from a passing freight train.
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 has been here.
Tenaska crews will work closely with the Warren County Highway Department 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 Warren County will likely take about 30 days. Tenaska teams are working diligently to schedule the work in a way that does not interfere with the harvesting season.
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.