Thousands of feet beneath the surface soil of Murrysville, the pulse of seismic testing will soon be rockin’ the geology.
Seismic testing, also known as echolocation, records the bounce back of low frequency sonic waves to build a sonogram model of underground rock formations. These tests can reveal where valuable gas and oil deposits lie. To map the underground landscape, testing companies send out large heavy trucks equipped with giant vibrator plates to trigger powerful shock waves. The trucks are called Thumpers, and the Thumpers are coming.
In Murrysville, the Thumper trucks from ION Geophysical Corporation of Houston, Texas, will arrive in February, after permit agents gather permission from enough property owners to make the testing feasible. ION is currently offering a small per-acre fee, about $5, for permission to do testing.
According to Russ Gentry, a project manager for ION, testing in Murrysville is part of three projects ION has in the southwestern Pennsylvania region. And ION’s efforts are part of a larger push to tap into abundant natural gas resources in the Marcellus Shale formation.
Although Mr. Gentry declined to say who is paying for the testing or how much the contracts are worth, he confirmed that a group of major gas and oil drilling companies is spending millions of dollars to have the testing work done. Property owners agree to let ION to sell the test results.
“We have three separate projects in at least 20 communities in this area," he said.
"“There is not a day goes by that I don’t get calls about seismic testing,” said Jim Morrison, Murrysville’s chief administrator. “And there are notification requirements they have to abide. For example, they have to offer a pre-and-post-test inspection of the property. We have met with ION three times to explain our ordinance and they have said they will comply.”
According to Mr. Gentry, there is a lot of background research that goes into it before testing begins.
“We have to research titles and identify who owns the mineral rights and the surface rights; it can take over a year before we are ready to talk to the owners,” he said. “Once the research is done, property owners are contacted to see if they are willing to allow testing and if there are any special considerations. They may want to restrict hours of access to a property or have features such as water wells or livestock on the property that we have to take into account. ”
The sheer size of the operation is impressive. A testing area may range in size from 10 to 50 square miles. Thousands of receivers called geophones are laid out in a grid pattern to detect the reflection of sonic signals generated either by the Thumpers or setting off a dynamite charge underground. Called a shot hole, this approach is typically used in areas where the trucks cannot get access. The low frequency sonic waves travel miles underground at great speeds ranging from about 2 to 8 miles per second. The velocity of the shock waves depends on the density and elasticity of the geological materials it passes through.
“We can test down as far as 30,000 feet. The shock waves bounce back at different obtuse angles and at slightly longer times depending on what density of material they are bouncing off,” Mr. Gentry said.
As part of the process, ION conducts a hazard survey to identify potential hazards such as pipelines, waterlines, wells, roads and rivers. The company also does an access survey, where it maps out properties to identify the best access points and where gates and access roads are located..
Even though the testing is not as disruptive as drilling, there are local laws that must be obeyed. To prevent potential damage from seismic vibrations, the municipal ordinance requires Thumper trucks to maintain a minimum distance of 150 feet from any building. Shot hole dynamite charges cannot be detonated within 300 feet of any building, water well or underground hazardous waste storage/disposal site.
Because of the size and weight of the trucks, ION would be responsible to pay for damage to roads or municipal property.
“I would emphasize that private property owners are negotiating their own agreements. They need to pay attention to the details of those agreements,” Mr. Morrison said.
Tim Means, freelance writer: firstname.lastname@example.org.