The Barnett Shale is more than 7,000 feet below the surface and is comprised of dense non-permeable rock. According to Dr. Ken Morgan, a geologist at Texas Christian University, “Solid hard rocks that are 7000 feet down don’t subside. You have more than a mile of solid rock that holds it all up. Subsidence occurs when you have loose, soft materials like in Houston (sands, clays, etc.) but not in cemented hard rocks like the Barnett Shale.”
Positive Results in ERG Study; Yet Compressor Engine Emissions Overestimated
Yet Compressor Engine Emissions Overestimated
The headline in the Fort Worth Star-Telegram on July 15, 2011, said it all: “Air quality study finds no major health threats.” This is a reference to the long-awaited results of the “City of Fort Worth Natural Gas Air Quality Study” that the City of Fort Worth commissioned about one year ago. A task force appointed by the City awarded the work to Eastern Research Group (ERG) based in Lexington, Mass.
People on all sides the discussion about the development of Barnett Shale natural gas have been eagerly awaiting the results of the study, calling the study the most comprehensive and important air quality study ever done. Overall, the study lives up to expectations as being very comprehensive and professionally done.
While I will post a comprehensive review of the entire ERG study, I wanted to first focus on one aspect of the study that is troublesome: ERG’s estimates of emissions from compressor engines.
ERG spent a lot of time, effort and resources taking samples of the air around natural gas well pads in Fort Worth. They even tested the air at “pre-production” sites where drilling and hydraulic fracturing were going on. However, when it came to evaluating the air at natural gas compressor sites, the ERG team estimated what emissions might be based on the engine specifications provided by the manufacturers without considering the emission control equipment that is installed on these engines.
Federal and state laws require controls on most compressor engines in the DFW area in order to meet strict emission standards. Additionally, TCEQ regulations require that emissions tests be performed on all stationary engines greater than 50 horsepower in the Dallas/Fort Worth Non-Attainment Area.
The resulting air emissions published by ERG are therefore a theoretical case, setting out the greatest possible emissions, which bear no resemblance to reality. When asked why they did not include the installed control devices in their calculations, ERG said that they wanted to be very “conservative,” meaning that they intentionally did not include emission controls in order to establish the worst-case scenario.
The problem is that ERG’s theoretical worst-case scenario from compressor engines resulted in this “key finding:” Compressor engines have a significant impact on emissions, especially the large line compressors found at compressor stations” (page 8-2 of the ERG report).
The correct statement should have been: “Compressor engines could have a significant impact on emissions if those engines were being operated without the required emission control devices, but that is not the case.” Unfortunately, that is not what ERG said.
In fact, ERG goes on the recommend that “3-way catalysts and/or catalytic oxidizers (should be used) on compressor station compressor engines” (page 8-6). This leads to another recommendation that electric compressor engines provide “an opportunity to eliminate emissions from compressor engines completely through the use of electric motors.” There are many problems with the wide-scale use of electric compressor engines, one of which is that they only shift the emissions to coal-fired electric generating plants and could worsen DFW’s air quality and ozone problems. I plan to discuss this in a separate posting within the coming weeks.
For now, it must be emphasized that all compressor engines operating in Fort Worth do have emission controls in place, which can reduce emissions from the engines by as much as 70-90%. Until these emission controls are factored in, statements suggesting that natural gas compressor engines are emitting formaldehyde and acrolein at levels that are causing offsite ambient air concentrations to exceed TCEQ’s short-term and long-term screening levels, are incorrect.