HARRISBURG, Pa. — The Pennsylvania Department of Environmental Protection reviewed a study proposing changes to existing requirements for coal mine pillars as well as alternative methods for constructing natural gas wells where coal is mined underground.
DEP found that the study did not provide results supporting changes.
“Natural gas extraction is increasingly intersecting with longwall mining, particularly in southwestern Pennsylvania,” said DEP Acting Secretary Patrick McDonnell. “While new drilling methods may make extraction more efficient, coal miners’ safety remains our primary concern. For this reason, DEP stands by the established regulatory benchmarks that we believe better protect miner safety and maintain the integrity of gas wells.”
Coal mine pillars are columns of coal or rock left in place in the mine to support overlying rock and furnish protection for gas wells drilled in the permitted area of a mine.
Currently, the size of pillars suitable for ensuring the integrity of gas wells and miners’ safety is specified by the Joint Coal and Gas Committee report, first published in 1957.
The new industry-agency study, titled the Gas Well Pillar Study Update,is the result of Act 2 of 2011, which called for a review of the 1957 study in light of modern longwall mining methods and their impact on natural gas well development.
The study was conducted by the John T. Boyd engineering consulting firm in cooperation with DEP, the Pennsylvania Coal Alliance and the Marcellus Shale Coalition. It was also reviewed by the federal Mine Safety and Health Administration, who shared DEP’s concerns.
The appropriate size of coal pillars around active, inactive and plugged oil and gas wells, along with well clusters, was examined to ensure the integrity of the well and to support the coal seam.
Any additional criteria that should be considered when approving pillars around an oil or gas well that penetrates a workable coal seam were also examined.
Field tests were conducted in 2013 and 2014 at CONSOL’s Enlow Fork Mine in Washington County to create a model to measure the impacts of ground movements related to longwall panel removal and the resulting potential for damage of typically constructed shale gas wells. Results showed that subsidence-related deformation could occur if a support pillar is not suitably sized.
“Our analysis of the new study recommendations concluded that they could not be implemented as an appropriate alternative to the 1957 Coal Pillar Study,” McDonnell said. “Should new data or methodologies be developed in the future, DEP will analyze their impact on the safety of our miners and the integrity of gas wells.”
Under the existing approach, there have been no incidents to date where drilling a natural gas well has compromised an active mining operation.
DEP’s review of the Gas Well Pillar Study Update is available at http://www.elibrary.dep.state.pa.us/dsweb/View/Collection-13194.