Gas well flowback matches Paleo brines
PENN STATE (US) — Brine water that flows back from gas wells in the Marcellus Shale region after fracking is many times saltier than seawater, with high contents of various elements, including radium and barium.
A new study finds that the chemistry is consistent with brines formed during the Paleozoic era.
The findings indicate that the brine flowback elements found in high levels in the late stages of hydraulic fracturing come from the ancient brines rather than from salts dissolved by the water and chemicals used as part of the fracking process.
For the study, the researchers analyzed data primarily from four sources:
- a report on brines from 40 conventional oil and gas wells in Pennsylvania
- data on flowback waters from 22 Marcellus gas wells in Pennsylvania that the state Bureau of Oil and Gas Management had collected
- flowback waters from two Marcellus gas wells from a previous study
- an industry study by the Marcellus Shale Coalition on flowback samples from eight horizontal wells that was reported in a Gas Technology Institute report.
Hydraulic fracturing, or fracking, is the process used to release natural gas from the shale formations deep underground. The process involves drilling down thousands of feet and, in the case of horizontal wells, sideways, then injecting a mixture of water, sand, and chemicals to release the gas.
The paper, accepted for publication by Applied Geochemistry, notes that about a quarter of the volume of fluid used for fracking returns to the surface, but with the brine as a major component.
The paper looked at fluids that flowed back within 90 days of fracking. The samples analyzed in the study come from wells in Pennsylvania, along with two from northern Virginia.
The analysis shows that the brine flowback had extremely high salinity that does not match the chemical composition of the solution put into the wells during the fracking process. Instead, the elements being released are similar to those deposited during the Paleozoic era, hundreds of millions of years ago.
Arthur W. Rose, professor emeritus at Penn State, says the naturally occurring radioactive materials being brought to the surface after having been 8,000 feet deep were deposited with formations in that era.
He notes that while much attention has been focused on the chemicals that are injected into the shale formation during the fracking process, also of concern is the release of elements such as barium and radium that have been in the ground for millions of years.
“Even if it’s diluted quite a bit, it’s still going to be above the drinking water limits,” Rose says. “There’s been very little research into this.”
Pennsylvania does have regulations on the disposal of fracking fluids. Rose says the findings highlight the importance of re-use and proper disposal of fracking fluids, including those from the later stages of drilling.
“Improper disposal of the flowback can lead to unsafe levels of these and other constituents in water, biota, and sediment from wells and streams,” the researchers note.
“The high salinity and toxicity of these waters must be a key criterion in the technology for disposal of both the flowback waters and the continuing outflow of the production waters,” the paper concludes.
Lara O. Haluszczak, a Penn State graduate and Lee R. Kump, professor and head of the Department of Geosciences, are co-authors of the study.
Source: Penn State