Another investigation by the Railroad Commission of Texas (RRC) has concluded that the evidence does not support allegations that Barnett Shale drilling and hydraulic fracturing activities contaminated a number of water wells with methane in the area of Range Resources Corp. gas wells.
"The occurrence of natural gas in the complainants' water wells may be attributed to processes unrelated to recent Barnett Shale gas production," RRC staff wrote in a report of their investigation, which was begun last year in the Silverado and Brazos neighborhoods in Parker County in North Texas.
Staff said gas from the Strawn Formation, which is shallower than the Barnett Shale, could have migrated and found its way into the aquifer feeding the water wells. The phenomenon would have been "...exacerbated by water well construction practices whereby some water wells have penetrated 'red beds' in the transition interval between the aquifer and the Strawn Formation," RRC staff wrote.
The findings are similar to those of an earlier investigation of well water contamination in the same area by activities of Range Resources (see Shale Daily,March 23, 2011).
The most recent investigation looked at nine water wells and found that contamination by Barnett Shale gas was "not indicated" because:
Surface casings of nearby Barnett gas wells "are sufficiently deep to isolate useable quality groundwater."
Bradenhead pressures were absent/low enough so as not to threaten surface casing integrity.
Producer records submitted to the RRC show that the tops of production casing cement are more than 600 feet above each gas well's productive zone.
Mechanical integrity tests of its wells by Range revealed no casing leaks.
A nearby Carrizo Oil & Gas Inc. well was correctly plugged across the fresh water interval.
Hydraulic fracturing was performed in the Barnett, which is about 5,700 feet below the ground surface and the base of the aquifer and the Barnett Shale are separated by about 5,300 feet of geological strata.
Commission staff said it is not planning any further investigation of the matter. "However, commission staff is aware of other ongoing studies of the occurrence of natural gas in groundwater in the Silverado neighborhood and welcomes the opportunity to review additional information that may become available in the future," it said.