Natural gas wells in and around Pavillion, WY, where gas-water contamination allegations have swirled for a number of years, were properly permitted and constructed, according to a draft report released by the Wyoming Oil and Gas Conservation Commission (WOGCC).
The draft report is the state's follow-up to earlier tests done by the U.S. Environmental Protection Agency (EPA), which at one time alleged that wells drilled by a unit of Encana Oil & Gas Inc. may have tainted water wells in the area (see Shale Daily, Dec. 9, 2011). EPA, however, abandoned its testing last year (see Shale Daily, Sept. 12, 2013).
WOGCC has carried on research in Pavillion with support from a $1.5 million grant from Encana (see Shale Daily, June 16).
The Canadian oil/gas producer praised the draft report findings, particularly one of six principal conclusions that said there was no indication of "casing or wellhead leaks" during testing of the space between the production and surface casings.
"The report confirms that the natural gas wells in the Pavillion Field were soundly constructed and provide no migration pathway into domestic water wells," a Colorado-based Encana U.S. spokesperson told NGI's Shale Daily on Monday.
The draft review and report was completed by former WOGCC interim supervisor Bob King, and David Dillion, an engineering consultant and former engineering manager for Colorado's Oil/Gas Conservation Commission. With involvement also from the current WOGCC oil/gas supervisor, Mark Watson, the draft report aimed to determine if gas and other constituents observed in the Pavillion domestic water wells are naturally occurring or the result of gas field development.
Watson said that the draft report is one of three that eventually will be compiled into a final report from the state Department of Environment Quality. The well integrity review now undergoes a 30-day public comment period, and within the next month a draft report of surface pits in the area will be released, he said.
Reviewing 50 gas wells within a one-quarter-mile range from 15 domestic water wells, the report noted that the water wells were completed at depths ranging from 30 to 750 feet, while about two-thirds of the gas wells are at much deeper depths (699 to 5,812 feet).
"Review of available records for gas wells determined that all wells were properly permitted, drilled, completed and operated in compliance with applicable state and/or federal rules and regulations, and in accordance with accepted industry standards and practices," the draft report said.
Both mechanical and bradenhead pressure testing were applied by the WOGCC researchers to gas well casings.
The draft report includes seven recommendations, ranging from obtaining more accurate water well information from written well records to consideration of installing groundwater monitor wells "to better understand fluid characteristics and groundwater flows."
There were three recommendations for producers:
- On a quarterly basis, monitor and bleed off bradenhead pressure of all gas wells with reported positive pressure readings;
- Obtain and submit to WOGCC cement bond logs for specific gas wells (Tribal 14-2, Tribal Pavillion 43-10 and Unit 22-12 wells); and
- Perform mechanical integrity tests on all gas wells with recurring bradenhead pressure not previously tested and report the results to WOGCC.
King said the study shows that many factors affect whether natural gas migrates into a water supply, including differences in pressure and underground permeability. Thus, he said, the shallower cased gas wells (representing one-third of those reviewed) do not necessarily cause contamination.