22-27 September 2019
Trade Fairs and Congress Center (FYCMA)
Europe/Madrid timezone

Regional Groundwater Contamination Related to Exploration & Production of Natural Gas – Pavillion Gas Field, Wind River Basin, Wyoming USA

24 Sep 2019, 12:00
15m
Conference room 1.A ()

Conference room 1.A

Oral Topic 8 - Groundwater quality and pollution processes Parallel

Speaker

Mr Mickel Wireman (Granite Ridge Groundwater)

Description

The Pavillion gas field is located in the Wind River Basin in north central WY, USA. Since the 1960s natural gas has been produced from the Tertiary age Wind River Formation which is comprised of lithologies associated with a fluvial depositional system. Commercial and non-commercial gas deposits, which originate in the underlying Ft. Union Formation, occur in discontinuous permeable sandstone and siltstone traps within the Wind River Formation which is about 1077 meters in the Pavillion area. Uncommonly shallow non-commercial deposits occur at depths less than 300 meters below the ground surface. There is no confining unit separating deeper, commercial gas zones from shallower, fresh water zones. Production in the gas field has occurred using conventional vertical wells and hydraulic fracturing, which was utilized at depths as shallow as 275 meters. About 170 vertical gas production wells have been completed within the 65 km2 gas field. In the early 1990s production well spacing increased from 1 well per 259 hectares to one per well 16.2 hectares. It is estimated that more than ½ of 170 wells were constructed and / or abandoned using methods and practices that are not appropriate for the hyrogeologic setting. There are 57 unlined pits which were used for disposal of drilling fluids and mud. Diesel based drilling fluid was used until the early 1990s. The upper part of the Wind River Formation functions as an aquifer and is the source of domestic and drinking water for numerous ranches and public water supply for the town of Pavillion. Approximately 90-100 water wells produce from the Wind River aquifer within the Pavillion gas field with depths range from 15 to 265 meters. In the early 1990s residents began experiencing taste and odor problems with domestic water. In 2005 a “blowout” fire occurred while drilling a new domestic water well. Groundwater quality data from 37 domestic wells, public water supply wells and two deep monitoring wells, obtained during the past 10 years, indicates significant groundwater contamination has occurs throughout a large area within the gas field. Contaminants include petroleum hydrocarbons (BTEX, DROs, GROs, methane), VOCs and SVOCs, metals and methanogenic and sulfide reducing bacteria. The primary sources of these contaminants are infiltration and migration of fluids from unlined pits, migration of drilling / production fluids and stray gas migration from improperly constructed /abandoned production wells. At least 10 domestic wells are located less than 300 meters from an unlined pit or a producing gas well. The United States Environmental Protection Agency, the Wyoming Department of Environmental Quality and local NGOs have been engaged in assessing the nature and extent of contamination and evaluating potential remedies that will provide sustainable water supplies to the effected water well owners.

Primary author

Mr Mickel Wireman (Granite Ridge Groundwater)

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