The problem to be solved is the disposal of millions of liters (gallons) of production water and flow-back water generated annually from the Rocky Mountain Region oil and gas industry in an environmentally-safe, low-cost, and efficient manner. One such technology used is evaporation of the water in lined containment ponds after separation and removal of the hydrocarbon component from the water. After removal of the hydrocarbons via oil/water separation equipment, the water is “cleaned” further by being evaporated and returned to the hydrologic cycle, allowing the brine and suspended solids to be settled or precipitated to the bottom.
Three projects—in Cisco, Utah, Dad, Wyoming, and Cheyenne, Wyoming—were designed as case studies to evaporate water in a series of geomembrane-lined ponds. The projects use high-density polyethylene (HDPE) as the top layer to protect the groundwater and enhance evaporation.
The three projects are complete and have been operational for a number of years. The production and flow-back water from oil and gas wells in the area local to each site is trucked to the sites for disposal. The water is evaporated in ponds lined with HDPE as the top layer by using a combination of factors that are favorable to the evaporative process, including the following:
- Natural characteristics of the site, including the arid climate, windy conditions, and numerous sunny days,
- The top liner in the ponds is black HDPE, which creates a hot surface, enhancing evaporation,
- HDPE liner was chosen to protect the surface and groundwater of the area; it is durable and chemical resistant.
These sites are also favorable due to other factors such as remoteness from populated areas, access to highways for trucks, deep groundwater, and geology.
The projects provide oil and gas production companies in the area with a large commercial alternative to production water and flow-back disposal versus numerous small ponds that may service only one well pad, or expensive re-injection wells, or even more expensive water recycling or treatment facilities. Based on similar capacity facilities, evaporation ponds tend to be 25 percent less costly to build. The regulatory agencies are favorable to these type commercial facilities for centralization and protection of the state’s waters. The facilities protect surface waters in the area due to the liner and the freeboard that is above the maximum water level—0.61 meters (m) (2 feet (ft)) (Utah) and 0.91m (3ft) (Wyoming). In Utah, secondary containment is also used in case of catastrophic berm failure per state requirement.
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