New Tool Provides Measurement-Based Emissions Estimates for Produced Water Ponds
Oil and natural gas deposits almost always occur in conjunction with subterranean water that comes to the surface when drilling for oil or natural gas. Because this “produced water” is fouled with organic compounds it cannot be released directly into the hydrosphere. One treatment method is to discharge the produced water into treatment ponds from which it is allowed to evaporate. However, the entrained organic compounds also evaporate, meaning that these ponds are a source of organic compound emissions. These emissions are a health hazard and can also act as ozone precursors, but until recently, no one had bothered to measure the organic compound emission rates.
From 2015 to 2017, the Bingham Research Center, in partnership with GSI Environmental Inc., an environmental consulting firm located in Austin, Texas, and under contract from the Air Quality Division of the Wyoming Department of Environmental Quality, measured atmospheric emissions and water quality at several pond facilities throughout the State of Wyoming. Then under a second project completed December 2019, again in partnership with GSI, we developed a mathematical model (the Wyoming Pond Emissions Calculator, or WyPEC) designed to be consistent with the dataset obtained previously. The final model has been packaged in a user-friendly Excel spreadsheet. Pond operators and governmental regulators can plug into WyPEC a few data points, such as the average monthly wind speed and temperature, water quality data, pond surface area, etc., and obtain monthly estimates of the emissions of a suite of organics, including alkanes, aromatics, and alcohols.
The project entailed comparing the field data against a number of different existing models with the plan to select the model with the best performance. However, as it turned out, no single model worked well across the full dataset, and the final version of WyPEC was constructed as a hybrid, combining the strengths of two of these models, along with several additional tweaks developed by us or by GSI.
The Wyoming Air Quality Division plans to use WyPEC to characterize organic compound emissions from all produced water ponds in the state, and the tool can be downloaded for free from our website or Wyoming DEQ's website (to view the latest WDEQ uploads, the document list must be sorted by date).
Comparison between observed pond emissions and the emissions predicted by WyPEC. Agreement is to within about an order of magnitude over six orders of magnitude in the emission.