WATER VOLUMES ASSOCIATED WITH BAKKEN FORMATION OIL DEVELOPMENT: REGIONAL-SCALE QUANTIFICATION, BUILDING FROM USGS ASSESSMENTS OF UNDISCOVERED OIL AND GAS RESOURCES

The quantities of water and proppant (often sand) associated with oil and gas development are receiving increased attention due to questions about sourcing, transportation, storage, and disposal. The quantities of water and proppant that could potentially be required and produced during the development and production of undiscovered oil and gas resources can be estimated on a regional scale using a methodology that builds on widely applied USGS oil and gas assessment methodologies. The assessment approach is probabilistic, and employs a Monte Carlo simulation framework to calculate all quantities as bounded estimates (with uncertainty bounds). The methodology applies specifically to oil and gas accumulations that are defined by the USGS as “continuous”, including shale oil and gas as well as tight sand plays; these are sometimes also referred to as “unconventional” resources.

In this presentation, we will describe the water/proppant assessment approach. We will also present data and analyses related to this work, primarily for the Bakken and Three Forks Formations in Montana and North Dakota in the Williston Basin. In the process, we will illustrate evolving trends in production practices for the area, including hydraulic fracturing, and we will discuss observed patterns in water production, including demonstrating an approach for calculating flowback water volumes.

Specifically, water use per well for hydraulic fracturing has risen steadily in recent years, linked to shifting hydraulic fracturing fluid types and to increasing well lateral lengths. The amount of proppant used per unit of water has been decreasing, as hydraulic fracturing fluid preferences have shifted from predominantly gel treatments to a greater percentage of hybrid and slickwater treatments. The percent of hydraulic fracturing fluid that returns as flowback can be estimated from monthly water and oil production data, and this percentage shows a decrease in recent years, likely corresponding with evolving production practices.