Organic compounds in produced waters from the Bakken Formation and Three Forks Formation in the Williston Basin, North Dakota

Matthew S Varonka,Tanya J Gallegos,Anne L Bates,Colin Doolan,William H Orem

doi:10.1016/j.heliyon.2020.e03590

Abstract

The organic composition of produced waters (flowback and formation waters) from the middle member of the Bakken Formation and the Three Forks Formation in the Williston Basin, North Dakota were examined to aid in the remediation of surface contamination and help develop treatment methods for produced-water recycling. Twelve produced water samples were collected from the Bakken and Three Forks Formations and analyzed for non-purgeable dissolved organic carbon (NPDOC), acetate, and extractable hydrocarbons. NPDOC and acetate concentrations from sampled wells from ranged from 33-190 mg per liter (mg/L) and 16–40 mg/L, respectively. Concentrations of individual extractable hydrocarbon compounds ranged from less than 1 to greater than 400 μg per liter (μg/L), and included polycyclic aromatic hydrocarbons (PAHs), phenolic compounds, glycol ethers, and cyclic ketones. While the limited number of samples, varying well production age, and lack of knowledge of on-going well treatments complicate conclusions, this report adds to the limited knowledge of organics in produced waters from the Bakken and Three Forks Formations.

Highlights

In the past decade, technological advances in hydraulic fracturing and horizontal drilling have spurred a boom in United States (U.S.) tight oil and shale gas production
Organic acids, persistent organics added during hydraulic fracturing, and formation leachates can all contribute to non-purgeable dissolved organic carbon (NPDOC)
NPDOC in samples collected in the Bakken and Three Forks Formations ranged from 33-190 mg per liter (mg/L), with a first quartile (Q1) of 42 mg/L, mean of 74 mg/ L, median of 69 mg/L, and a third quartile (Q3) of 95 mg/L (Table 1, Figure 3), which is about half the average concentration of similar tight oil formations like the Wolfcamp and “Cline” shales in the Permian Basin (Engle et al, 2016), but higher than concentrations measured in a brine pipeline sample in the Willison basin (Cozzarelli et al, 2017)

Summary

Introduction

Technological advances in hydraulic fracturing and horizontal drilling have spurred a boom in United States (U.S.) tight oil and shale gas production. Production in the Williston Basin increased, primarily as a result of production from the tight oil reservoirs, from approximately 300,000 barrels/day in 2010 to nearly 1, 500,000 barrels/day in 2019 (U.S.Energy Information Administration, 2019) from over 12,000 wells (North Dakota Department of Mineral Resources, 2019). The majority of these wells are completed in the Bakken Formation, which overlies the Three Forks Formation. In the Late Devonian-Early Mississippian Bakken Formation, much of the horizontal drilling focuses on the relatively porous sandstones, siltstones, and dolostones of the middle member, which is bordered by the source rock shales of the upper and lower members (Lillis, 2013). Recent drilling has targeted the Middle (2nd bench) and Lower Three Forks (3rd and 4th benches) (Gaswirth and Marra, 2015)

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Conclusion