Flowback verses first-flush: new information on the geochemistry of produced water from mandatory reporting

Abstract

Unconventional oil and gas development uses the subsurface injection of large amounts of a variety of industrial chemicals, and there are concerns about the return of these chemical to the surface with water produced with oil and gas from stimulated wells. Produced water, including any flowback of injected fluids, must be managed so as to protect human health and the environment, and understanding the chemistry of produced water from stimulated wells is necessary to ensure the safe management of produced water. In 2014, California instituted mandatory reporting for all well stimulations, including sampling produced water two times and comprehensive chemical characterization of fluids injected and fluids recovered from stimulated wells. In this study, we analyzed data from mandatory reporting with the objective of closing previously identified data gaps concerning oil-field chemical practices and the nature of flowback and produced water from stimulated wells. It was found that the plug-flow conceptual model of flowback developed in shale formations, where salinity increases over time as produced water is extracted, was not appropriate for characterizing produced water from unconventional wells in these oil reservoirs, which are predominately diatomite and sandstones. In these formations stimulation caused a "first-flush" phenomena, where salts and metals were initially high and then decreased in concentration over time, as more produced water was extracted. Although widely applied to meet regulatory requirements, total carbohydrate measurement was not found to be a good chemical indicator of hydraulic fracturing flowback. Mandatory reporting closed data-gaps concerning chemical use, provided new information on acid treatments, and allowed more detailed analysis of hydraulic fracturing practices, including comparison of water use by geological formation. Environmental signicanceMandatory reporting by industry allowed detailed analysis of hydraulic fracturing practices, including comparison of chemical use and produced water quality by geological formation. The pseudo-plug-ow conceptual model of owback developed in shale formations, where salinity increases over time as produced water is extracted, was not applicable to unconventional wells in these oil reservoirs, which are predominately diatomite and sandstones. In these formations stimulation caused a "rst-ush" phenomena, where salts and metals were initially high and then decreased in concentration over time, as more produced water was extracted. New information on acid treatments and the use of chemical indicators of owback indicate that acid fracturing treatments are infrequently applied and the use of chemical indicators needs to be further validated.

Method: Carbohydrate in Produced Water (Colorimetric)

“…Guar gum, a polysaccharide of galactose and mannose, is a common ingredient for hydraulic fracturing fluids [7]. Standard methods for measuring carbohydrates in flow-back and other produced water are needed, particularly in the context of reporting water quality data to regulatory agencies [6]. This method describes standard procedures for carbohydrate measurement that have been validated for use in produced water.…”

Recovery of Critical Metals from Aqueous Sources

“…Likewise, Sr is found to be significantly available in both Permian Basin (180 mg/L 45 ) and Marcellus shale region (32 mg/L 47 ), and the available inland produced water capacity exceeds the annual demand both nationally and globally. U.S. produced water concentrations for Mg, a marginally critical element in Figure 1, is found to be sufficient to exceed both the global and national demand (based on levels between 100 46 and 26,000 mg/L 45 ).…”

“…Technologies. There are existing and emerging separation technologies that can extract targeted inorganic constituents (e.g., metals), valuable or problematical, from complex aqueous mixtures as practiced within several application domains: water and wastewater treatment, aqueous-stream processing by the 45,46 (ppm)…”

An integrative method for identification and prioritization of constituents of concern in produced water from onshore oil and gas extraction

“…Produced water is the largest volumetric waste stream in oil and gas production; it is a combination of water that occurs from within or proximate to the hydrocarbon-bearing zone as well as any injected fluid used to stimulate or maintain production activities ( Fakhru’l-Razi et al, 2009 ). This wastewater has complex chemistry ( Stringfellow and Camarillo, 2019 ) and is generated during all types of petroleum hydrocarbon extraction activities, including conventional and unconventional production. As oil and gas production expands, so does the challenge to manage the estimated hundreds of billion gallons of wastewater generated per year from these activities ( Veil, 2015 ).…”