ANALYTICAL CHARACTERIZATION OF 

FLOWBACK WATERS IN THE FIELD 

Andrea Shramko 

Tor Palmgren 

Daniel Gallo 

Rahul Dixit 

M-I SWACO 

ABSTRACT 

As the development of unconventional gas sources increases, larger amounts of 

fresh water are needed in fracturing operations and more flowback water is being 

produced. Water use in various gas shale plays is becoming an issue due to limited 

availability of water resources, transportation issues, contamination concerns and 

regulatory pressures. Operators and services companies, therefore, increasingly seek 

ways to reuse the flowback water generated from fracturing operations so as to minimize 

the environmental and economical impact. Frequently, the additives in fracturing fluids 

are not compatible with the flowback water thus necessitating treatment before reuse. 

Understanding the composition of the flowback water is key to determining the extent of 

required treatment. 

Flowback waters are generally characterized by significant amounts of heavy 

metals, hardness, solids, salts, organic elements, polymers, biocides and traces of oils. 

Although various analytical techniques exist in the lab for their characterization, one of 

the greatest challenges is to analyze these waters in the field to enable rapid and reliable 

monitoring that allows for efficient decision making regarding required treatment or safe 

disposal. This paper reviews strengths and limitations of field techniques for 

characterization of flowback water, including colorimetric, titrimetric and absorbance 

methods. 

INTRODUCTION 

Significant deposits of natural gas exist in North America and around the world 

in numerous shale regions such as Barnett, Marcellus, Haynesville, Fayetteville to name a 

few. While well known to the oil and gas industry, these shales have not received close 

attention from natural gas operators until relatively recently due to inherent technical 

challenges related to their low permeability. However, there has been a growing interest 

in pursuing these resources during the last fifteen years with the onset of nonconventional 

drilling techniques using horizontal drilling coupled with oil well stimulation methods 

commonly referred to as hydraulic fracturing. Fracture fluids can be oil-based or waterbased. However, water-based fluids are the most common and least expensive and up to 

90% or more of the fractioning fluid formulation is composed of water. 

16th Annual Petroleum & Biofuels Environmental Conference (IPEC), Houston, November 3-5, 2009 
In a given well, one fracturing job can involve the injection of as much as 

100,000 barrels of water and may require additional fracturing to maximize yield. In the 

first three weeks of the hydraulic fracturing process, approximately 20 - 30% of the water 

used to fracture the well comes back to the surface and is called flowback water. It is 

generally contaminated with spent fracturing fluid chemicals and substances present in 

the shale itself. Until recently, and depending on location of the fracturing job, sourcing 

has been from surface waters and municipal water treatment facilities and discharging of 

the flowback water into disposal wells. However, reconstitution and reuse of flowback 

water for future fracturing operations presents advantages in the form of reduced fresh 

water quantities for fracturing operations and for the need of disposal options, with the 

concomitant reduction in operational cost and issues related to environmental and 

regulatory concerns. 

The flowback water is contaminated with suspended and dissolved solids, with 

the concentrations varying depending on location. Typical concentration ranges for such 

contaminants are captured in Table 1. Additional contaminants include traces of oil, 

bacteria, polymers and fractioning fluid chemicals. The goal of the flowback water 

treatment is to produce clear and largely desalinated water with minimum tendency to 

interfere with fractioning fluid components or with the shale formation. The degree of 

necessary desalination depends of the chemistry of the fracturing fluid and can range 

typically from 1,000 to 10,000 ppm total dissolved solids (TDS), although research has 

been cited in the literature regarding the development of fracturing fluid chemistries 

compatible with unaltered flowback water containing TDS levels up to 150,000 ppm. 

In the field, flowback is treated in stages involving pretreatment and desalination 

steps. Desalination treatment approaches include membrane and thermal technologies and 

the necessary level of pretreatment depends on the selected desalination method. 

Membrane technologies require the removal of oil, hardness, bacteria, and total 

suspended solids (TSS) due to scaling and potential fouling of the membrane surfaces. 

Thermal technologies are less susceptible to some of the contaminants, yet are sensitive 

to hardness and TSS because of scaling issues. In addition, the concentration of divalent 

ions in the water such as barium, calcium and magnesium may cause scaling and 

plugging of the formation and therefore need to be removed from the flowback water. 

Understanding the composition of the flowback water is essential in determining the 

extent of required treatment. 

While all water analyses required to characterize the flowback water before, 

during and after treatment can be performed at off-site laboratories, it is clear that the 

greatest challenge is to analyze the flowback water in the field in order to enable rapid 

and reliable monitoring for efficient decision making regarding required treatment, 

treatment performance or reuse, and safe disposal. 

Laboratory methods for analysis of flowback water range from titration to 

spectroscopic determinations such as atomic absorption (AA) and inductively coupled 

plasma (ICP), X-Ray Fluorescence (XRF); in some cases, these methods are cited as 

standard ASTM methods or practices. However, field operations for flowback water 

treatment frequently require evaluation techniques that are less delicate and easier to 

mobilize and use, yet are adequately accurate and reliable to permit operators and service 

providers to monitor key operational variables for timely process adjustment to ensure 

that target objectives are achieved. Available field methods, the subject of this paper, are 

typically based on colorimetric, conductometric and titration techniques. 
Table 1. Approximate Flowback Water Contaminant Ranges

Contaminants Concentration 

Range (ppm) Contaminants Concentration Range (ppm)

Alkalinity 100 - 600 Iron 50 – 300 

Calcium 500 – 12,000 Silica 50 - 300 

Magnesium 50 – 2,000 Sulfate 10 – 400 

Barium 50 – 9,000 Chloride 5,000 – 80,000 

Strontium 50 – 6,000 TDS 1,000 – 150,000 

Sodium 4,000 – 40,000 TSS 1,000 – 7,000 

EXPERIMENTAL METHODS AND 

MATERIALS 

Sample Collection 

Flowback water samples were collected in clean polypropylene containers from 

different shale locations in North America and shipped to the laboratory where both field 

techniques and analytical methods were used in their characterization. For preservation 

purposes, prior to shipment the samples were spiked with nitric acid and kept at 43°F 

(6°C) in accordance with EPA Guidelines Establishing Test Procedure for the Analysis of 

Pollutants under the Clean Water Act (CFR 40, Part 122, 136, et al.) as briefly 

summarized in Table 2. Samples were held at room temperature (68°F/20°C) before the 

analysis. 

Table 2. Summary of Collection and Preservation Methods 

 in Accordance with EPA Test Procedure Guidelines 

 (40 CFR, Part 122, 136, et al.) 

Analyte Acid Preservation/ 

Temperature Storage Time 

Alkalinity 6°C* 14 days 

Hardness and Metals Preservation pH ≤2 

Nitric Acid (1.5 ml/L)/NA 

Up to 6 months 

Chloride NA Up to 28 days 

Silica NA/6°C Up to 28 days 

Sulfate NA/6°C Up to 28 days 

* No acid preservative needed. 

Testing Methods 

Field analytical methods and laboratory analysis were employed in this study. 

The analytical determinations were done for benchmarking purposes. For the laboratory 

characterization AA and in some instances ICP was used for aluminum, barium, calcium, 

magnesium, manganese and silica, whereas ion chromatography (IC) was used for 

determining anionic species such as sulfate and chloride. Additionally, the laboratory 
used titration for chloride and alkalinity, and gravimetric methods for TSS and TDS. For 

the field analysis, colorimetric methods were used for the analysis of aluminum, barium, 

calcium, chloride, iron, magnesium, manganese, sulfate and silica. Titration methods 

were used for alkalinity, chloride, calcium and magnesium. Conductivity was used to 

evaluate TDS. Turbidity measurements were used in lieu of TSS measurement for the 

field due to the lack of a suitable field TSS method. 

The principle of colorimetric analysis involves the introduction of a reagent that 

produces a color when reacting with the element to be analyzed. The intensity of the 

color is proportional to the amount of that element in the specimen. The concentration of 

the element can be quantified in accordance with the Lambert-Beer Law by passing a 

light beam through the specimen as depicted in Figure 1. 

Figure 1. Schematic of the Lambert-Beer Law 

The concentration is automatically computed by the colorimetric spectrometer 

using the Lambert-Beer equation shown below: 

ۯ ൌ െ ܗܔ܏ ൬

۷૚

۷ܗ൰ ൌ є܋ܔ

where: 

A: Absorbance 

Io: Initial intensity 

I1: Transmitted intensity 

Є: Extinction coefficient 

Any preexisting color in the sample to be analyzed would interfere and will 

adversely affect the result of the colorimetric test. Flowback water is not always colorless 

and also typically turbid, which can cause interferences when using colorimetric 

techniques. Samples collected during the course of our analysis are depicted in Figure 2. 

In order to eliminate interference due to the color or turbidity of the analyzed samples, 

dilution techniques and filtration using a 0.45 μm filter were implemented. In addition to 

optical interferences, chemical interferences can also occur due to the presence of one or 

more elements that can react with the reagent added to produce the color or with the 

target analyte obscuring the true intensity of the color attributed to the concentration of 

C,

α 

Io I1

l

є
the analyte of interest. Chemical interferences associated with the analytes investigated in 

this study are summarized in Table 3. 

The principle of turbidimetric analysis involves the introduction of a reagent that 

produces a precipitate when reacted with the element to be analyzed, such as for the 

determination of barium and sulfate. The turbidity relies on detecting the transmittance of 

the light through the suspension and any inherent precipitate in the sample. Interferences 

are similar to those observed in the colorimetric methods. Chemical interferences 

associated with the analytes investigated in this study are summarized in Table 3. 

Conductivity methods measure the overall conduction associate with ions present 

in the water. The output of conductivity measurement, if given in units of microsiemens 

per centimeter (μs/cm), can be used to calculate concentration of TDS in the water in 

accordance with the following formula: 

TSD (ppm) = Conductivity (μs/cm) X 0.67 

Figure 2. Flowback Water Samples from Different Shales and Locations 

Table 3. Chemical Interferences Factors for Colorimetric Analysis of Flowback Waters 

Analyte Interferences 

Aluminum alkalinity 

Barium calcium, magnesium, silica, sodium 

chloride and strontium. 

Chloride pH below 3 or above 10. 

Iron calcium, chloride, magnesium, 

pH below 3 or above 10. 

Magnesium chromium, copper, iron, manganese 

and zinc. 

Manganese calcium, chloride, magnesium, iron, 

and pH below 3 or above 10. 

Silica phosphate and sulfide 

Sulfate calcium, magnesium, chloride and 

silica. 

Barnett 1 Barnett 2 Barnett 3 Marcellus
Titration methods are used in this study for quantification of alkalinity and as an 

alternative method for quantification of chloride, calcium and magnesium. Interferences 

for this method are similar to those in the aforementioned section. 

Differences in temperature and time of conducting the analysis are sources of 

error for colorimetric and turbidimetric methods. Measures to control these parameters 

should be taken in the field for the analysis. Recommended temperatures are 68 – 77°F 

(20 – 25°C). These conditions were controlled in our study. Reaction times were 

monitored for each chemical added in the colorimetric and turbidimetric methods. 

The concentration ranges for the field test methods vary widely by analyte and 

are summarized in Table 4. Therefore, it is frequently necessary to dilute the samples 

100- or 1,000-fold depending on the concentration of the analyte in the sample and the 

chemical interferences. Some trial and error experiments are usually required to hone into 

the proper dilution level. For this study, dilutions as high as 1:10,000 were used for ions 

such as calcium, magnesium and chlorides due to their high concentration in the 

flowback waters. 

Table 4. Field Analysis Concentration Ranges 

Analyte Range (mg/L) 

Alkalinity 10 to 4,000 

Iron 0.02 to 3.00 

Aluminum 0.008 to 0.8 

Calcium 0.05 to 1 

Magnesium 0.05 to 0.25 

Total Hardness 

(Titration for Ca and Mg) 

10 to 4,000 

Barium 2 to 100 

Chloride (colorimetric) 0.1 to 25 

Chloride (titration) 10 to 10,000 

Manganese 0.1 to 20 

Silica 1 to 100 

Sulfate 2 to 70 

Sample Preparation 

The samples were equilibrated to room temperature prior to analysis and 

subsequently filtered through a 13-mm diameter, 45-μm PVDF syringe filter to remove 

suspended solids to reduced interference with the analyses. The filtration was done for 

two reasons: first to duplicate the procedure used by the analytical lab, and secondly to 

remove TSS and all coarse contaminants that are usually removed during prefiltering 

stages prior to the actual flowback water treatment. Also, the samples were diluted to 

eliminate chemical and any other sources of interference and to be within the range 

specified by a given method. 

Equipment and Materials 

The experiments were conducted using a standard water quality field test kit. The 

equipment included in the test kit and used for this study included a combined 

pH/conductivity probe, turbidimeter, spectrometer, volumetric flasks (10, 50 and 100 

mL), a micropipette adjustable 0.1 to 1 mL, 10-mL pipette and 1-in/10-mL square glass 
sample cells. Chemical reagents in sealed aluminum packets were provided in the test kit. 

An instruction manual with a detailed test protocol was provided and validated during the 

experiments. The water quality field test kit was selected due to its portability, 

compactness and ability to provide methods for a wide range of analytes present in 

flowback water. 

RESULTS 

For the first round of experiments flowback water from Barnett Shale (Barnett 2) 

was tested using the field test kit, one day after sample collection including transportation 

and storage. The same sample was tested the following day by the analytical laboratory. 

At collection and for subsequent storage the sample was preserved in ice and brought to 

room temperature prior to analysis. 

After detecting discrepancies between the two data sets, it was decided that the 

field testing instrument needed to be tested for accuracy. Instrument accuracy was 

verified after running standard solutions of the ions of concern. For barium, an additional 

experiment was conducted to understand the interference with strontium for the method. 

Results for the barium method indicated that strontium would interfere strongly at 

concentrations higher than 100 ppm, subsequently increasing exponentially as the 

strontium concentration increases. After the potential instrument issues, the same sample 

was reanalyzed 26 days after collection by both the analytical lab and using the field test 

kit. Also, during the evaluation, it was noted that more accurate results were achieved by 

using volumetric flasks rather than graduated cylinder during the sample preparation. 

This was attributed to the precise calibration of the volumetric flask. Results for the first 

and second round of experiments are depicted in Table 5. Results for the field test kit 

using standards are shown in Table 6. 

Table 5. Comparison of Analytical Laboratory and Field Test Kit Results

Analyte 

First Run 

(1 and 2 days after 

collection) 

Second Run 

(26 days after collection) 

Field 

(mg/L) 

Analytical 

(mg/L) 

Field 

(mg/L) 

Analytical 

(mg/L) 

Alkalinity 640 510 NA NA 

Iron 21.9 12 10 7.8 

Aluminum 0.098 <0.1 0.021 <0.05 

Calcium 450 1,260 1,157 1,450 

Magnesium 1,320 171 181 172 

Barium 47 12 25 10 

Strontium - 275 - - 

Chloride (colorimetric) 16,200 16,800 16,300 16,700 Chloride (titration) 18,650 NA 

Manganese 2.0 0.27 40 1.9 

Potassium 0.0 90 105 91 

Silica 159 20 58.8 33 

Sulfate 500 169 180 174 
Table 6. Standard Analysis for Verification of Field Test Kit 

Analyte Concentration 

(mg/L) 

Standard 

Concentration 

(mg/L) 

Barium 10 13 

Strontium 100 1 

150 2 

200 44 

Calcium1 1,000 1,240 

Calcium2 1035 

Magnesium1 100 70 

Magnesium2 97 

Manganese 2.0 2.6 

Silica2 1,000 1,050 

Sulfate 100 94 

Notes: 

1. Results using graduated cylinder for dilution 

2. Results using volumetric flasks for dilution

After verification of proper operation of the instrument, various flowback water 

samples were analyzed both by the laboratory and using the test field kit. The results are 

summarized in Table 7 and Figures 3a and 3b. 

Table 7. Analytical and Field Test Kit Results for Various Flowback Waters

Analyte 

Barnett 1 Barnett 3 Marcellus 

Field 

(mg/L) 

Analytical 

(mg/L) 

Field 

(mg/L) 

Analytical 

(mg/L) 

Field 

(mg/L) 

Analytical 

(mg/L) 

Alkalinity 482 480 305 360 500 500 

Iron 1.00 0.50 30 63 43 38 

Aluminum <0.008 <0.1 0.00 0.50 <0.008 1 

Calcium 948 1,400 9,480 10,400 1,176 1,300 

Magnesium 209 180 1,272 880 127 100 

Chloride 14,400 23,100 113,000 95,750 8,000 16,400 

Manganese 19.8 1 8.7 5 40.0 2 

Silica 25.4 29 18.0 14 56.0 12 

Sulfate 16 32 200 430 <2 3 

Conductivity/ 

TDS 39,390 39,800 160,600 176,400 27,800 29,000 

Turbidity 

(NTU) 11 - 264 - 319 - 

pH 7 - 6 - 7 - 

Temperature 

(°C) 20 - 20 - 19 - 

 
Figure 3a. Analytical and Field Test Kit Results for Various Flowback Waters
Figure 3b. Analytical and Field Test Kit Results for Various Flowback Waters 

The results indicated relatively minor discrepancies between the two methods for 

alkalinity, calcium and TDS as measured by conductivity. Rather significant differences 

were observed for the remaining analytes. In the case of iron, the Barnett 1 and Marcellus 
samples showed similar results between the two methods whereas some deviation was 

seen for the Barnett 3 sample. The Barnett 3 sample presented a reddish color indicating 

iron precipitation, which could account for the lower reading using the field method 

requiring a 3-minute waiting period for chemical reaction with the colorimetric reagent 

whereas the atomic absorption techniques used in the analytical lab atomizes the sample 

avoiding the issue of precipitation. For aluminum, the discrepancy may be exaggerated 

due to the fact that the concentrations appear to be below the detection limits for both 

methods used. For magnesium, Barnett 1 and Marcellus samples results were relatively 

consistent between the two methods, whereas a greater discrepancy was observed for the 

Barnett 3 sample, A possible reason is the concentration of the sample was higher than 

0.25 mg/L, which is the maximum concentration allowed for the method to obtain 

accurate results. Further dilution would have been required for the sample. 

Regarding barium, the field method is not feasible due to unavoidable 

interference from the presence of strontium in the samples. For chloride, results obtained 

for all samples are inconsistent requiring further investigation. With respect to 

manganese, there were difficulties in making an accurate assessment of the violet color to 

be developed in the presence of manganese. Therefore, there could be issues with 

manganese regarding the use of colorimetric techniques. Further studies are needed. In 

the case of silica, the Barnett 1 and Barnett 3 samples appeared to exhibit similar results 

for both methods, whereas significant deviation was seen for the Marcellus sample, 

which may be attributable to the presence of sulfide in the sample. Although an analysis 

for sulfides was not performed on the Marcellus sample, it exhibited an unpleasant sulfur 

odor. Furthermore, the sulfate content in the Marcellus was not detectable, indicating the 

speciation of sulfur was towards sulfides. For sulfate analysis, discrepancies were 

observed between the methods and additional investigation is required to elucidate the 

causes. 

CONCLUSIONS AND RECOMMENDATIONS 

Four flowback water samples were evaluated for a string of analytes both by 

analytical laboratory techniques and by a field test kit. The purpose was to assess the 

feasibility of using the field test kit during flowback water treatment operations in the 

field. Comparison of the results indicates that additional work is needed to assess the 

implementation of the field instrument for analysis of chloride, iron, magnesium, silica, 

sulfate and manganese. The field method for barium is not appropriate for the analysis of 

barium due to interferences with strontium that is generally present in flowback waters. 

Research should be undertaken to develop a suitable field method to analyze barium and 

strontium, another common constituent in flowback waters. Current methods for these 

two analytes involve coprecipitation by sulfate thus masking the quantification of either 

one. For alkalinity, calcium and TDS the field test methods appear to be reliable to guide 

in assessing progress and performance and in decision making during treatment 

processes. 

It is recommended that a more in-depth study involving statistical analysis to 

determine repeatability of the field methods be pursued. 
REFERENCES 

Bergman, Elaine. Techniques for Water Analysis. The Royal Australian Chemical 

Institute, August 2009. 

Laidler, Kith. The World of Physical Chemistry. Oxford University Press. 1993. 

American Water Works Association. Standard Methods for the Examination of Water 

and Wastewater. Fifth Edition. 2005