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Water Management Techbook 2017

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EPmag.com | May 2017 | 41 WATER MANAGEMENT: CASE STUDIES fluid, so they do not provide long-term biocidal pro- tection during a typical multistage fracturing job. To address this issue, many operators supplement an oxidizing biocide treatment with a second, usu- ally nonoxidizing, biocide. The following case study compares the effectiveness of an oxidizing biocide treatment to a dual oxidizing/nonoxidizing biocide treatment for stimulation. Case study An operator in Oklahoma was looking to improve the performance of a standard ClO 2 treatment used for stimulation by incorporating a second biocide at the blender. Table 2 gives details of the stimulation application. Baseline results for ClO 2 were collected from 102 wells over a period of several years. Flowback samples were frequently collected from each well and analyzed for sulfate-reducing and acid-producing bacteria using standard bug bottles during a 90-day period. Positive bottles for both sulfate-reducing and acid-producing bacteria averaged 1.5 during the 90-day period with ClO 2 , but some individual results were as high as eight positive bottles for both types of bacteria. The first supplemental biocide evaluated was a thi- one-based product dosed at 0.25 gallons per thousand. While this dual treatment showed an improvement over ClO 2 alone against sulfate-reducing bacteria, performance declined against acid-producing bacte- ria (Figure 1). The reduced performance of this dual program is not surprising since thione biocides are not compatible with oxidizing agents like ClO 2 . The next supplemental biocide evaluated was Bellacide 300 dosed at 0.2 gallon per thousand. Compared to ClO 2 alone, the ClO 2 plus Bellacide 300 treatment reduced the average number of positive bottles from 1.5 to 1.2 for both sulfate-reducing and acid-producing bacteria. Bellacide 300 also was more effective against acid-producing bacteria than the thione biocide. In addition to the improved performance comparison to thione, Bellacide 300 was more cost-effective, resulting in a 25% cost savings for the operator. Summary The traditional fracturing fluid biocide selec- tion process overlooks some critical aspects of biocide compatibility and performance, which Biocide Fast kill Compatible with FR Compatible with pH buffers 10.5 (Borate) Compatible with gel and FR breakers Compatible with reducing agents Compatible with oxidizing biocides Long- lasting activity Corrosion inhibition Bellacide 300 SSSS SSSS SSSS SSSS SSSS SSSS SSSS SSS DBNPA SSSS SSSS S SSSS S S S S Glutaraldehyde SSSS SSSS SSS SS SS S S SS Glutaraldehyde/ Quaternary ammonium SSSS SSSS SSS SSS SS S SSS SSS Thione S SSSS SSS S SSSS S SS SSS Dimethyl-oxazolidine S SSSS SSS SSSS SS S SSS SS TABLE 1. A ranking of biocides used during the enhanced selection process shows Bellacide 300 to be a superior choice as compared to other options. (Data courtesy of BWA Water Additives) SSSS Superior SSS Very Good SS Average S Poor Basin Woodford Well type Horizontal Well size 45 stages, 7,500 bbl/stage Fluid type Hybrid Water source Mixture of fresh and produced TABLE 2. Stimulation application parameters for the Oklahoma case study are shown. (Data courtesy of BWA Water Additives)

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