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Water Management Techbook 2017

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46 | May 2017 | WATER MANAGEMENT: CASE STUDIES Further cost reduction for the operator was achieved by producing non-hazardous solid waste, which was fit for landfill disposal. Figure 2 depicts the challenge in treating produced and flowback water for any specific requirement. Unlike other water sources, oilfield waste streams are characterized by a significant variation in water quality day to day and at times hourly. It is critical to monitor the incoming water and adjust the chemical requirements to have a consistent effluent water qual- ity that will meet operator's specifications. During operation of this plant, the algorithm for chemical addition was completely functional and could predict the chemical demand as per changing water quality, leading to a significant reduction in operating expense and waste generated. The treated water quality met the operator's requirement 100% of the time (Figure 3). The data presented are an average of multiple daily measurements performed throughout the operating schedule. GES' SCE technology can reduce bivalent ions, primarily hardness and sulfates. In this particu- lar case the operator's major concerns for the effluent water included iron, oil and grease, total suspended solids (TSS), turbidity, pH and bacteria control. Iron concentration in treated water was on an average below 5 ppm. Iron present in higher concentrations can cause premature crosslinking of guar-based frac- turing fluids. The presence of higher concentration of TSS can impede the permeability of the proppant pack. This blockade can lead to lower production and in the worst case, formation damage. The SCE treatment has proven very effective in reducing TSS from the raw water (Figure 3). Treatment plant setup The SCE technology at its core is a proprietary chem- ical co-precipitation mechanism. It includes a pat- ented inclined plate clarifier with an opposing pitch blade thickener that helps in effective separation. As mentioned previously, the key objective of the process setup was to remove or reduce iron, oil and grease, TSS and turbidity combined with efficient solids separation, pH balancing, solids dewatering and disinfection. The produced water is continuously monitored in real time and fed into an enhanced gravity API oil water separator to recover residual hydrocarbons. The hydrocarbons are returned to the operator for further processing. With the addition of either a coagulant/ flocculant and/or a polymer, GES is able to alter the pH to affect precipitation while minimizing the amount of slurry generated. The treated water is then readjusted for pH and disinfected before it is stored in a downstream buffer storage. The water quality in the downstream storage also is sampled and monitored to ensure the final water quality meets the fracturing operation requirement. The leftover slurry is pressed to form solid cakes that can be classified and disposed FIGURE 2. Variability in water quality presents a significant challenge in water treatment. (Data courtesy of Gradiant Energy Service) 0 100 200 300 400 500 600 700 0 50 100 150 200 250 300 0 20 40 60 80 100 120 140 160 Tests TSS (mg/ltr) Iron, Turbidity (mg/ltr) Variability in Water Quality Turbidity Iron TSS

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