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Water Management Techbook 2018

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52 | April 2018 | WATER MANAGEMENT: CASE STUDIES water quality continued to worsen while in storage and began improving once the aeration system was installed. It took about five to seven days to get the water to an adequate quality (slightly positive ORP) and 14 days to get the water to a good quality (more than 100 ORP) (Figure 1). ORP is just one parameter to consider. Dissolved oxygen, iron and sulfides are just as important to evaluate the overall performance of the aeration system. Measuring these parameters also help verify if ORP is a good indicator of overall water quality. A review of the results for iron, sulfides and dissolved oxygen shows they are consistent with the changes in ORP. It can be verified that ORP provides a good indication of overall water quality and aeration system performance. In sampling a pit or tank, it is important that samples are taken from multiple locations and differ- ent depths. It is also important to evaluate the devi- ation between these results. Significant deviations can be a sign of dead zones or stratification. A review of the data shows the results are consistent, which is an indication of good mixing. Another technique to evaluate mixing is the use of temperature. A line of thermocouples for temperature measurement can be put into the water. There should be very little deviation from the top to the bottom. If there is a deviation, this is a sign of poor mixing or stratifica- tion. The portable aeration system being evaluated here is designed to provide mixing with aeration. Why is stratif ication a concern? Poor mixing can result in chlorides concentrating at the bot- tom of the pit. In a reuse program, increasing chlorides will increase the friction factor of the produced water, requiring an increase in friction reducer in completion f luids. To avoid this, a consistent f luid should be maintained by monitoring mixing. In this case study, a portable aeration system was evaluated. It was deployed in a 450,000-bbl pit and tested the water over four days. A deployment barge with a small crane attached was developed to deploy each mixer, while complying with confined space entry requirements. Produced water pits, although open, can meet the requirements for confined space entry. As a result, the deployment barge had to be outfitted with safety harnesses, communication and multiple self-contained breathing apparatus. Baseline testing was conducted to evaluate water quality changes before and after deployment. As expected, water quality improved and was main- tained. Pit water was regularly removed for a reuse program. Secondarily, mixing was evaluated, which also was found to be effective. Ultimately the porta- bility allowed the submersible aeration system to be removed and relocated without concerns requiring the pits to be empty. The key to the success of this aeration system was sizing it to account for water quality and its oxygen demand. n Big Pit Middle Big Pit North Big Pit South 10/25 11/1 11/8 11/15 11/22 Date ORP (mV) ORP 200 100 0 -100 -200 -300 -400 Figure 1. The general water quality in a Permian Basin produced water pit using ORP was tested in a 2016 study. (Data courtesy of Hydrozonix)

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