As industry operators seek to lower completion costs in a budget-driven environment, one approach is to mitigate water filtration methods in conjunction with the use of novel fracturing chemistry technologies. These chemistry solutions require systems that are robust enough to withstand high salinity and divalent environments and that have the ability to crosslink in water containing boron. The removal of bacteria is vital and is a fundamental step towards tangible production when using produced water. One seemingly unavoidable hurdle with produced water usage is free-floating iron content and destructive organics that can develop into increased instances of sludge and can result in concomitant formation damage. Use of an optimized pH and a two-step, oxidization-based process of bacteria control has proven to be a cost-effective solution for removing suspended solids and optimizing wells in which produced water is used.
Increased acceptance of oxidizing bactericides, such as chlorine dioxide, which quickly penetrate encapsulated bacteria, has enabled the use of produced water with reduced filtration. In this particular case study, chlorine dioxide was used for its ability to oxidize the blended produced water at a controlled rate while iron sulfide (FeS), solid soluble particles, suspended solids, and organic materials are flocculated out. This resulted in a more efficient method of wellsite filtration, which reduced cost approximately 78% per treated barrel. By using chlorine dioxide with controlled residence time (i.e., in a treatment tank that allows for adequate contact time), impurities are settled out of the solution, enabling more efficient removal of flocculants. Oxidization of FeS and iron transforms them from the soluble ferrous ion (Fe2+) to the ferric form (Fe3+) and results in accelerated settling of flocculated particles by final synthesis of ferric hydroxide (Fe(OH)3). This process avoids traditionally required downtime to remove discharged waste and/or transportation of waste throughout the completion process.
In summary, water reclamation is a widely adapted practice in US completions. Since 2013, the North American market value for produced water use has increased from $216 million to a projected $350 million by 2018. As more economical completion methods are continually being considered, advancements in fluid technology, such as the system exhibited in this case study, demonstrate operator savings of approximately $4.00 per barrel in filtration costs because the system is not affected by traditional interfering ions. In this case study, avoiding treatment costs amounted to more than $670,000 in cost reduction based on the downhole produced/fresh water ratio. Additional savings gained by not having to process water through prejob filtration resulted in lower per-day costs than are typical with elaborate filtration. As a result, use of this fluid system generated a comprehensive completion strategy that dramatically increased completion efficiencies without compromising targeted production.