Considering the current downturn in crude prices, there is a renewed interest in recycling produced water for reuse in hydraulic fracturing in the development of unconventional resource plays. As the hydrocarbons are produced, large quantities of water containing high amounts of total dissolved solids (TDS) are also produced in the process. Most of the produced water usually is reinjected into disposal wells. This practice has become a topic of public concern after reports of earthquakes began approximately 5 years ago in the central United States, where disposal wells are heavily used. Reusing produced water as the base fluid for hydraulic fracturing not only alleviates the operators’ dependence on fresh water but also lowers the overall cost of fracturing treatments.
Produced water usually is composed of natural formation water and flowback water. Flowback water is water that was a large component of fracturing fluids injected into a well at high pressure as a part of the hydraulic-fracturing treatment. Within a few hours to a few weeks after the fracturing job is completed, a portion of the injected water returns to the surface. It typically contains much higher levels of chemical constituents, including TDS, than the original fracturing fluid did.
The amount of produced water, and the chemical constituents (i.e., anions and cations) and their concentrations present in the produced water, usually varies significantly over the lifetime of a field. Early in the process, the water-generation rate can be a small fraction of the oil-production rate, but it can increase with time to tens of times the rate of oil produced. Compositionally, the changes are complex and field-specific because they are a function of formation mineralogy, oil and water (both in-situ and injected) chemistry, rock/fluid interactions, type of production, and the required additives for oil-production-related activities.
To reuse the high-TDS produced water as a base fluid for formulating crosslinked-gel-based fracturing fluids, the water must first be treated to remove ions that hinder the development of crosslinked fluid or that cause scale buildup in the wellbore. An ideal solution would be to reuse the high-TDS produced water in subsequent fracturing treatment with no treatment or fit-for-purpose treatment.
The papers featured this month deal with a fit-for-purpose treatment of produced water, a new guar-based system that allows the use of 100% produced water without treatment as a base fluid, and produced-water reinjection. I hope you enjoy reading the selected papers and search for additional papers in the OnePetro online library.
SPE 175206 Produced-Water Injection—The Challenges Faced by N. Bhola, Jorin, et al.
SPE 177067 The Integrated Approach to Formation-Water Management Part 2: Field Applications and Best Practices by R. Correa, AGIP Oil Ecuador, et al.
SPE 181588 Reuse of Produced Water by Membranes for Enhanced Oil Recovery by Remya Ravindran Nair, University of Stavanger, et al.
Syed A. Ali, SPE, Consultant
01 December 2016