Sustainable Approach of Turning Oily Produced Water into Slickwater for Unconventional Reservoir Development

Abstract

Abstract Produced water (PW) is generated in a large amount worldwide and has complex compositions. PW treatment is required to meet environmental regulations as well as reuse and recycling of PW. Meanwhile, plenty of water is needed for slickwater fracturing applications during unconventional reservoir development. This study aims to find effective ways to treat PW and formulate it into slickwater for fracturing operations to save fresh water and improve water sustainability. A synthetic high salinity oily produced water with overall salinity of more than 100,000 ppm was used. Searching effective chemicals and optimizing their dosages for PW treatment were based on measurements of oil-water separation time, floc volume and transmission intensity using stability analyzer which allows a step-by-step vertical scanning of dispersions. After treatment, PW was used to prepare slickwater. Hydration time and viscosity of selected dry friction reducer (DFR) in the PW were measured by rheometer, and friction reduction performance of the slickwater was evaluated by a standard friction flow loop system. The developed chemicals are efficient and economical for the PW treatment with short oil-water separation time, high oil removal efficiency, and low chemical dosage. Floc formed quickly and separated from the water phase in several minutes after chemical addition and clear bottom phase was observed. The oil content was reduced to less than 20ppm and total suspended solid was reduced by 80% within 10 minutes with the addition of 30ppm chemical. DFRs for unconventional reservoir development are selected in this work because of simple logistic handling under harsh environmental conditions comparing to liquid and emulsified friction reducers. An optimized DFR formulation which was compatible with treated PW was developed. The DFR was able to totally dissolve in PW in 1 minute. The viscosity of DFR in treated PW at different temperatures was almost same as that of solution prepared using synthetic brine. The friction reduction can reach up to 75% in less than 2 minutes. This indicates that the PW after treatment is applicable for either re-injection or reuse as base water for slickwater fracturing. This work provides the insight of oily produced water treatment by chemical method for slickwater fracturing. This significantly alleviates oilfield produced water discharge and improves water sustainability by saving large volume of fresh water for unconventional reservoir development.