Reuse of wastewater from hydraulic fracturing (flowback and produced water) is a sustainable option for wastewater management practice in unconventional oil and gas fields. Reuse reduces fresh water demand but also lowers the environmental footprint by reducing the storage and transportation of both fresh and wastewater. A successful reuse practice requires a thorough understanding of both the quantity and quality of the wastewater, and more importantly, its potential impacts on well

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... . In the first part of this study, wastewater production models were developed for horizontal shale wells in Wattenberg field .In addition, a solid characterization and distribution analysis on wells fractured with fresh and recycled water was performed to understand their impacts on wastewater quality. The second part of this study focuses on understanding the mechanisms of low salinity waterflood (LSF) in unconventional shale wells, and how oil recovery is impacted by the total dissolved solids (TDS) of the recycled brine. Results from the studies above are summarized in Chapter 4 through Chapter 7. A framework for water production prediction was developed in Chapter 4. Water production models were developed with Arps equation for horizontal wells from five fields in Wattenberg field. For a better data fitting and modeling, three time periods were defined: Frac flowback, transition period and produced water. The frac flowback period is the first one month after production starts, followed with 5 months of the transition period and, thereafter, produced Chapter 7 investigates two of the fundamental mechanisms of LSF, clay swelling and diffused double layer (DDL) expansion. Both mechanisms are impacted by the salinity/total dissolved solids (TDS) concentration of the injection water. To test these mechanisms, clay swelling tests and real-time contact angle measurements were performed in this study. Spontaneous imbibition was also conducted, with Niobrara shale core plugs from Denver-Julesburg Basin, to compare oil recovery from low salinity and high salinity brine. Results show an increase in oil recovery when the TDS of brine falls between 400 and 10,000 mg/L. These results also indicate that LSF improves oil recovery from unconventional shale formation, and therefore, an optimal TDS concentration exists for highest oil recovery. v TABLE OF CONTENTS ABSTRACT .