Desalination systems for the treatment of hypersaline produced water from unconventional oil and gas processes

Abstract

Conventional reserves has led to a boom in the use of hydraulic fracturing to recover oil and gas in North America. Among the most significant challenges associated with hydraulic fracturing is water resource management, as large quantities of water are both consumed and produced by the process. The management of produced water, the stream of water associated with a producing well, is particularly challenging as it can be hypersaline, with salinities as high as nine times seawater. Typical disposal strategies for produced water, such as deep well injection, can be unfeasible in many unconventional resource settings as a result of regulatory, environmental, and/or economic barriers. Consequently, on-site treatment and reuse-a part of which is desalination-has emerged as a strategy in many unconventional formations. However, although desalination systems are well understood in oceanographic and brackish groundwater contexts, their performance and design at significantly higher salinities is less well explored. In this thesis, this gap is addressed from the perspective of two major themes: energy consumption and scale formation, as these can be two of the most significant costs associated with operating high-salinity produced water desalination systems. Samples of produced water were obtained from three major formations, the Marcellus in Pennsylvania, the Permian in Texas, and the Maritimes in Nova Scotia, and abstracted to design-case samples for each location. A thermodynamic framework for analyzing high salinity desalination systems was developed, and traditional and emerging desalination technologies were modeled to assess the energetic performance of treating these high-salinity waters. A novel thermodynamic parameter, known as the equipartition factor, was developed and applied to several high-salinity desalination systems to understand the limits of energy efficiency under reasonable economic constraints. For emerging systems, novel hybridizations were analyzed which show the potential for improved performance. A model for predicting scale formation was developed and used to benchmark current pre-treatment practices. An improved pretreatment process was proposed that has the potential to cut chemical costs, significantly. Ultimately, the results of the thesis show that traditional seawater desalination rules of thumb do not apply: minimum and actual energy requirements of hypersaline desalination systems exceed their seawater counterparts by an order of magnitude, evaporative desalination systems are more efficient at high salinities than lower salinities, the scale-defined operating envelope can differ from formation to formation, and optimized, targeted pretreatment strategies have the potential to greatly reduce the cost of treatment. It is hoped that the results of this thesis will better inform future high-salinity desalination system development as well as current industrial practice.