Sustainability Driven Produced Water Treatment Technology Solution at Nano-Scale

Abstract Treatment and disposal costs of produced water from oil and gas operations remain the primary concern with the ongoing global push toward the transition to cleaner energy and Zero Liquid Discharge (ZLD). Gas floatation utilizing micro-size bubbles is commonly used in produced water treatment. However micro-size bubbles are not effective in removing dissolved oil (such as Benzene, Toluene, Ethyl-benzene, and Xylene) and usually require chemical pre-treatment to remove the emulsified oil. This paper aims to present the challenges, and lessons learned from produced water treatment technologies as well as recent technology development in nano-bubble floatation technology with a concept select study of pilot deployment at one of the terminals in Malaysia. First, state-of-the-art analysis of existing gas floatation technology to treat produced water is presented. From the analysis, the failures and lesson-learned from the technology implementations are identified. To improve the efficiency of gas floatation technology, the effects of reducing the micro-sized bubble to a nano-sized bubble, bubble concentration, and type of gas have been evaluated. Subsequently, several improvements are developed and tested to overcome existing gas floatation technology. The pilot application of this developed technology at one of the crude oil terminals in Malaysia, which include a feasibility study, concept selection and engineering of this technology is described as a case study. The typical gas floatation system is much less efficient in produced water where dissolved oil fraction is high and, in the presence of the fines solid. As a result, the required oil in water separation is not met leading to disposal limit compliance issues and the poor recovery of hydrocarbon in produced water. Changing operating envelope over time i.e., reduced production, increased water cut, and fines sand production, affects gas floatation efficiency over time. It is also not cost-effective to produce large volumes of microbubbles that are smaller than oil droplets. From our analysis, a significant improvement in oil-in-water (OIW) removal is achieved by controlling the bubble size, gas type, and bubble concentrations via a nano-bubble floatation unit. This technology successfully maintains the less than 10ppm OIW target removal and a further reduction in the required treatment stages and chemical consumption. The system is a promising technology for brown and green facilities, wet or dry terminals, or even for downhole applications to increase oil recovery. New design elements are proposed to increase separation efficiency under erratic multiphase-flow conditions, increased water cuts, and the presence of fine particles. Testing results of the compact, low-energy, high reliable nanoscale gas floatation system are presented and are a promising technology for both aging and new facilities.