In this paper we will discuss the factors that influence the strategy for produced water treatment and disposal. Various aspects of the produced water treatment plant will have an impact on the water quality achieved, for example operational parameters such as interface levels, differential pressure ratios, flowrates, pressures, temperatures, etc. The required specification for either discharge or reinjection is a key factor in determining the necessary process equipment and chemicals that are needed for the separation process. For injection, the water quality needed to be achieved are often more stringent as it has limitations on solids loadings and particle size as well as oil concentrations.
In this paper we will review a detailed case study that was conducted offshore in the UK North Sea. This site was struggling to achieve the water quality needed for reinjection. The work conducted quantified the key areas that were causing the process problems and explored options such as optimising existing separation equipment as well as maximising chemical efficiency.
The case study will highlight how the overall process performance was improved once the oily water separation challenges faced were identified and understood. Improved water quality was achieved by enhancing the chemical dose rates for one chemical and eliminating the use of another chemical as well as optimising several operating parameters for different parts of the treatment process. The overall work led to reduced operation costs and reduced production time whilst ultimately achieving water quality within the required specification without affecting the export oil quality.