Choosing Produced Water Treatment Technologies Based on Environmental Impact Reduction

Abstract

Abstract Reduced environmental impact should be the goal when choosing produced water treatment technologies. On the Norwegian sector the method used for quantifying this impact is the Environmental Impact Factor, EIF. This method is computerized in a tool that calculates the environmental impact from each of a number of chemical component groups that are present in produced water. Reinjection of produced water is obviously an option that should be considered if the reservoir needs pressure support. This paper, however, describes four new treatment technologies aimed at produced water being released to sea. The technologies are suitable for different produced water compositions. The four technologies described are the PECT-F (Performance enhancing coalescence technology) for enhanced removal of dispersed oil, the MPPE (Macro Porous Polymer Extraction) technology for removal of volatile aromatics, the CTour technology for the removal of heavy aromatics and alkylated phenols, and the Framopure C100 injection system for H2S scavenger. The potential of these technologies has been illustrated by choosing typical produced water compositions where one of these technologies has a significant potential to reduce the environmental impact. Given an estimated efficiency of these technologies, the EIF is calculated before and after applying the technology to show the reduced environmental impact obtained. The main conclusion is that knowledge is needed about which compounds contribute to the environmental impact of produced water before deciding which technology to use. Results are also presented that correlate the content of dispersed oil and PAH (poly aromatic hydrocarbons). Introduction The main focus in reducing the possible pollution from produced water to the sea has traditionally been on reducing the content of dispersed oil. Even though some countries have placed their attention on other compounds, international regulations like the new OSPAR regulations [1] still focus mainly on dispersed oil content in produced water. On the Norwegian sector of the North Sea, all operators must, in addition to fulfilling and reporting according to the dispersed oil regulations, report the total environmental impact of the produced water release to the sea to the Norwegian pollution authorities (SFT) [2]. This reporting is done on an annual basis and is based on thorough (GC-MS) analysis of the produced water to quantify the content of all compounds of interest. The method for quantifying the environmental impact is the Environmental Impact Factor, EIF [3], which relies on DREAM (Dose Related Risk and Effect Assessment Model) [4]. In this model a comparison is made between the concentrations of possible environmentally harmful compounds and the predicted no effect concentration, based on an environmental risk assessment approach. The compounds of interest are: PAH, NPD (naphthalenes, phenanthrenes and dibenzo-thiophenes), BTEX (Benzene, Toluene, Ethylbenzene and Xylene), phenol, alkylated phenols, metals, and added chemicals. The later being substances such as: production chemicals, corrosion-, scale-, and hydrate-inhibitors, separation chemicals, and H2S scavenger. The EIF is not only a valuable tool for quantifying the total environmental impact from one platform or a group of them, but also for evaluating the contribution from the different constituents in the produced water. The compositions of produced water from different fields vary significantly. Hence, each field should be evaluated with respect to which compounds contribute to the environmental risk. When selecting produced water treatment technologies, one should focus on the major contributors to reduce the total environmental impact. Experience has shown that the major contributors to the EIF are dispersed oil, volatile aromatics, heavy aromatics, alkylated phenols, and added chemicals.