Meeting the Zero Discharge Challenge for Produced Water

Abstract

Reduced environmental impact is 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. Re-injection of produced water is the preferred option, and mostly used when pressure support is required. This paper, however, describes new treatment technologies aimed at produced water being released to sea. The technologies are suitable for different produced water compositions. The components in the produced water that contribute to the environmental impact are mainly: aliphatic hydrocarbons, heavy aromatic compounds (PAH), alkylated phenols and man added production chemicals. At several Statoil operated fields the corrosion inhibitor and H2S scavenger are giving a significant contribution. Several new technologies will be described. Statoil has had a leading role and actively participated in the development and qualification of most of these technologies. The results from this work will be presented. The technologies will include the CTour process, Epcon CFU, droplet coalescing technologies as well as new technologies to reduce discharge of production chemicals. 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. 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. The new OSPAR regulations demanding less than 30 mg/l dispersed oil, and a 15 % reduction in total oil from year 2000 level will be implemented by 2006. 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 Control 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 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. In this paper three different technologies for produced water purification will be presented. The CTour process that is a liquid-liquid extraction process, the Epcon Compact Flotation Unit and Mare's Tail that is an oil droplet coalescer. In addition to these three technologies measures to reduce the environmental impact from production chemicals will be presented. Produced Water Purification Processes 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.

Review of technologies for oil and gas produced water treatment

“…In three sets of field trials conducted with the C-TOUR process, removal efficiency of dispersed oil, 2-3 ring PAHs, and NPD was 70%, for C 6 , and for C 6 phenols approximately 60%, and for C4-C5 phenols 20% [49].…”

Produced Water from Oil-Gas Plants: A Short Review on Challenges and Opportunities

“…The Epcon compact floatation unit is a vertical three phase separator cyclone which is capable of separating the oil, gas and water phases with separation efficiency of from 50 % up to 70 % for dispersed oil content of PW [13]. …”

Membrane operations for produced water treatment

“…The extraction of heavy hydrocarbons using light hydrocarbons has been used by some oil producers to remove the dissolved organics from the produced water [20]. Adsorption is another widely used technique for the removal of soluble organics [21].…”