Field-Proven Removal of Dissolved Hydrocarbons from Offshore Produced Water by the Macro Porous Polymer-Extraction Technology
Authors: Meijer D.Th. , Kuijvenhoven C.A.T. 
Published: October 2008

At the moment there are no field proven technologies available to remove dissolved hydrocarbons (aliphatics and mainly aromatics) from produced water on offshore platforms. Following a joined study of the NOGEPA (The Netherlands Oil and Gas Exploration and Production Association) and the Dutch Government, the Macro Porous Polymer Extraction (MPPE) technology was selected from 55 technologies as one of the most promising one. The MPPE process is removing the aromatics and aliphatics by an extraction process with the extraction liquid immobilized in the MPP particles. The MPPE particles can be regenerated in situ. The NAM Business unit Offshore and Akzo Nobel MPP Systems performed a successful 4 months full-scale field trial with the MPPE technology on the L2 gas platform (50% unmanned) in the North Sea. The main objective was to prove that the MPPE technology could obtain a separation efficiency of &gt;90% for aromatics and that it was robust and reliable to operate under Offshore North Sea winter conditions. The MPPE demo unit size with steam generator was restricted to fit into a standard 15 feet container treating produced water (2.7 m3 /h max flow platform), consisting of mainly equilibrium water and condensed overhead vapours from the glycol regeneration. This small unit realized removal efficiencies of 95 to 99,6% in aromatics with influent concentrations up to 200 mg/l. Aliphatics (2-4 mg/l) and poly aromatics (7 ?g/l) were very low and close to detection limits of used analytical equipment so that for these components only 50 to 75% removal could be observed. (Current commercial units and field tests show that &gt;99% removal efficiencies can be obtained). The effect of an unexpected surfactant spill on the removal performance was negligible. The availability was 95% due to minor mechanical problems in the steam generator and including downtime due to handling and unmanned periods. Potable water consumption for steam generation was 3.5 kg/m3 treated effluent water. Initially preventive prefiltration showed filter lifetimes from 1 to 2 months. A 6 weeks operation period without prefiltration did not lead to a pressure drop increase over the MPPE bed.

The remote control facility with laptop and mobile telephone appeared to be a cost efficient and operationally effective tool, enabling quick response, remote shut down/start up and adaptations of process conditions.

Introduction

Figure 1: Internal structure of the Macro Porous Polymer(available in full paper)

During the production of gas and condensate, water is coproduced in significant amounts. When producing gas offshore, this produced water normally is discharged into the sea. To minimize possible negative impact on the environment, maximum concentration limits have been defined for components, which may be present in the disposed water. In the Dutch sector of the North Sea the governmenthas restricted the amount of aliphatic (dispersed) hydrocarbons in produced water discharged into the sea: the monthlyaverage should remain below 40 mg/l.