Subsea Seawater Treatment and Injection - Performance Tests of Filtration Membrane Modules at Simulated Subsea Conditions

Abstract

The use of seawater treatment and injection to increase oil recovery is extensively practiced worldwide. Seawater can be treated at different levels to provide the required water quality compatible with the reservoir for pressure maintenance. In this respect, membrane technologies including ultrafiltration, nanofiltration and reverse osmosis can be used for fines, sulphates and salt removal respectively. The use of subsea treatment systems built on these filtration technologies is proposed as an alternative to bulky and heavy conventional topside systems. Subsea systems can eliminate the need for expensive floating facilities that often have space and weight restrictions. For a reliable operation of a subsea system it is required to verify the filtration membranes performance at water depths that can reach 3000 m (300 bar and 4°C). Laboratory tests of hollow fiber ultrafiltration (UF), spiral-wound nanofiltration (NF) and spiral-wound reverse osmosis (RO) membrane modules were performed at simulated deep-water conditions to assess their integrity and performance. A high-pressure dynamic testing system, with precision temperature and pressure control was built to enable accurate measurements. Short and long-term dynamic tests, including pressure cycling fatigue tests, were performed by operating membrane modules at the simulated subsea environment (300 bar and 4°C). Static tests were also performed to assess the impact of deep subsea conditions on membrane module structural integrity and membrane physical properties. The results indicate that the tested UF, NF, and RO membrane modules are promising for deep subsea applications. The mechanical integrity and membrane module performance were maintained within the predefined acceptable limits at both static and dynamic test conditions. These promising results are a big step towards the technical feasibility of using membrane technology for subsea seawater injection systems.