Osmotic membrane pressure actuator

Abstract

This master thesis has focused on the membrane for the osmotic membrane pressure actuator (OMPA). The OMPA is an autonomous inflow control device for intended use in oil and gas wells. Its function is to prevent water from entering the well from the reservoir. This enables improved production and better reservoir management and also minimizes problems caused by produced water upstream. Extreme conditions of high temperature and pressure exist in the offshore reservoir. A commercial membrane material for the OMPA does not exist and a membrane must therefore be developed with excellent thermal, chemical and mechanical stability. Several other important factors have been identified in this thesis. A literature review was conducted to find suitable membrane materials for the OMPA. This focused on materials with glass transition temperatures of >200oC and some ceramic membranes. This list was shortened by cross-referencing with hydrophilic materials and literature regarding osmosis or nanofiltration and the materials. This completed list is presented in this thesis. Three commercially available membranes were received for the experimental. These were partially characterized with thermogravimetric analysis and differential scanning calorimetry. Successful permeation tests were performed on two of these membranes; RO98pHt® polyamide membrane (Alfa Laval) and DuraMem® 150 polyimide membrane (Evonik MET Ltd). Water flux and solute flux and rejection were performed in a reverse osmosis dead end cell at temperatures 23oC, 50oC and 70oC and sodium chloride and sucrose were used as solutes. The RO98pHt® showed increased flux and rejection with increasing temperatures. This was attributed to increased solubility and diffusion of the solvent in the membrane at elevated temperatures. The DuraMem® 150 had increased rejection with temperature whilst the flux remained fairly constant. This was attributed to the effects of compaction counteracting the increased solubility and diffusion. Of the solutes, sucrose had the highest rejection because of its larger size. It may therefore be interesting as a draw solution for use in the OMPA. Neither membrane is suitable for direct use with the OMPA. However, the polyimide material in the DuraMem® 150 membrane may be of interest if fabricated with a more desirable morphology. From the theory and discussion presented in the thesis, an updated list of OMPA membrane requirements was constructed with methods in which to attain these requirements. The dependence of several of the requirements upon one another suggests the need for more experimental data at conditions closer to the field conditions. As commercially available membranes are currently non-existent, fabrication of membrane materials is the next step and some necessary starting literature has been provided. Finally, a new forward osmosis/pressure retarded osmosis rig design has been suggested which allows tests to be conducted at reservoir conditions which more closely mimics the intended operation of the OMPA.