Using an osmotic membrane pressure actuator (OMPA) for enhanced oil and gas recovery – the concept

The concept by using an osmotic membrane pressure actuator (OMPA) to shut down a water producing branch of an oil or gas well is being investigated and has been described in the current article. The OMPA valve can be installed in a side-branch of the main well pipeline, where oil flows on the feed side of the membrane and a concentrated salt solution is kept in a chamber on the other side (draw side). Any water present in the oil will induce water permeation through the membrane in to the draw solution. This will cause a pressure increase on the permeate (draw) side and trigger the valve to shut down the water producing branch of the pipeline. There are several material challenges for the membrane when operating under harsh well conditions – some of which are discussed in this work. As a reference, a commercial forward osmosis (FO) membrane was tested in both FO and pressure retarded (PRO) process conditions for studying the relationship between membrane water flux and response time, and the influence of the oil/water feed flow rates. These experiments were used as a base case. A suitablemembrane water flux from these data was predicted to be in the range of 0.08 to 0.3 L/(m2·) hr at the given well conditions (180 bar, 165°C), given the response time for closing off the water producing branch was around one week. Two other membrane materials with properties more suitable to withstand the expected harsh well conditions were chosen for further investigations – some experimental results are reported here. These materials are polybenzimidazole (PBI) doped with LiCl, and a proprietary fluoropolymer. (The development of the fluoropolymer is still ongoing and will be reported separately.) Further, in order to choose the best suited salt for the draw solution in the permeate chamber of OMPA, the osmotic pressure of three salts were investigated by using the simulation tool OLI Analyzer. From this investigation, it could be concluded that the drawing salt solution to be used in OMPA should be chosen from salts with low osmotic pressure, such as a mixture of Na2SO4 with NaCl. In lab, however, where operating conditions are much lower pressures and temperatures, it is useful to choose a salt like MgCl2 which will produce a high osmotic pressure also at these experimental lab conditions – MgCL2 was thus chosen for the bench-scale experiments reported here to mimic osmotic pressure at well conditions. From the experimental results and the simulation results from the OLI Analyzer, a response time for the OMPA valve could be estimated. If successfully designed, the OMPA valve has a great potential for enhanced oil and gas recovery (EOR, EGR) by shutting off water producing branches while the main part of the oil/condensate well continues to produce.