A novel use of drag reducing polymers as flow pattern modifiers in oil/water flow

Extensive studies on adding very small amounts of polymer (in parts-per-million) in single phase flows have reported a significant reduction in frictional drag which is manifested as a decrease in the pressure drop for a given flow rate or vice versa. Drag-reducing polymers are long-chain, ultra-high molecular weight polymers. The effectiveness of a drag reducer is normally expressed in terms of percent drag reduction. Since the discovery of such an effect by Tom in 1948, the technology found wide applications in reducing pumping costs in oil pipelines. The first commercial application of drag reduction technology in a crude oil pipeline was the Trans Alaska Pipeline System (TAPS) during 1979. Drag reduction of 21% and flow increase of 20% were achieved with the addition of only 10 ppm of polymer. Although the mechanism by which drag reducing polymers increase the pumpability of a fluid is not well understood, the successful application of this technology in TAPS has triggered a wider application in the oil industry in both production and transportation operations. Recently, some studies on using the drag reducing polymers in multiphase flow have also reported significant pressure drop for a given flow rate. This is induced from modulation of the turbulent properties of the phase with the additive and from changes in flow pattern. Zhang et al. (2005) reported the application of drag-reducing polymer (DRP) in ethylene glycol/water mixtures used as heating media in the Gullfacks Southfield. A 50% increase in the flow rate of the heating medium was achieved. In addition to the increase in flow rate and the decrease in pumping cost, a change in flow patterns was observed as a result of adding small amount of polymers to multiphase flow. Al-Wahaibi and Angeli (2007) have shown that flow patterns such as slug flow would change to stratified flow after injecting small amount of polymers. This favorable change in flow pattern can be utilized as a technology to enhance the separation efficiency of existing oil separators. The DRP can be injected upstream the separator to change the flow to stratified regime, hence, inducing phase segregation. Consequently, these segregated phases would need less retention time in the separator. Also, this flow regime would have less amount of emulsion to process. Oman is an oil-producing country with unfortunately large amounts of water produced along with oil (approx. 6-8 barrels of water per a barrel of oil) with an increasing trend for the future since more oil fields are becoming mature. Knowing that this production is from many small, scattered fields over a large area, this requires very long network of pipelines for transportation, large pumping costs, and efficient oil separators. It was the objective of the investigators proposing the project in hand to study how the implementation of the DRP technology would contribute to lowering unit cost of oil in Oman through improving pumpability and optimizing the separation facilities. We believe that funding such a project will not only find its fruits through technology implementation, but it would also contribute largely to reviving the scientific research activities in Oman under the leadership of his majesty Sultan Qaboos. The proposed project can be considered as a stepping stone towards having local expertise in the DRP technology and a state of art multiphase flow loop at Sultan Qaboos University. The proposed study necessitate a modification of the oil-water flow loop currently available in Sultan Qaboos University in order to study the flow at different inclination angles and different pipe diameters. New instrumentations such as a conductivity probe and an electrical resistance tomography will be needed to obtain an accurate identification of flow patterns. After the new flow loop is assembled, different commercial polymers will be objectively selected as DRPs for multiphase flow. The study will give special attention to the biopolymers for more environmentally friendly applications. Then, these polymers will be screened with respect to their drag reducing capabilities for the given flow patterns and solvent type. The effect of polymer chemistry, structure, molecular weight, charge type, charge density, mechanical stability, polymer concentrations on pressure drop and flow patterns will be investigated at different conditions of oil and water flow rates, inclination angles and pipe diameters. Different correlations between these different measureable parameters will be developed and guidelines for successful applications will be stated. This will act as a checklist for choosing the best alternative of polymers that can be used to get the optimum results for different oil-water flow conditions. The effect of the change of flow pattern to stratified regime on phase separation in the oil separators may also be investigated