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Numerical Study of Bottom Water Draw-Off of Stratified Oil-Water Pipe Flow Department of Mechanical and Industrial Engineering College of Engineering Sultan Qaboos University, Oman Yousef Zurigat Bssam Jubran Lyes Khezzar Salam Al-Far

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Plan zIntroduction & Objectives yOil-water Transport & dehydration issues zSimulation Model zResults zConclusions

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Water issues in Oil-Production zWell life extension results in increased water Production (98%) zNeed to separate water from oil (dehydration facilities cost money) zPre-separation may take place in transport pipelines zCan we take advantage of it?

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Concept of Bottom Water Draw Off zDepending upon prevailing conditions a water layer may form at the bottom of the pipe. zIt can then be selectively removed.

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Design Challenge of BWDO Concept zWhat is the maximum water flow rate that can be drawn off ( With Acceptable quality )? zHow can disturbance of the water/oil-in-water- dispersion interface be avoided? zIf several draw-off points are used, how will the interface and flow regimes in between draw points be affected?

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Objectives For a single draw-off pipe, investigate the variation of oil concentration in the draw-off pipe as a function of draw-off flow rate and interface position.(Interface location not known a priori!!) Investigate the maximum possible water flow rates with acceptable quality (oil concentration) for two consecutive draw-off pipes.

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Flow Regimes of Oil-Water Mixtures zDepending upon the oil superficial velocity several regimes are possible for horizontal water dominated flows:

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Geometry and Flow Parameters zMain pipe Diameter = 0.68 m zDraw-Off Pipe Diameter = 0.240 m zOil-flow rate = 8049 m3/day zWater flow rate = 43614 m3/day zInterface Location 25 cm from bottom of main pipe. zSimulation conducted with one and two draw-off pipes

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Modelling challenges zFlow is complex and two-phase (dispersions present) zTwo Approaches: 1. Single-Phase Flow Modeling: If negligible slip between the phases and hold-up take place-- In the present regime!! (water- cut=85%, water superficial velocity=1.3 m/s)! 2. Two-Fluid Flow Modeling: Actual Flow

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Mathematical Model SINGLE-PHASE FLOW MODEL zSteady, Single-phase, incompressible and turbulent flow. zPressure drop approaches that of single phase flow zFlow dynamics very similar to single phase flow zFull three-D simulation

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Quantitative analysis of draw-off water quality-Single : Phase Flow Model xInitial oil concentrations in the pipe regions above and below the interface are based on experimental data. The concentration of oil in free water assumed equal to 600 ppm in accordance with field data. xThe amounts of oil in the areas above- and below-the- interface streams which make up the draw-off flow are calculated based on the flow rates and the concentrations calculated in the first step above.

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Cut-off flow rates with water quality <2000 ppm from two tappings

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Two-Fluid Modeling zIn the PHOENICS, the concept of thermo- dynamic phase is used, i.e., the water and oil are treated as two different phases in the mixture. These two phases are in motion relative to each other due to the buoyancy effect, which leads to inter-phase momentum transfer. zThe Inter-Phase Slip Algorithm (IPSA) is adopted to predict the phenomenon in this work.

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Phase equations zEach phase is regarded as having its own distinct velocity components. zPhase velocities are linked by interphase momentum transfer - droplet drag, film surface friction etc. zEach phase may have its own temperature, enthalpy, and mass fraction of chemical species. zPhase concentrations are linked by interphase mass transfer.

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Phase equations (Cont.) ttime R i volume fraction of phase i i density of phase i i any conserved property of phase i velocity vector of phase i i exchange coefficient of the entity in phase i S i source rate of i

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Results

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Results (Cont.)

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Pipe 1Pipe 2

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Results (Cont.) y

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Acknowledgements PDOs FUNDING OF THIS WORK IS GRATEFULLY ACKNOWLEDGED

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