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The solvent & surfactant model

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Reservoir Simulation for Enhanced Oil Recovery
The solvent & surfactant model
(Eclipse Manual)

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The solvent & surfactant model

  1. 1. Prepared by: Group 5 The Solvent & Surfactant Models KhaledAl Shater Mohamed Sherif Mahrous Ramez Maher Aziz Ahmed Kamal Khalil George Ashraf HazemAL Nazer Hameda Abd-Elmawla Mahdi
  2. 2. Agenda  Introduction  The Solvent Model  Objectives of the Solvent Model  Applications of the Solvent Model  Todd & Longstaff Model  DataTreatment for Using the Solvent Model  The Surfactant Model  Introduction & Application  Surfactant Distribution  DataTreatment for Using the Surfactant Model
  3. 3. Introduction Flooding Miscible The Solvent Model Immiscible The Surfactant Model
  4. 4. The Solvent Model The Solvent Model
  5. 5. Objectives of the Solvent Model  The aim of this chapter is to enable modeling of reservoir recovery mechanisms in which injected fluids are miscible with the hydrocarbons in the reservoir.  A miscible displacement has the advantage over immiscible displacements such as water flooding, of enabling very high recoveries.An area swept by a miscible fluid typically leaves a very small residual oil saturation.  The ECLIPSE solvent extension allows you to model gas injection projects without going to the complexity and expense of using a compositional model  In Eclipse, the solvent extension implements theTodd and Longstaff empirical model for miscible floods.
  6. 6. Applications of the Solvent Model  The solvent model is used in any scheme in which the aim is to enhance the reservoir sweep by using a miscible injection fluid. Examples of solvent schemes are listed below: 1. High pressure dry gas processes, in which miscible flow conditions between the gas and the oil are found at the gas-oil contact . 2. A solvent such as LPG or propane may be injected as a‘slug’ to be followed by an extended period of lean gas injection.The slug fluid is miscible with both the gas and oil. 3. Certain non-hydrocarbon gases such as carbon dioxide produce miscible displacement of oil at pressures above a threshold value. 4. All-liquid miscible displacements by fluids such as alcohol, normally injected as a slug between the in-place oil and the injected chase water.
  7. 7. Todd & Longstaff Model  In Eclipse, the solvent extension implements theTodd and Longstaff empirical model for miscible floods.  The model classifies the reservoir into 3 possible miscibility combinations: 1. In regions of the reservoir containing only solvent and reservoir oil (possibly containing dissolved gas) the solvent and reservoir oil components are assumed to be miscible in all proportions and consequently only one hydrocarbon phase exists in the reservoir.The relative permeability requirements of the model are those for a two phase system (water/hydrocarbon). 2. In regions of the reservoir containing only oil and reservoir gas, the gas and oil components will be immiscible and will behave in a traditional black oil manner. 3. In regions containing both dry gas and solvent, an intermediate behavior is assumed to occur, resulting in an immiscible/miscible transition region.
  8. 8. Todd & Longstaff Mixing Parameter ω  The model introduces an empirical parameter, ω, whose value lies between 0 and 1, to represent the size of the dispersed zone in each grid cell.The value of ω thus controls the degree of fluid mixing within each grid cell.  A value of ω = 1 models the case when the size of the dispersed zone is much greater than a typical grid cell size and the hydrocarbon components can be considered to be fully mixed in each cell.  A value of ω = 0 models the effect of a negligibly thin dispersed zone between the gas and oil components, and the miscible components should then have the viscosity and density values of the pure components. In practical applications an intermediate value of ω would be needed to model incomplete mixing of the miscible components.  An intermediate value of ω results in a continuous solvent saturation increase behind the solvent front.Todd and Longstaff accounted for the effects of viscous fingering in 2D studies by setting ω = 2 /3 independently of mobility ratio. For field scale simulations they suggested setting ω = 1 /3 . However, in general history matching applications, the mixing parameter may be regarded as a useful history matching variable to account for any reservoir process inadequately modeled.
  9. 9. Data Treatment for Using the Solvent Model  The main differences between using the black oil simulator without the solvent model and using it with the solvent model are: i. Phases present. ii. Relative permeability data treatment. iii. PVT data treatment.
  10. 10. I. Phases Present  To initiate the Solvent model, the following keywords must be added to RUNSPEC section:
  11. 11. II. Relative Permeability Data Treatment Relative permeability data treatment depends on whether the displacement in the grids concerned is: 1. Fully miscible 2. Fully immiscible 3. Transition between miscible and immiscible regimes
  12. 12. 1. In case of fully miscible: In regions where solvent is displacing oil and the reservoir gas saturation is small, the hydrocarbon displacement is miscible. However, the 2-phase character of the water/hydrocarbon displacement needs to be taken into account.The relative permeabilities are given by:
  13. 13. 2. In case of fully immiscible: In the usual black-oil model the relative permeabilities for the 3 phases water, oil and gas are specified as follows:
  14. 14. 2. In case of fully Immiscible: When two gas components are present, the assumption is made that the total relative permeability of the gas phase is a function of the total gas saturation, Then the relative permeability of either gas component is taken as a function of the local solvent fraction within the gas phase,
  15. 15. 3. In case of Transition between miscible and immiscible: The transition algorithm has two steps: 1. Scale the relative permeability end points by the miscibility function. For example, the residual oil saturation is 2. Calculate the miscible and immiscible relative permeabilities, scaling for the new end points.Then the relative permeability is again an interpolation between the two using the miscibility function:
  16. 16. III. PVT Data Treatment The PVT data treatment is made for: 1. Viscosity 2. Density
  17. 17. 1. Viscosity data treatment: The following form is suggested byTodd and Longstaff for the effective oil and solvent viscosities to be used in an immiscible simulator.
  18. 18. 1. Viscosity data treatment: The mixture viscosities μmos , μmsg and μum are defined using the 1/4th-power fluid mixing rule, as follows:
  19. 19. 2. Density data treatment: The effective oil and solvent densities (ρo eff , ρs eff , ρg eff ) are now computed from the effective saturation fractions and the pure component densities (ρo , ρs , ρg ) using the following formulae:
  20. 20. 2. Density data treatment: The effective saturation fractions are calculated from:
  21. 21. The Surfactant Model The Surfactant Model
  22. 22. Introduction & Application  Most large oil fields are now produced with water-flooding to increase recovery oil, but there’s a large volume of unrecovered oil.  The remaining oil can be divided into two classes: o Residual oil to the water flood o Oil bypassed by the water flood  A surfactant flood is a tertiary recovery mechanism aimed at reducing the residual oil saturation in water swept zones
  23. 23.  The oil becomes immobile because of the surface tension between oil and water; the water pressure alone is unable to overcome the high capillary pressure required to move oil out of very small pore volumes.  A surfactant reduces the surface tension, hence reduces capillary pressure and allows water to displace extra oil. Introduction & Application
  24. 24. The surfactant Model  To modelThe surfactant, we need to calculate:  Its distribution at each grid block  Its effect on:  Water PVT data (Viscosity of water-surfactant mixture).  SCAL data (Capillary pressure, Relative permeability,Wettability).
  25. 25. Surfactant Distribution  The surfactant is assumed to exist only in the water phase not as a separate phase.  The user inputs the concentration of surfactant in the injection stream of each well.  The distribution of injected surfactant is modeled by solving a conservation equation for surfactant within the water phase.
  26. 26. Water PVT properties  The surfactant modifies the viscosity of the pure or salted water.  The surfactant viscosity is inputted as a function of surfactant concentration.  The water-surfactant solution viscosity calculated by:
  27. 27. Water PVT properties  If the Brine option is active, it’s calculated as:  Where:
  28. 28. SCAL data  The Surfactant effects various SCAL data like: Capillary pressure, Relative permeability,Wettability  To Study its effect we need to input tables of water-oil surface tension as a function of surfactant concentration in the water using (keyword SURFACT)
  29. 29. Calculation of the capillary number  The capillary number the ratio of viscous forces to capillary forces.The capillary number is calculated by:
  30. 30. The Relative Permeability model  The Relative Permeability model is essentially a transition from immiscible relative permeability curves at low capillary number to miscible relative permeability curves at high capillary number.You supply a table that describes the transition as a function of log10(capillary number).  The relative permeability used at a value of the miscibility function between the two extremes
  31. 31. The Relative Permeability model
  32. 32. Capillary pressure  The water oil capillary pressure will reduce as the concentration of surfactant increases and hence decreases the residual oil saturation.  The oil water capillary pressure is calculated by:
  33. 33. Treatment of adsorption  The tendency of the surfactant to be adsorbed by the rock will influence the success or failure of a surfactant flood  If the adsorption is too high, then large quantities of surfactant will be required to produce a small quantity of additional oil.  The quantity adsorbed is a function of the surrounding surfactant concentration.  To model it,The user is required to supply an adsorption isotherm as a function of surfactant concentration
  34. 34. Treatment of adsorption  The quantity of surfactant adsorbed on to the rock is given by: Matrix density
  35. 35. List of References: 1. EclipseTechnical Description Manuel, Chapters 62 & 64. 2. Todd, M.R. Longstaff,W.J, 1972. The Development,Testing, and Application Of a Numerical Simulator for Predicting Miscible Flood Performance. J. Pet.Technol, 24(6): 874-882
  36. 36. Thank You