Multiphase flow and nonaqueous phase liquids

Multiphase flow and nonaqueous phase liquids

1. 1 Multiphase Flow and Nonaqueous Phase Liquids IWRE412 Lecture No. 4

2. 2 Outline Non-aqueous Phase Liquids (NAPLs) Relative permeability of immiscible liquids Flow in a three-phase system

3. 3 Types of NAPLs DNAPL s: Immiscible fluids that are denser than water are called D ense N on A queous P hase L iquids Chlorinated hydrocarbons i.e. perchloroethylene , trichloroethylene (TCE), 1,1,1-trichloromethane, coal tar, creosote, pentachlorophenol LNAPL s: Immiscible fluids that are lighter than water are called L ight N on A queous P hase L iquids Gasoline, diesel fuel, pentachlorophenol dissolved in a carrier

4. Definitions NAPL -“Non-Aqueous Phase Liquid.” liquid that does not become a solution in water but rather floats on it, or sinks in it. Oil is a NAPL LNAPL - “Light Non-Aqueous Phase Liquid.”  It means a NAPL that is lighter than water, and therefore will float.  4

5. Definitions LNAPLs possess low levels of solubility When the amount present at the water surface is greater than the amount that can dissolve into the water, we get a free phase product lying on the water  5

6. 6 DNAPLs (Dense Liquids)

7. 7 LNAPLs – (Light Liquids)

8. 8 Environmental effects

9. 9 Saturation Ratio The fraction of the total voids occupied by the fluid of interest The sum of the saturation ratios of all the pore fluids including air will be equal to 1.0

10. 10 Wettability If the contact angle measured through the denser liquid is < 90 degrees, the liquid can wet the solid surface Water on glass In oil-water system, water will tend to preferentially wet the solid surface If the surface is dry and the oil comes into contact with the surface first, then it will become oil wet even in the presence of water Rain falling on a waxed car will bead rather than wet!

11. 11 Capillary pressure in an immiscible system P c = capillary pressure P nw = pressure of the non-wetting fluid P w = pressure of the wetting fluid

12. 12 Fluid Saturation States Water-wet vs. Oil-wet The cross-sectional area of pore space available for each fluid phase is less than the total void space Relative permeability exists for both wetting and non-wetting phase

13. 13 Medium Sand Air and water vs . Trichloroethylene (TCE) and water

14. 14 Fine Sand Air and water vs. TCE and water

15. 15 Relative permeability curves for water in the presence of TCE The nw-curve was obtained by injecting water into a medium initially saturated with TCE The w-curve was obtained by injecting TCE into a medium initially saturated with water

16. 16 k r-water vs. K r-TCE

17. 17 Relative permeability in a three-phase system Step 1: Obtain the relative permeability of water (k rw ) as a function of saturation ratio of water (S w ) in a water-nonaqueous phase system Step 2: Obtain the relative permeability of air (k ra ) as a function of the saturation ratio of air (S a ) in an air-nonaqueous phase system Step 3: Calculate the relative permeability of the nonaqueous phase liquid (k rn ) in the three-phase system using the following equation

18. 18 Relative permeability of a air-water-nonaqueous phase system = the k r of the nonaqueous phase at the residual saturation of water in a water-nonaqueous phase system = the k r of the nonaqueous phase system as a function of S w = the k r of the nonaqueous phase in an air-nonaqueous phase system as a function of S a

19. 19 Ternary diagram for k r-NAPL in an air-water-NAPL system Water is the wetting fluid Vadose zone

20. 20 Force vectors in multiphase flow Ground water is moving horizontally Gravitational force is vertically down LNAPLs will tend to rise due to buoyancy DNAPLs will tend to move downward

21. 21 Summary The relative permeability of fluids in a multiphase system is complex “Who came first?” plays a major role in subsequent fluid flow The capillary pressure will depend on the hysteresis effects The density and the immiscibility of the fluid plays a major role in flow processes

22. 22 Quantifying LNAPL

23. 23 Quantifying LNAPL Outline Migration of LNAPLs Partitioning of LNAPLs Quantifying LNAPLs

24. 24 Downward flow of Oil

25. 25 Subsurface distribution of LNAPL

26. 26 Volatilization of NAPLs NAPLs in the vadose zone can partition between: Vapour phase within the pore air Dissolved phase within the pore water Dissolved phase will come out of solution after migrating to non-contaminated areas

27. 27 Raolt’s Law P a = Vapour pressure of a component of NAPL mixture above the mixture x a = Mole fraction of the NAPL component P a n = Vapour pressure of the NAPL component in pure-phase form

28. 28 Vapour pressure of a component P = pressure V = volume M = mass R = ideal gas constant (0.08206 atm-L/mol-K) K = temperature in Kelvin degrees f w = molecular weight

29. 29 Concentration of a component M/V = concentration of the component

30. 30 Distribution of mobile oil and water

31. 31 Thickness of a floating LNAPL LNAPL is immobile above the capillary zone where the concentration is < S r-LNAPL LNAPL will be mobile when (S LNAPL + S w ) = 1.0, positive pressure exists S LNAPL > S r-LNAPL LNAPL will begin to flow into the monitoring well to the water table which is, initially, below the mobile LNAPL zone The LNAPL will push the water table down due to its weight and appear to be thicker This effect is greater for thin zones of LNAPL having thicker capillary zone

32. 32 Calculating the thickness of oil Pressure on either side of the oil-water interface is equal (neglecting capillary effects of the well) Based on the oil thickness in the monitoring well, the recoverable oil can be calculated

33. 33 Summary LNAPL will freely flow into the well only if it is under positive pressure The thickness of LNAPL in the well will be much greater than the actual thickness of the floating LNAPL Know how to quantify the LNAPL content