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Laboratory Experiment No. 10 Surface and Interfacial Tension Measurements Objective: To determine surface and interfacial tensions by the du Nouy method. Theory: Attraction between molecules of a liquid at its surface is directed towards the bulk of the fluid. Since part of its surface is exposed to air, gas, or the liquid's vapor, it will try to conform to the smallest area possible as if it were surrounded by an invisible contractile membrane. The tension that is created at the surface interface it called the surface tension and is measured in dynes per cm. The interface between two liquids or a liquid and a solid is called the interfacial tension. It is a measure of the energy expended in trying to reduce the area of contact to a minimum. The du Nouy ring method will be used to determine these two tensions. Procedure, Surface Tension: The instrument has been calibrated prior to the experiment. Handle it with extreme care. 1. Attach the clean platinum-iridium ring to the hook on the end of the lever arm. Be sure the arrest mechanism is holding the arm. 2. Place the glass vessel containing the liquid to be tested onto the sample table. Move the sample table around until it is directly under the ring. 3. Raise the table until the ring is immersed into the test liquid. Be sure to submerge the entire ring in the fluid. About 1/8 inch of depth is usually sufficient. 4. Release the torsion arm and zero the instrument. Adjust the knob on the right side of the case until the index and its image are exactly in line with the reference mark on the mirror. Be sure that the ring remains in the liquid as you do this maneuver. 5. Turn the knob below the main dial on the front of the case until the vernier reads zero on the outer scale. 6. Lower the sample table until the ring is in the surface of the liquid. Adjust the knob on the right side of the case to keep the index lined up with the line on the mirror. As the surface of the liquid becomes distended, it is important to keep the reference mark lined up. 7. Continue these adjustments simultaneously until the film at the surface breaks. The scale reading at the point of breakage is the surface tension. 8. Repeat steps 2-7 on all of the unknown fluids that have been provided for you. Equations: Absolute surface tension (S) is given in terms of dial reading (P) and a correction factor (F) as: S = P X F Where the correction factor (F) is given as: 0.01452P 1.679r 0.5 F = 0.7250 + + 0.04534 C² (P) - Pu) R The terms are defined as: C = Circumference of the ring, 5.92 cm. R = Radius of the ring, cm. r = Radius of wire, cm. R/r = 53.0322 P = Dial reading (Apparent Surface Tension, dynes/cm) pi = Density of the lower phase, 1.0 gm/cc. pu = Density of the upper phase, 0.01237 gm/cc. Laboratory Experiment No. 11 Capillary Pressure by Desaturation Method Objective: To measure the capillary pressure of a core sample. Theory: The interface between two immiscible fluids, such S gas and liquid or liquid and liquid, has a tendency to form a curved surface, contacting the smallest possible area per unit volume. A pressure differential exists between the two fluids and is measured on opposite sides of the curved surface. The pressure on the concave side of the curved surface is greatest. In small, capillary openings, this pressure becomes significant and is known as "capillary pressure". The capillary pressure relationship between air/oil, gas/oil, oil/water, air/brine or air/water in a hydrocarbon reservoir is subject to exploration concern and they relate to the saturation history of the formation. Typically, a reservoir is initially filled with water and subsequently some portion of water is displaced by migrating oil. The amount of the capillary pressure depends on the curvature of the interfacial surface according to the equation: 1 1 Pc = P1 - P2=0(++) = r1 r2 where: P1 - P2 = pressure differential between concave and convex side of the curved surface measured in dynes/cm². O = Interfacial tension in dynes/cm. r1 and r2 are the principle radii of curvature. If the curvature is a section of a sphere, the r1 and r2 become R and: 2ocos0 Pc = r Where: O = contact angle. Because capillary pressure is a function of curvature of the interface, then it should be apparent that it is determined by the saturation of the porous medium. In this experiment, the capillary pressure of brine in a porous medium is determined as a function of saturation. Procedure: 1. Measure the weight of the brine saturated core sample. Record saturated weight in grams together with the dry weight measured prior to saturation. 2. Make sure all valves are closed on the apparatus. 3. Remove top of cell. 4. Place a thin layer of diatomaceous earth on the ceramic plate and cover with a tissue paper. 5. Place sample over the tissue paper. Make sure there is a good contact between the sample and the ceramic plate. 6. Close the top of cell. 7. Open Valve-3 and establish a pressure of 2 psig on the High Pressure Gauge using High Pressure Regulator. 8. Adjust Low Pressure Regulator to have a 1/2 to 5/8 inch length of the treaded portion. 9. Open Valve-5 and Valve-6 and SLOWLY increase pressure to 2¹/² psig on the Intermediate and High Pressure Gauges. Use a clockwise rotation of the handle on the High Pressure Regulator. 10. Open Valve-7 and SLOWLY rotate clockwise the handle on the Low Regulator to establish a 1 psig on the Low Pressure Gauge. 11. Open Valve-2 12. Open Valve-8 and introduce the established pressure into the cell. 13. Slowly close Valve-2 after verifying the air flow. 14. SLOWLY open Valve-1 to start the drainage process. 15. After reaching equilibrium saturation conditions, close Valve-1, close Valve-8 and SLOWLY vent the cell through Valve-2. 16. Remove the top of cell. 17. Remove sample and weigh. 18. Place sample to the cell using the steps 4, 5, and 6 above. 19. Open Valve-8 then close Valve-2. 20. When the air starts to flow SLOWLY open Valve-1 21. Slowly adjust the High Pressure Regulator to establish 4 psig on the Intermediate Pressure Gauge. 22. Adjust Low Pressure Regulator to establish 2 psig on the Low Pressure Gauge. 23. After reaching equilibrium conditions, repeat steps 15, 16, 17, 18, 19, and 20. 24. Close Valve-6 and Valve-7. 25. SLOWLY open Valve-4 and introduce 4 psig into the cell. If necessary, adjust the High Pressure Regulator to yield EXACTLY 4 psi on the Intermediate Pressure Gauge. 26. After reaching equilibrium conditions, repeat steps 15, 16, 17, 18, 19, and 20. 27. SLOWLY rotate the High Pressure Regulator to establish 8 psig on the Intermediate Gauge. 28. After reaching equilibrium conditions, repeat steps 15, 16, 17, 18, 19, and 20. 29. SLOWLY rotate the High Pressure Regulator to establish 15 psig on the Intermediate Gauge. 30. After reaching equilibrium conditions, repeat steps 15, 16, 17, 18, 19, and 20. 31. Close Valve-5 and slowly adjust the High Pressure Gauge to 35 psig using High Pressure Regulator. 32. After reaching equilibrium conditions, repeat steps 15, 16, and 17. Results: 1. Calculate the brine saturation at each capillary pressure level. The sample is 100% saturated in the beginning of the experiment. The volume of brine is calculated using dry weight and the density of the brine. The ratio of brine volume at any pressure level divided by the total brine volume yields the saturation at that capillary pressure level. Vbrine (cc) = - 100% Saturated Core Weight (gm) Dry Core Weight (gm) P Density of Brine (gm/cc) Brine brine a P (fraction) TotalVbrine 2. Prepare a plot of Capillary Pressure versus Brine Saturation. 3. What are the uses of capillary pressure? 4. The rest of questions will be updated and uploaded with the acquired raw data after the experiment. Diagram of Capillary Pressure Panel: High Intermediate Low Pressure Pressure Pressure Gauge Gauge Gauge 0-60psi 0 15 psi 0 -5psi 5 6 Gauge Shut-off Low Pressure Shut-off 4 7 High Pressure to Cell Low Pressure to Cell High Pressure Low Pressure Regulator Regulator 3 Air Pressure Input Diagram of Capillary Pressure Cell: Valve-2 Valve-8 Air Air Capillary Pressure Cell Valve-1 Brine

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