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Q913 rfp w1 lec 4

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Q913 rfp w1 lec 4

  1. 1. Reservoir Fluid Properties Course (1st Ed.)
  2. 2. 1. 2. 3. 4. Samples Sample Analysis Samples Quality Control K-Factor as A QC 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 2
  3. 3. 1. 2. 3. 4. Reservoir Fluid Course HC Alteration Properties of Natural Gases Properties of Crude Oils A. density B. Gas Solubility 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 3
  4. 4. Reservoir To optimize the production from an oil or a gas field, it is essential to have extensive knowledge of The volumetric and Phase changes The reservoir fluid is likely to undergo on its way from petroleum reservoir to oil refinery. Reservoir pressures typically range from 100 to 1500 bar (~1450-21000 psi!), and reservoir temperatures from 50 to 200 ° C (~120-390 °F). The well connecting the reservoir to the topside facilities can have a length of more than 2 km. 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 5
  5. 5. Well and Flowlines The pressure and temperature will gradually decrease in production well. It will further decrease in flowlines connecting the well to the process plant and in the process plant itself. Figure illustrates schematically the production path of a reservoir fluid. 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 6
  6. 6. Course Followed By Reservoir Fluid Course Followed By Reservoir Fluid from Reservoir to Ambient Conditions 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 7
  7. 7. Reservoir Fluid Alteration The conditions in the reservoir itself will also change as a result of production. A reservoir fluid, which in the exploration phase was either single-phase gas or single-phase oil, may sometime after production split into two phases. This phase split is the result of material being removed from the reservoir. With more space available for the remaining reservoir fluid, the pressure will decrease and may after some time reach the saturation pressure, at which a second phase (gas or oil) starts to form. 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 9
  8. 8. PVT Properties  PVT properties is the general term used to express the volumetric behavior of a reservoir fluid as a function of pressure and temperature. An essential PVT property is The saturation pressure At reservoir temperature. 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 10
  9. 9. Fluid Composition Alteration  From the time the reservoir pressure reaches the saturation pressure and a second phase starts to form, the composition of the produced well stream will most likely change Because the production primarily comes from either the gas or the liquid zone. It is customary to use the volumes of oil and gas at atmospheric pressure and 15 ° C (60°F) as reference values. Atmospheric pressure (1 atm or 1.01325 bar) (14.5 psi) and 15 ° C are referred to as standard conditions. 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 11
  10. 10. Natural Gas Expression Conventionally, natural gas compositions are expressed in terms of mole fraction, weight fraction, and volume percent. These are derived as follows: Mole Fraction: the number of moles of the component divided by the total number of moles of all the components in the mixture. (yi=ni/n) Weight Fraction: is defined as the weight of that component divided by the total weight. (wi=mi/m) Volume Fraction: is defined as the volume of that compound divided by the total volume of the mixture. (vi=Vi/V) 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 13
  11. 11. Mixture Apparent Molecular Weight If yi represents the mole fraction of the ith component in a gas mixture, the apparent molecular weight is defined mathematically by the following equation: 𝑴𝑾 𝒂 = 𝒚 𝒊 ∙ 𝑴𝑾 𝒊 𝒊=1 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 14
  12. 12. Ideal Gas Mixture Density and Specific Gravity The density of an ideal gas mixture is calculated by: 𝝆𝒈= 𝒑𝑴𝑾 𝒂 𝑹𝑻 The specific gravity is defined as the ratio of the gas density to that of the air. Both densities must be taken at the same temperature and pressure, or: 𝜸𝒈= 2013 H. AlamiNia 𝝆𝒈 𝝆 𝒂𝒊𝒓 = 𝑴𝑾 𝒂 𝑴𝑾 𝒂 = 𝑴𝑾 𝒂𝒊𝒓 28.96 Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 15
  13. 13. Compressibility of Natural Gases A knowledge of the variability of fluid compressibility with pressure and temperature is essential in performing many reservoir engineering calculations. For a liquid phase, the compressibility is small and usually assumed to be constant. For a gas phase, the compressibility is neither small nor constant. 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 16
  14. 14. Gas Compressibility Definition By definition, the isothermal gas compressibility is the change in volume per unit volume for a unit change in pressure, or, in equation form: 1 𝒑𝒔𝒊 𝑪𝒈=− 1 𝑽 𝜕𝑽 𝜕𝒑 = 𝑻 1 1 − 𝒑 𝒁 𝜕𝒁 𝜕𝒑 𝑻 For an ideal gas, Z = 1 and (∂Z/∂p) T = 0, therefore Cg=1/p For calculating isothermal pseudo-reduced compressibility (Cr) in terms of the pseudo-reduced pressure and temperature by simply replacing p. with (Ppc Ppr) we have Cr=CgPpc 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 17
  15. 15. Gas Formation Volume Factor Definition The gas formation volume factor is used to relate the volume of gas, as measured at reservoir conditions, to the volume of the gas as measured at standard conditions, i.e., 60°F and 14. 7 psia. This gas property is then defined as the actual volume occupied by a certain amount of gas at a specified pressure and temperature, divided by the volume occupied by the same amount of gas at standard conditions. 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 18
  16. 16. Bg Expression In an equation form, the relationship is expressed as 𝑩𝒈= 𝑽 𝒑,𝑻 𝑽 𝒔𝒄 Where Bg = gas formation volume factor, ft3/scf Vp, T = volume of gas at pressure p and temperature T, ft3. And V sc = volume of gas at standard conditions, scf 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 19
  17. 17. Bg Expression for Real Gases Applying the real gas EoS to the above relationship gives 𝒁𝒏𝑹𝑻 𝒑 𝑩𝒈= 𝒁 𝒔𝒄 = 1)𝒏𝑹𝑻 𝒔𝒄 𝒑 𝒔𝒄 𝒑 𝒔𝒄 = 14.7 = 𝑻 𝒔𝒄 = 60 + 460 = 520 𝒁𝑻 𝒇𝒕3 = 0.02827 , 𝒑 𝒔𝒄𝒇 𝒁𝑻 𝒃𝒃𝒍 = 0.005035 , 𝒑 𝒔𝒄𝒇 2013 H. AlamiNia 𝒁𝑻 𝒑 Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 20
  18. 18. Gas Expansion Factor The reciprocal of the gas formation volume factor is called the Gas Expansion Factor and designated by the symbol Eg, or 𝑬𝒈 𝒑 = 35.37 , 𝒁𝑻 𝒑 = 198.6 , 𝒁𝑻 2013 H. AlamiNia 𝒔𝒄𝒇 𝒇𝒕3 𝒔𝒄𝒇 𝒃𝒃𝒍 Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 21
  19. 19. Physical and Chemical Properties of Crude Oils Petroleum (an equivalent term is “crude oil") is a complex mixture consisting predominantly of hydrocarbons, and containing sulfur, nitrogen, oxygen, and helium as minor constituents. The physical and chemical properties of crude oils vary considerably and are dependent on the concentration of the various types of hydrocarbons and minor constituents present. 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 24
  20. 20. Physical Properties of Petroleum Physical properties of primary interest in petroleum engineering studies include: Fluid densities Isothermal compressibility Solution gas-oil ratios Oil formation volume factor Fluid viscosities Bubble-point pressure Surface tension 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 25
  21. 21. Determination of Physical Properties Data on most of these fluid properties is usually determined by laboratory experiments performed on samples of actual reservoir fluids. In the absence of experimentally measured properties of crude oils, it· is necessary for the petroleum engineer to determine the properties from empirically derived correlations. 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 26
  22. 22. Crude Oil Density Density: The crude oil density is defined as the mass of a unit volume of the crude at a specified pressure and temperature. It is usually expressed in pounds per cubic foot. Specific gravity: The specific gravity of a crude oil is defined as the ratio of the density of the oil to that of water. Both densities are measured at 60°F and atmospheric pressure. 𝜸𝒐 = 2013 H. AlamiNia 𝝆𝒐 𝝆𝒘 Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 27
  23. 23. Crude Oil Density Determination As the density of water at 60°F is close to 1 g/cm3, the 60°F/60°F specific gravity of an oil sample will take approximately the same value as the density of the oil sample in g/cm3. During the last forty years, numerous methods of calculating the density of crude oils have been proposed. There are two approaches available in the literature to calculate liquid density: The equation-of-state approach The liquid density-correlation approach. 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 28
  24. 24. Standing's Method Standing (1981) proposed an empirical correlation for estimating the oil formation volume factor as a function of the gas solubility Rs, the specific gravity of stock tank oil γo, the specific gravity of solution gas γg and the system temperature T. 𝝆𝒐 = 62.4𝜸 𝒐 + 0.0136𝑹 𝒔 𝜸 𝒈 0.972 + 0.000147 𝑹𝒔 𝜸𝒈 𝜸𝒐 1.175 0.5 + 1.25 𝑻 − 460 Where T =system temperature, °R & γo = specific gravity of stock-tank oil 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 29
  25. 25. API Although the density and specific gravity are used extensively in the petroleum industry, the API gravity is the preferred gravity scale. This gravity scale is precisely related to the specific gravity by the following expression: 𝑨𝑷𝑰 = 141.5 − 131.5 𝑺𝑮 = 𝜸 𝒐 The density of an oil from a flash to standard conditions has traditionally been expressed as API gravity. The API gravities of crude oils usually range from 47° API for the lighter crude oils to 10° API for the heavier asphaltic crude oils. 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 30
  26. 26. Gas Solubility The gas solubility Rs is defined as the number of standard cubic feet of gas which will dissolve in one stock-tank barrel of crude oil at certain pressure and temperature. The solubility of a natural gas in a crude oil is a strong function of the pressure, the temperature, the API gravity, and the gas gravity. To determine Rs, beside experimental analysis there are many correlations (including: Beal's Correlation, Standing's Correlation, Lasater's Correlation, Vasquez-Beggs' Correlation, Glaso's Correlation, Marhoun's Correlation) 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 32
  27. 27. Rs vs. P and Rs vs. T Relationships 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 33
  28. 28. Rs Relationships API Gravity-Rs Relationship 2013 H. AlamiNia Gas Gravity vs. Gas Solubility Relationship Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 34
  29. 29. Rs vs. P For a particular gas and crude oil to exist at a constant temperature, the solubility increases with pressure until the saturation pressure is reached. At the saturation pressure (bubble-point pressure) all the available gases are dissolved in the oil and the gas solubility reaches its maximum value. 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 35
  30. 30. An Idealized Rs-P Diagram for an Undersaturated Oil A typical gas solubility curve, as a function of pressure for an undersaturated crude oil 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 36
  31. 31. Rs vs. P in Reality Rather than measuring the amount of gas that will dissolve in a given stock-tank crude oil as the pressure is increased, it is customary to determine the amount of gas that will come out of a sample of reservoir crude oil as pressure decreases. As the pressure is reduced from the initial reservoir pressure pi, to the bubble-point pressure Pb, no gas evolves from the oil and consequently the gas solubility remains constant at its maximum value of Rsb· Below the bubble-point pressure, the solution gas is liberated and the value of Rs decreases with pressure. 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 37
  32. 32. 1. Tarek, A. (1989). Hydrocarbon Phase Behavior (Gulf Publishing Company, Houston). Ch2 & Ch3 & Ch4. 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 38
  33. 33. 1. Formation Volume Factor A. Oil B. Total (two phase) 2. Property Constants 2013 H. AlamiNia Reservoir Fluid Properties Course: Reservoir Hydrocarbons (Natural gas & Crude Oil) 39

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