ch6 - CHAPTER6 PropertiesofDryGases q...

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CHAPTER 6  Properties of Dry Gases Properties of Dry Gases Gas Formation Volume Factor  (B g ) Isothermal Coefficient of  Compressibility (C g ) Pseudoreduced   Coefficient   of  Compressibility (C pr ) Coefficient of Viscosity of Gas  ( μ g ) 6 - 1
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Standard Pressure Determined by political jurisdiction.  Varies  from state to state. 14.65 psia in Texas. 15.025 psia in Alabama. See Table 6.1 of McCain for values for  other states. Conversion of pressure from  atmospheres (atm) to psia The conversion factor is a constant,  14.696  psia/atm Conversion of gauge pressure (psig)  to absolute pressure (psia) psia = psig + barometric pressure (psi) at  the time the pressure  gauge was calibrated. 6 - 2
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At sea level, barometric pressure   14.7 psi 6 - 3
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Gas Formation Volume Factor (B g ) The gas formation volume factor (B g ) is the  reservoir volume that would be occupied by 1  standard cubic foot of gas. A mathematical expression can be derived for B by application of the real gas law to a fixed mass  (mole) of gas at reservoir conditions and at  standard conditions. For a fixed mass of real gas, from real gas law,   P R V R Z R T R   =   P sc V sc Z sc T sc (1) where the subscript “R” indicates reservoir  conditions and “sc” indicates standard  conditions. 6 - 4
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Gas Formation Volume Factor (B g ) (continued) Rearrangement of Eq. 1 gives B g  as   B g   =   V R V sc   =   P sc Z sc T sc   Z R T R P R (2) Now, P sc  = 14.7 psia T sc  = 520 ˚R Z sc  = 1.0 Substitution of these constants into Eq. 2 gives  the gas formation volume factor as   B g   =   0.02827   Z R T R P R   res cu ft scf (3) 6 - 5
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Gas Formation Volume Factor (B g ) (continued) Units of B g : Although B g  is dimensionless, we attach units  such as shown in Eq. 3 (reservoir cubic foot per  standard cubic foot) to it to allow us to correctly  apply the factor in our various engineering  calculations.  The units also serve to remind us of what B represents: the reservoir volume that 1 standard  cubic foot of gas would occupy at the current  reservoir pressure and temperature. Noting that  1 barrel = 5.615 cubic feet , B can also be rewritten as   B g   =   0.00503   Z R T R P R   res barrel scf (4) 6 - 6
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where the units are now in reservoir barrel per  standard cubic foot. 6 - 7
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Gas Formation Volume Factor (B g ) (continued) Some questions about B g : 1. Is B g  a constant throughout the life of a gas  reservoir? If not, why not? 2.
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This note was uploaded on 02/28/2011 for the course PGE 312 taught by Professor Peters during the Spring '08 term at University of Texas at Austin.

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ch6 - CHAPTER6 PropertiesofDryGases q...

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