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PETE 310
Lectures # 12 -13
Properties of Dry Gases
(pages 165-187)
Phase Diagram of a Dry Gas Reservoir
Temperature
Pre
ss
ure
Path of Production
Initial Reservoir Conditions
Separator Conditions
CP
DRY GAS RESERVOIRS:– GOR > 100,000 SCF/STB– No liquid produced at surface– Mostly methane
Standard Conditions
Unify volumes to common grounds for sales and regulatory purposes– T = 60 0F
– P = 14.65 – 15.025 (State dependent)
Then
VM = RTsc/Psc
Reservoir Engineering Properties of Dry Gases
Gas formation volume factor Bg
Reservoir ConditionsReservoir Conditions
Standard ConditionsStandard Conditions
[res bbl/SCF] or [ft3/SCF]
Gas Formation Volume Factor
SC
Rg V
VB
Volume of an arbitrary amount Volume of an arbitrary amount of gas at reservoir T & P of gas at reservoir T & P
Volume of Volume of SAMESAME amount at amount at
standard T & P standard T & P
[res bbl/SCF] or [ft3/SCF]
Gas Formation Volume Factor
SC
SCSC
P
nRTZP
ZnRT
Bg
Gas Formation Volume Factor
[res bbl/SCF] or [ft3/SCF]
Gas Formation Volume Factor
Viscosity Definition & Units
Viscosity is a measure of the resistance to flow exerted by a fluid
This is called dynamic viscosity and has units of
centipoise = g mass / 100 sec cm
Kinematic viscosity is viscosity / density, units are in
centistokes = centipoise /g/cc
Reservoir Engineering Properties of Dry Gases
Gas Viscosity
Vis
cosi
ty (
cp)
Vis
cosi
ty (
cp)
PressurePressure
T increasingT increasing
100oF
150oF
200oF
100oF
150oF
200oF
Viscosity of Ethane
Viscosity of Gases at Atmospheric Pressure
Viscosity of Gas Mixtures
See example 6-9 See example 6-9
Example
Example
Read Molecular Weights table A-1 page 492
Read Viscosities figure 6-7
Apply formula…
Gas Viscosity if Composition is Unknown
Still at atmospheric Still at atmospheric pressure!pressure!
Viscosity Corrections
Viscosity of Gases at High Pressure
=ratio*=ratio*atat
Viscosity of Gases at High Pressure
make suremake sureyou checkyou checkthe the specificspecificgravity gravity rangerange
Accuracy for Viscosity Correlations?
At low Ppr and low gravities + 2%
Agreement is less accurate as specific gravity increases (fig. 6-12 has about 20% accuracy)
Isothermal Compressibility
Definition
– Derivative is evaluated at constant T = TA and specified pressure P = PA
AT
AAg P
V
VTPC
1
,
Isothermal Gas Compressibility
P1
V2V1
TB
P2
Vave= (V1+V2)/2
ATaveAAg PP
VV
VTPC
21
211,
TA
PA
Isothermal Compressibility (Cg)
Isothermal Compressibility
Using ideal gas equation
Isothermal Compressibility
Using real gas equation
GasGasCompressibilityCompressibility