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