25- Gas Calcs

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SURFACE TESTING

GAS CALCULATIONS

ELC,Melun

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Gas Calculations

Gas flowrate is calculated from the differential

pressureacross the daniel orifice plate and staticpressure, as measured by the Barton Chart

Recorder.

hw = Differential Pressure (in. of H20)

Pf = Separator pressure (psia)measured

downstream of Plate

fw PhCQ

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Fu = Unit Conversion Factor

Fb = Basic Orifice Factor

Fg = Specific Gravity Factor

Y2 = Expansion Factor

Ftf = Flowing Temperature Factor

Fpv = Supercompressibility Factor

Gas CalculationsNumerical Constant

pvtfgbu FFYFFFC 2

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Gas Information Sheet

Explains basic theory behindgas calculation

Lists main data about

metering devices. e.g.

Daniel Line Bore Specific Gravity

Measurement

Shows selection of Fu to give

desired output units andreference conditions

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Gas Calculations - Example

Values already marked on the

sheet come from the Well Testing

Reading SheetsWith Separator Static &

Differential Pressures being themost important measurements

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NOTE THE UNITSEspecially psia for P

Most of the factors have no units

The output units of

the gas rate come

from the choice of

Fu

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FuUnit Conversion Factor

Value depends on

the reference

conditions used

and the units of

gas rate desired

Normally reference

conditions are:

14.73 psi

60 degF

In this case we desire scf/day

Fu = 24

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Note Number of Decimal Places Required

Also

- - - 2 3 3 2 4 4 4 4 1

Number of decimal places for Gas Rates depends

on how large rate is, and how we report it:

SCFD 0 dp

MSCFD 1 dp

MMSCFD 2dp

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Start the calculations.

10.12660265 fw Ph

126.10

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TABLES

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FbBasic Orifice Factor

Depends on:

Daniel Line Bore: IDof the metering tube

Plate on side of

Daniel

Normally 5.761 in.

Orifice Diameter (in)

Fb = 455.03

D = 5.761

in

d = 1.5 in

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TABLES

or EQUATION

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FgSpecific Gravity Factor

Fg corrects the gas flow equation forgas factors that have a s.g. notequal to 1

Calculated by a simple equation

Or can be taken from the table.

(Interpolate values)

Fg = (1.1834+1.1818)/2=

1.1826

s.g. =

0.715

..

1

gsFg

Interpolate

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TABLES or

GRAPH

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Y2Expansion Factor

Y2 takes into account the change in specific gravity of

the gas as its velocity and pressure change through

the orifice

Can be calculated from either:

Tables

Chart (very user unfriendly!)

2 xpans on ac or -

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Into the table we input:

Dont try to interpolate thetable, just round to thenearest 1 dp and use this

value

2 xpans on ac or -

Tables

Y2 = 1.0013

3.0~260.0761.55.1

Dd

2.0~226.0

265

60

f

w

P

h

Y E i F t Ch t

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The chart is normally only used if we are outside the range of thetables. To use:

Draw a line between Pf and hw using the parabolic axis.

There is a choice of scales so you must be consistent. i.e. ifreading Pf from the outer scale of the big parabola, you mustread hw from the outer scale of the big parabola.

Where this line intersects the horizontal axis, draw a linevertically up.

From the horizontal axis, take the orifice diameter and govertically up until we hit the Line bore line, then horizontally

across. From the intersection of the horizontal and vertical lines draw

a line to the reference point A and where this line intersectsthe vertical axis we can read off Y2.

Y2Expansion Factor - Chart

Y Expansion Factor - Chart

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Y2Expansion Factor - Chart

Example

Pf = 180 psig

Hw = 260 in H20

Line Bore = 4.026 in

Orifice Size = 2.125 inhw = 260in

Pf = 180 psig

d = 2.125 in

Y2= 1.0083

G C l l ti E l

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TABLES or

EQUATION

F Flowing Temperature Factor

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FtfFlowing Temperature Factor

Ftfcorrects the gas rate forflowing temperatures that arenot 60 degF

Calculated by an equation

Or can be taken from thetable

Ftf =0.9768

Tf= 85degF

degC2.273556.288

degF460

520

f

f

tf

T

TF

Gas Calculations Example

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TABLES or

CHART

F Supercompressibility Factor

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FpvSupercompressibility Factor

FpvCorrects the gas flow rate for the fact that real

gases deviate from the ideal behavior as predicted by

Boyles law.

To calculate it we need:

Separator Static Pressure (psig)

Gas Specific Gravity

Flowing Temperature

Can be calculated from either:

Tables

Chart

F Supercompressibility Factor Table (1)

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FpvSupercompressibility FactorTable (1)

Second table corrects thisFpvfor the flowing

temperature

Input:

Fpv

Tf

Each heading isinclusive to next higherheading. Do notinterpolate

Fpv (uncorrected)=

Pf

= 265 psia = 250

psigsg = 0.715

F Supercompressibility Factor Table (2)

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Fpv Supercompressibility Factor Table (2)

First table calculates Fpv,then we must correct

for temperature

Input:

Pf (psig)

s.g.

Each heading isinclusive to next higherheading. Do notinterpolate

Fpv= 1.027

Fpv= 1.032 psig

Tf = 85 degF

F Supercompressibility Factor Chart

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The chart is normally only used if we are outside the range of the tables.

To use:

1. Left Hand Chart bottom axis - Flowing Temperature govertically upwards

2. Intersect with specific gravity line and go horizontally into RightHand Chart

3. Intersection of this line with Separator Pressure (psig) frombottom axis gives Fpv @ 60 degF

FpvSupercompressibility FactorChart

F Supercompressibility Factor Chart

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Fpv Supercompressibility Factor Chart

Example:

Pf = 250 psig

Tf = 85 degF

Sg = 0.71585 degF 250 psig


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C = Fu.Fb.Fg.Y2.Ftf.Fpv

= 24 x 455.03 x 1.1826 x 1.0013 x 0.9768 x 1.0270= 12972.9

12972.9


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12972.9

Qgas = C.(hw.Pf)1/2

= 12972.9 x 126.10

= 1635882.7 SCFD

= 1.64 MMSCFD

1.64


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12972.9 1.64

Cumul. = 1.64 /1440 x 15

= 0.0170 MMSCF

= 17.0 MSCF

17.0


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Gas Ca cu a o s a p e

The remaining lines can then be completed in

the same way.


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p


the same way.


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p


the same way.


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p


the same way.


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the same way.


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the same way.

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THE END

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25- Gas Calcs