GasCals v. 1.3 β

What it’s doing:

This program calculates the Shut In Wellhead Pressure (when it is given the reservoir pressure)

for a well full with gas, and the Reservoir pressure in static and flowing conditions (steady

flow) when the wellhead pressure is known.

How it’s do it:

The calculation is done by the Cullender-Smith method. The gas viscosity is based on the Carr,

Kobayashi and Burrows for gas mixtures corrected for mixtures with N2, CO2 and H2S. The

compressibility factor is calculated with Peng - Robinson equation of state.

The program should be used for vertical or near vertical wells.

How it works:

- Input data in the light yellow fields. If the gas composition is unknown, input 100 (percents)

in the cell of Methane and 0 in all the rest of the components.

Mole Name

[%]

C1 (CH4) 80.57

C2 (C2H6) 6.95

C3 (C3H8) 2.47

iC4 (C4H10) 0.405

nC4 (C4H10) 0.695

iC5 (C5H12) 0.26

nC5 (C5H12) 0.36

C6 (C6H14) 0.62

C7 (C7H16) 0.44

C8 (C8H18) 0.385

CO2 6.685

N2 0.16

H2S

O2

- In the temperature profile the data can be input manually or it can be generated based on the

surface data + a temperature gradient. Please note this temperature profile is the temperature

distribution in the column of gas filling the hole, not the rock's temperature profile. If you don’t

have the temperature profile you can chose a straight line (drawn between the surface

temperature and the reservoir temperature or an exponential function like

where a can be 2 to 7 (for example) and b can be 0.2 to 0.5 (for example). However at the

moment this function it’s not implemented and you have to generate the points on a separate

excel sheet, copy and paste them on the cells L5 to M26.

The calculation interval is 1/1000 of the TVD of the well for the version β.

Example: a=3, b=0.3, Ts=110 [ºC], Tres = 146 [ºC]

Temp profile

TVDTVDTVDTVD Tem pTem pTem pTem p

[m] [ºC]

0 110.00

50 119.70

110 122.29

190 124.48

270 126.09

400 128.10

600 130.44

900 133.09

1,300 135.78

1,600 137.44

1,900 138.89

2,090 139.73

2,280 140.51

2,470 141.26

2,660 141.96

2,850 142.63

3,040 143.26

3,230 143.88

3,420 144.46

3,610 145.02

3,800 145.57

4,000 146.12

Temperature profile

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

0 50 100 150 200

Temp [ºC]

TV

D [m

]

bTVDaTsTVDT ×+=)(

Calculate

WHP

Example temperature profile (linear) generated:

Fill Reservoir pressure and TVD, and press

The result will be shown in:

Temp profile

TVDTVDTVDTVD Tem pTem pTem pTem p

[m] [ºC]

0 110.00

190 111.90

380 113.80

570 115.70

760 117.60

950 119.50

1,140 121.40

1,330 123.30

1,520 125.20

1,710 127.10

1,900 129.00

2,090 130.90

2,280 132.80

2,470 134.70

2,660 136.60

2,850 138.50

3,040 140.40

3,230 142.30

3,420 144.20

3,610 146.10

3,800 148.00

4,000 150.00

Reservoir

Pressure TVD

[psi] [m]

11,230 4,000

Wellhead

pressure

[psi]

9,036.1

Temperature profile

0

500

1,000

1,500

2,000

2,500

3,000

3,500

4,000

4,500

0 50 100 150 200

Temp [ºC]

TV

D [m

]

To calculate the Reservoir Pressure either static or flowing well, fill in the wellhead pressure,

select the appropriate option, and click the button:

Wellhead

pressure

[psi]

8,921.7

However for the well flowing (once again, steady flow) you have to fill supplementary data:

Flow Flowing path

rate ID Rough.

[Mscfd] [in] [in]

12000 2.441 0.0023

The measuring units are customizable except the Flow Rate, Pipe ID and Roughness, at least in

version β. You have the possibility to select the desired units for the different parameters by

pressing the "Change units" button.

However this will not convert the data you input!

The interpolated values for pressure, compressibility factor, density and temperature are

provided on the sheet “Charts”.

The input sheet is not "fool proof" therefore pay attention to the data you fill in, to the

measuring units you use and to get 100% by the summation of the fractions of mole of the

mixture (cell B30).

Calculate BHP

Static Flowing