Determine Bottom Hole Pressure from Wellhead Pressure in a Dry Gas Well

Gas behaves differently from fluid therefore you cannot use a simple hydrostatic formula to determine reservoir pressure. Gas is compressible but fluid is incompressible.


The formula to determine the bottom hole pressure of dry gas well is shown below;

equation 1


Where; Pbh = bottom hole pressure in psia (absolute pressure)

Pwh = wellhead pressure in psia (absolute pressure)

H = true vertical depth of the well

Sg = specific gravity of gas

R = 53.36 ft-lb/lb-R (gas constant for API standard condition air)

Tav = average temperature in Rankin (Rankin = Fahrenheit + 460) Continue reading

Pipe Light Calculation

Pipe light, which is a special term in a snubbing operation, describes the condition of the well which well head pressure and buoyancy acting upward against a cross sectional area of pipe is greater than weight of the string. If the light pipe condition is happened and the string is not controlled by the snubbing unit, the string will be pushed out of the well.

 Pipe Light Calculation 1

You may see this VDO showing the pipe light condition. The string of tubular (I am not sure if it is a drill pipe or a tubing) was pushed out by the wellbore pressure. This is the great example of pipe light condition.

After knowing the concept of the light pipe, we will apply it to determine how many feet of tubular required snubbing into the well before the weight will overcome the surface pressure plus buoyancy force.

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Estimated mud weight required to safely drill the well

I have an interesting question to share with you about how to estimate minimum mud weight required to safely TD the well.

The question is shown below.

7” casing shoe was set at 6,500’MD/5,000’ TVD. The geologist team in town expects 2 hydrocarbon reservoirs and information is listed below;

Formation sand A: Expected depth 5,500’ TVD, pressure gradient is 0.48 psi/ft.

Formation sand B: Expected depth 8,800’ TVD, pressure gradient is 0.49 psi/ft.

The planned TD is 9200’MD/9000’TVD and the drilling team requires 250 psi overbalance while drilling.

What is the mud weight required to drill the well with 250 psi overbalance?

First of all, let’s draw a simple diagram like this.

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