Hello Reservoir Engineer

[srinigeol]

How to determine the limiting maximum pressure drawdown for producing a gas well.

[vinomarky]

Drawdown = Reservoir Pressure - Flowing Bottom Hole Pressure (FBHP)

Assuming you know the reservoir pressure, we have to determine the minimum flowing bottom hole pressure that you can achieve (which will give you your maximum drawdown)

Here, there are a number of factors - I've listed below a non-exhaustive list - that need to be considered;

1. Production mode - natural or artificial lift
A nodal analysis will yield the equilibrium BHFP for a given minimum wellhead pressure. Essentially you will be solving two sets of equations, the first being for a given BHFP what rate will the reservoir give you (intake curve). The second is for a given wellhead pressure and fluid rate(s), what BHFP would be required to push it up through the tubing (Tubing Intake Curve). Where the two curves intersect will be your solution. If you have artificial lift, then you can use the same approach, but substitute the tubing curve with the artificial lift curve.

2. As inferred from the above, the watercut/GOR, tubing ID, depth & wellhead pressure will all affect your solution

3. Physical limits - for pumps what are the maximum rates that they can run at? Often there is a minimum fluid above the pump (BHFP) needed to avoid burning your pump out. Do you have any sand production problems with too much drawdown? Will you have too much gas/water coning/cusping with too much drawdown?

Note: yes, I realize you were talking gas wells and so are probably talking natural lift only, but included the rest for completeness, and there are indeed some gas wells on artificial lift (ie CBM)

You get the idea - good luck

[srinigeol]

Sir,
thanks a lot for clear cut explanation with the factors affecting the Drawdown.
I will be very happy if you can tell me abt how to determine the minimum FBHP for a well..in connection to determine the maximum allowable d/dn for optimum production.
Is there any particular analysis..
pl. guide me...

[ELgharib]

As u are dealing with a gas well,

From a reservoir standpoint: if a retrograde condensate reservoir u should consider the dew point and the condensate banking that will be created. Also consider the migration of fine and water. Another important point is the turbulence within the reservoir....and the associated consequences.

From a completion side....U should look at ur completion(gravel pack, sand screens...etcc) and which drawdown they can withstand and finally the limit of your tubing size(should be determined from Nodal Anlysis).

I hope to have been useful to u.

Regards

[khan123]

In addition to above, you need to consider the Critical rate in order to prevent any water conning in the well-bore. And water holding factor for a particular tubing need to be taken in consideration.

Regards