Average reservoir pressure calculation

[Smriti]

Hi all,
can anyone tell me how to calculate average flowing reservoir pressure for a gas reservoir with 18 wells flowing.i need it to do some material balance for the gas field.

Thanks,
Smriti

[Chee Koh Peh]

Smrtri,

I presume you intend to use a flowing material balance (Fekete). Am I correct here?

Have you attempted to plot all the wells flowing bottom hole pressure vs time on a single graph? This will tell you if the pressure depletion is uniform throughout the reservoir i.e. if the reservoir is acting as single tank. If it is then the below approach will give you a reasonable first pass GIIP answer.

As a first pass, in this case you can pick any well as long as you sure it is not suffering from interference from any other wells and is in pseudo steady state flow, and use that as the fields flowing bottom hole pressure profile and complete a flowing material balance using the entire fields production Gp.

I would advise you not to perform flowing material balances on single wells and (sum these up) until you absolutely sure all wells are in pseudo state flow i.e. all wells have felt their boundaries, otherwise you will over estimate the GIIP as until pseudo state flow occurs well drainage areas cannot be calculated.

Rgrds

Chee Koh Peh..

[Smriti]

Hi Chee,

Thanks for this valuable information...
yes I am using flowing material balance for GIIP calculation..
But was confused about taking the average flowing reservoir pressure.Plot of FBHP vs time on single graph is showing almost the same pressure depletion trend..

Rgds,
Smriti

[darcyoil]

If by your query you mean P-bar, then you get a very good estimate by invoking a shape in your regression analysis model when you are performing your pressure transient analysis work. Confirm yes or no, and I will expound further.

[Smriti]

actually there are many wells flowing at different rates..so for material balance i need to have average reservoir pressure (for the field)..the question was how to calculate it in flowing condition as for different flowrates flowing bottom hole pressure is different based on fluctuations in flow rate..
pressure can be in bar or psi ...

[vamsikrishnaprasad]

a123