static gadient

[guizados]

Hello everybody

3 questions please

I want to know how to extrapolate the static pressure to get the reservoir pressure?

what is the utility from knowing the contact inside the tbg?

if we don't have full segregation between fluids inside the tbg is it reliable to take the results regading the pressure?

thanks

[guizados]

nothing to say??

[guizados]

difficult question?

[vinomarky]

It's a trivially simple problem, but you dont specify how and where you are measuring your pressures. THP + Sonalog? BHP gauge (if so, at what depth relative to the producing interval and fluid contact)? Casing pressure + Sonalog?

The utility to use: Excel & simple hydrostatic calcs. Just think it through, its not difficult.

Does foam interface make less reliable?: Yes, but serves to provide an upper bound of BHP's

[guizados]

thanks vinomarky

am talking about BHP(static gradient) , the guage is above the perfos and generally above the WOC inside the tbg....just a static gradient...generally we are determining the Pressure at a datum depth ...what I know is that this is not the reservoir Pressure even the time for the SG is long...how to extrapolate this Pressure to get the reservoir one....and the principle question is what is the utility to know the level of water inside the tubing

[vinomarky]

I normally build a simple fine scale simulation model and match, so dont have oodles of experience with this. I'd suggest that simple extrapolation could be achieved using Horner type approach, the key assumption is what pumping time to use.

Horner extrapolation is normally used for PTA, as such a steady (or pseudo steady) state system is a different beastie. If your well has been producing for (say) 2 months, then using a 2 month pumping time with this approach would not be appropriate, as most of this period was not transient (Assuming you are not talking about really low perm systems).

I would hazard a guess that if you calculate (or even better, through historical production behaviour infer) what the time required to get out of transient flow (ie how long the initial 'flush' production phase is before your production follows a normal depletion trend), and use this as the pumping time tp

Then plot Pressure vs log10(ts / (ts + tp)), where ts = shutin time

And extrapolate to ts / (ts + tp) = 1

[guizados]

thanks a lot vinomarky , have you an idea about the water level inside the tbg, what does it used for?

[vinomarky]

C'mon ... think

Your gauge is above the perfs - you know the pressure at the gauge, how to you calculate what the pressure is at the perfs? Simply by adding the head between the perfs and the gauge. Is that fluid oil? gas? water? Mixture? Knowing what fluid(s) and where the contacts are beneath your gauge will allow you to calculate pressure at the perfs. If you don't know, and cannot infer by other means, then you can bound the range of possible pressure by assuming different fluids.