Dew Point >> Reservoir Pressure

[Chee Koh Peh]

Ladies and Gents,

Need your advice....

MDT samples are gas condensate in newly discovered reservoir (no production), reservoir pressure 2600psi. Client takes three samples. They do the PVT analysis and calculate the dew point to be 3200psi.

So here we have a reservoir pressure of 2600 psi and calculated (constant mass study) dew point of 3200 psi.

Client suggests the sample was taken very close to the GOC i.e. is oversaturated.

Has anyone seen anything similar before?

Thanks

Chee Koh Peh

[brhm]

ideally you can not calculate higher saturation pressure from a sampled "single phase" fluid. It should be a sampling problem if you have collected two phases...
if they claim they have sampled two phases, than try to estimate pressure at GOC and see if it is any near your saturation pressure. anyway it makes the sample and calculations wrong. so do not rely on these samples at all....

[Chee Koh Peh]

ideally you can not calculate higher saturation pressure from a sampled "single phase" fluid. It should be a sampling problem if you have collected two phases...
if they claim they have sampled two phases, than try to estimate pressure at GOC and see if it is any near your saturation pressure. anyway it makes the sample and calculations wrong. so do not rely on these samples at all....

The reservoir pressure at log derived GOC is still 300 psi below the saturation pressure.

Thanks, I've been thinking about this a little more. If the sample was taken in the transition zone it implies a compositional gradient exists in the reservoir.

The dew point will gradually increase with depth in a compositional gradient scenario simply because of a greater of C6+ concentration, assuming the reservoir is at thermodynamic equilibrium. At the GOC the saturation pressure must equal the reservoir pressure (beginning of liquid drop out) for the liquid phase to exist. That is the dew point can never exceed the reservoir pressure. i.e. where the dew point is below the reservoir pressure you are in the gas zone, where the dew point equals the reservoir pressure you are at the GOC and in liquid zone (volatile oil).

If the have claimed to have sampled two phases why are the calculations wrong?

Thanks

Chee Koh Peh

[brhm]

you can ask them how they would know the solution gas oil ratio and producing gas oil ratio? in your case you will have higher or lower condensate who knows?

[jojeecares]

First of all i would suggest that you may also carry out surface recombination sampling through separator as well. Secondly, if the results are same, there shouldn't be much astonishment as this is a common phenomenon observed in many fields. What your reservoir pressure has indicated probably exists at a depth of 4500 ft. The recombination sample collected by MDT has accurately determined the dew point at 3200 psi which means your initial reservoir is lower than the saliquid saturation pressure and therefore there exists an oil rim that seperates oil from gas. (In this particular case, oil refers to condensate). During draw off from reservoir, condensate being lighter moves alongwith gas. gas in this case moves as a result of capillary action.

[paolomaldini]

Thanks