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How to correct the coreplugs water saturation (CSW) to reservoir conditions (overburden correction)?
what do we correct permeability (K) for overburden and saturation?
Look forward to hearing.
Thanks!
Originally Posted by vinomarky
Its an interesting issue, and probably more complex than you appreciate
On one hand, the mechanics of correcting (a) perm for klinkenberg and overburden (b) porosity for overburden and (c) lab measured capillary pressures to reservoir conditions are relatively well understood
When you are measuring water saturations though (at given lab measured pressures), the saturation is a function of pore throat size distribution. So while if (for example) a 10mD (klinkenberg corrected) rock under equivalent to 10si reservoir differential pressure exhibits 40% Sw, would that mean if you then correct for overburden and (lets guess) the perm reduces to 6mD that the saturation woud be the same?
I would tend to argue no, that the surface measurements you are making are a function of pore throat size, and by correcting the perm to downhole condutions you are in effect accounting for a reduction in pore throat size. In other words, I normally take the approach that the saturation behaviour from a 10mD sample (klinkenberg corrected, surface conditions) will be the same as the behaviour for a 10mD (OB corrected) sample because their pore throat size distribution should be similar.
So, simple answer to your question is;
You dont normally correct Sw to reservoir conditions, you correct lab capillary pressure (ratios of sigmacostheta lab to reservoir) and perm/poro to reservoir condictions through pressure corrected tests.
The more complex answer is that (at least for me) while you still need to correct lab Pc to reservoir Pc, I am unconvinced that correcting surface K to reservoir K (for purposes of describing saturation height functions) adds any more accuracy. You may well still need to correct surface to reservoir K/Poro to properly describe your reservoir fabric (especially in low perm reservoirs where the correction can be substantial), but I normally lean toward using the uncorrected perm to anchor saturation height functions against.
Hopefully I've helped and not just added to the confusion!
On one hand, the mechanics of correcting (a) perm for klinkenberg and overburden (b) porosity for overburden and (c) lab measured capillary pressures to reservoir conditions are relatively well understood
When you are measuring water saturations though (at given lab measured pressures), the saturation is a function of pore throat size distribution. So while if (for example) a 10mD (klinkenberg corrected) rock under equivalent to 10si reservoir differential pressure exhibits 40% Sw, would that mean if you then correct for overburden and (lets guess) the perm reduces to 6mD that the saturation woud be the same?
I would tend to argue no, that the surface measurements you are making are a function of pore throat size, and by correcting the perm to downhole condutions you are in effect accounting for a reduction in pore throat size. In other words, I normally take the approach that the saturation behaviour from a 10mD sample (klinkenberg corrected, surface conditions) will be the same as the behaviour for a 10mD (OB corrected) sample because their pore throat size distribution should be similar.
So, simple answer to your question is;
You dont normally correct Sw to reservoir conditions, you correct lab capillary pressure (ratios of sigmacostheta lab to reservoir) and perm/poro to reservoir condictions through pressure corrected tests.
The more complex answer is that (at least for me) while you still need to correct lab Pc to reservoir Pc, I am unconvinced that correcting surface K to reservoir K (for purposes of describing saturation height functions) adds any more accuracy. You may well still need to correct surface to reservoir K/Poro to properly describe your reservoir fabric (especially in low perm reservoirs where the correction can be substantial), but I normally lean toward using the uncorrected perm to anchor saturation height functions against.
Hopefully I've helped and not just added to the confusion!
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