Donald G. Hill, Ph.D., 

R.Gp., R.G., R.P.G.

Consulting Petrophysicist

"The World is my District"

 

California Registered Geophysicist No. 170

California Registered Geologist No. 6043

Kentucky Registered Professional Geologist No. 1624

Texas Licensed Professional Geophysicist No. 6289

 

Core Measurements on Vuggy Carbonates Can be Misleading

 

PhiPCT.gif

The log (density/neutron cross-plot) porosity, in the core/log porosity cross-plot above, is systematically much higher than the routine core analysis helium porosity, measured on cores from the same depths.  It is not unusual for routine core analysis (KPS) porosities to differ from from log estimates.  KPS porosities, however, are usually larger than the log values because the routine core measurements are made at ambient (i.e., unconfined) pressures.  The cross-plot above shows the exact opposite relationship.   

CAST1100.GIF

The reason for the above Log/Core porosity cross-plots relationships are obvious from the acoustic borehole televiewer (BHTV) false color synthetic core images.  The reservoir rock is riddled with small (pea sized to thumb nail sized) vugs, which manifest themselves as small protuberances on the outside of the BHTV synthetic core images.  Routine KPS measurements, using two different protocols, did not see these small vugs and yielded the matrix porosity only, while the wireline porosity is the total (including vuggy) porosity.

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Contact:  Donald G. Hill at: Cell/Business Phone:  +(925) 437-5748,   FAX:   +(309) 420-7354,   Home Phone:  +(925) 947-1541  

E-Mail:  dgh@hillpetro.com

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