Page 62 - Well Logging and Formation Evaluation

52 Well Logging and Formation Evaluation

core porosity

log density (g/cc)

Figure 3.2.1 Core Calibration of Porosity

through the data so that the core grain density is honored, and then to
extrapolate the line to the point at which core porosity is unity to deter-
mine the appropriate fluid density. Note that this has to be done separately
in any gas, oil, and water legs. In theory the fluid densities thus derived
should be close to those assumed during the quicklook analyses. Differ-
ences might occur due to:

1. Slight miscalibration of the density log
2. Effect of certain mud chemicals (e.g., barite) on the density log
3. Invasion being less or more than previously assumed
4. Problems with the core plug measurements or conversion to in-situ

Whatever the reason for the apparent fluid densities being what they
are, the combination of the assumed grain and fluid densities, when
applied to the density log, will at least ensure that the log porosities match
the core densities. Where the fluid densities are anomalous, one would
probably want to use them in only the current well, and possibly only over
the cored interval. If, however, the densities agree with the values