Page 50 - Well Logging and Formation Evaluation

40 Well Logging and Formation Evaluation

7. Correct Ec(BHT) to standard temperature using:

Ec 25 C) = Ec BHT)*298 ( 273+ BHT).
(
∞
(
8. Determine the mud filtrate salinity from R mf and temperature.
9. Determine Q vshale using the appropriate chart as supplied by the
contractor. Or else use Q vshale = 4mmol/cc.
10. With the appropriate chart, use Ec(25°C), mud salinity, and Q vshale to
determine the formation-water salinity.
11. Convert the formation-water salinity to R w using the BHT.

At the end of the day it is essential that the model used calculates
100% water in known virgin water-bearing reservoirs. If this is not the
case, you may be certain that the S w calculated in the reservoir will be
incorrect.

2.6 PRESENTING THE RESULTS

Having calculated the f and S w curves, it is usually required to provide
averages over various formation zones. This should be done as follows.
First of all determine over which depths the results should be broken up.
Apart from the formation boundaries as agreed upon with the geologist,
further subdivision should be made for any possible changes in fluid type
or zones where the data are of particularly poor quality, or at any points
where there is marked change in log character. A table such as Table 2.6.1
should be produced.
Note that the average porosity is given by:

h
f ( )average =Â f i h, where is the net thickness. (2.6.1)
The average value of S w is given by

( S w )average =Â i f * S wi Âf . (2.6.2)
i

Where a permeability transform is available, the average permeability
over each major sand body should also be presented.
Usually the net may be defined on the basis of a V sh cutoff. However,
where this has not been possible, a porosity cutoff should be used.
Generally, the cutoff point should be set at a value equivalent to a per-