Page 52 - Well Logging and Formation Evaluation

42 Well Logging and Formation Evaluation

Exercise 2.1 Quicklook Exercise

Using the log data presented in Appendix 1 (test1 well), do the following:

1. Pick GR sa and GR sh from inspection of the logs.
2. Calculate V sh.
3. Pick the likely position of the OWC.
4. Assuming appropriate fluid densities for the oil and water legs (well
was drilled with fresh WBM) and a grain density of 2.66g/cc, calcu-
late the porosity.
5. Set the porosity to zero wherever V sh > 0.5.
6. Make a Pickett plot over the water-bearing interval.
7. Assuming that m = n = 2, choose an appropriate R w.
8. Calculate S w using Archie’s equation.
9. Check the assumed position of the OWC. If it needs to be moved,
recalculate the porosity (and S w) accordingly.
10. Calculate SHPOR. Display SHPOR in the same depth track as the
porosity.
11. Divide the formation into appropriate intervals and calculate sums and
averages.
12. Suggest points for the formation pressure tool.

2.7 PRESSURE/SAMPLING

In most cases there will be a requirement to run the pressure/sampling
tool to acquire pretests and possibly downhole samples. While these data
are also used by the reservoir engineer and production technologist, they
can be extremely valuable to the petrophysicist in determining the fluids
present in the formation.
Pretests can provide the following information:
• The depths of any FWLs or GOC in the well
• The in-situ fluid densities of the gas, oil, and water legs
• The absolute value of the aquifer pressure and formation pressure
• A qualitative indication of mobility and permeability
• The bottomhole pressure and temperature in the wellbore

Additionally, acquiring downhole samples can provide the following
information: