Page 140 - Well Logging and Formation Evaluation

130 Well Logging and Formation Evaluation

case that can be made on behalf of his company. Clearly the petrophysi-
cist has a duty to calculate parameters using accepted and correct method-
ologies. However, it is perfectly reasonable that the methodologies should
be chosen and applied in such a way that they happen to provide the most
favorable equity position for his company.
It is not always obvious how the equity will be affected by a differ-
ent choice of methods and parameters. Therefore, the first step is to set
up a model that will enable the effects of changing parameters and
models on the equity position to be determined quickly. This is most
easily done as follows. Choose a well on either side of the boundary
that may be considered reasonably representative of the existing
wells. In some cases, it might be necessary to choose more than one
well, particularly if both gas and oil are present. Copy all the raw
log data into a spreadsheet. Set up the following parameters as global
variables:

• V sh cutoff
• Porosity cutoff
• Grain density
• Fluid density, gas leg
• Fluid density, oil leg
• Fluid density, water leg
• R w
• m
• n
• FWL
• Gas/oil contact (GOC)
• J function, S wirr
• J function, a value
• J function, b value
• J function, scos(q) (oil/water)
• J function, scos(q) (gas/water)
• Oil density
• Gas density
• Water density
• Gas factor (for converting in-situ gas volume to oil volume)

Set up the evaluation of the wells in terms of the above variables so
that you are able to provide proxies for the equity variables for each well
as follows: