Page 142 - Well Logging and Formation Evaluation

132 Well Logging and Formation Evaluation

the maximum will give an indication of which basis for determination is
likely to be the most favorable to your company. However, we will assume
for further discussions that the BOE method is decided upon as being the
most reasonable basis for equity determination.
At this point it is probably best to decide whether it is going to be advan-
tageous to push for a saturation/height function approach to saturation
determination or to opt for a simple Archie approach. Arguments that can
be used in favor of either approach are:

Pro Archie:
• It is relatively easy to agree on the Archie input parameters, particu-
larly if SCAL (special core analysis) data are available and the water
leg has been logged.
• Most petrophysicists will tend to average capillary (cap)-curve data a
different way, and it is hard to agree on a common saturation/height
function.

Pro J Function:
• Saturation/height functions are the only acceptable way to do volu-
metrics in a field.
• This is the type of function that will be used for the dynamic model, so
it should also be used for the volumetrics.

The next step is to determine the relative weight that each of the various
input parameters has on the equity. This is done by varying the input param-
eters sequentially within justifiable ranges and observing the effects on
EQ(BOE 1 ) and EQ(BOE 2 ). The result might be as shown in Figure 9.3.1.
These results tell you where you can hope to make the most impact on
equity. If negotiating which parameters to use with partners, you can
decide up front where you should make a strong case for a particular
parameter being used, possibly in exchange for being more lax on another
parameter.

Net/Gross

If the wells on your side of the boundary tend to have formations of
poorer quality than those on the opposing side, it is in your interest to
push for little or no cutoffs to be applied. As stated in Chapter 2, there are
many good arguments for not applying cutoffs, but even those that are
applied can be calculated in a way that is favorable to your side through