Page 143 - Well Logging and Formation Evaluation

Equity Determinations 133

0.25 0.5
gas factor
1.7 n 2.1
Parameter 0.35 2.63 vshco 2.68
rhog
0.6
0.08 porco 0.15

1.8 m 2.2

–6.00% –4.00% –2.00% 0.00% 2.00% 4.00% 6.00%
Equity Points

Figure 9.3.1 Effect of Petrophysical Parameters on Equity

the way that V sh is calculated and the V sh cutoff that is applied. If the
wells on your side are relatively good, you could make an argument that
for equity, as distinct from normal calculations of HIIP (hydrocarbons
initially in place), it is only reasonable to include sands that are likely to
contribute to production via the base-case development scenario, rather
than to include those that could conceivably produce, given some exotic
recovery mechanism yet to be devised.
If using a V sh cutoff results in lower equity than using a porosity cutoff
(based on the density) or density/neutron crossover, then you can make a
case for using an alternative method. If net/gross is a property that will
be mapped over the reservoir, you need to further consider how this
mapping will be done. Within commercial contouring packages, there are
different algorithms that can be used for this that will give different equity
results. You might also consider it in your interest to propose just using a
constant net/gross over the entire field or using a different constant on
either side of the boundary.

Porosity

Assuming that the density log method is being used to determine
porosity, you can investigate which choice of fluid density and grain