Page 190 - Hydrocarbon Exploration and Production Second Edition

Volumetric Estimation 177

1 1
1000 1200
1400 0
OWC 10
20
20
10
1 2
0
Structure map Net sand map (m)
(channel)

Thickness
(m) 4 3
20
1
0
10
20
10 10 20
OWC
0
Area (m 2)
Net oil sand volume Net oil sand (m)
Figure 7.3 Net oil sand mapping and area^thickness method.

7.2. Expressing Uncertainty

As shown in Section 7.1, the calculation of volumetrics for a field involves
the combination of a number of input parameters. It should be realised that each
of these has a range of uncertainty in its estimation. The extent of this range of
uncertainty will depend upon the amount of data available, and the accuracy of that
data. The value in combining ranges of uncertainty in the input parameters to give
a range of estimates for STOIIP, GIIP and UR is that both upside potential and
downside risks can be quantified. Using a single figure to represent, say STOIIP,
may lead to missed opportunities, or unrecognised risk.
The range of uncertainty in the UR may be too large to commit to a particular
development plan, and field appraisal may be required to reduce the uncertainty
and allow a more suitable development plan to be formed. Unless the range of
uncertainty is quantified using statistical techniques and representations, the need