October 31, 1975 - Gerald R. Ford Presidential Library and Museum

eserve est"imates. Such a detailed search and confirmation of data
would tend to defeat the purpose of rapid machine processing for determining
reserve estimates.
Operators Survey Comparisons
Reserve estimates of crude oil developed by decline curve analysis
for 88 fields in Kansas, Oklahoma, and Texas were compared with the
appropriate estimates from the Operators Survey for the same fields.
These estimates were for fie1ds with decline curve reserves in excess of
two million barrels in Kansas and Ok1ahoma and in excess of five million
barre1s in Texas. Table 19 indicates the results of field by field
comparison of reserves.
Table 19--COMPARISON OF CRUDE OIL RESERVE ESTIMATES,
DECLINE CURVE ANALYSIS VS. OPERATORS SURVEY
Decline Curve Est. as Decline Curve
a Percent of Survey
Est.
No. of
·Fields Reserves
(MMBb1s)
Survey Reserves
(MMBb1s)
Under 50 7 56.9 139.0
50 - 89 14 265.3 354.7
90 - 109 7 112. 1 116.2
110 - 149 17 281.3 222.4
150 and over 43 749.8 363.0
Total 88 1,465.4 1,195.3
As Table 19 illustrates, the reserve estimates from decline curve
analysis tended to be higher than those from the Operators Survey. The
aggregate reserve totals for the 88 fields indicate that the decline
curve figures were 20.8 percent higher than those of the Operators
Survey while the aggregate reserve totals for the 47 Texas fields were
only 9.5 percent higher. A small part of this can be explained by the
fact that prior to 1971, Texas production was affected by Statewide
allowables. Therefore, there were insufficient significant data available
to project hyperbolic declines for any Texas fields,and only
exponential declines were projected. The hyperbolic projections used for
some fields in Kansas and Oklahoma tend to compute more optimistic
reserve es'timates because of the fl atting of the curve.
Major Field Studies Comparisons
Only three of the fields studied by FEA that were amenable to decline
curve analysis had comparable 1974 reserve estimates. The reserves from
the decline curves were 19 percent higher than the corresponding reserves
from the engineering studies.
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