Deepwater Gulf of Mexico 2004: America's Expanding ... - OCS BBS

RESERVE POTENTIAL
This report has examined the history of reserve growth in the GOM. Figure 56 illustrates results of
the latest drilling in the GOM, suggesting very significant production volumes in the near future.
Predicting future discoveries is more difficult. To address the amount of hydrocarbons yet to be
discovered in the GOM, this report will briefly examine one indicator — the “creaming curve” —
and one detailed study — 2000 Assessment of Conventionally Recoverable Hydrocarbon Resources
of the Gulf of Mexico and Atlantic Outer Continental Shelf as of January 1, 1999 (Lore et al., 2001),
commonly known as the 2000 Assessment.
This modified creaming curve (only successful tests are plotted), figure 57, shows the discovered and
implies the undiscovered hydrocarbon volumes in the GOM. The creaming curve plots “cumulative
number of fields by discovery date” against “cumulative discovered hydrocarbon volumes.” Many
such curves demonstrate that the largest fields tend to be discovered early in the exploration cycle.
This phenomenon results in a curve having a steep slope during the early (immature) phase of
exploration and becoming flatter in the mature phase of exploration, when smaller fields are
generally discovered.
Figure 57 contains two creaming curves. The shallow-water GOM is characterized by a curve
typical of a mature trend. The recent slope of the curve is very flat since, in general, smaller fields
are being discovered. Unless a dramatic new exploration play is recognized, only limited reserves
will be added. This prediction is supported by figures 51, 52, 53, and 56, all of which show a decline
in field discovery size and added reserves from the shallow-water GOM over the last 20 years.
The deepwater creaming curve contains fewer field discoveries; however, these fields tend to be
large, resulting in a curve with a steep slope. This slope indicates an area that is still in an immature
exploration phase with many large fields awaiting discovery. The limited number of discoveries,
steep slope of the curve, and large amount of hydrocarbon volumes already discovered support this
prediction.
A more quantitative and geologic-based estimate of future discoveries in the GOM is the
2000 Assessment (Lore et al., 2001), summarized in figure 58. The deepwater is expected to have
ultimate reserves of approximately 71 billion barrels of oil equivalent (BOE), of which 56.4 billion
BOE remains to be discovered. 1 Compare this with the shallow-water ultimate reserves of
approximately 65 billion BOE, of which 15.2 billion BOE remain to be discovered.
1 The forecasts were based on the MMS report Atlas of Gulf of Mexico Gas and Oil Sands (Bascle, 2001).
Each producing field and reservoir in the GOM was assigned to a hydrocarbon play. The 2000 Assessment
(Lore et al., 2001) then forecast the number of hydrocarbons remaining to be discovered in the GOM on the
following factors:
• the number and size of discovered accumulations in an established play
• an estimate of the number of undiscovered accumulations in a play
• lognormal size distribution for these accumulations
The MMS then predicted the size of undiscovered accumulations in each play. Frontier or conceptual plays
were modeled on similar but more mature plays. The undiscovered accumulations were then aggregated for all
92 plays in the 2000 Assessment. To compare reserve numbers from mature fields, recent field discoveries, and
estimates from undiscovered fields, cumulative growth factors were used in the 2000 Assessment. It has been
widely observed that a field’s size “grows” throughout its lifespan. Reasons for this growth vary widely, but
may include areal extension of existing reservoirs, discovery of new reservoirs, improvement in production
procedures, and the natural conservatism of early estimates. A detailed discussion of reserve appreciation and
cumulative growth factors may be found starting on page 49 of the 2000 Assessment. The estimated ultimate
recovery volumes were then used for the forecasts in the 2000 Assessment.
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