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Selected Features of Giant Fields, Using Maps and Histograms
By
M.K. Horn1
Search and Discovery Article #10068 (2004)
1M.K. Horn & Associates, Tulsa, OK ([email protected])
Introduction
AAPG Memoir 78, Giant Oil and Gas Fields of the Decade
1990-1999, contains a CD-ROM (Horn, 2003) with tabulation, in thirty columns in
EXCEL format, of information for each of 877 giant fields discovered in the
period 1866-2003. This tabulation, which has recently been updated to 2004
(Horn, 2004), now includes 910 giants (500 million barrels of oil, 3 trillion
cubic feet of gas, or equivalent in ultimate recovery). As part of the update,
the interactive Microsoft mapping program MapPoint was utilized for presenting
68 maps of sedimentary provinces maps, an 
example
of which is shown in
Figure 1.
In this presentation, analysis of the tabulation of the giant fields is extended by examining in detail certain parameters given in the compilation. Specifically, maps (again using MapPoint), as well as EXCEL frequency histograms, are the means of summarizing major features. Since MapPoint is an interactive program, a myriad of examples could have been prepared for this “tour.”
Seven examples using 25 maps and/or histograms are
presented here. The reader is encouraged to explore some of the other
possibilities by utilizing MapPoint (which complements EXCEL and is readily
available from Microsoft) to generate maps using the data on the CD-ROM that
accompanies Memoir 78 or the revised version.
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Figure 3. Middle East sector of the map of giant oil and gas fields. |
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Figure 2 is a global map of the oil and gas giants. Green represents oil fields and red represents gas fields. Figure 3 shows, at a larger scale, the Middle East sector of this map. Note the separation of the oil and gas fields into specific sub-sectors. A similar separation of oil and gas provinces is present in West Siberia, as shown in Figure 4.
Example 2:
Discovery Year
Figures 5-6
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Figure 5. Map of giant fields, categorized according to years since discovery. |
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Figure 6. Frequency graph of giant fields in years since their discovery. |
As noted above, the compilation of giant
fields (Horn, 2003, 2004) includes all fields with ultimate
recovery of 500 million barrels of oil, 3 trillion cubic feet of gas, or
the equivalent. However, this compilation may be misleading if one seeks
information with regard to present oil and gas reserves
derived from the giant fields. For example, a giant with an ultimate
recovery of 1000 million barrels equivalent discovered in 1930 is of
significantly less importance from a resource standpoint than a giant
with an ultimate recovery of 1000 million barrels equivalent discovered
in 1990. The discovery year is thus a key to relative importance today,
as discussed in more detail in the next example.
Even so, in itself, a map of the discovery year for giant fields (Figure 5) is interesting since it provides an historical perspective of the relative shifts of the oil and gas industry during the last 150 years, A frequency histogram (Figure 6) shows that giant oil and gas discoveries peaked 31 to 45 years ago.
Example 3:
Ultimate Recoverable, Remaining, and Depleted Reserves
Figures 7-12
Figure 7 is sized
pie chart showing estimate of remaining recoverable and depleted
reserves, both in MMBOE, in giant fields of North America. The sum of
remaining and depleted reserves is ultimate recoverable. As described in
Memoir 78 (CD-ROM, C. Appendix, 1. Contents), for each field, the
estimate of remaining equivalent reserves is based on an exponential
decline of 3.4% (equivalent to a half-life of 20 years). Decline is
computed as starting seven years after discovery, although exceptions
are taken into account, such as in the Canadian Arctic.
Figures 8, 9, and 10 illustrate, respectively, similar sized pie charts for the North Sea, portions of Europe, Asia and Africa, and Brazil.
Figure 11 is a
frequency histogram of field size based on ultimate recoverable. As
expected, it shows a predominance of fields with ultimate recoverables
of 500-1000 MMBOE. Figure 12 is a frequency
histogram of field size based on remaining reserves, showing an
overwhelming predominance of fields with less than or equal to 1000
MMBOE. In fact, 380 fields have remaining reserves of less than 320
MMBOE and 535 fields have less than 500 MMBOE.
Example 4:
Lithology
Figures 13-16
Figures 13,
14, 15, and
16 are maps of the reservoir lithology in
giant fields, respectively, of the Eastern Hemisphere, North America,
South America, and northern South America, with the last example
utilizing the “zoom “ feature of MapPoint. Note the lithology bands in
the figures, especially Figure 13. Also note
the preponderance of carbonate reservoirs in the Middle East and of
clastic reservoirs in the giant fields of South America.
Example 5:
Trap Type
Figures 17-18
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Figure 18. Map of trap types in giant fields of West Siberia. |
A global map of trap types is shown in Figure 17. As expected, structural traps predominate. In the West Siberia, however (Figure 18), stratigraphic/combination traps are well represented, especially in the southern sector of the West Siberian basin.
Example 6:
Geologic Age of Reservoirs
Figures 19-22
Figure 19 is a global map of the geologic age of the reservoirs in the giant fields. As expected, the younger reservoirs tend to be toward the continental margins. Figure 20 is a polar view of the geologic age of giants.
The interval in age, from the youngest (approximately 1 Ma) to the oldest reservoir (600 Ma) in the giant fields, is portrayed in Figure 21. A frequency histogram of the age interval (Figure 22) shows a peak in the number of fields producing from Mesozoic reservoirs.
Example 7.
Depth of the Primary Producing Reservoirs in Giant Fields
Figures 23-25
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Figure 25. Frequency histogram of reservoir depths of giant fields. |
Figure 23 is a map
of the depth of the primary producing reservoirs in giant fields. The
fields are grouped into deep, intermediate, and shallow.
Figure 24 is a polar global view of giant
field depths. Figure 25 is frequency
histogram of the reservoir depth (in km) of giant fields. The greatest
number of fields produces from depths of 1.51-4.49 km.
Horn, M.K., 2003, Giant fields 1868-2003 (CD-ROM), in Halbouty, M.K., ed., Giant oil and gas fields of the decade 1990-1999: AAPG Memoir 78, 340p.
Horn, M.K., 2004, Giant fields
1868-2004 (CD-ROM): AAPG/Datapages Miscellaneous Data
Series, version
1.2 (revision of Horn, 2003).