Page 75 - The Petroleum System From Source to Trap

3. Petroleum Systems of the World Involving Upper Jurassic Source Rocks 67

Rather than using the petroleum system, Magara system and the Kimmeridgian hot shale-Brent(!) and
(1992, p. 71) contrasts "the ratio of the richest to the possibly the Lam-Amla' ah(!) petroleum systems (Figure
poorest petroliferous basin, in terms of average organic 3.7). In this case, the available BOE (dark gray histogram)
concentration, may be less than 20 to 1" while "the ratio in the Hanifa-Arab system, by unit area, is only half that
of the concentration (BOE-km2) of accumulated oil of the Kimmeridgian hot shale-Brent system and only
(petroleum) in the richest sedimentary basin to that in three-fourths of that estimated for the Lam-Amla'ah, yet
the poorest basin among those basins containing 'giant' the recovery efficiency (light gray histogram) for the
and 'supergiant' fields is more than 500 to 1." As previ­ Hanifa-Arab is 3.5 times higher. This anomaly coincides
ously mentioned, the recovery efficiency of world class with a rating of the other plumbing ingredients wherein
petroleum systems is estimated to range from 4 to 0.04%, the Hanifa-Arab system is twice as high as the
or a range of 100 to 1. Kimmeridgian hot shale-Brent system.
Demaison and Huizinga (Chapter 4, this volume) In general, published remarks that relate to the
emphasize that after the SPI, basin configuration, Hanifa-Arab other plumbing ingredients include (1) a
migration pathways, and drainage areas are the next highly effective and extensive regional evaporite seal; (2)
most important factors to petroleum recovery. Magara the nearly regional extent of the continuous, highly
(1992) emphasizes source rocks character and quality, porous and permeable lime sand Arab Zone reservoir
including the combination of organic concentration, series (the extent of the reservoir rocks is nearly the size
duration of oil generation, thickness of the oil window, of the Alberta basin); (3) growing traps (salt-assisted
source rocks age factor, dynamics, and ratio of fluid block anticlines, flowage, and reefs) with areal sizes up to
expulsion, as well as indicating other factors such as type 900 mi2 and HC columns over 1 0 00 ft (Law, 1 9 57;
of trap, reservoir rocks, cap rocks, and organic matter in Wilson, 1975; Murris, 1984); and (4) plumbing dynamics
source rocks as having great influence on the recovery that allowed for regional (> 0 0 mi) pre-Campanian
1
efficiency. Ulmishek and Harrison (1984) in describing lateral migration.
"independent petroliferous systems" follow Jones (1975) In summary, there are several published comments
and Weeks (1975) by emphasizing trap, reservoir rocks, about the Kimmeridgian hot shale-Brent petroleum
cap rocks, and dynamics as being of equal importance to system. First, effective source-seal shales provide
that of source rocks in petroleum accumulations. presource reservoir rocks with a good cap, although
Perrodon (1980; 1 9 83) and North (1985) treat these postsource shale cap rocks apparently involve consider­
"petroleum plumbing factors" indirectly, but in more able vertical leakage. Second, spacially limited deltaic
detail. sandstones, marine sandstone fans, chalks, and turbiditic
The relative importance of the active source rock in sandstones are locally excellent reservoir rocks but lack
any petroleum system is not only axiomatic; its character the continuity and extent of the Arab zone reservoir.
and plumbing greatly influence recovery efficiency. Third, traps include excellent growing, tilted fault block,
Within the limits of this study, the importance of the salt flowage (diapiric), and compaction and pinch-out
"plumbing ingredient" of the active source rock is noted stratigraphic traps. In general, the province has many
by the widespread essentially humic (locally marine) structural traps. However, the field areal size ratio of the
Lower-Middle Jurassic source rock shales that have Kimmeridgian hot shale-Brent petroleum system area is
contributed only 5% of the BOE from Jurassic source 0.07% (field areal size to petroleum system areal extent),
rocks. These Lower-Middle Jurassic gas-prone source while the same ratio in the Hanifa-Arab is 0.20%. Finally,
rocks are in the same area and presumably the same rift basin fault systems with vertical drainage dynamics
general reservoir, cap, trap, and dynamic habitat as the develop considerable leakage in this system and
high rank, often anoxic Upper Jurassic source rocks that preclude extensive BOE build-up by lateral migration.
account for 95% of the BOE from Jurassic source rocks. The higher TCX:: values and higher gravity crude oils
Another example of the relative importance of the of the Kimmeridgian hot shales-Brent system source
source rock can be observed in Figure 3.7 where the rocks than those of the Hanifa-Arab system indicate that
Bazhenov-Neocomian(!) system in West Siberia, the a greater expulsion efficiency and relatively earlier initia­
Vaca Muerta-Sierras Blancas(!) system in Neuquen, and tion of expulsion probably occurred in the Kimmerid­
the Maril-Taro(.) system in Papua have essentially the gian hot shale-Brent petroleum system (see Palciauskas,
same rating as the other plumbing ingredients (dashed 1991). Although this petroleum system may have had
line) but have a diminishing availability of potential higher rank primary migration, the closely juxtaposed
million BOE generated per square mile from within the regional seal, regional reservoir rocks, and regional
area of each system's mature (spent) source rocks (dark source rocks, together with the trap size of the
gray histogram). In this case, the petroleum system Hanifa-Arab plumbing ingredients, are more effective
recovery efficiency (light gray histogram) and estimated and rank above their counterparts in the Kimmeridgian
ultimate conventionally recoverable million BOE (solid hot shale-Brent system, while the vertical drainage of
line) parallel the diminishing amounts of mature source this system displays less effective dynamics than the
rocks (dark gray histogram). extensive lateral drainage of the Hanifa-Arab petroleum
However, an even more obvious case for the greater system.
importance of "other'' plumbing ingredients and their Another observation becomes apparent when
influence on the petroleum system recovery efficiency is comparing coastal rift basins with their pods of thick
the comparison between the Hanifa-Arab(!) petroleum source rocks to the thinner source rocks of the fold belt