Exploration Insights | 7
Have hydrocarbons migrated?
Is the target organic-lean? Are the hydrocarbons in-situ?
Is the target organic-rich?
Tight Play Shale Play
Above
Source
Below
Source
e.g. Austin Chalk Three Forks Granite Wash
Deep-marine claystone
Is there intercalation within
the source unit?
Between
Source Restricted to
Source Interbedded
Source Pure
Source
Middle Bakken Spraberry Eagle Ford Wooford
Adjacent to
Source
Shallow-marine claystone
Shallow-marine sandstone
Shale play
Tight play
Salina evaporites
Organic-rich mudstone
Deep-marine carbonate
Shallow-marine carbonate
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Figure 2> Simplified verson of the Neftex ® classification scheme differentiating play type and stratigraphic organization within
unconventional resource plays
barrels of oil was estimated for the basin (Jackson
et al., 2019). Initial tests have also been carried
out in the time-equivalent Diyab Formation in
the United Arab Emirates (Baig et al., 2017), and
the “Najmah Kerogen” unit in Kuwait (Rao et al.,
2015).
The middle (S2) (J80–J110) and upper (S3)
(J100–J110) shale plays correspond to
interbedded organic-rich mudstone packages
in the upper Hanifa and Jubaila formations,
respectively. Both plays are classified as
interbedded source shale plays, but the target
lithology changes from a calcareous mudstone in
the Hanifa Formation to an argillaceous mudstone
in the Jubaila Formation. These play types are
potential secondary unconventional shale play
targets, which might provide an additional upside
in distal areas of the intrashelf basins.
The juxtaposition of mature source rocks with
low porosity, low permeability, organic-lean
carbonates suggests tight play potential within
the Middle–Late Jurassic resource interval
across the Middle East. Above-source (T4) (J110),
below-source (T5) (J60), between-source (T6)
(J80–J90), and adjacent-to-source (T7) (J70–J90)
carbonate tight plays are recognized. The above-
source, below-source, and between-source plays
are reliant upon vertical migration into the tight
reservoir from the underlying or overlying source
rock units. The adjacent-to-source play is reliant
upon lateral migration of hydrocarbons from the
mature source kitchen.
In Kuwait, above-source and below-source tight
carbonate reservoirs are currently on production
within the Najmah and Sargelu formations,
respectively. These tight carbonates, with well-
developed natural fracture systems, are separated
by the Najmah Kerogen unit, which acts as the
primary source horizon (Al-Failakawi et al., 2019).
Additionally, above-source tight play potential is
recognized within the Khaleej al-Bahrain Basin,
where organic-lean dolomitized carbonates of
the Hanifa Formation directly overlie source units
within the Tuwaiq Mountain Formation (Al Ansari
et al., 2016).
ANALOGUES
Analogues for emerging plays should focus on
the vital geological components that drive the
prospectivity of the plays and inform exploration,
appraisal, and play development decisions.
In some instances, there may not be a single
analogue that characterizes all aspects of a
play. This is certainly the case for the Middle–
Late Jurassic of the Middle East, where no
single analogue sufficiently characterizes all the
unconventional plays within the resource interval.
A pragmatic approach is to identify several
analogues that characterize different components
of the resource interval from the macroscale (e.g.
stratigraphic architecture) to the microscale (e.g.
porosity development). The following sections
discuss four key analogues, which together
provide insights into the Middle–Late Jurassic
resource interval of the Middle East.
Stratigraphic Architecture Analogue:
Vaca Muerta
The stratigraphic architecture and controls on
lithological variability within the Middle–Late
Jurassic resource interval are similar to the
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2
1
4
1
2
3
Tuwaiq Mountain interbedded source, carbonate mudstone shale play (JS1)
Hanifa interbedded source, carbonate mudstone shale play (JS2)
Jubaila interbedded source, argillaceous mudstone shale play (JS3)
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5
6
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What is the geometric relationship between the target unit(s)
and the source unit?
Legend
6 | Halliburton Landmark
Sargelu below source, carbonate tight play (projected onto section (JS4)
Hanifa/Najmah above source, carbonate tight play (JS5)
Hanifa between source, carbonate tight play (JS6)
Hanifa adjacent to source, carbonate tight play (JS7)
Figure 3> Stratigraphic organization and unconventional play conceptualization within the Middle–Late Jurassic resource interval of the
Middle East (refer to Figure 1 for location).
Vaca Muerta-Quintuco resource interval in
the Neuquén Basin, Argentina (Figure 4). Both
resource intervals were deposited across low-
angle carbonate ramp systems, and are long-
lived with deposition occurring across several
cycles of 3rd order sea level fluctuation. This has
resulted in distinctive clinoform sequences that
prograded during sea-level fall (HST+LST) and
retrograded during sea-level rise (TST) (Figure 4).
There is a similar, and to some extent, predictable
control over stratigraphic organization within
both resource intervals, so exploration concepts
developed in the Vaca Muerta play are likely to
be highly applicable to the Middle–Late Jurassic
carbonate ramp systems across the Middle East.
The high-graded stratigraphic domain (HSD)
concept developed within the Vaca Muerta play
can be readily applied to the Tuwaiq Mountain
(S1) and Hanifa (S2) shale plays (Bromhead et
al., 2017). This concept uses gross depositional
environment maps in a sequence stratigraphic
framework to determine the distribution of
domains (with a vertical and lateral extent),
where organic-rich mudstones are intercalated
with more brittle organic-lean carbonates. This
powerful tool helps to predict stratigraphic
organization within low-angle carbonate ramp
systems, and to characterize mechanical
stratigraphy (Figure 4). The HSD concept can
be used at the basin scale to help predict the
distribution of landing zones and fracture baffles
within the play. For example, the laterally
continuous Hanifa anhydrite could form an
effective fracture baffle, enabling the possibility
of a dual-layer development with potential landing
zones within both the Tuwaiq Mountain and
Hanifa plays.
Natural Fracturing and Trapping
Mechanisms Analogue: Austin Chalk
This analogue is relevant for the tight plays
conceptualized within the Middle–Late Jurassic
resource interval of the Middle East. These
tight plays are heavily reliant on natural fracture
systems, due to the intrinsically low porosity and
permeability of tight carbonate reservoirs.
The Austin Chalk in the U.S. Western Gulf is a
prime example of an established tight carbonate
play, where production is strongly impacted by
the natural fracture network (Pearson et al., 2012).
The Austin Chalk is a dual porosity system, where
hydrocarbon storage capacity is provided by
both matrix porosity and fracture porosity. Matrix
permeability is typically low (0.1 to 0.5 mD), but