Əsas səhifə AAPG Memoirs Analog models of faults associated with salt doming and wrenching: application to offshore United...

Analog models of faults associated with salt doming and wrenching: application to offshore United Arab Emirates

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2005
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AAPG Memoirs
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10.1306/1033718M852969
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Yamada, Y., H. Okamura, Y. Tamura, and F. Tsuneyama, 2005, Analog Models of
Faults Associated with Salt Doming and Wrenching: Application to offshore
United Arab Emirates, in R. Sorkhabi and Y. Tsuji, eds., Faults, fluid flow, and
petroleum traps: AAPG Memoir 85, p. 95 – 106.

Analog Models of Faults Associated with
Salt Doming and Wrenching: Application
to offshore United Arab Emirates
Yasuhiro Yamada1
Japan Petroleum Exploration Co., Ltd., Research Center, Chiba, Japan

Hitoshi Okamura2
Technology Research Center, Japan National Oil Corporation, Chiba, Japan

Yoshihiko Tamura
Japan Oil Development Co., Ltd., Tokyo, Japan

Futoshi Tsuneyama3
Technology Research Center, Japan National Oil Corporation, Chiba, Japan

ABSTRACT

R

egional stress has a significant impact on fault development during the formation of salt dome structures. To examine such effects of wrenching, we conducted a series of analog experiments of updoming using dry, granular materials
and observed the deformation on the top free surface. The experiments included three
deformation styles: (1) updoming followed by wrenching, (2) simultaneous updoming
and wrenching, and (3) wrenching followed by updoming. In the first series of the
experiments, the faults produced by simple updoming were overprinted by two strikeslip fault systems that were generated by the subsequent wrenching. The second series of
experiments with the configuration of simultaneous updoming and wrenching generated normal faults in a direction perpendicular to relative extension by the wrench.
In the third series of experiments, the Riedel and anti-Riedel shear faults formed by

1

Present address: Department of Earth Resources Engineering, Kyoto University, Kyoto, Japan.
Present address: INPEX Co., Tokyo, Japan.
Present address: Department of Geophysics, Stanford University, Stanford, California, U.S.A.

2
3

Copyright n2005 by The American Association of Petroleum Geologists.
DOI:10.1306/1033718M852969

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Yamada et al.

wrenching were deformed by the subsequent ; updoming and were overprinted by the
faults related to the updoming.
These experimental results are applied to the fault systems observed above dome
structures in the United Arab Emirates region, where extensive faults in the northwest–
southeast direction have developed. By analogy, these faults were probably formed during
an updoming and simultaneous wrenching. The direction of simple shear inferred from
a comparison of real faults and experimental results suggests that dextral wrenching
caused by the Oman stress regime during the Late Cretaceous affected the region at the
time of the updoming.

INTRODUCTION
Fault systems above salt domes have been investigated by analog experiments for decades (e.g., Parker
and McDowell, 1951, 1955; Cloos, 1955; Withjack and
Scheiner, 1982; Davison et al., 1993; Alsop, 1996). These
experiments provide an ideal situation in which both
the experimental configuration and the resulting deformation are known. Several geometric and kinematic
models for salt domes have been proposed based on analog experiments and have been subsequently applied to
real salt-related structures (e.g., Vendeville and Jackson,
1992a, b). These experiments have expanded our knowledge of fault system development around salt domes
and are also useful for predicting subsurface fluid flow
associated with faults acting as migration pathways.
Experiments on simple updoming have been performed by many researchers following the pioneer works
of Parker and McDowell (1951, 1955) and Cloos (1955).
These researchers used wet clay and dry sand as sedimentary overburden and a pushing rigid plug (Cloos,
1955) or asphalt (Parker and McDowell, 1951, 1955)
to simulate salt. Despite this difference in the material for salt, both experiments demonstrated that radial
normal faults are a common structural feature developed above a dome. Parker and McDowell (1955) have
also noticed that fault patterns are controlled by the
size and shape of the salt dome, the overburden thickness, and the amount of uplift. The elliptical dome experiments of these authors showed that major normal
faults generated along the long axis of the antiform.
The effects of regional stress on fault patterns above
a dome were investigated by Withjack and Scheiner
(1982). They performed experiments having two dome
shapes, circular and elliptical, with simultaneously applied extensional or compressional stress. Their wet clay
models showed that regional stress also affects the fault
patterns produced by updoming. Updoming with extension generated normal faults perpendicular to the
extension direction, as well as minor strike-slip faults at
the rim. With compression, doming produced normal
faults that are parallel to the compression direction at
the center of the dome and reverse faults that are per-

pendicular to the compression at the periphery. The
normal faults curved at their tips and showed a strikeslip element of the displacement.
The current research on dynamically scaled experiments of salt-related structures generally uses substrates of viscous fluids such as polydimethylsiloxane
to model the ductile behavior of salt, and the results
of these experiments have been successfully applied
to a large number of real structures (e.g., Koyi, 1988,
1996; Jackson et al., 1990; Vendeville and Jackson, 1992a;
Jackson, 1995, and references therein). These works recognized that most salt diapers initiate and grow by
differential loading of the overburden, and the buoyancy of salt is inadequate as the driving force of salt
movement. Waltham (1997) demonstrated with numerical simulations that the mechanism can be well explained by differential loading, folding of the overburden, and drag by a moving overburden.
The modeling technique using viscous fluids is,
however, difficult to control particular geometries of
salt structures to form. This is why we used a geometrically constrained balloon instead of ductile substrates
for the updoming of salt.
Fault patterns generated in a wrench tectonic setting have also been investigated by analog experiments
(e.g., Wilcox et al., 1973; Naylor et al., 1986). The shearbox experiments by Wilcox et al. (1973) showed characteristic fault patterns, including the Riedel and antiRiedel faults, normal faults, and reverse faults. The
direction of these faults agrees with that predicted by
the presumable stress field: the normal faults perpendicular to the relative extension and the reverse faults
perpendicular to the relative compression. The Riedel and
anti-Riedel faults are a conjugate set of strike-slip faults
having an axis in the relative compression direction.
To examine the effects of regional wrench on faults
above a dome structure, we have conducted a series of
analog experiments with dry granular material. The
effects of deformation sequence of updoming and
wrenching are also examined. Six representative results
are described and compared with the fault system
observed above a dome structure in the United Arab
Emirates (U.A.E.) region.

Analog Models of Faults Associated with Salt Doming and Wrenching

FIGURE 1. Experimental rig:
(a) apparatus; (b) updoming
apparatus; (c) dome shapes.

EXPERIMENTAL
PROCEDURE
Apparatus
The experimental apparatus used for this study had
a rectangular rubber sheet,
creating regional stress, attached to two metal base plates that could be moved
independently by two oil-pressured actuators (Figure 1a).
One actuator generated extension and contraction by
pulling and pushing a plate, and the other actuator moved
the second base plate perpendicular to the extension and
contraction direction, thus producing simple shear. For
this study, the displacement rates of the actuator were
between 1.33  10 3 and 5.0  10 3 cm s 1 (5.2  10 4
and 1.97  10 3 in. s 1). It was ensured that no unnecessary folding of the rubber sheet occurred during
experiments. This was achieved by extending the rubber
sheet 10%, and then, the actuator for extension was fixed
at the position throughout the experimental program.
Each side of the base plate had fixed vertical end-walls,
forming a deformation box, and its initial dimension
was 100  100  20 cm (39  39  8 in.) (length  width
 height).
Updoming was produced by an apparatus with a
rubber balloon inflated by a water pump (Figure 1b).
The balloon was sandwiched with two metal plates, one
of which has a hole simulating circular or elliptical
dome geometry. The apparatus was placed under the
rubber sheet described above, and its top surface was
entirely coated with fine powder to reduce friction to
the overlain sheet on which experimental material was
deposited. The size of the circular dome was 17.8 cm
(7 in.) in diameter, and that of the elliptical dome was
20 cm (8 in.) in the long axis and 15.6 cm (6.14 in.) in
the short axis (Figure 1c). The direction of the elliptical
dome in the experiments is shown in Figure 1c. The rate
of updoming was between 2.78  10 4 and 1.56 
10 3 cm s 1 (1.1  10 4 and 6.1  10 4 in. s 1).
Combinations of updoming and shear produced by
the rubber sheet can create a variety of experimental
configurations. To analyze the effects of the deformation sequence of updoming (2-cm [0.8-in.] height) and
wrenching (20% shear strain), three types of kinematics
were applied to the experiments. The first kinematic
type (type I) was simple updoming, followed by dextral
wrenching. In the second kinematic type (type II),

updoming was simultaneous with dextral wrenching.
In the third kinematic type of experiment (type III),
dextral wrenching was followed by updoming.

Modeling Material
The modeling material employed was homogeneous dry glass beads, which is a cohesionless spherical
material and fails in accordance with the Navier –
Coulomb criteria. Such granular materials (e.g., dry sand)
are appropriate to model the brittle deformation of the
upper crust and have been successfully used for various
tectonic environments (see Koyi, 1996; Cobbold and
Castro, 1999, and references therein). Artificial microspheres are also commonly used where the shear strength
of dry sand is too strong (e.g., McClay et al., 1998). Physical properties of such experimental materials have been
measured by shear tests, and the microspheres are now
regarded as an appropriate material for analog experiments (Schellart, 2000; Rossi and Storti, 2003).
The glass beads we used were of 45 – 63 mm in diameter, with a grain density of 2.50 g/cm3. The internal
friction angle and the friction coefficient were 25.58
and 0.48, respectively. The glass beads were evenly
sprinkled on the rubber sheet, and the top free surface
was flattened with a scraper every few millimeters. This
procedure was repeated until the material reached the
required thickness. The initial thickness of the material
was 4 cm (1.6 in.) in our experiments. The scaling ratio
of the models to natural structures is approximately
10 5; thus, 1 cm (0.4 in.) in the model scales to 1 km
(0.6 mi) in nature.

Limitations
Physical modeling requires simplification of structural deformation processes, which are products of
various processes over geologic timescales, so that experimental models can be constructed in the laboratory (Vendeville and Cobbold, 1988). This inherent

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limitation must be kept in mind, especially when applying the model results to natural examples. The experiments in this chapter include the following constraints and assumptions: use of granular material, no
variation in the overburden thickness, assumption of
homogeneous brittle nature of the overburden, constant rate of deformation, no mechanical compaction
or chemical diagenesis during deformation, and exclusion of the effects of fluid flow and heat.
The updoming apparatus we used in this study may
be regarded as classic because it does not agree with the
recent knowledge of salt movement mechanism (e.g.,
Waltham, 1997). However, the purpose of our experiments is
to examine the fault geometry above a salt dome where
local extension is generally produced by the updoming.
Such local extension can be similarly produced with our
simple updoming apparatus, and we can use the experimental results to assume the background tectonics of
a region as a first-order approximation.

which were clearly developed in the region free from
the influence of updoming. No reverse faults were observed around the dome.

Kinematic Type III
During the dextral wrench stage, two strike-slip fault
systems were generated on the free surface (Figure 2d).
They had almost the same geometries as those of the
strike-slip faults observed in the region apart from the
dome in the types I and II experiments. Subsequent
updoming produced radial normal faults of short
length and occurring on the dome, similar to those of
the type I experiments (Figure 2e). The reverse faults
observed in the type I experiment were not developed
here. The preexisting strike-slip faults were slightly deformed by the updoming and were overprinted by the
radial faults.

Elliptical Dome Experiments

EXPERIMENTAL RESULTS
Circular Dome Experiments
Kinematic Type I
Structures produced on the top free surface of the experiments during updoming included radial normal
faults above the dome and circular reverse faults on the
periphery (Figure 2a). The radial faults were generally short
(about 3 cm [1.2 in.] or less) and developed particularly
at the dome’s flank, which approximately corresponds
to the point of minimum curvature in the topographic
relief of the experimental surface. The reverse faults were
generally short and segmented and were observed in the
gently dipping region on the periphery of the dome.
During the subsequent dextral wrench stage, two
strike-slip fault systems corresponding to the Riedel (dextral) and the anti-Riedel (sinistral) shear were observed
on the free surface of the experiments (Figure 2b). These
were relatively long (as much as 30 cm [12 in.]) and
almost straight, but not clearly developed above the
dome. The faults slightly changed their direction at the
flank of the dome, where the preexisting normal faults
were cut by the latter strike-slip faults.

Kinematic Type I
Updoming produced normal faults above the dome
and circular reverse faults on the periphery (Figure 3a).
The normal faults formed with a trend roughly parallel
to the long axis, and they splayed outward at the flanks.
The reverse faults were short and segmented, similar to
those of the circular dome experiments.
Subsequent dextral wrench produced strike-slip
fault systems except at the crest of the dome (Figure 3b).
On the flanks, the radial normal faults were overprinted
by the Riedel and anti-Riedel faults. These are similar to
those of the circular dome experiments.

Kinematic Type II
Simultaneous updoming and dextral wrenching
generated a distinct normal fault system above the
dome (Figure 3c). These faults were generally long (as
much as about 10 cm [4 in.]) and dipped toward the
center of the dome. Their strike was perpendicular to
the relative extension generated by the wrench. At the
flank of the dome, the fault branched into two strikeslip fault systems, which were also developed in the
region free from the influence of updoming.

Kinematic Type II
When updoming was produced simultaneously
with dextral wrenching, a distinct normal fault system
developed on the dome (Figure 2c). These faults were
generally long (as much as 10 cm [4 in.]) and dipped
toward the center of the dome. Their strike was perpendicular to the direction of relative extension that
was generated by the wrench. At the flank of the dome,
these faults branched into strike-slip fault systems,

Kinematic Type III
The results of the dextral wrench stage were identical to the circular dome experiments (Figure 3d; also
see Figure 2d) because of similarities in the experimental configuration. This indicates good reproducibility of the experiments. Subsequent updoming produced short normal faults, similar to those of the type I
experiment (Figure 3e). The reverse faults observed in

FIGURE 2. Results of the circular dome experiments: (a) after simple updoming stage (the kinematic type I); (b) after subsequent dextral wrench (the kinematic
type I); (c) after updoming with simultaneous dextral wrench (the kinematic type II); (d) after dextral wrench (the kinematic type III); (e) after subsequent simple
updoming (the kinematic type III).

Analog Models of Faults Associated with Salt Doming and Wrenching
99

FIGURE 3. Results of the elliptical dome experiments: (a) after simple updoming stage (the kinematic type I); (b) after subsequent dextral wrench (the kinematic
type I); (c) after updoming with simultaneous dextral wrench (the kinematic type II); (d) after dextral wrench (the kinematic type III); (e) after subsequent simple
updoming (the kinematic type III).

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Analog Models of Faults Associated with Salt Doming and Wrenching

the type I experiments were not developed. The preexisting strike-slip faults were slightly deformed by the updoming and were overprinted by the short normal faults.

Summary and Discussions of
Experimental Results
Our experiments clearly showed that faulting was
controlled by the regional stress applied to the experiment. During the updoming in the types I and III
experiments, faults observed on the free surface were
similar to those reported from simple updoming experiments (e.g., Parker and McDowell, 1951, 1955; Cloos,
1955; Withjack and Scheiner, 1982). With wrenching,
two strike-slip fault systems were developed as also observed in the previous shear-box experiments (e.g.,
Cloos, 1955; Naylor et al., 1986; Richard et al., 1995).
In the experiments of the kinematic type II, the
stress field above the dome was a combination of updoming and wrenching. The updoming obviously generated layer-parallel extension around the dome, whereas the wrenching produced a stress field in which the
intermediate principal stress axis was in the vertical direction. Their combined stress should have the least
principal compressive stress axis horizontally, parallel
to the relative extension caused by the wrench, and the
maximum principal compressive stress axis vertically
(the gravity). This stress orientation explains the geometry of the characteristic normal faults above the dome
in the kinematic type II experiments.
Types I and III model results also showed that a
change in the stress field could cause interactions of
faults that were generated earlier and those that were
formed later. In the experiments of kinematic type III, the
reverse faults observed in the type I experiments were
less developed. Because the difference in the wrenching
stage of type I and that of type III is only the existence of
the strike-slip faults, the contractional stress around the
dome in the type III experiment might be partly consumed by minor reactivation of the strike-slip faults during the updoming. Such effects of preexisting faults have
been particularly observed in the inverted basins (e.g.,
Cooper and Williams, 1989; Buchanan and Buchanan,
1995; Yamada, 1999), where extensional faults have significant impacts on the subsequent inversion geometry.

APPLICATION TO FAULTS
ABOVE SALT DOMES OFFSHORE
UNITED ARAB EMIRATES
Several domal structures exist in the Middle East,
and many of them are faulted at their reservoir horizons (Al-Husseini and Chimblo, 1994; Cosgrove and

Jubralla, 1994; Mendeck and Al-Madani, 1994; Carman,
1996; Edgell, 1996; Honda et al., 1996; Alsharhan and
Salah, 1997; Grutsch et al., 1998; Johnson et al., 2002).
Figure 4 shows schematic diagrams of fault patterns
above such dome structures around the United Arab
Emirates (U.A.E.) region. It is apparent that the structures
are traversed by many northwest – southeast-trending
normal faults, sometimes in an oblique direction to
the longitudinal axis of the structure (Figure 4a, d). This
suggests that the faults and their geometries were generated under a regional tectonic regime. To discuss the
origin of these faults, the regional tectonics of the U.A.E.
is briefly reviewed, and then the experimental results
of this study are compared.

Tectonic Outline of the U.A.E. Region
The U.A.E. is situated in the southeastern part of
the Arabian Plate and located in a Hormuz salt basin
(Figure 5). The distribution of the Cambrian salt is
strongly controlled by the tectonic environment of
the basin (Edgell, 1996; Alsharhan and Salah, 1997)
and bounded by three main orientations (Talbot and
Alavi, 1996). Two boundaries in the north – south and
northeast–southwest directions are of the 1000–600-Ma
terrane-accreted fabric, and the northwest – southeasttrending boundaries are parallel to the Najd transcurrent faults that were formed about 600 Ma in the PanAfrican basement (Husseini and Husseini, 1990; Talbot
and Alavi, 1996). These tectonic lines place major controls on the petroleum provinces of the region and also
may have affected the local stress fields during the subsequent tectonic history.
The regional tectonics have been investigated especially from the Iranian side of the salt basin (e.g., Talbot
and Alavi, 1996), whereas information from the U.A.E.
side is mainly obtained by petroleum companies and
thus is not widely published. Alsharhan and Salah
(1997) summarized the regional tectonics that affected
the structural configuration of the U.A.E. and suggested
that the basin has experienced six main tectonic stages
from the late Paleozoic to the present. The first two stages
older than the Late Jurassic were extensional tectonics
related to the opening of the Neotethys. Then the tectonics changed to a compressional regime (including four
stages) because of subduction of the Neotethys and collision of the Afro-Arabia Plate with the Sanandaj – Sirjan
block of the Persian Plate. Because of the subduction,
the Neotethys closed, and the subsequent collision
formed the Oman Mountains and the Zagros fold belt.
Marzouk and El Sattar (1994) examined the geometry and location of the dome structures in the U.A.E.
region and proposed that the region was affected by
two major stress regimes: the Oman stress and the Zagros
stress. The Oman stress was named after the tectonic

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Yamada et al.

FIGURE 4. Fault patterns
above dome structures
around the U.A.E. region.

Detailed observations of
the structural geometry and
the subsidence and uplifting
history of the U.A.E. region
suggest that most of the preserved strains are not products
of compressional stress but
are related to shear deformation (Marzouk and El Sattar,
1994). This is supported by
a recent three-dimensional
(3-D) seismic survey revealing that the faults are actually fault zones composed of
arrays of minor en echelon
faults, and that the fault zones
can be interpreted as conjugate shears ( Johnson et al.,
2002). This shear stress should
have strong impact on the
fault development in the
U.A.E. region.

Updoming

activity during the Late Cretaceous, which formed the
Oman Mountains. The principal horizontal stress was
east–west, and the primary shear directions of the Oman
stress are illustrated in Figure 6a. Because the U.A.E. region is relatively close to the convergent plate boundary
east of the Oman Mountains, the indications of strain by
the Oman stress are well preserved. During the Cenozoic,
the direction of the principal horizontal stress in the region has been northeast – southwest, which concords
with the current Arabian Plate motion vector relative to
the Eurasian Plate. This stress is referred to as the Zagros
stress because it was active during the formation of the
Zagros Mountains. Figure 6b shows the primary shear
directions of the Zagros stress. The indications of this
shear strain are, however, not obvious in the U.A.E.
region, probably because of its distant location from
the deformation front of the Zagros Mountains.

The sedimentary rocks in
the U.A.E. region are generally flat with few gentle structural undulations (Alsharhan
and Salah, 1997), and even at
salt domes, the reservoir horizon dips mostly dip less than
28 (e.g., Alsharhan, 1990).
To understand the timing and magnitude of
uplifting of dome structures, the lateral variation in
sedimentary thicknesses was examined on seismic
sections. The target dome structures are located in the
offshore U.A.E. These results (Figure 7) suggest that the
rate of the updoming of each structure in the region
generally reached its maximum in the Late Cretaceous.
Some structures ceased updoming activity in the early
Tertiary, whereas others have continued until the Quaternary. In conjunction with arguments by Talbot and
Alavi (1996) and Alsharhan and Salah (1997) that the
Hormuz Salt did not start to rise until the Jurassic or
the Early Cretaceous, we suggest that the dome structures rapidly developed during the Late Cretaceous.
This updoming history suggests that the Oman stress
significantly influenced the U.A.E. region and triggered
the salt movement.

Analog Models of Faults Associated with Salt Doming and Wrenching

FIGURE 5. The current plate tectonic setting around the Arabian Plate (modified from Marzouk and El Sattar, 1994).

Comparison with Experimental Results
Faults that developed above the salt domes in the
U.A.E. region are highly directional and show little
influence of updoming geometry (Figure 4). In addition, no clear evidence exists
for radial faults. These facts
suggest that the domes in
the U.A.E. region generally
have not experienced an

FIGURE 6. Two stress regimes
that affected the U.A.E. region
(modified from Marzouk
and El Sattar, 1994): (a) the
Oman stress with the maximum horizontal compression
in the east – west direction;
(b) the Zagros stress with the
maximum horizontal compression in the northeast –
southwest direction.

‘‘updoming-only’’ stage corresponding to the kinematic
types I and III of the experiments. This implies that the
regional tectonics were significantly active and strongly
affected the stress field when the dome structures formed.
This tectonic activity, as well as the possible reactivation

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Yamada et al.

southwest (Figure 8b). The experimental results of sinistral wrenching can be obtained by making mirror images
of the original experiments. By using these mirror images,
the direction of the possible sinistral wrench is determined as north-northwest–south-southeast (Figure 8c).
These two scenarios are geometrically equivalent,
and both are possible on the basis of the experimental
results. More refined determination can be made by
comparison with the regional tectonic history. As mentioned above, the region was influenced by two major
stresses, resulting in a primary shear having four directions. The dextral wrench in the east-northeast –
west-southwest direction can be correlated with the
primary shear of the Oman stress (Figure 6a); however, no sinistral wrench in the north-northwest–southsoutheast direction can be found in the tectonic history
(cf. Figure 6). This strongly suggests that the faults
above the dome structures in Figure 4 formed during an
updoming event with simultaneous dextral wrench,
which is a primary shear caused by the Cretaceous Oman
stress. This timing of the updoming agrees with the
results of the relative growth pattern of the structural
development shown in Figure 7.

Subsurface Fluid Flow

FIGURE 7. Relative structural growth of dome structures
offshore the U.A.E. The curvature was estimated from
sediment thickness changes on seismic sections. Note that
the doming was most profound between 100 and 90 Ma.

of preexisting fault systems and deformation of the
overburden, could have triggered the active diapirism
of the salt in the U.A.E. region.
The northwest – southeast-trending faults of the
U.A.E. domes (Figure 4) can be compared with the fault
pattern in the kinematic type II experiment, which also
produced a dominant fault system in the direction of
the relative extension caused by the wrenching. If the
faults in the U.A.E. region were generated in a similar
tectonic setting as that of the type II experiment,
the direction of the wrench can be inferred from the
comparison of the fault patterns observed in the field
and those produced by the experiments. Because the
type II experiment included a dextral wrenching, a
direct correlation of the faults in the real domes and
those in the experiments indicates the direction of
the possible dextral wrench to be east-northeast–west-

The experiments presented in this chapter provide basic information on fault distribution above salt
domes in a wrench tectonic setting. Because faults are
an important migration pathway of subsurface fluids,
the knowledge of fault development processes and
geometries derived from the experiments helps to predict possible fault systems and migration pathways
in the basin even in the absence of 3-D seismic data.
The deformation styles observed in the experiments
can also be used to approximate the internal strain in
each block segmented by the faults. This knowledge
is, in turn, useful to predict possible fracture systems
on subseismic scales and to construct fractured reservoir models, including reservoir heterogeneity induced by faults.

CONCLUSIONS
The geometry of faults that developed above salt
domes is controlled by regional stress. Our experiments
with combinations of updoming and wrenching demonstrated that the faults are generated in a direction
perpendicular to the relative extension caused by the
wrench. The faults obviously change their geometry if
the regional stress is converted from simple updoming
to wrench or vice versa. The faults generated after the
stress conversion are affected by the preexisting faults;
thus, the resultant geometry of the faults is determined
by the sequence of the stresses.

Analog Models of Faults Associated with Salt Doming and Wrenching

FIGURE 8. Two possible
scenarios of shear directions
to explain the faults above
the dome structures around
the U.A.E.: (a) schematic
illustration of a dome and
faults of the region; (b) shear
direction in case of dextral
shear; (c) shear direction in
case of sinistral shear. Note
that all fault directions are
all northwest – southeast.

The experiments also
suggest that the dome structures characterized by a series of northwest–southeastdirected normal faults in the
offshore U.A.E. were developed under a regional stress
field that triggered the active
diapirism of salt at deeper
structural levels.
A comparison with the
experimental results (updoming with dextral wrench)
and their mirror images (updoming with sinistral wrench)
suggests that the faults observed in the U.A.E. dome
structures were probably generated by updoming with
simultaneous dextral wrench in an east-northeast–westsouthwest direction. This wrench component may correspond to the primary shear of the Oman stress regime
that was active during the Late Cretaceous. The timing of
updoming inferred from sedimentary thickness changes
on seismic sections supports this interpretation.
These experimental results are useful to analyze
faults above dome structures in the regions even with
poor seismic quality, to predict possible fault systems and migration pathways, and to construct models of fractured reservoir in petroleum fields.

ACKNOWLEDGMENTS
This research was conducted as a part of the Carbonate Reservoir Research Project at Japan National Oil
Corporation – Technology Research Center ( presently
Japan Oil, Gas and Metals National Corporation). We
acknowledge permissions to publish this work from
the Abu Dhabi National Oil Company, the Japan Oil
Development Co., Ltd., the Japan National Oil Corporation, and the Japan Petroleum Exploration Co., Ltd.
This chapter was reviewed by Hiroaki Komuro, Christopher Talbot, Ken McClay, and Rasoul Sorkhabi, whose
comments greatly improved the manuscript.

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