An Investigation of Abnormal Fluid Pressure within an Evaporitic Cap Rock in the Gavbandi Area of Iran and its Impact on the Planning of Gas Exploration Wells

A synthesis of well logs was carried out and drilling mud weight data were analyzed to figure out anomalous high fluid pressure within the Triassic evaporitic cap rock (the Dashtak formation) and study its impact on the geometry of anticlinal traps in the gas rich Gavbandi province located in the southeast part of the Zagros Mountains. The results indicated that the location of anticlinal traps at the depth in which the Permian Dehram Group reservoir unit exists is horizontally displaced with respect to surficial crest of many anticlines within the Gavbandi area. This crestal shift may be induced by abnormally high fluid pressure in the ¿A evaporate¿ member of the Dashtak formation, detected in many exploration wells across the area. When fluid pressure increases due to compaction during shortening, the higher shaliness could probably cap more fluids and consequently increase the fluid pressure within the Dashtak formation. Anomalous high fluid pressure decreases internal friction and shear strength of rock units and facilitates fracturing and faulting within the Dashtak formation, which consequently causes crestal shift of anticlinal traps. This should be taken into account when planning a new exploration well in Gavbandi area in order to prevent trap drilling

Impact of the Late Triassic Dashtak intermediate detachment horizon on anticline geometry in the Central Frontal Fars, SE Zagros fold belt, Iran

Integration of 2-D seismic lines, well data and field studies allow us to determine the geometry variations of anticlines in the highly prolific Central Frontal Fars region in the SE Zagros fold belt. These variations are directly related to changes in thickness of the principal evaporitic intermediate detachment level, located along the Late Triassic Dashtak Formation. Anticlines of short wavelength contain a significant over-thickening of the evaporitic detachment level in their crestal domain that may reach 1900m (from an original thickness of 550-800m). Folds containing thick Dashtak evaporites show decoupling across the detachment level and, thus, a shift of the anticline crest in the underlying Permo-Triassic carbonates of the Dehram Group, which form the major gas reservoir in the Central Frontal Fars. Four main parameters control the extent and distribution of the decoupled anticlines in the study area: (a) original large thickness of the Late Triassic evaporitic basin; (b) coinciding larger amounts of anhydrites with increasing total thickness of formation; (c) parallel occurrences of abnormally high fluid pressures; and (d) shortening variations across, and along, the strike of specific folds. The present work relating the different parameters of the Dashtak evaporites with the anticline geometry allows a better understanding of the fold geometry variations with depth, which is applicable to oil and gas exploration in the SE Zagros and other similar hydrocarbon provinces characterised by intermediate detachment horizonsPeer reviewe

Mapping Quaternary faults in the west of Kavir Plain, north-central Iran, from satellite imageries

Numerous Quaternary faults are found in north-central Iran with an insignificant history of seismic activity. Having either strike-slip or thrust mechanisms, these faults are potentially active and therefore capable of creating destructive earthquakes. In this paper, Landsat Enhanced Thematic Mapper Plus (ETM+) images were used, for the first time, to map these Quaternary faults located in an abandoned area to the west of Kavir Plain in north-central Iran. We also demonstrate the use of satellite imagery to identify Quaternary faults in an unpopulated area using geomorphological features, such as deformed quaternary alluviums, deflected stream channels, shutter ridges and sag ponds, and also fault scarps. The major mapped faults have two main northwest and northeast trends. These faults are following the trends of their counterparts in the eastern and western Alborz range. Despite the evidence of activity in the Quaternary faults, no large earthquakes have been recorded in the study area and therefore they can be considered as only potentially active faults. This is because of the lack of historically recorded earthquakes in the abandoned area in the past centuries or to extensively developed evaporate layers at depths that cause most of the recent deformations to occur aseismically

3-D Structure of permian reservoir and timing of deformation in frontal fars, Zagros Fold-thrust belt

Evolution of the Zagros-Makran Fold Belts, Darius Workshop, 2012, 14-15 May 201

A study of Quaternary structures in the Qom region, West Central Iran

West Central Iran comprises numerous Quaternary faults. Having either strike-slip or thrust mechanisms, these faults are potentially active and therefore capable of creating destructive earthquakes. In this paper, we use satellite images as well as field trips to identify these active faults in the Qom region. The Qom and Indes faults are the main NW-trending faults along which a Quaternary restraining step-over zone has formed. Kamarkuh, Mohsen Abad, and Ferdows anticlines are potentially active structures that formed in this restraining step-over zone. There are some thrusts and anticlines, such as the Alborz anticline and Alborz fault, which are parallel to strike-slip faults such as the Qom fault, indicating deformation partitioning in the area. In addition to NW-trending structures, there is an important NE-trending fault known as the Qomrud fault that has deformed Quaternary deposits and affected Kushk-e-Nosrat fault, Alborz anticline, and Qomrud River. The results of this study imply that the major Quaternary faults of West Central Iran and their restraining step-over zones are potentially active

Post-Neogene right-lateral strike–slip tectonics at the north-western edge of the Lut Block (Kuh-e–Sarhangi Fault), Central Iran

Late Cenozoic strike-slip tectonics and active faulting in Central Iran have been extensively described in the last decades. This study presents results of integrated structural and geomorphological analyses along the Kuh-e-Sarhangi Fault, a major NE-SW striking brittle deformation zone that cuts across the basement and Neogene-Quaternary cover successions at the north-western edge of the Lut Block. Structural investigations document post-Neogene NE-SW dextral transpressive tectonics and geomorphic evidence support a Late Quaternary age for the faulted alluvial fan deposits along the bedrock range fronts. Northward, the nearly parallel Great Kavir (Doruneh) Fault is known to have active left-lateral strike-slip kinematics, and its easternmost segment was considered as the northern margin of the Lut Block. The new findings impose reconsideration of the current regional kinematic models, with implications on the seismogenic fault networks of Central Iran

Magnetostratigraphic constraints on the timing of deformation in Frontal Fars Arc (Zagros Folded Belt, Iran).

14th Castle Meeting (Magiber VIII) , Évora ,31 agosto-6 de septiembre 2014The Zagros Mountain Belt is the result of the closure of the Neo-Tethys Ocean during the convergence between the Arabian and the Eurasian plates. From NE to SW the belt is divided into five parallel structural domains (Figure 1): (1) the Urumieh-Dokhtar magmatic arc, (2) the Sanandaj–Sirjan metamorphic and magmatic zone, (3) the Imbricated Belt, (4) the Simply Folded Belt, and (5) the Mesopotamian- Persian Gulf foreland basin. The Simply Folded Belt and the Mesopotamian foreland basin are the most external domains of the Zagros orogen. The Mountain Front trace defines two salient (Lurestan arc and Fars arc) and two re-entrants (Kirkuk Embayment and Dezful Embayment). The beginning of compression in the Zagros Belt was loosely constrained until recent magnetostratigraphic works in the upper continental successions shed some light on the timing of deformation (Figure 1). Magnetostratigraphic dating of syntectonic sediments indicates that deformation reached the frontal part of the Lurestan arc around 7.5 Ma and was active until the Pliocene-Pleistocene boundary (Homke et al, 2004). A similar study suggested older ages, around 11 Ma, for initiation of folding in the inner part of the Zagros belt (Emami, 2008). To the southeast, in more internal areas of the Simply Folded Belt near the NE side of the Fars arc, magnetostratigraphic dating indicates that folding occurred at 14–15 Ma (Khadivi et al. 2010). In order to extend and refine the timing of deformation in the frontal Fars area, a new magnetostratigraphic section was sampled in the Dowlatabad growth syncline. 208 sites were drilled along a ~ 2200 m stratigraphic section at an average sampling resolution of 10 m/site. The ages obtained were combined with ages provided by 5 samples for 87Sr/86Sr isotopes, 20 samples for calcareous nannoplankton and 5 large samples for low temperature thermochronology. Integration of all these results provides an accurate timing for the evolution of folding, drainage distribution and geohistory of this region

Impact of salt layers interaction on the salt flow kinematics and diapirism in the Eastern Persian Gulf, Iran: Constraints from seismic interpretation, sequential restoration, and physical modelling.

Interpretation of reflection seismic profiles, sequential restoration, and physical modelling are presented to understand the kinematics of salt flow and diapirism in the Eastern Persian Gulf, offshore Southern Iran. Salt tectonics in this area result from the overlapping Ediacaran-Early Cambrian Hormuz Salt, which is regionally present, and Oligocene-Early Miocene Fars Salt, which is locally developed. The Hormuz and Fars salts began flowing at Cambrian(?) and Early Miocene times, respectively. Diapirs fed by the Hormuz Salt rose passively during Palaeozoic and Mesozoic times and were rejuvenated by contractional deformation events in the Cenozoic. Fars-Salt structures exist either as salt walls and anticlines around those diapirs of Hormuz Salt that developed allochthonous salt bodies during a Palaeocene-Eocene contractional squeezing before deposition of the Fars Salt, or as gentle shallow salt pillows above deep pillows of Hormuz Salt, suggesting a kinematic linkage. Flow of Fars Salt was mainly triggered by differential sedimentary loading. It seems that its lateral flow kinematics was controlled by the behaviour of the underlying Hormuz-Salt sheets. More than ~10-km-long salt sheets were efficiently evacuated back towards the Hormuz-Salt diapir, and consequently, maintained the Fars-Salt evacuation and flow to the same direction, accompanied by welding of both salt layers. Conversely, smaller, less than ~3-km-long salt sheets allowed limited salt evacuation or rearrangement that was probably still sufficient to trigger Fars-Salt flow near the central (Hormuz-Salt) diapir. Fars-Salt evacuation was enhanced by differential sedimentary loading, resulting in incipient primary welds. Subsequently, the depocentres migrated towards the areas of available Fars Salt away from the central diapir. In both cases, layer-parallel shortening related to regional contraction probably played also a role in triggering the Fars-Salt flow at Early Miocene, but was more influential at later stages by squeezing the salt structures (Hormuz and Fars) since about Late Miocene onwards