Journal of Petroleum Geology (17475457)40(4)pp. 413-426
Reservoir quality in the carbonates of the late Oligocene – early Miocene Asmari Formation at oilfields in SW Iran is enhanced by the presence of a well-developed fracture network. In anticlinal structures, fracture density is partly controlled by geometrical parameters such as the fold curvature. In this study, a geometrical analysis of the Asmari Formation at the NW-SE oriented Aghajari Anticline in the Dezful Embayment is presented, and is based on inscribed circle and curvature analyses of the fold. Iso-curvature and fracture potential maps of the Asmari Formation based on the geometrical analysis are compared to the results of fracture density logs determined from image logs at four widely-spaced wells, and to dynamic mud loss data. The geometrical analysis demonstrates that in areas of high curvature (such as the SE and NW parts of the SW limb of the Aghajari Anticline and the central part of the NE limb), the fracture density is high. Regions of high curvature (in plan or section view) have the greatest potential to develop open fractures. The predicted fracture density distribution based on the geometrical analysis of the Asmari Formation is in good agreement with actual fracture data from the four wells and with mud loss data from the Aghajari oilfield. © 2017 The Authors. Journal of Petroleum Geology © 2017 Scientific Press Ltd
Tectonophysics (00401951)687pp. 56-65
Although the role of various basal and intermediate decollement levels on structural style is well documented individually in many folded terrains, the interaction between basal and intermediate decollements is poorly constrained. This study uses results of two scaled sand-box models shortened from one end to study the variation in structural development in response to varying basal friction and its consequent interaction with intermediate decollement horizons. Two models with similar incompetent intermediate decollement, but with different basal friction (with and without a thick basal decollement), were prepared analogous for the eastern and the western parts of the Razak basement fault in the Fars Region of the eastern part of the Zagros fold thrust belt (ZFTB). Combined results of scaled models with geological observations are used to argue that the basal decollement friction characteristics govern propagation of deformation front. In addition, model results, analogues to north-south direction, show that deformation complexity and disharmonic folding exist in the section where the intermediate decollement has been activated in response to the shortening without the basal decollement (throughout the western part of the Razak basement fault where less thickness of the Hormuz series as the basal decollement has been documented compared to its eastern part). In other words, the complexity in deformation is less portrayed along sections where basal friction beneath the model decreases (e.g. the eastern part of the Razak basement fault). We argue here that, in addition to other parameters (not presented in this study) interaction of intermediate decollement levels with basal decollement friction characteristics could explain decoupling between structures within the sedimentary column of the Fars Region of the eastern part of the Zagros fold thrust belt. © 2016 Elsevier B.V.
International Journal Of Earth Sciences (14373254)105(3)pp. 869-883
The preexisting north–south trending basement faults and their reactivation played an important role during the evolution of the Zagros fold–thrust belt. The Anaran Basement Fault (ABF) in the Lurestan region, NW of the Zagros, has been considered as a N–S trending basement lineament, although its surface structural expression is still debated. In this study, we use satellite images and field observations to identify and analyze the fractures in the sedimentary cover above the ABF. Fracture analysis demonstrates that approaching the ABF, the fracture pattern changes. The fractures association with reactivation of the deep-seated preexisting ABF can be categorized in four sets based on their directions. The mean direction for maximum compressional stress is different between the fault- and fold-related fractures within and around the ABF shear zone. We estimated an orientation of N30° ± 5° for the fault-related fractures and N45° ± 5° for the fold-related fracture sets outside of the ABF shear zone. This difference suggests that the fold-related and fault-related fracture sets have been formed in different two stages of deformation throughout the area. The axial traces of some folds, especially the Anaran anticline, demonstrate a right-lateral offset along the ABF, such that, in central part of the Anaran anticline, the fold axis of this anticline is changed from its original NW–SE trend to approximately north–south trend of the ABF. © 2015, Springer-Verlag Berlin Heidelberg.
Journal of Structural Geology (01918141)65pp. 17-32
Although the role of various basal decollement levels on structural style and deformation propagation is well documented in many folded belts, the effect of lateral variation in intermediate decollements is poorly constrained. This work uses results of three scaled sand-box models shortened from one end to study the variation in structural development between areas with a ductile intermediate decollement and areas without (or with a thinner) intermediate decollement. Combined results of scaled models with field observations are used to argue that the presence of mechanically different intermediate decollement horizons within the Zagros stratigraphy has resulted in deformation partitioning between the Lurestan and Izeh zones. A thick intermediate decollement facilitates a faster propagation of deformation front and a lower taper in comparison with a thinner (or non-existing) intermediate decollement during compression. However, the effect of lateral thickness variation in the intermediate decollement on propagation of deformation is less profound than the effect of mechanical differences in basal decollements. © 2014 Elsevier Ltd.
International Journal Of Earth Sciences (14373254)102(8)pp. 2117-2135
Systematic analog models are run to study the variation in deformation across basement steps in the Zagros fold-thrust belt. Our model results demonstrate that basement configuration/topography influences the sedimentation thickness and, hence, the kinematics and geometric evolution of the fold and thrust belt. The greater the difference in thickness between the adjacent cover units across a basement step, the sharper and clearer will be the offset of the deformation front. Based on model results, we conclude that in a fold-thrust belt, where basement step/topography is covered by a layer of ductile salt acting as a decollement, the effect of the salt decollement on the evolution of the belt is far greater than the effect of thickness variation of the cover units. © 2013 Springer-Verlag Berlin Heidelberg.
Computers and Geosciences (00983004)48pp. 280-288
In this paper, the concept of vulnerability is used to measure the capacity to withstand earthquake disasters in different regions. The purpose of vulnerability analysis is to identify appropriate actions that can be taken to reduce the vulnerability before the potential for damage is realized. The objective of this paper is to determine the vulnerability of different parts of a city against earthquake by data envelopment analysis (DEA). A numerical example demonstrates the application of the DEA for the 20th district of Tehran. © 2012 Elsevier Ltd.
Deformation fronts of fold-thrust belts vary widely in type, geometry and spatial organization. This contribution seeks to understand the effect of lateral variation of intermediate decollement on the deformation front geometry of the ZFTB using analogue models. In order to understand the effect of lateral variation of intermediate decollement on the deformation front geometry of the ZFTB, we will successively focus on two particular regions where recent studies has been done: the Izeh zone and Lurestan which are both situated in the Zagros simply folded belt adjacent togetherIn this study, we use systematic scaled analogue models to investigate the effect of spatial distribution of the intermediate decollement on the deformation style in the Zagros fold and thrust belt.
Journal of Petroleum Geology (17475457)32(1)pp. 5-19
The evolution of the central part of the Lurestan region in the Zagros fold-and-thrust belt has been studied using newly generated isopach maps for different time intervals between the Late Cretaceous and the Miocene. The study was based on existing geological maps, gravity data, measured stratigraphic surface sections, original field work and well data. Understanding the processes which have influenced facies and thickness variations in the study area will have a significant impact on future hydrocarbon exploration. Cenomanian carbonates assigned to the Sarvak Formation, the main reservoir unit in the study area, are composed of both pelagic and neritic facies. These facies occur along the roughly north-south trending "Anaran lineament", interpreted to represent a palaeohigh, which influenced patterns of sedimentation in the Cretaceous-Tertiary. The palaeohigh formed as a result of the reactivation of a basement lineament in the Late Cretaceous. The continuing influence of this lineament on patterns of sedimentation during Oligocene - early Miocene time is indicated by a range of evidence including the presence of clinoform geometries. Analysis of sedimentary thicknesses in the Zagros foreland basin between the Late Cretaceous and the early Miocene indicates progressive SWward migration of the depocentre. Late Cretaceous ophiolite obduction and plate margin convergence exerted a major influence on stratigraphic architecture, and controlled depocentre migration and foreland basin evolution. © 2009 Scientific Press Ltd.
Three main decollement units whithin the sedimentary pile of the Lurestan region were distingushed based on the field observation, seismic data and dipmeter logs from drilled wells. The effect of these decollement units on folding style was studied based on the constructed balanced regional cross section.
Journal of the Geological Society (2041479X)166(6)pp. 1101-1115
The structural style of the folds from the central part of the Lurestan salient located in the NW portion of the Zagros Fold-Thrust Belt has been studied by constructing a regional balanced cross-section from field data, existing geological maps, seismic profiles, stratigraphic surface sections and well data. The regional balanced structural cross-section that is constructed from the High Zagros Fault to the Mountain Front Fault highlights the difference in the folding style across the area. The vertical and lateral changes in the style of the folding indicate the influence of mechano-stratigraphic contrast between the sedimentary units. Three main décollement levels (the basal Lower Palaeozoic, the intermediate Triassic, and the upper Upper Cretaceous-Lower Palaeocene) have been interpreted. Folds developed during the Zagros Fold-Thrust Belt evolution above and below these décollement horizons are decoupled from each other and are different in both geometry and size. Similarly, thickness and facies changes of some formations across the region cause lateral variation in folding pattern from the north to the south. Polyharmonic folds exist in the south, where the different structural levels are relatively strongly coupled. To the north, however, strongly disharmonic folding occurs where a combination of increased décollement thickness and decreased mechanical competence has led to decoupling at different structural levels. This change in folding style has a direct impact on hydrocarbon exploration in the area. To reduce structural risk in exploration, the incorporation of high-resolution deep seismic data with the surface geology is recommended for future hydrocarbon exploration activities within the Lurestan region. © 2009 Geological Society of London.
