E. Kosari; A. Bahroudi; M. Talebian; A. Chehrazi
Abstract
One of the essential studies in exploration, exploitation and development of hydrocarbon fields is to evaluate the fault and fracture systems and the role that they can play in reservoir quality and geometry. If the hydrocarbon reservoir is a fractured carbonate reservoir, assessing the mentioned properties ...
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One of the essential studies in exploration, exploitation and development of hydrocarbon fields is to evaluate the fault and fracture systems and the role that they can play in reservoir quality and geometry. If the hydrocarbon reservoir is a fractured carbonate reservoir, assessing the mentioned properties is of great importance. Assessment of the structures should be done simultaneously because of their close relations, and the their probable genesis connection should be revealed. In this research, subsurface data including 2D seismic profiles, underground contour maps and FMI log and eventually analogue modeling have been used for evaluation of probable scenarios explaining formation of faults and fractures. The studied area is located at the front of Zagros deformation belt and the Zagros stresses have apparently not affected it. Two sets of faults of different geometry and role have been detected; the first reverse set (N-S trending) was apparently controller of the reservoir geometry in the structure; the second normal set (NW-SE trending) are most likely causative of the main fractures in the field. It is likely that positive inversion tectonic of the basin led to the development of this field in form of a pop-up structure. Based on the interpretations, the internal normal faults have been formed probably by the rise of Hormuz salt or by local stretching due to left-lateral component of the boundary reverse faults. Using interpretation of drilling-induced fractures and break-outs derived from FMI, trends of the Shmax and Shmin are determined. Also it was revealed that the natural fractures and the main set 2 of faults are sub-parallel with the fractures induced by drilling. Therefore, the compatibility between trends of the natural fractures, breakouts and local normal faults can suggest a tectonic origin for the natural fractures.
M Mirzaei; L Soheili; V Ebrahimzadeh Ardestani; A Teymorian Motlagh
Abstract
The main objective of interpretation of acquired gravity data on the Earth's surface is to determine the contrasts in density or shape/dimension of mass anomalies. Interpretation of gravity data can be done through an inversion process. In this research, a block model has been considered for the subsurface ...
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The main objective of interpretation of acquired gravity data on the Earth's surface is to determine the contrasts in density or shape/dimension of mass anomalies. Interpretation of gravity data can be done through an inversion process. In this research, a block model has been considered for the subsurface anomalous mass. By considering a constant initial density (about 2.6 gr/cm3) for all blocks and by using inversion method, distribution of density of the anomalous mass was estimated and interpreted. In this research, Occam method is used to invert 246 gravity data collected in 2007. Results of the gravity data inversion show sufficient fit between observed and calculated gravity data. Using this inversion method, distribution of density in the subsurface layers related to sediments and basement are estimated in this area. Since there is a density contrast between sedimentary layers and basement, the estimated density distribution can help to explore the lithology of formations as well as the discontinuities in them. Densities less than 2 gr/cm3 in horizontal and vertical sections obtained from the inversion are attributed to the alluviums. The depth of these sediments, which include sand, silt and clay of different percentages, is estimated to be less than about 200 m. Unequal density distribution along the layers is taken to indicate fractures. In fact, these fractures are associated with part of the Tabarteh fault in this area, which caused numerous earthquakes (but less than 5 Richters in magnitude) around the Arak and Dawood Abad cities in past years.
A Amirpour Asl Miandoab; Q Sohrabi
Abstract
In this study, horizontal gradient and analytic signal methods have been applied to the reduced aeromagnetic data poled to Iran, to explore subsurface structures in the region. By using these two methods, it is possible to present a map of major geologic-magnetic structures especially large-scale faults ...
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In this study, horizontal gradient and analytic signal methods have been applied to the reduced aeromagnetic data poled to Iran, to explore subsurface structures in the region. By using these two methods, it is possible to present a map of major geologic-magnetic structures especially large-scale faults displaying magnetic signal in the region. Qualitative and quantitative results of this study were then prepared as maps and compared with previous studies. Finally, the agreements and disagreements observed against the previous studies were explained.
M.S Mirkamali; H.R Ramazi; M.R Bakhtiari; H Ramesh
Abstract
This study has focused on identifying fault systems in the HormuzStrait area using compilation of seismic attributes and artificial neural networks. Faults and fractures play an important role in creating areas of high porosity and permeability. In addition, they cut off the cap and reservoir rocks along ...
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This study has focused on identifying fault systems in the HormuzStrait area using compilation of seismic attributes and artificial neural networks. Faults and fractures play an important role in creating areas of high porosity and permeability. In addition, they cut off the cap and reservoir rocks along fluid migration pathways. Intense tectonic activities and salt tectonics have resulted in complex structures in the Strait of Hormuz area. Therefore, precise identification of faults and fracture zones and their extensions has special importance in increasing petroleum production from traps. In order to identify the geometry and kinematics of faults in the Mishan and Aghajari Formations and in the units under the base-Guri unconformity in the HormuzStrait area (eastern part of the Persian Gulf), we have used structural imaging and visualization techniques of seismic interpretation. The structural imaging of the fault zones was obtained by this technique based on the integration of input attributes in an artificial neural network system and creating new attributes. First, a set of advanced attributes were introduced as input for the artificial neural network system to train and compile the calculated attributes on fault and non-fault interpreted points. As a powerful exploration tool, finally, the fault cube was obtained to precisely identify fault systems and better detect faults and fractures in quantitative modeling of the area. As a result of integrated attributes, the high correlation between the faults within the fault cube provides more accurate and reliable tracking of fault extensions. Therefore, three types of fault systems were identified in study area, which are thought to be results of the extensional and compressional tectonics of the Oman Orogeny, vertical tectonic movements of the Zagros Orogeny, and syn-sedimentary salt movements.
SH Pourbeyranvand; M Tatar
Abstract
Having knowledge of stress variations in the Zagros region, southwest Iran is necessary to study the deformation resulting from oblique collision between the Eurasian & the Arabian plates and to obtain insight into the complicated tectonics of the region. In this study, earthquakes focal mechanism ...
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Having knowledge of stress variations in the Zagros region, southwest Iran is necessary to study the deformation resulting from oblique collision between the Eurasian & the Arabian plates and to obtain insight into the complicated tectonics of the region. In this study, earthquakes focal mechanism data were used to collect information on the state of stress in 12 subdivisions of the data including teleseismic and local events in the Zagros region. The stress axis show noticeable variations in the Zagros region, especially around the Oman Line. The angular difference between the stress & strain axis increases from the southeast to the northwest of the ZagrosMountain. The deformation partitioning due to pre-existing faults and fractures and introducing a weak zone in the NW Zagros under the influence of the Main Recent Fault activity may explain this increasing.
B Zamani; M Jalilpour; M Moayyed; M Faridi
Abstract
The Study area is located in 15km Northeast of Tabriz in East-Azarbaidjan province. The rock units in the study area are limited and consist of different members of the Upper red formation (Miocene). Salt bed (Miocene) that diapired is related to the base of the mentioned formation. Due to the rising ...
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The Study area is located in 15km Northeast of Tabriz in East-Azarbaidjan province. The rock units in the study area are limited and consist of different members of the Upper red formation (Miocene). Salt bed (Miocene) that diapired is related to the base of the mentioned formation. Due to the rising of this salt diapir, various structures such as marginal reverse faults, radial normal faults, folds and karsts are developed. In the Northern part of the Tabriz fault, there are a set of basin structures and diapirs, which all have a NW-SE extension axis. The Khaje salt diapir is formed in the southern margin of one of these basins. The different parameters affecting the rising of this salt diapir from which the most important one is the tectonic regime of the study area. The compressional stress causes the formation of these basins. Furthermore, the contact between the Tabriz fault and Nahand (NW-SE) minor fault prepared a weak zone to rise the Khaje salt diapir. After the beginning of rising, other parameters such as buoyancy force, stability of compressional stresses and differential loading have caused the continuing and rising of the Khaje salt diapir. The Khaje salt diapir is young and still rising. In addition, analytical model analysis is evaluated diapirism initiation time about 31000 years. In terms of purity amount, NaCl percentage is very high; where there are no KCl and MgCl2 impurities; therefore, it is suitable for dissolution process. The marly interbeds of salt would make some difficulties in dissolution process. From the gas storage point of view, the depth of salt diapir and the evaluation of the reservoir volume are essential for underground researches and in order to get the accurate results 2D and 3D seismic studies are needed.
B Zamani Gharechamani
Abstract
In the present study, the state of stress in SiahCheshme-Khoy fault zone area in the North-West of Iran has been analyzed based on the systematic inversion of focal mechanisms of earthquakes, and fault slip data, to characterise the stress regime controlling of most faults and earthquakes in this area. ...
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In the present study, the state of stress in SiahCheshme-Khoy fault zone area in the North-West of Iran has been analyzed based on the systematic inversion of focal mechanisms of earthquakes, and fault slip data, to characterise the stress regime controlling of most faults and earthquakes in this area. The calculated average stress regime in this area indicates major NW-SE trending compression which dominates stress regime in strike slip mode with an intermediate stress axis, σ2, close to vertical. Reconstructed stress has shown that average seismotectonic stress and average stress obtained from fault slip data do not have consistency due to of the multi stress regimes in this fault zone. Nonetheless stress separation analysis results for fault slip data and earthquake data have good consistency and their first and second analyzed stress regimes have the same trend. Also comparison between the results of the stress separation analysis between fault slip data and earthquake data, has shown that the second and third stress regime of this analysis are neotectonic stresses that controlling this fault zone movements. The forth stress regime also is a neostress regime that has been shown in seismotectonic stress separation analysis also, but it seems related to the deep faults. The first stress regime that have resulted from stress separation analysis of both field and earthquake data, it seems a paleostress regime which is not shown in seismic data analysis. Also reconstructed stresses in this study, have good consistency with the latest studies in this area especially with geodetic studies.
M. Talebian; S. H. Tabatabaei; M. Fattahi; M. Ghorashi; A. Beitollahi; A. Ghalandarzadeh; M.A. Riahi
Abstract
The Iranian plateau lies between the Arabian and Eurasian plates and accommodates approximately 22 mm/yr of N-S shortening. About 9 mm/y of this shortening is taken up by folding and thrusting in the Zagros while the remaining 13 mm/yr is taken up in the Alborz and Kopeh-Dagh. The Central Iran ...
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The Iranian plateau lies between the Arabian and Eurasian plates and accommodates approximately 22 mm/yr of N-S shortening. About 9 mm/y of this shortening is taken up by folding and thrusting in the Zagros while the remaining 13 mm/yr is taken up in the Alborz and Kopeh-Dagh. The Central Iran block is relatively stable and thus moves to the north with an average velocity of about 13 mm/y. As the stable Afghanistan block lies to the east, the northward motion of Central Iran produces a right-lateral shear in eastern Iran, which is distributed mainly over a few major faults to the west (~5 mm/yr) and east (~ 8 mm/yr) of the Lut desert. Limited information is available about the slip rates of individual faults in eastern Iran; therefore in this study we try to combine all geological, geodetic and available Quaternary dating results to estimate the fault slip rates and distribution of active deformation in eastern Iran. Finally, we report the results from OSL dating of samples taken from uplifted plain deposits near the south end of the Bam-Baravat fault. These results show that this fault is growing in the vertical direction with at a rate of ~ 0.5 mmy-1. Considering geometric relation between the Bam-Baravat and the south Bam earthquake fault, we estimate a slip rate of about 2 mm/y for the south Bam earthquake fault.
F. Yamini-Fard; A. S-Moradi; M. Hosseini; R. Norouzi
Abstract
From June 2004 to December 2008 low seismic activity was recorded near North-Tehran, Taleghan and Kahrizak faults and inside of Tehran city. In contrast, seismic activity along Mosha, Garmsar and North-Alborz faults is considerable. Generally seismic activity decreases from 51 degrees longitude to west. ...
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From June 2004 to December 2008 low seismic activity was recorded near North-Tehran, Taleghan and Kahrizak faults and inside of Tehran city. In contrast, seismic activity along Mosha, Garmsar and North-Alborz faults is considerable. Generally seismic activity decreases from 51 degrees longitude to west. Two earthquakes with 15 and 17 km depth were located in the west of Tehran city. The calculated focal mechanism for one of them is pure strike-slip. High seismic activity is observed along Mosha fault close to Damavand, Boumehen cities and Lavasant-e-Bozorg region. Calculated focal mechanisms along this fault includes both strike-slip, and reverse mechanisms that implies transpression motion, dominantly left-lateral slip along this fault that continued to Lavasanat region in south of the eastern end of the North Tehran fault. Precise location of some events shows depth range of 4-32 km. Generally, calculated focal mechanisms in studied region include both strike-slip and reverse mechanisms and seems that in southern part, approaching Central Iran, reverse mechanisms are dominant. It implies slip partitioning in southern margin of Central Alborz.
A.R. Javaheri Niestanak; A. Javaherian; N. Amini
Abstract
Coherency attribute is one of the proper tools in interpretation of structural discontinuities and stratigraphy features in 3-D seismic data. Coherency measurements in three dimensions discuss trace-to-trace similarity and therefore represent interpretable changes in these cases. The similar traces are ...
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Coherency attribute is one of the proper tools in interpretation of structural discontinuities and stratigraphy features in 3-D seismic data. Coherency measurements in three dimensions discuss trace-to-trace similarity and therefore represent interpretable changes in these cases. The similar traces are mapped with high coherence coefficients while anomalies and discontinuities have low coherence coefficients. Coherency attribute shows evaluation criterion of lateral changes in the seismic response, caused by variation in structure, stratigraphy, lithology, porosity and the presence of hydrocarbon. Output of this attribute is a coherence cube which illustrates structural discontinuities and stratigraphy features with higher resolution. In this paper, the application of two conventional coherency attributes based on eigenstructure and crosscorrelation for detection of faults in 3-D synthetic seismic data and actual seismic data is presented.
Considering the experimental results, this method has an appropriate response to low SNR for 3-D synthetic models and 3-D actual data. In addition, the comparison of eigenstructure -based coherency attribute method with crosscorrelation-based coherency attribute method indicates the former has higher resolution for detection faults than the latter.
