The Asmari Formation Oligo-Miocene in age is one of the most important reservoir rocks in SW Iran and Zagros basin and composed of carbonate rocks and locally sandstones and evaporates. In this research, reservoir qua...The Asmari Formation Oligo-Miocene in age is one of the most important reservoir rocks in SW Iran and Zagros basin and composed of carbonate rocks and locally sandstones and evaporates. In this research, reservoir quality controlling factors have been investigated in a well in one of the oil fields in Dezful Embayment, SW Iran. Based on this research, depositional environment, diagenesis and fracturing have been affected on reservoir quality. 3 distinct depositional settings can be recognized in the studied interval including tidal flat, lagoon, and shoal. Among these depositional setting, shoal environment with ooid grainstone microfacies along with interparticle porosity shows good reservoir characteristics. Diagenetic processes also play an important role on reservoir quality;dolomitization and dissolution have positive effects on porosity and enhances reservoir quality, while cementation, anhydritization and compaction have negative effect on it. Fracturing is another important factor affected on the carbonate reservoirs especially in the Asmari Formation.展开更多
The Asmari Formation in the G oilfield on the Iran-Iraq border is a fractured-porous multi-lithology mixed reservoir, for which fracture is an important factor affecting oil productivity and water cut. The characteriz...The Asmari Formation in the G oilfield on the Iran-Iraq border is a fractured-porous multi-lithology mixed reservoir, for which fracture is an important factor affecting oil productivity and water cut. The characterization and modeling of fractures in the carbonate reservoir of G oilfield are challenging due to weak conventional well log responses of fractures and a lack of specific logs, such as image logs. This study proposes an integrated approach for characterizing and modeling fractures in the carbonate reservoir. The features, formation mechanism, influencing factors, and prediction methods of fractures in the Asmari Formation carbonate reservoirs of G oilfield were studied using core observation, thin section, image log, cross-dipole acoustic log (CDAL), geomechanics numerical simulation (GNS), and production data. According to CDAL-based fracture density interpretation, GNS-based fracture intensity prediction between wells, and DFN-based rock fracture properties modeling, the quantitative fracture characterization for G oilfield was realized. This research shows that the fractures in the Asamri Formation are mainly medium-to high-angle shear fractures. The substantial compression stress during the Miocene played a major role in the formation of the prominent fractures and determined their trend in the region, with primary trends of NNW-SSE and NNE-SSW. The fracture distribution has regularity, and the fractures in zone A dolomites are more highly developed than that in zone B limestones vertically. Horizontally, fractures intensity is mainly controlled by faults and structural location. The results of this study may benefit the optimization of well design during field development. From 2019 to 2021, three horizontal wells pilot tests were deployed in the fractures belt in zone A, and these fractures prominently increased the permeability of tight dolomite reservoirs. The initial production of the wells is four to five times the average production of other wells in the area, showing a good development effect. Meanwhile, the updated numerical simulation validates that the history match accuracy of water cut based on the dual-porosity model is significantly improved, proving the fracture evaluation and prediction results to be relatively reliable and applicable.展开更多
The Asmari Formation deposited in the Zagros foreland basin during the OligoceneMiocene.Lithologically,the Asmari Formation consists of limestone,dolomitic limestone,dolomite,argillaceous limestone,some anhydrite （Ka...The Asmari Formation deposited in the Zagros foreland basin during the OligoceneMiocene.Lithologically,the Asmari Formation consists of limestone,dolomitic limestone,dolomite,argillaceous limestone,some anhydrite （Kalhur Member） and sandstones （Ahwaz Member）.This study is based on the analysis of core samples from four subsurface sections （wells Mn-68,Mn-281,Mn-292 and Mn-312） in the Marun Oilfieid in the Dezful embayment subzone in order to infer their provenance and tectonic setting of the Ahwaz Sandstone Member.Petrographical data reveal that the Ahwaz Sandstone comprises 97.5% quartz,1.6% feldspar,and 0.9% rock fragments and all samples are classified as quartz arenites.The provenance and tectonic setting of the Ahwaz Sandstone have been assessed using integrated petrographic and geochemical studies.Petrographic analysis reveals that mono-and poly-crystalline quartz grains from metamorphic and igneous rocks of a craton interior setting were the dominant sources.Chemically,major and trace element concentrations in the rocks of the Ahwaz Sandstone indicate deposition in a passive continental margin setting.As indicated by the CIW index （chemical index of weathering） of the Ahwaz Sandstone （average value of 82） their source area underwent ＂intense＂ recycling but ＂moderate to high＂ degree of chemical weathering.The petrography and geochemistry results are consistent with a tropical,humid climate and low-relief highlands.展开更多
Outcrop and microscopic studies have been applied in this research paper in order to find out the Asmari Formation depositional sequences in the Shajabil Anticline section located at the north of the Izeh Zone,Zagros ...Outcrop and microscopic studies have been applied in this research paper in order to find out the Asmari Formation depositional sequences in the Shajabil Anticline section located at the north of the Izeh Zone,Zagros Basin,Iran.Five depositional sequences were identified based on 11 facies types （bioclast Nummulitidae Lepidocyclinidae packstone,bioclast perforate foraminifera Nephrolepidina Miogypsinoides wackestone-packstone,bioclast perforate foraminifera Corallinacea wackestone-packstone,bioclast echinoid Neorotalia Brachiopoda wackestone-packstone,coral floatstone-rudstone,bioclast Corallinacea imperforate foraminifera wackestone-packstone,bioclast imperforate foraminifera Archaias wackestone-packstone,bioclast imperforate foraminifera Dendritina wackestone-packstone-grainstone,bioclast imperforate foraminifera Borelis wackestonepackstone and very fine sandy mudstone） corresponding to the tidal flat,restricted and semirestricted lagoon and open marine environments of an inner and middle shelf areas.Well-exposed outcrop horizons of Thalassinoides at the study section are a favorable tool for the regional outcrop sequence stratigraphy.Thalassinoides is considered as an outcrop key-bed for recognition of the Rupelian-Chattian maximum flooding depositional sequence.Coral remnants （small colonies） in outcrop exposures also are associated with the HST depositional sequence （Chattian） for the Asmari Formation.The most important achievement of this research is use of associated maximum flooding surfaces （Pg30,Pg40,Pg50,Ngl0 and Ng20） in the Arabian plate.These maximum flooding surfaces could be recorded as an isochrones surface.展开更多
Knowing the current condition of the faults and fractures in a reservoir is crucial for production and injection activities.A good estimation of the fault reactivation potential in the current stress field is a useful...Knowing the current condition of the faults and fractures in a reservoir is crucial for production and injection activities.A good estimation of the fault reactivation potential in the current stress field is a useful tool for locating the appropriate spot to drill injection wells and to calculate the maximum sustainable pore pressure in enhanced oil recovery and geosequestration projects.In this study,after specifying the current stress state in the Gachsaran oilfield based on Anderson’s faulting theory,the reactivation tendency of four faults(F1,F2,F3,and F4)in the Asmari reservoir is analyzed using 3D Mohr diagrams and slip tendency factors.Results showed that all the faults are stable in the current stress state,and F2 has the potential to undergo the highest pore pressure build-up in the field.On the other hand,F3 has the proper conditions(i.e.,strike and dip referring to σHmax orientation)for reactivation.Stress polygons were also applied to show the effect of the pore pressure increase on fault stability,in a graphical manner.According to the results,the best location for drilling a new injection well in this part of the field is the NW side of F2,due to the lower risk of reactivation.It was found that both methods of 3D Mohr diagrams and slip tendency factors predict similar results,and with the lack of image logs for stress orientation determination,the slip tendency method can be applied.The results of such studies can also be used for locating safe injection points and determining the injection pressure prior to numerical modeling in further geomechanical studies.展开更多
Shear wave velocity has numerous applications in geomechanical, petrophysical and geophysical studies of hydrocarbon reserves. However, data related to shear wave velocity isn’t available for all wells, especially ol...Shear wave velocity has numerous applications in geomechanical, petrophysical and geophysical studies of hydrocarbon reserves. However, data related to shear wave velocity isn’t available for all wells, especially old wells and it is very important to estimate this parameter using other well logging. Hence, lots of methods have been developed to estimate these data using other available information of reservoir. In this study, after processing and removing inappropriate petrophysical data, we estimated petrophysical properties affecting shear wave velocity of the reservoir and statistical methods were used to establish relationship between effective petrophysical properties and shear wave velocity. To predict (VS), first we used empirical relationships and then multivariate regression methods and neural networks were used. Multiple regression method is a powerful method that uses correlation between available information and desired parameter. Using this method, we can identify parameters affecting estimation of shear wave velocity. Neural networks can also be trained quickly and present a stable model for predicting shear wave velocity. For this reason, this method is known as “dynamic regression” compared with multiple regression. Neural network used in this study is not like a black box because we have used the results of multiple regression that can easily modify prediction of shear wave velocity through appropriate combination of data. The same information that was intended for multiple regression was used as input in neural networks, and shear wave velocity was obtained using compressional wave velocity and well logging data (neutron, density, gamma and deep resistivity) in carbonate rocks. The results show that methods applied in this carbonate reservoir was successful, so that shear wave velocity was predicted with about 92 and 95 percents of correlation coefficient in multiple regression and neural network method, respectively. Therefore, we propose using these methods to estimate shear wave velocity in wells without this parameter.展开更多
The distribution of good reservoir quality and its causes is the main challenges in carbonate reservoir characterization.This study investigates the effects of diagenetic processes on the reservoir quality of the carb...The distribution of good reservoir quality and its causes is the main challenges in carbonate reservoir characterization.This study investigates the effects of diagenetic processes on the reservoir quality of the carbonate successions of the Asmari Formation,in the Marun oil field,southwest Iran.The study applies an integrated approach including core petrography,petrophysical rock typing,stable carbon and oxygen isotopes as well as major and trace elements analyses.Petrographic studies and geochemical analyses express that the Asmari limestones have been affected mainly by compaction,dissolution,recrystallization,calcite and anhydrite cementation and dolomitization.Among those diagenetic overprints,dolomitization and dissolution played an important role to enhance the reservoir quality of the formation.Moreover,four types of dolomites were recognized and the rate of dolomitization increases toward the top of the Asmari carbonate successions.Possible models for dolomitization include mixing zone,brine reflux,seepage reflux and tidal pumping of seawater.Employing Flow Zone Index and Discrete Rock Type concepts led to classification of the Asmari reservoir into seven reservoir rock types.Integrating reservoir rock typing with petrographic studies and geochemical analyses also confirms that reservoir quality of the Asmari Fm.would have been mainly controlled by diagenetic processes.Moreover,stable isotopes,trace elements and facies analyses support the idea that carbonate intervals of the Asmari Formation were deposited in a warm,shallow-water environment under a saline condition.展开更多
Asmari anticline is a NW-SE fold in the Dezful Embayment sub-basin of Zagros. Fars group (Late Moicene-Quaternary) is cropping out in the cores of anticlines in this area, but Pabdeh and Asmari formations (Oligocene-E...Asmari anticline is a NW-SE fold in the Dezful Embayment sub-basin of Zagros. Fars group (Late Moicene-Quaternary) is cropping out in the cores of anticlines in this area, but Pabdeh and Asmari formations (Oligocene-Early Miocene) have cropped out only in Asmari anticline in the Dezful Embayment. Therefore, it has formed a unique exposure for above formations. In order to this situation, folding mechanism of Asmari anticline has investigated in this research. According to our?results, Asmari anticline has two mechanisms: flexural-slip in post-Cretaceous sequences?(Khami-Quaternary) and fault-bend folding in pre-Cretaceous sequences. So, there is a hybrid folding mechanism that has introduced for the first time in this paper.展开更多
The Asmari Formation （a giant hydrocarbon reservoir） is a thick carbonate sequence of the Oligocene Miocene in the Zagros Basin, southwest of h＇an. This formation is exposed at Tang-e-Lendeh in the Fars interior zo...The Asmari Formation （a giant hydrocarbon reservoir） is a thick carbonate sequence of the Oligocene Miocene in the Zagros Basin, southwest of h＇an. This formation is exposed at Tang-e-Lendeh in the Fars interior zone with a thickness of 190 m comprising medium and thick to massive bedded carbonates. The age of the Asmari Formation in the study area is the late Oligocene （Chattian）-early Miocene （Burdigalian）. Ten microfacies are defined, characterizing a gradual shallowing upward trend; the related environments are as follows： open marine （MF 8-10）, restricted lagoon （MF 6-7）, shoal （MF 3 5）, lagoon （MF 2）, and tidal fiat （MF 1 ）. Based on the environmental interpretations, a homoclinal ramp consisting of inner and middle parts prevails. MF 3-7 are characterized by the occmrence of large and small porcelaneous benthic foraminifera representing a shallow-water setting of an inner ramp, influenced by wave and tidal pro- cesses. MF 8-10, with large particles of coral and algae, represent a deeper fair weather wave base of a middle ramp setting.展开更多
文摘The Asmari Formation Oligo-Miocene in age is one of the most important reservoir rocks in SW Iran and Zagros basin and composed of carbonate rocks and locally sandstones and evaporates. In this research, reservoir quality controlling factors have been investigated in a well in one of the oil fields in Dezful Embayment, SW Iran. Based on this research, depositional environment, diagenesis and fracturing have been affected on reservoir quality. 3 distinct depositional settings can be recognized in the studied interval including tidal flat, lagoon, and shoal. Among these depositional setting, shoal environment with ooid grainstone microfacies along with interparticle porosity shows good reservoir characteristics. Diagenetic processes also play an important role on reservoir quality;dolomitization and dissolution have positive effects on porosity and enhances reservoir quality, while cementation, anhydritization and compaction have negative effect on it. Fracturing is another important factor affected on the carbonate reservoirs especially in the Asmari Formation.
基金supported by the National Science and Technology Major Project“Reservoir Characterization of Typical Thick Carbonate Reservoirs in the Middle East”(Grant No.2017ZX05032004-001).
文摘The Asmari Formation in the G oilfield on the Iran-Iraq border is a fractured-porous multi-lithology mixed reservoir, for which fracture is an important factor affecting oil productivity and water cut. The characterization and modeling of fractures in the carbonate reservoir of G oilfield are challenging due to weak conventional well log responses of fractures and a lack of specific logs, such as image logs. This study proposes an integrated approach for characterizing and modeling fractures in the carbonate reservoir. The features, formation mechanism, influencing factors, and prediction methods of fractures in the Asmari Formation carbonate reservoirs of G oilfield were studied using core observation, thin section, image log, cross-dipole acoustic log (CDAL), geomechanics numerical simulation (GNS), and production data. According to CDAL-based fracture density interpretation, GNS-based fracture intensity prediction between wells, and DFN-based rock fracture properties modeling, the quantitative fracture characterization for G oilfield was realized. This research shows that the fractures in the Asamri Formation are mainly medium-to high-angle shear fractures. The substantial compression stress during the Miocene played a major role in the formation of the prominent fractures and determined their trend in the region, with primary trends of NNW-SSE and NNE-SSW. The fracture distribution has regularity, and the fractures in zone A dolomites are more highly developed than that in zone B limestones vertically. Horizontally, fractures intensity is mainly controlled by faults and structural location. The results of this study may benefit the optimization of well design during field development. From 2019 to 2021, three horizontal wells pilot tests were deployed in the fractures belt in zone A, and these fractures prominently increased the permeability of tight dolomite reservoirs. The initial production of the wells is four to five times the average production of other wells in the area, showing a good development effect. Meanwhile, the updated numerical simulation validates that the history match accuracy of water cut based on the dual-porosity model is significantly improved, proving the fracture evaluation and prediction results to be relatively reliable and applicable.
基金the Ferdowsi University of Mashhad for their logistic support during this study
文摘The Asmari Formation deposited in the Zagros foreland basin during the OligoceneMiocene.Lithologically,the Asmari Formation consists of limestone,dolomitic limestone,dolomite,argillaceous limestone,some anhydrite （Kalhur Member） and sandstones （Ahwaz Member）.This study is based on the analysis of core samples from four subsurface sections （wells Mn-68,Mn-281,Mn-292 and Mn-312） in the Marun Oilfieid in the Dezful embayment subzone in order to infer their provenance and tectonic setting of the Ahwaz Sandstone Member.Petrographical data reveal that the Ahwaz Sandstone comprises 97.5% quartz,1.6% feldspar,and 0.9% rock fragments and all samples are classified as quartz arenites.The provenance and tectonic setting of the Ahwaz Sandstone have been assessed using integrated petrographic and geochemical studies.Petrographic analysis reveals that mono-and poly-crystalline quartz grains from metamorphic and igneous rocks of a craton interior setting were the dominant sources.Chemically,major and trace element concentrations in the rocks of the Ahwaz Sandstone indicate deposition in a passive continental margin setting.As indicated by the CIW index （chemical index of weathering） of the Ahwaz Sandstone （average value of 82） their source area underwent ＂intense＂ recycling but ＂moderate to high＂ degree of chemical weathering.The petrography and geochemistry results are consistent with a tropical,humid climate and low-relief highlands.
文摘Outcrop and microscopic studies have been applied in this research paper in order to find out the Asmari Formation depositional sequences in the Shajabil Anticline section located at the north of the Izeh Zone,Zagros Basin,Iran.Five depositional sequences were identified based on 11 facies types （bioclast Nummulitidae Lepidocyclinidae packstone,bioclast perforate foraminifera Nephrolepidina Miogypsinoides wackestone-packstone,bioclast perforate foraminifera Corallinacea wackestone-packstone,bioclast echinoid Neorotalia Brachiopoda wackestone-packstone,coral floatstone-rudstone,bioclast Corallinacea imperforate foraminifera wackestone-packstone,bioclast imperforate foraminifera Archaias wackestone-packstone,bioclast imperforate foraminifera Dendritina wackestone-packstone-grainstone,bioclast imperforate foraminifera Borelis wackestonepackstone and very fine sandy mudstone） corresponding to the tidal flat,restricted and semirestricted lagoon and open marine environments of an inner and middle shelf areas.Well-exposed outcrop horizons of Thalassinoides at the study section are a favorable tool for the regional outcrop sequence stratigraphy.Thalassinoides is considered as an outcrop key-bed for recognition of the Rupelian-Chattian maximum flooding depositional sequence.Coral remnants （small colonies） in outcrop exposures also are associated with the HST depositional sequence （Chattian） for the Asmari Formation.The most important achievement of this research is use of associated maximum flooding surfaces （Pg30,Pg40,Pg50,Ngl0 and Ng20） in the Arabian plate.These maximum flooding surfaces could be recorded as an isochrones surface.
文摘Knowing the current condition of the faults and fractures in a reservoir is crucial for production and injection activities.A good estimation of the fault reactivation potential in the current stress field is a useful tool for locating the appropriate spot to drill injection wells and to calculate the maximum sustainable pore pressure in enhanced oil recovery and geosequestration projects.In this study,after specifying the current stress state in the Gachsaran oilfield based on Anderson’s faulting theory,the reactivation tendency of four faults(F1,F2,F3,and F4)in the Asmari reservoir is analyzed using 3D Mohr diagrams and slip tendency factors.Results showed that all the faults are stable in the current stress state,and F2 has the potential to undergo the highest pore pressure build-up in the field.On the other hand,F3 has the proper conditions(i.e.,strike and dip referring to σHmax orientation)for reactivation.Stress polygons were also applied to show the effect of the pore pressure increase on fault stability,in a graphical manner.According to the results,the best location for drilling a new injection well in this part of the field is the NW side of F2,due to the lower risk of reactivation.It was found that both methods of 3D Mohr diagrams and slip tendency factors predict similar results,and with the lack of image logs for stress orientation determination,the slip tendency method can be applied.The results of such studies can also be used for locating safe injection points and determining the injection pressure prior to numerical modeling in further geomechanical studies.
文摘Shear wave velocity has numerous applications in geomechanical, petrophysical and geophysical studies of hydrocarbon reserves. However, data related to shear wave velocity isn’t available for all wells, especially old wells and it is very important to estimate this parameter using other well logging. Hence, lots of methods have been developed to estimate these data using other available information of reservoir. In this study, after processing and removing inappropriate petrophysical data, we estimated petrophysical properties affecting shear wave velocity of the reservoir and statistical methods were used to establish relationship between effective petrophysical properties and shear wave velocity. To predict (VS), first we used empirical relationships and then multivariate regression methods and neural networks were used. Multiple regression method is a powerful method that uses correlation between available information and desired parameter. Using this method, we can identify parameters affecting estimation of shear wave velocity. Neural networks can also be trained quickly and present a stable model for predicting shear wave velocity. For this reason, this method is known as “dynamic regression” compared with multiple regression. Neural network used in this study is not like a black box because we have used the results of multiple regression that can easily modify prediction of shear wave velocity through appropriate combination of data. The same information that was intended for multiple regression was used as input in neural networks, and shear wave velocity was obtained using compressional wave velocity and well logging data (neutron, density, gamma and deep resistivity) in carbonate rocks. The results show that methods applied in this carbonate reservoir was successful, so that shear wave velocity was predicted with about 92 and 95 percents of correlation coefficient in multiple regression and neural network method, respectively. Therefore, we propose using these methods to estimate shear wave velocity in wells without this parameter.
基金Ferdowsi University of Mashhad for their logistic and financial support during this study(Project No.3/27852)NSERC for their support.
文摘The distribution of good reservoir quality and its causes is the main challenges in carbonate reservoir characterization.This study investigates the effects of diagenetic processes on the reservoir quality of the carbonate successions of the Asmari Formation,in the Marun oil field,southwest Iran.The study applies an integrated approach including core petrography,petrophysical rock typing,stable carbon and oxygen isotopes as well as major and trace elements analyses.Petrographic studies and geochemical analyses express that the Asmari limestones have been affected mainly by compaction,dissolution,recrystallization,calcite and anhydrite cementation and dolomitization.Among those diagenetic overprints,dolomitization and dissolution played an important role to enhance the reservoir quality of the formation.Moreover,four types of dolomites were recognized and the rate of dolomitization increases toward the top of the Asmari carbonate successions.Possible models for dolomitization include mixing zone,brine reflux,seepage reflux and tidal pumping of seawater.Employing Flow Zone Index and Discrete Rock Type concepts led to classification of the Asmari reservoir into seven reservoir rock types.Integrating reservoir rock typing with petrographic studies and geochemical analyses also confirms that reservoir quality of the Asmari Fm.would have been mainly controlled by diagenetic processes.Moreover,stable isotopes,trace elements and facies analyses support the idea that carbonate intervals of the Asmari Formation were deposited in a warm,shallow-water environment under a saline condition.
文摘Asmari anticline is a NW-SE fold in the Dezful Embayment sub-basin of Zagros. Fars group (Late Moicene-Quaternary) is cropping out in the cores of anticlines in this area, but Pabdeh and Asmari formations (Oligocene-Early Miocene) have cropped out only in Asmari anticline in the Dezful Embayment. Therefore, it has formed a unique exposure for above formations. In order to this situation, folding mechanism of Asmari anticline has investigated in this research. According to our?results, Asmari anticline has two mechanisms: flexural-slip in post-Cretaceous sequences?(Khami-Quaternary) and fault-bend folding in pre-Cretaceous sequences. So, there is a hybrid folding mechanism that has introduced for the first time in this paper.
文摘The Asmari Formation （a giant hydrocarbon reservoir） is a thick carbonate sequence of the Oligocene Miocene in the Zagros Basin, southwest of h＇an. This formation is exposed at Tang-e-Lendeh in the Fars interior zone with a thickness of 190 m comprising medium and thick to massive bedded carbonates. The age of the Asmari Formation in the study area is the late Oligocene （Chattian）-early Miocene （Burdigalian）. Ten microfacies are defined, characterizing a gradual shallowing upward trend; the related environments are as follows： open marine （MF 8-10）, restricted lagoon （MF 6-7）, shoal （MF 3 5）, lagoon （MF 2）, and tidal fiat （MF 1 ）. Based on the environmental interpretations, a homoclinal ramp consisting of inner and middle parts prevails. MF 3-7 are characterized by the occmrence of large and small porcelaneous benthic foraminifera representing a shallow-water setting of an inner ramp, influenced by wave and tidal pro- cesses. MF 8-10, with large particles of coral and algae, represent a deeper fair weather wave base of a middle ramp setting.
