International Petroleum Technology Conference, 2014
The Cretaceous-aged reservoirs of Iran and their counterparts on the Arabian platform are among t... more The Cretaceous-aged reservoirs of Iran and their counterparts on the Arabian platform are among the most important carbonate reservoirs developed under the warm equable climate. Intense tectonic activities combined with the eustatic sea-level changes caused sporadic exposures of these carbonate successions in SW Iran and some other areas of the Middle East. Under the domination of warm and humid climate and long-term exposures, several erosional disconformities formed throughout these successions. To investigate these palaeoexposure surfaces, petrographic and geochemical studies were carried out in four subsurface sections of giant and supergiant oilfields located in northern and southern parts of the Dezful Embayment. Some of the most important diagenetic features (such as extensive meteoric dissolution/karstification, palaeosol development, and collapsed-dissolution brecciation) were used as evidence for recognition of main palaeoexposure surfaces and associated karsts. Isotopic composition (δ13C and δ18O) and trace element concentrations of these carbonate rocks were used to elaborate the effects of these surfaces on diagenetic evolutions of palaeo-karstic Bangestan reservoirs. Both carbon and oxygen isotope ratios show a spectacular decline just below these disconformities in comparison with the expected values for the simultaneous marine carbonates, indicating that the Bangestan carbonates underwent extensive meteoric diagenesis. Elemental concentrations (Mn, Fe, and Sr) also point to moderate to intense meteoric diagenetic alterations associated with the palaeoexposure surfaces.
Journal of Stratigraphy and Sedimentology Researches, 2020
<strong>Abstract</strong> The Fahliyan Formation is a member of the Khami Group with ... more <strong>Abstract</strong> The Fahliyan Formation is a member of the Khami Group with Neocomian–Barremian age. In two surface sections in the Izeh Zone and two wells of the southern Dezful Embayment, it includes 12 microfacies deposited on four facies belts as tidal flat, inner ramp (lagoon, <em>Lithocodium</em>–algal mounds and bioclastic–peloidal shoals), middle ramp and outer ramp. A homoclinal ramp model is proposed as its depositional environment. Important diagenetic alterations are dissolution, micritization, compaction, dolomitization, silicification, pyritization, cementation and fracturing. They represent marine, meteoric and shallow to deep burial diagenetic realms. Sequence stratigraphic analysis resulted in the recognition of four depositional sequences that seem to be third-order sequences, according to their relative ages (biozones), thickness and correlation with neighboring areas. Reservoir quality evaluation indicates coupled imprints of facies characteristics and diagenetic alterations on reservoir properties of this formation. Important reservoir units are formed in <em>Lithocodium</em>–algal mounds/patch-reefs (in the Garangan Field) and high-energy facies of shoal setting (in the Gachsaran Field). They include primary pore types such as intra- and interparticle pores and mainly concentrated in highstand systems tracts (HSTs) of depositional sequences. Some secondary pores are also present that include dissolution vugs and molds. In addition, middle ramp facies provide some reservoir units in the transgressive systems tracts (TSTs). No macroscopic pores are recorded in these facies and micropores are responsible for high reservoir quality. <strong>Keywords:</strong> Fahliyan Formation, Depositional sequences, Diagenesis, Reservoir quality, Central Zagros <strong><br clear="all" /> </strong> <strong>Introduction</strong> The Neocomian–Barremian Fahliyan Formation is a member of the Khami Group that form important hydrocarbon reservoir in SW Iran (James and Wynd 1965). Tectonic activities an [...]
سازند فهلیان شامل توالی کربناتۀ نسبتا ضخیمی از گروه خامی به سن نئوکومین- بارمین است. مطالعه‌های ر... more سازند فهلیان شامل توالی کربناتۀ نسبتا ضخیمی از گروه خامی به سن نئوکومین- بارمین است. مطالعه‌های رسوب‌شناسی انجام‌شده روی این سازند در دو برش از زون ایذه و دو چاه از بخش جنوبی فروافتادگی دزفول به شناسایی 12 ریزرخساره در چهار کمربند رخسارهای شامل پهنۀ جزرومدی، رمپ درونی (لاگون، پشته‌های لیتوکودیومی- جلبکی و شول‌های بایوکلستی- پلوئیدی)، رمپ میانی و رمپ بیرونی منجر شد. محیط رسوب‌گذاری سازند فهلیان در ناحیۀ مطالعه‌شده، رمپ کربناتۀ هم‌شیب پیشنهاد می‌شود. مهم‌ترین فرایندهای دیاژنزی شناسایی‌شده شامل انحلال، میکرایتی‌شدن، تراکم، دولومیتی‌شدن، سیلیسی‌شدن، پیریتی‌شدن، سیمانی‌شدن و شکستگی است که طی مراحل مختلف دیاژنز دریایی، جوی و دفنی کم‌عمق تا عمیق ایجاد شده‌اند. مطالعه‌های چینه‌نگاری سکانسی به تفکیک چهار سکانس رسوبی در این سازند منجر شدند که با‌توجه‌به سن نسبی آنها بر اساس بایوزون‌های تفکیک‌شده، ضخامت سکانس‌ها و تطابق آنها با نواحی مجاور به‌طور محتمل سکانس‌های ردۀ سوم هستند. مطالعه‌های کیفیت مخزنی گویای تأثیر ویژگیهای رخسارهای و فرایندهای دیاژنزی بر ویژگیهای مخزنی سازند فهلیان است. رخسار...
Journal of Petroleum Exploration and Production, 2021
Knowledge of initial fluids saturation has great importance in hydrocarbon reservoir analysis and... more Knowledge of initial fluids saturation has great importance in hydrocarbon reservoir analysis and modelling. Distribution of initial water saturation (Swi) in 3D models dictates the original oil in place (STOIIP), which consequently influences reserve estimation and dynamic modelling. Calculation of initial water saturation in heterogeneous carbonate reservoirs always is a challenging task, because these reservoirs have complex depositional and diagenetic history with a complex pore network. This paper aims to model the initial water saturation in a pore facies framework, in a heterogeneous carbonate reservoir. Petrographic studies were accomplished to define depositional facies, diagenetic features and pore types. Accordingly, isolated pores are dominant in the upper parts, while the lower intervals contain more interconnected interparticle pore types. Generally, in the upper and middle parts of the reservoir, diagenetic alterations such as cementation and compaction decreased the ...
Journal of Petroleum Science and Engineering, 2021
Abstract This study integrates quantitative analysis of reservoir properties with geological para... more Abstract This study integrates quantitative analysis of reservoir properties with geological parameters to discriminate the reservoir heterogeneities in the Permian–Triassic sequences of the Persian Gulf. To achieve this goal, geological analysis of core samples and thin sections were integrated with petrophysical logs and porosity–permeability data. For quantitative assessment of reservoir heterogeneity, Coefficient of Variation (CV), Dykstra-Parsons Coefficient (VDP) and Lorenz Coefficient (VLC) were used along with the concept of Hydraulic Flow Units (HFU). Depositional facies, diagenetic alterations and sequence stratigraphic framework of the reservoir were used as a basis for the interpretation of geological heterogeneities. Accordingly, 14 microfacies types and 5 facies belts have been defined and indicate a low-angle (homoclinal) ramp model. Complex diagenesis history of these sequences includes marine, hypersaline and shallow to deep burial diagenesis that considerably altered the primary distribution of reservoir properties. A comparison of tested methods revealed that the CV is the best approach for quantification of heterogeneity in targeted reservoir. Consequently, the K4 and K2 are proposed as the most homogeneous units with a dominance of grain-supported facies of shoal setting, intense effects of hypersaline dissolution and lesser effect of compaction and cementation. The K3 and K1 units show high levels of heterogeneity resulting from the combined facies changes and diagenetic alterations (dolomitization, cementation and compaction). Finally, sequence stratigraphic framework of reservoir heterogeneities is discussed for all reservoir units and can be used as a basis for ongoing reservoir studies of the Permian–Triassic sequences in the Persian Gulf and the Middle East.
Abstract New high-resolution biostratigraphy and facies analyses indicate that a Coniacian-Santon... more Abstract New high-resolution biostratigraphy and facies analyses indicate that a Coniacian-Santonian homoclinal carbonate ramp (Ilam Fm.) developed on the subaerially exposed mid-Turonian surface at the top of Sarvak Fm. in Fars zone of the Zagros Basin (northeastern margin of the Arabian Plate). Spatial facies distribution, sequence stratigraphy, and lateral variation in the thickness of Ilam Fm., as well as extend of erosion of the underlying Sarvak Fm. suggest that a combination of regional tectonic activities and global sea-level changes controlled the development of this succession. A major tectonic configuration in the Zagros belt including several basement faults subdivide the belt into different blocks with distinctive sedimentary records. Reactivation of these preexisting basement faults during Late Cretaceous provided a horst and graben geometry due to the closure of Neo-Tethys. Three of our studied sections are located on an upthrown block, bounded between Kazerun and Karebas basement faults, include inner and mid-ramp deposits. These sections represent an eastward deepening trend which correspond to eastward tilting of this fault block. The easternmost section is located in the eastern neighboring downthrown block , bounded between Karebas and Bastak faults, and includes outer ramp and basin deposits confirming a significant paleo-bathymetrical contrast between the two blocks. Furthermore, eastward thickening of the Ilam Fm. independently confirms the increase of accommodation space, as a result of deeper depositional condition, toward center of the Fars zone. Absence of subaerial exposure features at top of the Sarvak Fm. in the downthrown block shows that the global sea-level fall and regional tectonic regime also controlled the extend of unconformity underlying the Coniacian-Santonian platform deposits (Ilam Fm.).
Journal of Petroleum Science and Engineering, 2021
Abstract Dariyan Formation (Aptian) is one of the important hydrocarbon reservoirs in the Persian... more Abstract Dariyan Formation (Aptian) is one of the important hydrocarbon reservoirs in the Persian Gulf. In this reservoir, porosity is controlled by various depositional and diagenetic factors. This study integrates petrographic, geochemical, petrophysical and reservoir quality data to distinguish various pore types and their evolution in two fields selected from the SE and NW Persian Gulf. Primary (depositional) and secondary (diagenetic) pore types are differentiated using the results of macroscopic (core) and microscopic (thin section and SEM) petrographic studies. Pore size distribution and reservoir importance are evaluated by MICP and porosity–permeability measurements on core-plug samples. Macroscopic pores are formed within the grain-dominated and dissolved mud-dominated facies that are located in the RST of third-order sequences, especially within the lower carbonate unit. Micropores are recorded in mud-dominated facies of middle to outer ramp settings with minor effects of meteoric dissolution. Accordingly, evolution in an open diagenetic system with high water/rock ratio is proposed for grain-supported facies, and a closed diagenetic system for mud-dominated intervals. There are close relationships between micrite micro-textures (MTCs) and reservoir properties of mud-dominated facies. A dynamic pore evolution model is presented for the Dariyan Formation that integrates all depositional and diagenetic features in sequence stratigraphic framework. This model can be used for ongoing reservoir studies of this formation in hydrocarbon fields of the Persian Gulf.
Aptian carbonates, major hydrocarbon reservoirs in the Persian Gulf, were deposited on a ramp-lik... more Aptian carbonates, major hydrocarbon reservoirs in the Persian Gulf, were deposited on a ramp-like platform to intrashelf basinal setting under the controls of tectonics and eustasy. Coated grains (oncoids and pisoids) are abundant and show different textures and internal microstructures depending on the stratigraphic position. These Aptian coated grains are divided according to their texture, cortex composition, morphology, type of biota and internal structure, based on petrographic (routine petrography, cathodoluminescence and scanning electron microscope) and geochemical analyses. Accordingly, four types of oncoid and a pisoid group are identified. Oncoid types 1 and 2 along with pisoids typically formed during phases of relative sea-level fall developed within the regressive systems tract (RST). They are commonly associated with shallow-marine (inner ramp), high-energy shoal facies and occur below exposure horizons, at sequence boundaries. Oncoid types 3 and 4 show micro-encrusters (i.e. Lithocodium aggregatum and Bacinella irregularis) and usually occur in a wackestone texture that indicates deposition in a low-energy lagoonal setting with low sedimentation rate during rises in relative sea level (i.e. a transgressive systems tract: TST). Stable carbon and oxygen isotopes are used to define the OAE1a and its environmental effects in the Dariyan Formation. Palaeoenvironmental proxies reflecting energy level, sedimentation rate and trophic level are evaluated for Aptian sedimentary sequences deposited on the southern margin of the Neo-Tethys Ocean.
This study delineates reservoir and non-reservoir zones in the Lower Cretaceous Dariyan Formation... more This study delineates reservoir and non-reservoir zones in the Lower Cretaceous Dariyan Formation as units that are characteristic of the stratigraphic section representative of portions of the Persian Gulf offshore area. Reservoir rock types are categorized by textural and diagenetic properties. Static flow zones were delineated by porosity and permeability measurements of cored intervals. Electrofacies were prepared from clusters of petrophysical data to define reservoir zones for areas lacking wells with cored intervals. The attributes of these reservoirs are integrated into a sequence stratigraphic framework. This research indicates that rock types and reservoir zones of the Dariyan Formation differ in the studied fields located to the west and to the east in the Persian Gulf. These differences are interpreted to have resulted from a differing tectonostratigraphic framework that controlled depositional facies and subsequent diagenesis. For example, reservoirs associated with the lower and upper carbonate units of the Dariyan Formation have different lithofacies and diagenetic modifications that resulted from deposition at two intrashelf basins at areas to the northwest and to the southeast in the Persian Gulf, and subsequent exposure to meteoric water flows during subaerial exposure.
This study focuses on the variations in facies characteristics, depositional environments, and se... more This study focuses on the variations in facies characteristics, depositional environments, and sedimentary sequences of the Fahliyan Formation carbonate succession (Neocomian-Barremian) as one of the petroliferous units in the Middle East. Accordingly, four surface and subsurface sections were selected from the Dezful Embayment and Izeh Zone of the central Zagros, SW Iran. A shoal-algal facies dominated homoclinal ramp is proposed as the general depositional setting of this formation. It shows remarkable variations in facies belts, their abundance and thickness in the study area. Four third-order depositional sequences are differentiated in studied outcrops of the Izeh Zone. Interaction of tectonics, eustasy, and sedimentation (carbonate production) rates are discussed for depositional sequences and three tectono-sedimentary models are presented for the Fahliyan Formation that correspond to depositional sequences I to III of this formation. Variations in thickness, facies, diagenesis, and allochemical grains are discussed for each tectono-sedimentary model. Comparison of the acquired results with the proposed models of active tectonic basins suggests a fault-block platform in an extensional rift basin for the Fahliyan Formation in the study area.
Journal of Petroleum Science and Engineering, 2018
Lower Cretaceous sequences of the Burgan Formation are notable siliciclastic reservoirs in the Mi... more Lower Cretaceous sequences of the Burgan Formation are notable siliciclastic reservoirs in the Middle East. Despite of this importance, a little is known about various geological characteristics of this reservoir in Iranian northwestern part of the Persian Gulf. In this study, an integrated sedimentological and reservoir geological evaluation has been carried out on the Burgan reservoir using a complete dataset of drilled cores, core plugs, thin sections and petrophysical logs along with laboratory data including XRD analysis of all components to define grain's mineralogy and porosity-permeability data for reservoir quality evaluation. Depositional facies and environments are interpreted and correlated in sequence stratigraphic framework of targeted reservoir across the studied fields and then compared with stratigraphic equivalents in the Middle East. Seven facies types are recognized that indicate deposition in a transitional environment from siliciclastic-dominated delta setting into shallow-marine carbonate platform. Diagenesis study indicates a simple history of post-depositional events that includes near surface (marine) and shallow to deep burial realms. Diagenetic processes are grouped into two categories based on their effects on reservoir properties. They include porosity enhancing (i.e. dissolution and fracturing) and porosity reducing (compaction and cementation) diagenetic processes. Reservoir
Journal of Petroleum Science and Engineering, 2016
Chemical compaction features are important diagenetic imprints that generally interrupt reservoir... more Chemical compaction features are important diagenetic imprints that generally interrupt reservoir quality in most carbonate reservoirs. In the Permian-Triassic reservoirs of South Pars Field, they are recorded in various types and intensities. High-to low amplitude stylolites and solution seams are concentrated within the K1 to K4 units of the upper Dalan and Kangan formations, depending on their facies characteristics, diagenetic alterations and dominant lithology. In these units, there are some meaningful trends between the chemical compaction zones and sequence stratigraphic positions including the systems tracts of third-order sequences. Control of chemical compaction on reservoir characteristics is evaluated by using the results of petrographic studies, petrophysical logs and core poroperm measurements. Internal reservoir architecture of the studied reservoirs is determined using the both hydraulic flow units and stratigraphic modified Lorenz plot approaches. Identified baffle and barrier units show close correspondence with chemically-compacted zones. This indicates that zones with high concentration of stylolites and solution seams can be considered as small-scale vertical flow barriers in the Permian-Triassic reservoirs of South Pars Field.
The Aptian carbonate reservoirs of Persian Gulf, known as the Dariyan Formation (Shu'aiba equival... more The Aptian carbonate reservoirs of Persian Gulf, known as the Dariyan Formation (Shu'aiba equivalent), are among the most important oil reservoirs of Iran. Despite its significance, a little is known about the facies characteristics, diagenetic history, sequence stratigraphy, and reservoir quality of this formation. Using the new core data, this study presents an integrated geological reservoir characterization of this formation in four giant fields in the Persian Gulf. Using the results of the facies analysis it could be suggested that this unit formed in a shallow carbonate platform surrounding intra-shelf basins of Kazhdumi and Bab in the western and eastern Persian Gulf, respectively. A major relative sea-level fall in the Late Aptian resulted in exposure of this unit and subsequent clastic influx as well as meteoric diagenesis. This phase of meteoric diagenesis has resulted in some important diagenetic features, special geochemical trends, and considerable variations in reservoir quality of the Dariyan Formation. Sequence stratigraphic interpretation of this formation has resulted in the recognition of 2 nd and 3 rd order depositional sequences in the studied wells. They are closely correlated across the studied wells in the Persian Gulf, SW Iran, and other places in the Arabian Plate. Reservoir characterization has revealed that the high quality units are
International Petroleum Technology Conference, 2014
The Cretaceous-aged reservoirs of Iran and their counterparts on the Arabian platform are among t... more The Cretaceous-aged reservoirs of Iran and their counterparts on the Arabian platform are among the most important carbonate reservoirs developed under the warm equable climate. Intense tectonic activities combined with the eustatic sea-level changes caused sporadic exposures of these carbonate successions in SW Iran and some other areas of the Middle East. Under the domination of warm and humid climate and long-term exposures, several erosional disconformities formed throughout these successions. To investigate these palaeoexposure surfaces, petrographic and geochemical studies were carried out in four subsurface sections of giant and supergiant oilfields located in northern and southern parts of the Dezful Embayment. Some of the most important diagenetic features (such as extensive meteoric dissolution/karstification, palaeosol development, and collapsed-dissolution brecciation) were used as evidence for recognition of main palaeoexposure surfaces and associated karsts. Isotopic composition (δ13C and δ18O) and trace element concentrations of these carbonate rocks were used to elaborate the effects of these surfaces on diagenetic evolutions of palaeo-karstic Bangestan reservoirs. Both carbon and oxygen isotope ratios show a spectacular decline just below these disconformities in comparison with the expected values for the simultaneous marine carbonates, indicating that the Bangestan carbonates underwent extensive meteoric diagenesis. Elemental concentrations (Mn, Fe, and Sr) also point to moderate to intense meteoric diagenetic alterations associated with the palaeoexposure surfaces.
Journal of Stratigraphy and Sedimentology Researches, 2020
<strong>Abstract</strong> The Fahliyan Formation is a member of the Khami Group with ... more <strong>Abstract</strong> The Fahliyan Formation is a member of the Khami Group with Neocomian–Barremian age. In two surface sections in the Izeh Zone and two wells of the southern Dezful Embayment, it includes 12 microfacies deposited on four facies belts as tidal flat, inner ramp (lagoon, <em>Lithocodium</em>–algal mounds and bioclastic–peloidal shoals), middle ramp and outer ramp. A homoclinal ramp model is proposed as its depositional environment. Important diagenetic alterations are dissolution, micritization, compaction, dolomitization, silicification, pyritization, cementation and fracturing. They represent marine, meteoric and shallow to deep burial diagenetic realms. Sequence stratigraphic analysis resulted in the recognition of four depositional sequences that seem to be third-order sequences, according to their relative ages (biozones), thickness and correlation with neighboring areas. Reservoir quality evaluation indicates coupled imprints of facies characteristics and diagenetic alterations on reservoir properties of this formation. Important reservoir units are formed in <em>Lithocodium</em>–algal mounds/patch-reefs (in the Garangan Field) and high-energy facies of shoal setting (in the Gachsaran Field). They include primary pore types such as intra- and interparticle pores and mainly concentrated in highstand systems tracts (HSTs) of depositional sequences. Some secondary pores are also present that include dissolution vugs and molds. In addition, middle ramp facies provide some reservoir units in the transgressive systems tracts (TSTs). No macroscopic pores are recorded in these facies and micropores are responsible for high reservoir quality. <strong>Keywords:</strong> Fahliyan Formation, Depositional sequences, Diagenesis, Reservoir quality, Central Zagros <strong><br clear="all" /> </strong> <strong>Introduction</strong> The Neocomian–Barremian Fahliyan Formation is a member of the Khami Group that form important hydrocarbon reservoir in SW Iran (James and Wynd 1965). Tectonic activities an [...]
سازند فهلیان شامل توالی کربناتۀ نسبتا ضخیمی از گروه خامی به سن نئوکومین- بارمین است. مطالعه‌های ر... more سازند فهلیان شامل توالی کربناتۀ نسبتا ضخیمی از گروه خامی به سن نئوکومین- بارمین است. مطالعه‌های رسوب‌شناسی انجام‌شده روی این سازند در دو برش از زون ایذه و دو چاه از بخش جنوبی فروافتادگی دزفول به شناسایی 12 ریزرخساره در چهار کمربند رخسارهای شامل پهنۀ جزرومدی، رمپ درونی (لاگون، پشته‌های لیتوکودیومی- جلبکی و شول‌های بایوکلستی- پلوئیدی)، رمپ میانی و رمپ بیرونی منجر شد. محیط رسوب‌گذاری سازند فهلیان در ناحیۀ مطالعه‌شده، رمپ کربناتۀ هم‌شیب پیشنهاد می‌شود. مهم‌ترین فرایندهای دیاژنزی شناسایی‌شده شامل انحلال، میکرایتی‌شدن، تراکم، دولومیتی‌شدن، سیلیسی‌شدن، پیریتی‌شدن، سیمانی‌شدن و شکستگی است که طی مراحل مختلف دیاژنز دریایی، جوی و دفنی کم‌عمق تا عمیق ایجاد شده‌اند. مطالعه‌های چینه‌نگاری سکانسی به تفکیک چهار سکانس رسوبی در این سازند منجر شدند که با‌توجه‌به سن نسبی آنها بر اساس بایوزون‌های تفکیک‌شده، ضخامت سکانس‌ها و تطابق آنها با نواحی مجاور به‌طور محتمل سکانس‌های ردۀ سوم هستند. مطالعه‌های کیفیت مخزنی گویای تأثیر ویژگیهای رخسارهای و فرایندهای دیاژنزی بر ویژگیهای مخزنی سازند فهلیان است. رخسار...
Journal of Petroleum Exploration and Production, 2021
Knowledge of initial fluids saturation has great importance in hydrocarbon reservoir analysis and... more Knowledge of initial fluids saturation has great importance in hydrocarbon reservoir analysis and modelling. Distribution of initial water saturation (Swi) in 3D models dictates the original oil in place (STOIIP), which consequently influences reserve estimation and dynamic modelling. Calculation of initial water saturation in heterogeneous carbonate reservoirs always is a challenging task, because these reservoirs have complex depositional and diagenetic history with a complex pore network. This paper aims to model the initial water saturation in a pore facies framework, in a heterogeneous carbonate reservoir. Petrographic studies were accomplished to define depositional facies, diagenetic features and pore types. Accordingly, isolated pores are dominant in the upper parts, while the lower intervals contain more interconnected interparticle pore types. Generally, in the upper and middle parts of the reservoir, diagenetic alterations such as cementation and compaction decreased the ...
Journal of Petroleum Science and Engineering, 2021
Abstract This study integrates quantitative analysis of reservoir properties with geological para... more Abstract This study integrates quantitative analysis of reservoir properties with geological parameters to discriminate the reservoir heterogeneities in the Permian–Triassic sequences of the Persian Gulf. To achieve this goal, geological analysis of core samples and thin sections were integrated with petrophysical logs and porosity–permeability data. For quantitative assessment of reservoir heterogeneity, Coefficient of Variation (CV), Dykstra-Parsons Coefficient (VDP) and Lorenz Coefficient (VLC) were used along with the concept of Hydraulic Flow Units (HFU). Depositional facies, diagenetic alterations and sequence stratigraphic framework of the reservoir were used as a basis for the interpretation of geological heterogeneities. Accordingly, 14 microfacies types and 5 facies belts have been defined and indicate a low-angle (homoclinal) ramp model. Complex diagenesis history of these sequences includes marine, hypersaline and shallow to deep burial diagenesis that considerably altered the primary distribution of reservoir properties. A comparison of tested methods revealed that the CV is the best approach for quantification of heterogeneity in targeted reservoir. Consequently, the K4 and K2 are proposed as the most homogeneous units with a dominance of grain-supported facies of shoal setting, intense effects of hypersaline dissolution and lesser effect of compaction and cementation. The K3 and K1 units show high levels of heterogeneity resulting from the combined facies changes and diagenetic alterations (dolomitization, cementation and compaction). Finally, sequence stratigraphic framework of reservoir heterogeneities is discussed for all reservoir units and can be used as a basis for ongoing reservoir studies of the Permian–Triassic sequences in the Persian Gulf and the Middle East.
Abstract New high-resolution biostratigraphy and facies analyses indicate that a Coniacian-Santon... more Abstract New high-resolution biostratigraphy and facies analyses indicate that a Coniacian-Santonian homoclinal carbonate ramp (Ilam Fm.) developed on the subaerially exposed mid-Turonian surface at the top of Sarvak Fm. in Fars zone of the Zagros Basin (northeastern margin of the Arabian Plate). Spatial facies distribution, sequence stratigraphy, and lateral variation in the thickness of Ilam Fm., as well as extend of erosion of the underlying Sarvak Fm. suggest that a combination of regional tectonic activities and global sea-level changes controlled the development of this succession. A major tectonic configuration in the Zagros belt including several basement faults subdivide the belt into different blocks with distinctive sedimentary records. Reactivation of these preexisting basement faults during Late Cretaceous provided a horst and graben geometry due to the closure of Neo-Tethys. Three of our studied sections are located on an upthrown block, bounded between Kazerun and Karebas basement faults, include inner and mid-ramp deposits. These sections represent an eastward deepening trend which correspond to eastward tilting of this fault block. The easternmost section is located in the eastern neighboring downthrown block , bounded between Karebas and Bastak faults, and includes outer ramp and basin deposits confirming a significant paleo-bathymetrical contrast between the two blocks. Furthermore, eastward thickening of the Ilam Fm. independently confirms the increase of accommodation space, as a result of deeper depositional condition, toward center of the Fars zone. Absence of subaerial exposure features at top of the Sarvak Fm. in the downthrown block shows that the global sea-level fall and regional tectonic regime also controlled the extend of unconformity underlying the Coniacian-Santonian platform deposits (Ilam Fm.).
Journal of Petroleum Science and Engineering, 2021
Abstract Dariyan Formation (Aptian) is one of the important hydrocarbon reservoirs in the Persian... more Abstract Dariyan Formation (Aptian) is one of the important hydrocarbon reservoirs in the Persian Gulf. In this reservoir, porosity is controlled by various depositional and diagenetic factors. This study integrates petrographic, geochemical, petrophysical and reservoir quality data to distinguish various pore types and their evolution in two fields selected from the SE and NW Persian Gulf. Primary (depositional) and secondary (diagenetic) pore types are differentiated using the results of macroscopic (core) and microscopic (thin section and SEM) petrographic studies. Pore size distribution and reservoir importance are evaluated by MICP and porosity–permeability measurements on core-plug samples. Macroscopic pores are formed within the grain-dominated and dissolved mud-dominated facies that are located in the RST of third-order sequences, especially within the lower carbonate unit. Micropores are recorded in mud-dominated facies of middle to outer ramp settings with minor effects of meteoric dissolution. Accordingly, evolution in an open diagenetic system with high water/rock ratio is proposed for grain-supported facies, and a closed diagenetic system for mud-dominated intervals. There are close relationships between micrite micro-textures (MTCs) and reservoir properties of mud-dominated facies. A dynamic pore evolution model is presented for the Dariyan Formation that integrates all depositional and diagenetic features in sequence stratigraphic framework. This model can be used for ongoing reservoir studies of this formation in hydrocarbon fields of the Persian Gulf.
Aptian carbonates, major hydrocarbon reservoirs in the Persian Gulf, were deposited on a ramp-lik... more Aptian carbonates, major hydrocarbon reservoirs in the Persian Gulf, were deposited on a ramp-like platform to intrashelf basinal setting under the controls of tectonics and eustasy. Coated grains (oncoids and pisoids) are abundant and show different textures and internal microstructures depending on the stratigraphic position. These Aptian coated grains are divided according to their texture, cortex composition, morphology, type of biota and internal structure, based on petrographic (routine petrography, cathodoluminescence and scanning electron microscope) and geochemical analyses. Accordingly, four types of oncoid and a pisoid group are identified. Oncoid types 1 and 2 along with pisoids typically formed during phases of relative sea-level fall developed within the regressive systems tract (RST). They are commonly associated with shallow-marine (inner ramp), high-energy shoal facies and occur below exposure horizons, at sequence boundaries. Oncoid types 3 and 4 show micro-encrusters (i.e. Lithocodium aggregatum and Bacinella irregularis) and usually occur in a wackestone texture that indicates deposition in a low-energy lagoonal setting with low sedimentation rate during rises in relative sea level (i.e. a transgressive systems tract: TST). Stable carbon and oxygen isotopes are used to define the OAE1a and its environmental effects in the Dariyan Formation. Palaeoenvironmental proxies reflecting energy level, sedimentation rate and trophic level are evaluated for Aptian sedimentary sequences deposited on the southern margin of the Neo-Tethys Ocean.
This study delineates reservoir and non-reservoir zones in the Lower Cretaceous Dariyan Formation... more This study delineates reservoir and non-reservoir zones in the Lower Cretaceous Dariyan Formation as units that are characteristic of the stratigraphic section representative of portions of the Persian Gulf offshore area. Reservoir rock types are categorized by textural and diagenetic properties. Static flow zones were delineated by porosity and permeability measurements of cored intervals. Electrofacies were prepared from clusters of petrophysical data to define reservoir zones for areas lacking wells with cored intervals. The attributes of these reservoirs are integrated into a sequence stratigraphic framework. This research indicates that rock types and reservoir zones of the Dariyan Formation differ in the studied fields located to the west and to the east in the Persian Gulf. These differences are interpreted to have resulted from a differing tectonostratigraphic framework that controlled depositional facies and subsequent diagenesis. For example, reservoirs associated with the lower and upper carbonate units of the Dariyan Formation have different lithofacies and diagenetic modifications that resulted from deposition at two intrashelf basins at areas to the northwest and to the southeast in the Persian Gulf, and subsequent exposure to meteoric water flows during subaerial exposure.
This study focuses on the variations in facies characteristics, depositional environments, and se... more This study focuses on the variations in facies characteristics, depositional environments, and sedimentary sequences of the Fahliyan Formation carbonate succession (Neocomian-Barremian) as one of the petroliferous units in the Middle East. Accordingly, four surface and subsurface sections were selected from the Dezful Embayment and Izeh Zone of the central Zagros, SW Iran. A shoal-algal facies dominated homoclinal ramp is proposed as the general depositional setting of this formation. It shows remarkable variations in facies belts, their abundance and thickness in the study area. Four third-order depositional sequences are differentiated in studied outcrops of the Izeh Zone. Interaction of tectonics, eustasy, and sedimentation (carbonate production) rates are discussed for depositional sequences and three tectono-sedimentary models are presented for the Fahliyan Formation that correspond to depositional sequences I to III of this formation. Variations in thickness, facies, diagenesis, and allochemical grains are discussed for each tectono-sedimentary model. Comparison of the acquired results with the proposed models of active tectonic basins suggests a fault-block platform in an extensional rift basin for the Fahliyan Formation in the study area.
Journal of Petroleum Science and Engineering, 2018
Lower Cretaceous sequences of the Burgan Formation are notable siliciclastic reservoirs in the Mi... more Lower Cretaceous sequences of the Burgan Formation are notable siliciclastic reservoirs in the Middle East. Despite of this importance, a little is known about various geological characteristics of this reservoir in Iranian northwestern part of the Persian Gulf. In this study, an integrated sedimentological and reservoir geological evaluation has been carried out on the Burgan reservoir using a complete dataset of drilled cores, core plugs, thin sections and petrophysical logs along with laboratory data including XRD analysis of all components to define grain's mineralogy and porosity-permeability data for reservoir quality evaluation. Depositional facies and environments are interpreted and correlated in sequence stratigraphic framework of targeted reservoir across the studied fields and then compared with stratigraphic equivalents in the Middle East. Seven facies types are recognized that indicate deposition in a transitional environment from siliciclastic-dominated delta setting into shallow-marine carbonate platform. Diagenesis study indicates a simple history of post-depositional events that includes near surface (marine) and shallow to deep burial realms. Diagenetic processes are grouped into two categories based on their effects on reservoir properties. They include porosity enhancing (i.e. dissolution and fracturing) and porosity reducing (compaction and cementation) diagenetic processes. Reservoir
Journal of Petroleum Science and Engineering, 2016
Chemical compaction features are important diagenetic imprints that generally interrupt reservoir... more Chemical compaction features are important diagenetic imprints that generally interrupt reservoir quality in most carbonate reservoirs. In the Permian-Triassic reservoirs of South Pars Field, they are recorded in various types and intensities. High-to low amplitude stylolites and solution seams are concentrated within the K1 to K4 units of the upper Dalan and Kangan formations, depending on their facies characteristics, diagenetic alterations and dominant lithology. In these units, there are some meaningful trends between the chemical compaction zones and sequence stratigraphic positions including the systems tracts of third-order sequences. Control of chemical compaction on reservoir characteristics is evaluated by using the results of petrographic studies, petrophysical logs and core poroperm measurements. Internal reservoir architecture of the studied reservoirs is determined using the both hydraulic flow units and stratigraphic modified Lorenz plot approaches. Identified baffle and barrier units show close correspondence with chemically-compacted zones. This indicates that zones with high concentration of stylolites and solution seams can be considered as small-scale vertical flow barriers in the Permian-Triassic reservoirs of South Pars Field.
The Aptian carbonate reservoirs of Persian Gulf, known as the Dariyan Formation (Shu'aiba equival... more The Aptian carbonate reservoirs of Persian Gulf, known as the Dariyan Formation (Shu'aiba equivalent), are among the most important oil reservoirs of Iran. Despite its significance, a little is known about the facies characteristics, diagenetic history, sequence stratigraphy, and reservoir quality of this formation. Using the new core data, this study presents an integrated geological reservoir characterization of this formation in four giant fields in the Persian Gulf. Using the results of the facies analysis it could be suggested that this unit formed in a shallow carbonate platform surrounding intra-shelf basins of Kazhdumi and Bab in the western and eastern Persian Gulf, respectively. A major relative sea-level fall in the Late Aptian resulted in exposure of this unit and subsequent clastic influx as well as meteoric diagenesis. This phase of meteoric diagenesis has resulted in some important diagenetic features, special geochemical trends, and considerable variations in reservoir quality of the Dariyan Formation. Sequence stratigraphic interpretation of this formation has resulted in the recognition of 2 nd and 3 rd order depositional sequences in the studied wells. They are closely correlated across the studied wells in the Persian Gulf, SW Iran, and other places in the Arabian Plate. Reservoir characterization has revealed that the high quality units are
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