Dalan Formation Research Articles

Reservoir properties distribution in the framework of sequence stratigraphic units: A case study from the Kangan Formation, Iranian offshore gas field, the Persian Gulf basin

The Lower Triassic Kangan and Upper Permian Dalan Formations have large volumes of gas and condensate reservoirs in the southern part of Iran and nearby countries. Shallow carbonate and evaporate succession of the gas bearing Kangan Formation in the Salman field was deposited in a shallow water carbonate ramp. The Salman field is a shared structure from which two-thirds is owned by Iran and the remaining portion is under territories of United Arab Emirates (UAE). The Kangan reservoir is traditionally subdivided into K2 and K1 zones. However, it has been divided into two depositional sequences based on the integration of seismic data criteria which are supposed to be a third-order sequence. In this study, the relationship between depositional sequences and reservoir properties have also been investigated. This paper mostly aims at finding and documenting the relation between depositional sequences and reservoir properties as well as constructing the related 3D geological model. Using and comparing three-dimensional (3D) seismic data and five well data particularly petrographic studies allow the recognition of 9 microfacies and two 3rd order sequences which are part of the Permian–Triassic Khuff Formation. In this study, three-dimensional models of sequences framework were constructed based on seismic and well data. Moreover, porosity and water saturation property models have constructed considering the sequence stratigraphic framework. According to the models, the high reservoir quality units mainly consist of grain-dominated rock fabrics, which are associated with shoal facies developed in the Late TST (transgressive system tract) and Early HST (highstand system tract). These results indicated high energy conditions in the transgressive sea-level rise. The supratidal, intertidal and lagoonal facies, presenting anhydrite and mud dominated rock fabrics showing a lower reservoir quality developed in the Late HST and Early TST. Therefore, the reservoir quality of HST is lower than TST. The reservoir quality of K2 is also much better than K1 and it is considered as the most prolific pay zone in the South Pars gas field. Based on the findings, the sequence stratigraphy framework in reservoir characterization plays a significant role in the better understanding of reservoir quality as well as reservoir property modeling.

Improving reservoir rock classification in heterogeneous carbonates using boosting and bagging strategies: A case study of early Triassic carbonates of coastal Fars, south Iran

An accurate reservoir characterization is a crucial task for the development of quantitative geological models and reservoir simulation. In the present research work, a novel view is presented on the reservoir characterization using the advantages of thin section image analysis and intelligent classification algorithms. The proposed methodology comprises three main steps. First, four classes of reservoir intervals are defined using a limited number of porosity and permeability values obtained from the core plugs of Kangan and Dalan formations. Then seven micro-scale features including distribution of pore types (interparticle, interaparticle, moldic, and vuggy), pore complexity, and cement distribution as well as textural characteristics are extracted from thin section images. Finally, the features extracted from each photomicrograph and its corresponding reservoir class are used as the training data for several intelligent classifiers including decision trees, discriminant analysis functions, support vector machines, K-nearest neighbor models and two ensemble algorithms, named bagging and boosting. The relationship between the micro-scale features and the reservoir classes was studied. Performance of all classifiers is evaluated using the concepts of accuracy, precision, recall, and harmonic average. The results obtained showed that the bagging decision tree delivered the best performance among the models and improved the accuracy of simple models up to 7.7% compared with the best single classifier.

Morphometric analysis of Middle Permian Eopolydiexodina and Monodiexodina species from the Dalan Formation, Zard‐Kuh Mountains, Zagros, Iran: An integration of traditional approach and quantitative analyses to identify fusulinid species

Eopolydiexodina and Monodiexodina individuals from the Middle Permian lower Dalan Member of the Dalan Formation in the Zard‐Kuh Mountains, southwest Iran, are quantitatively studied using histograms, normal probability plots, test of normality, and parametric (PCA and PCoA) and non‐parametric (NMDS) ordination techniques, in order to determine the accuracy of previously identified Eopolydiexodina and Monodiexodina species based on traditionally defined fusulinid parameters. Specimens of the genus Eopolydiexodina recorded in the lower Dalan Member have been previously assigned to one species and those of Monodiexodina are subdivided into one species and one subspecies. In the present study, 35 specimens from an Eopolydiexodina‐bearing bed in unit 11 and 40 individuals from a Monodiexodina‐bearing bed in unit 17 of the lower Dalan Member are selected. Observations of the histograms, normal probability plots, and test of normality for all the measured variables reveal that Eopolydiexodina and Monodiexodina individuals follow generally a normal distribution. The results of the principal component analysis (PCA), principle coordinate analysis (PCoA), and non‐metric multidimensional scaling (NMDS) suggest that the distribution of the studied individuals cannot be divided into different groups and only one species for Eopolydiexodina (E. aff. persica) and one species for Monodiexodina (M. aff. kattaensis) are identifiable. This study provides an example to show how the identification and definition of fusulinid species can be well constrained using both the traditional description approach and modern morphometric techniques together.

Comparison of LLNF, ANN, and COA-ANN Techniques in Modeling the Uniaxial Compressive Strength and Static Young’s Modulus of Limestone of the Dalan Formation

The uniaxial compressive strength and static Young’s modulus are among the key design parameters typically used in geotechnical engineering projects. In this paper, three artificial intelligence techniques, namely the local linear neuro-fuzzy (LLNF) technique, artificial neural network (ANN) and the hybrid cuckoo optimization algorithm-artificial neural network (COA-ANN), were used to estimate the uniaxial compressive strength and the static Young’s modulus of limestone. For this purpose, 115 limestone samples were subjected to the tests of uniaxial compressive strength, ultrasonic velocity, and physical properties (density and porosity) tests. From the laboratory results obtained, the values of the P-wave velocity, density, porosity and dynamic Poisson’s ratio were tested as the model input parameters to determine the best input configuration for estimating the uniaxial compressive strength and the static Young’s modulus. Different models with different input combinations were practiced, and the models with the highest estimation accuracy are reported here. Performance evaluation was carried out using three criteria including coefficient of determination, variance accounted for, and normalized mean-square error. Evaluating the correlation coefficients and error criteria resulting from the three methods used demonstrates the superiority of LLNF method to ANN and COA-ANN methods. The developed ANN models display lower correlation coefficients and higher amount of error compared to the other models. However, using cuckoo optimization algorithm has led to significant improvement in accuracy and precision of estimations carried out by ANN and has improved its efficiency. Results have confirmed that the employed hybrid method outperforms in estimating untrained data (test data) compared to the LLNF and ANN methods.

Microporosity evolution in Iranian reservoirs, Dalan and Dariyan formations, the central Persian Gulf

Tight limestones with high amounts of microporosity will be the main targets of future hydrocarbon exploration and production in Middle East. In this paper, microporosity evolution in two Iranian reservoirs, Dalan and Dariyan formations, is investigated. These two formations represent the main hydrocarbon reservoirs in most of the Iranian hydrocarbon fields. Aptian Dariyan Formation is mainly composed of mud-dominated samples deposited in a ramp environment. The upper part of Permian Dalan Formation has the same facies distribution while the lower part is composed mainly of grain-dominated samples. Mud-dominated facies of Dariyan Formation have high porosity with moderate to low permeability. Micrites are rounded with punctic to serrate contacts. In contrast, mud-dominated facies of Dalan Formation have low porosity and permeability. SEM studies revealed that micrite texture has a major effect on final reservoir properties of these two formations. MICP and SEM studies showed that in grain-dominated samples of Dalan Formation, both small and large pore size throats are present. Mud-dominated samples of this formation are composed of micrites with compact-anhedral shape and coalescent contacts. These results combined with diagenetic studies confirmed the role of meteoric dissolution in microporosity development in both formations. In humid conditions of the Aptian time, micrites have been dissolved and a large amounts of microporosity have been developed. In contrast, in dry conditions of Late Permian, the original fabric of the micrites preserved until the late stages of burial. Rounded micrites are present in Dalan Formation where meteoric dissolution had a major effect on porosity development in this formation.

Assessment Reservoir Barriers to Understanding Their Effects on Reservoir Compartmentalization of Kangan and Dalan Formations, Central Persian Gulf

Assessment Reservoir Barriers to Understanding Their Effects on Reservoir Compartmentalization of Kangan and Dalan Formations, Central Persian Gulf

Facies, Depositional Environment and Sequence Stratigraphy of Dalan Formation in Persian Gulf (Qatar-South Fars Arch) Well SP-A Subsurface Section

Objectives: Facies, depositional environment and sedimentary cycles of Dalan Formation in the South Pars gas field are the aspects that this paper is focused on. Methods/Statistical Analysis: Three hundred and seventy-eight thin-sections prepared from cutting and cores were evaluated by using petrographic microscope. Corel Draw X6, Autodesk Map, Corel Photo-Paint, Autodesk Map, DN2 Microscopy Image Processing System, Geocalc and Auto Cad 2014 employed for this research. Findings: Twenty-four major facies in five facies associations were identified comprising Tidal flat (A), Lagoon (B), Shoal (C), Open marine (D) and Mid ramp (E). The Dalan Formation was deposited in inner to mid parts of a homoclinal ramp. The sequence stratigraphy studies revealed the seven main third– order sedimentary cycles in the well SP-A. The shoal ooid grainstone facies with intergranular, moldicand fracture porosity comprise the main reservoir facies of the Dalan Formation. Dissolution, dolomitization, anhydritization, compaction and cementation are the main diagenetic processes in this formation which played an important role in the quality of the reservoir. Applications/Improvements: The results obtained from this paper, can be used to construct a major depositional framework in the Qatar-South Fars Arch for later exploration purposes.

Integration of core data, well logs and seismic attributes for identification of the low reservoir quality units with unswept gas in the carbonate rocks of the world’s largest gas field

Tight zones of the gas bearing Kangan and Dalan formations of the South Pars gas field contain a considerable amount of unswept gas due to their low porosity, low permeability and isolated pore types. The current study, integrates core data, rock elastic properties and 3D seismic attributes to delineate tight and low-reservoir-quality zones of the South Pars gas field. In the first step, the dynamic reservoir geomechanical parameters were calculated based on empirical relationships from well log data. The log-derived elastic moduli were validated with the available laboratory measurements of core data. Cross plots between estimated porosity and elastic parameters based on Young’s modulus indicate that low porosity zone coincide with high values of Young’s module. The results were validated with petrographic studies of the available thin sections. The core samples with low porosity and permeability are correlated with strong rocks with tight matrix frameworks and high elastic values. Subsequently, rock elastic properties including Young’s modulus and Poisson’s ratio along with porosity were estimated by using neural networks from a collection of 3D post-stack seismic attributes, such as acoustic impedance (AI), instantaneous phase of AI and apparent polarity. Distinguishing low reservoir quality areas in pay zones with unswept gas is then facilitated by locating low porosity and high elastic modulus values. Anhydrite zones are identified and eliminated as non-pay zones due to their characterization of zero porosity and high Young modulus values. The methodology described has applications for unconventional reservoirs more generally, because it is able to distinguish low porosity and permeability zones that are potentially productive from those unprospective zones with negligible reservoir quality.

Reservoir quality along a homoclinal carbonate ramp deposit: The Permian Upper Dalan Formation, South Pars Field, Persian Gulf Basin

Permo-Triassic carbonate successions host some of the largest oil and gas reserves in the Arabian Plate, including the world's largest gas reservoirs of the Upper Dalan and the Kangan formations in the South Pars Gas Field, Persian Gulf Basin. Both formations are stratigraphically equivalent to the Upper Khuff Formation which has been long recognized as a major oil and gas reservoir in the Arabian Peninsula. The Permian Upper Dalan Formation is composed mainly of mixed carbonate-evaporite sequences that formed on a laterally continuous homoclinal carbonate ramp with significant variations in reservoir heterogeneity and quality. They can be grouped in 18 microfacies. High reservoir qualities are found within high-energy shoal environments with a tendency of the best reservoir quality to occur towards the basin in a mid-ramp setting. In contrast, low-energy tidal flat environments exhibit the poorest reservoir quality. Reservoir quality from lagoonal environments is diverse. Diagenesis has significantly affected reservoir properties by both enhancing and destroying original porosity and permeability. Bivariate plots of porosity and permeability values, combined with thin section petrography indicate that pore-filling “pervasive” and poikilotopic anhydrite cements had the greatest negative impact on the reservoir quality whereas dolomitization and dissolution of grains and cements played the most positive role. Two third-order sequence stratigraphic cycles link lithologies and depositional environments to sea-level fluctuations. HSTs are associated with better reservoir characteristics than TSTs.

Paleoenvironmental, diagenetic, and eustatic controls on the Permo–Triassic carbonate–evaporite reservoir quality, Upper Dalan and Kangan formations, Lavan Gas Field, Zagros Basin

Permo–Triassic (P–T) successions in Iran are known as one of the most extensive carbonate–evaporite sequences in the world, holding prolific hydrocarbon accumulations, such as the gas fields in the Zagros Basin. This study addresses the impact of paleoenvironmental changes across the P–T extinction boundary, variations in eustatic level and diagenesis on the carbonate reservoir quality of the Permo–Triassic Upper Dalan and Kangan formations in the Lavan Gas Field (offshore Zagros). A total of eight lithofacies have been defined and interpreted, representing the shallower parts (inner ramp to shoal) of a carbonate homoclinal ramp. The diagenetic features show the mixing influence of marine, meteoric and burial processes, with prevalence of multistage dolomitization and late meteoric‐related imprints. The main dolomitization processes are interpreted to be penecontemporaneous and associated with continuous seawater reflux and high evaporation within the intertidal environment. Combined analysis of facies and petrophysical properties has been utilized to define six rock types, including RT4 (grainstones from oolitic shoals) as the best reservoir, whereas RT1 (supratidal anhydrite) is acting as the main cap rock within the studied carbonate–evaporite sequence. Multiscale characterization of lithological and petrophysical properties suggest that the Upper Dalan Formation has a single reservoir unit (D1), whereas the Kangan Formation may be divided into two reservoir units (K1 and K2). The best reservoir quality is promoted by dissolution and dolomitization associated with late Transgressive Sequence Tracts (TST) to early Highstand Sequence Tracts (HST) sequences, while low reservoir quality corresponds to late HST sequences accompanied by pore‐occluded cements. Petrophysical analysis suggest better porosity‐permability for the Upper Dalan than for the Kangan Formation. This observation is closely associated with the different nature of lithofacies, where the Kangan Formation contains more fine‐grained carbonate rocks, and the higher intensity of porosity‐grain dolomitization in the Upper Dalan Formation. This study provides a better understanding on reservoir quality prediction across the P–T boundary and the effect of eustatic fluctuations and diagenesis in controlling porosity‐permeability evolution with similar settings elsewhere.

Application of gamma deviation log (GDL) in sequence stratigraphy of carbonate strata, an example from offshore Persian Gulf, Iran

The application of gamma ray data as a non-destructive, inexpensive geophysical survey tool with a very high resolution and coverage provides the potential for a better understanding of sequence stratigraphic boundaries in carbonate strata in this study. Three wells’ GR data from Permian–Triassic Kangan and upper Dalan formations in one of the central Persian Gulf Iranian hydrocarbon fields have been used for this purpose. The difference between each data point with the well average GR shows the deviation of each measurement from the base value. Regarding the same physical, chemical and biological conditions (genetic relationship) in each sequence, GR deviations show the same deviation trend within each sequence. The cumulative distribution of these deviations is therefore increasing or decreasing constantly in each sequence. Calculation of GR deviation cumulative distribution exactly showed the Kangan-Dalan (Permian–Triassic) boundary. The average GR value of each sequence then used for the new deviation calculation and new boundaries detected in second level analysis. The turnovers determined in this method were correlated with the sequence stratigraphic boundaries of the studied formations provided by the core analysis, sedimentological methods. The new method applied successfully to the 10 wells in the field and provided the same results. The results demonstrate the applicability of the method in carbonate strata for sequence stratigraphic purposes.

A New Approach to Permian System in the Section of Gahkum Mountain (Zagros-Iran)

The deposits of Permian system in Kuh-e-Gahkum consist of 480 m clastic subdiffusion of Faraghan Formation and carbonates of Dalan Formation. In this section, the sediments of Faraghan Formation, which is gradationally overlain by Dalan formation, unconformably overlies Zakin Formation (Lower Carboniferous). In the upper part, Kangan Formation rests on the Permian deposits with an erosional and unconformable contact. Studying the microscopic thin sections led to the identification of 37 genera and 37 species of Foraminifera as well as 14 genera and 15 species of algae. According to the identified foraminifera in Faraghan and Dalan Formations, the age of the rock units in Permian system is assigned to Julfian-Asselian.

Drilling fluid loss control via implementing the FMI and DSI logs to protect environment

Implementing the drilling fluids in drilling operations is of paramount importance owing to the variety of applications and benefits they provide. Materials added to drilling fluid could cause numerous environmental problems in soil and water resources, and these problems are more pronounced in offshore as compared to land fields. Heavy metals such as mercury, barium, arsenic, lead, and nickel exist in drilling fluid, which bring detrimental damages to the environment. Moreover, heavy metals exist in oil-based muds due to presence of oil where their nickel and vanadium are much greater than other heavy metals. Additive materials and heavy metals existing in drilling fluid could pose irreparable environmental damage if fluid loss into the formation occurs. Regarding to the fact that drilling fluid loss occurs via the open fractures in the wellbore, the main aim of this study is to evaluation of wellbore fractures via implementing the FMI log and fracturing pressure using the slowness of compressional and shear waves. A total of 61 fractures in Dalan formation and 72 fractures in Kangan formation are interpreted and fracturing pressure for these formations, ranges between 8400 and 9450 psi. Implementing the results obtained from this study, drilling fluid loss into the formation and subsequent environmental damage could be prohibited via controlling the pumping pressure and density variation of drilling fluid in accordance with the formation fracturing pressure.

Ocean Chemistry Revealed by Mineralogical and Geochemical Evidence at the Permian‐Triassic Mass Extinction, Offshore the Persian Gulf, Iran

AbstractThe Upper Permian Dalan Formation and the Lower Triassic Kangan Formation in the Persian Gulf area are mainly composed of shallow marine facies limestone and dolomite. Two subsurface‐cored intervals were investigated in order to understand the original mineralogy and paleoceanic conditions. The decreasing trend of Sr concentration in these deposits shows that aragonite was precipitated during the Late Permian and then gradually changed to calcite toward the Permian‐Triassic boundary (PTB). The dissolution rate of aragonite decreased from 60 m below the PTB toward the boundary, with the only exception at 10 m below the Permian‐Triassic Boundary (PTB) due to the Permian‐Triassic unconformity in this region. The increasing trend of Mg/Ca ratio in a global scale at the end‐Permian time shows that the interpreted variation of mineralogy does not result from the change of this ratio. The increasing pCO2 and decreasing pH are considered to be the main controlling factors. The increase of Ca2+ at the end‐Permian time due to the input of meteoric waters is too little to fully compensate this effect A local maximum of the Si content just at the PTB confirms the input of runoff waters.

Microfacies Analysis, Geochemical and Petrographic Evidences for Recognition of Original Carbonate Mineralogy of Dalan Formation in the South Pars gas field

Microfacies Analysis, Geochemical and Petrographic Evidences for Recognition of Original Carbonate Mineralogy of Dalan Formation in the South Pars gas field

THE EVOLUTIONARY DEVELOPMENT OF GLOBIVALVULINA SPECIES AND THEIR STRATIGRAPHIC DISTRIBUTION IN UPPER PERMIAN SEDIMENTS OF THE KUSHAKOUL CANYON, IN HIGH ZAGROS, IRAN: WITH A REVIEW OF THEIR SITUATION IN BIOSTRATIGRAPHY OF DALAN FORMATION

The subfamily of Biseriammininae includes genera that have kind of great species diversity in the sediments of Upper Permian in the most parts of Iran, particularly Zagros Mountains. As the complete section of Upper Permian sediments is exposed in the Zagros basin, the Oshtoran-kuh region has been selected of this study. Sections of the different genera have been drawn by camera Lucida instrument and species have been differentiated based on the structural properties of the shell. Generally, 24 species of Globivalvulina genus, 8 species of Paraglobivalvulina genus and 1 species of Paraglobivalvulinoides genus have been identified and the evolutionary pattern of these genera and their species are presented. In addition, biostratigraphic studies of revealed ten biozones based on the fuzolinids and small foraminifers identified in Dalan Formation in Zagros basin, Iran.

Porosity and permeability prediction from well logs using an adaptive neuro-fuzzy inference system in a naturally fractured gas-condensate reservoir

ABSTRACTInterpretation of petrophysical log is one of the most useful and important tools in petroleum geology. Well logs help determine the physical characteristics of a reservoir, such as lithology, porosity, permeability, producer regions and their depth and thickness, and also differentiating between oil and gas and water in a reservoir and defining hydrocarbon reserve. A continual record of the physical characteristics of rocks in various depths is called well logs. Petrophysical logs usually include gamma ray, spontaneous potential, resistance, density, neutron, nuclear magnetic resonance, and sonic. The purpose of this study is to determine those characteristics of the reservoir that cannot be specified directly through present measuring well logs, using an intelligent problem-solving system of neuro-fuzzy. In this study, porosity and permeability are determined as two of the most important reservoir characteristics having much influence on reservoir understanding, reservoir reserve, and capability of reservoir production. The system of determining reservoir characteristics (neuro-fuzzy) was tested on collected well log data from oil and gas fields in the south of Iran. The most important result obtained in this study is that if all data influencing one of the reservoir characteristics are presented to the neuro-fuzzy system, then this system will be an excellent model with low error for determining all of the complex characteristics of the reservoir. These produced intelligent systems predict porosity and permeability completely on training and testing data and the correlation coefficient is near 1 and normalized mean square error is near to zero. Engineers and researchers can predict the reservoir characteristics with very good precision by these intelligent systems. The results of this study prove that a neuro-fuzzy intelligent system is a very powerful tool for determining permeability and porosity at the wells of a naturally fractured gas condensate reservoir. It is the first time to predict porosity and permeability from well logs using adaptive neuro-fuzzy inference system in a naturally fractured gas-condensate reservoir in Khuff Formation (Kangan and Upper Dalan Formation), which is a heterogeneous formation with a wide range of permeability and porosity in the Middle East; this method predicts permeability and porosity precisely in this heterogeneous formation. The other novelty of this study is the choice of appropriate input parameters to determine porosity and permeability precisely. Because of the heterogeneous condition of naturally fractured gas-condensate reservoirs in Khuff Formation, the appropriate input parameters cause the system to train optimally and thus increase the system ability to estimate the output in various conditions precisely.

Facies, Sedimentary Environment and Sequence Stratigraphy of Dalan Formation in South Fars, Iran —(Qatar-South Fars Arch) Well ASL-A

Dalan Formation is one of the most important gas reservoirs of south and southwest Iran which it belongs to Dehram Group and its age is Middle to Late Permian. The Dalan formation is interpreted as reflecting a major tectono-eustatic event related to the onset of rapid thermal subsidence of the early Neo-Tethys passive margin in Arabia and Iran, and the drowning of its rift shoulders. The Dalan formation consists mainly of medium to thick-bedded oolitic to micritic shallow-marine carbonate, with intercalations of evaporates. This formation overlies the Faraghan formation and extends up into the Lower Triassic kangan formation. The current paper is focused on the facies, sedimentary environment and sequence Stratigraphy study of the Middle to Upper Permian Dalan formation in the West Assaluyeh gas field the subsurface section of well ASL-A. Based on microfacies analysis and significant founa and flora, nineteen major facies in five facies associations including Tidal flat (A), Lagoon (B), Shoal (C), Open marine (D) and Mid ramp (E) were recognized in the Dalan formation. Facies analysis and those comparisons with modern and ancient environments indicated that the Dalan formation was deposited inner to mid parts of a homoclinal ramp. The sequence stratigraphy studies on the Dalan formation in this gas field led to assessment of seven main sedimentary sequences of the third-order in the Assaluyeh field, well ASL-A. The boundary between the third-order sequences with the Faraghan formation and between the Nar and Upper Dalan members are Subaerial Unconformity (SU) and the boundaries between the third-order sequences with each other and also with the Kangan formation are Correlative Conformity (CC). The main diagenetic processes in this formation are dolomitization, dissolution, anhydritization, cementation and compaction which played a significant role in improving reservoir quality. The shoal ooid grainstone facies with intergranular and oomoldic porosity comprise the main reservoir facies of the Dalan formation.

Porosity and Rock-Typing in Hydrocarbon Reservoirs Case Study in Upper Member of Dalan Formation in Kish Gas Field, South of Zagros, Iran

To estimate the volume of oil and gas in the hydrocarbon reservoirs, the rock-typing must be considered. The volume and type of available space in the reservoir rocks (porosity) and the ease of hydrocarbons flow (permeability) are important in the classification of rock-types. In the field study, touching-vug Porosities (intergranular, intercrystalline and brecciate) increase the total porosity and form high quality rock-types, on the other side, separated-vug porosities (such as moldic, intraparticle and vuggy) increase the total porosity but do not play a large role in the production of hydrocarbon. In this paper, based on the SCAL data (Special Core Analysis) and according to amount of irreducible water saturation (Swir) and capillary pressure, the reservoir rocks are divided into 4 classes including Reservoir Rock-Types 1 to Reservoir Rock-Types 4 (RRTs-1 to RRTs-4). By study of the prepared thin sections, we investigated the role of porosity in the rock-typing. Among the rock-types, category 1 is the best type-reservoir and category 4 is non-reservoir. Probably, the latest diagenetic process determines the quality rocks, not sedimentary environments.

Folding Style Analysis of the Tabnak Sweet Gas Field, Zagros, Iran

The Zagros fold-thrust belt in Iran is home to one of the enormous petroleum producing reservoirs in the word. The Tabnak gas field in this belt is one of the enormous sweet gas fields that discovered on the land. This anticlinal structure is located in the Coastal Fars sub-basin and is bounded from North by the Varavi gas field, from South by the Kuh-e Madar anticline, from East by Assaluyeh gas field and from West by Kuh-e Dehnow anticline. Its length is about 80 km and width is about 15 km. This structure is asymmetric anticline and is located with irregular near the Assaluyeh gas field. The Tabnak gas field is deepest structure between anticlines in the Coastal Fars area. This gas field has a special place for accommodating the enormous Hydrocarbon resources and for this reason, it is very important for Iran country. In this structure, the Dashtak, Kangan and upper Dalan Formations have Hydrocarbon. Analysis and description of fold style elements are essential for structural studies. Based on this case, the comparison of the fold styles and folding mechanism is possible. The main aim in this research is the analysis of the fold style elements of the Tabnak anticline for determining the folding pattern and tectonic regime on this structure. This case has very important for Hydrocarbon exploration between gas fields in the Fars area. In this research, we used the Tectonics FP software, Global Mapper software and geological maps and reports of Iranian National Oil Company. In addition, we used common classification of fold for indicating folding mechanism of the Tabnak anticlinal structure. Based on analysis of the fold style elements, the Tabnak anticlinal structure has variation in fold style. This structure has three different fold styles in different parts. The changes of fold axis, axial plane characteristics and fold classification confirmed several fold styles in different parts of the Tabnak anticline. These changes are observed specially in B-B', F-F' and G-G' sections of this anticline. It seems that these parts have been suffered more deformation in the study anticline. In addition, based on interlimb and folding angle, fold type is close type in all of parts. The close type required more accuracy, because the close type may be ensigns of complication regime. In the study area, G-G' and F-F' section of the Tabnak gas field probable show folding style changes have been affected by Gavbandy Paleo-high.