Kangan Formation Research Articles

Exploring comparative heterogeneity management for precise water saturation assessment in carbonate formations: Dean-Stark measurements and beyond

Accurate determination of water saturation is a critical aspect of reservoir characterization and development potential of a hydrocarbon field. The inherent heterogeneity in carbonate reservoirs significantly influences the Archie equation coefficients and, consequently, water saturation calculations. In this study, 160 direct core sample water saturation measurements using the Dean-Stark method have been used. The primary goal was to identify the most suitable reservoir heterogeneity management approach for water saturation calculation. The research focuses on the Dalan and Kangan formations (equivalent to Khuff Formation), known as some of the most hydrocarbon-rich (gas) reservoirs globally, located in the western part of the Persian Gulf. To manage reservoir heterogeneity, we employed various techniques, including Winland R35, flow zone indicator, Lucia, pore types, and electrofacies, utilizing porosity and permeability core data, thin section studies, and well-logging data to classify the studied intervals into more homogeneous categories. Subsequently, we measured Archie parameters and, for the first time, water saturations derived from Dean-Stark measurements were compared with Archie saturations from various heterogeneity management methods. Additionally, the influence of geological and petrophysical parameters on the accuracy of water saturation calculations in different rock types is discussed. Our results highlighted the significance of geometrical attributes of pore types, pore throat radius, and permeability as key factors affecting the precision of water saturation calculations. Moreover, our investigation revealed that Lucia's rock typing methodology exerted a substantial influence on the control of permeability and the distribution of water saturation within the reservoir. Our analysis revealed that the electrofacies method provided the most precise estimates for water saturation, with a mean difference of 0.07 (v/v) units compared to the Dean-Stark method. Subsequently, the accuracy of predicted water saturation in rock types determined by the Lucia method, with a mean error of 0.09 (v/v), ranked second among the rock typing methods. Winland R35 and flow zone indicator methods exhibited the highest uncertainty in water saturation estimation, with mean differences of 0.23 and 0.21 (v/v), respectively, compared to the Dean-Stark method.

Tectono-sedimentary evolution of prolific Permo-Triassic petroleum reservoirs offshore Iran: Insights from seismic stratigraphy

The foreland basin extending through the Persian Gulf is one of the world's most prolific petroleum resource-bearing regions. The structural evolution of parts of that basin has been strongly influenced by Late Proterozoic/Early Cambrian Hormuz Salt formation movements, which have also controlled the distribution of petroleum resource accumulations. Fields SP and BL are characterized to distinguish the tectono-sedimentary evolution of the central and eastern parts of the basin, respectively. Field-SP is located within the Qatar Arch in the central part of the basin, whereas Field-BL is situated in the southeastern part of the basin and is tectonically influenced by the Hormuz Salt movements. 3D seismic data and information from two exploration wells are assessed in detail to define and compare the deformation history of the Permo-Triassic succession in these two fields. The Dalan (Upper Permian) and Kangan (Lower Triassic) formations and their equivalent Khuff Formation to the west host more than thirty-three known gas and gas-condensate fields within the basin that have evolved structurally in this tectono-sedimentary setting. This study integrates 3D seismic, well log, core, and thin section analysis from two wellbores drilled in the two studied fields. It applies seismic stratigraphic methods and principles to distinguish the architecture of relevant depositional tracts and interfaces and determine how they have evolved through geologic time. The results reveal that the different thicknesses of the Hormuz Salt (Cambrian) underlying the two studied fields, and the salt tectonic activity it has driven, are ultimately responsible for the distinctive structural evolutions and Permo-Triassic reservoir qualities observed in those fields. The significance of this finding is that by applying the developed seismic stratigraphy techniques integrated with existing well data on a regional basis offers the opportunity to identify undrilled exploration targets with an improved chance of containing high-quality Dalan/Kangan reservoir sections.

Sequence stratigraphy, diagenesis and geological zonation of the lower Triassic carbonate reservoir of the Kangan formation from the central to Northern Persian Gulf

Sequence stratigraphy, diagenesis and geological zonation of the lower Triassic carbonate reservoir of the Kangan formation from the central to Northern Persian Gulf

An enhancement in the petrophysical evaluation in a vuggy carbonate gas reservoir by integrating the core data and empirical methods, Zagros basin, south of Iran

The presence of vuggy pore types poses challenges in accurately assessing effective porosity. This study focuses on the significant scientific issue of improving petrophysical evaluation in vuggy carbonate gas reservoirs. The Kangan Formation is one of the main gas reservoir formations in the southern Zagros region, Iran. The main objective of the current research is to distinguish and exclude the influence of vuggy pore types from effective porosity in the reservoir pay zones of the Kangan reservoir.In the current research, a combination of full suite logs, image logs, core analysis, and thin section studies was employed. The image logs illustrate that vuggy porosity is abundant in the Kangan Formation and these results are confirmed by the available core thin sections, specifically in Zone Kangan_B; Additionally, the cross plots of compressional velocity versus bulk density and total porosity, as a part of rock physics study, indicate the characteristics of the vuggy reservoir. Two methods are utilized to quantify vuggy porosity. The first method, the Velocity Deviation Log (VDL) approach, identifies various available pore types, especially vugs. The second method is a newly proposed approach that can exclude vuggy porosity from the computed effective porosity. In this novel approach, a variable porosity exponent (m) is derived by adopting the Lucia equation to exclude vuggy porosity from the effective porosity computations. Thus, petrophysical evaluation can be implemented based on the constant and variable “m”. Comparing both petrophysical results, it is evident that the amounts of effective porosity and water saturation are modified in the vuggy-bearing intervals. Applying the proposed approach will improve the accuracy of petrophysical properties and lead to the proper calculation of the hydrocarbon volume in the carbonate reservoir rocks containing isolated vugs, particularly in gas-bearing reservoirs where conventional logs are affected by gas contents.

Deep Dive into the factors influencing acoustic velocity in the Dalan-Kangan formations, the central Persian Gulf

The propagation of acoustic waves in rocks is directly influenced by the rocks’ elastic properties. To evaluate petrophysical properties from acoustic data, it is essential to understand the factors that influence the variations in acoustic velocity of sedimentary rocks. Carbonate reservoirs are heterogeneous, and their evaluation is complicated. A closer look at the factors affecting the elastic properties of these rocks is essential because they reveal important information about the reservoir properties and their formation evaluation. Rock physics modeling relies on laboratory-measured acoustic data. This study, however, employs acoustic logs to elucidate the key factors influencing sonic velocity, offering a more comprehensive and field-applicable perspective. Samples were prepared from the Permian–Triassic Upper Dalan and Kangan formations. Porosity, permeability, sedimentary textures, mineralogy, and pore types were investigated. Furthermore, compressional, shear, and Stoneley well-logs data were recorded and converted to acoustic velocity in the sampled interval. Porosity-velocity modeling based on the differential effective medium (DEM) theory was performed for different values of equivalent pore aspect ratio (EPAR). The results show that there is a strong inverse relationship between acoustic velocities and porosity. Acoustic velocities also exhibit an inverse correlation with permeability, but the strength of these relationships is relatively weak. Acoustic velocities are not affected by carbonate textures. A specific texture may exhibit different velocities due to the influence of diagenetic processes. Mineralogy has only a minor influence on acoustic velocities. Dolostones have a slightly higher velocity than limestones, but the difference is insignificant. Stoneley log values are slightly different in limestone and dolostone, because this wave propagates along the mud-borehole interface. The velocities were affected by the variations in pore types within the studied formations. Therefore, in carbonate rocks, porosity, and the pore types play a significant role in controlling acoustic velocities. The value of EPAR = 0.15 can be considered as the boundary between stiff pores (moldic and vuggy) and soft pores (interparticle, intercrystalline, micro-intercrystalline, and microporosity). The lower EPAR value of interparticle pores in limestones compared to dolostones can be attributed to diagenetic processes such as dolomitization and compaction. The findings of this study can help to better understand what factors affect acoustic velocity in carbonate rocks. This study also shows that acoustic logs data can be effectively used in rock physics modeling and pore type identification. By identifying the pore types, it is possible to recognize diagenetic processes and determine the rock types to control the heterogeneity and estimate reservoir quality.

Analyzing in situ stresses and wellbore stability in one of the south Iranian hydrocarbon gas reservoirs

This study aims to analyze in situ stresses and wellbore stability in one of the Iranian gas reservoirs by using well log data, including density, sonic (compressional and shear slowness), porosity, formation micro-image (FMI) logs, modular formation dynamics tester (MDT), and rock mechanical tests. The high burial depth, high pore pressure, and strike-slip stress regime of the field require an optimal design of geomechanical parameters based on an integrated data set consisting of static and dynamic data, which is available for this study. Firstly, poroelastic modulus and vertical stress were calculated. Afterward, the Eaton’s equation was used to estimate pore pressure from well logging data. The geomechanical parameters were also calibrated through the interpretation of image data, the use of the modular formation dynamics tester (MDT), and laboratory rock mechanic tests. Employing poroelastic equations, the lowest and highest horizontal stresses were calculated. It was shown that the maximum horizontal stress and minimum horizontal stress correspond to sigma H and sigma h, indicating the strike-slope fault regime. The findings of this research indicated that the equivalent mud weight (EMW) resulted in 10–13 ppg suitable for the Kangan Formation and 11–14 ppg suitable for the Dalan Formation. Additionally, the well azimuth in the NE-SW direction provided the best stability for drilling the encountered formations. Therefore, the results of this study serve as cost-effective tools in planning adjacent wells in carbonate formations of gas field to predict the wellbore stability and safe mud window.

Investigating the reservoir quality of the Early Triassic succession with a new perspective on diagenesis and sequence stratigraphy in the center of the Persian Gulf, South Pars

The central part of the Persian Gulf has one of the largest gas fields in the world. This field was formed during the formation of the Neo-Tethys Sea and the Permo-Triassic period. In this research, the Earlier Triassic part of this area has been studied in Well A. The Earlier Triassic gas field in the Iranian part is called the Kangan Formation and is equivalent to the upper part of the Khuff Formation in the Arabian plate. This research is based on the petrography studies, diagenesis processes, and sequence stratigraphy with the help of core analysis data and petrophysical data (full suite logs). The main goal of this research is to evaluate the reservoir quality and classify the production potential of gas reservoirs by relating the two-variable diagrams of Permeability versus porosity and their expansion in the Earlier Triassic of the region. The studies showed that the reservoir properties of the Kangan Formation were formed under the influence of various factors: Sedimentation processes, regional tectonics, diagenesis processes, and their sequence. The sedimentation processes have been created under the influence of the sedimentation environment and the transgressive-regressive of the sea in different sequences. Each environment has different reservoir properties depending on its energy, depth, salinity, oxygen and organisms. In the studied area, 12 diagenesis processes in several diagenesis areas such as meteoric vadose, marine phreatic, meteoric, and a combination of them along with eight cement and eight types of porosity with different effects on reservoir quality were identified and the limits of each were specified. In the studied area, based on petrographic studies, the third and fourth-order sequences were determined and the reservoir quality was accurately determined by the system tracts of the third and fourth-order sequences and their location were determined. Finally, the reservoir quality of the Kangan Formation was determined based on a set of reservoir potentials in diagenesis processes (porosity and permeability) and according to the sequence stratigraphy of the region. In addition, their results were compared with the results of petrophysical logs, water, and gas saturation. Then, permeable and extractable areas and impermeable and non-reservoir areas of the Kangan Formation were determined. This research showed that the Earlier Triassic sequence in the central part of the Persian Gulf could be divided into four zones, zone one and three, which have non-reservoir potential and are mostly evaporitic and mudstone. Zones two and four have reservoir potential and often have dolomite and grainstone facies in the environment of the central shoal and the active tidal zone.

Biostratigraphy of Upper Permian-Lower Triassic Reservoir Units in one of the South Pars Field wells

In this study, the biostratigraphy of the reservoir sediments of the upper part of the Dalan Formation (Late Permian, Lopingian) and the reservoir part of the Kangan Formation (Early Triassic) from one of the well in the northern part of South Pars field are studied. The results of studies are presented as three local biozones recognized and defined. Based on these studies, a Late Permian age (Dorashamian/Changhsingian) for the upper Dalan Member an Early?—Middle Triassic age (Scythian?—Anisian) for the lower part of the Kangan Formation, suggested. Also, based on microfossils stratigraphical distribution, and studying succession and continuity of locally defined biozones, it was distinguished a hiatus between Dalan and Kangan formations. Therefore it could be mentioned that the Dorashmian age is the youngest part of the Dalan Formation.

The effects of planar structures on reservoir quality of Triassic Kangan formation in the central Persian Gulf, an integrated approach

Planar structures including stylolites, solution seams, dense streaks, bedding and cross-bedding surfaces, and fractures of carbonate Early Triassic Kangan Formation were evaluated in the central Persian Gulf. Core X-ray computed tomography (CT), Fullbore Formation Micro-Imager (FMI) log, and cores were used to detect the structures. Furthermore, conventional borehole logging data, routine core analysis, and petrographic thin sections were employed to assess the reservoir properties. Stereographic projections demonstrated that the reservoir has two sets of planar structures. The first group contains shallowly-dipping structures, consisting of stylolites, solution seams, dense streaks, bedding and cross-bedding surfaces. These structures have been created by sedimentary and diagenetic processes. The other set includes deformation-related structures that are steeply-dipping and occurred scarcely, like fractures. Spearman correlation coefficients between the frequency of each planar structure and reservoir characteristics (porosity and permeability) were calculated to reveal the numerical relationship between the parameters. The significant correlation coefficients indicate that stylolites, solution seams, and filled tension gashes diminish reservoir quality while bedding and cross-bedding surfaces have enhanced reservoir characteristics. The strongest correlation was observed as a strong negative relationship between the frequency of stylolites and permeability in K2 reservoir unit. This study implies that sedimentary and diagenetic factors are more effective in controlling the reservoir quality than deformation factors in the studied formation. The present work also indicates that each used method has unique advantages and disadvantages. Therefore, simultaneous utilization of the methods to investigate planar structures would have the best efficiency.

Application of Statistical Methods to Biomarkers for Geochemical Evaluation and Genetic Type Determination of Gas Condensates in the Persian Gulf and Coastal Fars, Southern Iran

AbstractIn a comprehensive geochemical study, the genetic relationships among 14 samples of gas condensates from the Persian Gulf were investigated for the purpose of evaluating the respective source rocks in terms of both age and sedimentary paleoenvironment. Chemometric analysis was used for categorization and determination of a certitude range to determine the genetic type of the condensate families in the studied basin. The samples were collected from Late Permian – Triassic reservoirs (Dalan and Kangan formations) located in 6 gasfields (gas condensate) hosting some of Iran's most important gas/gas condensate reserves. Obtained by gas chromatography‐mass spectrometry (GC‐MS), a total of 16 biomarker parameters (10 maturity‐related parameters and 6 sedimentary environment‐related parameters) were used to evaluate the samples in terms of thermal maturity (and hence their positions in the maturity chart), the sedimentary environment of the source rock and the lithology. Application of Hierarchical Clustering Analysis (HCA) and Principal Component Analysis (PCA) to the collected data led to the categorization of the samples into three main genetic groups, I–III. Groups I and III were found to be located in the east and the west of the Persian Gulf, respectively, while Group II was developed between the two other groups.

A syngenetic classification of anhydrite textures in carbonate reservoirs and its relationship with reservoir quality: a case study from the Permo-Triassic Dalan and Kangan formations

A syngenetic classification of anhydrite textures in carbonate reservoirs and its relationship with reservoir quality: a case study from the Permo-Triassic Dalan and Kangan formations

The effect of frequency bandwidth on DSI anisotropy evaluation

Anisotropy evaluation in carbonate rocks plays a pivotal role in their reservoir characterization and modeling. This study demonstrates the benefits of advanced interpretation using the Dipole Shear Sonic Imager (DSI) log data for anisotropy evaluations of porous media. Splitting the shear wave into fast and slow components, with different polarizations and velocities, provides useful indications of formation anisotropy. Fast shear waves travel faster in directions parallel to layering and fracturing while slow shear waves travel more slowly perpendicular to layering and fracture networks. Quantifying the difference between fast and slow shear velocities provides a measure of acoustic anisotropy in the medium penetrated.The purpose of the research is to evaluate the effects of frequency bandwidth on the depth of the wave propagation rates and slowness values for anisotropy analysis, thus four bandwidth frequencies: 1–2 kHz, 2–4 kHz, 4–6 kHz, and 1–5 kHz are selected and examined in a vertical drilled well in the gas reservoirs of Upper Dalan Member, and Kangan Formations in the South Pars Gas-Condensate Field.The frequency filtering, semblance analysis, and slowness picking are done on waveforms for frequency-slowness dispersion analysis and slowness correction. The dispersion correction for bandwidth 4–6 kHz isn't performed completely in good hole condition intervals, because high- frequencies around 6 kHz are absorption due to the intrinsic attenuation of the rocks. Therefore, the considered bandwidth is decreased to 4–5.5 kHz. In the following, Alford rotation, align waveforms, and calculation and evaluation of derived fast and slow components are done for deriving the azimuth of the fast shear wave for each bandwidth of waveforms. The dominant trend of the azimuth of anisotropy is that aligned with the azimuth of the fast shear wave.The azimuth of the fast shear wave as azimuth of anisotropy and its corresponding intervals are compared with the results of image log data for the same well interval. This made it possible to reject or confirm the findings of the DSI acoustic anisotropy analysis for each bandwidth considered.In the low bandwidth frequency (1–2 kHz), the differences in slowness, energy, travel time, and penetration depth are more extreme than those recorded by the other bandwidths considered. The azimuth of anisotropy is NW-SE with a slight E-W trend. However, the azimuth of anisotropy was found to be contrary to the image log interpretation where the dominant trend is NE-SW.The dominant trend of the azimuth of anisotropy for bandwidth 2–4 kHz is NE-SW with a slight E-W trend. The anisotropy directions and zones are consistent with those identified from the wellbore image log results. Moreover, the penetration depth is meaningful and far away from the borehole drilling and mud effects. These results suggest that the bandwidth (2–4 kHz) is best suited for acoustic anisotropy analysis of wellbore sections using Dipole Shear Sonic Imager (DSI) recorded data in this well.The trends of the azimuth of anisotropy for bandwidth 4–5.5 kHz are NE-SW, and NW-SE, with expanded tolerance azimuth of anisotropy. The results that have been achieved in a small penetration depth and close to the borehole wall are affected by signal absorption and attenuation in flushed and transition areas. This leads to some errors and inconsistencies with the image log interpretation.The trends of the azimuth of anisotropy for bandwidth 1–5 kHz are NE-SW, NW-SE, and E-W. The outcomes are the consequence of the variety of directions and zones associated with this wider bandwidth, together with the penetration depths of the waveforms in the diverse zones considered. However, the azimuth of anisotropy is inconsistent with the image log interpretation.

Feasibility Study of Fracture Propagation Controlled by Use of Managed Pressure Drilling during Laser-Assisted Drilling Operation

Summary Managed pressure drilling (MPD) is a form of drilling that allows greater and more precise wellbore pressure control than conventional drilling. In addition, the mud weight used will be lower than for the conventional mud weight, and a secondary choke or frictional pressure will be applied on the surface to create a combined annular pressure profile within the well. For this paper, we investigated the effect of high power fiber laser heat tension on the carbonate rock body of the Kangan Formation during the irradiation process with accurate simulation work and by comparing the model with experimental results. First, the enforced stress by heat from the laser source was analyzed, and then the fracture propagation pattern in the rock body throughout the entire irradiation process was obtained. This research presented the weakening and fracturing mechanism that was generated from heat exposure during laser irradiation and determined numerical results for fracture pressure before and after laser irradiation. Also, MPD as an effective technology to control this induced anomaly was proposed during the laser-assisted drilling (LAD) operation to prevent any loss, gain, hole instability, or other drilling problem related to this fracturing and weakening.

Analysis of fractures in the Dalan and Kangan carbonate reservoirs using FMI logs: Sefid-Zakhur gas field in the Fars Province, Iran

Fracture evaluation is very important in the carbonate reservoirs, particularly fractured reservoir, due to the high impact of fractures on the reservoir permeability. Assessment of fracture parameters of reservoirs is necessary to optimize oil production. Image logs are regarded the best methods for this aim. This study aims to use electrical image logs in the Dalan and Kangan Formations reservoir in the Zagros Basin, SW Iran. This paper presents the new findings of analysis of the effective structures on reservoir quality of the Dalan and Kangan Formations in one of the Iranian gas fields by using FMI image logs. Formation micro-imager (FMI) was taken along with petrophysical logs from depth 4677–5253. FMI data were processed and evaluated. Through this assessment, different types of natural structures such as the fracture (open, close) and bedding planes were identified. The data analysis presented different fracture sets that have a different orientation to the anticline axis. All identified bed contacts were used to determine the structural dip. The general structural dip is interpreted to be 40 degrees toward N15E, with a corresponding strike of N75W-S75E. The total fractures encountered are in three categories: major-conductive, medium-conductive, and minor-conductive fractures. Fracture apertures with values more than 0.01 cm can be the highest value of fracture aperture with a value of more than 0.1 cm, which can be observed at 5013–5015 m, 5023 m, and 5065–5070 m. The range of fracture porosity from conductive fractures is computed to be 0–0.6%. Fractures with porosity range of more than 0.4% can be observed at 4953–4960 m, 4966 m, 4973–4980 m, 5020 m, 5113 m, and 5153 m (Lower Dalan). The highest fracture porosity can be observed at 4954 and 5020 m (close to 0.6%). The main productive zones appear to be 5160–5110 m, 5030–5000 m, 4980–4910 m, and 4830–4770 m. In this section of the reservoir, the high density, porosity, and aperture of the natural conductive/open fractures at certain intervals may indicate high productivity zones at these particular places. Considering the conductive/open fracture apertures, a production profile for a reservoir can be predicted from the fracture-enhanced permeability, with the assumption that the production of the reservoir is fracture-controlled. With the same assumption for the reservoirs within the 5.875-in. section of the well, a predictive production profile was constructed by integrating the fracture apertures.

Astronomical forcing variations of the Upper Dalan Member (Late Permian) in the South Pars gas field, Persian Gulf, Iran

• Orbital cycles detected the in the Late Permian strata of South Pars gas field Iran. • Prolific gas reservoirs units K1 to K4 units) formed over a time interval of 4.8 ± 0.3 Myr. • Sediment accumulation rates of the Upper Dalan Member range from ~3.5 to ~18 cm/kyr. • Depositional duration of the Upper Dalan Member estimated to be 3.2 Myr ± 0.2 Myr. • Eight 405-kyr long-eccentricity cycles were identified from well log analysis. The Late Permian sedimentary succession in the Iranian offshore Persian Gulf, formed under arid paleoclimate conditions, has been poorly studied in terms of astronomical forcing evidence. In this study, petrophysical logs are applied as paleoclimate proxies. They are used to investigate the astronomical forcing of the arid paleoclimate during the Late Permian together with the sediment accumulation rates (SAR) of the Upper Dalan Member (UDM) in two wells drilled in the South Pars gas field. Evidence of Milankovitch cycles (eccentricity, obliquity, and precession) was detected in both of the studied wells. By application of a combination of different methods (e.g., spectral analysis, COCO/eCOCO analysis), the SAR of the UDM was estimated to be in the range of ~3.5 to ~18 cm/kyr. Based on the 405 kyr long-eccentricity cycles extracted from the spectral gamma ray (SGR) logs, a floating astronomical time scale (ATS) of 3.2 ± 0.2 Myr was established for the UDM. This is equivalent to the depositional duration of the UDM in the studied wells. The Kangan Formation and UDM (K1 to K4 units) of southwestern and offshore of Iran were deposited during an astronomical duration of 4.8 ± 0.3 Myr. Additionally, the accumulation of organic matter in the studied reservoir units was compared with the SAR. The effects of SAR on the total organic carbon (TOC) variations were detected and correlated in four different segments of the UDM.

Facies, sequence framework, and reservoir quality along a Triassic carbonate ramp: Kangan Formation, South Pars Field, Persian Gulf Superbasin

The Lower Triassic Kangan Formation of the Persian Gulf Superbasin forms one of the largest reservoirs in the South Pars/North Field, the world's largest gas field. The upper Khuff-equivalent, gas-hosting carbonate-evaporite succession was formed on a gently-sloping, homoclinal carbonate ramp in a warm, tropical aragonite sea under a hot-and-arid greenhouse climate. This study explores the impact of vertical variations in depositional facies and diagenetic features on the reservoir quality to improve the prediction of the subsurface facies and hydraulic flow unit distribution.Detailed core logging and petrographic analysis resulted in the recognition of twelve distinct carbonate-evaporite facies that are grouped into four major facies associations, from shallowest to deepest: supratidal to restricted subtidal, lagoon, carbonate shoal, and shallow mid-ramp. The facies associations are stacked into two long-term sequences KS2 (58 m) and KS1 (77 m) bounded by anhydrites and/or unconformities; three higher frequency sequences (KS1a, KS1b, and KS1c) can be identified within the KS1. Based on the petrophysical properties, sedimentary facies characteristics and their diagenetic modifications, five hydraulic flow units (HFUs) are identified, with the best porosity-permeability values and flow- and storage capacities in the late transgressive (TSTs) and the earliest highstand systems tracts (HSTs) of the two long-term sequences. The reservoir quality and the distribution of hydraulic flow units are a product of interactions between primary mineralogy, depositional facies and their stacking, and the early- and late-diagenetic alterations. The reservoir quality decreases in landward direction, being the lowest in the mud-supported textures of the lagoon and supratidal to restricted subtidal facies associations. The seaward improvement in reservoir quality reflects a change to grain-supported textures that formed along the tide-and wave-agitated ooid-bioclastic shoals, whereas the best reservoir quality characterizes the shallow mid-ramp open-marine facies association, where secondary porosity was improved by dissolution and dolomitization. Both the early and late diagenetic dolomitization overall improved the reservoir quality, with the dolomitization pathways controlled by the porosity and permeability heterogeneity in the original depositional facies. The results may be useful in reservoir modeling, recognition of the productive zones, and the further development of the South Pars/North Dome Field.

Example of applied outcrop analysis and its significance as an analogue for surrounding giant gas-fields; Case study of Kuh-e-Surmeh region, southwestern Iran

Outcrops provide crucial information that can be used for the improvement of subsurface geological modeling. The present work provides a great example of such an application from a study on two well-known carbonate reservoirs uniquely exposed in the Kuh-e-Surmeh region, south-west Iran. Surface geology data were collected through extensive field study while the equivalent subsurface geology was reviewed based on bore reports available from the nearby giant gas-fields. Moreover, Schmidt hammer data were collected to investigate the variation in outcrop's uniaxial strength and detailed fracture analysis was carried out using Unmanned Aerial Vehicle (UAV) photography and direct field observations in selected stations. At the end, dolomite and limestone were identified as the dominant lithology of outcrops, greater apparent fracture intensity values were estimated for Kangan formation (P21=0.46) and the base of upper Dalan formation (P21=0.48). Moreover, fracture density (P20) was shown to be directly related to the formation uniaxial strength and the height of fractures was revealed to be inversely proportional to the thickness of sublayers. At the end, the collected surface and subsurface data were found to be in a general good agreement in terms of the stratigraphic location of fractured zones and mineralogy data, specifically, for the case of upper Dalan formation.

Cyclostratigraphy of the Lower Triassic Kangan Formation in the Salman gas field, eastern Persian Gulf, Iran

Cyclostratigraphy plays a pivotal role in detecting and reporting Milankovitch cycles in sedimentary successions which allows for creating an independent astronomical time scale and estimates of sediment accumulation rates. In this study, cyclostratigraphic analysis of petrophysical logs from Lower Triassic Kangan Formation was performed in two wells of the Salman gas field, eastern part of the Persian Gulf, Iran. The results of power spectral analysis in the two studied wells reveal the main spectral peaks at wavelengths of long-eccentricity, short-eccentricity, obliquity, and precession cycles. Based on the orbital tuning using the long-eccentricity cycles, a floating astronomical time scale was established, according to which the depositional duration of Kangan Formation was estimated to be 1.6 ± 0.1 Myr. As well as, the duration of the Induan Stage of the Early Triassic Epoch in this study is estimated to be at least 1.6 Myr. Also, by integrating cyclostratigraphic analysis, results of the statistical methods of sedimentation rate evaluation, i.e., evolutionary correlation coefficient (COCO), it was estimated that the sedimentation rates of Kangan Formation in the two studied wells of Salman gas field increased from ~8 cm/kyr in the bottom to about 12–18 cm/kyr in the upper part, which were linked with the delayed life recovery in Early Triassic. We also observed an enhanced sedimentary noise (ESN) interval in eCOCO maps of the K1 member (upper part of Kangan Formation) at two studied wells, which were linked with the global sea-level fall in the late Griesbachian substage of the Early Triassic. The results of this study show that cyclostratigraphy has made an effective contribution towards analyzing sea-level change and estimating sediment accumulation rates and depositional duration of the Kangan Formation.

Porosity system analysis and its relation to the permeability of the reservoir zones in the Upper Dalan Member and Kangan Formation: A case study, one of the gas fields in the Zagros Coastal Fars, SW Iran

The studied gas field is located in the Coastal Fars structural zone of the folded Zagros, in the west of Hormozgan Province and on the Gavbandi highland. The Dehram Group forms gas reservoirs in this field. The results of macroscopic and microscopic studies and routine core analysis of the Upper Dalan Member and Kangan Formation show that porosity with an average of 14.51% in the Kangan Formation is more than Upper Dalan Member with an average of 8.29% (certain intervals of the well cores); however, the Upper Dalan Member with an average of 10.8 md (10.8 × × 10−3 μm2) has higher permeability than Kangan Formation with an average of 3.54 md (3.54 × × 10−3 μm2). The Grain-supported facies (in accordance with Ka-2 reservoir zone) of the Kangan Formation has the best reservoir quality with an average of 10.7% effective porosity and 43.3% total water saturation; while in the Upper Dalan Member, mud-supported facies (in accordance with UDL-5 reservoir zone) has the best reservoir quality with an average of 10.2% effective porosity, and 36.7% total water saturation where the dolomitization process has been the most important factor for increasing the reservoir quality in these facies. The porosity type of the Kangan reservoir (oolitic grainstone of shoal facies belt in Ka-2 reservoir zone) is isolated moldic and vuggy those generates high porosity and low permeability values in this formation but in some intervals, the isolated molds and vugs are connected by channel and fracture; therefore increased the value of permeability. The tidal flat facies belt of Upper Dalan member has high porosity and permeability and good reservoir quality in the UDL-2, UDL-5 and UDL-6 reservoir zones, with respect to the tidal flat facies of the Kangan Formation, which is related to dolomitization processes that generate intercrystalline porosity type. Finally, both the depositional environment and diagenetic processes controlled the distribution characteristics of reservoir quality, as seen in the relation between porosity and permeability.

1D and 2D basin modeling, in evaluating the hydrocarbon generation-migration-accumulation potential, at coastal Fars Area, Southern Iran

One of the giant hydrocarbon generation zones in Iran has been developed in the south of the Zagros Mountain Range (i.e., South Zagros), located between the South Zagros and the Persian Gulf in a foreland basin known for high levels of exploration uncertainties (due to the presence of complex structures, multiple source layers, and migration pathways). In this basin, the Permotriassic formations provide for the main reservoir strata, while the hydrocarbon content is deemed to be derived from the “hot shales” of the Silurian-Ordovician Sarchahan Formation, serving as source rock. As the focus of the present research, the Coastal Fars region is developed along the shores of southern Iran and hosts a number of gas reservoirs that have been increasingly discovered since 1970. Developed in the Permotriassic siliciclastics and carbonates of the Faraghan, Dalan, and Kangan Formations, gas reservoirs have made the Coastal Fars a hot zone for exploration and production activities. In this research, one 2D and five 1D models of the basin (at five exploration wells) were constructed to evaluate the maturity of the main Silurian-Ordovician source rock and further investigate the hydrocarbon charge, timing, migration pathways, and accumulation sites. The models were then utilized to investigate the relationship between the presence of multiple shale layers and hydrocarbon content of the reservoir at one of the studied wells using Rock-Eval analysis. This study showed that an uplift that happened after the hydrocarbon generation has led to a dry hole in the study area. The results indicated that the Sarchahan Formation is probably the main source rock across the region, according to previous researches in this area its organic contents were dated back to the late Ordovician rather than the Silurian. The shale intercalations across the reservoirs (Kangan and Upper Dalan), especially in the Khayam Field, were found to produce more than 90% of their hydrocarbon generation potential. No non-indigenous hydrocarbon was identified across the study area, implying that the entire hydrocarbon content was generated by the identified source rocks. Laboratory analysis indicated the presence of type II and type III kerogen at a local heat flow rate of about 65 mW/m2 since the Cretaceous. In total, the Sarchahan Formation was found to reach a maximum burial depth of 6 km, making it matured to overmatured all over the study area.