Chemical compaction features as potential barriers in the permian-triassic reservoirs of south pars field, southern Iran (original) (raw)
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Journal of Petroleum Science and Engineering, 2016
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.
Controls on Reservoir Quality in the Early Triassic Kangan Formation, Iran
The Early Triassic Kangan Formation is one of the most prolific gas reservoirs in Iran. The formation consists in two reservoir units: K2 and K1 in the area of investigation. Ten facies are distinguished in the Kangan Formation. These facies are interpreted as peritidal, lagoonal, shoal and fore shoal deposits. Two depositional sequences, Khuff sequence-2 (KS-2) and KS-1 are differentiated based on facies stacking patterns.
Geological Journal, 2009
The Permian-Triassic boundary (PTB) is a worldwide event characterized by the most extensive mass extinction in the history of life. In the Persian Gulf, the rock record of this time interval host one of the most important hydrocarbon reserves in the world: the South Pars Gas Field and its southern extension, the North Dome (or North Field). These carbonate and evaporite successions were sampled in eight wells for petrographic, geochemical and porosity-permeability studies. An important characteristic of the Dalan and Kangan formations is the centimetre-scale lithological heterogeneities caused by facies changes and diagenetic imprints that led to the compartmentalization of these reservoirs. These Permian-Triassic (P-T) sediments were deposited in a shallow marine homoclinal ramp. The PTB in this hydrocarbon field is represented by a reworked coarse-grained intraclastic/ bioclastic grainstone facies deposited during a marine transgression. Prolonged subaerial exposure in the P-T transition caused hypersaline and meteoric diagenesis, including extensive cementation, dolomitization and some dissolution, influencing reservoir characteristics of bordering units. Both d 18 O and d 13 C values in this succession mirror worldwide excursions typical of other P-T sections, with some variations due to diagenetic alterations. A pronounced decline in 87 Sr/ 86 Sr values, reflective of global seawater geochemistry for most of the Permian is evident in our data. Reservoir quality declines through the late Permian, as a result of facies change and diagenesis. The Late Permian is succeeded by a Triassic transgressive facies and decline in reservoir quality.
Geologica acta, 2014
Owing to their tightness, intra reservoir barriers have the potential to prevent homogenization of reservoir fluids and so cause compartmentalization. Identification of these barriers is an important step during reservoir evaluation. In order to achieve this, three main approaches: i) detailed petrographic and core analysis, ii) petrophysical studies (flow unit concept) and iii) geochemical analysis (strontium residual salt analysis) were applied systematically in the Permo-Triassic carbonate reservoirs (Dalan and Kangan formations) of a supergiant gas reservoir located in the Central Persian Gulf. Integration of these approaches has led to a full clarification of the intra reservoir barriers. Petrographic examinations revealed the potential stratigraphic barriers to fluids flow created by various depositional/ diagenetic characteristics. Petrophysical data such as poroperm values, pore throat size distribution and scanning electron microscopy (SEM) analysis were used to differentiate the reservoir flow units from non-reservoir rock. According to different trends in 87Sr/86Sr ratios of residual salts, the existence of flow barriers was evaluated and proved. Finally, by integrating these approaches, three intra reservoir barriers were introduced in the studied reservoir interval. These intra reservoir barriers are depositional and diagenetic in nature and are located in stratal positions with sequence stratigraphic significance. The possibility of reservoir compartmentalization was evaluated in the studied wells, and then their existence was predicted at the adjacent fields. As shown in this study, integration of petrographic examinations with flow unit determination in a sequence stratigraphic framework has the potential for recognizing intra reservoir barriers and predicting compartmentalization of the studied Permo-Triassic reservoirs.
Appraisal of intra-reservoir barriers in the Permo-Triassic successions of the Central Persian Gulf
Geologica Acta, 2014
Owing to their tightness, intra reservoir barriers have the potential to prevent homogenization of reservoir fluids and so cause compartmentalization. Identification of these barriers is an important step during reservoir evaluation. In order to achieve this, three main approaches: i) detailed petrographic and core analysis, ii) petrophysical studies (flow unit concept) and iii) geochemical analysis (strontium residual salt analysis) were applied systematically in the Permo-Triassic carbonate reservoirs (Dalan and Kangan formations) of a supergiant gas reservoir located in the Central Persian Gulf. Integration of these approaches has led to a full clarification of the intra reservoir barriers. Petrographic examinations revealed the potential stratigraphic barriers to fluids flow created by various depositional/ diagenetic characteristics. Petrophysical data such as poroperm values, pore throat size distribution and scanning electron microscopy (SEM) analysis were used to differentiate the reservoir flow units from non-reservoir rock. According to different trends in 87Sr/86Sr ratios of residual salts, the existence of flow barriers was evaluated and proved. Finally, by integrating these approaches, three intra reservoir barriers were introduced in the studied reservoir interval. These intra reservoir barriers are depositional and diagenetic in nature and are located in stratal positions with sequence stratigraphic significance. The possibility of reservoir compartmentalization was evaluated in the studied wells, and then their existence was predicted at the adjacent fields. As shown in this study, integration of petrographic examinations with flow unit determination in a sequence stratigraphic framework has the potential for recognizing intra reservoir barriers and predicting compartmentalization of the studied Permo-Triassic reservoirs.
Controls on Reservoir Quality in the Lower Triassic Kangan Formation, Southern Persian Gulf
Journal of Petroleum Geology, 2008
The Lower Triassic Kangan Formation together with the underlying Upper Permian Dalan Formation forms one of the most important reservoirs for natural gas in the Middle East. The carbonate-dominated Kangan Formation was studied at a gasfield in the southern Persian Gulf and some 100 m of core were examined at micro-and macro scales. Twelve microfacies were identified. Previous studies have divided the Kangan Formation reservoir into Lower (K2) and Upper (K1) Units. The Lower Kangan can divided into two subunits (K2b and K2a), while three subunits (K1c, K1b and K1a) are recognised in the Upper Kangan. Diagenetic processes have affected reservoir quality in the Kangan Formation in different ways. Processes improving reservoir quality include dissolution, dolomitization and fracturing, while reservoir quality was decreased by cementation, and chemical and mechanical compaction. Micritization and neomorphism have had both positive and negative effects. Fracture development has improved reservoir quality, particularly in dolomitic intervals.
2011
The Lower Triassic Kangan Formation, one of the most productive petroleum reservoirs of south and southwest Iran, was formed in an extensional basin in the expanded Neotethys Ocean. The Basin was formed as a result of the Late Permian continental drift between Cimeria and Gondwana. The Kangan Formation is over 160 meters thick and consists mainly of carbonates and evaporites. It is unconformably underlain by the Upper Permian Dalan Formation and is conformably overlain by the Upper Triassic Dashtak Formation. Detailed petrographic investigation and well log analysis of the Kangan Formation in (Salman Field) and (Minab Field) led to the recognition of arid tidal-flat, back barrier lagoon and barrier/shoal facies belts related to an inner part of a homoclinal ramp platform. Vertical facies changes and cycle stacking patterns demonstrate that the Kangan Formation consists of three depositional sequences, each consisting of transgressive and highstand systems tracts and each bounded abo...
Reservoir facies controlling factors in the Upper Permian Dalan Formation, SW Iran
The Upper Permian Dalan Formation is an economically significant gas and condensate reservoir in the Fars region of southwest Iran. It is composed mainly of limestone and dolostone. Facies analyses, depositional environments and diagenetic processes of the Dalan Formation at eight drilled wells and reference section at the Surmeh anticline were studied. Field and petrographic studies combined with wireline well logs analyses and available seismic images resulted in recognition of various carbonate facies related to tidal flat, lagoon, shoal, basinal facies tracts, siliciclastic and evaporitic facies deposited on a carbonate ramp. Petrographic investigations and facies analyses of the Dalan Formation, led to the recognition of aragonite mineralogy and diagenetic environments of the Dalan Formation, which resulted in recognition of controlling factors of reservoir facies. Grainstone facies deposited on paleohighs have marine cements with isopachous and fibrous fabrics, which leaching of grains created porous intervals. On the other hand, grainstone facies deposited in places with lower palaeogeographic positions, not only show limited distribution but also have been affected much more by deep burial cements and diagenetic processes, which resulted in loosing their reservoir properties. This study suggests that paleohighs had played main role in the diagenetic sequences and reservoir facies distribution.