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 ...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.展开更多
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 (perm...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.展开更多
The upper Dalan and Kangan or Permian-Triassic carbonate formations in the central the Persian Gulf are considered as world's giant gas reservoirs.The primary purpose of this research is to model and evaluate the ...The upper Dalan and Kangan or Permian-Triassic carbonate formations in the central the Persian Gulf are considered as world's giant gas reservoirs.The primary purpose of this research is to model and evaluate the relationship between hydraulic flow units(HFUs),electrofacies and microfacies with systems tracts of Permian-Triassic sequences.By integrating the results of core data,petrographic studies,and petrophysical logs of the studied formations,hydraulic flow units and electrofacies were identified.Based on the results of petrographic studies,twelve microfacies were identified in terms of textural and depositional characteristics.Based on depositional setting,sedimentary facies and INPEFA values obtained from gamma ray log and gamma deviation log(GDL)in the context of sequence stratigraphy,zonation of Dalan and Kangan reservoirs is carried out.The zonation boundaries correspond to the key stratal surfaces(sequence boundary and maximum flooding surface).Seven petrographic rock types(PRT)were identified for the upper Dalan-Kangan reservoirs based on sedimentary texture,diagenetic process and dominant pores.Using porosity and permeability data from the core analysis,five hydraulic flow units were identified based on the flow zone indicator(FZI)method.Using multi-resolution graph-based clustering(MRGC)four electrofacies were detected from petrophysical data(gamma,neutron,density and acoustic logs).Subsequently,the INPEFA,GDL and electrofacies were spatially modeled using the sequential indicator simulation(SIS)and sequential Gaussian simulation(SGS)geostatistical methods.Finally,a clear agreement was revealed between the reservoir zones and the stratigraphic sequence framework.It this regard,the microfacies belonging to the high-energy and grain-dominated settings(packstone,grainstone)of leeward shoal,shoal and seaward shoal belts have the best reservoir units due to the influence of dissolution and dolomitization.The best reservoir units in the Permian-Triassic deposits in the middle of the upper Dalan and lower Kangan are developed in UDS4,upper KS2 and middle KS1 units.On the other hand,mud-dominated facies(mudstone,wackestone)and anhydrite textures are mostly associated with the low-energy lagoonal environments,between tidal flat and Sabkha.Non-reservoir units have been formed in the upper Dalan/Kangan and in the transgressive systems tract of UDS3-a,KS2-a and the lower and upper part of KS1 transgressive-highstand systems tract.展开更多
文摘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.
文摘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.
文摘The upper Dalan and Kangan or Permian-Triassic carbonate formations in the central the Persian Gulf are considered as world's giant gas reservoirs.The primary purpose of this research is to model and evaluate the relationship between hydraulic flow units(HFUs),electrofacies and microfacies with systems tracts of Permian-Triassic sequences.By integrating the results of core data,petrographic studies,and petrophysical logs of the studied formations,hydraulic flow units and electrofacies were identified.Based on the results of petrographic studies,twelve microfacies were identified in terms of textural and depositional characteristics.Based on depositional setting,sedimentary facies and INPEFA values obtained from gamma ray log and gamma deviation log(GDL)in the context of sequence stratigraphy,zonation of Dalan and Kangan reservoirs is carried out.The zonation boundaries correspond to the key stratal surfaces(sequence boundary and maximum flooding surface).Seven petrographic rock types(PRT)were identified for the upper Dalan-Kangan reservoirs based on sedimentary texture,diagenetic process and dominant pores.Using porosity and permeability data from the core analysis,five hydraulic flow units were identified based on the flow zone indicator(FZI)method.Using multi-resolution graph-based clustering(MRGC)four electrofacies were detected from petrophysical data(gamma,neutron,density and acoustic logs).Subsequently,the INPEFA,GDL and electrofacies were spatially modeled using the sequential indicator simulation(SIS)and sequential Gaussian simulation(SGS)geostatistical methods.Finally,a clear agreement was revealed between the reservoir zones and the stratigraphic sequence framework.It this regard,the microfacies belonging to the high-energy and grain-dominated settings(packstone,grainstone)of leeward shoal,shoal and seaward shoal belts have the best reservoir units due to the influence of dissolution and dolomitization.The best reservoir units in the Permian-Triassic deposits in the middle of the upper Dalan and lower Kangan are developed in UDS4,upper KS2 and middle KS1 units.On the other hand,mud-dominated facies(mudstone,wackestone)and anhydrite textures are mostly associated with the low-energy lagoonal environments,between tidal flat and Sabkha.Non-reservoir units have been formed in the upper Dalan/Kangan and in the transgressive systems tract of UDS3-a,KS2-a and the lower and upper part of KS1 transgressive-highstand systems tract.
