A REVIEW OF PERMO-TRIASSIC RESERVOIR ROCKS IN THE ZAGROS AREA, SW IRAN: INFLUENCE OF THE QATAR-FARS ARCH (original) (raw)
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Open Journal of Geology, 2016
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 * Corresponding author. N. Rezavand et al. 945 comprise the main reservoir facies of the Dalan formation.
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.
A new insight into the evolution of the Qatar Arch to recognize faults and a new gas field
Journal of Petroleum Exploration and Production Technology, 2023
Despite the previous interpretations of the evolutionary scenarios of the Qatar Arch, the present study aimed to present a new complementary scenario to lay out the probable effects of another basement fault, corresponding to the physical shape of the Arch. A remote sensing study was carried out based on geological and geophysical data interpretations, obtained from some national and international databases, including GIS-based global geology data of Harvard University, the free-air gravity anomaly data from the World Gravity Map (WGM), and the airborne geophysical project of the National Geosciences Database of Iran (NGDIR). Results revealed that offshore extrapolation of the Trans Arabian-Bostaneh Fault (TABF) lineament through the morphological boundary of Hauterivian-Barremian (HB) formations and the offshore extrapolation of the Kazerun fault could produce a new complementary model for the Qatar Arch evolution. Based on the particular shape of the Arch (i.e., narrowing and uplifting to the south influenced by the Kazerun basement fault and the rotation of TABF), we can propose that these faults crossed each other after the Barremian age, created a particular shape of the Qatar Arch, and influenced beneath the Fars hinterland. The obtained geophysical gravity data also showed a good match between structural units and faults with maximum values corresponding to the Qatar Arch and minimum values relating to the thick sediment field in the Fars region. In conclusion, the present study contributes to a new proposition about exploring the possible faults and a new gas field situated in the interior territory of Iran. All of these interpretations will provide a new insight to improve the extant knowledge in the geology and petroleum evolution of the study area, such as the Plate tectonic events and the creation of possible reservoirs in future.
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.
A Historical Account of the Stratigraphy of Qatar, Middle-East (1816 to 2015)
The document as a whole is an extremely valuable source of historical information for who ever wants to understand the background history behind the stratigraphical units in Qatar as we know them today. Up to now, all this information was scattered throughout several public domain papers and records, or very difficult to access. In addition to gathering all this publicly available information into one complete file, the document contains some unique items such as the transcripts of interviews with Mr. Abdallah Salatt (first Qatari geologist) and Dr. Claude Cavelier (first color geological map of Qatar and still the most extensive geological survey of the country). Several email communications also took place between the author and Mr. Anthony J. Standring (paleontologist who worked on the first Qatar deep well DK-0065 in 1959), the son of Mr. Walter Sugden (geologist in Qatar in the 1950's) and the son and daughter of Dr. Alan H. Smout who published in 1954 an important geological document on Qatar; the latter is provided in its entirety in appendix 3.
Geoarabia -Manama-
The Miocene deposits of the Dam Formation were deposited in a narrow seaway stretching along the western edge of the Qatar Arch. During the initial stages of basin evolution the rising Zagros Mts. delivered debris in this fore deep basin. The paleocurrent and paleogeographic zonation are reflected by the heavy mineral assemblage, by the spatial distribution of phyllosilicates and the various types of sulphate. From NW towards the SE, the contents of smectite and palygorskite increase, whereas the illite and kaolinite contents decrease. Mega crystals of gypsum are found in the NW and massive fine-grained gypsum in the SE of the basin. During the waning stages of basin subsidence, the Arabian Shield became more and more important as a source for the Miocene sediments. In this study, the Dam Formation was subdivided into 7 members/lithofacies associations (lower, middle, upper Salwa, and Al Nakhsh Members, Abu Samrah Member). The Salwa Members at the base of the Dam Formation consists of heterolithic siliciclasticcalcareous sediments which were laid down under meso-to microtidal conditions. The Al Nakhsh Members formed under macrotidal conditions with sub-to supratidal depositional environments passing into continental ones. Celestite, gypsum, and microbial mats (stromatolites) are very widespread in these sabkha sediments. Crystals of gypsum and the thickness of stromatolites tremendously increase towards younger sediments indicating thereby a close genetic link between growth of microbial domes and gypsum precipitation. Throughout the Abu Samrah Member marine calcareous sediments were deposited in a microtidal wave-dominated environment. Dissolution of Eocene evaporites at depth governed the lithofacies differentiation in the Miocene Dam Formation.
Early Tertiary sediments are widely exposed in Qatar and only in coastal areas and a few places inland do Holocene deposits mask them. The variable resistance to weathering of the Tertiary sediments is responsible for the general low-relief landscape interspersed with flat-topped hills, the most prominent of which are in western Qatar where they are the surface expression of the Dukhan anticline. The early Tertiary was a time of shallow-marine sedimentation and several transgressive and regressive cycles occurred. Sedimentation began on a dolomitic carbonate shelf, which gave way to a mixed carbonate-siliciclastic shelf that became increasingly calcitic. Coarsening-upward sequences with fine-grained muddy sediments at the base and grainstones and boundstones on top attested to a cyclic change in the energy regime. Small-scale cycles and major unconformities resulted from eustatic sea-level changes. In the Dukhan study area, the most prominent sequence boundary was near the Ypresian-Lutetian boundary. Following this hiatus, a Lutetian transgressive system tract evolved that was terminated by a maximum flooding surface correlated with the named MFS Pg20. Minor unconformities and NE-trending faults of post-Miocene age resulted from the interplay of local diapiric salt movements in the Dukhan anticline and a regionally changing stress field. Extensional faulting was succeeded by a compressional phase that caused the reactivation of some normal faults as steeply dipping reverse faults. Diagenetic processes and the pervasive etching of the landscape formed ferrous, siliceous, and gypsiferous duricrusts. Phosphate was reworked and concentrated above the Ypresian-Lutetian unconformity. Ferricretes were derived from iron-bearing phyllosilicates and disulfides. Ferric iron-oxide hydrates were the result of oxidizing conditions but their parent material furnished evidence of less-oxygenated conditions and a rising sea level during the Lutetian transgression. The studies provided information on the economic potential of aggregates, clay, hydraulic binders, and building stones, and the prediction of subsidence-prone areas.