Controls on depositional facies in Upper Cretaceous carbonate reservoirs in the Zagros area and the Persian Gulf, Iran (original) (raw)
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Journal of Petroleum Geology, 2009
Upper Jurassic carbonates of the Mozduran Formation constitute the principal reservoir intervals at the giant Khangiran and Gonbadli gasfields in the Kopet Dagh Basin, NE Iran. These carbonates were investigated using detailed field studies and petrographic and wireline log analyses in order to clarify their depositional facies and sequence stratigraphy. Facies were interpreted to reflect deep basin, fore-shoal, shelf margin, lagoon, tidal flat and coastal plain depositional systems.The Mozduran Formation is composed of six depositional sequences. Thickness variations were controlled by differential subsidence. Aggradation on the platform margin and reduced carbonate production in the deep basin together with differential subsidence resulted in the creation of a narrow seaway during the late Oxfordian. Petrographic studies suggest that Mozduran Formation carbonates had a low-Mg calcite mineralogy during the Oxfordian, and an aragonite to high-Mg calcite mineralogy during the Kimmeridgian. Reservoir pay zones are located in highstand systems tracts within the lower and middle Kimmeridgian depositional sequences. The rapid lateral thickness variations of these sequences were controlled by tectonic factors, leading to compartmentalization of the Mozduran Formation reservoir with the possible creation of stratigraphic traps, especially at the Khangiran field.
Marine and Petroleum Geology, 2019
This study focuses on the variations in facies characteristics, depositional environments, and sedimentary sequences of the Fahliyan Formation carbonate succession (Neocomian-Barremian) as one of the petroliferous units in the Middle East. Accordingly, four surface and subsurface sections were selected from the Dezful Embayment and Izeh Zone of the central Zagros, SW Iran. A shoal-algal facies dominated homoclinal ramp is proposed as the general depositional setting of this formation. It shows remarkable variations in facies belts, their abundance and thickness in the study area. Four third-order depositional sequences are differentiated in studied outcrops of the Izeh Zone. Interaction of tectonics, eustasy, and sedimentation (carbonate production) rates are discussed for depositional sequences and three tectono-sedimentary models are presented for the Fahliyan Formation that correspond to depositional sequences I to III of this formation. Variations in thickness, facies, diagenesis, and allochemical grains are discussed for each tectono-sedimentary model. Comparison of the acquired results with the proposed models of active tectonic basins suggests a fault-block platform in an extensional rift basin for the Fahliyan Formation in the study area.
Journal of Petroleum Geology, 2004
The Oligo-Miocene Asmari Formation is one of the most important petroleum reservoir units in the Zagros Basin of south and SW Iran. It mainly consists of limestones and dolomitic limestones with interbedded shales, together with a few intervals of sandstone and gypsum assigned to the Ahwaz and Kalhur Members, respectively. The Asmari Formation rests on the thin-bedded limestones of the Jahrum Formation (Paleocene-Eocene). In this paper, we report on the lithofacies characteristics of these two formations using data from three measured outcrop sections near Shiraz in SW Iran. From field and petrographic data, we have identified four major lithofacies and twelve subfacies which are interpreted to have been deposited in open-marine, shoal, lagoon and tidal flat settings. We show that the Asmari and Jahrum Formations constitute two separate depositional sequences which are separated by a thin palaeosol, representing a type-one sequence boundary which can be correlated with global curves of relative sea-level. Each depositional sequence is composed of many metre-scale shallowing-upward parasequences. This is the first time that the Asmari and Jahrum Formations have been differentiated in the study area. We hope that this study will lead to a better understanding of the Asmari Formation in the subsurface in other parts of the Zagros Basin.
Marine and Petroleum Geology, 2015
The Aptian carbonate reservoirs of Persian Gulf, known as the Dariyan Formation (Shu'aiba equivalent), are among the most important oil reservoirs of Iran. Despite its significance, a little is known about the facies characteristics, diagenetic history, sequence stratigraphy, and reservoir quality of this formation. Using the new core data, this study presents an integrated geological reservoir characterization of this formation in four giant fields in the Persian Gulf. Using the results of the facies analysis it could be suggested that this unit formed in a shallow carbonate platform surrounding intra-shelf basins of Kazhdumi and Bab in the western and eastern Persian Gulf, respectively. A major relative sea-level fall in the Late Aptian resulted in exposure of this unit and subsequent clastic influx as well as meteoric diagenesis. This phase of meteoric diagenesis has resulted in some important diagenetic features, special geochemical trends, and considerable variations in reservoir quality of the Dariyan Formation. Sequence stratigraphic interpretation of this formation has resulted in the recognition of 2 nd and 3 rd order depositional sequences in the studied wells. They are closely correlated across the studied wells in the Persian Gulf, SW Iran, and other places in the Arabian Plate. Reservoir characterization has revealed that the high quality units are
Facies, 2013
Integrated facies and diagenetic analyses within a sequence stratigraphic framework were carried out on mid-Cretaceous Sarvak carbonate reservoirs in five giant and supergiant oilfields in the central and southern parts of the Dezful Embayment, SW Iran. Results of facies analysis indicate a homoclinal ramp-type carbonate platform for this formation with the frequencies of different facies associations in six wells reflecting their approximate position in the sedimentary model. Diagenetic studies indicate periods of subaerial exposure with different intensities and durations in the upper Sarvak carbonates producing karstified profiles, dissolution-collapse breccias, and thick bauxitic-lateritic horizons. Sequence stratigraphic interpretations show that the tectonic evolution of the NE margin of the Arabian Plate (Zagros Basin) during Cenomanian-Turonian times shaped the facies characteristics, diagenetic features, and strongly influenced reservoir formation. Reactivation of basement-block faults and halokinetic movements (related to the Hormoz salt series) in the middle Cretaceous, resulted in the development of several paleohighs and troughs in the Dezful Embayment hydrocarbon province. Movements on these structures generated two and locally three disconformities in the upper parts of Sarvak Formation in this region. The paleohighs played an important role in reservoir evolution within the Sarvak Formation in three giant-supergiant oilfields (including Gachsaran, Rage -Safid, and Abteymour oilfields) but where these structures are absent reservoir quality is low.
Middle Cretaceous Carbonate Reservoirs, Fahud Field and Northwestern Oman: DISCUSSION
AAPG Bulletin, 1986
Reservoir facies in Fahud field and tliroughout northwestern Oman are in shallow-shelf carbonates of the middle Cretaceous Mishrif and Mauddud Formations. Interparticle porosity formed in the Mishrif as sand aprons of lithoclast and skeletal grainstones surrounding fault-block islands, and less commonly in the Mauddud as biostromes of rudist packstones. Moldic porosity after fine rudist debris is more common than interparticle porosity and occurs in thicker stratigraphic units, interpreted to have formed locally in meteoric-water lenses associated with islands, and regionally during subaerial exposure associated with sea level lows. LOCATION The carbonate reservoir rocks discussed in this paper are located rn northwestern Oman (Figure 1). The area is situated near the eastern margin of the Arabian subplate and lies southwest of the Oman Mountains. Known reservoirs and exploration targets in the area occur primarily in shallow-shelf carbonates of Lower Cretaceous (Berriasian through Aptian) and middle Cretaceous (Albian-Cenomanian) ages. This paper describes lithologies and porosity types of middle Cretaceous reservoir rocks that we have examined in the subsurface and in outcrop in northwestern Oman, and that are similar to those of large fields in the immediate area. The largest of these fields, Fahud field, has been described by Tschopp (1967) and is summarized here. CRETACEOUS GEOLOGIC HISTORY The middle Cretaceous carbonates of northwestern Oman represent the culmination of a period of dominantly carbonate deposition that lasted about 150 m.y. from the Late Permian to the earliest Tlironian of the Late Cretaceous (Saint-Marc, 1978; Murris, 1980). In general, carbonate deposition was dominant because the area was located a considerable distance away from terrigenous detritus shed from the Saudi Arabian shield (Figure 2). Unconformities in the sedimentary sequence are inter
Journal of Petroleum Geology, 2013
Cretaceous carbonates host major hydrocarbon reserves in SW Iran and elsewhere in the Arabian Plate. Tectonic activity combined with eustatic sea-level changes resulted in periodic exposure of these carbonates which were subsequently modified by meteoric diagenesis under a warm and humid climate. Long-term exposure led to the formation of several disconformity surfaces within the middle Cretaceous succession which had important effects on the interval's reservoir characteristics. These disconformity surfaces in the Dezful Embayment were investigated using microfacies, diagenetic and geochemical studies at five subsurface sections. Facies differences across these boundaries, together with features such as karstification, palaeosol development and collapse-dissolution breccias, were used to identify emergent surfaces. Stable oxygen and carbon isotope ratios and trace element profiles indicate intense meteoric diagenesis. Disconformities were dated using biostratigraphic studies. The results indicate the presence of two major erosional disconformities: one is located at the Cenomanian-Turonian boundary separating the middle Sarvak Formation from its upper part; and the other is in the mid-Turonian at the boundary between the Sarvak and Ilam Formations. The latter disconformity is correlatable throughout the Arabian Plate.
Marine and Petroleum Geology, 2015
This study covers a 300 km long, NE/SW oriented transect including five outcrop sections, and provides new biostratigraphic data and a sequence stratigraphic interpretation of the Albian, Cenomanian and Turonian sediments (Kazhdumi and Sarvak Formations) present in Coastal Fars (SW Iran). Two different carbonate depositional systems are distinguished, one for the Albian and one for the Cenomanian/ Turonian. During the Albian eustatic control was the dominant factor influencing sedimentation, while during the Cenomanian and Turonian large and small scale tectonics were dominant. This resulted in significant thickness variations and local diagenetic overprint of the sequence boundaries.
Original mineralogy of the Upper Jurassic carbonates in the Kopet-Dagh Basin , NE Iran
2011
The Kopet Dagh Basin in northeast Iran contains giant Khangiran and Gonbadli gas fields. This study deals with the main hydrocarbon reservoir of Upper Jurassic (Oxfordian-Tithonian) Mozduran Formation, which is composed mainly of limestone and dolomite, with minor amounts of marl/shale, siliciclastics and evaporites. The objective of this study is carbonate mineralogy of the Mozduran Formation. Thin sections were stained by alizarin-red S to detect dolomitization of grains and cements. Regarding diagenetic products and their diagenetic environments, selected samples were observed with a cathodoluminescent microscope (Nikon CL, CCL 8200) at the Research Institute of Petroleum Industry (R.I.P.I). Detailed field studies, petrographic investigations and facies analyses of eight surface sections and four wells, led to the recognition of several facies that define deep basin, fore-shoal, shelf margin, lagoonal, tidal flat and coastal plain facies belts, which deposited on a rimmed-shelf a...