Stratigraphy and Palaeontology
Ali Asaadi; Ali Imandoust; Mehdi Sarfi; Mehdi Ghane Ezabadi
Abstract
The Lower Cretaceous Fahliyan Formation is one of the main oil reservoirs in the Persian Gulf. In this study, for investigating facies characteristics, depositional environment, diagenetic features, sequence stratigraphy and describing factors controlling reservoir quality, the integration of the results ...
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The Lower Cretaceous Fahliyan Formation is one of the main oil reservoirs in the Persian Gulf. In this study, for investigating facies characteristics, depositional environment, diagenetic features, sequence stratigraphy and describing factors controlling reservoir quality, the integration of the results from core description, petrographic studies, and petrophysical data was utilized. Nine main facies were recognized and grouped in four facies belts of lagoon, shoal, patch reef and shallow open marine, indicating deposition of the formation in a carbonate ramp platform. Various diagenetic processes that influenced facies, occurred in marine, meteoric, and burial diagenetic realms. Four main pore types have been identified in the reservoir that include interparticle, moldic, vuggy, and microporosity. From the sequence stratigraphy point of view, three third-order sequences which are correlatable within the Fahliyan Formation were identified. The development of grainstone and algal rudstone/floatstone in shoal/ patch reef sub-environment played an important role in developing the high reservoir. In view of their controls on reservoir quality and pore system, diagenetic features can be categorized into two classes: (1) diagenetic processes enhancing reservoir quality that include dissolution and fracturing, and (2) diagenetic processes reducing reservoir quality that include cementation and compaction.
Sedimentology
Umid Kakemem; Mohammad Adabi; Ehsan Dehyadegari
Abstract
Depositional texture, sedimentary structure and present fauna led to characterize twelve carbonate- evaporate facies. These facies were classified in three facies belts including tidal flat, lagoon and shoal. Developpment of tidal zones together with evaporate deposits and thrombolite facies (signs to ...
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Depositional texture, sedimentary structure and present fauna led to characterize twelve carbonate- evaporate facies. These facies were classified in three facies belts including tidal flat, lagoon and shoal. Developpment of tidal zones together with evaporate deposits and thrombolite facies (signs to a shallow depositional environment), the absence of continuous reef‐frame builders, high production of carbonate mud, absents of calciturbidite, tempestites deposits and slump structures are evidences for a homoclinal carbonate ramp setting. The facies based on petrophysical characteristics which is the results of depositional texture and diagenesis are classified in seven reservoir rock types. In which, the first rock type (RT1) has weak reservoir property and toward RT7 reservoir quality will increase. Facies variation related to sea level fluctuations led to subdivide the whole strata into two 3rd order sequences. Facies stacking patterns in the sequences characterized by subtidal facies (lagoon and shoal) tend to have the most reservoir quality that covered by evaporative (Mf1) and peritidal facies (Mf2 to Mf4) with low-reservoir quality. The most reservoir quality in both K1 and K2 reservoir zones is coincident with late TST, maximum flooding surface (mfs) and late HST in identified depositional sequences which is settled in high-energy shoal facies intervals.
R. Kadkhodaie-Ilkhchi; B. Nouri; R. Jodeyri
Abstract
The Upper Dalan and Kangan formations with the late Permian- early Triassic age are considered as the main reservoir rocks of some fields in the Persian Gulf. These formations with carbonate-evaporate interval are composed of shoal, lagoon and tidal flat facies deposited in shallow parts of a carbonate ...
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The Upper Dalan and Kangan formations with the late Permian- early Triassic age are considered as the main reservoir rocks of some fields in the Persian Gulf. These formations with carbonate-evaporate interval are composed of shoal, lagoon and tidal flat facies deposited in shallow parts of a carbonate ramp under the warm and arid climate condition. In these facies, dolomitization is a common diagenetic process which has been discussed in terms of the formation, distribution and its relationship with the reservoir quality. This process with regard to the original sedimentary properties, and also the effect of such diagenetic processes as dissolution and anhydrite cementation, has different effect on the reservoir characteristics. Dolomite has been mainly distributed as replacement with an insignificant part as cement. Fine crystalline replacive dolomites in mud dominated facies of tidal flats, have been formed by surface evaporation and pore water concentration in early diagenesis. In contrast, replacive dolomites in grain dominated facies, as fabric selective and non-fabric selective, have been developed by the effect of evaporate brines penetration during the burial diagenesis. In these facies, anhydrite has been formed as patchy and pervasive cement. Dolomitic facies with pervasive anhydrite, similar to fine crystalline facies of tidal flats, show low reservoir quality. Dolomitic facies with patchy anhydrite and also coarse crystalline replacive dolomites have higher reservoir quality. The results show that dolomitization when is associated with development of fabric destructive and coarse replacement dolomites, especially within the grain dominated facies, has an effective role on reservoir quality improvement.
S. Faramarzi; H. Rahimpour-Bonab; M. Ranjbaran
Abstract
The Sarvak Formation is one of the most important carbonate reservoirs of Iran. The main objective of this study is to evaluate reservoir quality of the formation by integration of petrographic studies and core porosity-permeability data in three key wells in a giant oilfield of the Abadan Plain, SW ...
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The Sarvak Formation is one of the most important carbonate reservoirs of Iran. The main objective of this study is to evaluate reservoir quality of the formation by integration of petrographic studies and core porosity-permeability data in three key wells in a giant oilfield of the Abadan Plain, SW Iran. Petrographic studies led to the identification of 13 microfacies that are grouped into three main facies belts including lagoon, shoal, and open marine (talus and slope) which deposited in an isolated carbonate platform. The main diagenetic processes affecting the Sarvak Formation are micritization, bioturbation, recrystallization, dissolution, cementation, physical and chemical compaction, dolomitization and silicification, along with fracturing. According to the results, the reservoir quality of the Sarvak reservoir is a function of both primary depositional facies and secondary diagenetic processes. Evaluation of impacts of depositional facies on reservoir quality indicated that the rudist-bearing intervals (especially rudist debris zones) have high reservoir quality. Dissolution and cementation are the most pervasive diagenetic processes affecting the formation, and occurred due to widespread meteoric diagenesis. Dissolution and fracturing are the chief factors that lead to the improvement of porosity-permeability, whilst calcite cementation and compaction have destructed reservoir quality of the studied interval. This study may assist better understand the geological parameters controlling reservoir quality of Sarvak Formation in the Abadan Plain oilfields.
M.R Rahmani; R Moussavi – Harami; M Arian
Abstract
Dariyan formation is one of the oil reservoirs in the south pars field. This formation has been studied in wells SPO-1, SPO -2 and Spo-3. Thickness of Dariyan formation in mentioned wells are 109, 113 and 114 meters respectively. Based on the studies of thin sections from the Dariyan formation of three ...
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Dariyan formation is one of the oil reservoirs in the south pars field. This formation has been studied in wells SPO-1, SPO -2 and Spo-3. Thickness of Dariyan formation in mentioned wells are 109, 113 and 114 meters respectively. Based on the studies of thin sections from the Dariyan formation of three above mentioned wells, nine carbonate and one detrital facies have been identified within four facies associations including tidal flat (Mudstone), lagoon (Bioclast mudstone to wackstone, Bioclast peloid wackstone to packstone, Bioclast peloid packstone to grainstone, Algal boundstone), Mid ramp (Echinoid mollusk wackstone to packstone, Orbitolina wackstone to packstone, Framestone, Floatstone) and outer ramp (Shale). Facies studies indicate that Dariyan formation has been deposited in a homoclinal ramp.The Dariyan formation has been affected by four diagenetic stages, including marine, meteoric, burial and uplift. The most important identified diagenetic processes are micritization, bioturbation, geopetal, physical and chemical compaction, cementation, neomorphism, replacement, dissolution, fracturing and filling. Among the all diagenesis process, dissolution and fracturing are the major processes improving reservoir quality. In Contrary, physical compaction and especially cementation are the main processes redusing reservoir quality. Dissolution process with generating secondary porosity consists of vuggy and moldic, has important effect on increasing of porosity. Most of the dissolution features have been produced during the meteoric diagenesis and less through burial diagenesis. Dissolution process with develop the vuggy pores caused to connect them in some case and also affected on fractures , stylolites and previous diagenetic cements in upper and lower members of daryian formation which eventually has been increased permeability and reservoir quality. Also, Fracturing, the main other diagenetic process with connect the some individual vuggy and moldic pores together has effective role to increase the permeability and reservoir quality in upper and lower parts of Dariyan formation.
H Vafaei; M Peyravi
Abstract
The Kish gas-field is one of the world’s largest gas-fields, and consists of two reservoir rocks of Kangan (Lower Triassic) and Dalan (Late Permian) formations in the Zagros sedimentary basin. In this study, the Kangan formation has been examined. In this research, in addition to the use of raw ...
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The Kish gas-field is one of the world’s largest gas-fields, and consists of two reservoir rocks of Kangan (Lower Triassic) and Dalan (Late Permian) formations in the Zagros sedimentary basin. In this study, the Kangan formation has been examined. In this research, in addition to the use of raw data obtained from logging of a drilled well from the whole extent of the field, probabilistic petrophysics evaluation method was used to assess the petrophysical properties (shale volume, lithology, porosity and water saturation) of the Kangan formation. A method based on statistics and possibilities was also utilized to interpret the graphs (logs) with the help of multi-mineral model, a module of Multimin Software. Based on the results of this assessment and the use of lithology-determining cross-plots, as well as standard charts of Schlumberger, the dominant lithology of the Kangan formation in the studied well was recognized as calcite, dolomite, some anhydrite and small amounts of shale. The ultimate aim of the petrophysical evaluation in hydrocarbon studies of the Kish gas-field is to provide proper inputs to the reservoir static model. In order to make a more detailed study, this formation was divided into two parts, K1 and K2. As a whole, the calculated volume shale in the Kangan formation in this well is low and in K2 part is less. This could be considered as a reason for the equal effective porosity in most of the points along the well.
A Ghorbani; M.H Adabi; S Sohrabi
Abstract
The Sirri E (Esfand) and D (Dena) Oil Fields are located in the south of the Persian Gulf. The Upper Sarvak (Mishrif Member) Formation, late Cretaceous (Cenomanian-Turonian) in age, is underlain by the argillaceous limestone of Khatiyah and by the late Turonian unconformity overlain by the Laffan Shale ...
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The Sirri E (Esfand) and D (Dena) Oil Fields are located in the south of the Persian Gulf. The Upper Sarvak (Mishrif Member) Formation, late Cretaceous (Cenomanian-Turonian) in age, is underlain by the argillaceous limestone of Khatiyah and by the late Turonian unconformity overlain by the Laffan Shale in mentioned two oil fields. On the basis of petrographic and geochemical evidences (elemental analysis such as Mg, Ca, Sr, Mn) and oxygen and carbon isotope values, aragonite was original carbonate mineralogy for the carbonates of the Upper Sarvak (Mishrif Member) Formation in (Well A) in the Sirri E Field. The geochemical studies and δ18O and δ13C illustrate that these carbonates were affected by meteoric diagenesis in hot and arid climate and in semi-closed to open diagenetic system with thin soil layer. Temperature calculation based on the oxygen isotope value of the least-altered sample and δw around of -1 SMOW for Cretaceous, show that the seawater temperature was around 34˚C during the deposition of the Upper Sarvak (Mishrif Member) Formation. With regards to the highly altered samples and light oxygen values the temperature should be probably related to the shallow burial diagenesis. Petrographic studies of thin sections of the well A in the Sirri E Field and the well B in the Sirri D Field show the effect of diagenetic processes such as micritization, dissolution, cementation, neomorphism, pressure solution, physical compaction, fracture and dolomitization on the reservoir quality of the Upper Sarvak (Mishrif Member) Formation. The most important diagenetic factor that increased the reservoir quality is dissolution, which occurred in the meteoric diagenesis. However, the most important diagenetic factor that decreased the reservoir quality is the expansion of various kinds of cement especially large blocky cement, which occurred in the burial diagenesis.
S Parham; M.R Kamali
Abstract
The Dalan Upper member (Permian) with carbonates and evaporite interlayer is one of the most important gas reservoirs in the folded Zagros area and Persian Gulf. In this investigation porosity types, their genesis and controlling factors have been studied at Surmeh surface section and a subsurface section ...
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The Dalan Upper member (Permian) with carbonates and evaporite interlayer is one of the most important gas reservoirs in the folded Zagros area and Persian Gulf. In this investigation porosity types, their genesis and controlling factors have been studied at Surmeh surface section and a subsurface section in Persian Gulf. Based on the new genetic classification of Ahr (2008) for carbonate porosity, porosity is created or altered by hybrids of depositional processes, diagenetic processes and mechanical fracturing in the studied intervals. In subsurface samples, porosity is hybrid of depositional and diagenetic types. In grain-supported microfacies, like ooidgrainstone related to the shoal environment, interparticle porosity is created which is a type of depositional porosity. Moldic, vuggy and intercrystallineporosity, which are diagenetic types of porosity,were formed in the later stages of diagenesis. Therefore, porosity in this microfacies is facies-selective and facies map can be used as a proxy for porosity distribution map. In surface section, besides depositional and diagenetic porosity, fracturing and brecciation are also significant. Brecciationoccured as a result of dissolution of anhydrite of Nar Member and formed the solution collapse breccias. Active tectonic in the folded Zagros belt and folding are another possible sources of fracturing in the surface samples. The properm data of routine analysis shows that the reservoir characteristic of the studied interval is heterogeneous.So, it has been compartmentalized into six zones with different reservoir qualities from poor to very good.