The Asmari Giant Reservoirs (original) (raw)
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2019
The present study focuses on facies analysis and the reservoir characteristics of the Asmari Formation in the Aghajari oilfield (located in the Zagros fold-thrust belt, southwest Iran), and how they are linked to depositional environments and reservoir characteristics. This formation consists of about 380 m carbonates with some siliciclastic intercalations. Based on the integration of 1200 m of core description and petrographic analyses of 2500 thin sections, 9 carbonate and 1 evaporite microfacies along with 2 siliciclastic petrofacies were identified. Facies analysis shows that the Asmari Formation sediments were deposited in a homoclinal carbonate ramp within open marine (facies association A), shoal (facies association B), restricted lagoon (facies association C), tidal flat (facies association D), and beach (petrofacies E) environments. Macroscopic and microscopic studies reveal that the main porosity types include interparticle, growth framework, vuggy, intercrystaline, moldic...
2021
The Asmari Formation (Oligocene-Miocene), as one of the main carbonate petroleum reservoirs of the Middle East, represents strongly variable reservoir quality on regional and local scale. One outcrop analogue (Syah-koh Anticline) and a well-A (oilfield at western Lorestan basin), both situated in western Iran, were investigated to address the reservoir characteristics. The 12 microfacies identified reflect deposition on a broad carbonate ramp reflecting an outer, mid and inner ramp setting. Three third-order depositional sequences are deduced based on interpreted Gamma-ray, sonic logs and stratal stacking patterns. The identified sequences and existence of a thicker evaporite succession in well-A points to more restricted depositional conditions with reduced connection to the open sea from the Syah-koh Anticline towards well-A. The diagenetic modifications revealed micritization, dissolution, cementation, fracturing, dolomitization and compaction. Petrographic and δ13C and δ18O anal...
The Petroleum System of Zubair Formation in Selected Oil fields- Southern Iraq Supervised by
2012
The Lower Cretaceous Zubair Formation is the most important reservoir in south of Iraq and adjacent countries, as well as the shale intervals may be the possible source rock. The main parameters of the possible source rock within Zubair Formation are satisfying, in terms of quantity, quality, and thermal maturity. Thirty eight samples (15 cores 23 cuttings) are analyzed to determine the pyrolysis parameters in addition to the inverted data from The Oil Exploration Company and South Oil Company in Iraq, as well as nine rock samples (6 core and 3 cuttings) are introduced to GC/MS analysis. On the other hand, six oil samples have been analyzed to determine the carbon isotopes, biomarkers, composition and correlation. Quantitative analysis is done with Gas Charmotagraphy/Mass Spectrometry (GC/MS). All these data are mainly obtained from Nassiriah, Gharraf, Rafidain oil fields in Euphrates Subzone, as well as from Rumaila North, Rumaila South, Zubair, and West Qurna oil fields in Zubair Subzone. Early-peak oil generation has been indicated from the vitrinite reflectance (Ro) to the chosen samples in the Zubair Subzone (Ro range 0.5-0.7%), while in Euphrates Subzone, the maturity is indicated as immature-early oil generation due to shallow depths of Zubair Formation, as well as the terrestrial supply of organic matters . On the other hand, the optical investigation revealed that the formation is within the mature zone dependent of the thermal alteration and spores color indices. From the total organic carbon (TOC) values point of view, shale intervals within Zubair Formation are generally good to excellent as source rocks, except in the lower parts, namely the Lower Shale Member in Zubair Subzone, which has fair amounts of the total carbon content. While the kerogen types are mainly type III gas - oil prone, mix type II/III oil-gas prone, and type II oil prone, which the later concentrated in the upper and lower sandstone members. The dominant type of organic matters was the amorphous organic matters (AOM), which is principally related to oil prone source rock. The Rock-Eval Pyrolysis shows that the organic geochemical properties presented an effective and/or potential source rock depending on the values of S1, S2, and S3 and their derivatives. This source rock has started the oil expulsion, where the S1/TOC values were mainly more than 0.2 mgHC / gTOC. The source related biomarkers suggested that the reservoir oils of Zubair Formation and the source rock extracted oils indicate the same origin, depositional environment, sulfur content, and maturity level. The depositional environment of the source rock is indicated as the anoxic, shallow marine offshore facies of the prodelta shale intervals, which is located within the multistory sand bodies. The modeling explains that the Zubair Formation, wholly, has been entered the onset, partially, the peak, and rarely the end of oil generation in the studied Subzones. This conclusion depends on the calculated temperatures, geothermal gradients, and vitrinite reflectance calibration. Hence the migration pathway has been estimated to be primarily, the highly permeable and porous reservoir carrier beds, which allowed the oils to migrate horizontally up dip into the west, northwest, and southwest of the Mesopotamian zone, and secondarily Tachadid-Al-Qurna fault, which may allow the oils to move east-west in all directions. The reservoir rock within the multistory sand bodies had well properties in terms of porosity and permeability. The porosity ranges 18-30%, and the permeability ranges 100-1000md. The seal rock in the upper and lower parts of the formation is precisely efficient, which contain high mud content with low permeability sometimes approximately up to zero value.