A Review of Permo‐triassic Reservoir Rocks in the Zagros Area, Sw Iran: Influence of the Qatar‐fars Arch

Abstract

Four “supergiant” and numerous giant gasfields have been discovered in the Zagros area of SW Iran. The gasfields are concentrated in the eastern part of the foldbelt, in Fars Province and the adjacent offshore, and produce from Permo‐Triassic carbonates equivalent to the Khuff Formation. The carbonates belong to the upper member of the Dalan Formation and the overlying Kangan Formation. Reservoir rock quality is strongly influenced by tectonic setting and depositional environment, and also by diagenesis. The highest quality reservoirs occur in oolitic shoal facies; fracturing (especially in onshore fields) and dolomitisation (in offshore fields) have also influenced reservoir quality. Anhydrite plugging is common in reservoirs in offshore fields, while calcite cementation is dominant in onshore reservoirs. Facies variations in the Dalan‐Kangan Formations appear to correspond to syndepositional palaeohighs and depocentres. In the Eastern Zagros (Fars area), thickening of the Dalan Formation corresponds to a Mid‐Late Permian depocentre referred to here as the Permian Fars Basin. As a result of sea level fall, this depocentre evolved into a hypersaline lagoon with evaporite deposition (Nar Member). In the Triassic, the depocentre evolved into a palaeohigh as indicated by thinning and facies changes in the Kangan Formation. The results of this study draw attention to variations in the reservoir quality of the Dalan‐Kangan Formations. Much of this variation was due to the influence of the Qatar‐Fars Arch.

3d Basin Modelling in the Central Persian Gulf, Offshore Iran

“…This palaeo-high separates a western basin from an eastern basin in which thick Hormuz salt was deposited. The palaeo-high is overlain by a comparatively reduced Phanerozoic sedimentary cover reflecting the episodic growth of the Qatar -South Fars Arch (Perotti et al, 2011;Esrafili-Dizaji and Rahimpour-Bonab, 2013).…”

“…Permo-Triassic rocks are separated from the underlying rocks by a major unconformity (Bordenave and Hegre, 2005;. The Permian succession is composed of the Faraghan Formation (transgressive siliciclastics) and the Dalan Formation which comprises Lower Dalan, Nar and Upper Dalan members (Esrafili-Dizaji and Rahimpour-Bonab, 2013;Rahimpour-Bonab et al, 2010).…”

Flow Unit Characterisation in the Permian‐triassic Carbonate Reservoir Succession at South Pars Gasfield, Offshore Iran

“…This area is underlain by the NNE-SSW trending Qatar -South Fars Arch which is bounded by the Zagros fold-and-thrust belt to the NNE (Alsharhan and Nairn, 1997;Konyuhov and Maleki, 2006;Bashari, 2005;Perotti et al, 2011). The Arch was a positive structure for much of the Palaeozoic but gradually subsided in the Jurassic (Saint-Marc, 1978;Esrafili-Dizaji and Rahimpour-Bonab, 2013). Due to Hercynian upwarping in the Late Palaeozoic, the sedimentary cover thins over the Arch, and over similar structures elsewhere in the Arabian Plate (Alsharhan and Nairn, 2003).…”

Paleoenvironmental, diagenetic, and eustatic controls on the Permo–Triassic carbonate–evaporite reservoir quality, Upper Dalan and Kangan formations, Lavan Gas Field, Zagros Basin

“…In the Zagros Basin (Iran), the Upper Dalan and Kangan formations hold one of the largest gas reserves in the Middle East and also the world. Considering this importance, a sizable number of studies on the sedimentology, diagenesis, and reservoir quality have been done on the Permo–Triassic strata of the region (e.g., Abdolmaleki, Tavakoli, & Asadi‐Eskandar, ; Amel, Jafarian, Husinec, Koeshidayatullah, & Swennen, ; Bordenave, ; Esrafili‐Dizaji & Rahimpour‐Bonab, ; Haase & Aigner, ; Insalaco et al, ; Kashfi, ; Peyravi, Rahimpour‐Bonab, Nader, & Kamali, ; Rahimpour‐Bonab, Asadi‐Eskandar, & Sonei, ; Rahimpour‐Bonab, Esrafili‐Dizaji, & Tavakoli, ; Sharland et al, ; Tavakoli, Rahimpour‐Bonab, & Esrafili‐Dizaji, ). The sedimentologic, stratigraphic, and diagenetic attributes of the Upper Dalan (K3) and Kangan (K1, K2) formations of the Lavan Gas Field (Figure ) however, did not receive enough consideration to understand their depositional setting, diagenetic properties, and the effect of the sea‐level fluctuations on the reservoir qualities of the strata.…”

“…In the Zagros Basin (Iran), the Upper Dalan and Kangan formations hold one of the largest gas reserves in the Middle East and also the world. Considering this importance, a sizable number of studies on the sedimentology, diagenesis, and reservoir quality have been done on the Permo-Triassic strata of the region (e.g., Abdolmaleki, Tavakoli, & Asadi-Eskandar, 2016;Amel, Jafarian, Husinec, Koeshidayatullah, & Swennen, 2015;Bordenave, 2008;Esrafili-Dizaji & Rahimpour-Bonab, 2013;Haase & Aigner, 2013;Insalaco et al, 2006;Kashfi, 1992;Peyravi, Rahimpour-Bonab, Nader, & Kamali, 2015;Rahimpour-Bonab, Asadi-Eskandar, & Sonei, 2009;Rahimpour-Bonab, Esrafili-Dizaji, & Tavakoli, 2010;Sharland et al, 2001;Tavakoli, Rahimpour-Bonab, & Esrafili-Dizaji, 2011). (Goldhammer, Dunn, & Hardie, 1990;Husinec & Jelaska, 2006;Koeshidayatullah, Al-Ramadan, Collier, & Hughes, 2016;Salad Hersi, Abbasi, & Al-Harthy, 2016;Salad Hersi, Lavoie, & Nowlan, 2002), and these repeated shallowing-upward cycles may record important information on spatio-temporal changes of reservoir quality in the studied sequence.…”