Improved Reservoir Characterization of a Giant Iranian Reservoir; The Asmari Formation in the Ahwaz Field, SW Iran
A. Linjordet1, N. Pickard2, M. Khanna1, D.B.
Sollien1, Kh. Haidari3, B. Beiranvand4,
A. Reza Shakeri4, Z. Karimi Mosadegh4, T. Røsaasen1, A. Miryan3
1Statoil ASA, 4035, Stavanger, Norway, <[email protected]>
2Cambridge Carbonates, UK
An IOR study has been performed of the Asmari Formation of the giant Ahwaz Field in southwestern Iran.
This poster presents the integrated reservoir description of the Asmari Formation as input to the construction of a 3D geomodel used as basis for the IOR drainage strategies studies.
Structural definition was established by seismic interpretation on 26 2D seismic sections. Improved volume control on the flanks was obtained.
The Ahwaz Asmari Formation consists of inter-bedded carbonate, sandstone and shale of Late Oligocene to Early/Mid Miocene age. The Ahwaz Asmari Fm. has 16 wells that have recovered cores. The mixed siliciclastic/ carbonate reservoir has undergone post depositional diagenesis, which have had an impact on reservoir characteristics. Calcite cementation and dissolution, dolomitisation and particularly precipitation of anhydrite cements have destroyed porosity in both the carbonates and siliciclastic sands in the Ahwaz field.
Lithology interpreted from logs in 338 wells has been the main source to establish the new Ahwaz Asmari reservoir subdivision, though the lithological subdivision has been made within a sequence stratigraphic framework, that is based on studies of the cored wells.
Evaluation of more than 6000 thin-sections in three key wells supports the geological and petrophysical interpretation. The petrophysical interpretation included mineralogy, porosity, permeability and water saturation. A water-saturation versus depth relation (J-function) was combined with fluid contacts to identify the flooding pattern.
Biostratigraphic data, in combination with Strontium age dating, has been used to constrain the sequence stratigraphic framework. New biostratigraphic work by RIPI, in combination with a review of existing regional biostratigraphy and acquisition of Strontium age data from Ahwaz and other fields in the region (Bibi-Hakimeh and Marun) has improved our understanding of how the Zagros Trough was filled during the deposition of the Asmari Formation. Moreover, it has contributed to improved understanding of the Ahwaz Asmari sand-carbonate reservoir architecture.
The Lower Asmari sands (A7 to Pabdeh Fm.) were deposited in a restricted area during sea-level Low-stands, while the Middle an Upper Asmari (A1-A6) were deposited over a widespread carbonate ramp and contain Transgressive and High stand sands.
The results were used to construct the Ahwaz Asmari geo-model.