Stratigraphic architecture and depositional–diagenetic evolution of Oligocene–Miocene carbonate–evaporite platform in the southern margin of the Neo-Tethys Ocean, Lurestan zone of Zagros, Iran

Depositional and diagenetic controls on reservoir quality of the uppermost Jurassic–Lower Cretaceous sequences in the Persian Gulf; a focus on J–K boundary

Impacts of mineralogy and pore throat structure on the movable fluid of tight sandstone gas reservoirs in coal measure strata: A case study of the Shanxi formation along the southeastern margin of the Ordos Basin

Tight sandstone reservoirs have ultralow physical properties and strong heterogeneity, and there is a need to describe the corresponding pore structure characteristics systematically to promote research on unconventional reservoirs. The pore structure, controlled by the diagenesis and volcanic activity of the tight reservoirs in the third member of the Shahejie Formation (Es3) of the Gaoshangpu structural belt in the Nanpu Sag, is studied by high-pressure mercury injection, nuclear magnetic resonance, and constant-rate-controlled mercury porosimetry. The results show that the Es3 reservoir can be divided into three types: the pore radii of Type I reservoirs range from 120 to 180 μm, and the throat radii are larger than 1 μm, resulting in good pore connectivity; pore radii of Type II reservoirs are approximately 100 μm, and the throat radii range from 0.1 to 1 μm, resulting in moderate pore connectivity; and pore radii of Type III reservoirs are much smaller than 100 μm, and the throat radii are smaller than 0.1 μm, resulting in worst pore connectivity. The pore size of Type I reservoirs is most sensitive to compaction, and the pore connectivity is mainly controlled by carbonate cementation; the pore throat size and pore connectivity of Type II reservoirs are seriously affected by clay cementation, and pores are mainly formed by dissolution. However, the pore structure of Type III reservoirs is the worst among those investigated in this study but can be further improved by dissolution to a certain extent. Volcanic activity controls cementation and affects dissolution, thus changing the pore structure. A pore structure evolution model is established, which can provide a reference for future oil gas exploration.

https://pubs.acs.org/doi/pdf/10.1021/acsomega.1c04573

Pore Structure Characteristics and Controlling Factors of a Tight Sandstone Reservoir in the Paleogene Shahejie Formation, Nanpu Sag, Bohai Bay Basin, China

Ilam Formation (Santonian) is a member of the Bangestan Group, as an important oil reservoir of SW Iran. Various geological and reservoir quality aspects of this formation were discussed in the Zagros area. However, depositional–diagenetic controls on pore types of this formation are not defined, especially in the Abadan Plain. In this study, an integrated sedimentological and petrophysical evaluation has been carried out in six subsurface sections of this formation throughout the Abadan Plain. Facies analysis indicates deposition in shallow- to deep marine settings of a ramp-like carbonate platform. It includes lagoon, shoal, middle ramp, outer ramp and basinal settings. Various diagenetic alterations have been recorded including carbonate cementation, dissolution, mechanical to chemical compaction and fracturing. They indicate marine to meteoric and shallow- to deep burial diagenetic realms for the Ilam Fm. Controls of depositional and diagenetic processes on reservoir quality and pore types have been evaluated by integrating well logs and porosity–permeability data with petrographic evidence in sequence stratigraphic framework. Accordingly, a higher-order and three lower-order sequences have been defined and correlated across the study area. Various pore types of the reservoir are differentiated and classified into five classes: interparticle, intra-particle/skeletal, vuggy/moldic, fractures and micropores. Accordingly, two reservoir intervals are defined in the Ilam formation that include the following: (1) microporous mud-dominated reservoir in TST of higher-order sequence, in the lower Ilam, and (2) macroporous grain-supported facies in RST of higher-order sequence, in upper part of the Ilam formation.

Controls of depositional facies and diagenetic processes on reservoir quality of the Santonian carbonate sequences (Ilam Formation) in the Abadan Plain, Iran

Porosity evolution in sequence stratigraphic framework: a case from Cretaceous carbonate reservoir in the Persian Gulf, southern Iran

Aptian carbonates, major hydrocarbon reservoirs in the Persian Gulf, were deposited on a ramp-like platform to intrashelf basinal setting under the controls of tectonics and eustasy. Coated grains (oncoids and pisoids) are abundant and show different textures and internal microstructures depending on the stratigraphic position. These Aptian coated grains are divided according to their texture, cortex composition, morphology, type of biota and internal structure, based on petrographic (routine petrography, cathodoluminescence and scanning electron microscope) and geochemical analyses. Accordingly, four types of oncoid and a pisoid group are identified. Oncoid types 1 and 2 along with pisoids typically formed during phases of relative sea-level fall developed within the regressive systems tract (RST). They are commonly associated with shallow-marine (inner ramp), high-energy shoal facies and occur below exposure horizons, at sequence boundaries. Oncoid types 3 and 4 show micro-encrusters (i.e. Lithocodium aggregatum and Bacinella irregularis) and usually occur in a wackestone texture that indicates deposition in a low-energy lagoonal setting with low sedimentation rate during rises in relative sea level (i.e. a transgressive systems tract: TST). Stable carbon and oxygen isotopes are used to define the OAE1a and its environmental effects in the Dariyan Formation. Palaeoenvironmental proxies reflecting energy level, sedimentation rate and trophic level are evaluated for Aptian sedimentary sequences deposited on the southern margin of the Neo-Tethys Ocean.

Coated grain petrography and geochemistry as palaeoenvironmental proxies for the Aptian strata of the southern Neo-Tethys Ocean, Persian Gulf, Iran

Reservoir characterization of fluvio-deltaic sandstone packages in the framework of depositional environment and diagenesis, the South Caspian Sea Basin

Mohammad Bahrehvar

Papers

Porosity evolution in sequence stratigraphic framework: a case from Cretaceous carbonate reservoir in the Persian Gulf, southern Iran

Coated grain petrography and geochemistry as palaeoenvironmental proxies for the Aptian strata of the southern Neo-Tethys Ocean, Persian Gulf, Iran

Depositional and diagenetic controls on reservoir quality of the uppermost Jurassic–Lower Cretaceous sequences in the Persian Gulf; a focus on J–K boundary

Reservoir characterization of fluvio-deltaic sandstone packages in the framework of depositional environment and diagenesis, the South Caspian Sea Basin

Integration of geoscience data to delineate quality of the Asmari reservoir, Iranian part of the Persian Gulf basin