Investigating the reservoir quality of the Early Triassic succession with a new perspective on diagenesis and sequence stratigraphy in the center of the Persian Gulf, South Pars

Abstract

The central part of the Persian Gulf has one of the largest gas fields in the world. This field was formed during the formation of the Neo-Tethys Sea and the Permo-Triassic period. In this research, the Earlier Triassic part of this area has been studied in Well A. The Earlier Triassic gas field in the Iranian part is called the Kangan Formation and is equivalent to the upper part of the Khuff Formation in the Arabian plate. This research is based on the petrography studies, diagenesis processes, and sequence stratigraphy with the help of core analysis data and petrophysical data (full suite logs). The main goal of this research is to evaluate the reservoir quality and classify the production potential of gas reservoirs by relating the two-variable diagrams of Permeability versus porosity and their expansion in the Earlier Triassic of the region. The studies showed that the reservoir properties of the Kangan Formation were formed under the influence of various factors: Sedimentation processes, regional tectonics, diagenesis processes, and their sequence. The sedimentation processes have been created under the influence of the sedimentation environment and the transgressive-regressive of the sea in different sequences. Each environment has different reservoir properties depending on its energy, depth, salinity, oxygen and organisms. In the studied area, 12 diagenesis processes in several diagenesis areas such as meteoric vadose, marine phreatic, meteoric, and a combination of them along with eight cement and eight types of porosity with different effects on reservoir quality were identified and the limits of each were specified. In the studied area, based on petrographic studies, the third and fourth-order sequences were determined and the reservoir quality was accurately determined by the system tracts of the third and fourth-order sequences and their location were determined. Finally, the reservoir quality of the Kangan Formation was determined based on a set of reservoir potentials in diagenesis processes (porosity and permeability) and according to the sequence stratigraphy of the region. In addition, their results were compared with the results of petrophysical logs, water, and gas saturation. Then, permeable and extractable areas and impermeable and non-reservoir areas of the Kangan Formation were determined. This research showed that the Earlier Triassic sequence in the central part of the Persian Gulf could be divided into four zones, zone one and three, which have non-reservoir potential and are mostly evaporitic and mudstone. Zones two and four have reservoir potential and often have dolomite and grainstone facies in the environment of the central shoal and the active tidal zone.