مطالعه چينه شناسي، تنوع فابريكي و تغييرات دياژنزي رسوبات سولفاته در پوش سنگ(بخش 1 سازند گچساران) ميدان نفتي آغاجاري

The Study of Stratigraphy., Fabric and Diagenetic Changes of Sulfate Deposits in the Caprock (Member 1 of Gachsaran Formation) of the Agh-Jari Oil Field

Sulphate deposits are one of the important constituents of oilfields and usually form the cap rock of hydrocarbon reservoirs. In the present study, sulphate sediments of the Agha Jari oilfieldʹs cap rock are investigated. In this field, member 1 of Gachsaran Formation with 50 m mean thickness of anhydrite, marl, limestone and bituminous shale is considered as the cap rock. In the present study, the following methods are used: Gamma ray & Sonic well logs, Microscopic thin sections, Scanning Electron Microscope with elemental analyzer (SEM-EDS) and Carbon Isotope. With consideration of lithostratigraphic column of the field, 7-8 separate anhydrite units with different levels of thickness are recognized. Anhydrite sediments show various textures and fabrics such as nodular, lath, decussate, enterolithic and blocky some of which are used to determine the depositional environment and their alteration during burial. Anhydritization, cementation, recrytalization, compaction and replacement are the most important diagenetic processes of sulphate deposits in the Agha Jari oilfield. Carbon Isotopic (513C) studies of associated carbonate layers in anhydrites, show the value of %o -20.4. All of lithological, petrographical and isotopic data indicate intermediate depositional environment (lagoon or sabkha).