Microfacies and Diagenetic Processes of the Late Jurassic Naokelekan Formation in selected wells at Balad, Ajil and Baiji Oilfields, Central Iraq

Abstract

This work depends on detailed petrographic and diagenetic processes studies of collected cutting rock samples, from the Late Jurassic Naokelekan Formation from Ajil-8, Balad-1 and Baiji-1 wells. Based on the thin sections study, the formation contains various petrographic components represented by pelecypods, calcispheres, planktonic and benthonic foraminifera, in addition to the groundmass of micrite and microspars. Many diagenetic processes affected the rock successions such as, compaction, micritization, authigenic minerals (pyrite), cementation, neomorphism, dissolution, porosity, replacement and dolomitization. The detailed microfacies analysis reveals that the rock successions consist mainly of three microfacies including; lime mudstone, which is divided into non-fossiliferous lime mudstone, bioclastic lime mudstone and planktonic foraminiferal lime mudstone, lime wackestone which also divided into calcispheres lime wackestone, benthonic lime wackestone, and pelcypodal lime wackestone, and lime packstone include, bioclastic lime packstone, peloidal lime packstone, and calcispheres lime packestone. The overall characters of these microfacies indicate the formation was deposited in two different environments: (1) shallow marine subtidal environment at the lower and upper parts (2) outer shelf in an euxinic environment at its middle part