Facies Analyses and Diagenetic features development of Albian - Aptian Succession in the Wset Qurna oil field, Southern Iraq

Abstract

The Carbonate-clastic succession in this study is represented by the Shuaiba and Nahr Umr Formations deposited during the Albian - Aptian Sequence. The present study includes petrography, microfacies analyses, and studying reservoir characterizations for 5 boreholes within West Qurna oil field in the study area. According to the type of study succession (clastic – Carbonate) there are two types of facies analyses:-Carbonate facies analysis, which showed five major microfacies were recognized in the succession of the Shuaiba Formation, bioclastic mudstones to wackstone, Orbitolina wackestone to packstone, Miliolids wackestone, Peloidal wackestone to packstone and mudstone to wackestone identified as an open shelf toward the deep basin. Clastic facies analyses which shown five major facies were recognized in the succession of the Nahr Umr Formation according to petrographic observation with gamma ray and spontaneous potential well logs. These facies identified four depositional environments within the Nahr Umr Formation; bay fill, delta plain, delta front, and braided river. The studied sequence was affected by five major diagenetic processes, these are: micritization, cementation, dissolution, dolomitization and compaction. The disparity in the distribution of the effect of diagenetic processes in different studied sections indicates that the sea more quickly and completely receded from the northern region of area study. And the central region remained under the influence of fluctuations in sea level, while the southern region least affected by this fluctuation.