Stratigraphic Sequence and Diagenetic Effects of the Upper Qamchuqa Formation in Khabaz and Kirkuk Oil Fields, Northern Iraq

Abstract

The Upper Qamchuqa Formation was deposited in Zagros foreland basin in the north of Iraq during the Late Albian age. Two boreholes from Kirkuk oil field (K-229) and Khabaz oil field (Kz-4) are selected in the current study, where 100 samples of cores and cutting were used to determine diagenetic evolution of the Upper Qamchuqa Formation. Five major sub-environments can be diagnosed within the Upper Qamchuqa sequence, they are: shallow-open marine environment, semi-restricted marine environment, restricted marine environment, shoal and deep outer ramp environment. The diagenesis process are contain the physical or chemical variations in sedimentary rocks and sediments that happen after the deposition, where many diagenetic process effect on the Upper Qamchuqa Formation which are: Micritization, Cementation with three types (blocky, drusy,and syntaxial calcite overgrowth cement ), Dolomitization with three types too (scattered, Pervasive coarsely ,and saddle dolomite), neomorphism, recrystallization, silicification, dissolution and compaction (mechanical and chemical). There are four sedimentary cycles: cycle A extends from the upper part of the underlying Upper Sarmord Formation (TST) to the shallow open marine facies (HST) of the lower part of Lower Qamchuqa in k-229 which ended with shoal facies, cycle B on the other hand, shows a grain dominated facies where the carbonates buildup kept pace with the still relative sea level (keep up) during high stand which deposited under semi-restricted and restricted successively, cycle C shows a marked variation in thickness within the sections (K-229 and Kz-4); it is greatest thickness was noticed at k-229 where its lower part is mostly mud dominated in Kz-4, and cycle D shows a distinct variation in facies change from grain-rich to mud-poor lithology of restricted to semi-restricted facies in the East (k-229) to predominantly restricted marine conditions at the central area (Kz-4).