The Diagenesis Processes of the Hartha Formation in Majnoon Oil Field, Southern Iraq

Abstract

The Hartha Formation is the shallowest of the major Majnoon oil field reservoirs. It is a 120 m thick carbonate platform deposit with an age of the Upper Campanian - Maastrichtian. It overlies the regional top of the Sa'di Formation unconformity and is in turn overlain by the Shiranish Formation. This research concentrated on diagenetic processes and petrophysical properties in the Hartha Formation in the Majnoon Oilfield, located in southern Iraq. The Hartha Formation was deposited on a carbonate ramp setting. It is subdivided into four main zones (A1, A2, B1, and B2), where A2 is the majority reservoir. Sixity of thin sections were made from several wells (MJ-29, MJ-47, MJ-88, MJ-91, MJ-92, and MJ-93). This formation was influenced by a number of digenetic processes, such as neomorphism, cementation, dolomitization, dissolution, and compaction. Dolomitization, dissolution, and cementation are the three main diagenetic processes in the current study. Detailed petrographic analysis of the dolomitization indicates that the dolomite formed is of two types (pervasive and selective) in the formation. The formation is affected by tectonic subsidence which is main controlling factor that achieved the paleogeography of the study area. This is produced different thicknesses of the formation along the structure, and the facies that formed the formation varied as a result of the variation of the relative sea level.This study aims to determine the extent of the impact of diagenetic processes on the porosity of the formation and thus impacts on the quality of the formation.