Mineralogy, Porosity, and Permeability Relationship through the Yamama Formation in the Halfaya Oilfield, Southern Iraq

Abstract

The present study aims to evaluate porosity and permeability in the Late Cretaceous Yamama Formation in the Halfaya oil field. The formation is divided by Maysan Oil Company into three main units (YRA, YRB, and YRC), with the upper unit (YRA) further subdivided into six subunits based on facies distribution. The dominant pore types were identified using bulk volume water relationships and include mainly chalky to intercrystalline porosity, with occasional vuggy porosity. The results show relatively low porosity values (5–12%), which significantly affect permeability, with most values below 1 mD, resulting in poor reservoir performance. Due to the limited availability of core data, the study also aimed to identify the most suitable empirical relationship for estimating permeability from well logs; 7 wells were used in the study. The XF6 well showed the best results, which is located southeast of the fold. The Wyllie equation showed better agreement with core permeability data than the Timur and Coates equations and was therefore adopted for permeability estimation. Weinland analysis indicates that most units fall within the Microport range, suggesting very low productivity unless enhanced recovery methods are applied. However, some units fall within the Macroport range of nearly 1000 BPD and exhibit better reservoir quality and higher production potential. The petrophysical results are supported by scanning electron microscope (SEM) analysis, which confirmed the identified pore types and revealed the presence of minerals( pyrite, feldspar, calcite,  barite, chlorite, and minor quartz ), and the presence of dolomite and the clay content both negatively affect porosity and permeability.