The impact of fractures and planar structures on the quality of the Upper Jurassic Mozduran reservoir, Kopet Dagh basin (Northeast Iran)

Abstract

In this study, based on stereographic projections, two sets of planar structures were identified in the Mozduran reservoir, a prolific reservoir in Northeast Iran. The first set includes shallow structures, consisting of stylolites, solution seams, dense veins, and bedding planes. These structures were created by both sedimentary and diagenetic processes and do not have much effect on reservoir quality. The second set includes structures are related to deformation, and these have a substantial impact on increasing the reservoir quality. To investigate the relationships between the types of fractures and their respective influences on reservoir quality, the production logging tool (PLT) gas production rate data was utilized. This analysis revealed that in fractured zones 2 and 4 of Mozduran reservoir, where fractures and flat structures have increased the quality of the reservoir, the PLT gas production rate also increases. Conversely, in areas where filled fractures and diagenetic processes have negatively affected reservoir quality, the PLT gas production rate decreases. This pattern indicates the contrasting impact of planar features on reservoir quality. Moreover, a higher frequency of fractures corresponds to a higher permeability in the Mozduran reservoir of Well #B, whereas a lower frequency of fractures corresponds to lower permeability in that reservoir in Well #A. These relationships confirm the positive influence of fractures on the Mozduran reservoir quality. The study results reveal that deformation variables in the examined reservoir have greater impacts on its quality than the sedimentary and diagenetic porosity/permeability components, but those impacts can have both positive and negative consequences.