The effects of planar structures on reservoir quality of Triassic Kangan formation in the central Persian Gulf, an integrated approach

Abstract

Planar structures including stylolites, solution seams, dense streaks, bedding and cross-bedding surfaces, and fractures of carbonate Early Triassic Kangan Formation were evaluated in the central Persian Gulf. Core X-ray computed tomography (CT), Fullbore Formation Micro-Imager (FMI) log, and cores were used to detect the structures. Furthermore, conventional borehole logging data, routine core analysis, and petrographic thin sections were employed to assess the reservoir properties. Stereographic projections demonstrated that the reservoir has two sets of planar structures. The first group contains shallowly-dipping structures, consisting of stylolites, solution seams, dense streaks, bedding and cross-bedding surfaces. These structures have been created by sedimentary and diagenetic processes. The other set includes deformation-related structures that are steeply-dipping and occurred scarcely, like fractures. Spearman correlation coefficients between the frequency of each planar structure and reservoir characteristics (porosity and permeability) were calculated to reveal the numerical relationship between the parameters. The significant correlation coefficients indicate that stylolites, solution seams, and filled tension gashes diminish reservoir quality while bedding and cross-bedding surfaces have enhanced reservoir characteristics. The strongest correlation was observed as a strong negative relationship between the frequency of stylolites and permeability in K2 reservoir unit. This study implies that sedimentary and diagenetic factors are more effective in controlling the reservoir quality than deformation factors in the studied formation. The present work also indicates that each used method has unique advantages and disadvantages. Therefore, simultaneous utilization of the methods to investigate planar structures would have the best efficiency.