Quantification of the effect of fracturing on heterogeneity and reservoir quality of deep-water carbonate reservoirs

Abstract

The Shiranish Formation represents one of the most important fractured reservoirs in northern Iraq. In this work, the petrophysical properties of the formation have been fully characterised using microscopy, core analysis, and well log analysis using conventional methods as well as new quantitative diagenetic approaches. During this work we have developed methods to quantify a petrophysical heterogeneity index (χ), reservoir quality indicator (RQI), and fracture effect index (FEI) for each of the stratigraphic units of the formation. The FEI was calculated by dividing the difference between the mean permeability of the wireline log data and the mean permeability of the unfractured core plug samples by the difference between the mean porosity of the wireline log data and the mean porosity of the unfractured core plug samples. This study shows that the Shiranish Formation has a fracturing pore system in all the characterised units, but it is particularly well developed in U.4, which shows the best reservoir quality (A and B). The new methods developed in this study can be applied to any carbonate formation to provide a trustworthy way to obtain a reservoir quality indicator linked to the petrophysical heterogeneity of the studied formation.