Utilizing Advanced Stratigraphic Quantification Technique to Assess the Spatial Variability of A-03 Reservoir, Case Study – Onshore Niger Delta

Abstract The characterization and understanding of spatial variability in reservoir properties remain exigent for accurate reservoir performance predictions due to the inherent uncertainty associated with complex geological formations. The performance of G-41h well is a case in point. The well was drilled and completed in the A-03 reservoir. However, the well's performance was observed to be subpar when compared with the older G-31h well also drilled and completed in the same reservoir. Therefore, understanding the spatial distribution and variability of reservoir properties, and correlating them with well production performance, becomes critical. This study presents the workflow of quantitative stratigraphy techniques employed to enhance and expedite the characterization of reservoir heterogeneity. The systematic approach integrates multiple sources of high-resolution data such as Well logs, Seismic attributes, Biostrat and Core data to quantify the spatial variations in lithofacies, sedimentary architecture, and reservoir properties. By applying techniques, the rock type distribution plot generated indicated that reservoir heterogeneity (Lorenz Coefficient) varies in conjunction with a decreasing net-to-gross (NTG) ratio. Additionally, heterogeneity fluctuates within similar NTG ranges, while the variation in sand rock quality increases. Stratigraphic heterogeneity curves further validate the presence of multiple sand types within the A-03 reservoir. A Rock Quality Index (RQI) that was used to quantify the flow character of the A-03 reservoir, ranging from 0.23 to 1 allowed for the classification of four distinct rock types; shale, low quality (LQ), mid-quality (MQ) and high quality (HQ). The Lorenz map generated illustrates the distribution of reservoir heterogeneity across the reservoir. In addition, the Lorenz map with an overlaid pie chart provided insights into the spatial distribution of Facies and their associated reservoir properties within the A-03 sand. The study results indicate that the G-41h well is located within the low-to-mid quality rock type region, whereas the G-31h well is positioned within the high-quality rock type zone. This contributed to improved understanding of G-41h production performance in the A-03 reservoir. Ultimately, improved performance predictions and optimal infill well placement within the reservoir will be facilitated.