Identification of Trends Driving Reservoir Heterogeneity at Multiple Stratigraphic Intervals in a Giant Middle Eastern Carbonate Reservoir.

Abstract

Abstract Oilfield A is a low relief structure consisting of multiple stacked reservoirs. Three reservoir intervals show different trends of reservoir property distribution. Lateral reservoir property degradation in Oilfield A is correlated to increased vertical heterogeneity. Understanding the driving mechanism for the controls on reservoir property distribution is therefore essential for effective well placement, well spacing and achieving the expected ultimate recovery from the oilfield. Previous integrated reservoir characterization studies in Oilfield A have identified a link between chemical compaction, reservoir thickness, cementation and reservoir property distribution in Reservoir 2. As part of reservoir model building and subsequent structural updates, thickness maps have been constructed from well data for each reservoir unit as an early indicator of possible reservoir property trends. The maps show trends which are integrated with other data, both static and dynamic in order to validate their impact. To establish correlations, thickness maps were compared to maps of log porosity, facies, diagenetic features, geophysical attributes, cumulative oil production and water cut. Reservoir thickness shows a good correlation to reservoir property distribution in several different reservoirs in Oilfield A. Reservoir 3 shows a south-east to north-west trend of reservoir degradation, Reservoir 2 shows a north to south trend of reservoir degradation, while Reservoir 1, shows a west to east trend of reservoir degradation. Chemical compaction has been shown to drive reservoir property degradation in all three reservoirs. An increased abundance of stylolites is noted in the thinnest, most cemented, poorest quality parts of the three reservoirs. Since chemical compaction (stylolitisation) is a process which starts in the burial diagenetic realm and since all three reservoirs show a similar paragenetic history it is logical to expect all three reservoirs have a similar burial history. However, the trends observed in the three stacked reservoir intervals are orthogonal to opposite. Reservoir properties are rarely randomly distributed in oil reservoirs. Integrating static and dynamic data together in Oilfield A has shown that compaction is the dominant driver of reservoir degradation in three stacked reservoirs. Understanding the trends controlling lateral and vertical reservoir heterogeneity due to compaction is essential in appraisal and development well planning as well as increasing expected ultimate recovery as part of increased and enhanced oil recovery projects.