Geological Models Comparison and Selection for Multi-layered Sandstone Reservoirs

Abstract

Abstract The inter-zone and intra-zone heterogeneity are the key issues for multi-layered sandstone reservoirs. While usually lots of equal probability fine geological models which match all constrained data can be built, and how to select the representative models for reservoir simulation is a problem. This paper presents how to compare different geological models and select representative models in detail for a multi-layered sandstone reservoir in Middle East. Through detailed geological characterization and dynamic description, different equal-probability geological models are built. And through geological check and analysis on each model, a preliminary comparison and understanding of each model are conducted, including gridding method comparison, vertical and lateral connectivity comparison etc. Then based on streamline numerical simulation, performance of each zone, each well for each model are compared in detail. Most performance are as we expected, but some are outliers. Through detailed analysis, the fundamental reasons for performance difference and major factors impacting on reservoir performance are determined. Finally, three models are selected for next reservoir simulation. Take K reservoir in Middle East for example, it is a large multi-layered sandstone reservoir of deltaic environment. K is influenced by fluvial, tide and wave, which results in great variations of sand bodies’ distribution, reservoir quality and connectivity. Nine equal-probability geocellular models of K reservoir are built, which use three different lateral connectivity patterns with three vertical gridding approaches representing different vertical connectivity during modelling. Model expected performance are firstly determined based on geological analysis of each model. Then, based on streamline simulation, performance comparison including water cut variation, recovery, etc. are conducted to all models for the zone level, member level and model level. Three models are finally selected which represent Upside model with good lateral and vertical connectivity, Expected model with medium connectivity and Downside model with poor connectivity respectively. These models can be used for reservoir development strategy and risk management study. This paper offers a case study of geological model comparison and selection mainly based on streamline simulation for a multi-layered sandstone reservoir. It ensures the selected models have reservoir heterogeneity correctly characterized, and the selected models are then used for the next development strategy and risk management study. It also provides a methodology and reference case for engineers to study on other similar reservoirs.