Case Study of Fine Geological Modeling for Mishrif Carbonate Reservoir of H Oilfield in Iraq

Abstract Accurate geological characterization for complex carbonate reservoirs plays an important role in guiding the optimal oilfield development. Mishrif Formation of H Oilfield in south of Iraq is the most important target among several Cretaceous oil-bearing carbonate formations due to the high OOIP proportion. It is composed mainly of bioclastic limestone with multiple pore types. It is massive reservoir with medium porosity and low permeability. The great variation of vertical and lateral reservoir quality leads to poor relationship between porosity and permeability which brings great challenge in reservoir characterization and favorable area identification. This paper presents the comprehensive reservoir evaluation and characterization in combination of all data available. The sedimentology and stratigraphy are reviewed in terms of depositional environment and lateral stratigraphic correlation. The variability inherent to the depositional mode and digenesis leads to complex reservoir geometry and pore types. Rock typing is examined based on core measurements and well logs to get the improved correlation coefficient between porosity and permeability. Neutral network method is used to propagate the rock types to un-cored wells to get the accurate permeability estimation. Facies model and rock type model are built constrained by the seismic inversion reservoir prediction results which provide crucial information on carbonate proportions distribution, especially in areas with low well control. Permeability model is generated constrained by rock type and porosity which can indicate the reservoir flow capacity. Based on the integrated reservoir model, horizontal wells and multilateral wells for Mishrif Formation are proposed and optimized in the good reservoir quality area. The high individual well production rate verified that the well placements upon fine reservoir modeling are successful.