Improved Carbonate Reservoir Characterization: A Case Study from a Supergiant Field in Southern of Iraq

The objective of this work is to characterize the porosity distribution and the types of carbonate facies in the Mishrif reservoir in the West Qurna/1 Oil Field using seismic inversion results, well log data, rock physics model and core data analysis. Identification of the pore system and the spatial distribution of lithology are keys for constructing Mishrif reservoir model, which have a great impact on the development of the most prolific reservoir in the field Mishrif reservoir. Seismic inversion process is transforming of seismic response into a quantitative elastic properties of the reservoir rocks. It enables the modeling of porosity and lithology distribution in 3D space away from well control. In order to achieve the aim of the work, a step wise approach will be taken. First of all, the vertical distribution of porosity based on well log data and its relationship with elastic properties was undertaken. A model-based seismic inversion guided by rock physic analysis modeling was applied across the high resolution 3-D seismic data, and integrated with core data for validating at Mishrif intervals. The porosity volume was then generated over the entire West Qurna/1 field based on the linear-regression analysis. The interpretation of seismically derived characterization in the Mishrif reservoir observed a different lateral distribution of acoustic impedance. The results were correlated with computed acoustic impedance log and core analysis data to classify lithofacies of the Mishrif interval. The resulting porosity volume was validated with well log data where good consistency was indicated. By slicing through the porosity volume, it shows a high porosity in many carbonate features with low acoustic impedance which reflect a good reservoir quality (grainstone tidal channel or the accumulation of corals and mounds facies). This observation implied that Mishrif zones displayed a wide range of porosity and lithology fluctuations due to the impact of depositional environment. The workflow provided insight into the porosity distribution and quantification of its influence on dynamic reservoir behavior. The estimation of the porosity based on seismic data, can increase the reliability of reservoir characteristics through providing a more detailed of porosity distribution in interwell regions. Overall, this study will ultimately lead to improve the development plan of wells in terms of production performance, and economic value of the West Qurna/1 oil field and similar heterogeneous carbonate reservoirs.