炭酸塩岩シーケンス層序に基づく油層地質モデリング―中東下部白亜系炭酸塩岩油田の例―

Abstract

A carbonate reservoir of a giant oil field, the Early Cretaceous Kharaib Formation in the Middle East, has complex limestone lithofacies, and unexpected breakthrough of injection water has been observed at some of the wells. Previous studies have suggested that the heterogeneous reservoir property which cause in the unexpected breakthrough of the water is mainly related to lithofacies changes within the reservoir. To make a better estimate of the reservoir property distribution, high-frequency sequence stratigraphy has been developed in the field. Integrating detailed core observation, well-log correlation and stacking pattern analysis for the reservoir, we identified fifteen lithofacies and six high frequency (4-5th order) sequences in the reservoir interval, and the depositional models for each systems tract were derived. We are building a new reservoir simulation model with this integration such as layering scheme, distribution of lithofacies and reservoir properties derived from high frequency sequence stratigraphy. Field scale lithofacies model was constructed based upon the regional depositional concepts, isopach trends for each sequence stratigraphic unit and observed core lithofacies. The layering scheme for the new reservoir model is defined based on sequence stratigraphic interpretation, and the sub-layers are derived from subdivision of sequence stratigraphic units into proportional smaller layers to represent the vertical lithofacies variation. 3D seismic data is utilized to construct the framework of the structural model with fault geometry. Permeability model is constructed by deterministic method using lithofacies model and regression function of relationship between porosity and permeability for each lithofacies. In addition, Flow Zone Indicator (FZI) which is parameter of combination of porosity and permeability based on Pulsed Neutron Capture (PNC) log data, is also integrated for the permeability modeling in order to represent heterogeneity of high permeability and match with the behavior of injected water. The above-mentioned methodology makes it possible to modify the flow model by geological concepts, e.g. by review of lithofacies model and permeability estimation, during history matching in the next dynamic reservoir simulation phase.