The objective of the work was to characterize the pore system of the Mishrif carbonates of the Zubair Field (onshore Iraq), using the Simultaneous Seismic Inversion results, geostatistical information (extracted from wells and seismic data) and rock physics modeling, which allowed to robustly transform impedance to porosity and additionally, to implement the internal Eni approach CaSRC (Carbonate Seismic Reservoir Characterization), including the Frame Flexibility Factor (FFF) to discriminate reservoir quality facies in terms of hydrocarbons productivity.
A seismic inversion was performed to produce elastic properties from seismic data. These property volumes were used to describe the lateral distribution of petrophysical parameters, while well data provided information about the vertical distribution of porosity and its relationships with the elastic properties. These data were then quantitatively integrated by applying a geostatistical approach to generate a porosity volume that honors all the available data and to compute a Seismic Facies volume, as additional property related to FFF, according to the estimated relationships between elastic and gross rock frame. Finally, an optimal average velocity volume was built by integrating structural information and inverted velocities, to properly locate the delivered seismic properties in a calibrated depth domain, suitable for reservoir modeling activities.
The analysis of seismically derived properties within the Mishrif Formation was carried out by vertically dividing the carbonate sequence in three units and estimating at each level the porosity distribution through an appropriate property mapping. The results highlighted a different lateral distribution for each layer. The upper one shows better porosities in the northwestern field sector, while the middle interval confirms an improvement of reservoir quality moving to the central-southwestern part. The lower interval shows globally poor porosity values along the field. As well as porosity, the seismic facies volume (driven by FFF) was analyzed separately layer by layer and mode maps were extracted. These maps shown that the lateral distribution of the best quality rocks is different among the intervals and change laterally inside of them. Furthermore, they shown that the main facies distribution trends, even though correlated to the predicted porosity, can provide additional information in terms of gross rock frame, where porosity type and mineral distribution represent key elements in assessing reservoir quality and, ultimately, suitable new well locations.
The interpretation of property maps using geological keys allowed to improve the robustness of recognized depositional trends, successfully used with the delivered volumes as driver for facies and property population within the generalized reservoir modeling workflow.