Use of Seismic-Derived Attribute for Internal Reservoir Description: A Case History

Sala, Claudio, Luca Baruffini, Fabio Luoni, Anna Pizzo, Marco Rovellini, ENI -Exploration & Production, San Donato Milanese, Italy

The opening of the deep-water frontier highlights the importance of integrating well data with the information coming from different sources, to reduce the appraisal costs and improve the reservoir knowledge. The presented case history illustrates a semi-quantitative approach for integrating seismic information for the internal reservoir description.

The reservoir is characterised by deep-water channel-lobe systems. The complex inter­nal architecture reflects the coexistence of surge-type gravity flow and sustained currents. These two mechanisms, together with the channel system evolution have a big impact in the facies distribution and, in the view of reservoir management, in the geometry and in the quality of the sands.

In this perspective, a reliable and constrained distribution of the heterogeneity in the reservoir levels is a basic factor to optimise the development, reducing uncertainties and minimizing risk.

The applied approach uses the seismic information for facies distribution, integrating data at the well and seismic scale, also accounting for the peculiar sand deposition mecha­nisms of the current sedimentary environment.

Using a statistical methodology, well logs and core data are used to define a very detailed facies distribution at the well (well-facies). In parallel, the seismic volume has been invert­ed to elastic attribute and calibrated to acoustic facies (seis-facies) defined by petroacoustic­elastic modelling using well data.

Next, a quantitative relationship has been found between well-facies and seis-facies. The final distribution of well-facies has been obtained using the 3D seis-facies volume to steer the geostatistical simulations, capturing the depositional system heterogeneity and evolution. Petrophysical properties are finally simulated inside each facies according with the core analysis and the log interpretation.

At the end, a series of reliable pictures of the reservoir obtained with this methodology has been successfully used for a trustworthy reserves risk assesment and for the well plan optimisation.