A high-resolution survey with a total of 2300 km 2 of 3D reflection seismic data was acquired over the Al Shaheen Field, Block 5, offshore Qatar, from October 2006 to April 2007. Reverberations from the hard shallow water bottom and other types of noise limited the value of the original processing. Re-processing using new technologies has produced a step change in quality resulting in cleaner images for interpretation and superior angle stacks for inversion.The multiples were removed by applying an enhanced processing workflow based on a predictive, data-driven algorithm. The workflow involved attenuating short-period water-layer related multiples -a process that is referred to as shallow water demultiple (SWD). The SWD method makes use of water-layer multiples in the data to reconstruct the missing water-bottom primary reflection, and then uses the reflection for predicting these shallow multiples. The method takes into account the spatial varying nature of the subsurface. Since the multiple model predicted by SWD has similar amplitude and phase as the input data, very short matching filters can be utilised in the adaptive subtraction process.These processing improvements have influenced a broad spectrum of interpretations such as better structural representation including fault mapping and improved understanding of facies. In conclusion, detailed and careful testing has resulted in new added value from this large high resolution 3D data set by applying technologies that were not available when the data was acquired and processed in 2006-2008.

A comprehensive seismic interpretation programme was recently initiated with the purpose of further increasing the use of 3D seismic data for reservoir characterisation and field development in the Al Shaheen Field, offshore Qatar. Reprocessing of existing seismic data was part of the programme to ensure best data quality for the interpretation. The Al Shaheen Field is a layered carbonate dominated field with multiple reservoirs at different stages of development. Reservoir characterisation is a key driver for both new development areas in the field and for optimisation of existing development areas. Geological topics relevant to reservoir characterisation and field development where seismic data support the reservoir models include faults, reservoir architecture and properties. In this study we present results of integrated seismic interpretations aiming at improving the reservoir characterisation. The results span three of the important reservoirs: Kharaib, Shuaiba, and Mauddud. Through seismic interpretation and integration with geological data and concepts, a consistent field-wide fault framework has been defined. A complex channel system in the Shuaiba reservoir and clinoforms in Mauddud have been mapped. The porosity distribution in the Kharaib reservoir has been estimated using seismic attributes. Additionally all the main geological surfaces defining the general structure and stratigraphy have been mapped. For some results the confidence is high and they can be used directly in the reservoir characterisation and building of static and dynamic models. Other results are less certain e.g. porosity of the Kharaib reservoir. Where this is the case, the results are used to help define uncertainty ranges for the models, as well as enabling testing of different scenarios in the modelling. Properly integrated with all available field data, the value of seismic data is to help create a spatial understanding of geological features that cannot be achieved from well data alone.