Step Change In Shallow Water Reflection Seismic By Advances In De-multiple Techniques

Abstract

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.

Integration of Seismic Forward Modelling, Seismic Interpretation and Core and Log Analysis, Shuaiba Build-Up Area, Al Shaheen Field, Block 5 and Block 5 Extension, Offshore Qatar

“…This re-processing especially improved multiple removal and enhanced the validity of the amplitudes in the seismic dataset (Rønde et al, 2014) by applying technologies that were not available when the 3D seismic data was first processed. The 3D seismic data is a high-resolution dataset that was acquired over the full block from September 2006 to April 2007.…”

Applications of Geophysics to the Al Shaheen Field, Qatar, for Reservoir Characterisation and Field Development

“…However, at reservoir level the seismic fault density from the original MOQ06 dataset did not match these observations well as fault density appeared almost uniform across the block. It was only after the reprocessing (Roende et al, 2014), and the removal of acquisition imprints and other artefacts that are especially detrimental to fault imaging, that it was possible to use seismic more confidently for interpretation of faults. Edge enhancing attributes were used and the apparent dip attribute (at three angles) was preferred as it provided a sharp fault definition on time slices.…”

“…Two of the objectives of the reprocessing effort (Roende et al, 2014) were to improve imaging and preserve reliable amplitudes. These improvements allow for more detailed sequence stratigraphic interpretation and have had a significant impact on the understanding of the Mauddud reservoir, which is currently in the very early stages of development as well as the Shuaiba which is more extensively drilled and produced.…”

“…The aim was to suppress multiples and noise in order to give reliable amplitudes and to minimise the effect of heterogeneities in the overburden. This improved dataset became available during 2012 (Roende et al, 2014) and delivered improved imaging and increased resolution at reservoir level. Based on the formation velocities and the dominant frequency, a resolution of around 15 m (50 ft) may be estimated, which at target should now make it possible to map clinoforms and small channels.…”