Publications

A Multi-Azimuth Pre-Stack Depth Migration (PSDM) reprocessing was performed on Sisi-Nubi 3D seismic data in 2010. Besides its traditional purpose to obtain a better structural image, this reprocessed data is intended to be used for future pre-stack seismic reservoir characterization (SRC) studies, requiring amplitude and phase to be preserved. On Sisi-Nubi, the main geophysical challenges are related to a complex geological setting with strong lateral lithology variations, provoking important statics, seismic signal attenuation and amplitude variation. The standard processing quality control (QC) performed with the data-processing contractor cannot always guarantee that the final processing will deliver results that are appropriate for SRC studies. This paper describes a set of internal AVO (Amplitude Varitions with Offset)-based QCs whose main objective is to monitor the seismic quality in terms of signal preservation.The first stage of the method consists of building a referential of QCs on former 2005 Pre-Stack Time Migration (PSTM) data and of identifying the key steps of the 2010 processing sequence that may be detrimental to amplitude stability and may also have a negative impact on signal phase, signal-to-noise, etc. In the second stage, angle sub-stack cubes are produced after each of these key steps and QCs are performed on these intermediate results. The QCs consist of analyzing 10 parameters or Seismic Quality Indexes that can be grouped into 3 main categories: Geological Representativity (bandwidth index, resolution, and noise attenuation), Offset Consistency (cross correlation, phase & time-shift dispersions, and stretch), and Spatial Stability (stretch dispersion, lateral amplitude variation, and resolution dispersion). After compiling all the QC parameters, the evolution of each parameter is assessed using the former 2005 PSTM data as reference.Because it is performed all along the processing workflow, this monitoring introduces an approach that enables qualitative and quantitative control of the PSDM processing with regard to the AVO response in the pre-stack domain. Indeed, at every important stage, recommendations or modifications can be submitted to the contractor performing the data-processing. To conclude, the final processing results have to bring as much geological information as possible, producing preserved relative amplitudes with minimal artificial variations and laterally stable responses.