Effective and careful noise attenuations are crucial for any seismic processing project to control and assure the product quality. The robustness of the data processing can be often identified and quantified by existing well data in production oil and gas fields during the processing. However, if we drill new infill and/or appraisal wells on the flank of the structure based on the processed seismic data, we always need to address the thorny issue of unforeseen mismatching between predicted and actual geological formation tops.
In this paper, we present a recent seismic re-processing study from an offshore an Abu Dhabi oil field utilizing relevant seismic processing techniques to overcome these problems as a case study. The original data processed in 2006-2007 exhibits several technical issues: wavelet instability, poor signal-to-noise ratio, limited resolution and offset range, remnant acquisition footprint and multiples. This imperfect dataset led to significant depth discrepancies on a recent appraisal well that was planned using this seismic dataset.
The recent processing techniques such as adaptive subtraction of ground roll, 3D deconvolution, 3D Radon-demultiple, 3D projection filtering in the OVT (offset vector tile) domain were carefully applied to address these issues. In addition, we demonstrated that PreSTM (prestack time migration) is an effective de-noise tool while unnecessary and harmful noise attenuations could not be applied to the data because of the potential damage to diffractions and signals before PreSTM. These noise attenuation efforts allowed longer offset ranges into the stack, which proved to be the crucial factor in improving the seismic data quality.
Our recent structural interpretation results based on the reprocessing have successfully demonstrated more accurate depth matching on key geological formation tops at this appraisal well location. In addition, blind test utilizing nearly all wells in the field has reinforced our observations. Since subtle reservoir depth variation at each well location will make significant changes to oil production and recovery factor in this particular field, this cast history brought added value to the field development plan particularly for planning horizontal hole drilling and optimizing appraisal well locations.