Integration of Well Data Into the Seismic Processing Graph for Fluid Contrast Detection in Avo Attributes

At a field in the north of West Siberia, an exploration well located on the basis of a geological model that relied on a bright-spot AVO anomaly encountered a watersaturated reservoir instead of the predicted gas saturation, as confirmed by formation testing with fluid sampling. The wrong prediction was caused by the mixing of gas- and watersaturated reservoirs in the AVO indicator domain (intercept– gradient) in the 2022 processing results, whereas synthetic seismogram modelling indicated a confident separation of saturation types: the gas reservoir corresponds to AVO class 4, and the water-saturated reservoir to class 3. To resolve this contradiction, four multi-vintage seismic surveys (vibroseis and dynamite sources) were reprocessed using the results of five wells and continuous interpretation-driven quality control. After each significant processing step, a seismic-to-well tie, an assessment of the AVO distribution at well locations, and a signal-to-noise estimate were performed, with the results integrated on a radar chart of control parameters. All controlled parameters improved: the dominant frequency increased from 30 to 38 Hz, the spectral bandwidth – from 45 to 52 Hz, the signal-to-noise ratio – from 12 to 13, the seismic-tosynthetic correlation coefficient – from 0.59 to 0.73, and the AVO correlation coefficient – from 0.7 to 0.8. As a result, the model-predicted separation of gas- and water-saturated reservoirs in AVO attributes was reproduced on the real data, and the key processing procedures ensuring conditioned results were identified.

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