oa Shaybah 3D Amplitude Inversion with Interbed Multiple Modeling

Amplitude inversion has been used routinely throughout the industry to help assess the reservoir<br>quality and derive reservoir properties such as porosity. In cases where interbed multiple<br>contaminations interfere with the primary reflectivity, the inversion results are questionable unless<br>interbed multiples can be simulated in the inversion procedure.<br>In this paper, we demonstrate the use of zero-offset modeling, to simulate interbed multiples,<br>observed in a 3D seismic dataset, acquired over the Shaybah oil field. We identified the interval from<br>which interbed multiples were generated and produced a reasonable 3D impedance model for use in<br>the field’s development drilling program.<br>A “layer-stripping” type modeling approach was used to identify the interval from which the interbed<br>multiples were generated. Three key geologic intervals between the surface and the base of the<br>reservoir were identified as candidates for the starting layer from which the interbed multiples were<br>modeled. To begin, the shallowest formation of the three was designated as the starting layer.<br>Synthetic traces with primary and interbed multiple reflections were generated and compared with the<br>measured seismic data. This procedure was repeated for the deeper two consecutive formations. At the<br>conclusion of this modeling exercise, it was determined that using the shallowest formation as the<br>starting layer produced the best match between the synthetic and measured seismic data.<br>The inversion algorithm used a model-based method where the starting model was generated by<br>interpolating known log impedances between existing well control based on the interpreted seismic<br>time horizons. The initial model was then optimized by iteratively updating the impedance to minimize<br>the error between the synthetic, generated from the model, and the seismic. The final inversion results<br>were evaluated by matching the measured 3D seismic data to the impedance logs at the wells.<br>Comparison of seismic and inverted impedance volumes showed that the top of the reservoir was more<br>clearly defined by the impedance volume; whereas the 3D seismic signature for the top of the reservoir<br>is poorly defined due to the presence of the multiple interference.