Abstract
This study focuses on the role of the CDP (common depth point) gathers in the evaluation stage of the geological prospects using the AVO (amplitude versus offset) analysis of the 3D seismic data and the Pre-stack inversion to differentiate between both gas bearing and dry sands and to understand the reservoir configuration and its relation to the different amplitude response through analyzing two encountered similar amplitude response in two different locations but with different drilling results, although they have the same stratigraphic sequences and structural setting. The results led to a high success of exploration ratio as the positives vastly outweigh the negatives. Several lessons have been learned from the negative results-which how to differentiate between the similar amplitude responses for two dry and gas discovery wells-by understanding the relation between the near traces (near offset) and the far traces (far offset) from the CDP gathers in order to reduce the amplitude anomalies to their right justification. Consequently, a variation in the reflectivity strength is observed, which is controlled by the elastic properties of the rocks: Compressional wave (Vp), Shear wave (Vs) and density. These properties are affected by the lithology and fluid contents. The analysis of the CDP gathers and the inversion results help in validating the prospects before drilling and in determining the response of the seismic amplitude variation with the offset, so it is possible to confirm the amplitude anomaly if it is related to hydrocarbon or not.
For more details:
http://sciaeon.org/articles/Impact-of-the-CDP-Gathers-and-Pre-Stack-Seismic-Inversion-in-the-Prospect-Evaluation-Onshore-Nile-Delta-Egypt.pdf
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Journal of Geology and Geoscience 