A Contribution of the CDP Gathers and Pre-Stack Seismic Inversion in the Prospect Evaluation: A Case Study of El Mansoura Field, Nile Delta, Egypt

Abstract

This case study showing the usefulness of the Common Depth Point (CDP’s) analysis to assess the amplitude response which is similar at two cases (gas-bearing and dry sands) after stack, using the Amplitude Versus Offset (AVO) analysis and the pre-stack inversion to understand the reservoir configuration and its relationship to the different amplitude response. The results led to a high success of exploration ratio as the positives vastly outweigh the negatives. Several lessons have been learned, which how to differentiate between the similar amplitude responses for two dry and gas discovery wells-by understanding the relationship 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 mechanical properties of the rocks: compression wave (VP), shear wave (Vs) and density. These properties are affected by litho logy and fluid contents. The analysis of the CDP’s gathers and the inversion results help in validating the prospects before drilling and in determining the response of the seismic amplitude deviation with the offset, so it is possible to confirm the amplitude anomaly if it is related to hydrocarbon or not.