Modelling and Attenuation of Mode Conversion Noise: A Case Study of Egypt Offshore

In regions with significant salt presence, such as the Eastern Mediterranean, the pronounced contrast in acoustic velocity between salt bodies and surrounding sediments often leads to the generation of converted wave modes. These arise when compressional (P-wave) energy transforms into shear (S-wave) energy upon encountering the high-contrast boundaries at the top or base of the salt. As the converted waves travel at slower velocities, their arrival times differ from primary reflections and can appear as deeper, misleading signals in seismic records. This energy, if not properly managed, can hinder the accurate interpretation of subsurface structures. One of the primary challenges in hydrocarbon exploration within the Messinian salt province of the Eastern Mediterranean is the contamination of P-wave images by such converted modes. The salt layer in this area typically exhibits interval velocities around 4200– 4300 m/s, while the surrounding post- and pre-Messinian sediments display significantly lower velocities, ranging from 2400 to 3000 m/s. These sharp contrasts promote the generation of converted wave events, particularly at steeply dipping salt interfaces, and frequently lead to complex interference patterns in seismic images. Although some of these converted events can enhance illumination and provide additional insight into subsurface geometry, they more often act as noise that obscures true reflections, especially in sub-salt targets where accurate imaging is critical. Among the various converted wave types, those converting at both the top and base of salt formations—such as PSPP and PPSP—pose a significant problem due to their higher amplitudes and complex moveout behavior. Symmetrical modes like PSSP, while theoretically present, often typically not observed in the field dataset due to weaker amplitude and longer travel times. Standard suppression techniques include filtering based on velocity discrimination or targeted muting via travel-time modeling, but these approaches may be ineffective in areas with irregular salt geometry.