Gulf of Suez: An Integrated G&G Study for Structural Model Definition

Manera, Martina ¹; Andreoletti, Clara ¹; De Vincenzi, Luca ²; Sayed Adb El Fattah, Mohmoud ²
(1)eni e&p, San Donato Milanes, Italy. (2) Petrobel, Cairo, Egypt.

A case study of velocity model building is presented in the Gulf of Suez offshore. Goals of the project were to calculate the most accurate velocity model and, consequentially, to obtain the most reliable seismic volume in depth honouring well information.

The challenging aspect of the area was the presence of high velocity evaporitic layers generating internal multiples that completely mask the low energy true signal. In particular, multiples jeopardize the determination of geological dips, produce image distortions, and obliterate energy from the deeper horizons.

Miocene clastic deposits have already been exploited as typical plays in the area for decades and, currently, the deeper Lower Senonian (Matulla Formation) reservoir is an attractive target. Unfortunately, structural complexity of the area and poor seismic imaging are detrimental to a correct interpretation, with risk of mismatch between prognosed and actual well data.

Standard methodologies for suppressing internal multiples failed due to lack of velocity discrimination between multiples and primaries and technologies based on cross correlation for internal multiple attenuation are not industrial tools, yet. Therefore, in order to have a suitable seismic volume for a reliable interpretation, Reverse Time Migration (RTM) was used, linked with well driven velocity analysis. A velocity model in depth reconstructed via eni proprietary software combined with interactive interpretation of key horizons allowed obtaining a geologically consistent PSDM volume.

Reverse Time Migration is the most accurate tool for imaging below evaporites as well as in complex geology, by illuminating the deeper events normally hidden by “smile” artefacts in conventional Kirchhoff migration. Moreover, by limiting the maximum frequency to 20 Hz we were able to avoid interference effects due to higher frequency multiples.

An integrated approach between building a complex 3D velocity model (driven by well data and geological knowledge of the area) and the most sophisticated migration algorithm, i.e.: RTM, demonstrated to be the key solution for a good seismic imaging of the deeper reflectors in the area of study. Such a methodology not only improved the imaging, but also achieved the most realistic structural reconstruction of the subsurface, with positive consequences on both exploration and development activities.

AAPG Search and Discovery Article #90135©2011 AAPG International Conference and Exhibition, Milan, Italy, 23-26 October 2011.