Nicolas Chazalnoel

Velocity Model Building Methodology And PSDM In Deep Water Gulf of Mexico: A Case History

Between 2000 and 2001 CGG acquired a 3-D dataset in the Green Canyon area of Gulf of Mexico with the aim to improve the image of potentially hydrocarbon bearing subsalt sediments. Pre-stack depth imaging was selected as the imaging method of choice, and the processing included maximum energy travel time calculation combined with turning wave ray tracing and Kirchhoff based migration. The velocity model building included a careful definition of the initial velocity volume with salt mask option followed by six iterations of migration based velocity model updating. In between iterations, the velocity volume was smoothed using regression analysis followed by depth varying conical filtering. Through careful selection of migration parameters and the preservation of the low frequency signal spectrum in the data, we were able to image steep dipping events beyond 90 degrees. A close integration of interpretation, processing and model building were the key elements of this depth-imaging project.

3D Finite-offset Depth Tomography Model Building: Green Canyon, Gulf of Mexico

A more detailed velocity analysis is required for successful pre-stack depth migration model building and tomographic methods offer a potential solution. However, migration velocity analysis is often a underdetermined problem. We present a new finite-offset depth tomography scheme that overcomes the problems of non-linearity and allows us to perform automatic dense velocity analysis in structurally complex areas were classical linear methods fail. We demonstrate the advantage of the new tomography scheme on a deep offshore Gulf of Mexico dataset from the Green Canyon area.

Application of 3D Interbed Multiple Attenuation in the Santos Basin, Brazil

Imaging of pre-salt reservoirs in the Santos Basin can be significantly affected by the presence of strong interbed multiples in the data. These multiples can be predicted using a data-driven, true azimuth convolution method similar to surface-related multiple elimination (SRME), and removed using a suitably constrained subtraction technique. We discuss the application of this method to Santos Basin data, and present results on 2D synthetic data and 3D real data.

Application of Interbed Multiple Attenuation In the Santos Basin, Brazil

Imaging of pre-salt reservoirs in the Santos Basin can be significantly affected by the presence of strong interbed multiples in the data. These multiples can be predicted using a data-driven, true azimuth convolution method similar to surface-related multiple elimination (SRME), and removed using a suitably constrained subtraction technique. We discuss the application of this method to Santos Basin data, and present initial results on both synthetic and real data from the Tupi oilfield.

RTM Technology For Improved Salt Imaging in the Santos Basin, Brazil

Reverse time migration (RTM) is now recognized as a powerful imaging tool. With its ability to account for rapid spatial variations in the velocity model and to utilize all wavefront information, RTM can produce superior images of the most complex structures. This is why RTM is frequently used to interpret salt structures in regions known to have complex salt geometries like the Gulf of Mexico. With the application of recent advancements such as Vector Offset Output and 3D angle gathers, the imaging capability of RTM is enhanced even further. In this paper we demonstrate that significant improvements result when advanced RTM tools are used for salt imaging even in the Santos Basin in offshore Brazil where the salt geology is relatively simple compared to the Gulf of Mexico.