Soazig Le Bégat

Practical aspects and applications of 2D stereotomography

Stereotomography is a new velocity estimation method. This tomographic approach aims at retrieving subsurface velocities from prestack seismic data. In addition to traveltimes, the slope of locally coherent events are picked simultaneously in common offset, common source, common receiver, and common midpoint gathers. As the picking is realized on locally coherent events, they do not need to be interpreted in terms of reflection on given interfaces, but may represent diffractions or reflections from anywhere in the image. In the high‐frequency approximation, each one of these events corresponds to a ray trajectory in the subsurface. Stereotomography consists of picking and analyzing these events to update both the associated ray paths and velocity model. In this paper, we describe the implementation of two critical features needed to put stereotomography into practice: an automatic picking tool and a robust multiscale iterative inversion technique. Applications to 2D reflection seismic are presented on syn...

2D Walk-Away Transmission Stereotomography

We present a 2D slope borehole tomography method handling walk-away transmitted data. The specific parameterization of stereotomographic model, including both velocity field and ray parameters, leads us to propose an original way to process direct arrivals at well : pairs of direct arrivals are created and processed as surface reflected data would be. Such an approach allows to keep a common inversion formalism and to perform final model QC. Moreover, specific information brought by direct arrivals, such as one way travel times, are introduced in the inversion process as a priori information. This approach was tested on synthetic picks and applied to a real data set.

Preserved Amplitude Depth Imaging : Application to an OBC Line (Mahogany)

We present an application of our D elastic prestack depth processing sequence to an OBC line recorded on the Mahogany eld This sequence is based on ray tracing in smooth velocity models and oriented towards amplitude preservation Common Image Gathers CIG in the angle domain are computed by P P and P S migra tion inversion using a smooth Vp velocity macro model and a Vs velocity macro model deduced from the Vp model by a D law