Francisco Ortigosa

Evaluation of 3D RTM On HPC Platforms

Reverse Time Migration (RTM) has become the latest chapter in seismic imaging for geologically complex subsurface areas. In particular has proven to be very useful for the subsaly oil plays of the US Gulf of Mexico. However, RTM cannot be applied extensively due to the extreme computational demand. The recent availability of multi-core processors, homogeneous and heterogeneous, may provide the required compute power. In this paper, we benchmark an effective RTM algorithm on several HPC platforms to assess viability of hardware.

3D Reverse-time Migration With Hybrid Finite Difference-pseudospectral Method

We propose a 3D reverse-time migration (RTM) using an hybrid Finite Difference (FD) pseudospectral algorithm to solve the two-way acoustic equation. This mainly consists of forward-backward 2D FFT in lateral dimensions (x-y plane) and 1D FD in the depth dimension. This algorithm allows us to get high order accuracy and simplifies the computation of cross derivatives. Therefore our RTM allows to deal with the case of 3D isotropic media, VTI media (Zhou et al., 2006b) and 3D TTI media. The 3D TTI media case lies on a new anisotropic wave equations system (Lesage et al., 2008), which is an extension of 3D VTI media (Zhou et al., 2006b) and 2D TTI media equations (Zhou et al., 2006a) of Zhou et al. . This system is based on the combination of two 3D rotations which permits us to deduce 3D TTI equations from 3D VTI equations. In this work, we recall the formalization for 3D isotropic, 3D VTI and 3D TTI media, we also describe the implementation of the method to solve the proposed 3D TTI equations. To validate our proposal, we carry out impulse response experiments for modeling and migration.

Speeding up RTM Velocity Model Building beyond Algorithmics

Summary. In this paper we show the unique role of Reverse Time Migration (RTM) as tool for Velocity Model Building (VMB). But for this new use of RTM we need a relative speed up of two orders of magnitude in processing. We discuss how to achieve this target beyond algorithms.

3D migration of a simulated wide‐azimuth towed‐streamer survey

A 3D synthetic wide-azimuth towed-streamer (WATS) dataset is migrated with different migration techniques. These migration techniques are suited for imaging complex overburden. First, a wave-equation method based on a oneway propagator is used. Second, a two-way method that utilizes one-way propagators for the wavefield extrapolation downward and upward is tested. Finally, a method based on the solution of the two-way acoustic wave equation, also known as Reverse Time Migration (RTM) is selected.

Geologically Constrained Full Waveform Inversion – Theory

The waveform inversion problem is inherently ill-posed. Traditionally, regularization terms are used to address this issue. For waveform inversion, where the model is expected to have many details reflecting the physical properties of the Earth, regularization and data fitting can work in opposite directions, slowing down convergence. In this paper, we constrain the velocity model with a model-space preconditioning scheme based on directional Laplacian filters. This preconditioning strategy preserves the details of the velocity model while smoothing the solution along known geological dips. The Laplacian filters have the property to smooth or kill local events according to a local dip field. By construction, these filters can be inverted and used in a preconditioned waveform-inversion scheme to yield geologically meaningful models. We illustrate on a 2-D synthetic example how preconditioning with non-stationary directional Laplacian filters outperforms traditional waveform inversion when sparse data are inverted for. We think that preconditioning could benefit waveform inversion of real data where (for instance) irregular geometry, coherent noise and lack of low frequencies are present.

Seismic modeling for structure interpretation in Venezuela's Sipororo Field

We used seismic modeling and imaging to verify the structural interpretation of a seismic section from a geologically complex area in an onshore field in Venezuela. By analyzing PSTM image problems and combining with nearby well information, we derived a new structure/velocity model, and reproduced the image problems by prestack time migration of the synthetic seismic data acquired from this new structure model.

Modeling of wide‐azimuth towed‐streamer surveys with high‐performance computing

Subsalt imaging in deepwater is still a challenging process even with high quality data and sophisticated algorithms. The reasons are usually poorly defined velocity models and illumination effects in general. Wide-azimuth data acquisition has proven to yield some of the required information (Regone, 2006; Herrmann et al., 2007). However, there is still more investigation required to find the proper survey acquisition geometry for different imaging algorithms.

Reservoir characterization in Burgos Basin using simultaneous inversion

This paper summarizes results obtained in the identification of sandy geobodies that have potential gas accumulations in an area of Burgos Basin.

Cascaded Sweeps- A Method to Improve Vibroseis Acquisition Efficiency: A Field Test

One of the techniques introduced in the last decade to address the improvement in productivity for vibroseis land acquisition was the cascaded sweep method (Andersen, 1995; Moerig et al., 2001). The potential to reduce the acquisition time by using this method comes from reducing the listening and system resetting time by concatenating the sweeps. In the summer of 2004 Repsol-YPF and WesternGeco conducted a field experiment in the Reynosa-Monterrey Block, Mexico, to determine if the use of the cascaded sweep method could be beneficial for the seismic exploration program planned for this block. In this article we present the results of this field experiment.

Simple and Efficient Preconditioning for Full Waveform Inversion in the Context of Seismic Imaging

Full Waveform Inversion is an ill-posed problem. As such, it needs mathematical and numerical tools to improve convergence and avoid falling into local minima. This is a crucial issue, especially when using bad starting models for inversion. The question addressed here is whether Full Waveform Inversion should be suitable for seismic imaging. To answer this problem, we simulate a simple seismic experiment that consists in two square velocity anomalies surrounded by a homogeneous medium. The difficulty here results in the homogeneous starting model used for inversion and the acquisition design that is not suitable for inverting this kind of features. Because the physical problem shows mostly reflective behaviour, retrieving model parameters is very challenging. Nevertheless, we will show that the preconditioner presented in this work allows us to recover accurately both position and velocity values of the reservoirs, leading to very precise images of both anomalies after applying Reverse Time Migration.