Musa Maharramov

Localized Image-difference Wave-equation Tomography

Current wave-equation tomography techniques based on migrated image differences, such as those observed in 4D data sets, use the image difference as a measure of velocity misfit. Computation of the objective function gradient is accomplished by the adjoint application of the derivative of the imaging operator to this image difference. In all techniques developed to date this process is carried out by computing the gradient over a relatively large number of depth steps, and then optimizing the objective function globally over the entire range. In this abstract, we extend this concept to compute the gradient and objective function locally, within several or even one depth step at a time. In principle, for objective functions that are sharply peaked around the global minimum, and have other minima elsewhere, this localization should reduce the possibility of falling into a false minimum, and significantly reduce the number of iterations required in the optimization. In addition, since the velocity is optimized in depth as the extrapolation proceeds, the method is significantly more immune to cycle-skipping at higher frequencies than global methods.

Azimuthal velocity uncertainty: estimation and application

Azimuthal velocity models for HTI (Horizontal Transverse Isotropy) media are extensively and widely used for land seismic exploration in North America, North Africa and the Middle East. A surface fitting technique honouring all azimuths can invert for an HTI velocity model, which can then be used to perform azimuthally dependent NMO to flatten the CMP gathers. When performing the velocity inversion it is important to estimate the degree of confidence in the estimated velocity model. The main subject of this paper is velocity uncertainty estimation. Furthermore, we investigate the estimated errors in the model parameters with varying acquisition direction for various offset-azimuth distributions including azimuthal sectors and Common Offset Vector (COV) classes. The application of the technique to WAZ land data from Algeria illustrates the strength of the proposed technology.

Azimuthal AVO Analysis: Stabilizing the Model Parameters

AVO is an important tool in the interpretation of seismic data. Azimuthal AVO models (AVAZ) have been used to characterize fracture distributions and directions in HTI (Horizontal Transverse Isotropy) media. The main subject of this paper is a method for the stabilization of AVAZ parameters. We present an extension of the technique of Whitcombe, Dyce, McKenzie and Hoeber (2004) for gradient stabilization in the standard 2-term AVO model given by the Shuey equation to the case of Ruger and Tsvankin’s (1997) azimuthal AVO analysis. We also investigate the estimated errors in the AVAZ model parameters with varying HTI isotropy plane direction for a selection of offset-azimuth distributions, including azimuthal sectors and Common Offset Vector (COV) classes. The application of the technique to WAZ land data from Algeria illustrates the use of the techniques.