1,721,107 research outputs found
ESP Experiments along CROP profiles (03 and 18): remarks on the optimal source-receivers configuration
No full text
Design of crustal acquisitions: Vibroseis vs. Explosive and Expanding Spread experiments
No full text3D fourier reconstruction of irregularly sampled seismic Gathers : analysis of the extended model resolution matrix
No full textFourier reconstruction is basically a linear inverse problem that attempts to recover the Fourier spectrum of the seismic wave-field from irregularly sampled data along the spatial coordinates. The estimated Fourier coefficients are then used to reconstruct the data in a regular grid via a standard inverse Fourier transform (IDFT or IFFT). Unfortunately, this kind of inverse problem is usually under-determined and illconditioned. For this reason the Fourier reconstruction with minimum norm (FRMN) adopts a weighted damped least-squares inversion to retrieve a unique and stable solution. In this work we show how damping can introduce deleterious artifacts on the reconstructed 3D data. To quantitatively describe this issue, we introduce the concept of extended resolution matrix (ERM) and we formulate the reconstruction problem as an appraisal problem. Through the simultaneous analysis of the ERM and of the noise term, we can assess the validity of the reconstructed data and verify the possible bias introduced by the inversion process. Also, we can guide the parametrization of the forward problem to minimize the occurrence of unwanted artifacts. Real data from a 3D marine common shot gather are used to discuss our approach and to show the results of FMNR reconstruction
Iterative deconvolutions to compensate wavelet stretching on 4th order traveltime kinematic
Full text linkSource to receiver distances employed in seismic data acquisition have been steadily increasing and it is now common to work with data acquired with more than 10 km of offset. Sub-basalt exploration and seismic undershooting are just two applications where long-offset reflections are valuable. However, such reflections are often subjected to muting to avoid NMO stretch artifacts, thus causing a loss of valuable information. It is therefore of interest to find ways to avoid the distortions caused by the standard NMO correction and to retrieve these portions of the recorded wavefield for a better use in the processing. To this end we develop a non-stretch NMO correction based on a wavelet estimation and on a iterative procedure of partial NMO correction and deconvolution. To drive the corrections we make use of 4th order traveltime curves, that further extend the offset range of usable reflections. Then we estimate time and space variant wavelets, by means of SVD along the sought traveltimes, that become the desired output for the deconvolution trying to retrieve the original shapes of the partially stretched wavelets. We test our method on a synthetic gather presenting time and offset varying wavelets and noise. This example demonstrate that our new algorithm effectively limits the stretching associated with the NMO correction and enables the recovery of those portions of the stacked sections which are typically ruled out by the mute function in the standard NMO correction
Non-stretch fourth order nmo through iterative partial corrections and deconvolution
No full textSource to receiver distances employed in seismic data acquisition have been steadily increasing and it is now common to work with data acquired with more than 10 km of offset. Sub-basalt exploration and seismic undershooting are just two applications where long-offset reflections are valuable. However, such reflections are often subjected to muting to avoid NMO stretch artifacts, thus causing a loss of valuable information. It is therefore of interest to find ways to avoid the distortions caused by the standard NMO correction and to retrieve these portions of the recorded wavefield for a better use in the processing. To this end we develop a non-stretch NMO correction based on a wavelet estimation and on a iterative procedure of partial NMO correction and deconvolution. To drive the corrections we make use of 4th order traveltime curves, that further extend the offset range of usable reflections. Then we estimate time and space variant wavelets, by means of SVD along the sought traveltimes, that become the desired output for the deconvolution trying to retrieve the original shapes of the partially stretched wavelets. We test our method on synthetic data and we perform a blind test on real data simulating an undershooting acquisition
Vp/Vs Ratios through Multicomponent Velocity Analysis
No full textA key step in the multicomponent data processing is the computation of the Vp/Vs ratios. In this paper we show that a multicomponent velocity analysis can combine information from horizontal and vertical components into a single panel and can therefore improve the accuracy of the velocity estimate. In addition a multicomponent velocity analysis followed by Common Conversion Points binning can indicate the Vp/Vs ratios that produce the optimum focusing of the coherence panel in the case of dipping reflectors. The multicomponent panel, in which the velocity analysis is performed, is obtained by adding in quadrature the horizontal and the vertical responses. One of the main advantages is that the velocity analysis carried out on a single gather facilitates the velocity picking that, otherwise, would have to be repeated for each orthogonal component. Moreover, lithologic bounds on the Vp/Vs ratio can be more easily checked because the trends of pure and converted waves are mapped together. Tests performed on synthetic and real data show that the multicomponent velocity analysis provides accurate velocity estimations even for data at the early steps of processing
- …
