Detecção de camadas delgadas usando sísmica de reflexão

Abstract

Improvement of vertical resolution in seismic data is one of the major challenges for the seismic reflection method. The main problem is related to the larger loss of high frequencies relative to the lower ones during seismic wave propagation. As a consequence, the contribution of lower frequencies in the final section is significantly greater than the corresponding one due to higher frequencies. In principle, this situation should not constitute an obstacle to the full recovery of the spectrum, because of the powerful tools available in seismic processing, designed to equalize all frequencies that are present in the data volume. The main reason why these tools in general do not succeed is the presence of noise, for example random noise. Such situation gives rise to a critical frequency, such that all frequencies above it are impossible to recover and, as a consequence, the seismic pulse cannot be made short enough to allow for optimal resolution. Methods to solve the problem by means of random noise attenuation have been extensively investigated and tested without relevant results. The alternative to such techniques is the enhancement of the multiplicity that can be used for stacking. Since the amplitude decays exponentially with frequency, a large multiplicity is necessary in order to attain a significant effective frequency gain. The capability to attain extremely large multiplicity is exactly the main virtue of the Common Reflection Surface (CRS) method. In this paper, we propose the strategy of combining the CRS method with the spectral whitening, a known frequency-recovery technique, so as to optimize vertical resolution in seismic data and, as a consequence, improve the discrimination of thin reservoirs. First tests on synthetic and real data shown in this work are very encouraging and permit to conclude that the proposed approach has a good potential for practical application.