Data processing CDP as fields of the reflected waves is sufficiently described in the literature, while the methods of working with scattered waves has not been studied. The authors propose a method of preparation of the seismic material to highlight the scattered waves from the General field of seismic data CDP. The recommendations on the choice and selection of procedure parameters, increasing the reliability of the obtained material.
To obtain the scattered wave field was used an original method based on a mathematically exact solution of the inverse scattering problem in the acoustic approximation, according to multiple beams, allowing to obtain a temporary cubes scattered and reflected waves. Cuba and cuts scattered waves are the basis for the prediction of hydrocarbon deposits with fractured reservoir.
The input data for this study was the model of the seismogram(Fig.1), and real seismic 3D content. Methods for the preparation of the seismic material was developed based on the analysis of stacks of scattered waves at different stages of processing, obtained from the data is complicated by various noise without them. The results of processing the scattered wave field for the real environments was correlated with borehole data.
All scattering objects are highlighted on the cut refractors (Fig.3), some brighter, some less (depending on contrast). High-contrast scatterers are visible on the context of the full-field (Fig.2), the average overall discern, but weak is not visible, hide them strong reflected waves. This result will be the benchmark against which to compare the results of future experiments.
The influence of random noise
In the generated model data is added white noise of three different levels of intensity – low, medium and high (with a maximum excess noise level above the level of the useful signal in 2, 3 and 4 times). On the migrated sections reflecting boundary are highlighted easily even in data with high noise level due to the in-phase summation of the reflected hodographs (Fig. 4).
This experiment shows the importance of procedure, noise reduction, and in particular the fact that the scattered wave field is more sensitive to noise than the field of the reflected waves. Weak-contrast refractors can easily be confused with residual noise on the result of the scattered component. As a recommendation for noise abatement procedures during standard processing of seismic data, it is necessary to note the need for a more thorough cleaning from noise, at least in the target intervals (where the expected scattered objects).
To assess the effect of random noise were prepared two sets of data, respectively, received two cubes. Common are the following procedures:
- automatic revision;
- the statics correction;
- surface-consistent amplitude correction;
An additional procedure for the second cube is the application of cleaning procedures from high-amplitude bursts.
Figure 6 shows the vertical slices of the cube of the reflected waves. The cut left visible artifacts of migration on the amplitude of the surges, but they do not interfere with the allocation of the reflecting horizons.
Figure 7 presents vertical slices of the cube scattered waves. The above-described artifacts here look like the most intense anomalies (Fig.7, left).
In the presented example, we can verify that the residual interference can give false anomalies scattered wave, obscures a real anomaly, such as that associated with faults. Thorough cleaning of seismograms on the one hand allows to suppress the noise, preventing the allocation of the scattered waves, on the other hand too rigid parameters, cleaning procedures, it is possible to suppress the amplitude associated with refractors.
The suppression of random noise is the most important step in the preparation of seismograms to calculate the scattered component. Selection of parameters of the cleaning procedures necessary to control, receiving slit scattering of waves and coordinating them with geologicheskim structure of the study area. Also, this process is iterative and can be repeatedly korrektiruete based on the data of geological and geophysical interpretation.
Studies have shown that the scattered wave is very sensitive to random and coherent wave interference, which appear either as a false anomaly, or create a background noise that complicates the allocation of anomalies associated with geological discontinuities (fracture zones). The underestimation of medium – and high-frequency statics leads to the appearance of false anomalies due to incomplete removal of the reflected component, and long-period statics – wrong localization of anomalies in the plan. The amplitude of heterogeneity is also manifested in the form of false anomalies in the scattered wave field. Using special instructional techniques developed during the research, we developed a new processing sequence, which allowed us to obtain reliable seismic material scattered waves to improve the efficiency of interpretation and accuracy of prediction of hydrocarbon deposits associated with fractured-type reservoirs.
- Kremlev A.N., Erokhin G. N., Starikov L. E., Rodin S.V.  Fracture and cavernous reservoirs prospecting by the CSP prestack migration method. 73th EAGE Conference & Exhibition. http://earthdoc.org/detail.php?pubid=50142
- CSP is a comprehensive approach to the problems of search and microseismic monitoring of hard-to-recover reserves of hydrocarbons / G. N. Yerokhin, A. N. Kremlev, A. V. Kirichek, E. V. Anokhina et al. / / Collection of scientific works “ВНИИНЕФТЬ” «Technologies of increase of efficiency of development of oil fields». Issue 152. P. 45-64. Moscow, 2015