A Study On Corresponding Relationship Between Scattering Wave Characteristics And Heterogeneous Geologic Bodies

With increasing development of exploration for oil and gas, prospecting targets havebecome complex heterogeneous medium. According to scattering theory, in heterogeneousmedium, when the scale of geologic bodies can be comparable to seismic wavelength,seismic wave will produce scattering while it encounters geologic bodies. Different scale andconstitute heterogeneous geologic bodies may produce different seismic wave scattering.Consequently, the distribution and character of heterogeneity can be concluded fromscattering. Furthermore, heterogeneity is always associated with more geologic structure, oiland gas and ore resource. Therefore, it is widely and practicably valuable to study seismicscattering theory in complex heterogeneous medium.Main research contents and conclusions in the article are following.First, complex heterogeneous medium was described using statistical method.Two-dimensional (2-D) random medium model and 2-D random-homogeneous mediummodel were constructed. Two independent autocorrelation lengths (a and b) in randommedium described the mean scale of heterogeneous anomaly in horizontal and deepdirections, respectively. The corresponding relationship between autocorrelation lengths andthe scale of geologic bodies was studied by velocity variation and variance.Second, through solving acoustic wave equation by finite-difference method, models inrandom medium were forward modeled. The results showed that scattering wave produced byrandom perturbations was obviously displayed in seismic section. With lateral autocorrelationlengths becoming larger, scattering event in section gradually became reflecting event. Withdominant frequency of source becoming higher, events in section became fine and short. Forrandom-homogeneous medium, scattering wave appeared within the lower part of sectioncaused by random perturbations.Third, extracting seismic record of single trace, it was shown that scattered wave wasdistributed in total seismic record. Amplitude spectra of three kinds of seismic waves, namelydirect wave, scattered wave, reflected wave, had similar shape under the condition ofdifferent lateral autocorrelation lengths. Energy of direct wave was the strongest in the threekinds of seismic waves. Owing to influence of scattered wave, amplitude spectrum of directwave was distorted as the autocorrelation lengths became larger. Energy of scattered wavewas the stronger one in the three kinds of seismic waves and its amplitude fluctuatedextremely. Energy of reflected wave was the weakest in the three kinds of seismic waves andits amplitude had many peaks.Fourth, the attributes of the three kinds of seismic waves in time and frequency domainwere picked up, and the corresponding relationship between the scale of heterogeneousgeologic bodies and seismic attributes was concluded. When the scale of geologic bodies andwavelength can be comparable or the scale of geologic bodies is smaller than wavelength (a/λ≤1), the attribute values of the three kinds of seismic waves increased as theautocorrelation lengths became larger. When the scale of geologic bodies is larger thanwavelength (a/λ>1), with the autocorrelation lengths becoming larger, the attribute values ofdirect wave and reflected wave decreased and the attribute values of scattered wave had atrend of increase.Fifth, event continuity of scattered wave was discussed by coherence technique, and thecorresponding relationship between heterogeneous geologic bodies and the coherence valueswas concluded. For the small scale model(a<1m,b<1m,a/λ<0.05), with the scale of geologicbodies becoming larger, the coherence values had a trend of increase, but it is not obvious.For the large scale model(a>1m,b>1m,a/λ>0.05), with the scale of geologic bodiesbecoming larger, the coherence values increased distinctly.