Statistical Characteristics of the Internal Structure of the Seismic Background over a Hydrocarbon Deposit

Abstract

The fine structure of the seismic background in the territory of an oil field was studied using polyspectral analysis and surrogate models. The statistical test for Gaussianity and linearity showed that the natural seismic background in the 1–50 Hz frequency range is a nonlinear process. Bicoherence graphs revealed statistically significant peaks of phase-coupled triplets with a characteristic geometry of peak clustering in the triangular principal domain. To analyze the quasi-noise component of the seismic background, surrogate time series with a randomized phase spectrum were generated, the bispectra of which are free of triplet peaks. Bispectral analysis of surrogate series showed the presence of a non-Gaussian quasi-noise component in the seismic background in the frequency range of 1–6 Hz. Previously, the results of the analysis of the used set of records by two completely different methods, each of which extracts information from different components of the seismic background, quasi-noise and regular, were published. These studies showed that each of the two components contains information sufficient to estimate the total thickness of the productive intervals under the recording point. Based on the results of the bispectral analysis and the features of the algorithms of the two methods, a conclusion was made that the quadratically phase-coupled triplets and the non-Gaussian quasi-noise component in the field territory are manifestations of endogenic seismic emission and are generated by the same nonlinear process developing in the vicinity of an oil-saturated reservoir. The mechanism of seismic emission should be sought in the class of phenomena with quadratic nonlinearity. The statistical characteristics of the internal structure of the seismic background near oil wells have similar features that differ greatly from the statistical characteristics of the seismic record near a “dry” well located outside the reservoir and not producing oil. Previously unknown prognostic features of the oil/water saturation type of rocks have been identified.