The interpretation of 3-component seismic data has certain difficulties and requires some specialty because P-wave and converted-wave data show a large differences in travel time, amplitude, frequency, and phase. In this paper, four key steps in multiwave seismic data interpretation are introduced, including PP and PS wave calibration, PP and PS wave matching, combined attribute analysis of PP and PS waves, and combined inversion. Using this combined information distilled from multiwave data we have successfully made lithology and fluid recognition in the SLG 3C3D and SH 3C3D areas.
Multiwave seismic exploration was developed based on pwave seismic exploration. Using p-wave or s-wave sources and a 3-component receiver to record the p-wave, s-wave or converted wave, more information can be acquired from field seismic records. In addition, more useful information can be obtained for imaging of geological structure, defining fracture and porosity, and interpreting reservoir lithology. In practice, multiwave seismic exploration is usually performed in the mode of pwave source and converted-wave receiver, i.e. PP and PS waves are the received data.
Because p-wave and s-wave velocity are varied and travel paths are different, the p-wave and converted-wave seismic data show large differences in travel time, amplitude, frequency, and phase. The interpretation of 3-component seismic data is of certain difficulty and specialty. PP and PS wave horizon calibration and horizon contrast are the basis for multiwave seismic data interpretation. PP and PS seismic wave matching is a necessary step to distill useful information from multiwave data. Combined attribute analysis of PP and PS wave and combined inversion will afford many attributes in predicting subsurface lithology.
P-wave and converted-wave horizon calibration and horizon contrast is an essential step in interpreting multiwave seismic data. But converted-wave calibration is not the same as that of p-waves or s-waves. VSP multiwave seismic logging or p-wave and s-wave sonic logging are required(Zhao, B., 2007).
(1) Using the full wave-train log P-wave horizon calibration is conducted by contrasting a synthetic seismogram in normal incidence with a p-wave stacked section. Because converted-wave data has zero amplitude when the angle of incidence is zero, the converted-wave calibration is made to contrast by a near offset stacked data of the pre-stack synthetic seismogram with the converted-wave stacked section.
(2) Using VSP data Zero offset or non-zero offset of a corridor stack of PP wave and P-SV wave are used to compare with seismic data.
(3) Comparison of reflection and structural characteristics of p-waves and converted-waves When there is only a p-wave well log, and no s-wave log or VSP data, the p-wave calibration must be made first. Then reference points in the converted-wave data must be found by apparent similar wave group in both the p-wave and converted-wave sections. There must also be the establishment of a further position of reflection.
Here we only discuss the event matching problem between the p-wave and converted-wave.
