Conversion Point Estimation By Searching Optimal Angle And Ray Tracing Of Converted Wave

P-SV converted wave exploration is the main body of the multi-wave multi-component seismic exploration, compared to the P-wave exploration, P-SV converted wave exploration can provide a more rich underground petrophysical information, and this play an important role on lithology inversion, extraction of fracture parameters, as well as gas detection. P-SV converted wave data processing is an important conversion wave technology research, and it is more difficulty than conventional P-wave exploration. Due to historical reasons and the hardware and software resource constraints, P-SV converted wave seismic data processing has basically adopted the P-wave seismic data processing models and ideas. However, due to the conversion wave has low frequency, low-speed, low signal to noise ratio, and the characteristics of asymmetric ray paths, for the P-wave processing is relatively mature and stable technology, but can not satisfy the basic assumptions and precision of the converted wave. At present, the main research of P-SV converted-wave processing contents include: wave field separation, conversion point's position gathering, velocity analysis, NMO, CCP gathering, conversion wave static correction, DMO correction and migration imaging.In P-SV converted wave data processing, common reflection point stack and migration imaging need converted wave's travel time and ray path.Therefore, in this paper, we chose the shortest ray path, developed ray tracing algorithm and basic process for converted wave. The the shortest ray path has higher accuracy and efficiency, and it is stable and does not have blind area,.It can trace travel time of all points, apply to any model of complex geological structure, it is a widely used method of ray tracing. Using the the shortest ray path method to model the level of homogeneous (single-layer, multi-layer) formation. This method has been tracking the converted wave P-wave ray path and the S-wave ray path is broken line, longer than than the true ray path length, the calculation of travel time longer than the theoretical value, and this makes the final ray path travel time and location of the deviation. Converted wave ray path is asymmetry. In the level of homogeneous (single-layer, multi-layer) formation, the converted-wave conversion point offset deviation from the center, near the side of the receiving point, the greater the offset,the grater distance the conversion offset point departure from the focal point.In tilted stratum, a smaller offset, the converted-wave conversion point offset deviation from the focal point shot at the near side; with greater offset, converted-wave conversion point deviation from the offset from the first point decreases and then increases ,near the side of the receiving point.The calculation of Converted-wave conversion point puts direct impact on technology development such as:speed analysis, common-conversion point gather, converted wave stack, converted wave prestack migration. In this paper, we propose the method by searching optimal angle to seek conversion points'position, given the computing formula of the level of two-dimensional homogeneous strata (single-layer media, multi-media), tilted strata, and through the establishment of the theoretical model to calculation, in the source point and receiver are determined, calculat the conversion points precise. Compared with the iterative algorithm, the difference of the level of single-layer uniform layer with each point calculated by the method by searching optimal angle (grid spacing of 20m) is samller than the result calculated by iterative algorithm. The biggest difference of the method by searching optimal angle is far lass than 0.01 percentage,and the biggest difference of the three times iteration is bigger than 0.01 percentage; Multi-homogeneous medium, the biggest difference of each point is samller than it calculated by iterative algorithm.The biggest difference calculated by the method by searching optimal angle is less than 0.5 percentage,and the biggest difference calculated by times iteration is bigger than 1 percentage. The method by searching optimal angle has less difference higher precision than three times iteration,and the calculating formula is sample.In this paper, we use ray tracing to model synthetic seismogram of the converted wave. As for the level of uniformity for the formation (single-layer, multi-layer),when time distance curve of the converted wave is not hyperbolic, the curvature of the time distance curve of second reflective layer is samller than the curvature of the time distance curve of firt reflective layer. The time distance curve of the tilted strata the converted wave is not hyperbola,and it is influence by the stratigraphic dip.As for Converted wave data processing, common mid-point stacked profile for P-wave can not be used. Stacked profiles of converted wave should be common reflection point stack rather than common midpoint stack. Breaking point gather and stack are important in conventional of PS converted-wave processing. This paper we discusses the P-wave and S-wave velocity ratio and the depth of the reflecting interface's impact on breaking point,when the P-wave and S-wave velocity ratio is fixed, in the same seismic trace, the shallower the reflective interface,the greater the conversion point deviated from the receiver.To the same reflection depth, the position of the conversion point related to P-wave and S-wave velocity ratio, the bigger the velocity ratio, the greater the conversion point deviated from the center. This shows different speeds are correspond different Common conversion point gathering. When Common conversion point(CCP) gathering,P-wave and S-wave velocity ratio and the depth of the reflecting interfaces should be considered.We discuss the distribution of Common conversion point traces'demodulator probe. In this paper, we establish observing systems for the uniform two-tier level.We use ray-tracing algorithm simulate common conversion point traces, Collected common conversion point traces the first estimates P-wave and S-wave velocity ratio, and then calculating the sampling point position corresponds to the conversion, taking the conversion of the projection in the surface location at the Common Reflection Surface seismic data corresponding to these data, combination or Category may constitute a Common conversion point gather.