Research On PS-wave CCP Gather Generation For Tilted Interface

Since the multi-wave and multi-component seismic technology was applied to oil and gas exploration since 1970 s,it has not only been developed for a long term in both the theory and technique,but also has played an increasingly important role in underground seismic prospecting.Converted wave seismic acquisition can obtain both PP-wave and converted(PS)wave data,which is more conducive to predict lithology,fluid property and fracture distribution.However,because of the asymmetry of the propagation path of converted wave and the existence of tilted reflectors,the seismic propagation path becomes more complex.The common converted point(CCP)gathering is related to the quality of a series of seismic processing and interpretation results such as migration,stacking and imaging.Experts and scholars in the world have done a lot of work to locate the common converted point of horizontal interface,but the much more common situation in nature is of tiled reflectors.Although previous studies on CCP gathering of dip reflectors have made progress at a certain degree,most of them focus on processing in two-dimensional situation.Even if method about three-dimensional gathering for dip interface has been proposed before,it was a simple improvement of the two-dimensional calculation,and the calculation error of common converted point is beyond the expectation.The CCP gathering is an important procedure in the converted wave processing,and it is greatly related to the stacking effect of converted wave and the accuracy of S-wave velocity calculation.Therefore,the calculation method of CCP gathering in tilted reflectors has an important influence on the reliability of the conclusion.In this paper,aiming at CCP gathering in dipping strata,based on previous studies,I have carried out the following research and achieved the certain results based on the ray tracing principle.(1)On the basis of the formulas for calculating receiver points in horizontal strata,the formulas for 2-dimensional dip layer are derived.(2)On the basis of the receiver point formula of 2-dimensional in dip strata,3-dimensional model is considered,and the calculation formula and processing flow for 3-dimensional situation are further deduced and obtained.(3)The calculation of 2-dimensional and 3-dimensional common converted points have been tested with synthetic data.(4)To prospect gas hydrate reservoir in the permafrost in Muli Coalfield,Qinghai Province,lines of 2D3 C seismic data had been acquired,and then the common converted point gathering,stacking and imaging are carried out.Compared with the method of CCP gathering on the assumption of horizontal layer,method proposed in this study has been verified with effectiveness and feasibility.