How to Acquire Even Fold Distribution in A Converted-Wave Seismic Geometry

This paper proposed a new strategy for designing even converted-wave geometries with binning, calculating fold and selecting roll distance. Through analysis by the surface stacking charts, the projection positions of conversion points on horizontal direction regularly shift with two kinds of period. One is Common-Shot-Conversion-Point Interval (CSCP Interval) and the other is Common-Receiver-Conversion-Point Interval (CRCP Interval). If the two periods have common divisors and the bin size is several multiples of the maximal common divisor, the fold distribution will be even. Otherwise, a parallelogram consists of the conversion points on the surface stacking chart. One side is the total length of conversion points of the common receiver gather and the other is that of the common source gather. Based on the magnitude relationship of the two sides, converted-geometries can be divided into two kinds of pattern. Each kind of pattern has its special formula for calculating fold and roll distance. If the fold is not even, several certain parameters with the fixed velocity ratio must be changed according to the proposed method. Furthermore, the new strategy for converted-wave geometries can be also used for primary wave geometries.