基于起伏地表的合成平面波叠前深度偏移

Synthesized plane wave pre-stack depth migration from rugged surface

实践表明,波场延拓叠前深度偏移比Kirchhoff积分法成像精度高,但计算量大;而平面波叠前深度偏移比炮域叠前深度偏移运算效率高,且成像精度相当,但只适应水平地表。为此,介绍了一种适应起伏地表的合成平面波叠前深度偏移方法,其基本思路是:以地震排列的最高点所在平面为波场延拓起始面,将起伏地表的地震排列观测数据(检波点或炮点)向下延拓到地表最低点所在的水平基准面,实现波动方程基准面校正;在此平面上应用p变换将全部炮点合成为平面波震源,从而使全部炮记录分解成平面波记录;运用下行波方程、上行波方程分别将平面波震源波场、平面波记录波场沿深度方向外推,在每个深度进行波场相关并累加,获得该深度的成像波场值,得到共分角度的平面波偏移道集;将所有不同共分角度的平面波偏移道集按坐标叠加,得到基于起伏地表的合成平面波叠前深度偏移成像结果。四川龙驹坝地质模型的理论试算及四川实际山地资料HNT12线的处理结果表明:基于起伏地表的合成平面波叠前深度偏移成像结果的质量与传统炮域叠前深度偏移的结果相当,但运算效率显著提高,且适应起伏地表。

Pre-stack depth migration by wavefield continuation has higher precision than Kirchhoff integration method,but it has larger computation amount.Plane wave pre-stack depth migration,has higher computation efficiency than in shot domain,the two has almost the same imaging precision,but which is only suitable to horizontal surface. Therefore,we introduced a synthesized plane wave pre-stack depth migration method from rugged surface,which takes the plane of highest point of seismic array as the starting surface of wavefield continuation,the observation data(shot points or receiving points) of seismic array from rugged surface was downgoing continued to the horizontal datum of the lowest point at surface to realize datum correction of wave equation.On the plane,p transform was applied to composite all shot points into source of plane wave and decompose all shot records into plane wave records.Then,dowgoing-wave equation and upgoing-wave equation was separately used to extrapolate source wavefield and record wavefield of plane wave along depth direction.Thirdly,wavefield was correlated and accumulated at every depth to gain the imaging wavefield of the depth and obtain common sub-angle plane wave gather.Finally* all the migration gathers of plane wave with different angles were stacked by coordi- nate to obtain synthesized plane wave pre-stack depth migration result from rugged surface.The testing of numerical model of Longju area and actual data processing of HNT12 line in Sichuan Basin shows that the result of pre-stack depth migration of synthesis plane wave and in shot domain is almost the same,but the former one has higher computation efficiency and is suitable to rugged surface.