广角层速度分析

Interval velocity analysis with wide angle data

江汉石油学院物探系, 江陵434102

Department of Exploration Geophysics, Jianghan Petrolcum Institute, Jianglin 434102

广角层速度分析, 就是对大炮检距条件下获得的地震记录进行层速度分析。即直接利用共炮点(CSP)道集及其相应的水平叠加时间剖面, 在τ-p域内进行运动学层速度反演。从理论上可以证明, 任意给定一个激发点, 则每个地面观测点接收到的反射波和折射波的波至时间可以近似地分解为平面波在激发点的回声时间。与平面波从激发点滑行至观测点的滑行时间px之和(这里的p为平面波出射时的射线参数, x为炮检距)。对简单的倾斜层状介质, 可以从其水平叠加时间剖面上获得各反射界面对应同相轴的时间和倾角, 而此时波至时间的分解, 允许在经过τ-p变换的CSP道集上逐层向下递推反演速度。理论和实践都证明, 此方法求取的层速度精度高于Dix公式, 抗干扰能力较强。与现行层速度分析方法相比, 本方法计算量小。

The wide angle interval velocity analysis is refered to the intcrval velocity analysis for seismic data of Iargc offset. It can be rcalized by pcrforming kinematic interval velocity invcrsion in τ-p domain on CSP gather and corresponding horizontally stackcd time section. The thcory can be established that for any shot point, the arrival time of the reflections and refractions which are received on the ground can be approximately represented by the summation of thc plane wave's echo time τ at the shot point and the plane wave's travel time px from the shot timc to the rcceiver,where p is the ray paramcter of the emerging plane wave and x is the shot-receiver distance. For dipping layered media, the time and dip of each reflection event can be picked up from horizontally stacked time section. And interval velocities can accordingly be inversed downward layer by layer from the CSP gather which is after τ-p transform due to thc seperation of arriva1 times. Theory and practice show that the proposed mcthod generates more precise interval velocity than Dix formula do, is more powcrful in resistance to interference, and takes less computation time compared to the interval velocity analysis method commonly used.