基于自适应速度趋势函数的约束层速度反演方法

An improved constrained velocity inversion algorithm for geological structures

论文研究了复杂构造区初始层速度约束反演问题。首先得出初始层速度模型的精度对偏移速度建模的质量和迭代稳定尤为重要,常规方法在构造复杂区使初始速度模型产生的误差易导致最终偏移速度模型地质意义失真、真实构造特征掩盖等问题。提升初始速度模型与地下地质特征的匹配和精度成为关键。基于此,论文提出了基于自适应速度趋势函数的约束层速度反演方法。在常规方法的基础上,利用复相关法在时间域剖面上获得地质构造的连续性与变化,并将其作为构造响应算子形成针对性的影响域和权重融入速度趋势函数中,使该函数自适应地质构造特征,提升初始速度模型的精度。再通过对基准速度和速度趋势对深度的梯度进行样条拟合,构建趋势函数的全局高频异常约束,有效预防在构造突变区产生异常高频,进一步增强算法的稳健和可靠性。理论模型和实际数据的测试,验证了本文方法的有效性,反演得到的层速度模型更符合地质规律,并能更好地解决构造复杂区层速度模型的连续性问题,有利于提高复杂构造叠前深度偏移成像精度。

In complex geological regions,owing to complex structures and various small-scale local geological bodies,the conventional initial migration layer velocity modeling method is prone to abnormal oscillation and loss of key details of velocity,thereby making the solution of velocity update fall within the local optimum.In addition,this method makes velocity modeling cannot iteratively update quickly and effectively.Hence,in this study,we propose an improved constrained velocity inversion(CVI)method for complex geological regions,which is based on the traditional CVI method,by forming an adaptive velocity trend function.A three-dimensional composite correlation function was introduced into the inversion equation system,through which the nonconstant influence radii and weights that adaptively change with the geological structure characteristics were automatically obtained,and these nonconstant influence radii and weights were also introduced into the inversion equation system.Meanwhile,we processed the key parameters of the adaptive velocity trend function(i.e.,the velocity of the geological datum and the gradient of the velocity trend function to depth)by piecewise spline fitting,which further globally constrained the velocity model horizontally to significantly avoid lateral high-frequency anomalies in the velocity model.With theoretical and field datasets,the proposed method resulted in constrained interval instantaneous velocity models,which were well-matched and conformed to the geological structure and features,and further facilitated the imaging quality of pre-stack depth migration in complex geological regions.