复杂构造转换波静校正方法研究及应用

Research and application of static correction method for converted waves of complex structures

目前转换波静校正技术方法众多,已成为多分量勘探不可或缺的重要组成部分。然而,这些方法还面临一些实际困难和问题:(1)面波反演法存在面波发散、难以确定频散周期及复杂探区面波信噪比低、频散曲线拾取困难等问题;(2)初至波静校正方法中的层析反演和折射法的转换波初至信噪比低,尤其在复杂探区拾取初至很难;(3)共检波点道集叠加纵波构造约束法要求地下反射界面变化相对平缓或者水平。因此,上述方法目前都不适合复杂构造转换波静校正。为此,提出一种复杂构造转换波静校正方法,具体步骤为:(1)通过层位拉平方法消除转换波静校正构造项,克服层位基本水平的限制。首先拾取P-P波CMP叠加信噪比较高的构造层位,并计算层位拉平投影时差,用投影时差“拉平”叠前数据;(2)将层位拉平数据转换到共检波点域并重新完成共检波点P-P波速度分析,以使共检波点道集的每道速度相同,消除复杂构造横向速度剧烈变化及速度分析精度不高造成的道间动校正误差,既可以使共检波点同相叠加、提高信噪比,又减少了速度精度不高对地震道剩余静校正量的影响;(3)把P-P波构造层位拉平的投影时差转换到P-SV域拉平P-SV波叠前数据,在共检波点域重新完成P-SV波共检波点速度分析,提高P-SV波共检波点道集叠加剖面信噪比和分辨率,最终提高P-SV波共检波点道集叠加层位拾取精度和效率。通过构造层位拉平和共检波点域速度分析,再利用P-P波构造约束转换波静校正方法可提高复杂构造转换波静校正计算精度和效率。

At present,there are many static correction methods for converted waves,which have become an indispensable part of multi-component exploration.However,these methods still face some practical problems:①The surface wave inversion method faces the problem of surface wave divergence and low signal-to-noise ratio of surface wave in complex exploration areas,and it has difficulty in determining dispersion period and picking up dispersion curves.②In the static correction method for the first arrival wave,the first-arrival signal-to-noise ratio of converted waves by tomography inversion and refraction method is low,and it is difficult to pick up the first arrival,especially in complex exploration areas.③The structural constraint method of common detector gather stacking longitudinal wave requires that the change in underground reflection interface should be relatively gentle or horizontal.Therefore,the above methods are not suitable for static correction of converted waves in complex exploration areas.As a result,a static correction method for converted waves based on complex structures is proposed.The specific steps are as follows:①We eliminate the structural items in the static correction of converted waves by horizon flattening to overcome the limitation of the horizontal interface.First,we pick up the structural horizon with a high signal-to-noise ratio in P-P wave CMP stacking,calculate the horizon flattening projection moveout,and use the moveout to flatten the pre-stack data.②We convert the flattened horizon data to the common receiver point domain and complete the velocity analysis of the P-P wave of the common receiver point again so that each common receiver point trace has the same velocity.This process eliminates the inter-trace dynamic correction error caused by the drastic change in lateral velocity in complex structures and the low accuracy of velocity analysis.It can not only enable the common receiver points to realize in-phase stacking and improve the signal-to-noise ratio but also reduce the impact of a low velocity accuracy on the residual static correction of seismic traces.③We convert the projection moveout of the flattened P-P wave structural horizon into to P-SV domain to flatten the pre-stack data of the P-SV wave,restart the velocity analysis of the P-SV wave in the common receiver point domain,improve the stacking signal-to-noise ratio and resolution of P-SV wave common detector gather,and finally enhance the stacking horizon picking accuracy and efficiency of P-SV wave common detector gather.Through structural horizon flattening and velocity analysis in the common receiver point domain,we further use the static correction method for converted waves with P-P wave structural constraints to improve the calculation accuracy and efficiency of static correction of converted waves based on complex structures.