正演模拟技术在地震采集设计中的应用

The application of forward modeling technique in seismic acquisition design

随着地震勘探开发的不断深入和发展,地震勘探的主战场逐渐向复杂地区转移.复杂地区既指地表条件复杂的地区,也指地下地质构造和地层条件复杂的地区,这些都对地震勘探提出了新的挑战和更高的要求.地震正演模拟正是开展此类问题研究的一个重要手段和方法.目前市场上具有正演模拟功能的软件大多是根据射线理论采用射线追踪的方法来完成正演模拟的,这种方法不能很好地反映地震波的动力学特征,特别是在复杂地区难以得到正确的结果.本文利用高阶有限差分有效克服了常规有限差分算法求解波动方程的频散问题,并以高效的OpenMP并行计算模式进行了并行优化,较大程度上提高了正演计算的速度和精度;同时实现了二阶Higdon边界条件,改善了边界吸收效果;也在一定程度上提高了计算速度.塔中地区主要目的层埋藏深,逆断层发育,地震反射特征复杂,增加了地震勘探的难度.本文依据该地区的地质模型,利用波动方程正演技术论证了该地区的地震采集观测系统,为该区地震采集观测系统的设计提供了科学依据.

With the further development of seismic exploration and exploitation,the main field of seismic exploration is gradually turned to the complex regions,which not only refer to the areas with complex surface conditions,such as mountainous region,hill,Gobi,desert,loess covered terrains and so on;but also refer to the areas with complex subsurface geological structure and complex formation conditions,such as complex fault block areas in the east China,overthrust zones in western China and coal bed blind zones in Ili basin etc.New challenges and higher requirements are made on seismic exploration by all these.Aiming at difficulties which face in seismic exploration,seismic forward modeling is an important means and methods to perform the study of such problems.For time being the software in the worldwide market which has the function of seismic forward modeling mostly uses the method of ray-tracing to complete forward modeling based on the ray theory,which cannot reflect well dynamics characteristic of seismic wave,therefore correct results can＇t be obtained in the complex area.Although forward modeling module was used based on sonic wave equation for some kinds of software,second-order finite difference was used,the speed is therefore slow,and the precision is also low,it＇s difficult to be widely applied in real production.In this paper,by using high-order finite-difference,the dispersion problem of solving wave equation is effectively overcome compared with conventional finite-difference algorithm,and efficient OpenMP parallel computational model is used for parallel optimization,the speed and accuracy of forward calculation is improved to a large extent;meanwhile second-order Higdon boundary condition is realized and the effect of boundary absorption is improved to increase the computational speed to some extent too.The buried depth of main target layer in Tazhong region is very deep,reverse faults are developed in this region,the characteristics of seismic reflection are also complex,which increase the difficulty of seismic exploration in this region.Forward modeling is an important technology to carry out seismic method study in this area.In this paper based on the geological model in this region,geometry system of seismic acquisition is verified by using wave equation forward modeling technique,and a scientific basis is provided for seismic acquisition geometry design in this region.