【作者】 徐秀刚；

【导师】 李振春；

【作者基本信息】 中国石油大学 ， 地质资源与地质工程， 2010， 博士

【摘要】 随着地震勘探和油气开发难度的增大以及油气藏复杂性的增加,对地震勘探精度的要求越来越高,因此要求偏移方法不仅能够得到地下构造的相位信息,还需要得到与地下反射系数成比例的振幅信息,这样,保幅成像技术受到越来越多的重视。共聚焦点技术是一种较新的地震偏移技术,它基于等时原理,通过两步聚焦(即激发聚焦和检波聚焦)来完成叠前地震偏移成像,它的技术优势是在不需要正确速度模型的情况下,只依靠聚焦算子的迭代更新,就可以实现最终速度模型的重建以及最终偏移成像结果的生成。前人基于共聚焦点进行成像,基本上是采用基于射线理论来实现,这种方法的计算效率较高,但是其成像精度不能满足保幅成像的要求,本论文在前人的基础上,采用了基于波动理论来实现共聚焦点技术的两步聚焦,并在此基础上抽取共聚焦点道集,通过考虑波前扩散的影响,设计了消除采集效应和传播效应的保幅算子,采用波动方程的保幅延拓算子,提高算法的保幅性,最终采用保幅型成像条件实现共聚焦点技术的保幅偏移成像。和常规共聚焦点偏移结果相比,基于波动理论的保幅CFP偏移结果成像精度更高,较好补偿了几何扩散造成的振幅损失。为解决起伏地表的影响,本文采用两步聚焦的思路来实现基于共聚焦点技术的基准面重建,该方法进行基准面重建的关键是聚焦算子的生成,通过将聚焦算子作用于炮记录和共聚焦点道集,最终消除起伏地表对于地下构造的影响,和常规时移静校正相比,该方法能更好的消除起伏地表的影响,基于重建后的成像结果其成像精度更高,但其不足之处在于,重建基准面后的记录由于两步聚焦的影响,其信噪比变差,重建后偏移结果的中深层能量变弱,这是今后需要改进的地方。为实现对于复杂地表和地下复杂构造的共聚焦点偏移成像,本论文借助共聚焦点技术中的合成聚焦算子和面炮合成理论,基于波场“逐步累加”的直接下延法实现了基于起伏地表的共聚焦点成像,该方法首先合成起伏地表条件下的合成聚焦算子,然后应用合成面炮理论合成生成共聚焦点道集,最终基于起伏地表条件下的波动方程延拓法生成最终的偏移结果。该方法在选取较少聚焦点的情况下就可以达到和炮域波动方程叠前深度偏移一样的成像效果,计算效率得到了提高。进一步通过波动方程法保幅延拓算子的引入以及采用平滑窗函数的成像条件,实现基于共聚焦点道集的保幅偏移成像。模型资料和实际资料的试处理验证了基于共聚焦点技术进行复杂条件下保幅偏移成像的正确性、有效性和实用性,其和常规偏移结果相对比,其成像的精度更高,对于目的构造的刻画更加清晰,较好的补偿了几何扩散造成的振幅损失。更多还原

【Abstract】 Along with the increasing difficulty of the seismic exploration and oil/gas development,also with the increasing complexity of the reservoir, the requirement of the seismic exploration precision is more and more high, now the migration method not only can offer the phase information of the surface structure, but also can provide the amplitude which is in ratio to the reflection coefficient, then Preserved-amplitude prestack migration is more and more popular.The common focus point technology is a new seismic migration method, it based on the principle of the equal travel time, can realize the migration by two focusing steps (that is focusing in emission and focusing in detection), its technical advantage is that not needing the correct velocity model, by the iteration of the focusing operator, it can get the correct velocity model and final correct migration result. In the past, researchers realize the CFP migration based on the ray theory, the method’s capacity is high, but the migration precision does not satisfy the requirement of the preserved amplitude migration. This thesis based on the wave equation theory come true the two focusing steps, by the wave equation theory get the CFP gather, We fully considere the influences of wave front diffusion, design the amplitude-preserved operator which can eliminate the effect of receivers and propagation, based on the wave equation extrapolation preserved amplitude operator improve the preserved amplitude of the algorithm,finally get the true amplitude migration result of the CFP method by the preserved amplitude migration condition. Comparing the preserved amplitude CFP migration based on the wave theory with the common CFP migration, the precision of the result is higher, it can compensate the loss of the geometric diffusion.We achieve the redatuming based on the common focus point method by the two focusing steps, the key of the method is the generation of the focusing operator, by the redatuming wo can elimate the influence of the rugged topography to the sub-surface structure, its processing result is better than the conventional time shift static, and the shortcoming of the method is the new record after CFP-based redatuming by the influence of the focusing steps has lower S/N ratio, the energy of the middle and deep zone after the redatuming is lower, this is the aspect that we improve in the future.Using the common focus-point technology to the migration of the irregular surface, by the synthesis focusing operator and the theory of synthesis areal source,“wave field downward continuation”based on accumulating step by step is a valid way to solve the problem of irregular surface common focus point migration. The method first synthesizes the synthesis focusing operator of the irregular surface, then uses the theory of synthesis areal source to generate the common focus point gather, and at last gets the migration result based on the irregular surface according to the wave equation continuation. The key of the method is how to combile the CFP technology and the wave equation continuation theory. the calculation efficiency is improved, we can only choose a few of the focusing points, then get the migration result which is similar to the conventional common shot-records gather migration result. Further using the preserved amplitude wave equation continuation operator and the smooth function migration condition,then we can get the preserved amplitude migration result based on the CFP gather. Tests on model and actual data processing show the validity and the practicability on the complex surface migration. Comparing with the common CFP migration, the precision of the result is higher, it has good migriaon quality of the target layer,and can compensate the loss of the geometric diffusion.更多还原