四川盆地火成岩发育区地震波传播规律及成像方法

Seismic wave propagation rule and imaging method in igneous rock development area of sichuan basin

多口钻井证实四川盆地西南部地区发育火成岩,火成岩主要分布在龙潭组内部,火成岩发育区地震资料存在岩下地震同相轴连续性较差、反射能量弱等现象,火成岩下屏蔽效应机理不清、岩下地震反射井震标定能量相位差异大,明确火成岩区地震波传播规律是地震资料采集、处理解释的基础。这里从地震波反射透射基本原理出发,阐述了火成岩地层的反射透射能量及对下伏地层的屏蔽机理,利用波动方程地震模拟及偏移,分析了不同火成岩分布模型对下伏地层地震信号的屏蔽作用,采用低频补偿、逆时偏移等方法改善岩下成像质量。结果表明:火成岩发育会不同程度导致下伏地层地震透射能量的衰减,纵向多套火层岩发育时,下伏地层屏蔽效应明显,发育区地震表现为类似生物礁的外形隆起、内部杂乱反射特征,下部多次反射较多且能量较强。通过低频优势频带保护处理、利用全波场波动方程偏移成像等方式可以改善岩下地震成像质量。

Various drilling confirmed in the southwest sichuan basin development of igneous rock,which is mainly distributed in the longtan group interior. The seismic data of igneous rock zones exist rock under seismic event continuity is poorer. The phenomenon such as weak reflection energy,shielding effect mechanism is not clear under the igneous rock. Rock under seismic reflection well seismic energy calibration phase difference is big in clear igneous rock area. Seismic wave propagation law is the foundation of seismic data acquisition,processing and interpretation. In this paper,starting from the basic principle of seismic reflection transmission,this paper expounds the reflection transmission energy of igneous rock formation and the shielding mechanism of the underlying strata,using the wave equation seismic modeling and migration are analyzed under the different igneous rock distribution model on the formation of seismic signal shielding effect,by adopting the method of frequency compensation,reverse-time migration to improve image quality under the rock. The results showed that the development of igneous rock would lead to the attenuation of seismic transmission energy of the lower overburden layer to different degrees. The shielding effect of the lower overburden layer was obvious during the development of multiple overburden layers in the vertical. The quality of seismic imaging under rock can be improved by using low frequency dominant band protection and full wave equation migration imaging.