利用瑞雷面波调查表层结构的可行性分析

FEASIBILITY ANALYSIS OF SURVEYING SURFACE STRUCTURE WITH RAYLEIGH GROUND ROLL WAVE

石油地震勘探记录中的瑞雷面波能量强、衰减慢,可利用时频分析理论来描述其频散分量的时间—频率分布特征。石油勘探中,所关注的地表结构可简化为低速带、降速带和高速基岩三层模型,面波的大部分能量都集中在基阶模态中,形成的频散特征相对简单。因此,利用石油地震勘探记录中的瑞雷面波来调查表层结构是可行的,它具有中等尺度的探测能力。但石油勘探从激发到接收,都采取各种方式来压制面波,因而需要开展多方面的研究:①结合面波、折射初至波和微测井信息的联合反演;②地震记录中适合面波分析的炮检距范围、道间距与表层分辨率的关系;③排列横向地形起伏变化对面波传播规律的影响;④高保真提纯面波信号的方法;⑤运用时频分析提取频散曲线的方法;⑥针对三层结构的面波正反演方法。总之,充分利用地震记录中的面波信息调查表层结构将会为静校正量的计算和地震精确成像提供新的技术手段。

Rayleigh ground roll waves in seismic records are characterized by strong energy and slow attenuation and the time-frequency distribution of their dispersive component can be described through time-frequency analysis. In petroleum exploration, the surface structure can be generalized into a three-layer model, including a low velocity, a deceleration and a high velocity layer. The energy of ground roll waves is largely concentrated in basic-module modality and the dispersive features are relatively simple. Therefore, it is feasible to survey surface structure by using the Rayleigh ground roll waves with moderate detectability. However, various methods are used to suppress surface waves from shooting to receiving in the process of seismic survey, thus research should be carried out in the following aspects: ① joint inversion with surface wave, refraction first break and microlog data; ② offset range and the relation between group interval and surface resolution suitable for use in surface wave analysis; ③ the influences of lateral relief of array on propagation of surface waves; ④ method for Hi-Fi purification of surface wave signals; ⑤ method for extracting dispersive curve through time-frequency analysis; ⑥ forward modeling and inversion methods of surface wave in view of three-layer structure. Surface structure survey by using the surface wave information in seismic records can provide a new method for calculation of static correction and accurate seismic imaging.