广角地震反射在四川盆地超深储层勘探中的应用

Application of wide-angle seismic reflection to exploration of ultra deep reservoirs in Sichuan Basin

当地腹存在高速屏蔽层时,高速层对地震波向下传播及深部地层反射信息向上传播都起到屏蔽作用,使得深部地层的反射信息难以获取。地震勘探中,当炮检距增大到一定程度或入射角到达临界角时,可接收到一种特殊的波——广角反射波,对其处理成像可以提高深层反射能量,从而提高地震资料品质。针对四川盆地震旦系等超深储层,开展了广角反射地震资料采集与处理的研究与应用。结果表明:①四川盆地寒武系、震旦系超深地层,是可以获得较好的广角反射资料的,采集中最大偏移距应在20 km左右,且要有足够的覆盖次数;②广角反射的偏移距大,受球面扩散和地层衰减的影响严重,在采集中应考虑更大激发能量;③广角反射资料的去噪处理和动校正是影响成像的关键技术,通过循序渐进的逐步去噪、分频去噪、多域去噪,可以得到高信噪比资料,利用各项异性+4次高阶动校正方法可以较好地解决动校正问题;④广角反射波与正常地震反射波存在相位变化,且相位随入射角的变化而变化,二者的有机叠加还需进行精细的相位校正。

A high-velocity layer may shield one downward propagation of seismic wave and another upward propagation of reflection information from deeper strata.As a result,if this shield layer exists in the subsurface,it is difficult to obtain the reflection information of deeper strata.In seismic exploration,when offset increases to a certain extent or an incident angle reaches critical value,a kind of special wave called wide-angle reflection wave can be received.And its processing and imaging can increase reflection energy of deeper strata in order to improve seismic-data quality.So,both acquisition and processing of wide-angle reflection seismic data were studied and applied to ultra deep Sinian reservoirs,Sichuan Basin.Results show that,(1)better wide-angle reflection data can be acquired from ultra deep Cambrian and Sinian reservoirs.In the process of data acquisition,the maximum offset shall be about 20 km and the fold shall be enough;(2)its offset is large and seriously affected by spherical spread and formation attenuation,so it is recommended to apply stronger excitation energy in the process of acquisition;(3)noise-removal processing and normal moveout(NMO)correction of wide-angle reflection data are the key technologies affecting imaging results.The data with high signal-to-noise ratio can be obtained by carrying out step-by-step noise removal,frequency-division noise removal,and multi-domain noise removal gradually.The problem of NMO correction can be better solved by means of anisotropy+quartic high-order NMO method;and(4)the wide-angle reflection wave is different from normal seismic reflection wave in term of phase,and the phase varies with incident angle,so the organic superposition of both waves needs fine phase correction.