南海北部中生界地震成像制约因素分析

Constraints on mesozoic seismic imaging in the Northern South China Sea

南海北部中生界油气勘探积累了多个年度、多次采集、多种处理方案的地震资料,但地震成像品质总体上仍难以满足目前中生界油气勘探研究需求,对制约地震成像的影响因素认识不一,缺乏系统对比论证。通过对地质背景及沉积特征的分析,以现有二维地震资料为基础,建立典型地质结构模型并正演模拟,对制约中生界地震成像品质的地质、地球物理因素进行剖析对比和论证,从定性和定量的角度明确了不同地质条件下造成现有地震资料品质差的主控因素。研究表明,制约中生界地震成像的主要因素是海底及中新生界之间的两个强反射界面、中生界地层内部波阻抗差异小所导致的低信噪比;绕射波、多次波等各种干扰波异常发育使有效信号难以识别和成像;崎岖海底造成照明能量散射等。南海北部中生界制约地震成像因素的明确为后续中生界地震数据采集、处理提供了有效指导及技术支持,并进一步提出通过适当加大震源容量、提高覆盖次数、深沉放枪缆、高维度,获得更多深层有效反射波能量的采集建议;通过自适应鬼波压制、多域提高信噪比处理及基于频率谐振能量补偿等技术解决弱反射问题,宽频组合解决多次波发育问题,基于地质、折射波增强速度规律认识,沿层高密度速度拾取提高速度分析精度等处理建议。

There are different vintages of seismic data acquired and processed using different parameters in the northern South China Sea,but imaging quality is not good enough for Mesozoic hydrocarbon exploration.It is necessary to conduct an in-depth study of major controls on seismic imaging.Based on available 2D seismic data,we investigate geologic setting and sedimentation in this area and perform forward modeling of the representative geologic framework to dissect geologic and geophysical factors related to seismic imaging of the Mesozoic Erathem and establish major controls on seismic imaging qualitatively and quantitatively in different geologic conditions.The major controls include two strong reflection boundaries at the seabed and Cenozoic bottom,low signal to noise ratio caused by small impedance contrasts inside the Mesozoic Erathem,various disturbing waves such as diffracted waves and multiples that blur effective signals,and scattered illumination energy induced by irregular seabed.The in-depth study of major controls on seismic imaging offers support to seismic data acquisition and processing targeting the Mesozoic Erathem in this area.Corresponding acquisition solutions include increasing excitation energy,folds,sinking depth of air gun cables,and dimensions to obtain more deep-zone reflection energy.Corresponding processing solutions include self-adaptive ghost suppression,multi-domain high signal-to-noise ratio processing,and energy compensation based on frequency resonance to address the issue of weak reflections,broadband integrated filtering to attenuate multiples,and high-precision velocity analysis through along-horizon high-density velocity picking based on the understanding of geology and refracted waves.