大陆架科学钻探CSDP-2井的垂直地震剖面测量

Vertical seismic profiling survey on the Well CSDP-2 of the “Continental Shelf Drilling Program”

南黄海海相地层的地震波场特征和层位标定一直是困扰地震勘探的重要问题.为了近距离、高精度和高分辨率地观测井周围构造特征和岩石性质引起的波场变化,为地震资料的采集、处理与解释提供地震波衰减规律、速度与层位标定等信息,对大陆架科学钻探CSDP-2井实施了近零偏移距垂直地震剖面(VSP)观测.针对海相地层顶部强反射界面地震波穿透难的问题,采用了大容量气枪震源并设计了气枪阵列组合方式,提高了激发地震波的能量,获得了强反射界面之下清晰的PP、PS下行波和上行波信号.采用了三分量偏振合成、组合滤波和波场分离等处理方法,对VSP观测数据进行处理,获得了海相三叠系-志留系的精细的纵波、横波速度结构和地层吸收因子等物性数据,建立了钻井地层、测井、VSP上行波和多道地震剖面对应关系,实现了不同尺度的地质和地球物理属性资料的有效衔接,标定了钻井地质剖面上各深度地质体的地震反射特性,厘定了过井地震剖面上反射同相轴的地质属性.此次观测取得的纵波、横波速度信息,成为建立南黄海海相地层速度模型主要的资料来源,也是地震资料的岩性反演处理不可缺少的信息.

Seismic wave field characteristics and layers calibration of the marine strata in the South Yellow Sea Basin(SYSB)have always been crucial problems in seismic exploration.In order to reveal the feature and velocity of seismic wave attenuation,and layers calibration during seismic data acquisition,processing and interpretation process,a close,high precision,and highresolution observation of the structural characteristics around the well and wave field changes caused by rock properties were conducted,and a near zero offset vertical seismic profile(VSP)observation was carried out in the well CSDP-2 of the "Continental Shelf Drilling Program".Aiming at solving the difficult of seismic wave downgoing,which was caused by higher wave impedance of marine strata top-interface,high-capacity airguns were used and airguns array pattern were designed to increase the excitation energy.Up-going and down-going PP,PS waves beneath the higher wave impedance interface were recorded in the profiles.The VSP data were processed by applying the three component polarization synthesis,combined filtering,wave field separation methods.The results revealed detailed rock properties during the Triassic and Silurian,such as rock absorbability quality factor(Q),P-wave and S-wave velocity,and the corresponding relationship between drilling-hole formation,logging,VSP upgoing waves and multi-channel data was established.Thus the geological and geophysical attributes of different scales were connected effectively,and the seismic reflection characteristics of geological bodies at different depths of the profile were distinguished,and the geological attributes of refection event across the drilling-hole in the seismic profile were determined.The P-wave and S-wave velocity obtained from the VSP observation in this study will be an important basis for seismic model building of the marine stratum,and will better serve the seismic lithologic inversions in the SYSB.