转换波处理关键技术及应用——以四川盆地沙溪庙组致密气藏为例

Key techniques for converted-wave processing:Examples from tight gas reservoirs of Shaximiao Formation,Sichuan Basin

四川盆地中部地区中侏罗统沙溪庙组为三角洲前缘沉积,水下分流河道砂体发育,储层的非均质性强,仅根据纵波地震资料难以准确刻画出河道甜点。为此,2020年在川中QL地区采集了三维多波地震资料,通过对原始地震资料的分析,攻克了转换波处理难点,形成了一套基于转换波综合静校正、分步多域联合噪声压制、各向异性四参数速度分析、OVT域叠前时间偏移的关键处理技术及流程。处理结果表明:(1)形成的处理技术与流程合理,获得了波组特征清晰、信噪比较高、浅层同相轴连续性好、偏移归位合理的转换波地震资料;(2)通过转换波合成记录标定对比,目的层段的波形特征、波组关系与井旁地震道吻合较好;与纵波合成记录对比,两者波组特征相似,能满足联合解释的要求;(3)转换波地震资料刻画河道形态与纵波相似,但河道砂体更宽,分布范围更广并且河道的边界更清晰。

As a sort of deltaic front deposition with well-developed underwater distributary channel sandbodies,the Middle Jurassic Shaximiao Formation in central Sichuan Basin characters strong heterogeneity.It is difficult to accurately depict channel sweetspots solely based on P-wave seismic data.So,some original 3D multi-wave seismic data acquired from QL area of central basin was analyzed in 2020.Afterwards,a set of key techniques and processes have been developed for converted-wave processing in accordance with comprehensive static correction of converted wave,step-by-step multi-domain joint noise suppression,anisotropic four-parameter velocity analysis,OVT domain prestack time migration(PreSTM).Results show that(i)the developed techniques and processes are reasonable,and the obtained converted-wave data enjoys clear wave group characteristics,high signal-to-noise ratio,good continuity of event in the shallow,and rational migration homing;(ii)after calibration on synthetic seismograms of converted wave,it is found that both waveform characteristics and wave group relation in the target are in good agreement with seismic traces near borehole.Comparison with the synthetic seismograms of P-wave reveals similar characteristics of both converted-wave group to P-wave group,which are qualified for a joint interpretation;and(iii)the channel geometry depicted from the converted wave resembles that from the P-wave,but wider for the channel sandbody with larger extension and more vivid sandbody boundary.