典型河流相叠置砂体构型的地震相位特征分析

Seismic phases of typical superimposed fluvial sandstone architectures

河流相储层中由于河道迁移、切削等因素形成的不连续边界常常阻碍了储层内部流体的流动,增大了剩余油气的开采难度。受地震分辨率的限制,这些不连续边界在常规地震剖面上一般难以识别。通过模型试验,提出了一种应用于河流相薄互层砂体的提高频率分辨率的相位谱计算方法,即将一个周期时窗的地震数据末端补零至适当长度,再进行傅里叶变换,求取展开相位谱和积分展开相位,可增加其稳定性;其次,基于典型河流相叠置砂体构型,建立不同纵向高程差的两组砂体叠置模型,分析不同叠置样式的地震相位特征,认为相位异常值与砂体不连续夹层厚度存在定性关系,利用积分展开相位可以较好地识别砂体不连续边界。噪声实验认为信噪比大于5∶1时,识别结果可信。将该方法应用于渤海南部海域某工区实际地震数据,识别出两处砂体叠置区域,其结果与测井识别出的叠置情况吻合。应用结果表明,将地震数据周期时窗尾端补零求取的积分展开相位在识别叠置砂体不连续边界稳定且有效。

Fluvial reservoir discontinuities caused by channel migration and truncation are unfavorable for fluid flow and remaining oil and gas recovery,and seismic resolution is usually not high enough to detect these discontinuities.Based on model tests,we develop a computational method of phase spectrum to increase frequency resolution for identifying thin interbedded fluvial sands.A Fourier transform of seismic data,which are padded with zeros at the end of the time window to make the fundamental period longer and improve robustness,is executed to obtain unwrapped phase spectrum and integration-based unwrapped phase.Based on typical fluvial sandstone stacking configuration,we establish two groups of superimposed sandstone models with different heights to analyze their phase responses.Owing to the qualitative relationship between phase anomalies and discontinuous interbedded sandstone thickness,it is feasible to use integration-based unwrapped phase to identify sandstone discontinuities,particularly when the signal-to-noise ratio is larger than 5∶1.We apply this method to a survey in the southern Bohai Sea and identify two areas with superimposed sands,which agree with log interpretation.The method of padding with zeros and integration-based unwrapped phase is demonstrated to be stable and effective in discontinuity detection for superimposed sandstones.