陆相汕藏中砂泥岩互层时移地震遮掩效应及其对时移地震资料解释的影响

从差异波形特征的角度出发,分析时移地震差异波形特征与砂泥岩互层油藏中油层速度变化的关系.通过建立由5层地层组成的楔形地质模型,运用褶积公式及时移地震求差公式,得到泥岩速度为2 400 m/s和砂岩速度为2 700 m/s条件下,互层中砂岩速度变化±150 m/s的时移地震响应.研究结果表明砂泥岩互层的差异波形是一个多峰复合波,泥岩夹层的厚度是决定差异波形特征的一个主要因素,并且存在一个临界值,即四分之一主波长;如果泥岩夹层的厚度小于这一临界值,就会发生遮掩效应,即顶部油层的时移地震响应可以掩盖中、下部油层的时移地震响应.

Masking of Sand/Mud Interbeds in Non-marine Reservoirs and It''''s Effect on Time-lapse Seismic Data Interpretation

Taking the differential characteristics of the timelapse seismic waveform as a breakthrough point,the relation between the characteristics and velocity of sand/mud interbeds in non-marine reservoirs is analyzed.Under the following conditions,(1)a five-layer model which consists of mud and shale,(2)P-wave velocity in mud is 2,400 m/s,(3)P-wave velocity in sand is 2,700 m/s,and(4)variation in shear wave velocity in sand is 150 m/s,the study simulates the time-lapse seismic waveform of the five-layer model by the use of convolution and time-lapse difference formula.It is revealed that the time-lapse seismic waveform of interbeds is a multi-peak complex wave,and the thickness of middle shale is a critical factor for the characteristics of the seismic waveforms,which has a critical value about to a quarter of wavelength.The masking effect could be created when the thickness of middle shale is less than this value,in the other word,the time-lapse seismic responses of the upper layers will mask those of the bottom lays.