面向粘滞声学介质叠前吸收补偿偏移的等效Q值模型建立——以松辽盆地北部为例

Establishment of equivalent Q-model for pre-stack absorption compensation migration in viscous acoustic media-A case study in Northern Songliao Basin

建立三维等效Q值(Q_(e))模型是实现粘滞声学介质吸收补偿叠前时间偏移的前提。准确建立Q值模型的难度大,阻碍了地震衰减补偿类方法的应用,其中依据反射地震数据的振幅随频率变化关系求取Q_(e),受薄层干涉及数据高频噪声的影响,制约了Q_(e)的准确求取。提出了常数Q值偏移扫描和频带宽度评价Q值的方法。推导出常数Q值条件下粘滞声学介质吸收补偿叠前时间偏移算法,实现快速偏移扫描,获得一组不同Q值的叠前时间偏移剖面和道集,用于Q_(e)拾取。在Q_(e)拾取中,合理选择频谱分析窗口的大小,突出数据的局部特征,为避免薄层干涉引起的主频变化,以频谱宽度最大为准则评价控制点所拾取Q_(e)的合理性,而频带宽度则依据补偿结果的噪声水平确定。利用地层Q值与速度的关系,由偏移均方根速度场求得三维Q_(e)模型。松辽盆地实际地震资料的粘滞声学介质吸收补偿叠前时间偏移结果表明:与常规叠前时间偏移处理结果相比,该方法成像剖面频带展宽近20 Hz,剖面振幅属性与井的符合率提高30%,应用该方法的资料设计部署的多口水平井,均准确入靶,砂岩钻遇率达80%。

A three-dimensional equivalent Q-model(Q_(e))must be established to realize the absorption compensation pre-stack time migration of the viscous acoustic medium.Considering an accurate Q-value model is difficult to establish,the application of seismic attenuation compensation methods has been limited.The Q_(e)is calculated based on the correlation between the amplitude of reflected seismic data and frequency.The accurate calculation of Q_(e)is restricted by thin-layer interference and high-frequency noise.An innovative method for evaluating the rationality of the Q value via constant Q-value migration scanning and the frequency bandwidth is proposed.First,the absorption compensation pre-stack time migration algorithm of the viscous acoustic medium under a constant Q value is derived to realize rapid migration scanning,and a set of pre-stack time migration profiles and gathers with different Q values are obtained for Q_(e)pickup.In Q_(e)pickup,an appropriate size must be selected for the spectrum analysis window to highlight the local characteristics of the data investigated.The maximum spectrum width is used as a criterion to evaluate the rationality of Q_(e)picked up by control points to avoid a change in the dominant frequency caused by thin-layer interference;the frequency bandwidth is determined based on the noise level of the compensation results.Using the relationship between the formation Q value and velocity,a three-dimensional Q_(e)is obtained based on the migration of the root-mean-square velocity field.The results of absorption compensation pre-stack time migration of viscous acoustic medium based on actual seismic data in the Songliao Basin show that compared with the conventional pre-stack time migration processing results,the imaging data frequency band of this method broadened by approximately 20 Hz,and the coincidence rate of the profile amplitude to wells improved by 30%.Multiple horizontal wells,designed and deployed using the data obtained using this method,accurately achieved the target,and the maximum drilling rate of sandstone was 80%.