合成声波测井的薄层响应

Thin-bed response in synthetic acoustic log

合成声波测井是一种由地震反射数据转换成层速度的普遍应用方法。只有在零相位全通子波的情况下，利用此法才能得到正确反映层速度变化的结果。对于单个界面的响应，缺乏高频成分使界面清晰度变差；缺乏低频成分使速度值畸变；同时缺乏高频和低频成分，则兼有以上二者的影响、利用简化的界面响应图解可说明单层会成声波测井响应的特征。缺少高频成分对于厚层来说，只降低界面的清晰性，而对于薄层来说则会影响层速度和视厚度。缺个低频成分对甚薄层影响很小，而且随着层厚的增大，速度畸变也增大，甚至在层内出现很大的反向速度异常。同时缺个低频和高频成分，对薄层来说接近于缺个高频的情况，对于厚层则接近于缺少低频的情况。频带的相对宽度（高截频和低截频的比值）决定速度精度的上限。

Synthetic acoustic log is a widelyAiused method for converting seismic reflection datainto interval velocities. Only in the case of zero-phase all-pass wavelets, can the methodoffer good interval velocity variations. So far as the response of a single interface, lackof high-frequency contents results in poor clarity of interface, lack of low-frequencycontents brings distorted velocities, and lack of both of thern causes the above two phe-nornena. Concise diagram of interface response can show the response feature of single-bed synthetic acoustic log. Lack of high frequency contents only darnages the clarity ofthick bed, but influences both interval velocity and apparent thickness of thin bed. Lackof lowaifrequency contents brings little influence on very thin bed; and it causes highervelocity distortion for thicker bed, even terrible inverse velocity anomaly in formation.Lack of both low-frequency contents and high-frequency contents causes the influenceon thin bed which is similar to that resulting from lack of high-frequency, but brings theinfluence upon thick bed which is analogous to that caused by lack of low-frequency con-tents. The relative width of frequency band (the ratio of high-cut frequency to low-cutfrequency) determines the upper lirnit of velocity accuracy.