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三分量垂直地震剖面(VSP)目前所用的检波器,对于水平要素的井下定位来说还没有形成体系。为了对这些检波器接收到的信号进行分析并作出相关,必须严格地标定水平分量的方位。利用直达纵波水平投影线性极化这一假设,就能建立起一个一致的水平坐标系统。有许多方法可用来分析并确定线性极化信号平面投影的方位,诸如矢端曲线图、振幅分析和极化分析法。当振幅分析和极化分析的直方图技术应用于线性极化直达波时,已被证实它是自动定位的一种有效方法。直方图法可以将二维直角坐标(水平分量X、Y)转换为极坐标R、θ(均为时间函数)。假如噪音是随机极化同时信噪比大于1,这时包含着孤立的、线性极化角度为θ’的同相轴在内的θ(t)直方图,将在θ’处出现峰值。由于在水平分量X、Y较小的情况下θ(t)对噪音很敏感,用振幅R(t)或R2(t)对直方图进行加权证明是有效的。从经验上来说,对于直方图的自动检测能给出最好结果的方法(对数据窗的大小、直方图仓(bin)的宽度以及噪音都很不敏感)是利用R2进行加权的。地面冲击震源既产生直达纵波又可产生直达横波。利用与钻井相距350英尺的气爆震源(Dinoseis)所做的垂直地震剖面,是从井深1655英尺处至地表每隔20英尺用电驱动的、紧贴井壁的三分量检波器进行记录,所得垂直分量和水平分量的资料都是优质的。浅的垂直地震剖面的一个实例可用来证实在水平面(H_p)内折射P波能有效地定位,这大大有助于诸横波的相关。继之通过对H_p和垂直分量的取向,最终可作出直达P波矢量(P_d)。与P_d正交的矢量包含了较为纯净的横波,而这种信噪比较高的横波分量更适于进行横波层速度分析。在定向以后,由较强的P波转换而形成的下行S波可以出现在350英尺的深度附近。
The currently used geophones of the three-component vertical seismic profile (VSP) have not yet formed a system for the downhole positioning of horizontal elements. In order to analyze and correlate the signals received by these detectors, the azimuth of the horizontal component must be strictly scaled. Using the assumption of linear polarizations of horizontal P-wave projection, a consistent horizontal coordinate system can be established. There are many ways to analyze and determine the orientation of the linearly polarized signal plane projection, such as the sagittal curve, amplitude analysis, and polarization analysis. When the histogram technique of amplitude analysis and polarization analysis is applied to linearly polarized direct waves, it has been proved that it is an effective method for automatic positioning. Histogram method can be two-dimensional rectangular coordinates (horizontal component X, Y) is converted to polar coordinates R, θ (are time functions). If the noise is randomized and the signal-to-noise ratio is greater than 1, a θ (t) histogram of isolated, linearly polarized events with theta ’’ events will appear at θ ’. Since θ (t) is sensitive to noise in the case where the horizontal component X, Y is small, it is effective to weight the histogram with amplitude R (t) or R2 (t). Empirically, methods that give the best results for automatic detection of histograms (which are insensitive to the size of the data window, the width of the bin, and the noise) are weighted using R2. The ground impact source not only produces direct longitudinal waves but also produces direct transverse waves. Vertical seismic profiles made using a Dinoseis 350 feet away from the well were recorded electronically from a borehole depth of 1655 feet to the surface at a distance of 20 feet from the wellbore close to the three-component geophone The vertical and horizontal components of the data are high quality. An example of a shallow vertical seismic profile can be used to demonstrate that refraction of P waves within the horizontal plane (H_p) can be effectively localized, which greatly contributes to the correlation of shear waves. Then through the orientation of H_p and the vertical component, a direct P wave vector (P_d) can be finally made. The vector orthogonal to P_d contains a purer shear wave, and this shear-wave component with higher signal-to-noise ratio is more suitable for transverse wave velocity analysis. After orienting, the descending S-wave formed by the stronger P-wave conversion can appear near 350 feet.