相对折射静校正方法

在那些风化层横向变化剧烈、相邻两个接收点之间静校正值差别很大的地区，采用常规的高程校正和根据小折射或微测井控制点资料作线性内插，已无法求得合适的基准面静校正值。在这种情况下，剩余静校正量已超过反射波波形的1/2周期，即使采用剩余自动静校正方法也不可能取得满意的效果。为了解决上述问题，人们曾提出采用拾取生产记录初至时间计算基准面静校正量的各式各样初至折射法。这些方法均可称为绝对折射法。此类方法的特点是必须确定真正的初至时间，且在计算中要求追踪同一层的折射波，否则就会造成静校正计算误差和出现不闭合的问题。相对折射静校正方法(RRS)则是从共炮点远道记录求取高速折射层的到达时间，并在小折射或微测井控制点数据控制下进行内插计算，求取各炮点和接收点的基准面静校正值。就同一炮记录而言，两道折射波到达的时间差可分为两个部分：一部分是由于地表风化层的变化造成的时差，而另一部分则是由于折射波沿折射界面滑行及由此高速折射层至风化层底界之间旅行时差所引起的。显然，第二部分折射时差应与炮检距呈线性关系；而第一部分时差应是随机的高频分量，这部分时差可通过线性校正方法将其分离出来。由于环境噪声的影响，折射波到达时间很可能存在某些误差。为此，RRS方法要求在一对控制点间计算5至10张共炮点记录的折射时差，再根据控制点数据对每个记录作线性校正求得每个桩号的基准面静校正值。这样，在每个接收点上就会有5个以上的基准面静校正值，然后取其平均值作为该点的校正值。同时还可求得该点校正值的均方根误差。合成记录理论试算的结果表明，用RRS方法求得的基准面静校正值误差一般只在±3ms之内，最大不超过±5ms。两个地表变化较大地区实际资料的处理结果告诉我们，用RRS计算的基准面静校正值与简单线性内插算得的值相差100ms以上；用RRS数据处理的剖面，其结果远比用内插法数据处理的剖面要好。此法能适应于山区等复杂地表区。RRS方法的独道之处是不要求真正的初始时间，也不必追踪同一折射层。该方法使用简便，能很好地控制计算质量。目前，采用RRS方法编制的IBM微机程序已在野外生产中得到广泛的应用。

Relative refraction statics,

In the region where weathered layer varies terribly in lateral direction so that two adjacent receiver points show very big static moveout，appropriate datum static-correetien values can not be calcu-fated using conventional elevation correction and the linear interpola-tion whose control boint data are taken from short-refraction survey and microlog，in such a case，even automatic residual static correction can not be used to bring satisfactory result because residual static correction value is above half period of reflection waveform. People have put forward various first-arrival refraction methods for calcula-ring datum static correction values with the use of first-arrival times in raw seismic data，These methods can be called absolute refraction method，These methods need to determine real first-arrival times and to track the same refraction wave，otherwise statics errors and mis-tie will appear，Relative refraction statics(RRS)includes the essentials:(1)to take the arrival times of high-velocity refraction from far traces of common-shot records，(2)to make interpolation with reference to the control-point data of short-refraction survey or microlog so as to calcu-late datum static-correction values at shotpoints and receiver points，The total refraction moveout between two adjacent traces of a common-shot record consists of(1)the moveout due to weathered layer variation and(2)the moveout between the travel times of refraction waves which go along refractor and then travel from the refractor to the bottom of the weathered layer respectively，It is clear that the second moveout is linear with offset while the first moveout is a random high-frequency component，which can be separated out using linear correction， Errors in refraction arrival times likely appear because of the influ-once of environmental noise，Hence，RRS method requires to calculate the refraction moveouts of 5～10 common-shot records between two adja-cent control points，then computes datum static correction values of each receiver point by making linear correction of each record in light of control point data.Thus，there are more than 5 datum static-correction values for each receiver point，and the resultant correction value at each receiver point can be obtained by taking an average over all datum static-correction values at the point，Furthermore，the mean square error of static correction value at this point can be calculated，The theoretical result of syntl}ietic records show that the error of datum static correction value calculated using RRS is usually less than±3ms，seldom less than ±5ms，The processing results of seismic data collected from two areas where surface condition varies greatly shovr that the difference between datum static correction values calculated using RRS and the linear it tergolation respectively may be above 100 ms at most，and that the seismic sections obtained using RRS is much better than the seismic sections obtained using the linear interpolation，This method is applicable to some complicated areas，such as mountainous district and so on，Its originality is nether calculating real initial time nor tracking same refra-ctor，It is easy and controls quality very well，RRS program for IBM personal computer is widely used in field exploration.