摘要
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
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-correction values can not be calculated using conventional elevation correction and the linear interpolation whose control point 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 calculating 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 calculate datum static-correction values at shotpoints and receiver points.The total refraction moveout between two adjacent traces of a commonshot 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 influence of environmental noises.Hence, RRS method requires to calculate the refraction moveouts of 5～10 common-shot records between two adjacent control points, then computes datum static correction values of each receiver point by makin
出处
《石油地球物理勘探》
EI
CSCD
北大核心
1990年第4期407-428,516,共23页
Oil Geophysical Prospecting
关键词
高程校正
基准面静校正
剩余自动静校正
相对折射静校正
elevation correction
datum static-correction
automatic residual static correction
relative refraction statics
