层速度求取方法及速度谱横向密度对速度场精度的影响

用于常规地震数据成像的速度谱数据通常不能满足水平井的钻探需求。为此,借助前人的方法和经验,根据研究区的实际地震、地质情况,在保证参与速度建场数据精确且影响因素相同的前提下,应用不同密度(500m×500m,250m×250m,125m×125m)的速度谱数据进行空变速度建场,重点分析了层速度求取方法和速度谱横向密度对速度场精度的影响,为水平井的顺利入靶奠定了基础。通过对比、分析发现:1当速度谱数据不能控制速度的横向变化时,井间的深度预测结果会产生很大的不确定性,这与速度谱控制点的分布有关;2大间隔速度谱导致局部速度变化被忽略,随着速度谱的加密,速度在水平方向的细节特征更加突出、丰富,明显提升了横向控制能力,有利于提高井间速度场的精度;3通过后验井证明,应用模型迭代求取层速度建场的效果优于Dix公式,但相对于速度谱密度对速度场的影响而言,层速度转换方法的影响相对要小。

Influences of interval velocity calculation method and spectrum lateral density on velocity field accuracy

Velocity spectrum used to seismic imaging cannot usually meet requirements of horizontal well drilling. In order to adapt the need of horizontal well drilling, we use accurate velocity spectrum data with different density(500m×500m, 250m×250m, 125m×125m) but the same influent factors to build velocity field based on seismic and geology situation in the study area. We analyze the influence of interval velocity calculation method and spectrum lateral density on velocity field accuracy, which provides a foundation for targets of horizontal well drilling. The following observations are obtained based our analysis:A. when velocity lateral changes cannot be controlled by spectrum, depth prediction is uncertain. This may be because of different location of control points; B. Local velocity changes caused by velocity spectrum with low density are easily ignored; when spectrum density gets higher, velocity lateral details are more obvious, and lateral control ability of velocity spectrum is also improved and higher accuracy is obtained; C. Based on drilled well tests, interval velocity calculation by model iteration inversion is more accurate than interval velocity calculation by the Dix formula for velocity field construction, but interval velocity calculation methods have fewer influences on the velocity field accuracy.