﻿ 基于一步法层析速度建模方法建立
 地球物理学报  2021, Vol. 64 Issue (4): 1412-1418 PDF

Establishment of an one-step method for modeling tomographic velocity
XU JiaLiang, ZHANG Bing, WANG WeiHong, SHI Ying
School of Earth sciences, Northeast Petroleum University, Daqing 163318, China
Abstract: The modeling of tomographic velocity requires the use of migration results to update and iterate the layer velocity field. When the velocity is not accurate, the phase axis will bend; this kind of bending in the geophysics field is called residual curvature. In this paper, the residual curvature is analyzed in common domain image gathers, and a concept of the true residual curvature is proposed, which includes zero offset residual curvature and non-zero offset residual curvature. These two kinds of residual curvature have great influence on velocity update. According to this concept, a new method of true residual curvature tomography is proposed in this paper. This method can make the layer velocity model updating convergence more fully. Proved by the model data and actual data, the proposed method is effective and feasible. Compared with the conventional method, our method has faster convergence speed and higher accuracy. It can ensure the precision of the modeling layer velocity field and enhance the calculation efficiency. It saves a lot of time for subsequent migration imaging and other processes.
Keywords: Tomography    One-step method    Implicit residual time difference    Iterative update
0 引言

1 算法建立

 图 1 常规剩余时差层析成像 (a) 1次更新；(b) 2次更新；(c) 3次更新；(d) 4次更新. Fig. 1 Conventional residual time difference tomography (a) First update; (b) Second update; (c) Third update; (d) Fourth update.

 图 2 隐式剩余时差 Fig. 2 Implicit residual time difference

 图 3 局部偏移距观测系统 Fig. 3 Local observation system of migration offset

 (1)

V1为剩余速度，当利用比真实速度偏大的偏移速度进行波场延拓时，上述关系式可表示为：

 (2)

 (3)

 (4)

 (5)

ΔZ1为显式剩余时差：

 (6)

 (7)

 (8)

 (9)

 (10)

 (11)

2 模型试算

 图 4 正演速度模型 Fig. 4 Forward velocity model
 图 5 单炮记录 Fig. 5 Single shot recording

 图 6 (a) 初始速度模型；(b) 常规方法；(c) 本文方法 Fig. 6 (a) Initial velocity model; (b) Conventional method; (c) Our method

 图 7 (a) 常规方法；(b) 本文方法 Fig. 7 (a) Conventional method; (b) Our method
3 实际数据应用

 图 8 (a) 常规层析方法速度建模结果；(b) 本文提出方法速度建模结果；(c) 抽取围井速度曲线与实钻声波测井速度曲线比较 Fig. 8 (a) Velocity modeling results by conventional tomography; (b) Velocity modeling results by new method; (c) Comparison of velocity curves of extractive circum-well and acoustic logging in real drilling

 图 9 (a) 常规层析方法偏移道集; (b) 本文方法偏移道集 Fig. 9 (a) Migration gathers by conventional tomography method; (b) Migration gathers by new method
4 结论

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