井间地震波形层析成像在大庆长垣油田的应用

Crosshole seismic waveform tomography in Changyuan Oilfield,Daqing

本文在简要介绍波形层析成像原理的基础上,给出了波形层析反演的主要实现步骤及反演策略。由于实际地震数据往往是有限带宽的,并且缺少低频成分,波形层析成像需要一个好的初始模型以填补低频缺失。在反演每一次迭代过程中同时使用一组频率数据,以抑制数据噪声的影响。在反演中必须对模型进行平滑约束,以降低数据噪声、射线覆盖范围的不均匀和短波长模型参数剧烈变化的影响。本文应用频率域波形层析成像重建了井距230m井间地震速度场。虽然地质情况复杂、速度变化剧烈,使反演问题高度非线性,但是波形层析成像结果还是能够提供真实可信的地质信息。

Based on waveform tomography,this paper discusses the main steps and strategy of the waveform tomography inversion.As real data are usually band limited due to low frequency missing,a good initial model is needed for waveform tomography,to fill in missed low frequency before the inversion.In the inversion stage,agroup of frequencies are used simultaneously in every iteration to suppress noise in the frequency domain.A smoothness constraint on the model in the inversion reduces impacts of noise,non-linearity of the problem,and strong sensitivities of short wavelength model variations.Using waveform tomography in the frequency domain,we reconstruct seismic velocity field between two boreholes with a distance of 230 m.The waveform tomography results provide real and believable geological information that can be tracked between the boreholes although the inversion problem becomes highly non linear due to local geology complexity and rough velocity variations.