二维Offset平面波有限差分法叠前时间偏移

Finite-difference pre-stack time migration of 2D offset plane wave

（同济大学海洋与地球科学学院海洋地质国家重点实验室，上海200092）

State Key Laboratory of Marine Geology, School of Ocean and Earth Science, Tongji University, Shanghai 200092, China

在岩性油气藏勘探中，保振幅或保波形成像是进行储层特征分析和参数估计的基础。由于Kirchhoff积分叠前时间偏移、F-K域波动方程叠前时间偏移不适应弱横向变速介质情形，因此，基于偏移距（Offset）域平面波偏移思想，提出了Offset平面波有限差分法叠前时间偏移方法。讨论了CMP道集平面波分解原理，推导了Offset平面波方程及其有限差分解法，给出了角度道集生成方法。利用大庆油田的一个横向缓变的速度模型，对Offset平面波有限差分法叠前时间偏移方法的有效性进行了验证。结果表明，该方法适应缓横向变速介质情形，波场外推算子保幅，计算效率高，可以为AVP/AVA分析提供较好的基础数据。

Amplitude-preserving or waveform-preserving imaging results are the basis for reservoir characterizing and parameter estimating in lithologic reservoir exploration. Kirchhoff integral pre-stack time migration and F-K domain wave equation pre-stack time migration is not suitable for the medium with gradual transverse change in velocity. Therefore, an offset plane wave finite-difference pre-stack time migration method was proposed. The CMP gather plane wave decomposition was discussed. Offset plane wave equation was derived and its finite-difference solution was given. Then, an approach for generating angle imaging gather is deduced. A velocity model with gradual transverse change from Daqing oilfield was used to verify the fidelity of the method. The results show that the method is suitable for the medium with gradual transverse change in velocity, can preserve amplitude of field extrapolation operator and provide better basic data for sequent AVP/AVA analysis.