地震分频迭代反演在薄层河道砂体预测中的应用

Application of seismic frequency-divided iterative inversion in the prediction of thinly laminated channel sand bodies

龙凤山地区河道砂储层符合典型岩性油气藏特征,其砂体厚度薄、河道窄、岩性纵横向非均质性强,对5 m以下储层预测难度大。分频迭代反演充分利用全频段地震资料,对不同频段、尺度的地震信息逐级传递,优化反演结果。文中具体利用匹配追踪算法实现地震信号频段划分得到不同尺度地震数据体,在测井约束下,以低频大尺度的反演结果作为下一级频段反演的初始模型,调整反演结果;在反演过程中,通过相关算法自适应选取子波,增强反演准确性,基于贝叶斯理论自适应选取正则化参数,调节分辨率和稳定性关系达到最佳平衡,避免反演出现混沌现象。2019年该区新钻四口井钻遇营城组1-2-6和1-2-8小层的气层,同反演预测结果吻合。证明本文方法相较于常规分频反演而言,具有反演精度高、忠实于地震信息、频段应用充分的优点,可以有效提高薄层河道砂的识别能力,指导相关岩性油气藏的勘探开发。

The channel sand reservoirs in the Longfengshan area have the characteristics of typical lithologic reservoirs.This area has thin sand bodies,narrow channels,and strong vertical and horizontal lithologic heterogeneity.It is difficult to predict the reservoirs at a depth of 5 m or greater.The frequency-divided iterative inversion can fully utilize the full-frequency band seismic data and transmit the seismic information of different frequency bands and scales step by step,thus optimizing the inversion results.In this study,the seismic signal frequency bands were divided using the matching pursuit algorithm to obtain seismic data volumes of different scales.Under the constraints of log data,the low-frequency,large-scale inversion results were used as the initial model for the next-order frequency band inversion,and the inversion results.During the inversion,wavelets were adaptively selected using the correlation algorithm to enhance the inversion accuracy.Regularization parameters were adaptively selected based on the Bayesian theory to adjust the relationship between resolution and stability to achieve the optimal balance and avoid chaos in inversion.In 2019,gas reservoirs in subzones 1-2-6 and 1-2-8 of the Yingcheng Formation were encountered in the drilling of four wells in the Longfengshan area.This result is consistent with the inversion prediction results.Therefore,compared with conventional frequency division inversion,the method proposed in this study has the advantages of high inversion accuracy,coincidence with seismic information,and full application of frequency bands.This method can effectively improve the identification performance of thinly laminated channel sand bodies and guide the exploration and development of related lithologic reservoirs.