基于OBN地震的EEI反演在西非深水A区储层预测中的应用

常规拖缆三维地震难以满足西非深水A区块复杂目标、隐蔽油气藏评价的需求, 海底节点(OBN)地震勘探已经成为精细勘探开发的主要技术手段。对比分析了研究区OBN地震与拖缆地震的采集和处理参数, 明确了OBN地震资料具有更高的信噪比、更宽的频带、更好的保幅性。对目的层段开展了5个分角度叠加资料的井震标定, 相关系数达0.84~0.91, 为开展叠前地震反演提供了良好的基础资料。针对研究区小于10 m的薄储层预测难题, 开展了扩展弹性阻抗(EEI)反演, 以孔隙度曲线作为储层预测的目标曲线进行EEI计算, 获得不同角度对应的EEI曲线, 并与孔隙度曲线进行相关性分析, 发现当旋转角度χ为29°时, EEI曲线与孔隙度曲线具有最大的负相关性, 为最优角度。建立了EEI(29°)与孔隙度的线性关系, 通过岩石物理正演以及测井解释储层孔隙度门槛值, 定量计算出目的层反演砂岩储层EEI门槛值为5 000 g·cm^-3·m·s^-1。对比分析了基于不同地震数据的EEI反演结果, 认为基于OBN地震数据的EEI反演在储层预测方面效果更好, 适用性更强。

After more than 20 years of 3D seismic exploration in deepwater Block A, West Africa, conventional Towed-Streamer (TS) technique is insufficient for complicated reservoir characterization, and Ocean Bottom Node (OBN) technique has become a good alternative.As per a comparative study on acquisition and processing parameters, OBN data show higher signal-to-noise ratio, wider band (3~100 Hz for OBN versus 8~73 Hz for TS), wider azimuth, and better amplitude preservation than TS data.To improve the prediction accuracy of deepwater sandstone reservoirs and effectively guide drilling deployment, we use OBN data to perform Extended Elastic Impedance (EEI) inversion through χ-angle optimization and quantitative threshold calculation.For 5 partial stacks, the correlation coefficient of well-to-seismic calibration is as high as 0.84~0.91 at the interval of interest.Porosity is used as the indicator for reservoir prediction below 10 m as the greatest negative correlation is reached at the angle 29°.The linear relationship between EEI (29°) and porosity is then established.Through petrophysical modeling and logging interpretation, reservoir porosity threshold is estimated to correspond to EEI (29°) threshold of 5 000 g·cm^-3·m·s^-1.Inversion results using different data sets show that OBN-based EEI (29°) inversion performs better than TS-based inversion for thin reservoir prediction.