基于绕射波的储层预测方法及其应用

Development and application of an effective method for reservoir predication based on seismic diffraction

碳酸盐岩缝洞、孔洞型油气藏在石油勘探中占有很大比重,其中储层预测是难题。反射波勘探时由于假设反射界面为光滑且无限大平面,因此受到纵向、横向分辨率限制,不能有效识别碳酸盐岩缝洞、孔洞型油气藏等该类地质体。基于绕射波的储层预测方法可从地震数据中去除反射波后,只利用地震波场中的绕射信息进行分析。绕射波利用的难点在于绕射波为弱信号,掩盖在强反射背景下,因此,需要去除反射能量以突显绕射信息。基于反射波与绕射波的相关性差异,给出了一种绕射波分离方法。该方法结合平面波破坏滤波与中值滤波,利用正则化反演迭代算法求取反射波平滑倾角场,同时沿着估计出的倾角进行中值滤波,进而计算出波形、振幅稳定的反射数据,最后由地震数据减去预测出的反射波,实现绕射波提取。数值模型及实际应用效果表明,该方法能够有效提取层间岩溶、溶洞、孔洞等地质信息,对碳酸盐岩缝洞型油气藏研究具有重要意义。

Carbonate fractured and cavernous reservoirs account for a large proportion in petroleum exploration, for which reservoir prediction is a tough issue. As seismic reflection method assumes the reflection interface to be an infinite smooth plane, its application is restricted by the horizontal and vertical resolutions, which cannot detect geological bodies such as carbonate fractured and cavernous reservoirs. The seismic diffraction method for reservoir prediction only analyzes diffraction information in the seismic wave field after the removal of reflected waves from seismic data. The difficulty in using diffraction is related to the weak signal of diffracted waves which can be masked in the context of strong reflection. Thus, it is required to remove the reflected energy for highlighting the diffraction information. Based on the correlation difference between reflection and diffraction, this study presents a diffraction separation method via a combination of plane-wave destruction filter and medium filter. The proposed method adopts the regularization inversion algorithm to obtain the smooth dip angel filed of reflection, and then implements medium filter along the estimated dip angle to calculate the reflection data with stable wavelet and constant amplitude. Finally, diffraction extraction is accomplished by subtracting the predicted reflected waves from the seismic data. Numerical simulation and practical application demonstrate that the diffraction-based method can effectively extract geological information of interlayer karsts, caves, and vugs, showing a good perspective for studying carbonate fractured and cavernous reservoirs.