Azimuthally variation of elastic impedances for fracture estimation
Azimuthally variation of elastic impedances for fracture estimation
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DOI：
10.1016/j.petrol.2019.05.063
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发表时间：
2019-10
影响因子：
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通讯作者：
Zhengqian Ma;Xingyao Yin;Z. Zong;Mingshui Song;Yanguang Wang;Chen Zuqing-;Jinlei Li;Liu Xiaojing
中科院分区：
文献类型：
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作者：
Zhengqian Ma;Xingyao Yin;Z. Zong;Mingshui Song;Yanguang Wang;Chen Zuqing-;Jinlei Li;Liu Xiaojing
裂缝参数包括裂缝方向和裂缝密度，是工程和勘探地球物理领域的重要信息。然而，由于方位地震资料的信噪比有限，如何从地震资料中简明、稳定地估计裂缝参数仍然是一个挑战。提出了一种基于方位角傅里叶级数变化的方位角各向异性弹性阻抗（azimuthal AEI）表征裂缝分布的方法。首先，导出了截断傅立叶级数形式的方位AEI方程，以减少裂缝参数估计中未知参数的数量；此外，利用KL （karhunen - lo<e:1>）变换提取反射振幅随方位角变化的主要特征，减弱方位角叠前地震资料的随机噪声。然后用约束稀疏尖峰反演方法对KL变换后的方位叠前地震资料进行方位AEI估计。结合方位角AEI方程的傅里叶级数和裂缝方向先验信息，提出了一种新的方位角AEI方程，可以估计无90°模糊的裂缝方向。利用二阶傅里叶系数可以估计出方位AEI各向异性梯度的偏估计，从而预测裂缝密度。此外，我们还介绍了一种比基于各向异性梯度的裂缝密度估计方法更简便的方法，即在方位角域中利用方位AEI的自然对数（SDNL）的标准差进行裂缝密度估计。综合算例表明，即使在方位角30°采样间隔稀疏的情况下，创新的一次波方位角AEI方程和裂缝参数估计方法也具有合理性和鲁棒性。现场数据算例表明，该方法在裂缝参数预测中是有效的。
Fracture parameters including fracture orientation and fracture density, work as significant information in the fields of the engineering and exploration geophysics. However, it nowadays still remains challenging to concisely and stably estimate those fracture parameters from seismic data due to the limited signal to noise ratio of the azimuthal seismic data. A method based on azimuthally anisotropic elastic impedance (azimuthal AEI) in terms of Fourier series variation with azimuth is proposed to characterize the fracture distribution. Firstly, the azimuthal AEI equation in terms of truncated Fourier series is derived to reduce the number of unknown parameters in the fracture parameters estimation. In addition, KL (Karhunen-Loève) transformation is used to extract the primary feature of reflection amplitude variation with azimuth and weaken the random noise for azimuthal pre-stack seismic data. And then the azimuthal AEI is estimated from KL transformed azimuthal pre-stack seismic data with the constrained sparse spike inversion method. The fracture orientation without 90° ambiguity can be estimated by an innovative azimuthal AEI equation incorporating the azimuthal AEI equation in terms of Fourier series and the fracture orientation prior information. And the biased estimate for the anisotropic gradient of the azimuthal AEI can be estimated from the second order Fourier coefficient to forecast the fracture density. Besides, we introduce a more convenient way, which is employing the standard deviation of the nature logarithm (SDNL) of the azimuthal AEI in the azimuth domain, than that based on the anisotropic gradient in the fracture density estimation. The synthetic cases demonstrate the rationality and robustness of the innovative primary wave azimuthal AEI equation and the fracture parameters estimation method even with sparse 30° sampling interval in the azimuth. A field data example demonstrates that the proposed method is effective and efficient in the fracture parameters prediction.