基于叠前方位各向异性的火山岩裂缝预测——以松辽盆地南部LFS地区为例

Prediction of volcanic fractures based on prestack azimuthal anisotropy:A case study of LFS area in southern Songliao Basin

利用叠前方位道集地震数据进行各向异性参数反演是目前裂缝预测的主要方法之一,其中RÜGER近似方程和傅里叶级数展开式2种算法应用较为广泛,RÜGER近似方程中的各向异性梯度与傅里叶级数展开式的二阶项均可以表征裂缝强度。应用2种方程在单层界面、实钻井裂缝层分别对比了计算方法的适用性,并在实际火山岩发育区对比了裂缝空间预测结果。单界面模型2种方程预测裂缝强度存在量纲差异,RÜGER近似方程裂缝强度值域大于傅里叶级数展开式计算结果,RÜGER近似方程计算裂缝方位存在多解性,可能为垂直裂缝方向;井上裂缝层应用2种方法计算裂缝方位和强度结果基本一致;在松辽盆地南部LFS地区火山岩地层应用2种方法分别预测裂缝发育情况,傅里叶级数二阶项相比方位各向异性梯度,与电成像测井解释裂缝强度吻合稍好,且预测裂缝方位与成像测井解释方位相同。研究认为,在火山岩领域傅里叶级数方程预测裂缝方法更适于推广应用。

Anisotropic parameter inversion based on pre-stack azimuth gather seismic data is one of the primary methods for fracture prediction,among which two algorithms,RÜGER approximate equation and Fourier series expansion,are more widely used.Both the anisotropic gradient in the RÜGER approximate equation and the second-order term in the Fourier series expansion can characterize the crack intensity.In the experiment,the applicability of applying this two equations was compared in the single-layer interface and the fracture layer of the actual drilled wells,respectively,and the fracture spatial prediction results were compared in the actual volcanic rock development zone.There are dimensional differences in the prediction of fracture strength between the two equations of single interface model.The range of fracture strength of RÜGER approximation equation is larger than that of Fourier series expansion.Multiple results exist for the calculation of fracture orientation using the RÜGER approximation equation,which may result in an orientation perpendicular to the fracture.However,when applied to the fractured layers observed in wells,both methods yielded broadly consistent results regarding fracture orientation and strength.In the application to the volcanic rock formation of the LFS area in the southern Songliao Basin,the Fourier series'second-order term slightly outperformed the RÜGER equation in aligning with the fracture strength interpretations derived from electrical imaging logging.Additionally,the predicted fracture orientations from both methods matched those interpreted from imaging logging.It is concluded that the Fourier series equation for predicting fractures is more suitable for popularization and application in the field of volcanic rocks.