Abstract:The seismic responses of carbonate fracture-cavity,channels,and faults are all discontinuous anomalies;however,the application of gradient structure-tensor (GST) to delineate carbonate fracture-cavity boundary is relatively rare. Therefore,the influence of each calculation link on the result is analyzed based on previous studies and according to the detailed calculation method of the GST attribute and its geometric significance. The results of technical principle analysis and actual seismic data tests are as follows. ① The smooth calculation of tensor matrix elements,as the key to the whole technique,makes the structure-tensor matrix contain the features in the maximum gradient energy direction and the changing features in all orthogonal directions. The smooth of gradient elements can suppress background noise to some extent and improve the signal-to-noise ratio of the final calculation. ② Both the second and the third eigenvalues have an ideal ability to describe the carbonate fracture cavities,reflecting the three-dimensional morphological characteristics of the fracture cavities from different perspectives. By the selection or combination of the second and third eigenvalue attributes,the carbonate fracture-cavity boundary can be characterized effectively in the suitable range of low-value interception and display. ③ With drilling information as a scale to the dimensionless eigenvalues,the linear combination of eigenvalues is essentially a multi-constrained solution,which incorporates the detailed features of the second and third eigenvalues and effectively solves the problem of inconsistent values for different drilling scales. In conclusion,compared with conventional attributes such as amplitude change rate,the GST attribute can describe carbonate fracture-cavity more continuously,thus reflecting the corrosion law to a certain extent.
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