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Seismic Data High-density Velocity Analysis Using Residual Normal Moveout

Author: XingXing
Tutor: MengXiaoHong
School: Chinese Geology University (Beijing)
Course: Earth Exploration and Information Technology
Keywords: Velocity analysis Interval velocity Dix formula Least squares
CLC: P631.4
Type: Master's thesis
Year: 2009
Downloads: 46
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Abstract

In this dissertation ,we achieve the method of High-density Velocity analysis using residual normal moveout. Following the NMO we scan the residual normal moveout in all seismic CDP data,then automatic pick accurate stacking velocity to get a planar velocity profile,finally getting the velocity of the underground media.The method is base on traditional NMO,which has good efficiency in scanning and high resolution.In order to optimize the velocity spectrum , The dissertation achieves the idea of finding the center.The main idea of the above theory is as follows: separating the profile to lots of sub-spaces, finding its gravity center ,then assigning the value of the space center to the gravity center. When gravity center departure away from center of its subsection, the value assigned to gravity center is smaller than the actual one, but non other than gravity center anastomoses fully with its subsection center ,the assigned value equal to the actual one. By doing so it makes a smooth velocity spectrum and it helps us to pick up velocity. But automatic picking can bring abnormal velocity,which causes stacking problem.In order to eliminate the abnormal velocity the dissertation achieves the 3D interpolation with locally scaled regression, the basis theory is using the around N point of the point of picking up to linear function imitating it, getting the coefficient using least squares methods, then use it to replace the original value. Because it uses the value around it, it can achieve a smoothing effect, when applying the method to velocity profile can eliminate the abnormal velocity and discontinuity between different CDP.Finally the dissertation is about using root-mean-square velocity to get interval velocity and the dissertation use Dix formulation compute interval velocity. In the presence of the rapid and large variations and other interference, Dix inversion will bring much error and unreasonable velocity profile. So this dissertation expressed a form of an operator to the formulation, which is introduced in the dimension of time and space. The dissertation regularize the differential operator to penalize rapid velocity variation and random noise, and a smooth velocity profile is produced. But the real rapid velocity variation could be suppressed. For example ,in some complicated geological conditions (carbonate rock , salt bodies or strong faulting ) ,the rapid velocity variation is normal, so the dissertation use a regularization technique with edge-preserving operator that yields smooth velocities while preserving sharp geologic interval velocity contrasts. In order to achieve the above algorithm, we apply it to model data and real data, and we achieve good results.In this dissertation all the algorithms are independently achieved using C++ programming, including the residual velocity analysis and its auxiliary methods(the idea of finding the center of the spectrum, 3D interpolation with locally scaled regression), all of which are applied to the simple models (horizontal layers models)and the actual seismic data; The optimization method of Dix interval velocity inversion is conducted in tilted fault model and the Syncline model, as well as the actual seismic data were studied. All the methods are achieved more than we have the desired effect.

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