A Wavelet-Analysis-Based New Approach for Interference Elimination in Geochemical Hydrocarbon Exploration |
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| Authors: | Liuping Zhang Guoping Bai and Yixian Xu |
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| Institution: | (1) Key Laboratory of Mineral Resource, Institute of Geology and Geophysics, Chinese Academy of Science, Beijing, 100029, People's Republic of China;(2) Basin & Reservoir Research Center, University of Petroleum, Beijing, 102249, People's Republic of China;(3) Geophysical Department, China University of Geosciences, Wuhan, Hubei, 430074, People's Republic of China |
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| Abstract: | Guidance for petroleum prospecting is provided by authentic geochemical anomalies, obtained after interference has been eliminated in the original data from a geochemical survey for hydrocarbons. However, this elimination is a complicated process. Few working models or effective methods for interference elimination have been proposed, hampering a wider acceptance of geochemical prospecting as a viable tool for hydrocarbon exploration. This study focuses on the models for different types of interference and developing techniques for interference elimination. We first restudied the geometric nature of hydrocarbon anomalies and interference on the basis of Zhang, L., and Lia, Z. (J. China Univ. Geosci., v. 9, no. 1, p. 72–80, 1998). From this, we determined that at least two types of interference are present in the data of a surface geochemical survey for hydrocarbons. One is the superimposition type originating mainly from microorganisms and contamination, and the other is the multiplication type resulting from variations in soil mineral components. We then established digital conceptual models for both types of interference based on the geometry of anomalies and interference. Finally, we used wavelet analysis to eliminate both types of interference in the models for testing. As Morlet wavelet and symmetric border treatment fit the geometric characteristics of the anomalies and interference, they were used in this study. We found that pre-wavelet analysis treatment is different for different types of interference. For the multiplication type, log-transformation and normalization are needed before wavelet analysis whereas only normalization is needed for the superimposition type. In practice, one needs to identify the type of interference. Therefore, the criteria for determining the interference type were first established geochemically in this study. The newly developed techniques were then applied to the data of acid-extractable hydrocarbons of soils in the Eastern Anan Sag, Inner Mongolia where traditional techniques had failed to eliminate the interference in these data. Using our new techniques, we determined the interference was the multiplication type. This new approach enabled us to satisfactorily eliminate the interference in the original data. It should be noted that our study indicates that the multiplication type of interference is much more common and severe than previously thought. |
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| Keywords: | conceptual model superimposition interference multiplication interference Mallat algorithm hydrocarbon indicator |
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