Well logs play a very important role in exploration and even exploitation of energy resources, but they usually contain kinds of noises which affect the results of the geological interpretation of them. It is common knowledge that wavelet transform does better than Fourier transform in noise removal and suppression of such non-stationary signals as logging signals. However, there are variable choices of the parameters such as the wavelet basis (mother wavelet function), the thresholding rule and the decomposition level etc. in denoising with the wavelet transform. In this paper, the wavelet denoising theory and steps are briefly introduced first, and then lots of numerical experiments on real well logs were done by the authors with different combination of the parameters and the denoising effect analyzed by comparison of the differences between the predenoising and post-denoising signals with difference value calculation and frequency spectral analysis. The experiment results show that the wavelet basis 'sym8', the soft threshold rule 'heursure' and 5-level decomposition are outstanding in the wavelet denoising of well logging data. Furthermore, we took the AC (acoustic logs) well logging data of a certain borehole in Jiyang Depression, Shandong province of North China, for a case study to check the combination of the parameters settled above. It is found that the denoised acoustic logging signal outperforms the original one in revealing the geological information of gas bearing layers. So, we believe that the wavelet transform can do an excellent job in the denoising of well logs on condition that the related parameters are set properly. Also, the authors assume that it would be of bright prospect to extract and reveal some more geological information such as stratigraphic sequences, sedimentary facies and reservoir properties etc. with reasonable denoising process of different kinds of logging data at certain scales.
Red beds are not entirely red sometimes, in which grey-green spheroids or irregular spots can be found. However, the formation mechanism of grey-green spheroids or irregular spots in red beds is not clear so far. Samples taken from well JK1 in Jiaozhou area of Jiaolai Basin displayed that the reduction spheroids have more Vanadium (V) element, less TFe 3 O 4 and Lead (Pb) element, almost the same content of other elements such as FeO and so on, comparing the red parts of the samples. The existence of organisms can explain the existence of green reductive spheres in the red beds formed under the oxidation environment.
The Miocene aged Shanwang Formation from the Shanwang National Geopark in China represents a succession of lacustrine diatomaceous shales containing an abundant and diverse biota with lagerstätte fossilization of soft tissues. To date, the Shanwang Formation has not been investigated for cyclostratigraphy nor has it been dated with high precision methods. Now we use thorium data as a paleoenvironmental and paleoclimatic proxy to conduct a detailed cyclostratigraphic analysis. A new and simple cyclostratigraphic method, Wavelet Scale Series Analysis (WSSA), using the Wavelet Analysis toolbox in Matlab, is developed to recognize Milankovitch cycles. A total of three short eccentricity and fifteen precession cycles are identified; obliquity cycles are not apparent. In the sedimentary succession, the corresponding precession and short eccentricity cycles are 1.17 m and 4.98 m thick respectively, with this verified by Correlation Coefficient (COCO) analysis and Multitaper-Method (MTM) spectral analysis. We estimate the studied interval was deposited over a duration of 0.3 Myr with a depositional rate of c. 5.7 cm/kyr. Paleomagnetic and radio isotope dating data shows that the diatomaceous shale was deposited during Chron C5En, which places it at approximately 18.5 Ma during the Burdigalian stage of the Early Miocene, rather than in the Middle Miocene as previously thought. The Shanwang lagerstätte biota therefore predates the Middle Miocene Climate Optimum (MMCO) and did not form within it. The geological time scale with a high resolution of 20 kyr was set accordingly.
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