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Rujun Chen
Université de Rouen, M2C, UMR 6143, CNRS, Morphodynamique Continentale et Cⓞtière, Mont Saint Aignan, France.

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Journal article
Published: 01 May 2018 in GEOPHYSICS
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We applied the principal component geostatistical approach (PCGA) to the inversion of time-domain induced polarization data in terms of resistivity and chargeability distributions. The PCGA presents two major advantages over standard methods: (1) It avoids the storage of the usually large covariance matrix, which contains the geostatistical information, by factorizing it in a product of low-rank matrices. (2) It does not assemble the Jacobian matrix per se. We determine the robustness of this approach with three examples. We first reconstruct the electrical conductivity and chargeability fields of two synthetic models generated using the geostatistical software Stanford Geostatistical Modeling Software. The PCGA approach performs better than the Tikhonov-based regularization approach when the true fields are very heterogeneous and the amount of data is limited. The third example is devoted to a field study over the former Lewis coal mine in Colorado (USA). We perform a 3D localization of the burning front of this coal seam fire by applying our geostatistical inverse methodology to a time-domain induced-polarization data set. In this case, the horizontal components of the semivariogram are determined from a self-potential map and the correlation length scale for the vertical component is determined from the known thickness of the coal bed. The tomogram presents a high normalized chargeability associated with the burning front. We evaluate the high normalized chargeability of the burning front in terms of the physical mechanism associated with the cation exchange capacity of the coal and the effect of temperature. This demonstrates the potential of the geostatistical inversion and its suitability for inverting geophysical data, especially when the data density is sparse. In the case of coal seam fires, we determine the suitability of the induced polarization method to localize the burning front and the effect of temperature on the normalized chargeability.

ACS Style

Abdellahi Soueid Ahmed; André Revil; Abdel Jardani; Rujun Chen. 3D geostatistical inversion of induced polarization data and its application to coal seam fires. GEOPHYSICS 2018, 83, E133 -E150.

AMA Style

Abdellahi Soueid Ahmed, André Revil, Abdel Jardani, Rujun Chen. 3D geostatistical inversion of induced polarization data and its application to coal seam fires. GEOPHYSICS. 2018; 83 (3):E133-E150.

Chicago/Turabian Style

Abdellahi Soueid Ahmed; André Revil; Abdel Jardani; Rujun Chen. 2018. "3D geostatistical inversion of induced polarization data and its application to coal seam fires." GEOPHYSICS 83, no. 3: E133-E150.

Journal article
Published: 01 March 2018 in GEOPHYSICS
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The exploration of podiform chromites in the Indus Yarlong Zangbo suture zone of southern Tibet has proved difficult because most known deposits pinch out and then reappear in the same direction. Several ground-based geophysical approaches such as gravity, magnetic, and controlled-source audio-frequency magnetotelluric (CSAMT) methods have been applied to explore for these chromite deposits but have mostly failed to delineate prospective areas. We have evaluated a successful podiform chromite exploration case history that is based on AMT. More than 8000 AMT stations were used in this study within a [Formula: see text] area of the ophiolite belt. Line separations were 80 or 40 m, and the station separation was 20 m. We implemented Bostick conversion and nonlinear conjugate gradient inversions for data interpretation, whereas 2D resistivity sections and 3D resistivity imaging were used to elucidate the inner structure and distribution of rock faces within the Luobusa ophiolite. Results from rock physics and drilling further indicate that resistivity-anomaly domains from these AMT results are correlated with rock faces in terms of fresh harzburgite, altered harzburgite and dunite, and they can thus be connected to concealed deposits. Therefore, we have developed three resistivity-anomaly models for chromite exploration, and we delineated several prospective regions containing exploitable deposits within the Luobusa ophiolite. Seven of the nine verified boreholes discussed in this paper intersected with chromite deposits; one comprises the largest and highest grade chromite deposit in China to date. Our AMT results provide the impetus for future chromite exploration in Tibet and enable a refined understanding of the structure and distribution of rock faces within the Luobusa ophiolite.

ACS Style

Lanfang He; Ling Chen; Dorji; Zhanxiang He; Xuben Wang; Bayi Xiao; Ligui Xu; Xuefang Zhao; Xiaolu Xi; Hongchun Yao; Rujun Chen. Mapping chromite deposits with audio magnetotellurics in the Luobusa ophiolite of southern Tibet. GEOPHYSICS 2018, 83, B47 -B57.

AMA Style

Lanfang He, Ling Chen, Dorji, Zhanxiang He, Xuben Wang, Bayi Xiao, Ligui Xu, Xuefang Zhao, Xiaolu Xi, Hongchun Yao, Rujun Chen. Mapping chromite deposits with audio magnetotellurics in the Luobusa ophiolite of southern Tibet. GEOPHYSICS. 2018; 83 (2):B47-B57.

Chicago/Turabian Style

Lanfang He; Ling Chen; Dorji; Zhanxiang He; Xuben Wang; Bayi Xiao; Ligui Xu; Xuefang Zhao; Xiaolu Xi; Hongchun Yao; Rujun Chen. 2018. "Mapping chromite deposits with audio magnetotellurics in the Luobusa ophiolite of southern Tibet." GEOPHYSICS 83, no. 2: B47-B57.

Review
Published: 27 November 2017
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ACS Style

Rujun Chen. Review of Multifunction waveform generator for EM receiver testing by Rujun Chen. 2017, 1 .

AMA Style

Rujun Chen. Review of Multifunction waveform generator for EM receiver testing by Rujun Chen. . 2017; ():1.

Chicago/Turabian Style

Rujun Chen. 2017. "Review of Multifunction waveform generator for EM receiver testing by Rujun Chen." , no. : 1.

Journal article
Published: 01 September 2017 in GEOPHYSICS
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In induced-polarization (IP) surveys, the raw data are usually distorted significantly by the presence of electromagnetic (EM) interferences, including cultural noise. Several methods have been proposed to improve the signal-to-noise ratio of these data. However, signal processing in an electromagnetically noisy environment is still a challenging problem. We have determined a new and simple technique based on the analysis of the correlation between the measured potential and the injected primary current signals. This processing is applied to the data acquired using a new frequency-domain IP method called the spread-spectrum induced-polarization (SSIP) approach. In this approach, we use a pseudorandom m-sequence (also called the maximum length sequence) for the injected primary current. One of the advantages of this sequence is to be essentially spectrally flat in a given frequency range. Therefore, complex resistivity can be determined simultaneously at various frequencies. A new SSIP data set is acquired in the vicinity of Baiyin mine, Gansu Province, China. The correlation between potential difference and transmitting current signals for each period can be used to assess data quality. Only when the correlation coefficient between the two signals is greater than 0.5 can the SSIP data be used for subsequent processing and tomography. We determine what threshold value should be used for the correlation coefficient to extract high-quality apparent complex resistivity data and eliminate EM-contaminated data. We then compare the pseudosections with and without using the correlation analysis. When the correlation analysis is used, the noisy data are filtered out, and the target anomaly obtained through tomography is clearly enhanced. The inversion results of the apparent complex resistivity (amplitude and phase) for the survey area are consistent with some independent geologic and drilling information regarding the position of the ore body demonstrating the effectiveness of the approach.

ACS Style

Weiqiang Liu; Rujun Chen; Hongzhu Cai; Weibin Luo; André Revil. Correlation analysis for spread-spectrum induced-polarization signal processing in electromagnetically noisy environments. GEOPHYSICS 2017, 82, E243 -E256.

AMA Style

Weiqiang Liu, Rujun Chen, Hongzhu Cai, Weibin Luo, André Revil. Correlation analysis for spread-spectrum induced-polarization signal processing in electromagnetically noisy environments. GEOPHYSICS. 2017; 82 (5):E243-E256.

Chicago/Turabian Style

Weiqiang Liu; Rujun Chen; Hongzhu Cai; Weibin Luo; André Revil. 2017. "Correlation analysis for spread-spectrum induced-polarization signal processing in electromagnetically noisy environments." GEOPHYSICS 82, no. 5: E243-E256.

Journal article
Published: 01 July 2017 in GEOPHYSICS
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Shale gas is a particularly important research target on Chinese energy resources, especially in the Upper Yangtze region. Complex topography and geologic conditions challenge seismic exploration of shale gas in this area, and ground-based electromagnetic (EM) methods are used to aid recognition of the best reservoirs. However, the electrical properties of organic shale (EPOS) and its correlation to shale-gas petrology remain poorly understood. We studied EPOS and their correlation to shale petrology by measuring and analyzing the petrochemical features and complex impedance of rock samples from the Silurian Longmaxi and Cambrian Niutitang Formations in the Upper Yangtze, southwest China. Our study indicates that the organic shale in the Upper Yangtze features low resistivity and high polarizability in terms of a high negative phase, but no obvious low resistivity is observed among shaly sandstone and shales with lower and higher total organic carbon. Pyrite and quartz contents in the organic shale dominantly contribute to the EPOS with different mechanisms. Our result indicates that the EPOS bear relations to the petrology parameters of organic shale, which is essential for shale-gas evaluation and exploration. The correlation between EPOS and the shale-gas petrology promoted a new way for shale-gas exploration with complex geology, topography, and surface conditions in China, especially in the Upper Yangtze region, by using the ground-based EM method to evaluate the parameters of shale gas and to aid to delimit the productive reservoirs (“sweet spots”).

ACS Style

Lanfang He; Ling Chen; Xuben Wang; Zhengjiang Wang; Bing Zhang; Ligui Xu; Xuejun Liu; Weili Li; Rujun Chen. Electrical properties and its correlation to the petrology of the Upper Yangtze organic shales. GEOPHYSICS 2017, 82, D199 -D209.

AMA Style

Lanfang He, Ling Chen, Xuben Wang, Zhengjiang Wang, Bing Zhang, Ligui Xu, Xuejun Liu, Weili Li, Rujun Chen. Electrical properties and its correlation to the petrology of the Upper Yangtze organic shales. GEOPHYSICS. 2017; 82 (4):D199-D209.

Chicago/Turabian Style

Lanfang He; Ling Chen; Xuben Wang; Zhengjiang Wang; Bing Zhang; Ligui Xu; Xuejun Liu; Weili Li; Rujun Chen. 2017. "Electrical properties and its correlation to the petrology of the Upper Yangtze organic shales." GEOPHYSICS 82, no. 4: D199-D209.

Journal article
Published: 01 December 2016 in Journal of Applied Geophysics
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In this paper, we investigated the robust processing of noisy spread spectrum induced polarization (SSIP) data. SSIP is a new frequency domain induced polarization method that transmits pseudo-random m-sequence as source current where m-sequence is a broadband signal. The potential information at multiple frequencies can be obtained through in measurement. Removing the noise is a crucial problem for SSIP data processing. Considering that the ordinary mean stack and digital filter if not capable of reducing the impulse noise effectively in SSIP data processing, the impact of impulse noise will remain in the complex resistivity spectrum that will affect the interpretation of profile anomalies. We implemented a robust statistical method to SSIP data processing. The robust least-squares regression is used to fit and remove the linear trend from the original data before stacking. The robust M estimate is used to stack the data of all periods. The robust smooth filter is used to suppress the residual noise for data after stacking. For robust statistical scheme, the most appropriate influence function and iterative algorithm are chosen by testing the simulated data to suppress the outliers' influence. We tested the benefits of the robust SSIP data processing using examples of SSIP data recorded in a test site beside a mine in Gansu Province, China.

ACS Style

Weiqiang Liu; Rujun Chen; Hongzhu Cai; Weibin Luo. Robust statistical methods for impulse noise suppressing of spread spectrum induced polarization data, with application to a mine site, Gansu province, China. Journal of Applied Geophysics 2016, 135, 397 -407.

AMA Style

Weiqiang Liu, Rujun Chen, Hongzhu Cai, Weibin Luo. Robust statistical methods for impulse noise suppressing of spread spectrum induced polarization data, with application to a mine site, Gansu province, China. Journal of Applied Geophysics. 2016; 135 ():397-407.

Chicago/Turabian Style

Weiqiang Liu; Rujun Chen; Hongzhu Cai; Weibin Luo. 2016. "Robust statistical methods for impulse noise suppressing of spread spectrum induced polarization data, with application to a mine site, Gansu province, China." Journal of Applied Geophysics 135, no. : 397-407.

Journal article
Published: 22 October 2016 in Energies
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Southwestern Tibet plays a crucial role in the protection of the ecological environment and biodiversity of Southern Asia but lacks energy in terms of both power and fuel. The widely distributed geothermal resources in this region could be considered as potential alternative sources of power and heat. However, most of the known geothermal fields in Southwestern Tibet are poorly prospected and currently almost no geothermal energy is exploited. Here we present a case study mapping the Mapamyum (QP) geothermal field of Southwestern Tibet using audio magnetotellurics (AMT) and magnetotellurics (MT) methods. AMT in the frequency range 11.5–11,500 Hz was used to map the upper part of this geothermal reservoir to a depth of 1000 m, and MT in the frequency range 0.001–320 Hz was used to map the heat source, thermal fluid path, and lower part of the geothermal reservoir to a depth greater than 1000 m. Data from 1300 MT and 680 AMT stations were acquired around the geothermal field. Bostick conversion with electromagnetic array profiling (EMAP) filtering and nonlinear conjugate gradient inversion (NLCGI) was used for data inversion. The AMT and MT results presented here elucidate the geoelectric structure of the QP geothermal field, and provide a background for understanding the reservoir, the thermal fluid path, and the heat source of the geothermal system. We identified a low resistivity anomaly characterized by resistivity in the range of 1–8 Ω∙m at a depth greater than 7 km. This feature was interpreted as a potential reflection of the partially melted magma in the upper crust, which might correlate to mantle upwelling along the Karakorum fault. It is likely that the magma is the heat source of the QP geothermal system, and potentially provides new geophysical evidence to understand the occurrence of the partially melted magmas in the upper crust in Southwestern Tibet.

ACS Style

Lanfang He; Ling Chen; Dorji; Xiaolu Xi; Xuefeng Zhao; Rujun Chen; Hongchun Yao. Mapping the Geothermal System Using AMT and MT in the Mapamyum (QP) Field, Lake Manasarovar, Southwestern Tibet. Energies 2016, 9, 855 .

AMA Style

Lanfang He, Ling Chen, Dorji, Xiaolu Xi, Xuefeng Zhao, Rujun Chen, Hongchun Yao. Mapping the Geothermal System Using AMT and MT in the Mapamyum (QP) Field, Lake Manasarovar, Southwestern Tibet. Energies. 2016; 9 (10):855.

Chicago/Turabian Style

Lanfang He; Ling Chen; Dorji; Xiaolu Xi; Xuefeng Zhao; Rujun Chen; Hongchun Yao. 2016. "Mapping the Geothermal System Using AMT and MT in the Mapamyum (QP) Field, Lake Manasarovar, Southwestern Tibet." Energies 9, no. 10: 855.

Conference paper
Published: 01 September 2021
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ACS Style

Yangfeng Yang; Xu Zhang; Rujun Chen; Hongchun Yao; Fuguo Chang; Pei Zeng; Xin He; Biwen Xiang. 精密激电法在斑岩型铜钼矿找矿突破中的成功应用. 2021, 1 .

AMA Style

Yangfeng Yang, Xu Zhang, Rujun Chen, Hongchun Yao, Fuguo Chang, Pei Zeng, Xin He, Biwen Xiang. 精密激电法在斑岩型铜钼矿找矿突破中的成功应用. . 2021; ():1.

Chicago/Turabian Style

Yangfeng Yang; Xu Zhang; Rujun Chen; Hongchun Yao; Fuguo Chang; Pei Zeng; Xin He; Biwen Xiang. 2021. "精密激电法在斑岩型铜钼矿找矿突破中的成功应用." , no. : 1.