The Experts below are selected from a list of 231 Experts worldwide ranked by ideXlab platform
Asoke K. Nandi - One of the best experts on this subject based on the ideXlab platform.
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Fast communication: Generalized Gamma Density-based score functions for fast and flexible ICA
Signal Processing, 2007Co-Authors: Kostas Kokkinakis, Asoke K. NandiAbstract:In this contribution, we propose an entirely novel family of flexible score functions for blind source separation (BSS), based on the family of generalized Gamma densities. To blindly extract the independent source signals, we resort to the popular FastICA approach, whilst to adaptively estimate the parameters of such score functions, we use an efficient method based on maximum likelihood (ML). Experimental results with sources employing a wide range of statistical distributions, indicate that the proposed flexible FastICA (FF-ICA) technique significantly outperforms conventional independent component analysis (ICA) methods, which operate only on a fixed score function regime.
Quanying Zhang - One of the best experts on this subject based on the ideXlab platform.
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Application analysis on the different neutron Gamma Density (NGD) logging methods.
Applied radiation and isotopes : including data instrumentation and methods for use in agriculture industry and medicine, 2021Co-Authors: Quanying Zhang, Feng Zhang, Chao Yuan, Rui Deng, Guobin LiuAbstract:Abstract Neutron Gamma Density (NGD) logging is the most promising alternative to the traditional Density logging (GGD), which is of significance for resolving the radiation and safety issues in oil industry. However, due to the different HI correction methods, multiple NGD methods based on the fast neutron, thermal neutron, and capture Gamma detection coexist in the well-logging field, and show considerable differences in the tool specifications. To clarify these differences and guide the NGD development, three typical NGD methods using the fast neutron count ratio, thermal neutron count ratio, and capture Gamma count ratio (abbreviated as NGD-FC, NGD-TC, and NGD-CC methods) are selected as representatives for comparative study. Using the Monte Carole simulation, an integrated NGD tool model was established for studying the differences of three NGD methods in the logging responses, data processing methods, and environmental applications. Research shows that, although the three NGD methods have different measurement systems and data processing methods, the three methods can get rid of the HI effect and obtain accurate formation Density. The changes of wellbore size and wellbore fluid have similar and significant impact on the three NGD methods and lead to large Density errors, especially for the large-size wellbore or wellbore gas conditions. In the different lithology conditions, three methods have good performances, but the NGD-FC and NGD-CC methods have smaller Density errors than NGD-TC method. Compared to the other two NGD methods, the NGD-FC method also has a perfect performance in the oil or gas-saturated formation, while NGD-TC and NGD-CC methods have extremely large errors in the gas-saturated formation. Besides, the NGD-FC method are hardly affected by the formation water salinity, the NGD-TC method is slightly affected, while the NGD-CC method is greatly affected. This study can provide a guidance for the tool design, data processing and environment correction of the NGD technology.
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a comparative study on the neutron Gamma Density and Gamma Gamma Density logging
Journal of Petroleum Science and Engineering, 2019Co-Authors: Feng Zhang, Quanying Zhang, Chao Yuan, Xinguang Wang, Xiaoyang ZhangAbstract:Abstract With the increasing demand for the radioisotope-free operations, using pulsed neutron Gamma Density (NGD) instead of Gamma-Gamma Density (GGD) has become increasingly important for the development of logging while drilling (LWD) technology. However, due to the different logging mechanisms, there are huge differences between GGD and NGD in the instrument designs, measurement methods, and instrument specifications. To further promote the NGD development, a comparative study on GGD and NGD was carried out from theoretical and simulation aspects. Based on the theoretical methods, the differences between GGD and NGD in the Gamma sources, field distribution, methods for Density measurement and instrument specifications were systematically elaborated. Then, using the Monte Carlo simulation, the GGD and NGD models were built to quantitatively verify the theoretical results. Last, the detailed performances of NGD and GGD methods in different logging environments were compared. Results showed that the theoretical results are highly consistent with the simulation results. The Density sensitivity of NGD is less than half that of GGD, but the depth of investigation (DOI) approaches twice that of GGD. The Density precision and vertical resolution of NGD are less than those of GGD. Additionally, compared to GGD, NGD also has an excellent performance in different pore fluid and lithology formations, but it is easily affected by borehole factors. The research can provide quantitative performance evaluations for the NGD replacing GGD in LWD logging.
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a method for determining Density based on Gamma ray and fast neutron detection using a cs2liycl6 detector in neutron Gamma Density logging
Applied Radiation and Isotopes, 2018Co-Authors: Feng Zhang, Quanying Zhang, R P Gardner, Huizhong Yan, Lili Tian, Qian ChenAbstract:Abstract With the increasing demand for radioisotope-free operations, pulsed neutron-Gamma Density (NGD) has become increasingly important for logging-while-drilling (LWD) development. However, current NGD tools, adopting the multiple-detector array design, are not conducive to the simplification of instrument design and measurement system. To break obstacles, based on the fast neutron-Gamma coupled theory, a new Density measurement method was proposed. Further, combined with the neutron-Gamma simultaneous detection characteristics of the Cs2LiYCl6 (CLYC) detector, an NGD measurement system consisting of a D-T source and one CLYC detector was used. Results show that the new method is capable of determining formation Density using a single CLYC detector, which can not only avoid complex instrument systems but also improve Density sensitivity. Moreover, the applicability of the new Density method was well verified by Monte Carlo simulation. Additionally, the method was successfully applied in a simulated well, and Density results are in good agreement with the benchmarked formations. The research provides theoretical guidance for NGD instrument design.
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a method to describe inelastic Gamma field distribution in neutron Gamma Density logging
Applied Radiation and Isotopes, 2017Co-Authors: Feng Zhang, Quanying Zhang, Xinguang Wang, Juntao Liu, Wenbao Jia, Fei Qiu, Xiaoyang ZhangAbstract:Pulsed neutron Gamma Density logging (NGD) is of great significance for radioprotection and Density measurement in LWD, however, the current methods have difficulty in quantitative calculation and single factor analysis for the inelastic Gamma field distribution. In order to clarify the NGD mechanism, a new method is developed to describe the inelastic Gamma field distribution. Based on the fast-neutron scattering and Gamma attenuation, the inelastic Gamma field distribution is characterized by the inelastic scattering cross section, fast-neutron scattering free path, formation Density and other parameters. And the contribution of formation parameters on the field distribution is quantitatively analyzed. The results shows the contribution of Density attenuation is opposite to that of inelastic scattering cross section and fast-neutron scattering free path. And as the detector-spacing increases, the Density attenuation gradually plays a dominant role in the Gamma field distribution, which means large detector-spacing is more favorable for the Density measurement. Besides, the relationship of Density sensitivity and detector spacing was studied according to this Gamma field distribution, therefore, the spacing of near and far Gamma ray detector is determined. The research provides theoretical guidance for the tool parameter design and Density determination of pulsed neutron Gamma Density logging technique.
Carlos Torres-verdín - One of the best experts on this subject based on the ideXlab platform.
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Fast modeling of Gamma-Gamma Density measurementsvia Gamma-ray point-kernel approximationsGamma-Gamma Density measurements
GEOPHYSICS, 2019Co-Authors: Mathilde Luycx, Carlos Torres-verdínAbstract:Forward-modeling algorithms based on flux sensitivity functions are commonly recognized as fast, reliable, and the most efficient way to implement inversion-based interpretation algorithms for borehole nuclear measurements. Second-order sensitivity functions enhance the accuracy of fast-forward-modeling algorithms in complex geometries: In the presence of standoff, Density accuracy is improved up to 70% compared with first-order approximations. However, second-order sensitivity functions can only be generated with the Monte Carlo [Formula: see text]-Particle code for perturbations in bulk Density, material composition, and reaction cross sections; therefore, their use is limited to Gamma-Gamma borehole Density measurements. We have developed an alternative method to second-order approximations in complex 3D geometries. It is the first step toward future improvements to simulate borehole environmental effects across arbitrary well trajectories for nuclear measurements based on coupled neutron and Gamma-ray transport. The Gamma flux-difference (GFD) method quantifies Gamma-ray flux perturbations using exponential point kernels and Rytov approximations. Gamma-ray point kernels are corrected for flux buildup and flux perturbations caused by radial heterogeneities, i.e., standoff. Correction coefficients are calculated by flux-fitting 1D radial sensitivity functions yielded by MCNP to the 1D exponential Gamma-ray kernel; they depend on standoff and mud Density, but they are negligibly affected by formation properties. The GFD method is benchmarked against Monte Carlo calculations. Compared with first-order approximations, it improves simulated Density accuracy across regions of significant contrasting properties, up to [Formula: see text] with 3.18 cm (1.25 in) standoff and freshwater mud. The GFD method yields a maximum Density error of [Formula: see text] across complex geometries and up to up to 4.45 cm (1.75 in) standoff, similar to that achieved by second-order forward modeling algorithms. Moreover, the principles behind GFD approximations can be adapted to measurements based on coupled neutron and Gamma-ray transport.
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Physics, applications, and limitations of borehole neutron-Gamma Density measurements
GEOPHYSICS, 2019Co-Authors: Mathilde Luycx, Carlos Torres-verdínAbstract:Radioactive chemical sources can pose security, health, and environmental risks when used to estimate rock porosity in situ. The oil industry has been developing solutions to eliminate radioactive chemical sources in borehole nuclear logging. Pulsed neutron generators have successfully replaced chemical sources in neutron tools, but cesium-137 is still mainly used for borehole Density measurements. Neutron-activated Gamma-ray measurements (neutron-Gamma) are a possible alternative to radioactive chemical sources in Density tools. Despite recent advances, the measurement faces challenges regarding Density accuracy across diverse solid and fluid rock compositions and nonnegligible sensitivity to borehole environmental effects. We have examined a theoretical, albeit realistic, logging-while-drilling neutron-Gamma Density (NGD) tool operating with two inelastic Gamma-ray detectors and two fast neutron detectors. With a strong emphasis on measurement physics and source-sensor design, the tool delivers Density accuracies comparable to those of Gamma-Gamma Density (GGD) tools with [Formula: see text] error in shale-free formations and [Formula: see text] in shale and shaly formations. Our work also compares NGD with GGD in terms of depth of investigation (DOI), vertical resolution, and sensitivity to borehole environmental effects to determine optimal logging conditions. NGD accuracy is limited in the presence of standoff. With inputs of caliper and mud type, empirical Density corrections can be applied up to 0.64 cm (0.25 in) standoff. NGD also has limited applicability in thinly bedded formations with maximum vertical resolution of 76 cm (2.5 ft). However, the measurement outperforms GGD in the presence of invasion because its DOI is twice as large.
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Rapid forward modeling of logging-while-drilling neutron-Gamma Density measurements
GEOPHYSICS, 2018Co-Authors: Mathilde Luycx, Carlos Torres-verdínAbstract:Neutron-activated Gamma-ray (neutron-Gamma) logging-while-drilling (LWD) measurements deliver bulk Density estimates without using a chemical source. The assessment of bulk Density is based on neutron-induced non-capture Gamma rays, corrected for neutron transport by combining particle counts acquired at two Gamma-ray detectors and two fast neutron detectors. Particle counts from all four detectors are necessary to deliver one Density measurement whose accuracy compares well to that of the Gamma-Gamma Density instruments. Thereafter, borehole environmental effects are mitigated with empirical corrections based on Monte Carlo (MC) modeling. Such corrections should be avoided for standoff values greater than 0.63 cm (0.25 in) because they are no longer independent of formation properties. Neutron-Gamma Density measurements are also influenced by bed-boundary and layer-thickness effects. Thinly bedded formations, invasion, high-angle/horizontal (HA/HZ) wells, and enlarged boreholes can all mask true formation bulk Density when implementing conventional petrophysical interpretation. Although MC methods accurately simulate 3D environmental and geometrical effects, they are computationally expensive and are thus impractical for real-time interpretation. Layer-by-layer bulk Density can, however, be estimated using rapid numerical simulations coupled with inversion procedures. We have developed a rapid modeling algorithm to accurately simulate LWD neutron-Gamma Density measurements. Simulations are based on a theoretical, albeit realistic, LWD neutron-Gamma Density tool operating with a 14.1 MeV pulsed neutron source. The algorithm uses flux sensitivity functions and first-order Taylor series approximations to simulate particle counts at each detector before they are processed with a Density estimation algorithm. Rigorous benchmarks against the Monte Carlo N-particle code in vertical and HA/HZ wells, across diverse solid and fluid rock compositions, thin beds, and in the presence of invasion, yield average Density errors of less than 1% ([Formula: see text]) in approximately [Formula: see text] the time required of MC modeling.
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Resolution and Accuracy of Neutron-Gamma Density Measurements Compared to Conventional Gamma-Gamma Density Measurements
Day 2 Tue October 10 2017, 2017Co-Authors: Mathilde Luycx, Carlos Torres-verdínAbstract:Abstract Density measurements are widely used for the in-situ assessment of formation porosity. Traditionally, bulk Density is measured with a Gamma-Gamma Density tool using a radioactive chemical source. Neutron-Gamma Density was recently developed to infer porosity with non-chemical sources. It is therefore imperative to quantify the differences in spatial resolution and accuracy between the two measurements and the corresponding impact on petrophysical interpretation practices. We designed a theoretical, albeit practical logging-while-drilling (LWD) Neutron-Gamma Density tool and optimized source-detector spacing for maximum accuracy. The tool design comprises a 14 MeV neutron source, two Gamma ray detectors and two fast neutron detectors. Counts ratios are used to establish a linear relationship with formation bulk Density. This design yields an accuracy of 0.0147 g/cm3 in shale-free formations, and 0.0182 g/cm3 in shales, to be compared to the accuracy of traditional Gamma-Gamma Density measurements (0.015 g/cm3). Neutron-Gamma Density uses inputs from all four detectors in an effort to set apartCompton scattering effects needed to calculatebulk Density. Consequently, the spine-and-rib correction technique is not implemented in real time, leaving the measurement vulnerable to borehole environmental effects and mainly standoff. Standoff should be limited to 0.25 in for light mud, leading to a 0.05 g/cm3 correction ofbulk Density. While the vertical resolution of Gamma-Gamma Density is approximately 1 ft, results obtained from synthetic cases show that the vertical resolution of Neutron-Gamma Density is limited to 2.5 ft. The vertical resolution of Neutron-Gamma Density competes against improved depth of investigation. Neutron-Gamma Density is less affected by invasion than Gamma-Gamma Density. Depth of investigation of Neutron-Gamma Density is approximately 9.5 in, i.e. twice as long as the depth of investigation of Gamma-Gamma Density (~4 in). The main technical challenge of Neutron-Gamma Density is measurement reliability across diverse solid and fluid rock compositions. Synthetic examples show that the tool design accurately resolves formation Density in shale and shaly formations, high-Density formations such as anhydrite, and formations saturated with low-Density gas. In these cases, the accuracy is similar to that of Gamma-Gamma Density and the measurement remains reliable for porosity estimates within +/- 1 pu. We introduce a new tool design for a radioisotope-free, in-situ measurement of bulk Density based on two-particle transport. This optimized tool design is the first one to provide an accuracy that compares to Gamma-Gamma Density in clean and shaly formations. Synthetic cases serve to compare the measurements and provide insight about the conditions when Neutron-Gamma Density can be used as an alternative to Gamma-Gamma Density while achieving equivalent accuracy and performance.
Kostas Kokkinakis - One of the best experts on this subject based on the ideXlab platform.
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Fast communication: Generalized Gamma Density-based score functions for fast and flexible ICA
Signal Processing, 2007Co-Authors: Kostas Kokkinakis, Asoke K. NandiAbstract:In this contribution, we propose an entirely novel family of flexible score functions for blind source separation (BSS), based on the family of generalized Gamma densities. To blindly extract the independent source signals, we resort to the popular FastICA approach, whilst to adaptively estimate the parameters of such score functions, we use an efficient method based on maximum likelihood (ML). Experimental results with sources employing a wide range of statistical distributions, indicate that the proposed flexible FastICA (FF-ICA) technique significantly outperforms conventional independent component analysis (ICA) methods, which operate only on a fixed score function regime.
Feng Zhang - One of the best experts on this subject based on the ideXlab platform.
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Application analysis on the different neutron Gamma Density (NGD) logging methods.
Applied radiation and isotopes : including data instrumentation and methods for use in agriculture industry and medicine, 2021Co-Authors: Quanying Zhang, Feng Zhang, Chao Yuan, Rui Deng, Guobin LiuAbstract:Abstract Neutron Gamma Density (NGD) logging is the most promising alternative to the traditional Density logging (GGD), which is of significance for resolving the radiation and safety issues in oil industry. However, due to the different HI correction methods, multiple NGD methods based on the fast neutron, thermal neutron, and capture Gamma detection coexist in the well-logging field, and show considerable differences in the tool specifications. To clarify these differences and guide the NGD development, three typical NGD methods using the fast neutron count ratio, thermal neutron count ratio, and capture Gamma count ratio (abbreviated as NGD-FC, NGD-TC, and NGD-CC methods) are selected as representatives for comparative study. Using the Monte Carole simulation, an integrated NGD tool model was established for studying the differences of three NGD methods in the logging responses, data processing methods, and environmental applications. Research shows that, although the three NGD methods have different measurement systems and data processing methods, the three methods can get rid of the HI effect and obtain accurate formation Density. The changes of wellbore size and wellbore fluid have similar and significant impact on the three NGD methods and lead to large Density errors, especially for the large-size wellbore or wellbore gas conditions. In the different lithology conditions, three methods have good performances, but the NGD-FC and NGD-CC methods have smaller Density errors than NGD-TC method. Compared to the other two NGD methods, the NGD-FC method also has a perfect performance in the oil or gas-saturated formation, while NGD-TC and NGD-CC methods have extremely large errors in the gas-saturated formation. Besides, the NGD-FC method are hardly affected by the formation water salinity, the NGD-TC method is slightly affected, while the NGD-CC method is greatly affected. This study can provide a guidance for the tool design, data processing and environment correction of the NGD technology.
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a comparative study on the neutron Gamma Density and Gamma Gamma Density logging
Journal of Petroleum Science and Engineering, 2019Co-Authors: Feng Zhang, Quanying Zhang, Chao Yuan, Xinguang Wang, Xiaoyang ZhangAbstract:Abstract With the increasing demand for the radioisotope-free operations, using pulsed neutron Gamma Density (NGD) instead of Gamma-Gamma Density (GGD) has become increasingly important for the development of logging while drilling (LWD) technology. However, due to the different logging mechanisms, there are huge differences between GGD and NGD in the instrument designs, measurement methods, and instrument specifications. To further promote the NGD development, a comparative study on GGD and NGD was carried out from theoretical and simulation aspects. Based on the theoretical methods, the differences between GGD and NGD in the Gamma sources, field distribution, methods for Density measurement and instrument specifications were systematically elaborated. Then, using the Monte Carlo simulation, the GGD and NGD models were built to quantitatively verify the theoretical results. Last, the detailed performances of NGD and GGD methods in different logging environments were compared. Results showed that the theoretical results are highly consistent with the simulation results. The Density sensitivity of NGD is less than half that of GGD, but the depth of investigation (DOI) approaches twice that of GGD. The Density precision and vertical resolution of NGD are less than those of GGD. Additionally, compared to GGD, NGD also has an excellent performance in different pore fluid and lithology formations, but it is easily affected by borehole factors. The research can provide quantitative performance evaluations for the NGD replacing GGD in LWD logging.
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Improvement in the method for borehole caliper measurement based on azimuthal Gamma-Gamma Density well logging.
Applied Radiation and Isotopes, 2018Co-Authors: He Wu, Feng ZhangAbstract:Abstract Accurate characterization of the size and shape of the borehole is critical to the effective borehole correction for logging while drilling (LWD) measurements. It is also necessary for the real-time evaluation of geomechanical wellbore stability and for optimizing drilling operation and determining proper completion strategies. The pseudo-caliper measurement can be derived from LWD azimuthal Density measurement, where a linear empirical model is employed to calculate the tool standoffs. However, we found that as the tool standoff continues to increase, the model could no longer describe the variation in borehole size accurately. In this paper, the responses of LWD azimuthal Density measurement under different logging conditions are studied using the Monte Carlo modeling method. To improve the estimation of borehole geometry, a new model is proposed to determine tool standoffs and measure the borehole caliper. Simulation models with different degrees of borehole enlargement are built to investigate the performance of the model. Compared with the currently used method, the wellbore caliper values calculated using the new method are more consistent with the actual values. A field example with mechanical caliper measured from wireline logs is also presented to validate the effectiveness of the proposed method.
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a method for determining Density based on Gamma ray and fast neutron detection using a cs2liycl6 detector in neutron Gamma Density logging
Applied Radiation and Isotopes, 2018Co-Authors: Feng Zhang, Quanying Zhang, R P Gardner, Huizhong Yan, Lili Tian, Qian ChenAbstract:Abstract With the increasing demand for radioisotope-free operations, pulsed neutron-Gamma Density (NGD) has become increasingly important for logging-while-drilling (LWD) development. However, current NGD tools, adopting the multiple-detector array design, are not conducive to the simplification of instrument design and measurement system. To break obstacles, based on the fast neutron-Gamma coupled theory, a new Density measurement method was proposed. Further, combined with the neutron-Gamma simultaneous detection characteristics of the Cs2LiYCl6 (CLYC) detector, an NGD measurement system consisting of a D-T source and one CLYC detector was used. Results show that the new method is capable of determining formation Density using a single CLYC detector, which can not only avoid complex instrument systems but also improve Density sensitivity. Moreover, the applicability of the new Density method was well verified by Monte Carlo simulation. Additionally, the method was successfully applied in a simulated well, and Density results are in good agreement with the benchmarked formations. The research provides theoretical guidance for NGD instrument design.
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a method to describe inelastic Gamma field distribution in neutron Gamma Density logging
Applied Radiation and Isotopes, 2017Co-Authors: Feng Zhang, Quanying Zhang, Xinguang Wang, Juntao Liu, Wenbao Jia, Fei Qiu, Xiaoyang ZhangAbstract:Pulsed neutron Gamma Density logging (NGD) is of great significance for radioprotection and Density measurement in LWD, however, the current methods have difficulty in quantitative calculation and single factor analysis for the inelastic Gamma field distribution. In order to clarify the NGD mechanism, a new method is developed to describe the inelastic Gamma field distribution. Based on the fast-neutron scattering and Gamma attenuation, the inelastic Gamma field distribution is characterized by the inelastic scattering cross section, fast-neutron scattering free path, formation Density and other parameters. And the contribution of formation parameters on the field distribution is quantitatively analyzed. The results shows the contribution of Density attenuation is opposite to that of inelastic scattering cross section and fast-neutron scattering free path. And as the detector-spacing increases, the Density attenuation gradually plays a dominant role in the Gamma field distribution, which means large detector-spacing is more favorable for the Density measurement. Besides, the relationship of Density sensitivity and detector spacing was studied according to this Gamma field distribution, therefore, the spacing of near and far Gamma ray detector is determined. The research provides theoretical guidance for the tool parameter design and Density determination of pulsed neutron Gamma Density logging technique.
