Pub Date : 2023-03-20DOI: 10.1080/08123985.2023.2183115
Jeong-Mun Yu, Byoung-Yeop Kim, Y. Joo
Marine seismic surveys are widely used to explore oil and gas resources and monitor CO2 storage. In particular, ocean-bottom seismic surveys allow the acquisition of high-quality data without the influence of the water-layer environment. However, ocean-bottom seismic surveys are more expensive than streamer surveys and P-wave survey data exhibit free-surface multiples, which are persistent problems. PZ summation can be applied to process multicomponent ocean-bottom seismic data, which effectively reduces ghosting and water-layer reverberation by combining hydrophone and vertical geophone data. In this study, we processed and analysed ocean-bottom cable data from a shallow gas area offshore from Korea. In our field-survey simulation, PZ summation was applied to the synthetic data to separate up-going and down-going wavefields and attenuate free-surface multiples. In addition, improved image can be obtained compared to conventional stack section by applying seismic interferometry to the acquired up-going wavefield data.
{"title":"A processing for ocean-bottom multicomponent data with seismic interferometry: a case study of southern offshore in Korea","authors":"Jeong-Mun Yu, Byoung-Yeop Kim, Y. Joo","doi":"10.1080/08123985.2023.2183115","DOIUrl":"https://doi.org/10.1080/08123985.2023.2183115","url":null,"abstract":"Marine seismic surveys are widely used to explore oil and gas resources and monitor CO2 storage. In particular, ocean-bottom seismic surveys allow the acquisition of high-quality data without the influence of the water-layer environment. However, ocean-bottom seismic surveys are more expensive than streamer surveys and P-wave survey data exhibit free-surface multiples, which are persistent problems. PZ summation can be applied to process multicomponent ocean-bottom seismic data, which effectively reduces ghosting and water-layer reverberation by combining hydrophone and vertical geophone data. In this study, we processed and analysed ocean-bottom cable data from a shallow gas area offshore from Korea. In our field-survey simulation, PZ summation was applied to the synthetic data to separate up-going and down-going wavefields and attenuate free-surface multiples. In addition, improved image can be obtained compared to conventional stack section by applying seismic interferometry to the acquired up-going wavefield data.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"533 - 543"},"PeriodicalIF":0.9,"publicationDate":"2023-03-20","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49168054","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-17DOI: 10.1080/08123985.2023.2189584
Y. Ohta, T. Goto, Koki Kashiwaya, K. Koike
ABSTRACT Many studies have been conducted to analyse dielectric polarisation and the complex electrical conductivity characteristics by the Cole–Cole type relaxation approximating rocks with a uniform material. That method has revealed the correlation between metal contents and chargeability, between the central relaxation time and the metallic particle size, and so on. Based on the model’s success, such models have been extended to those with multiple capacitances. However, these models cannot represent the mechanism of electrical flow in rocks using equivalent circuits and cannot explain the electrical behaviour of rocks that deviates significantly from the assumptions of the models. Therefore, in this study, by re-evaluating Pelton’s equation, we strove to formulate an appropriate multiple-capacitance model expressed by an equivalent circuit, with the aim of ascertaining electrical features more easily and properly than through the convolution of electrical response functions. We achieved theoretical expansion of Pelton-type formulae to multiple capacitances. Our Double-Pelton equivalent circuit model (DPM) was applied to the observed complex conductivity curves of artificial samples including pyrite. The obtained parameters of our DPM were found to have a good correlation to the rock features. We achieved to show that the conductive mechanism of the complex geometrical features of rock samples can be modelled simply and effectively. The continuous efficiency of sulphide particles in the direction of the electric field, and pyrite particles which can act as bottleneck conductors as in percolation theory, are found to be playing an important role in electric conduction.
{"title":"Multi-capacitance electric relaxation model for complex electrical conductivity of sulphide ores","authors":"Y. Ohta, T. Goto, Koki Kashiwaya, K. Koike","doi":"10.1080/08123985.2023.2189584","DOIUrl":"https://doi.org/10.1080/08123985.2023.2189584","url":null,"abstract":"ABSTRACT Many studies have been conducted to analyse dielectric polarisation and the complex electrical conductivity characteristics by the Cole–Cole type relaxation approximating rocks with a uniform material. That method has revealed the correlation between metal contents and chargeability, between the central relaxation time and the metallic particle size, and so on. Based on the model’s success, such models have been extended to those with multiple capacitances. However, these models cannot represent the mechanism of electrical flow in rocks using equivalent circuits and cannot explain the electrical behaviour of rocks that deviates significantly from the assumptions of the models. Therefore, in this study, by re-evaluating Pelton’s equation, we strove to formulate an appropriate multiple-capacitance model expressed by an equivalent circuit, with the aim of ascertaining electrical features more easily and properly than through the convolution of electrical response functions. We achieved theoretical expansion of Pelton-type formulae to multiple capacitances. Our Double-Pelton equivalent circuit model (DPM) was applied to the observed complex conductivity curves of artificial samples including pyrite. The obtained parameters of our DPM were found to have a good correlation to the rock features. We achieved to show that the conductive mechanism of the complex geometrical features of rock samples can be modelled simply and effectively. The continuous efficiency of sulphide particles in the direction of the electric field, and pyrite particles which can act as bottleneck conductors as in percolation theory, are found to be playing an important role in electric conduction.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"463 - 473"},"PeriodicalIF":0.9,"publicationDate":"2023-03-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47436427","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-16DOI: 10.1080/08123985.2023.2168533
A. Saha, A. Dey
Soft clayey soils are generally improved by the consolidation process. The different improvement techniques which are in vogue include the use of stone columns, sand drains with and without preload and prefabricated vertical drains. Upon improvement, the soft soil attains a higher strength and better resistance to excessive settlement. The extent of this improvement of the soft soil is measured through different in-situ tests including Standard Penetration Test (SPT), Cone Penetration Test (CPT) and Pressuremeter Test. Most of these tests are invasive and require boreholes for the collection of soil samples. Geophysical tests can scan the entire area within a short time and can accurately interpret the extent of the improvement depending on the expertise of the investigators. Sometimes a combination of two or more geophysical tests is suitable for an accurate prediction of any change in soil properties. The present study is an attempt to measure the effect of ground treatment by implementing two types of geophysical tests, namely, Electrical Resistivity Tomography (ERT) and Multichannel Analysis of Surface Wave (MASW) near a by-pass road in Silchar, Assam. The tests were conducted on a newly constructed road embankment that had undergone excessive settlement and was subsequently treated with stone columns with a preload. Both the geophysical tests showed improvement in soil properties as well as in the bearing capacity of the original soft soil. A bore log survey was also carried out before the improvement work to validate the results of the geophysical tests. Existing correlations among geophysical properties and soil properties were used to obtain the effect of improvement. It has been observed that geophysical tests can easily be carried out to accurately calculate the effect of improvement of soil properties. A combination of two or more geophysical methods yields a better understanding of the post-treatment results.
{"title":"Assessing combined analysis of electrical resistivity tomography and multichannel analysis of surface waves for ground improvement assessment near by-pass road, Silchar, Assam","authors":"A. Saha, A. Dey","doi":"10.1080/08123985.2023.2168533","DOIUrl":"https://doi.org/10.1080/08123985.2023.2168533","url":null,"abstract":"Soft clayey soils are generally improved by the consolidation process. The different improvement techniques which are in vogue include the use of stone columns, sand drains with and without preload and prefabricated vertical drains. Upon improvement, the soft soil attains a higher strength and better resistance to excessive settlement. The extent of this improvement of the soft soil is measured through different in-situ tests including Standard Penetration Test (SPT), Cone Penetration Test (CPT) and Pressuremeter Test. Most of these tests are invasive and require boreholes for the collection of soil samples. Geophysical tests can scan the entire area within a short time and can accurately interpret the extent of the improvement depending on the expertise of the investigators. Sometimes a combination of two or more geophysical tests is suitable for an accurate prediction of any change in soil properties. The present study is an attempt to measure the effect of ground treatment by implementing two types of geophysical tests, namely, Electrical Resistivity Tomography (ERT) and Multichannel Analysis of Surface Wave (MASW) near a by-pass road in Silchar, Assam. The tests were conducted on a newly constructed road embankment that had undergone excessive settlement and was subsequently treated with stone columns with a preload. Both the geophysical tests showed improvement in soil properties as well as in the bearing capacity of the original soft soil. A bore log survey was also carried out before the improvement work to validate the results of the geophysical tests. Existing correlations among geophysical properties and soil properties were used to obtain the effect of improvement. It has been observed that geophysical tests can easily be carried out to accurately calculate the effect of improvement of soil properties. A combination of two or more geophysical methods yields a better understanding of the post-treatment results.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"474 - 492"},"PeriodicalIF":0.9,"publicationDate":"2023-03-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"42724509","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-03-04DOI: 10.1080/08123985.2022.2082281
W. Mcneice, Richard S. Smith, E. Eshaghi
Magnetic susceptibilities measured on outcrop are often assumed to be reasonable values to use when modelling aeromagnetic data. We have undertaken two exercises to understand how useful these measurements are for magnetic modelling. Estimates of apparent magnetic susceptibility can also be derived from aeromagnetic data by mathematical transformation if certain stringent conditions are satisfied. In the first exercise comparison of these two sets of values shows that when the measured values are below 1 × 10−3 SI, there is no correlation between the measured and apparent values. Above this value, the measured and estimated values agree to within a factor of 10, so these measured values can only be used as very rough constraints. In the second exercise, a database of outcrop measured magnetic susceptibilities was used to estimate a mean value for each lithology. When the mean of the measured values was used in our forward modelling exercise, we obtained a poor fit. However, when we inserted additional layers with larger susceptibilities that are represented on the histogram of a regional compilation of that lithology, the fit was satisfactory. In some cases, these additional layers were located in areas where there is relatively large variability in the magnetic susceptibility values measured on nearby outcrops. A large database of outcrop magnetic susceptibilities proved useful for providing a reasonable initial guess and the range of values that encompass the possible heterogeneities in each rock type.
{"title":"How magnetic susceptibilities measured on outcrops can be used for modelling (and constraining inversions of) aeromagnetic data","authors":"W. Mcneice, Richard S. Smith, E. Eshaghi","doi":"10.1080/08123985.2022.2082281","DOIUrl":"https://doi.org/10.1080/08123985.2022.2082281","url":null,"abstract":"Magnetic susceptibilities measured on outcrop are often assumed to be reasonable values to use when modelling aeromagnetic data. We have undertaken two exercises to understand how useful these measurements are for magnetic modelling. Estimates of apparent magnetic susceptibility can also be derived from aeromagnetic data by mathematical transformation if certain stringent conditions are satisfied. In the first exercise comparison of these two sets of values shows that when the measured values are below 1 × 10−3 SI, there is no correlation between the measured and apparent values. Above this value, the measured and estimated values agree to within a factor of 10, so these measured values can only be used as very rough constraints. In the second exercise, a database of outcrop measured magnetic susceptibilities was used to estimate a mean value for each lithology. When the mean of the measured values was used in our forward modelling exercise, we obtained a poor fit. However, when we inserted additional layers with larger susceptibilities that are represented on the histogram of a regional compilation of that lithology, the fit was satisfactory. In some cases, these additional layers were located in areas where there is relatively large variability in the magnetic susceptibility values measured on nearby outcrops. A large database of outcrop magnetic susceptibilities proved useful for providing a reasonable initial guess and the range of values that encompass the possible heterogeneities in each rock type.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"189 - 204"},"PeriodicalIF":0.9,"publicationDate":"2023-03-04","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47966650","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-02-21DOI: 10.1080/08123985.2023.2176747
Gang Li, Wen Lei, C. Li, Lin-jiang Qin
ABSTRACT In shallow waters, the interpretation of the frequency-domain marine controlled-source electromagnetic (CSEM) data is challenging due to the airwave. The airwave dominates and will lead to misinterpretation of the data set. A differential-field approach is presented to attenuate the airwave for the shallow-water marine CSEM data. The difference of the fields between two consecutive receivers or source points is calculated and weighted by the geometric spreading related factor. By using differential fields, the detectability given by the field ratio between the models with and without the target is enhanced, which indicates that the impact of airwaves is suppressed.
{"title":"Enhanced detectability using differential fields for marine controlled-source EM data in shallow waters","authors":"Gang Li, Wen Lei, C. Li, Lin-jiang Qin","doi":"10.1080/08123985.2023.2176747","DOIUrl":"https://doi.org/10.1080/08123985.2023.2176747","url":null,"abstract":"ABSTRACT In shallow waters, the interpretation of the frequency-domain marine controlled-source electromagnetic (CSEM) data is challenging due to the airwave. The airwave dominates and will lead to misinterpretation of the data set. A differential-field approach is presented to attenuate the airwave for the shallow-water marine CSEM data. The difference of the fields between two consecutive receivers or source points is calculated and weighted by the geometric spreading related factor. By using differential fields, the detectability given by the field ratio between the models with and without the target is enhanced, which indicates that the impact of airwaves is suppressed.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"457 - 462"},"PeriodicalIF":0.9,"publicationDate":"2023-02-21","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"41470713","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-01-17DOI: 10.1080/08123985.2023.2166402
M. Musolino, S. Holford, R. King, R. Hillis
Accurate estimates of Unconfined Compressive Strength (UCS) are essential for a range of subsurface applications, including drilling wells for subsurface fluid extraction or injection. However, measuring UCS of subsurface rock samples through laboratory-based uniaxial and triaxial testing is time consuming, expensive, and potentially subject to individual sample variance. P-wave velocity logs are routinely obtained in petroleum basins and are commonly used to estimate UCS using empirically-derived correlations. In this study we analysed P-wave velocity data from 43 wells in the Cooper Basin, Australia and created mean ranges of expected UCS through the Tirrawarra, Toolachee, Patchawarra, Murteree Shale and Epsilon formations, using literature-derived P-wave velocity-UCS correlations, and also estimated UCS based on selected available laboratory-determined P-wave velocity measurements. These two suites of P-wave velocity-derived estimates of UCS are then compared to available results from laboratory uniaxial testing of core samples. Our analysis indicates that P-wave velocities, and subsequent derived estimates of UCS from P-wave wireline logs, are typically lower than those from laboratory-analysed samples. This may reflect a sampling bias towards the selection of strong rocks for laboratory UCS testing or lower estimates of UCS due to wellbore damage and pore space content (air or liquids) from P-wave log derived velocities. However, the laboratory-derived P-wave velocities generally agree with laboratory-derived UCS data from the Patchawarra, Murteree Shale and Epsilon formations when using published empirical velocity-strength correlations. A retrospective case study presents the impacts of different UCS estimates on mud weight required to produce observed borehole breakouts in the Epsilon Formation. Breakouts were observed 90 degrees to the orientation of SHmax (117° N) with a mean width of 51°, the breakouts were produced during drilling using a 9.7 ppg mud weight. The back-calculated estimate of UCS from the observed breakout widths at 9.7 ppg is 154 MPa. This sits between the UCS estimate of 171 MPa from uniaxial testing and 145 MPa from the mean of laboratory sample-derived P-wave velocities. Estimates of UCS from empirical correlations based solely on p-wave log-derived are far lower and vary between 87.3 and 114.4 MPa.
{"title":"Evaluating uncertainty in empirically derived unconfined compressive strength (UCS) estimates and implications for drilling applications; a case study from the Cooper Basin","authors":"M. Musolino, S. Holford, R. King, R. Hillis","doi":"10.1080/08123985.2023.2166402","DOIUrl":"https://doi.org/10.1080/08123985.2023.2166402","url":null,"abstract":"Accurate estimates of Unconfined Compressive Strength (UCS) are essential for a range of subsurface applications, including drilling wells for subsurface fluid extraction or injection. However, measuring UCS of subsurface rock samples through laboratory-based uniaxial and triaxial testing is time consuming, expensive, and potentially subject to individual sample variance. P-wave velocity logs are routinely obtained in petroleum basins and are commonly used to estimate UCS using empirically-derived correlations. In this study we analysed P-wave velocity data from 43 wells in the Cooper Basin, Australia and created mean ranges of expected UCS through the Tirrawarra, Toolachee, Patchawarra, Murteree Shale and Epsilon formations, using literature-derived P-wave velocity-UCS correlations, and also estimated UCS based on selected available laboratory-determined P-wave velocity measurements. These two suites of P-wave velocity-derived estimates of UCS are then compared to available results from laboratory uniaxial testing of core samples. Our analysis indicates that P-wave velocities, and subsequent derived estimates of UCS from P-wave wireline logs, are typically lower than those from laboratory-analysed samples. This may reflect a sampling bias towards the selection of strong rocks for laboratory UCS testing or lower estimates of UCS due to wellbore damage and pore space content (air or liquids) from P-wave log derived velocities. However, the laboratory-derived P-wave velocities generally agree with laboratory-derived UCS data from the Patchawarra, Murteree Shale and Epsilon formations when using published empirical velocity-strength correlations. A retrospective case study presents the impacts of different UCS estimates on mud weight required to produce observed borehole breakouts in the Epsilon Formation. Breakouts were observed 90 degrees to the orientation of SHmax (117° N) with a mean width of 51°, the breakouts were produced during drilling using a 9.7 ppg mud weight. The back-calculated estimate of UCS from the observed breakout widths at 9.7 ppg is 154 MPa. This sits between the UCS estimate of 171 MPa from uniaxial testing and 145 MPa from the mean of laboratory sample-derived P-wave velocities. Estimates of UCS from empirical correlations based solely on p-wave log-derived are far lower and vary between 87.3 and 114.4 MPa.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"493 - 508"},"PeriodicalIF":0.9,"publicationDate":"2023-01-17","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44486255","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-01-16DOI: 10.1080/08123985.2022.2162381
M. Protasov, D. Neklyudov
In the paper, we describe an original 3D travel-time tomography approach. It is based on the new realization of the bending method which to some extent takes into account the band-limited nature of real seismic signals propagation. As a result, two-point ray tracing provides more reliable ray trajectories and travel times in complex media. Another original feature of the proposed tomography is that the model is represented using the Chebyshev polynomials. Such parameterization allows analytical calculation of travel times and their derivatives with respect to model parameters and significantly reduces the number of parameters to be recovered during inversion compared to more common grid tomography. In certain situations, the proposed approach provides significant computational advantages. Numerical examples prove its efficiency.
{"title":"Fast 3D “wave-consistent” ray tomography based on a polynomial representation of a model","authors":"M. Protasov, D. Neklyudov","doi":"10.1080/08123985.2022.2162381","DOIUrl":"https://doi.org/10.1080/08123985.2022.2162381","url":null,"abstract":"In the paper, we describe an original 3D travel-time tomography approach. It is based on the new realization of the bending method which to some extent takes into account the band-limited nature of real seismic signals propagation. As a result, two-point ray tracing provides more reliable ray trajectories and travel times in complex media. Another original feature of the proposed tomography is that the model is represented using the Chebyshev polynomials. Such parameterization allows analytical calculation of travel times and their derivatives with respect to model parameters and significantly reduces the number of parameters to be recovered during inversion compared to more common grid tomography. In certain situations, the proposed approach provides significant computational advantages. Numerical examples prove its efficiency.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"441 - 456"},"PeriodicalIF":0.9,"publicationDate":"2023-01-16","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"44063744","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2023-01-09DOI: 10.1080/08123985.2022.2162382
Marc A. Vallée, Mouhamed Moussaoui
Estimating the electromagnetic response of a conductive sphere in a layered earth is of great interest in terms of both modelling and interpretating data acquired via geophysical electromagnetic methods where the target is at some distance from the source and receiver. This is particularly the case when using Airborne Electromagnetic Method (AEM) where the source and receiver are located at some height above the subsurface. This problem can be solved by utilising field expansions representing derivatives of cylindrical functions, which describe the fields propagating in the layered earth, and spherical functions, which describe the fields reflected by the sphere. Furthermore, these representations allow the development of relationships between cylindrical and spherical functions. These functions and subsequent relationships have been used to develop an algorithm for estimating the electromagnetic response of a conductive sphere in an isotropic layered earth. Software based on this algorithm has been tested on both synthetic and field data. The field data presented were collected with the AEM AirTEM system over the Reid-Mahaffy test site, Ontario, Canada. Results from these tests prove the importance and utility of integrating the sphere in a layered earth model in the AEM interpretation toolbox.
{"title":"Modelling the electromagnetic response of a sphere located in a layered earth","authors":"Marc A. Vallée, Mouhamed Moussaoui","doi":"10.1080/08123985.2022.2162382","DOIUrl":"https://doi.org/10.1080/08123985.2022.2162382","url":null,"abstract":"Estimating the electromagnetic response of a conductive sphere in a layered earth is of great interest in terms of both modelling and interpretating data acquired via geophysical electromagnetic methods where the target is at some distance from the source and receiver. This is particularly the case when using Airborne Electromagnetic Method (AEM) where the source and receiver are located at some height above the subsurface. This problem can be solved by utilising field expansions representing derivatives of cylindrical functions, which describe the fields propagating in the layered earth, and spherical functions, which describe the fields reflected by the sphere. Furthermore, these representations allow the development of relationships between cylindrical and spherical functions. These functions and subsequent relationships have been used to develop an algorithm for estimating the electromagnetic response of a conductive sphere in an isotropic layered earth. Software based on this algorithm has been tested on both synthetic and field data. The field data presented were collected with the AEM AirTEM system over the Reid-Mahaffy test site, Ontario, Canada. Results from these tests prove the importance and utility of integrating the sphere in a layered earth model in the AEM interpretation toolbox.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"362 - 375"},"PeriodicalIF":0.9,"publicationDate":"2023-01-09","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"49627208","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-12-12DOI: 10.1080/08123985.2022.2155514
Meijiao Wang, Yanhai Liu, Guangui Zou, De-Lin Teng, Jiasheng She
The Permian coal seams in eastern Yunnan and western Guizhou are thin, numerous, and staggered with other thin coal seams. Depicting the fine characteristics of coal reservoirs is pivotal for the safe and efficient exploitation of coal and coalbed methane (CBM), and is important for transparent mining. To improve the inverse resolution and accuracy of predicting reservoir thickness, this study used the model-based acoustic impedance (AI) inversion method that utilizes seismic and logging data. This method changes seismic data, reflecting stratigraphic interfaces, into AI data, reflecting lithologic structures. Moreover, it avoids the relevant assumptions of wavelets and reflection coefficients. Compared with other inversion methods, model-based AI inversion strengthens the description of thin reservoir horizontal and vertical changes. The results showed that comprehensively using intermediate-frequency seismic information and high-low-frequency logging data greatly broadens the seismic data frequency band and improves the dominant frequency of the reflected wave. Furthermore, the AI profile resolution and the prediction accuracy of the physical parameters for the target geological body can be improved. A cross-validation comparing the inverted thickness and measured thickness of borehole cores was applied to achieve fine prediction (error of appropriately 0.02–0.4 m), providing a basis for CBM development.
{"title":"Application of model-based acoustic impedance inversion in the prediction of thin interbedded coal seams: a case study in the Yuwang colliery, Yunnan Province","authors":"Meijiao Wang, Yanhai Liu, Guangui Zou, De-Lin Teng, Jiasheng She","doi":"10.1080/08123985.2022.2155514","DOIUrl":"https://doi.org/10.1080/08123985.2022.2155514","url":null,"abstract":"The Permian coal seams in eastern Yunnan and western Guizhou are thin, numerous, and staggered with other thin coal seams. Depicting the fine characteristics of coal reservoirs is pivotal for the safe and efficient exploitation of coal and coalbed methane (CBM), and is important for transparent mining. To improve the inverse resolution and accuracy of predicting reservoir thickness, this study used the model-based acoustic impedance (AI) inversion method that utilizes seismic and logging data. This method changes seismic data, reflecting stratigraphic interfaces, into AI data, reflecting lithologic structures. Moreover, it avoids the relevant assumptions of wavelets and reflection coefficients. Compared with other inversion methods, model-based AI inversion strengthens the description of thin reservoir horizontal and vertical changes. The results showed that comprehensively using intermediate-frequency seismic information and high-low-frequency logging data greatly broadens the seismic data frequency band and improves the dominant frequency of the reflected wave. Furthermore, the AI profile resolution and the prediction accuracy of the physical parameters for the target geological body can be improved. A cross-validation comparing the inverted thickness and measured thickness of borehole cores was applied to achieve fine prediction (error of appropriately 0.02–0.4 m), providing a basis for CBM development.","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"54 1","pages":"407 - 415"},"PeriodicalIF":0.9,"publicationDate":"2022-12-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"46133929","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2022-12-05DOI: 10.1080/08123985.2022.2144212
A. Kirkby, M. Doublier
{"title":"Synthetic magnetotelluric modelling of a regional fault network – implications for survey design and interpretation","authors":"A. Kirkby, M. Doublier","doi":"10.1080/08123985.2022.2144212","DOIUrl":"https://doi.org/10.1080/08123985.2022.2144212","url":null,"abstract":"","PeriodicalId":50460,"journal":{"name":"Exploration Geophysics","volume":"1 1","pages":""},"PeriodicalIF":0.9,"publicationDate":"2022-12-05","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"47385077","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":4,"RegionCategory":"地球科学","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
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