Pub Date : 2019-12-01DOI: 10.1080/22020586.2019.12073131
A. Guirou
Summary The increasing depth of investigation for sediment hosted copper mineralisation in the Central African Copperbelt requires the use of adequate geophysical methods such as natural source audio magnetotellurics (NSAMT) as opposed to conventional electrical geophysics techniques (resistivity/IP and time domain electromagnetics) which have limited depth of investigation. A NSAMT survey was carried out at the Solwezi East project near the Kansanshi copper mine in north-western Zambia in order to map a possible undercover domal structure which is thought to control mineralisation at the mine. A total of 50 line kilometres of NSAMT successfully identified a confined domal structure 1.2 km long and 700m wide buried at about 700m below surface. The mapped dome awaits a drill test to confirm the presence of economic mineralisation. NSAMT is proven to be successful for mapping buried domes at considerable depth.
{"title":"Mapping undercover domal structure using audio-magnetotellurics in Zambia.","authors":"A. Guirou","doi":"10.1080/22020586.2019.12073131","DOIUrl":"https://doi.org/10.1080/22020586.2019.12073131","url":null,"abstract":"Summary The increasing depth of investigation for sediment hosted copper mineralisation in the Central African Copperbelt requires the use of adequate geophysical methods such as natural source audio magnetotellurics (NSAMT) as opposed to conventional electrical geophysics techniques (resistivity/IP and time domain electromagnetics) which have limited depth of investigation. A NSAMT survey was carried out at the Solwezi East project near the Kansanshi copper mine in north-western Zambia in order to map a possible undercover domal structure which is thought to control mineralisation at the mine. A total of 50 line kilometres of NSAMT successfully identified a confined domal structure 1.2 km long and 700m wide buried at about 700m below surface. The mapped dome awaits a drill test to confirm the presence of economic mineralisation. NSAMT is proven to be successful for mapping buried domes at considerable depth.","PeriodicalId":8502,"journal":{"name":"ASEG Extended Abstracts","volume":"265 1","pages":"1 - 3"},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73472551","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/22020586.2019.12072965
T. Wells, S. Meffre, D. Cooke, J. Steadman, J. Hoye
Summary This research presents a new method for assessing magmatic fertility using pXRF in altered terranes using Zr and Y ratios. A study of global batholith related mineralised porphyries, highlights a low Zr fractionation trend. The depletion in Zr is associated with early crystallisation of titanite. Yttrium depletion is related to early crystallisation of both titanite and amphibole, an indication of hydrous melts. Previously differentiation of hydrous, potentially ore-forming (fertile) porphyries relied on Sr/Y from whole rock assay of least altered rocks. Finding samples in porphyry terranes where Sr can be demonstrated to be immobile is difficult given the ubiquity of hydrothermal alteration associated with porphyry emplacement. The requirement for unaltered samples is based on the mobility of Sr which precludes the widespread use of pXRF as quantitative assessment of LOI% (as a proxy for alteration) is beyond the current capabilities of the technology. Using comparatively immobile Zr and Y overcomes issues with alteration and provides a more reliable new indicator of magmatic fertility. In this case study, using a systematic workflow pXRF was successful in identifying the mineralising intrusions in the Northparkes intrusive complex using a Zr/Y vs. Y fertility indicator.
本研究提出了一种利用Zr和Y比值利用pXRF评价蚀变地体岩浆肥力的新方法。对全球岩基相关矿化斑岩的研究，强调了低Zr分馏趋势。锆的损耗与钛矿的早期结晶有关。钇的损耗与钛矿和角闪孔的早期结晶有关，表明存在含水熔体。以前，含水的、可能成矿的(肥沃的)斑岩的分异依赖于最小蚀变岩全岩的Sr/Y分析。由于普遍存在与斑岩侵位相关的热液蚀变，在斑岩地体中寻找锶可以被证明是不移动的样品是困难的。对未改变样品的要求是基于Sr的迁移率，这就排除了pXRF的广泛使用，因为LOI%的定量评估(作为改变的代理)超出了当前技术的能力。利用相对不动的Zr和Y克服了蚀变问题，提供了一个更可靠的岩浆生育力新指标。在这个案例研究中，pXRF使用系统的工作流程，利用Zr/Y vs. Y的矿化度指标，成功地识别了Northparkes侵入复合体中的矿化侵入。
{"title":"pXRF assessment of new magmatic fertility indicators in the Macquarie Arc","authors":"T. Wells, S. Meffre, D. Cooke, J. Steadman, J. Hoye","doi":"10.1080/22020586.2019.12072965","DOIUrl":"https://doi.org/10.1080/22020586.2019.12072965","url":null,"abstract":"Summary This research presents a new method for assessing magmatic fertility using pXRF in altered terranes using Zr and Y ratios. A study of global batholith related mineralised porphyries, highlights a low Zr fractionation trend. The depletion in Zr is associated with early crystallisation of titanite. Yttrium depletion is related to early crystallisation of both titanite and amphibole, an indication of hydrous melts. Previously differentiation of hydrous, potentially ore-forming (fertile) porphyries relied on Sr/Y from whole rock assay of least altered rocks. Finding samples in porphyry terranes where Sr can be demonstrated to be immobile is difficult given the ubiquity of hydrothermal alteration associated with porphyry emplacement. The requirement for unaltered samples is based on the mobility of Sr which precludes the widespread use of pXRF as quantitative assessment of LOI% (as a proxy for alteration) is beyond the current capabilities of the technology. Using comparatively immobile Zr and Y overcomes issues with alteration and provides a more reliable new indicator of magmatic fertility. In this case study, using a systematic workflow pXRF was successful in identifying the mineralising intrusions in the Northparkes intrusive complex using a Zr/Y vs. Y fertility indicator.","PeriodicalId":8502,"journal":{"name":"ASEG Extended Abstracts","volume":"188 1","pages":"1 - 4"},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"73943522","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/22020586.2019.12072941
D. Palmer
Summary The head wave coefficient (HWC), the refraction analogue of the reflection coefficient, is a complex function of the densities and the P- and S-wave velocities in both the weathered and sub-weathered regions. In general, the HWC increases with increasing P- and S-wave velocities in the weathered layer, but it decreases with increasing P- and S-wave seismic velocities in the sub-weathered layer. Unscaled S-wave velocities in the weathered and sub-weathered regions can be computed with the HWCs for each interface and the detailed P-wave seismic velocities in each layer, using various approximations for the HWC. In general, there is excellent agreement between the measured and computed HWCs. However, some form of traveltime-based estimate of the S-wave velocities is required to calibrate the amplitude-based estimates.
{"title":"Inverting the head wave coefficient with multi-fold near-surface seismic refraction data","authors":"D. Palmer","doi":"10.1080/22020586.2019.12072941","DOIUrl":"https://doi.org/10.1080/22020586.2019.12072941","url":null,"abstract":"Summary The head wave coefficient (HWC), the refraction analogue of the reflection coefficient, is a complex function of the densities and the P- and S-wave velocities in both the weathered and sub-weathered regions. In general, the HWC increases with increasing P- and S-wave velocities in the weathered layer, but it decreases with increasing P- and S-wave seismic velocities in the sub-weathered layer. Unscaled S-wave velocities in the weathered and sub-weathered regions can be computed with the HWCs for each interface and the detailed P-wave seismic velocities in each layer, using various approximations for the HWC. In general, there is excellent agreement between the measured and computed HWCs. However, some form of traveltime-based estimate of the S-wave velocities is required to calibrate the amplitude-based estimates.","PeriodicalId":8502,"journal":{"name":"ASEG Extended Abstracts","volume":"190 1","pages":"1 - 4"},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"75912246","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/22020586.2019.12072969
G. Selfe
Summary Downhole electromagnetic (DHEM) logging was undertaken within four holes drilled at the Las Cruces VMS body in Spain. The geology of the deposit is geophysically complex inasmuch as the background and overlying geology is conductive. A number of loop positions were pre-modelled in order to optimise coupling with the sulphides. The objective in all cases was to locate additional off-hole massive sulphides, belonging to both the main sulphide body and a smaller satellite body. The DHEM was undertaken with a variety of loop positions and at a number of base frequencies. Modelling was undertaken using Maxwell EM modelling software. In three of the holes, by using a number of thick plates and various conductive layers and half-spaces, the DHEM results could be explained by the known sulphides. In the case of a fourth hole, off-hole anomalies were located at depth. A new borehole was recommended based on these data. This borehole was later drilled and an extension to the satellite body intersected.
{"title":"DHEM at Las Cruces, Spain - successes and failures","authors":"G. Selfe","doi":"10.1080/22020586.2019.12072969","DOIUrl":"https://doi.org/10.1080/22020586.2019.12072969","url":null,"abstract":"Summary Downhole electromagnetic (DHEM) logging was undertaken within four holes drilled at the Las Cruces VMS body in Spain. The geology of the deposit is geophysically complex inasmuch as the background and overlying geology is conductive. A number of loop positions were pre-modelled in order to optimise coupling with the sulphides. The objective in all cases was to locate additional off-hole massive sulphides, belonging to both the main sulphide body and a smaller satellite body. The DHEM was undertaken with a variety of loop positions and at a number of base frequencies. Modelling was undertaken using Maxwell EM modelling software. In three of the holes, by using a number of thick plates and various conductive layers and half-spaces, the DHEM results could be explained by the known sulphides. In the case of a fourth hole, off-hole anomalies were located at depth. A new borehole was recommended based on these data. This borehole was later drilled and an extension to the satellite body intersected.","PeriodicalId":8502,"journal":{"name":"ASEG Extended Abstracts","volume":"5 1","pages":"1 - 3"},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"80059827","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/22020586.2019.12073144
Muhammad Ridha Adhari, M. Wilson, A. George
Summary This ongoing research evaluates a fractured carbonate reservoir in the Beekeeper Formation, Perth Basin, focused mainly on the Woodada Field. Previous reports identified a fractured carbonate system as the main hydrocarbon reservoir in the Woodada Field, yet there is no published detailed documentation of reservoir development. The aim of this research is to evaluate the depositional and diagenetic characteristics of the Beekeeper Formation, its fracture system development and their combined impacts on carbonate reservoir quality. This study employs multi-method geological analyses. Subsurface core description, standard microscopy, and acetate peel analyses have been conducted, while scanning electron microscopy, cathodoluminescence petrography, stable isotope geochemistry and fluid inclusion analyses are planned for the coming months. Preliminary results show that the carbonate of the Beekeeper Formation consists of packstone, rudstone, packstone-rudstone, floatstone-packstone and packstone-grainstone. The development of the Beekeeper Formation was affected by tectonic activity. The level of influence of tectonic processes, versus diagenesis and primary sedimentary facies on the development of fracture systems, pore system generation and reservoir quality is still being studied in detail. It is anticipated that this ongoing study will increase our understanding of the Woodada Gas Field and fractured carbonate plays in general.
{"title":"A re-evaluation of a fractured carbonate reservoir from the Perth Basin, Western Australia","authors":"Muhammad Ridha Adhari, M. Wilson, A. George","doi":"10.1080/22020586.2019.12073144","DOIUrl":"https://doi.org/10.1080/22020586.2019.12073144","url":null,"abstract":"Summary This ongoing research evaluates a fractured carbonate reservoir in the Beekeeper Formation, Perth Basin, focused mainly on the Woodada Field. Previous reports identified a fractured carbonate system as the main hydrocarbon reservoir in the Woodada Field, yet there is no published detailed documentation of reservoir development. The aim of this research is to evaluate the depositional and diagenetic characteristics of the Beekeeper Formation, its fracture system development and their combined impacts on carbonate reservoir quality. This study employs multi-method geological analyses. Subsurface core description, standard microscopy, and acetate peel analyses have been conducted, while scanning electron microscopy, cathodoluminescence petrography, stable isotope geochemistry and fluid inclusion analyses are planned for the coming months. Preliminary results show that the carbonate of the Beekeeper Formation consists of packstone, rudstone, packstone-rudstone, floatstone-packstone and packstone-grainstone. The development of the Beekeeper Formation was affected by tectonic activity. The level of influence of tectonic processes, versus diagenesis and primary sedimentary facies on the development of fracture systems, pore system generation and reservoir quality is still being studied in detail. It is anticipated that this ongoing study will increase our understanding of the Woodada Gas Field and fractured carbonate plays in general.","PeriodicalId":8502,"journal":{"name":"ASEG Extended Abstracts","volume":"23 1","pages":"1 - 3"},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"79054614","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/22020586.2019.12073040
Lendyn Philip
Summary Woodside Exploration routinely conducts large regional study projects to inform business decisions regarding new acreage, data acquisition and drilling. Whilst varied, these studies generically comprise phases of data collection and conditioning, analysis, collaboration and actions leading to assurance and finally completion. These studies are usually managed in a linear, or Waterfall, approach and time taken to complete these phases ranges from weeks to months depending upon complexity. An ‘Agile’ approach, originally developed for rapid software development, has been modified to fit geoscience studies insofar as we define a ‘Rapid Study Sprint’ (RSS) that combines the analysis and collaboration phases of the project into a facilitated workshop, at the end of which preliminary products must be completed. The RSS is analogous to a hackathon and leverages intense collaboration to drive fit-for-purpose outcomes. Woodside Exploration Australia held its first RSS in 2017 to produce a play-based exploration evaluation of the Jurassic (J50) Macedon play interval in the Exmouth Sub-basin, offshore Western Australia. In one day of intense collaboration, the RSS generated maps of equivalent quality to traditional regional studies. This paper compares the actual time and cost of this RSS with a notional project plan for a conventional regional study with the same objectives and deliverables. Comparison demonstrates that the RSS and conventional regional project has a similar ultimate duration. However, the distribution of effort and reward varies considerably; with a 40% cost saving attributed to the reduction in worked hours and delivery of usable products two weeks earlier. Savings are attributed to the core principles of Agile driving collaborative behaviours and simplifying business processes to focus effort on the highest priority areas to address the key project objectives.
{"title":"Adapting agile workflows to accelerate geoscience study results","authors":"Lendyn Philip","doi":"10.1080/22020586.2019.12073040","DOIUrl":"https://doi.org/10.1080/22020586.2019.12073040","url":null,"abstract":"Summary Woodside Exploration routinely conducts large regional study projects to inform business decisions regarding new acreage, data acquisition and drilling. Whilst varied, these studies generically comprise phases of data collection and conditioning, analysis, collaboration and actions leading to assurance and finally completion. These studies are usually managed in a linear, or Waterfall, approach and time taken to complete these phases ranges from weeks to months depending upon complexity. An ‘Agile’ approach, originally developed for rapid software development, has been modified to fit geoscience studies insofar as we define a ‘Rapid Study Sprint’ (RSS) that combines the analysis and collaboration phases of the project into a facilitated workshop, at the end of which preliminary products must be completed. The RSS is analogous to a hackathon and leverages intense collaboration to drive fit-for-purpose outcomes. Woodside Exploration Australia held its first RSS in 2017 to produce a play-based exploration evaluation of the Jurassic (J50) Macedon play interval in the Exmouth Sub-basin, offshore Western Australia. In one day of intense collaboration, the RSS generated maps of equivalent quality to traditional regional studies. This paper compares the actual time and cost of this RSS with a notional project plan for a conventional regional study with the same objectives and deliverables. Comparison demonstrates that the RSS and conventional regional project has a similar ultimate duration. However, the distribution of effort and reward varies considerably; with a 40% cost saving attributed to the reduction in worked hours and delivery of usable products two weeks earlier. Savings are attributed to the core principles of Agile driving collaborative behaviours and simplifying business processes to focus effort on the highest priority areas to address the key project objectives.","PeriodicalId":8502,"journal":{"name":"ASEG Extended Abstracts","volume":"24 1","pages":"1 - 2"},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85143439","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/22020586.2019.12073027
Y. Mei, Weihua Liu, R. Chopping
Summary The next generation of mineral and energy system discoveries in Australia will be made under deeper cover or water and require knowledge of the deep earth. Primarily, these discoveries will be driven by understanding the lithospheric properties and resource transport that underpin the systems. Nevertheless, our lack of good understanding of the physical-chemical properties of lithospheric scale mineral systems hinders our interpretation of available data and makes predictive models difficult to use. These properties are very difficult to measure in the laboratory but are accessible through molecular dynamic simulations. We used molecular dynamics simulations to investigate the chemical and physical properties of the NaCl-bearing fluids over wide range of temperature (25-1000 °C), pressure (1-60 kbar) and salinity (0-10 m) using high-performance computers. The equation-of-state, ion association and diffusion constant of NaCl solutions were predicted and fitted into an electrical conductivity model. By integrating predictive geophysical properties with large-scale models, this study will develop essential guides that underpin interpretation of geophysical data for mineral exploration.
{"title":"Equation-of-state and electrical conductivity of NaCl-bearing fluids in the deep Earth: insights from molecular simulations","authors":"Y. Mei, Weihua Liu, R. Chopping","doi":"10.1080/22020586.2019.12073027","DOIUrl":"https://doi.org/10.1080/22020586.2019.12073027","url":null,"abstract":"Summary The next generation of mineral and energy system discoveries in Australia will be made under deeper cover or water and require knowledge of the deep earth. Primarily, these discoveries will be driven by understanding the lithospheric properties and resource transport that underpin the systems. Nevertheless, our lack of good understanding of the physical-chemical properties of lithospheric scale mineral systems hinders our interpretation of available data and makes predictive models difficult to use. These properties are very difficult to measure in the laboratory but are accessible through molecular dynamic simulations. We used molecular dynamics simulations to investigate the chemical and physical properties of the NaCl-bearing fluids over wide range of temperature (25-1000 °C), pressure (1-60 kbar) and salinity (0-10 m) using high-performance computers. The equation-of-state, ion association and diffusion constant of NaCl solutions were predicted and fitted into an electrical conductivity model. By integrating predictive geophysical properties with large-scale models, this study will develop essential guides that underpin interpretation of geophysical data for mineral exploration.","PeriodicalId":8502,"journal":{"name":"ASEG Extended Abstracts","volume":"72 2 1","pages":"1 - 4"},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85506618","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/22020586.2019.12073244
J. Shadlow
Summary Reserves and Resources can be directly estimated by using seismic lithology prediction volumes generated from AVO inversion, calibrated to wells, to estimate sand rock volumes within a stratigraphic interval. However, high quality AVO inversion data and studies are not always available. This case study utilises recursive inversion to generate prediction cubes for input to geobody based gross rock volume estimates. Here, relative recursive inversions of the near and far seismic stacks are generated. EEI rotation theory was applied to calculate relative AI and Vp/Vs volumes. These have then been converted to band-limited absolute inversion volumes by adding a low frequency model built using seismic horizons, well logs and rock physics trends. Finally, probability density functions calibrated to wells were estimated to calculate lithology prediction volumes. A sand probability volume is then calculated using these probability density functions. A relative approach has not been applied due to poor separability of different lithologies in cross-plot space. This method is applied to an area where a single multiazimuth PSDM seismic survey covers two gas fields and several deep exploration prospects. However, previous inversion studies were limited to the individual fields (each inverted separately), incorporated fluid contact information and did not cover the deeper exploration, so were therefore considered sub-optimal. Although there is potential for results from this method to be “bad”, this case study was successful. The inversion volumes generated as part of this study enabled a wholistic view of the fields and exploration prospectivity, which had not been previously possible with the available QI volumes. The seismic data used for input was exceptionally good, and there was abundant well control to provide control and for use in blind testing. The amount of validation and quality-control applied to this project cannot be under-stated. It is critically important to be mindful of the limitations and broad assumptions that are applied as part of this work-flow. These include the addition of the low-frequency model, wavelet affects not being taken into account and depth decay of the lithology predictions due to the application of a single PDF.
{"title":"Using recursive inversion as input for gross-rock volume extraction from lithology prediction volumes: How bad can it be?","authors":"J. Shadlow","doi":"10.1080/22020586.2019.12073244","DOIUrl":"https://doi.org/10.1080/22020586.2019.12073244","url":null,"abstract":"Summary Reserves and Resources can be directly estimated by using seismic lithology prediction volumes generated from AVO inversion, calibrated to wells, to estimate sand rock volumes within a stratigraphic interval. However, high quality AVO inversion data and studies are not always available. This case study utilises recursive inversion to generate prediction cubes for input to geobody based gross rock volume estimates. Here, relative recursive inversions of the near and far seismic stacks are generated. EEI rotation theory was applied to calculate relative AI and Vp/Vs volumes. These have then been converted to band-limited absolute inversion volumes by adding a low frequency model built using seismic horizons, well logs and rock physics trends. Finally, probability density functions calibrated to wells were estimated to calculate lithology prediction volumes. A sand probability volume is then calculated using these probability density functions. A relative approach has not been applied due to poor separability of different lithologies in cross-plot space. This method is applied to an area where a single multiazimuth PSDM seismic survey covers two gas fields and several deep exploration prospects. However, previous inversion studies were limited to the individual fields (each inverted separately), incorporated fluid contact information and did not cover the deeper exploration, so were therefore considered sub-optimal. Although there is potential for results from this method to be “bad”, this case study was successful. The inversion volumes generated as part of this study enabled a wholistic view of the fields and exploration prospectivity, which had not been previously possible with the available QI volumes. The seismic data used for input was exceptionally good, and there was abundant well control to provide control and for use in blind testing. The amount of validation and quality-control applied to this project cannot be under-stated. It is critically important to be mindful of the limitations and broad assumptions that are applied as part of this work-flow. These include the addition of the low-frequency model, wavelet affects not being taken into account and depth decay of the lithology predictions due to the application of a single PDF.","PeriodicalId":8502,"journal":{"name":"ASEG Extended Abstracts","volume":"47 1","pages":"1 - 6"},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"85790924","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/22020586.2019.12073182
L. Vital, Clive Foss, V. C. Oliveira, V. C. F. Barbosa
Summary We created a funnel-shaped magnetic body from magnetite powder dispersed in plaster and used a travelling 3-component fluxgate magnetometer to map the magnetic field at a low elevation above it. This provided a dataset with signal and noise characteristics similar to those of a field survey, but for a source much better known than any buried geological body. We then used this survey data and the known source details to evaluate recovery of that information from inversions with different degrees of freedom and constraint. This provides guidance in evaluation of inversion results from field data for which the source characteristics are unknown. We found that because of small imperfections in the data and model, the inversion result closest to the truth, although fitting the data quite acceptably, is not the model with the smallest data misfit. Chasing further reduction in data misfit in some cases leads to inversion results which better fit the data but which diverge from the known magnetization. Furthermore, inversions to fit the noise-free field forward computed from a digital version of the model do not recover that exact model, with increasing deviation (but smaller data misfits) as increasing complexity is added to the inversion models.
{"title":"Magnetic Field Inversion – the cost of freedom","authors":"L. Vital, Clive Foss, V. C. Oliveira, V. C. F. Barbosa","doi":"10.1080/22020586.2019.12073182","DOIUrl":"https://doi.org/10.1080/22020586.2019.12073182","url":null,"abstract":"Summary We created a funnel-shaped magnetic body from magnetite powder dispersed in plaster and used a travelling 3-component fluxgate magnetometer to map the magnetic field at a low elevation above it. This provided a dataset with signal and noise characteristics similar to those of a field survey, but for a source much better known than any buried geological body. We then used this survey data and the known source details to evaluate recovery of that information from inversions with different degrees of freedom and constraint. This provides guidance in evaluation of inversion results from field data for which the source characteristics are unknown. We found that because of small imperfections in the data and model, the inversion result closest to the truth, although fitting the data quite acceptably, is not the model with the smallest data misfit. Chasing further reduction in data misfit in some cases leads to inversion results which better fit the data but which diverge from the known magnetization. Furthermore, inversions to fit the noise-free field forward computed from a digital version of the model do not recover that exact model, with increasing deviation (but smaller data misfits) as increasing complexity is added to the inversion models.","PeriodicalId":8502,"journal":{"name":"ASEG Extended Abstracts","volume":"33 1","pages":"1 - 5"},"PeriodicalIF":0.0,"publicationDate":"2019-12-01","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":null,"resultStr":null,"platform":"Semanticscholar","paperid":"78547614","PeriodicalName":null,"FirstCategoryId":null,"ListUrlMain":null,"RegionNum":0,"RegionCategory":"","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":"","EPubDate":null,"PubModel":null,"JCR":null,"JCRName":null,"Score":null,"Total":0}
Pub Date : 2019-12-01DOI: 10.1080/22020586.2019.12073056
Giada Bufarale, M. O’Leary, A. Stevens
Summary A high-resolution seismic survey was carried out across the metropolitan reach of the Swan River (Perth, Western Australia) to investigate its Late Quaternary sub-surficial geomorphology. Shallow imaging data, integrated with sediment cores, pre-existing literature (including dating) and LiDAR images, revealed three main units, forming a complex system of buried paleochannels, which developed during the Late Quaternary glacial sea level lowstands, and infilled during interglacial highstands. The deepest unit was interpreted as comprising estuarine to fluvial sediments of the Perth Formation, deposited during the Last Interglacial (~130-80 thousand years before present) in a wide paleo-valley that cut the basement. The sedimentary sequence of the overlaying middle unit belongs to the Swan River Formation, which consists of heterogenic fluvial to lacustrine sediments, deposited during the Last Glacial lowstand (~80-18 thousand years before present). The shallowest unit comprises Holocene fluvial and estuarine sediments, up to ten-thousand-year-old. This research represents the first environmental high-resolution acoustic investigation of the Swan River estuary. The findings have improved the understanding of the Late Quaternary Swan River development, providing a useful tool for modelling river onset and evolution, following sea level transgressions.
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