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EAGE-GSM 2nd Asia Pacific Meeting on Near Surface Geoscience and Engineering
- Conference date: April 24-25, 2019
- Location: Kuala Lumpur, Malaysia
- Published: 24 April 2019
1 - 20 of 80 results
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Integration of geoelectrical and seismic refraction data by means of fuzzy clustering for landslide investigation
More LessSummarySeismic and geoelectrical methods are powerful tools to investigate the landslides. The effectiveness of the investigation will significantly increase if we can exploit the strength of each method and complement its information into the combination model. The question is how we can put the models together. In this work, we utilize the advancement of fuzzy clustering technique to integrate seismic refraction and geoelectrical datasets in a co-operative inversion process. The fundamental idea to use fuzzy clustering is to build a model that resembles geology, particular rock units. We apply our method to a dataset acquired at Doi Ong Tuong, Hoa Binh province, Vietnam. The dataset includes refraction seismic and direct current data for landslide investigation. Seismic refraction is good at defining a structure to assist geoelectrical inversion. In turn, the geoelectrical method is sensitive to low resistivity media that usually relates to weakened zones, but is not good at structure definition. Our results are consistent with the borehole information. Applying fuzzy clustering again to the models of velocity and resistivity, we can create a clustering map that is more interpretable than using directly the inverted models.
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Characterization of Quaternary Deposit in Seberang Perai Selatan, Pulau Pinang Using Active, Passive and Hybrid MASW
Authors J. Ariffin, M.A. Mohamad Ismail and M.F. MohammadZakiSummarySoft quaternary deposit is widely found in Seberang Prai Selatan, Penang which consist of marine clay, silt and few thin layer of sand. Due to actively development of the rural part, assessment of soil before substructure design is becoming top priority. This study aims to provide a reliable characterization as a guide for marine clay properties estimation using in situ data of one-dimensional shear wave velocity using Active-MASW, Passive-MASW and Hybrid-MASW. The lowest Vs30 observed from Active MASW method (111.59 m/s) while highest Vs30 observed to be from Hybrid MASW (173.60 m/s). In overall, result of Vs30 using Passive MASW is approximately similar to Hybrid MASW. Active MASW-Hybrid MASW relationship show weak correlation with R2=0.12 while for Passive MASW-Hybrid MASW show strong correlation with R2=0.91. Active MASW-Passive MASW are weak correlated with R2=0.106. Combination of these methods which is Hybrid MASW must be referred in order to obtain reliable Vs along subsurface depth.
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Near-surface 2D seismic survey in the transition zone near Sakhalin island: case study
Authors A. Konkov, A. Turchkov, A. Oshkin, V. Ignatev, I. Polikarpov and A. SimakovSummaryThis paper is based on the results of shallow 2D seismic survey performed in the transition zone (land-shallow water) at the construction site of a bridge between mainland and Sakhalin Island (Eastern Russia). The purpose of the research was to obtain geological sections in the transition zone, that are necessary for further linking of marine and land seismic data. A special attention was given to assumptions on location of the upper boundary of a rocky base.
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Estimation of Anisotropy-Free Acoustic Impedance from Partial-Stack Seismic Inversion: A Case Study From Inas Field, Malay Basin
Authors M. Gouda, A.M.A. Salim and G. HamadaSummarySeismic velocity is a pivotal geophysical property that contains important information about Earth layers. The layering of Earth, clay content and fractures within layers are the main causes of the dependence of seismic velocity on the angle of incidence which is called: “Seismic Anisotropy”. Seismic anisotropy affects the velocity-dependant attributes such as Acoustic Impedance resulting in misinterpretation of seismic data. Consequently, anisotropy correction of acoustic impedance is important to mitigate the uncertainty. Anisotropy parameters can be obtained from core data and well logs with various methods. However, the common limitation in the previous work is that anisotropy is obtained at well locations neglecting the lateral heterogeneity of layers. This study aims to obtain anisotropy-free acoustic impedance (Zp0) from the partial-stack inversion of near, mid and far-angle stacks. The outputs of the inversion are used to obtain Zp0 by three different methods: the refactorization of Thomsen’s anisotropy equation, statistical modelling, and the Multi-Layer Feedforward Neural Network Theory (MLFN). The results obtained from the MLFN and the refactorized Thomsen’s model showed better matching with impedance logs, more obvious lateral continuity of layers and more enhanced amplitude spectrum compared to the uncorrected P-impedance. Such improvement reduces the uncertainty of the final reservoir model.
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Elimination of Internal Multiple using Inverse Scattering Series in Malay Basin - A Case Study
Authors H. Hashim, Y.M. Tang, A.H. Abdul Latiff and D.P. GhoshSummaryWith increasing hydrocarbon exploration in deepwater regions, the need to acquire accurate seismic data becomes much more important. One of the main challenges in acquiring seismic data in this area is the presence of internal multiple. This seismic multiples are usually considered as insignificant compared to the surface-related multiples, however if the target areas lies in a deeper region, it becomes much more prominent due to the weaker primary reflections. If this type of seismic noise is not handled correctly, it can effect the seismic reservoir and characterization and thus increasing the risk in oil exploration. Therefore a more advanced method needs to be applied, and one such method is the inverse scattering series. This method is data-driven therefore unlike other internal multiple attenuation technique, its does not require any prior information of the subsurface to predict the multiple. The application of this method in offshore Malay basin shows significant results, as the seismic data produced shows an improvement with a cleaner image compare to the one without any internal multiple removal.
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Reducing ERTM artifact arising from incorrectly imaged mode conversions in the dip-angle domain
More LessSummaryA straightforward and naive implementation of elastic reverse time migration (ERTM) might produce images that are not very useful mainly because they are filled with noises arising from incorrectly imaged mode conversions, cross-talk, and back-scattered energy. Therefore, we present a ERTM workflow that overcomes these problems. We first employ vector-based normalized cross-correlation imaging conditions (VBNICs) for PP and PS reflections to avoid cross-talk and polarity reversal. Based on Poynting-vector imaging condition, we implement angle filtering to reduce low-wavenumber and high-amplitude noise. Then, we efficiently extract dip-angle gathers by using Poynting vectors and finally utilize them to attenuate the artifact caused by non-physical wave-mode conversions because their slopes differ from the migration dip. Numerical examples demonstrate that the proposed ERTM workflow can produce images with less noise and higher quality.
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Site characterization with ambient seismic noise at the Norwegian Geo Test Sites
More LessSummaryThe objective of this study is to find an efficient way to measure bedrock depth and geotechnical parameters through the estimation of shear wave velocity, Vs. The Norwegian Geo Test Sites (NGTS) initiative aims to establish five national test sites as field laboratory for testing innovative soil investigation and foundation methods. We have measured ambient seismic noise data as well as Multichannel Analysis of Surface Waves (MASW) data at two NGTS sites, Onsøy and Halden. The results of the shear-wave inversions are compared with ground-truth measurements from the two well-characterized sites. The results obtained with the passive seismic test and the MASW active test are quite similar despite the fact the passive method requires less time and equipment in the field.
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Soil-Rock Interface Mapping in Jinan urban area using H/V Spectral Ratio of the Microtremor
More LessSummaryThe soil-rock interface is of great significance to urban construction and disaster prevention. In this paper, the H/V spectral ratio (HVSR method) based on the propagation characteristics of microtremor is used to mapping the interface in Jinan urban area, China. The results showed that the H/V curve types are depending on the type of bedrock and its weathering degree. Weak weathered limestone can use this method to obtain a better peak frequency-depth relationship, which can be used to estimate the depth of soil-rock interface in similar areas. However, the intrusive rocks with severe weathering can’t get ideal results.
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Marrying seismic attributes and geomechanical analysis for de-risking induced seismicity in unconventional reservoirs
Authors H. Abul Khair and M. AdamsSummaryInduced seismicity resulted from hydraulic fracturing is an unintended issue, and unpredicted by-product of tight reservoir development. We introduce a new workflow to identify the location and extent of the subtle faults (I.e. below or close to seismic resolution), which may also contribute to the risk of potential induced seismicity. A sequence of post stack seismic processing workflow is introduced. The location of the new identified subtle faults correlates well with the focus of the induced micro-seismicity events. Most Positive Curvature attribute identified a constant NW-SE fault orientation parallel to the Rocky Mountains. The stresses and pore pressures resulted from Mechanical earth models (ID MEM) were then applied on the interpreted faults, and fault susceptibility analysis was conducted. The authors suggest that N-NNE trending faults oriented to current day in-situ stress are critically stressed. This workflow offers a solution to avoid such critically stressed faults that may be prone to slip. It should be noted, that smaller scaled seismicity events, known as micro-seismicity should not be confused with larger events. This is primarily because micro-seismicity, and any seismicity under a Richter scale value of three are not believed to be associated with damage to buildings, or man-made structures.
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Construction of a 3D velocity model for microseismic event location on a monitored rock slope
Authors Z. Zhang, D. Arosio, A. Hojat, M. Taruselli and L. ZanziSummaryWe are planning a tomographic survey to characterize an unstable rock mass that has been monitored with a microseismic sensor network since 2013. An automatic algorithm is used to classify the events filtering noise and interferences. To interpret the events for monitoring the evolution of the fracture system within the rock mass, we are now developing a hypocenter location procedure. The algorithm needs a 3D velocity model. In this work, we discuss the preliminary source tests performed on site to select a portable source suitable for the harsh environment and the size of the monitored area. The small database generated with these tests has been also used to perform a location exercise using a constant velocity. The results are encouraging but it is clear that a 3D velocity model is required to improve the accuracy. Finally, the database has been used to perform a tomographic exercise to extract a preliminary 3D velocity model. The result seems meaningful and shows that despite the difficulties in deploying and moving sources and sensors (a 24-geophone spread will be combined with the microseismic network to increase the ray coverage) in the harsh environment of the rock cliff, the tomographic survey is promising.
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Pseudo-3D dual-frequency induced polarization for dam leakage detection
More LessSummaryThe dual-frequency induced polarization method has been applied in geophysical exploration for many years. Pseudo-3D dual-frequency IP array has also been improved based on the traditional 2D IP data acquisition system. In this study, we employed the method in the dam leakage detection. However, due to the limitation of the topography of the surveying field, 3D array is not the efficient way to acquire the dam leakage data. Based on the 3D resistivity cube, we infer the channel of the leakage in the dam. We give two possibilities of the dam leakage path.
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New wide-band EM system ARMT-5: case study - CSAMT survey at potassium deposit in frequency band 10Hz - 100 kHz
Authors A. Simakov, A. Shlykov and V. IgnatevSummaryThe new wide-band EM system ARMT-5 described in the abstract combines features of AMT and RMT devices. It is designed for implementation of a variety of electric survey methods: AMT, CSAMT, CSEM, RMT and CSRMT. Its wide frequency range (0.1 Hz – 1 MHz) enables the applying of this tool for the exploration of depths from first meters up to several kilometers for a broad spectrum of targets. CSAMT survey with this equipment has been successfully applied at the potassium deposit for recovering the geological structure at the depth of 300 meters. Measurements have been done in frequency band 10 Hz - 100 kHz.
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Analysis of Geophysical Datasets for Coastal Vulnerability and Asset Management
Authors P. Eccleston and A. SpyrouSummaryAnalysis of Geophysical Datasets including seismic refraction, MASW and Ground Penetrating Radar to assist with planning for coastal vulnerability and asset management along the sandy coastline of south west Western Australia
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Delineation of elastic properties and settlement of dam materials at the dam embankment using seismic methods
Authors S. Yordkayhun and K. WattanasenSummarySeismic refraction tomography and MASW analyses provided 2D compressional (Vp) and shearwave (Vs) velocity sections along the crest and downstream side of the Klong Sadao dam. The results of Vp and Vs investigation have shown that the settlement of material of the dam embankment is increasing with depth. Based on Vs30 values, the area falls in site class C and D, indicating the stiff soil to dense soil and soft rock beneath the dam. There are noticeable regions of weak zones as indicated by determined Poisson’s ratio. In addition, the calculated predominant period of the dam suggest that local earthquake with 0.1-0.4 s period can pose significant threat to the dam.
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Effects of irregular topography on Rayleigh-wave propagation in surface-wave exploration
Authors H. Yamanaka, S. Miyanaga and K. ChimotoSummaryWe have conducted finite difference simulation of wave propagation in a 3D shallow soil model with a surface irregularity similar to a river embankment. We found large scattering waves from edges of the surface layer in the synthetic vertical waves at sites on the surface along a surveying line of the crest. The scattering waves do not have significant effects on the dispersive features of Rayleigh waves at the sites close to the source location. However, the effects is large for the sites far from the source, and makes it difficult to apply ID surface wave theory to interpret observed data in the surface-wave exploration.
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Application of Geophysical Investigation to occurrence of settlement - A case study
SummaryOver the past several decades there has been a steady increase in the application of geophysical technique to many type of civil engineering problems. Main applications included the determination of depth of bedrock and physical properties of rock (Sharma 1997). Recently, geophysical method has become the alternative method of soil investigation due to cost, time efficiencies, and the quality of their researches (Sam Setchell, 2016). In this case study, occurrence of crack at house structure due to soil settlement had become one of problematic issues in geotechnical investigation. With the support of geophysical method, the characteristic and soil category can be determined.
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Petrophysical and Geotechnical Evaluation of Mesozoic Rocks from Central Lebanon
Authors M. Salah, M. Alqudah, A. Monzer and C DavidSummaryWe conducted several petrophysical measurements on forty nine core samples collected from the Jurassic and Cretaceous strata exposed at west central Lebanon to evaluate their petrophysical and elastic properties and study the effects of the depositional conditions, sediment composition, and subsequent diagenetic processes on the measured parameters. First, these rocks were petrographically studied to identify the lithofacies, porosity, and the main diagenetic features. In addition, these rocks were investigated under the scanning electron microscope (SEM) and by the X-ray diffraction (XRD) analysis to identify their mineralogy. The petrophysical measurements were performed on the core samples where porosity, permeability, bulk and grain densities were first determined, followed by measuring the seismic wave velocities. The main lithofacies of these rocks can be categorized mainly into carbonates and siliciclastics. The SEM and XRD analyses revealed that the main constituting minerals are calcite, quartz, dolomite, beside other accessory minerals. The studied rocks have generally low to moderate porosity, moderate to high bulk density, and very low permeability. The average Vp and Vs are 4263, and 2323 m/s, respectively, giving a Vp/Vs ratio of 1.83. We further calculated the elastic moduli of the studied rocks and established a number of relationships between the measured petrophysical and acoustic properties to examine their mutual interdependence and evaluate the effects of porosity, rock composition, depositional and diagenetic processes on the measured rock characteristics. We found that some samples, mainly carbonates, deviate significantly from the expected porosity-velocity and density-velocity trends. It is thought that coring-induced microcracking, originally-present micro- and intercrystalline pores in these carbonate rocks may account for these outliers.
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Characterization of the hot spring aquifers at Sungai Klah using potential fields geophysical methods
Authors J.S. Kayode, H. Arifin, M. Nawawi, A. Khalil and H. BaioumySummaryThe potential geophysical methods using gravity and ground magnetic were applied in an integrated strategy to characterized and lessen the ambiguities of the models generated. The gravity method was adopted to define subsurface rock contacts, (i.e., dykes and faults), using their density contrast. The Bouguer gravity anomaly map was generated from the data with the 3-D Euler deconvolution techniques applied in Geosoft Oasis Montaj software to delineate these rock contacts and sources of the subsurface anomalies emplace in the area thereby making it a powerful technique for assessing the depths and the geometry of the buried geologic sources for the hot water reservoir. The total intensity magnetic values recorded were corrected and plotted on a magnetic map for quantitative modeling and interpretation. The Euler deconvolution and Reduced-to-the-Pole (RTP) filters were applied to the data to produced more reliable detailed of the subsurface structures beneath the hot spring. Applications of integrated geophysical tools in addition to a well-known geology of the area under investigation minimizes ambiguities. The models obtained from the geophysical surveys showed that the aquifer could be probably at a few hundred meters deeper than the predicted.
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Heat flow distribution in southwest China calculated from the Curie depth
More LessSummarySouthwest China has well-developed geothermal resources due to the complete and intense geotectonic activities. Heat flow is an important geophysical property to represent thermal state of the earth and it is closely related to the Curie depth. Most previous studies are mainly based on estimation of heat flow from the Curie depth. To improve the quality and accuracy of heat flow, we propose an iteration approach of calculating the heterogeneous thermal conductivity laterally. Firstly, we calculate the distribution of surface heat production using the data of radioactive elements. Secondly, the thermal conductivity is obtained under the constraint of the Curie depth and surface heat production. Finally, the heat flow and its value underground of the study area can be obtained. The results show that the surface heat flow of southwest China is in line with the background trend of high in the southwest and low in the northeast. The surface heat flow are basically corresponding to the measured heat flow and regional geothermal anomaly.
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A preliminary ground magnetic and resistivity investigations on Deidei geothermal area, Papua New Guinea
By P. IrarueSummaryThe linear discontinuity in the magnetic data pattern which separates the contrasting magnetic intensity areas to the north and south coincides with the location and orientation of the major east-west trending and southerly dipping near vertical fault structure observed at Galagalalana and Seuseulina thermal sites in the west and also with the Bolousunamo fumarole site on higher land area toward the east. Moderate to low magnetic intensity anomalies were concentrated toward the south side of the linear discontinuity thus indicating intense hydrothermal activity (or alteration) toward the south. This also suggests that the localized up flow on the structure (faults) may have been pushed toward the south due to the N-S hydrological gradient thus causing demagnetization to the south. A preliminary model proposed for Deidei geothermal system suggests neutral chloride outflow at low land areas (Seuseulina and Yaiyaiboalana boiling springs) towards the west and steam and hot pressurized water up flow at higher land areas (Bolousunamo acid sulphate fumarole) toward the east.
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