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24th European Meeting of Environmental and Engineering Geophysics
- Conference date: September 9-12, 2018
- Location: Porto, Portugal
- Published: 09 September 2018
181 - 200 of 203 results
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Comparison of Ground-Roll Attenuation Methods for Near Surface Investigations
More LessSummaryIn this work four methods for Ground-Roll attenuation in a near surface data case are compared. The methods presented are: simple band-pass filtering, time-offset variant filtering based on the Short-Time Fourier-Transform, f-k filtering and time-offset variant filtering in the wavelet domain computed by means of the Continuous Wavelet Transform (CWT).
The experience carried out demonstrates that the wavelet filter performs better than the others methods. This is because the transformed domain provided by the CWT is able to offer an improved representation of the frequency components of the signal making it easy to identify the GR and to draw a time-offset-frequency filter. The outcomes of the methods are assessed on both shot and stack domain.
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Evaluation of Shallow Seismic Reflection Resolution on an Outcrop Analog to Campos Basin (Brazil) Sandstones Reservoirs
Authors O. Lima Neto, M.A. Cetale Santos, A. Theophilo Silva, F. Timoteo and E. Costa RamosSummaryThe use of the seismic reflection method to image targets with depths of 0–100 m has been increasing since the 1980’s. One of the most compromising issues of the using seismic reflection for shallow depths is its capacity to image structures with interpretable resolution. In this study, we use two modelling techniques, convolution and finite-difference acoustic modelling, to evaluate the feasibility of the seismic reflection method on an outcrop of the Volta Redonda Basin (Brazil) which is considered as an analog to poorly unconsolidated sandstones reservoirs in Brazil. The features of this outcrop were used to construct a 2D P-wave velocity model. Synthetic data, generated using three different dominant frequencies for the Ricker wavelet as the seismic source, were compared in order to access the resolution limits of the method. The synthetic sections yielded from the convolution served as guide to the acoustic modelling brute stacks. Raw shot gathers of the three frequencies were also analysed to recognize what features can be imaged and which frequency is capable of imaging them. The investigation of the synthetic dataset demonstrated that a minimum dominant frequency of 150 Hz is required to image the ultra shallow thin sedimentary beds present on the outcrop.
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Enhanced Cross-Well Seismic Inversion by Fuzzy C-Means Clustering
Authors D.T. Kieu, S.J. Rastin and A. KepicSummaryA cross-well tomography with a geostatistical constraint via fuzzy C-means clustering (FCM) is proposed to extract geologically realistic velocity models for acquisition during mineral resource definition drilling. Constraining a damped least squares inversion process with the additional requirement to keep velocity values in clusters counters the smearing of geological boundaries by the addition of smoothing constraints, which are typically used. The FCM center values were either set as priori known values from borehole measurements or estimated from the data during the cross-well inversion process. We have applied our FCM constrained inversion to three synthetic models and then compared these results to a conventional smoothness constrained inversion result. The three models approximate three simple-to-challenging possible scenarios within a polymetallic deposit embedded in meta-sedimentary rocks. A significant improvement resulted using FCM constraints in the recovery of the true structure, particularly at the boundaries, and various artifacts were better damped. The additional accuracy can provide considerable benefits in improve the resource models in the mine planning stage, and optimize ground-support design and blasting parameter estimation during mining.
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Evidences of Seismic Flysch Anisotropy in the Gulf of Trieste
Authors S. Picotti, M. Dal Cin, G. Böhm and M. BusettiSummaryThe Gulf of Trieste is a shallow epicontinental basin that is part of the northern Adriatic Sea. During the last decade, the National Institute of Oceanography and Experimental Geophysics (OGS) carried out three geophysical surveys in the Gulf of Trieste, collecting 630 km of Multichannel Seismic reflection profiles. Part of this dataset was used in the present work to build a tomographic velocity-depth model in the eastern portion of the gulf. This model gives information on the main surfaces and units (i.e., quaternary sediments, turbiditic flysch and carbonates) up to a depth of about 1600 m below sea level. Two main tomographic methods were applied in this work, allowing to build interval velocity models for both reflected and refracted seismic waves and to produce a detailed depth seismic section of the geological structures in the study area. In particular, the average vertical and horizontal P-wave velocities at the top of the flysch unit are about 2900 m/s and 3700 m/s, respectively, denoting a pronounced anisotropic effect. The large discrepancy between the two tomographic velocity values is here justified using the generalized Backus theory, and therefore interpreted as the anisotropic effect due to the laminated internal structure of the flysch unit.
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Joint Vp and Vs Monte Carlo Inversion from Surface Wave Data
Authors F. Khosro Anjom, S.M. Muriuki, C. Comina and V. SoccoSummaryGenerally, surface wave dispersion curves are inverted to estimate S-wave velocity models. We here show a joint inversion approach to invert for both VS and VP models. In this work, the WD relationship and dispersion curve are jointly inverted based on a Monte Carlo inversion scheme. A WD relationship is a relationship between dispersion curve wavelength and investigation depth. Formerly, it has been verified that WD relationship is highly sensitive to Poisson’s ratio. And, in this work, it is proven that involving the WD relationship in the inversion process, significantly improves the results of VS and VP. We apply the method to a synthetic case.
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Full-Waveform Inversion of Near-Surface Seismic Data in Anisotropic Media
More LessSummaryIn most shallow-seismic FWI studies, an isotropic assumption of the Earth is used, even if near-surface materials may exhibit strong seismic anisotropy. We investigate in this work the effects of anisotropy on surface waves and on shallow-seismic FWI. The comparison of seismograms calculated in isotropic and vertically transversely isotropic (VTI) models shows that Love waves have a higher sensitivity on anisotropy than Rayleigh waves, and are sensitive to both vertical and horizontal velocity. Therefore, we use Love waves for anisotropic FWI and invert for horizontal and vertical shear wave velocities simultaneously. We test the inversion on synthetic VTI data and compare the results of isotropic and anisotropic inversion. Ignoring anisotropy causes strong artifacts in the resulting models and neither horizontal nor vertical velocities are reconstructed. However, if we consider anisotropy and invert for horizontal and vertical velocity simultaneously, both velocity models can be reconstructed almost perfectly. We thus show the importance of considering anisotropy and the potential of anisotropic FWI in shallow-seismics, which improves the accuracy of the reconstructed subsurface models.
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Experiences from Microgravity Method Application in Abandoned Coal Mine Sites - Two Examples from Austria and Slovakia
Authors R. Pasteka, P. Zahorec, J. Papco, D. Kusnirak, R. Putiska, A. Mojzes, I. Zvara, M. Lesko, M. Bielik and M. PlakingerSummaryGeophysical detection and monitoring of subsurface cavities and subsidence effects over sites with mining activities is an very important task of near surface geophysics. Microgravity method can play an important role in the frame of such kind of research and monitoring. In our contribution we bring several examples (residual Bouguer anomalies interpretation) from the application of microgravity method together with other geophysical methods in sites with abandoned mining activities (brown coal mines in southern Austria and central Slovakia).
Microgravity research was able to detect important negative anomalies in both cases – the first one was connected with a real migrating mining cavity, the second was probably an old surface collapse filled by debris and mining waste (both objects have been verified by in-situ drilling). Application of other shallow geophysical methods (electro-magnetic induction, electrical resistivity tomography and shallow refraction seismic survey) in the second case helped us to interpret the received microgravity anomaly in a more correct way.
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Monitoring Wastewater Disposal Dynamics through Infiltration Ponds by Using Time-Lapse ERT Survey
Authors L. De Carlo, R. Masciale, I. Portoghese, M. Vurro and M.C. CaputoSummaryIn Italy, during the last decades, the infiltration ponds are increasingly used to dispose of effluent in the subsurface, according to the current regulation DL 152/06.
In Apulia Region, Southern Italy, about 30 wastewater treatment plants are connected to an infiltration ponds network where the effluent is naturally infiltrated in the unsaturated zone, exploiting its natural filtering capacities against organics, chemicals and contaminants.
At the same time, this approach could be particularly efficient in treatment plants located near the coastline to face contamination phenomena such as salt-water intrusion, as well as to artificially recharge shallow aquifer. The infiltration ponds are typically subjected to cyclic saturation and desaturation conditions that can affect the hydrological properties of the filtering medium, hence itd life cycle. Therefore, for the optimal management of the infiltration ponds, a detailed monitoring of infiltration dynamics is required. In the experimental test area of Castellana Grotte, more than 2000 m3/day are alternatively infiltrated into nine infiltration ponds. In order to evaluate infiltration patterns under different hydrological conditions, a time-lapse Electrical Resistivity Tomography (ERT) has been carried out in two periods of the year, in March and July, corresponding about to the maximum and minimum rainfall periods of a hydrological year.
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Near-Surface Characterization of the Llancanelo Lake Region (Argentina) by Surface-Wave Analysis of 2D Reflection Data
Authors L. Onnis, A.M. Osella, R. Violante and J. CarcioneSummaryThe inversion of surface-wave dispersion curves is a reliable method to derive near-surface shear-wave velocity profiles. In this contribution, we invert 2D seismic-reflection data acquired as part of a paleoenvironmental study of the Llancanelo Lake basin (southern Mendoza Province, Argentina), that cannot be used to image the first 50 m with reflection processing due to its characteristics. Though exhibiting severe spatial aliasing, the Rayleigh dispersion curves were successfully sampled and then inverted to obtain 2D shallow shear-wave velocity profiles. The results are compatible with the already known stratigraphy of the near-surface in the region, and provide more details on the uppermost layers, particularly some differences in the seismic response of different sedimentary deposits.
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Improving the Resolution of ERT Arrays Acquired with Few Electrodes from Mixing Concatenated Sections after Small Lateral Displacements
Authors A. Urruela, M. Himi, R. Lovera, L. Rivero, R. García, F. Pinheiro Lima Filho and A. CasasSummaryThe success of a subsurface exploration survey using ERT method depends largely on physical properties contrast, the complexity of target to be imaged and electronic array used. In this case, it is very important to consider the resolution and depth of research that can be achieved. On the one hand, the resolution depends on the spacing between the measuring points, which in turn depends on the number of electrodes available on the multielectrode resistivity meter used, while the penetration depth is a function of the separation between the current electrodes placed at both ends of the profile.
Then, for an instrument with low number of electrodes, there is a compromise between resolution and penetration. This restriction can be mitigated by using an array with enough extension for achieve the needed exploration depth and repeating the profile as many times as necessary with a lag equivalent to the spacing between adjacent electrodes needed for achieve the required resolution.
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A Time Space Groundwater Contamination investigation in an Industrial Site using Geophysical and Hydrochemical Methods
Authors T. Marques, C. Patinha, J. Ribeiro, E. Silva and M.J. Senos MatiasSummaryThe industrial chemical complex of Estarreja (ICCE), lat 40°45′N, long 8°35′ W, operates since the 1950’s. Several plants have disposed locally residues and effluents, discharging them into natural water lines, opening channels, surface and buried deposits, in an area that houses an important aquifer system. These residues range from heavy metals to organic compounds. The area around the ICCE has also been used for agriculture that exerts further pressure on local eco systems as there is a wide spread use of fertilizers. From 1998 onwards the area is been recovered and remediated by a joint effort of the Local Council, Industries and Environmental Authorities. This work presents more than thirty years of Geophysical and Hydrochemical data from the area. Because of space limitations, only selected data will be presented in the abstract. EM geophysical mapping provided an efficient tool to investigate contamination propagation and extension but, as expected, could not identify the pollutants themselves neither their origin. Hydrochemisty allows the identification of the pollutants as well as their origin. Theses environmental problems, that can affect public health, need the use of both Geophysics and Hydrochemistry if a thorough assessment of the contamination, evolution and monitoring, is to be carried out.
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Describing Necessity of Optimizing of Injection/Production Rate for One of Offshore Iranian Oil Filed-Case Study
Authors M. Rezaee, N. Yousofi, M.S. Safavi and M. Ghorbani sheikhneshinSummaryIn the daily operation of an oil and gas production system, a lot of decisions have to be taken that affects the volumes produced and the cost of production and the necessity of optimized products or processes prevails in many sectors of industry. Reservoir model is an important piece of the solution which should be updated by time. In time updating not only is important for reservoir modeling but also makes a lot of benefit along optimization. Task of gathering data comes up with monitoring tools and it’s inevitable. Before applying every solution or plan, it must have economic justification. In this study one of the Iranian offshore oil reservoir was studied to depict necessity of optimizing 29 wells of injection/production rate. At first, the reservoir model was constructed by ECLIPSE 2012 simulator, and then linked with coding program which is contained Genetic Algorithm. Finally by applying optimization in a certain period of time, some wells did not need to be closed compare to real operational stage and final recovery increased about 5.3 percent. This study shows monitoring play a main role for this field to increase the oil recovery. In addition, this job illustrates a scenario for wells operation.
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Seasonal ERT Monitoring of Subsurface Processes Connected to Freezing and Snow Melt
Authors D. Krzeminska, T. Starkloff and E. BloemSummaryFor a better understanding of processes that influence snowmelt infiltration and runoff, and their consequences on soil erosion during spring periods, we established a long-term winter-spring ERT transect in the Gryteland catchment (Norway). The ERT transect was 71m long, with 1m spacing between the electrodes. It covered a depression with a north and south facing slope. The readings were collected once a week. Additionally, transect was equipped with six TDR profiles, to registered soil moisture and temperature, at five depths (5, 10, 20, 30, 40 cm), for quantifying the ERT readings.
The ERT and TDR monitoring gave promising results and showed the potential of ERT monitoring for understanding the soil thermal and hydraulic processes occurring during a winter and early spring. There were visible differences in temporal trends and spatial variations in observed ERT patterns on the opposite facing, which are of special interest.
Herein, we would like to present the preliminary result of ERT experiment performed during winter 2015/2016 and discuss the advantages and limitations of our experiments. We would like to stimulate the discussion about the potential of ERT for spatial and temporal monitoring of soil hydraulic and thermal processes and indirect measurements of soil water content.
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In-Situ Geophysical and Hydro-Geochemical Monitoring for Landslide Dynamics (Lodève Landslide, France)
Authors N. Denchik, S. Gautier, M. Dupuy, C. Batiot, V. Léonardi, P.A. Pezard, M. Geeraert, G. Henry and D. NeyensSummaryThe Lodève landslide is located 60 km northeast of Montpellier (South of France). It corresponds to a deep-seated landslide (up to 50 m depth) with a slow slip displacement (4–6 mm/year). In this area the landslide activity is associated with intense precipitations events (called “Cévenol events”, 300–500 mm in few days) and the related dissolution of Triassic evaporite layers at depth. Considering a relatively simple geological context and the presence of a unique triggering factor, this landslide corresponds to a preferential natural observatory to study the impact of large rain events on the slow slope kinematics. A downhole monitoring was conducted since 2012 in order to image the water flows within the landslide in order to better understand the role of fluids in the slope instability. The landslide is investigated down to 60 m depth by two in situ permanent observatories for a geophysical (electrical resistivity and deformation) and an hydrogeochemical monitoring (pressure, pH, temperature, electrical conductivity, fluid sampling). This instrumentation helps to identify and characterize the active slip zones in the underground. The first results point out the relevance of the downhole monitoring to progress towards a better understanding of internal landslide processes in relation to climate forcing.
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Application of Geoelectric Methods for the Technogenic Accumulation of Lost Oil Products Detection and Localization
Authors S.P. Levashov, M.A. Yakymchuk, I.N. Korchagin and D. BozhezhaSummaryThe results of direct-prospecting methods using for searching and delineation of “man-made” fuel accumulations on the ground and underground petroleum storage facilities are analyzed. The studies were carried out with using the method of frequency-resonance processing of satellite images and geoelectric methods FSPEF and VERS. At the ground storage area 12 anomalous zones have been detected and mapped at the resonant frequencies of fuel samples from drilled wells. Within the contours of detected anomalies the most prospective areas for drilling wells to extract the “lost” fuel have been highlighted. The presence of man-made fuel accumulations in the contours of the detected anomalous zones has been confirmed by drilling. Within the fragment of investigated airport area two anomalous zones of the “aviation fuel” type have been detected and mapped. At the area of underground storage of diesel fuel the detailed ground-based works have been conducted with the geoelectric FSPEF and VERS methods using. As a result, the diesel residues of 5621.0 m3 and 243.0 m3 volume were detected and mapped in two underground tanks.. Conducted studies have demonstrated the high efficacy of individual methods of direct-prospecting geophysical technology for exploration and delineation of “man-made” petroleum accumulations.
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Geoelectrical Imaging of Concealed Objects with Capacitive Sensor Arrays
Authors O. Kuras, R. Swift, S. Uhlemann, P. Wilkinson, C. Inauen and P. MeldrumSummaryApplication of the geoelectrical imaging method with capacitively coupled (i.e. non-invasive) sensor arrays to the 3D tomographic reconstruction of man-made objects or structures buried at shallow depth. We present the results of proof-of-concept experiments using representative targets under controlled laboratory conditions. The study demonstrates that the approach can be used to reconstruct and visualise concealed objects, simulating a range of threats. The experimental work has confirmed the predictions from numerical simulations and reinforced the key constraints. 3D geoelectrical imaging could complement and enhance capabilities in security and defence for quantitative, volumetric and structural characterisation of the subsurface. In principle, the methodology is suitable for use on natural ground as well as on vertical walls or engineered structures (e.g. roads, foundations), including within buildings.
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Adiabatic Pulses to Improve MRS Measurements
By T. RadicSummaryThe Magnetic Resonance Sounding (MRS) Method allows for the direct quantification and characterization of non or weakly bounded water in near surface soil. MRS measurements in densely populated areas, like almost everywhere in central Europe, frequently cause S/R ratios of less than 1. This is why last year we have added a transmitter for the pre-polarization (PP) of the soil to our MRS apparatus MRS-MIDI-III. A field of 500 □T can be generated for several seconds within the 2 metre PP-Loop. In doing so, the nuclear magnetisation of the water within the upper 1–2 metres increases up to one magnitude. The directly following “conventional” MRS measurement then stimulates an up to 10 times greater response signal (FID). Recently we have added a further innovation to our instrument: an adiabatic pulse (AP). A Tx pulse to deviate the protons in the soil is normally constant in regards to frequency and amplitude. The specific characteristic of adiabatic pulses is that the frequency and/or current change during the pulse. Through this, the distribution of the sensitivity in the soil can be advantageously influenced and the signal amplitude increases by a factor of up to 3.
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Laboratory Experiments of Neutron Induced Gamma Ray Spectrometry Tool
More LessSummaryGamma spectral logging is a radioactive logging method that can measure the constituents of formation. This method of measuring the constituents of formation can be used not only for evaluation of unconventional reservoirs but also for evaluating the changes in water quality of groundwater and the interaction of aquifers with contaminated fluid and formation. In this study, two kinds of neutron source, three kinds of detectors and MCNP numerical modeling were used as basic studies for the equipment development of gamma spectrum. Gamma ray measurements were made using commercial products and self-developed systems. MCNP numerical modeling was applied to the design and performance prediction of sonde, and various rock blocks were used for the field test. Gamma spectra were measured in the neutron-capture gamma mode and some measured peaks included the effects of cylindrical pipes. Although the discrimination of the energy peaks of constituent elements in the measured gamma spectrum is not as easy as expected but the apparent components such as hydrogen in the water tank were well identified. It is expected that performance will be improved if it is continuously updated based on the test result up to the present.
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Magnetic and Mineralogy Analysis of Soils of Hydrocarbon Prospective Areas in Ukraine
Authors O. Menshov, R. Kuderavets and I. ChobotokSummaryThe magnetic minerals are responsible for the enhanced magnetic signals in soils and suggest a relationship exists between magnetic minerals and the alteration of hydrocarbons due to biodegradation process. All this processes cause the formation of local magnetic anomalies and changes of soils magnetic properties. We performed the studies at the territory of oil field Selyuhi in the Dnieper-Donets Depression for deeper understanding of the spatial distribution of soil magnetic susceptibility (MS) and to find the relations between MS and microseepage. The results of thermomagnetic studies we presented in a case of Starunia oil-ozokerite deposit, which is the main oil- and gas-bearing part of the Ukrainian Carpathians. We used the hysteresis parameters to detect the domain state of the magnetic minerals which are responsible for enhancing of magnetic susceptibility of soils and results in variation of the magnetic field at the areas of hydrocarbon deposits. The anomalies of soil MS were detected in close proximity to the productive hydrocarbon areas. The predominance of pyrrhotite and magnetite-like phase and pseudo-single domain grains were detected in the hydrocarbon impacted soils. Magnetic methods offer the advantage of low cost and time saving possibilities for hydrocarbon prospecting.
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A Case Study - Recognition the Source of Water Production in a Gas Field
Authors M. Mavaddat, E. Ghanaatpisheh Senani and S.M. MirbagheriSummaryFinding the source of water production is mandatory for preventing it. In order to find the source, different theories include water coning, correspondence between produced salt and produced gas, production from a layer behind casing, and production from formation water are investigated. It is concluded that the fourth theory is more probable for this field. Also, some suggestions are listed that help us monitor and control water production.
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