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72nd EAGE Conference and Exhibition incorporating SPE EUROPEC 2010
- Conference date: 14 Jun 2010 - 17 Jun 2010
- Location: Barcelona, Spain
- ISBN: 978-90-73781-86-3
- Published: 14 June 2010
401 - 500 of 797 results
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West Athabasca Grand Rapids Formation – A New SAGD Play
Authors M. E. Connelly and L. M. Weston BellmanThis presentation provides a description of Laricina Energy Ltd's proposed thermal project in the oil sands deposits of western Canada. The Grand Rapids Formation is a new play which, although similar in thickness, porosity and saturation to the established McMurray thermal plays, is a simpler, cleaner reservoir. The presence of an associated bottom water leg requires SAGD well placement within the bottom water interval to maximize bitumen recovery. Integration of core, logs and 3D seismic allow for 3D visualization of any barriers to vertical permeability, the bitumen-water contact and the porosity base. This information is key to planning the horizontal well placement for SAGD recovery.
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3D Oil Sands Reservoir Characterization for Exploration, Development and Monitoring
More LessThe objective of the process described here is to integrate all available seismic and well data to produce a volume of deterministically estimated reservoir properties. This effectively upgrades the utility and value of seismic data enabling the final product to be used in exploration, development, production monitoring, engineering and strategic decision-making. The workflow is illustrated using an oil sands example in the Nexen/Opti Long Lake area of northeastern Alberta, Canada where a 40 km2 3D seismic data set and over 100 regional wells were used to create a detailed volume of facies and fluids. The subsequent drilling results were compared with the predicted properties and showed very high average correlation of almost 80%.
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Reservoir Characterization Using a Streamline-assisted Ensemble Kalman Filter
Authors J. Choe, S. P. Jung, M. J. Yeo, H. Shin and W. BaeEnsemble Kalman filter (EnKF) is a recursive data process algorithm that uses continuous model updating. It has been proven that the EnKF is an efficient method for data assimilation, uncertainty assessment, and large scale problems in many engineering fields. However, the method has two common limitations: filter divergence and overshooting/undershooting. These are due to reduction of cross-covariance between model parameters and measurements. We propose a streamline-assisted ensemble Kalman filter that uses covariance localization according to the types of well and measurement data. This method enables selective updates of permeability, and therefore, providing more reliable permeability field estimations than the standard EnKF without overshooting/undershooting or filter divergence. In addition, it gives efficient uncertainty evaluations by considering the performances of each ensemble member.
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Stratigraphically Constrained Seismic 4D Inversion
Authors M. Ayzenberg and U. TheuneThe inversion result in a Bayesian setting is, among others, controlled by a prior model covariance matrix, which contains the expected a priori variances and correlations between the seismic properties. In time-lapse analysis, we expect that significant changes occur only in the reservoir sand units, whereas the changes in the surrounding rocks are expected to be negligibly small. In our extension of the Bayesian time-lapse inversion, we utilize this observation by using a vertically and horizontally varying model covariance matrix. In the parts of the data cube containing sands which may be affected by production, we allow for large changes by assigning large variance values. We use small variance values for the remainder of the data cube, which is most likely not affected by production. In order to control the spatial variation of the model covariance matrix, we exploit additional information. Such information can, for instance, be well-log data and interpreted seismic horizons. In this paper, we describe our experience of including stratigraphic interpretation into a 4D seismic inversion workflow. We demonstrate the benefits of this workflow for quantitative interpretation through synthetic and real data examples.
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Using 4D Sseismic to Monitor and Characterize Marimba Field, Campos Basin, Offshore Brazil
Authors M. Meira, K. T. P. Lima, V. M. Reis and S. R. MalaguttiUnderstanding saturation and pore-pressure changes is very relevant in mature fields, in this paper we used and compared two pre-stack 4D data, 1984-1999 Streamer-Streamer (S4D1) and 1999-2005 Streamer-OBC (S4D1) to monitor the Marimbá Field reservoirs – offshore Brazil, its oil production started in 1985. Time-lapse seismic data on this field have been successfully used since 2007 to understand the fluid behavior and estimate bypassed oil areas and had helped to take decisions, such as drilling development wells on a not drained area or to understand the water saturation increasing in wells. Initially was made a 4D seismic modeling to helped interpret time-lapse anomalies seen in the field, was identify approximately a 4% P-impedance contrast difference between oil and brine sands, which suggests that it may be possible to discriminate between oil sands and brine sands in 3D as well as 4D data. Further the two 4Ds data were interpreted in its respective period, generating important decisions for the field. In this paper we compares both results (S4D1 and S4D2) through its anomaly and NRMS maps indicating the possibility of use seismic not 4D dedicated to obtain time-lapse information.
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How Compaction Causes Misaligned Multiples and False Time Shifts in Time-lapse Seismic
More LessThis paper argues that in time lapse-seismic with significant overburden time shifts, the time shifts experienced by multiples will exceed those experienced by the surrounding primaries. These misaligned multiples will lead to an overestimate of measured time shifts, especially in areas where multiple energy is strong compared to primary energy. This mechanism explains high time shifts observed in the underburden that are hard to understand otherwise. The phenomenon is formulated in simple arithmetic terms, and is supported by both model computations and real observations on the Tyra field.
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Correlation of Well Activity to Time-lapsed Signatures in the Valhall Field for Enhanced Dynamic Interpretation
Authors Y. Huang, C. MacBeth, O. I. Barkved and J. P. Van GestelWe propose an innovative approach that uses well data to constrain the 4D seismic response and help reduce noise levels. Implementation of this well-centric approach requires multiple seismic surveys shot at frequent intervals over the same reservoir. There are now many fields for which such datasets have become available. One such example has been shown previously by Huang and MacBeth (2009) for the non-compacting Schiehallion field. Here we show a further application to the Life of Field Seismic (LoFS) data acquired over the compacting chalk of the Valhall field. The resultant signals identify only those areas of the seismic which are strongly consistent with the well activity, and hence define portions of the reservoir connected to the wells. This information unites the seismic and well domains without the use of the simulation model. The signal tends to be robust and have a much lower noise when compared to the individual 4D seismic difference signatures. This seismic attribute can be used as a diagnostic tool for examining reservoir connectivity and constraining the simulation model.
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The Dalia OBN Project
Authors E. Ceragioli, L. Bovet, J. Guilbot and S. Toinet2009, the first “industrial scale” Ocean Bottom Nodes (OBN) project over a fully operational production environment was completed by Total on the Dalia oilfield, Block 17, deep offshore Angola. A repeatability test was also performed as part of the operations. Block 17 geophysical response is characterised by weak absorption effects: frequencies up to 120Hz are often used for reservoir characterisation and monitoring. OBN are passive recording systems and source-to-receiver travel times must be reconciled after acquisition is completed. For these reasons, during all operations, great efforts were addressed to any possible cause of time misalignments, since the smallest errors could actually reflect in degradation of thin sedimentary features. When compared to streamer results, OBN processed data exhibit some minor loss in high frequency content but a clear gain towards the lower end of the spectrum. We demonstrate that OBN and streamer data can successfully be merged and that qualitative and quantitative 4D interpretations are possible, in good agreement with the petrophysical knowledge of the Dalia complex. Finally, the repeatability test validates the business model by which selected targets of a deep offshore field can effectively be monitored by fairly limited patches of retrievable OBN stations.
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Seismic Data Interpretation Dilemmas in CO2 Injection Monitoring
Authors R. D. Benson and T. L. DavisCombining the geologic, geophysical and petroleum engineering data allows an integrated approach to interpreting the time-lapse anomalies associated with CO2 injection. Rock physics measurements provide a basis for the relating the changes in fluid saturation, density, temperature, pressure, P-wave and S-wave velocity. Integrating both the P-wave and S-wave surface seismic data allows the separation of the fluid changes from the pressure changes, allowing a much more definitive interpretation of the anomalies associated with the CO2 injection process.
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A Derivative Free Optimization Method for Reservoir Characterization Inverse Problem
Authors D. Sinoquet, H. Langouët and S. Da VeigaReservoir characterization inverse problem aims at forecasting the production of a field from available production data. These data (pressure, oil/water/gas rates at the wells and 4D seismic data) are compared with simulated data to determine petrophysical properties of the reservoir. The underlying optimization problem requires dedicated techniques : derivatives are often not available, the associated forward problems are CPU time consuming and some constraints may be introduced to handle a priori information. In this paper, we propose a derivative free optimization method based on trust region approach coupled with local quadratic interpolating models of the cost function and of non linear constraints. Results obtained with this method on a synthetic reservoir application with the joint inversion of production data and 4D seismic data are presented. Its performances are compared with a classical sequential quadratic programming method in terms of numbers of simulation of the forward problem.
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Time-lapse Seismic AVP Analysis on the Sleipner CO2 Storage Monitoring Data Using CFP Processing
Authors F. P. Neele and R. J. ArtsCO2 has been injected into the Utsira Sand at Sleipner since 1996, with more than 11 million tonnes currently in the reservoir. Six time-lapse seismic monitoring surveys to follow the migration of the CO2 in the reservoir have been carried out. This paper describes a pre-stack data analysis of the top-most accumulation of the CO2. The aim is to validate the assumed rock physics framework by comparing the extracted time-lapse pre-stack amplitude versus ray-parameter (AVP) data with the expected response. To this end the application of an innovative processing scheme is proposed to extract the AVP-gathers from the Sleipner data. A clear match can be observed in the trend of the AVP behaviour for water saturated sand versus CO2 saturated sand.
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Landslide Prediction Using Geoelectrical Investigations
More LessAn issue like landslides in inhabited areas appears today as an important and obvious environmental problem, often called hazard, which, in nowadays’ concept of social, economical and ethical development, requests a careful and complex approach of which results must end up at a fast and efficient solving of the problem, respecting meanwhile the sustainable development principles. This study proposes an approach of the applicability of resistivity surveys in the attempt to efficiently predict landslides and the geometry of the future sliding body, before the active stage of the landslide. The investigated area is located in Romania – the municipality of Runcu, and it’s represented by a road with important stability problems. Such studies, executed after the first signs of instability have been noticed, can efficiently help predicting landslides appearance and can provide important information for their remediation, such as the size and shape of the affected body and the most vulnerable areas for losing cohesion.
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Water Storage Mapping and Stability Analysis of Pyroclastic Covers Through Resistivity Measurements
Authors E. Piegari and R. Di MaioThe landslides occurred in Campania Region (southern Italy) during last fifteen years have stressed the extreme susceptibility of the ash-fall deposits that cover the mountains surrounding the Mt. Somma-Vesuvius volcano. The resistivity tomography technique is able to give a very detailed image of the subsoil structural pattern on the basis of the high resistivity contrasts characterising the Campanian geological settings susceptible to landslides, i.e. pyroclastic soils overlapping a carbonate and/or lava basement. We describe a new conceptual approach that combines electrical resistivity tomographies and laboratory analyses to study the hazard assessment of pyroclastic covers. We report the results of a high-resolution 2D resistivity survey carried out in a test area (Sarno Mountains, southern Italy), and the results of laboratory analyses performed on undisturbed samples collected from the same area, devoted to the determination of characteristic curves electrical resistivity vs. water content. We use such characteristic curves to evaluate the water content of the investigated slope. Finally, we estimate the local empirical safety factor, recently introduced by the authors, in terms of local resistivities and slope angles and compare the values of this parameter with those of the 1D safety factor commonly used in the slope stability assessment.
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Surface-wave Profiling for Sinkhole Hazard Assessment Along the Eastern Dead Sea Shoreline, Ghor Al–Haditha, Jordan
Authors L. Bodet, P. Y. Galibert, A. Dhemaied, C. Camerlynck and A. Al-ZoubiThe surface-wave profiling method has been carried out for the estimation of subsurface shear-wave velocities at the Ghor Al-Haditha sinkholes area, in Jordan. Roll along acquisition and dispersion stacking were used to achieve multi-modal dispersion measurements along two profiles. The estimated dispersion showed strong lateral variations, apparently correlated with sinkholes. Preliminary blind inversion results confirmed these correlations: low shear-wave velocity anomalies were noticed in the vicinity of existing sinkholes and in the currently most active collapsing zone. Such anomalies could be explained by a systematic decompaction of shallow sediment layers, associated to the sinkhole development process.
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Seismogenic Sources in the Lower Tagus Area Using Geophysical Data
Authors C. C. Pinto, J. P. Carvalho, M. Costa, T. Rabeh, P. Terrinha, H. Duarte, J. Borges, B. Caldeira and J. CabralThe Lisbon and Lower Tagus Valley area have suffered the effect of historical earthquakes that caused important damages and loss of lives. Some of these earthquake sources are local but they are still poorly known due to the difficulty in finding geological outcrops, together with low-slip rates and erosion/sedimentation processes that erase surface ruptures. Identification of seismogenic sources capable of producing large earthquakes from low magnitude instrumental seismicity has also proved unreliable in other areas of the world. Therefore, for a proper assessment of seismogenic sources for seismic hazard purposes we have used recently reprocessed and reinterpreted seismic reflection, potential-field data and overlaid relocated epicentres. Here we present a revised structural interpretation of the area based on seismic data and a basement map produced by magnetic modelling, 2D Euler deconvolution and trend analysis. This basement map, which greatly enlarges the seismic coverage of the study area, has shown new insights into deep-seated structures of the Lower Tagus Valley area and their relationship with seismicity. The information from fault parameters collected in this work will also help to locate the sources of historical events such as the 1909 Benavente earthquake using finite-element strong-motion simulation and comparison with observed seismic intensities.
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3D Seismic Survey for Deep Geothermal Exploration at Unterhaching, Munich, Germany
Authors E. Lueschen, M. Dussel, R. Thomas and R. SchulzAn increasing number of low-enthalpy geothermal power plants are being implemented in the Munich area with holes drilled into the Malm (Upper Jurassic carbonates). Optimal development of geothermal productivity requires exploration of the geological structure, as well as information on the karstification of the Malm. A high-resolution 3D seismic volume has been acquired within an area of 27 km2 size for geothermal exploration and modelling purposes, located within the southern suburbs of Munich. First results show preferential hydraulic pathways along fault zones within the Malm reservoir which were partly active until Aquitanian (Lower Miocene). Additionally, a greater number of sinkholes have been identified at the top Malm, located along fault zones which constitute new possible targets for geothermal exploration.
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3D Diffraction and Mode-converted Scattering Signatures of Base-metal Deposits – Bathurst Mining Camp, Canada
Authors A. Malehmir and G. BellefleurThe localized and isolated nature of base-metal deposits and their significantly contrasting elastic properties can generate complex scattering wavefield that may include P-P, P-S, S-P and S-S wave-modes. Multicomponent VSP data confirms presence of multi wave-modes scattered at a deep-seated base-metal deposit in Halfmile Lake, Bathurst Mining Camp, Canada. However, multi wave-modes scattering from a massive sulphide deposit has not yet been recognized on surface seismic data. In this study, we investigate the possible presence of P-P, P-S, S-P, and S-S wave-modes scattered at a base-metal lens at depth of about 1.2 km on 3D surface seismic data acquired with point explosive sources and vertical geophones. We show that the deep lens produces a diagnostic P-P diffraction and could produce mode-converted scattering signals. Results from a target-oriented azimuthal scattering analysis based on 3D prestack migration reveals amplitude anomalies at the location of the base-metal lens for S-P waves and possibly P-S waves. The identification of S-P and P-S wave modes confirms that mode-converted scattering occurring at the deep sulfide lens was recorded on the 3D data. However, the real potential of these complementary wave modes for mineral exploration will only be realistically achieved using shear-wave and multi-component surveys.
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ThermoGIS – An Integrated Web-based Information System for Geothermal Exploration and Governmental Decision Support for M
Authors L. Kramers, J. D. A. M. Van Wees, H. F. Mijnlieff and R. A. KronimusThe use of geothermal energy through implementation of low enthalpy geothermal production systems for both electricity and heating has been growing rapidly in Europe. Geothermal activities can take considerable advantage of a wealth of existing oil and gas data. It is a major challenge to put this data and derived subsurface structural, temperature, and flow property models available to the geothermal community and to facilitate in quantitative assessment of geothermal potential of targeted areas, for both heat and electricity production (EGS) . In order to face this challenge, TNO has developed a public web-based 3D information system connected to a geothermal performance assessment tool. The public information system (thermoGIS) includes high resolution 3D geological models covering the complete onshore of the Netherlands, outlining key geothermal reservoirs and allowing to assess relevant parameters and underlying uncertainties therein. Users can obtain key reservoir parameters, and underlying uncertainties at any location and for any reservoir. In an automated workflow these parameters are fed into the performance assessment tool, in order to assess the probability of success to meet minimum requirements on key performance indicators. The use of the ThermoGIS will aid exploration business decisions and Dutch governmental institutions, law makers and insurance companies.
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The Modern Heat Flow Database of Norway and its Implications for Geothermal Energy
Authors C. Pascal, H. Elvebakk and O. OlesenThe Geological Survey of Norway is conducting the largest heat flow study in Norway ever carried out since the 1970s. In the framework of the Kontiki and HeatBar projects, we measured temperatures in 17 drillholes located in most regions of Norway mainland. In contrast with previous heat flow studies, most of our drillholes reach depths exceeding 800 m, allowing for correcting geothermal gradients for paleoclimatic effects and for estimating deep underground temperatures. The data were primarily used to calculate the relative amount of heat flow produced in the different units of the Norwegian basement and to extrapolate this information to the offshore areas. In addition, using the calculated heat flow values, recently published thermal properties of rocks in Norway and results from previous geological and geophysical studies, we computed underground temperatures at different depths. Relatively low temperatures are predicted down to 5 km in central and northern Norway, restricting the geothermal potential of these regions to the use of "low temperature fields" (i.e. < 100°C) but for the Oslo Region, the most populated region of Norway, our calculations suggest more favourable conditions. These preliminary findings need to be confirmed by more focused studies.
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Closed-loop Frequency MET Geophone – Operating Principles and Parameters
Authors V. M. Agafonov, E. I. Egorov and C. E. RiceA closed-loop, compact, wideband active geophone based on the MET sensing cell is designed. Experiments using an accurate shake table and noise analysis have been performed. The frequency response is flat within 3 dB in the 1 to 300 Hz range, the self-noise spectrum density 5*10-7 m/sec2/√Hz, and the THD at 18 mm/sec peak to peak input is 0.02%. The instrument tested has self-noise and linearity close to the best conventional geophones, but is more sensitive and has a wider operating frequency range.
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3D Near Surface Imaging Thanks to Refraction Tomography and Delay Method
Authors J. L. O. Mari and M. MendesThe refraction seismic technique is being used increasingly to obtain 3D subsurface images to address geologic exploration and engineering problem. There are, however, several problems in solving the non-linear problem associated to the refraction travel time inversion. Thus it is important to develop inversion strategies for the 3D imaging of near surface structures. One set of high-resolution seismic data collected over an experimental hydrogeological site located near Poitier-France, designed to perform both 3D refraction and reflection seismic surveying, is processed using a first arrivals inversion to determine reliable 3D velocity model with special emphasis on upper part of the near-surface heterogeneous aquifer. The inversion strategy is a hybrid algorithm combining conventional delay method with refraction tomography and we show how this technique can be used to extend in the 0 – 35 m depth interval the 3D velocity block obtained by a previous reflection study. We investigate the impact that the change from 2D to 3D dimension in data has in the velocity imaging. The final result obtained with 3D data emphasizes the geological structures mentioned in the reflection image, allowing a better recognition of their alignments (N90°) and shape.
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High Resolution 3D Tunnel Seismic Reflection at Olkiluoto, Finland
Authors C. Cosma, N. Enescu, M. Lahti, E. Heikkinen and T. AhokasONKALO is the underground rock characterisation built for the final disposal of spent nuclear fuel at Olkiluoto, Finland. Geology, geophysics, hydro-geology, geochemistry and rock mechanics contribute to bedrock studies conducted during repository construction to ensure the suitability of the bedrock for the final disposal. A high-resolution reflection seismic imaging pilot test was conducted in 2007, followed by a more ample survey in 2009. Lines 100m and 240m long were measured, with source stations spaced at 1m and receivers at 1m and 3m, respectively. Measurements in 2007 were conducted with a hand-held electro-mechanical source held against the tunnel wall. In 2009 a more energetic hydraulic source and was used on the tunnel wall and floor. Fractures were imaged several tens, respectively hundreds of meters from the tunnel. In 2007, the one-dimensional tunnel layout left a certain ambiguity regarding azimuth relative to the tunnel. The location of the target features was improved in 2009, by using 3-component receivers, two parallel source lines and 3D vector migration schemes. IP (Image Point) migration was found particularly useful for imaging narrow and roughly planar features of diverse orientations.
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In-situ Porosity and Permeability Estimation from the VSP Data Using Integrated Poroelastic Model
Authors A. Zhubayev and R. GhoseReliable estimates of in-situ porosity and permeability in the water-saturated near-surface soil layers are important in diverse engineering projects. However, it is difficult to obtain these estimates, especially in loose sandy soils. In particular, the estimation of in-situ permeability is extremely difficult. Also porosity and permeability are related parameters in porous formations. An approach which can simultaneously estimate the in-situ porosity and permeability values has added scientific merits. For this purpose, we have looked at poroelastic wave propagation in the subsoil. A field database for seismic dispersion was compiled to test the applicability of various poroelastcity models to water-saturated, onshore sands and clays, in the field seismic frequency range. Using the most applicable poroelastic models, we have presented a physics-based integration approach that combines P- and S-wave velocity and attenuation. We show the existence of convexity in the parameter domain when we integrate velocity with attenuation through a cost functional. This allows for estimation of both porosity and permeability uniquely and simultaneously. The approach was tested on synthetic VSP seismograms. With realistic error in data and model, the approach still appears to give reasonably accurate values of both porosity and permeability.
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Joint Inversion of P-waves Refraction Traveltimes and Surface Waves Dispersion Curves
Authors C. Piatti and L. V. SoccoRayleigh wave dispersion curves and P refraction travel times are jointly inverted through a damped least square algorithm which accounts simultaneously for both datasets, solving for common thicknesses and respective VP and VS values. The velocities are coupled through the introduction of P-wave velocity values that are used for both the refraction and the surface wave forward modelling. Since the sensitivity of surface waves to P-wave velocity is low, the problem is strongly coupled on the thicknesses and weakly coupled on the velocities. The surface wave - P-wave refraction joint inversion algorithm is effective in solving hidden layer problem, which would lead to big interpretational errors in the case of individual inversion of P dromocrones. The approach is effective for inversion of 1D layered models as shown in one example for the inversion of experimental data, leading to better results than individual inversions also in the case of surface waves.
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Comparative Study on Damping and Smoothing Constraints for the Inversion of Surface Waves Data
Authors G. S. Kritikakis and A. VafidisShear wave velocity determination from the ground roll, exhibits the last few years rapid development in near surface geophysics. The inversion of the dispersion curves is one of the most important steps during the processing of surface waves. This study focuses on the comparison of damping and smoothing constraints during the inversion. The strategy for the surface waves inversion is demonstrated employing two synthetic dispersion curves, which correspond to a model with gradually increasing velocity (GIV) and a low velocity layer (LVL) model. The inversion of synthetic dispersion curves shows that the lack of a-priory information on the initial model may lead to unrealistic Vs profiles, even if the fit between experimental and theoretical dispersion curves is satisfactory. Damping performs better for the examined LVL model, whereas smoothing is preferable for GIV model. Both inversion techniques were also applied on real data collected at an area of geotechnical interest. Real data inversion with damping and smoothing constraints produced different depths to the top of the lowermost soil formation, but the corresponding pseudo-sections encounter similarities regarding the overlaid layers. This study indicates that the choice of the most appropriate inversion technique and the use of any reliable a-priori information are crucial.
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Lateral Discontinuity Localization and Characetrization by Means of Enhanced Statistical Phase Analysis of Surface Waves
Authors G. Vignoli, C. L. Strobbia, G. Cassiani and P. L. VermeerMost standard procedures for dispersion analysis make use of multichannel wavefield transforms and the lateral velocity variations can be averaged spatially. On the other hand, the use of a local phase offset analysis can provide a very high lateral resolution. A new statistical enhanced multioffset phase analysis of surface wave data is presented. The phase processing of point receiver land data allows identification of velocity variations with a lateral resolution equal to the receiver spacing. An automatic procedure is set up to identify sharp lateral variation, and is tested on real land point receiver data.
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Verification of Soil Profiles Obtained from Experimental Rayleigh-wave Dispersion Inversion Using Synthetic Microtremors
Authors K. Tokeshi and L. V. SoccoAn attempt to discuss and/or verify the suitability of subsoil velocity models estimated from Monte-Carlo inversion using synthetic microtremors is performed. In the last 2 decades, experimental Rayleigh dispersion curve from passive microtremor measurements has been explored as a tool for estimating subsoil velocity profiles. The Monte Carlo inversion is one of the most popular methods to estimate them. However, it is also known that the Monte Carlo method gives non-uniqueness solutions. In this paper, the suitability of one of the solutions (the bad case) of soil profiles estimated from experimental surface wave dispersion curves at one site is discussed using the simulation method proposed by the authors in 2009. The simulation is carried out by controlling the magnitude of input sources at the ground surface, through the parameter: ratio of forces RF. As case study, microtremor measurements from an Alpine site are analyzed and compared with the synthetic ones. The synthetic vertical/horizontal dispersion curves and the synthetic classical/modified H/V spectral ratios for certain values of RF are compared with the experimental one. According to this comparison, the tested subsoil profile should be discarded. The proposed method would be a promising tool to resolve the problem of non-uniqueness.
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Rayleigh Wave Inversion for the Near-surface Characterization of Shallow Targets in Kuwait
Authors A. El-Emam, C. L. Strobbia, J. Al-Genai and J. RothNear-surface complexity can be particularly challenging in the case of shallow targets such as those in the Lower Fars shallow heavy oil reservoir in northern Kuwait. Some of the standard techniques have intrinsic limitations and can fail in the presence of a complex near surface, for instance with velocity inversions. To evaluate and test the potential of new near surface characterization approaches with point receiver data, a field test has been designed, acquired, and processed. More specifically, the aims of the test were demonstrating the advantages of the Rayleigh wave inversion for the near-surface characterization and statics, near-offset noise attenuation, and, in general, point-receiver processing. The results and the validation with well data confirm the robustness of surface wave methods for the near surface characterization, and the benefits of its integration into the data processing flow.
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Near-surface Characterization Using Point Receiver Data
Authors L. Velasco, C. Strobbia and A. LaakeThe effect of near-surface perturbations is still one of the key problems in land seismic surveys. Elastic near-surface characterization can provide a robust solution for the compensation of the effects of the shallow geology on surface seismic data. Seismic point receivers provide densely sampled data that enable the use of high-resolution methods for near-surface characterization. Near-offset refractions and surface wave inversion allow generation of shallow 3D depth models for P-wave and S-wave velocity. The two models reveal near-surface geological layers and lateral heterogeneities. A case study from the Gulf of Suez gravel planes demonstrates that lateral heterogeneities in shallow P-wave and S-wave velocity horizons map shallow faults. The results are validated by fault outcrop maps from remote sensing. For the first time the elastic near-surface model is being estimated from surface seismic data. Point-receiver technology provides geological information in a domain that is usually not accessible for seismic investigation. The approach to attenuate shallow seismic data in conventional acquisition is replaced by a method that focuses specifically on the extraction of shallow seismic data for geological mapping.
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Estimation and Application of Full Waveform Redatuming Operators
Authors P. R. Haffinger and D. J. VerschuurSeismic data quality can be severely affected by near-surface anomalies. The imprint of a complex near-surface can be removed by redatuming the data to a level below which the subsurface is assumed to be relatively simple. It has been shown that this can be achieved by using focusing operators that are estimated along a user-defined horizon below the near surface complexities. In the current implementation of the CFP-technology, the estimation of the focusing operators is done in terms of traveltimes only, based on a high-frequency approximation. The accompanying amplitudes are usually derived from a local homogeneous medium, which is obviously a simplification of reality. The parameterization of focusing operators in terms of traveltimes and simple amplitudes has produced encouraging results in the past, but cannot remove the near-surface complexities completely, leaving artifacts in the redatumed results. In this paper we propose a method that estimates the focusing operators in a full waveform manner, such that detailed amplitude and phase variations are included. Based on 2D synthetic data it is demonstrated that the resulting redatuming quality is improved and artifacts are reduced.
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Gabor Domain Analysis of Q in the Near-surface
Authors R. J. Ferguson, G. F. Margrave and K. W. HallWe present a Q estimation method where analysis is done in the Gabor domain. There, attenuation is estimated as a function of frequency (f), and Q (f) is computed through inversion of attenuation. We provide an example based on a 7-level, near-offset VSP consisting of 3-component receivers and sweeps. Eight, narrowband sweeps are used to span 10 Hz - 250 Hz for each source orientation. Two subunits are identified within the local formation that correspond to an expected 50 m of unsaturated media underlain by an aquifer. Our results demonstrate that attenuation varies near-linearly with frequency for the 95 m depth range. Strong values of attenuation that increase with frequency are found in the unsaturated unit, and weaker, decreasing attenuation is found in the saturated unit.
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Shear Wave Velocity Model from Surface Wave Analysis – A Field Case Example
Authors D. Boiero, R. Wisén, M. Maraschini and L. V. SoccoShear wave velocity models can be built through surface wave analysis. For the presented field case, preliminary data analysis has evidenced the possibility of retrieving several modes of vibration of Rayleigh waves and this suggest the use of a multimodal inversion algorithm to estimate a pseudo-3D shear wave velocity model. The full analysis has been performed starting from a preliminary Monte Carlo inversion applied on the representative dispersion curves. After the Monte Carlo inversion, which provides a consistent 1D reference model for each line, the dispersion curves have been inverted simultaneously adopting a linearised laterally constrained inversion (LCI) to obtain a pseudo-3D shear wave velocity model.
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Surface and Borehole Refraction Surveys in Copenhagen, Denmark
Authors K. Martinez and J. A. MendozaSeismic refraction imaging is a technique that has seen an increase of applications in engineering during recent years. In the work presented here a case of refraction tomography in the city of Copenhagen is discussed. The survey included two modalities; 1. a surface survey where 13.9 kilometers of crooked lines along segments of the planned underground metro were mapped, 2. borehole “walk-away” seismic refraction surveys in twenty nine boreholes located in proximity to the surface lines. The overall aim was to map the extension of the near-surface unconsolidated sediments and their interface with underlying sequences of limestone. The results showed it was possible to map the unconsolidated sediments and the underlying limestone. This led to a more reliable interpretation of the surface results along the sections where neither geology nor borehole data was available.
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An Interesting Property of the Seismic Wavefield – Scale Properties for Waveform Matching
Authors M. Maraschini, D. Boiero, S. Foti and L. V. SoccoIn this paper we present the application of scale properties on waveform matching. Scale properties are properties of seismic waves which can be used to save computational time in full waveform modelling and inversion. The adimensionalization of motion equation allows the possible models to be divided in classes, such that the full waveform of one of the element in a class can be easily calculated from the full waveform of another element in the same class. These properties have two main applications: the first one concerns the full waveform modelling; when the full waveform is calculated from a given profile, it is straightforward to calculate the full waveform for any of the profiles in the same class. The second application concerns the full waveform matching: when a experimental seismogram is recorded, and a synthetic one is calculated, before comparing them, it can be useful to change the synthetic model to another in the same class which is closer to the experimental one.
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Rock Physical Interpretation of Geophysical Data for Soil Profiling
By T. TakahashiTo study rock physical interpretation of geophysical data for soft soil profiling, the existing rock physics models are applied to seismic velocity and resistivity data obtained for saturated and unsaturated soft soils. For unsaturated soft soils in an earthen levee, the unconsolidated sand model is applied to S-wave velocity and porosity data. The porosity is converted to resistivity for making an S-wave velocity – Resistivity diagram which is used for constructing a soil profile from S-wave velocity and resistivity profiles on the levee, proving that it can be utilized for soil classification of soft soils. For saturated soft soils, the unconsolidated sand model and the binary sand/shale mixture model are applied to P- and S-wave velocity and porosity data. This application shows that the sandy shale model of the binary sand/shale mixture model can be used for modeling soft soils composed of sands and clays, but not of gravels. The diagram of velocity and resistivity converted from porosity with the Archie’s law shows its applicability for soil classification of saturated soft soils as the case of unsaturated soft soils.
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Using the EMS Approach to Minimise Environmental Impact of Seismic Operations
More LessBP Algeria Exploration’s (BPXA) work program during 2009 revolved around acquiring 2560 Sq Km of 3D Seismic Data in the Bourarhet Sud block, located 150km southwest of the town of In Amenas. The survey’s primary objective was to acquire 2560 Sq Km of high fold data (495 at 4km offset) in 8 months using a BP technique called Independent Simultaneous Sources (ISSTM). A further requirement for the Seismic Survey operated by Global Geophysical Services was that the operation was to be externally audited to provide objective evidence to demonstrate that an Environmental Management System (EMS) was operating effectively in conformity of the ISO 14001 standard. EMS’s key objective is to assure that environmental risks are clearly understood and form part of project planning, control measures are put in place to prevent or mitigate the impacts and the environmental performance is monitored and keeps improving. This paper describes the successful implementation of an EMS on a working seismic operation to a standard which enabled BPXA’s EMS to be awarded ISO 14001 Certification in September 2009.
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Distributed Vibration Measurements to Prevent Structural Damage – A Novel Application of Wireless Sensor Networks
Authors M. Piantanida, M. Veneziani, M. Fermi, S. Brigas and T. HarveiSeismic campaigns and hydrocarbon production activities can generate extensive amount of vibrations which can impact on the structural stability of equipment, infrastructures and buildings. This paper describes a novel application of Wireless Sensor Networks (WSN) designed to monitor in real time the amplitude and the frequency of vibrations reaching infrastructures and buildings, with the purpose of preventing structural damages. To address this application, a joint effort has been carried out by Eni and ABB to prototype a distributed vibration sensor network through the integration of an accelerometer into a WSN platform. The paper will present the design of the WSN architecture, as well as the tests and results that were achieved.
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Seismic Risk Analysis of Small Earthquakes Induced by Hydrocarbon Production in The Netherlands
Authors O. Leeuwenburgh, B. B. T. Wassing, P. H. Waarts, W. Roos, M. Nepveu, A. G. Muntendam-Bos and T. van EckIn the northern parts of The Netherlands, the exploitation of gas fields has induced small earthquakes. These induced earthquakes have occasionally caused damage to buildings. A workflow was developed in order to evaluate the seismic risk of the exploitation of hydrocarbon fields. A Bayesian analysis was performed to investigate the correlation between the reservoir properties and production specifics of the fields and the occurrence of induced earthquakes. Based on geomechanical and reservoir production key parameters, a probability of that induced seismicity will occur can be assigned to an individual hydrocarbon field. Probable ground motions for average surface conditions were obtained from a probabilistic seismic hazard analysis. Next, the impact of local soil conditions was taken into account by analysing the site response of shallow soil profiles. Finally, the relation of ground motions and probability of damage was investigated, using data on damage during past induced erathquakes. In this extended abstract a concise overview of this workflow is presented.
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A Governance Framework for Sustainable Oil and Gas Business Transformation
By B. MotocIn this paper, we are combining three modern social agency models into a more generic model of multi-agency governance of environmental, social and business objectives. The new model allows us to identify two main attributes of collaboration. For a successful integration that would lead to sustainability, we show what the relation these attributes need to satisfy is.
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Responsible Marine Seismic Exploration in an Area With a Piracy Risk – Indian Ocean Case Study
Authors N. Millar, K. Carroll, A. Camerer and T. EllisThe rapid increase in frequency and severity of pirate attacks in a number of hydrocarbon basins poses significant safety, cost and reputation risks to offshore seismic operations in piracy prone areas. We review the piracy risk analysis and mitigation strategy applied successfully to the Mbawa 3D marine seismic survey in an area close to Somalia’s southern border in December 2009. Information is provided from the perspectives of Operator, Seismic Contractor and Security Contractor and the paper covers legal, insurance, cost, risk analysis, logistical, stakeholder consultation and operational issues. The survey management knowledge developed during this operation is shared and suggestions on how to co-ordinate the seismic and security operations are included. The HSE results of the survey are presented including a review of the interactions with third party vessels encountered during the survey and a review of the regional piracy landscape before and during the seismic survey. The paper is concluded with suggested guidelines for managing piracy risks for marine seismic surveys
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Carbon Challenges
By E. T. HaynesThe oil and gas industry has tremendous business opportunities as fossil fuel resources deplete, and prices rise, over the next decades. It also has herculean challenges in terms of demonstrating relevance and being heard in the ever "greening" politics of our age. This talk offers a view from someone who was on the inside for many years, but has been in the "outside" environmental sector for the last 10 years.
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Modernisation of Saudi Cadastre
Authors M. Alrajhi and M. HawareyThe Ministry of Municipal and Rural Affairs (MOMRA) and the Ministry of Justice (MOJ) in the Kingdom of Saudi Arabia (KSA) have been mandated to carry out a whole new cadastre programme that encapsulates a completely new cadastral registration system that would revolutionize the way real estate and cadastral registation processes is transacted. While the MOMRA is in charge of all technical affairs, the MOJ is in charge of the adjudication operations. This paper will highlight the efforts spent over many years to prepare the foundation for this new programme.
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Investigation on Origins of Hydrogen Sulfide Production in Sweet Gas Fields
Authors E. Adibi Sedeh, M. Farrokhrouz and M. R. AsefHydrogen sulfide is a common unwanted material in gas reservoirs which should be removed in the process of refining. Although a large number of gas reservoirs in the world are sour, but sweet gas reservoirs can be found in some areas of the world, for example in south of Iran. Occurrence of hydrogen sulfide (H2S) in a sweet gas field was a major origin for site investigation. The situation became even worse after acidizing. The main cause of H2S forming was guessed to be formation rock types which were mainly composed of anhydrite. In order to make a better view of the work, chemical samples were taken from the well at different production rates and condition of hydrogen sulfide precipitation was simulated using software. The same situation existed for CO2 and design of the investigations started to remove these toxic gases. Further simulations proved that a modified acid mixture, in future acidizing operations, can reduce the amount of these gases significantly and environmental issues would be concerned seriously in such cases.
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Targeting for Geothermal Energy Production – Reservoir Characterization and Geothermal Potential of the Delft Sandstone
The Delft Geothermal Project is a broad consortium of governmental and industrial partners that aims to develop an innovative geothermal system at the TU Delft campus. In early 2011, a geothermal doublet will be drilled that targets the Delft Sandstone Member, a fluvial sandstone formation contained in a structural low at a depth between 1.7 and 2.4 km. Several wells were drilled in and around the target area in the 50s and 60s, primarily to explore known oil-bearing formations above the Delft Sandstone Member. Based on the analysis of logs, cores, and cutting data from these wells, and their correlation with re-interpreted 2D and 3D seismic, the target sandstone is subdivided into three units. The lower unit is considered a risky target, primarily because of the poor lateral and vertical connectivity between individual fluvial sandstone bodies. By contrast, in the upper unit, lateral and vertical connectivity between individual sandstone bodies is high, as are porosities (30%) and permeabilities (725-1130mD), which makes this unit an excellent target for geothermal energy production. Communication between the lower and upper unit is likely impeded by the presence of the middle unit, which as extremely low porosity and permeability.
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Exploration of the Deep Structure of the Central Greece Geothermal Field by Passive Seismic and Curie Depth Analysis
Authors V. K. Karastathis, J. Papoulia, B. Di Fiore, J. Makris, A. Tsambas, A. Stampolidis and G. A. PapadopoulosNew findings about the deep origin of the geothermal fields and volcanic centres of the North Evian Gulf area, Central Greece, were arisen by combining a three-dimensional traveltime inversion study of a microseismic dataset recorded of 37 portable stations together with a Curie depth point analysis based on aeromagnetic data. A possible magma chamber can be presumed by the detection of a low seismic velocity volume with high Poisson ratio values at depths below 8 km and the Curie point depth estimation at about 7-8 km depth as well. Besides, the analysis gave information about how the main large tectonic structures (NW-SE) and other important NE-SW faults can facilitate the hydrothermal flux of the local geothermal field.
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Enhanced Velocity Modeling for a Geothermal Project in the Southern Vienna Basin – A Stacking Velocity Approach
Authors C. G. Eichkitz and J. AmtmannVelocity models can be build based solely on or from a combination of checkshots, VSPs, sonic logs or seismic stacking velocities. Depending on the information available, the method of building a velocity model can vary (using interval velocities, average velocities, layer cake model, V0-K method, models based on geostatistical methods ...). The advantages and disadvantages of these methods have been described by numerous authors. In the course of a geothermal project in the southern Vienna Basin, the problem of a time to depth conversion arose. In the area of interest, only six wells with checkshot-information were available and, therefore, the usage of a simple V0-K method or layer cake method was not suitable. Hence, the application of available seismic stacking velocities for velocity modeling was tested. The stacking velocities were converted into interval and average velocities using the Dix equation. These velocity values were then sampled into a geo-grid and spatially distributed in the grid using geostatistical methods. The stacking velocities were compared where checkshots or sonic logs were available. The result of this velocity modeling procedure was a 3D velocity cube that can be used to depth convert the seismic profiles and the interpretation from the time domain.
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3-D Seismic Modelling of the Flin Flon VMS Mining Camp
Authors M. Malinowski, D. White and E. SchetselaarA 3-D seismic reflection volume acquired within the Flin Flon VMS mining camp has been compared with simulations for a 3-D seismo-geological model built for the camp. The simulations were conducted using phase screen 3-D elastic modelling in both prestack and post-stack mode. Some of the strong diffraction-like patterns present in the real data were not predicted by our model and hence, they could be used for direct ore targetting.
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Reflection Seismic Investigations in the Brunswick No. 6 Mining Area, Bathurst Mining Camp, Canada
Authors S. Cheraghi, A. Malehmir and G. BellefleurThe Bathurst Mining Camp of northern New Brunswick, Canada is a major base-metal producing region that includes the super-giant Brunswick No. 12 and smaller size Brunswick No. 6 mines. Seismic reflection data along with borehole geochemical and petrophysical measurements from the Brunswick No. 6 mine are studied in this work. Acoustic impedance values for the Brunswick horizon and host rock structures indicate that the mineralized horizon is not strongly reflective in comparison with the mafic-ultramafic rocks. Although the data is acquired in crystalline environment, it shows an excellent data quality with a series of steeply dipping reflections imaged down to 3 s. The results demonstrate that reflection seismic imaging is particularly effective for imaging structures of the Brunswick No. 6 mine, many of which intersect the surface and thus allow for correlation with surface geology. Even more encouraging, the Brunswick horizon and associated iron mineralization are identifiable within a distinctive reflective package that can be used as a guide for deep base-metal exploration in the region.
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Using Stochastic Borehole Seismic Velocity Tomography and Bayesian Simulation to Estimate Ni, Cu and Co Grades
Authors L. Perozzi, E. Gloaguen, S. Rondenay, A. Leite and G. McDowellIn the mining industry, conventional methods to build a block models of ore deposits are based on kriging or cokriging of grades for targeted minerals measured on core sample in fertile geologicals units. As the complexity of geological geometry increases, so does the complexity of the grade estimation. Without additional information on the geological framework, the definition of fertile zone is a low-precision exercise that requires extensive experience from the geologist. Recently, thanks to computer and geophysical tool improvements, seismic tomography became very attractive for many application fields. Indeed, this non-intrusive technique allows inferring the mechanical properties of the ground using travel times and amplitude analysis of the transmitted wavelet between two boreholes, hence provide additional information on the nature of the deposit. Application of the presented method to the Voisey's Bay deposit allows improving the knowledge of the geological framework and generating grades models with realistic spatial variability.
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Enhanced Airborne Detection of Perfect Conductors through Estimation of Primary Field Components
Authors A. Smiarowski, J. Macnae and R. BaileyThe induced electromagnetic field in very conductive targets, such as high-grade sulphide deposits, does not appreciably decay within the measurement time of an airborne EM system. Measurement of in-phase or on-time response in the presence of a large primary field is required to detect these targets. In this study, we calculate the primary field generated by the transmitter at the receiver and subtract this from the measured response to obtain the in-phase secondary response. Employing a large transmitter-receiver separation reduces the accuracy to which geometry of the system must be known, and GPS data provides the required resolution. A transmitter loop and a receiver bird were outfitted with GPS units, and towed by separate helicopters, 400m apart. This provided position and orientation information to calculate the primary field at the receiver. The in-phase total-field response of this survey configuration was sensitive enough to detect a very conductive plate target. Using magnetometer data from the receiver, we have now been able to resolve component data useful for determining the geometry of the target. It is hypothesized this configuration could detect a 200 x 100 m perfect conductor at 200m depth in a resistive host.
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Investigation of Rocks Electrochemical Activity
More LessIn the work electrochemical characteristics of various rocks including sulfide minerals of Kazakhstan deposits (Dzhezkazgansky, Leninogorsky, Uralsky and Akbakaisky) methods of own polarization, the caused polarization and a method of electrode potentials are investigated. It is shown that electric fields of the caused polarization allow to dismember cuts of wells and to reveal in them ore bodies. Cathodic polarization, characteristic for the majority of sulfides and almost absent in graphite, can be used for more exact interpretation of diagrams of potential of electrode polarization.
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Understanding Tectonic Evolution of the Crimea to Ensure Strategy for Hydrocarbon Prospecting Offshore Ukraine
Authors A. A. Kitchka and V. V. YudinNew mobilistic approach proven by field observations, palinspastic restorations, and new geodynamic model of the Black & Caspain Seas region produce new exploration background for oil and exploration offshore the Crimea. A new geological map of the Peninsula, its balanced geological cross-sections, and key onshore outcrops that reveal analogs to the hydrocarbon prospects offshore Crimea, are featured.
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The Structural Evolution and Tectonic Development of the Laptev Sea Region in Mesozoic and Cenozoic
Authors V. E. Verzhbitsky and A. K. KhudoleyThis study is based on the series of field works on Bel’kov Island (Eastern Laptev Sea region) and Khatanga Bay area (Western Laptev Sea region). It is widely known, that the Laptev Sea region is one of the remote and geologically complex areas of Russian Eastern Arctic. According to the existing seismic data, a number of large offshore sedimentary basins with significant proposed hydrocarbon potential, but very controversial in age and composition, were revealed on its shelf. No offshore wells were drilled there so far, thus all the information on the regional geology, is based on the very limited amount of marine seismic profiles and our knowledge on adjoining near-coastal areas. Here we are focusing on the problems of structural geology of the region studied. During the field works we have collected significant amount of structural-geological data, which allowed us to restore the main stages of structural/tectonic evolution of the Western and Eastern Laptev Sea region.
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Prediction of Flow Properties of Upper Cretaceous Continental Deposits from Petrophysical and Geological Data – T. Field
Authors E. Miley, D. V. Romanov and C. Elders• Core logging established that well 9 penetrated estuary deposits. The whole depositional environment model which was created by electrometric method show us the position of perspective reservoirs (point pars and crevasse splay) and river channel. • Different geophysical methods allow us to find dependence for calculating flow properties in wells when a lot of well logs are missing. • Geological model helps to estimate the quality of each of lithotypes by flow properties distribution. • The purpose of this Project was to predict flow properties and hence establish the reservoir production potential. Based on the above purpose the 3D geological model has been created, which allowed reservoir evaluation and reserves estimation and which can be used for future flow simulation modeling. • We recommend to do following for future studies: - drill a well in the north anticline structure - run full logging suite in all new wells - perform NL time measurements in cased well for establishing gas-oil contact precisely - take low-invasion core; - conduct palynology analysis of core data to specify depositional environment of Dl-III formation.
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Recent Tectonics in the Ouarzazate Basin, Moroccan Atlas – Structural Uplift and Shortening Rate from Quaternary Markers
Authors A. Pastor, A. Teixell and M. L. ArboleyaThe Atlas system elevation does not correspond with the crustal shortening registered. Previous studies suggest than a great part of the present Atlas topography is due to a recent (late Cenozoic) long wavelength mantle upwelling. In this framework, we have investigated the nature and rates of recent (Quaternary) compressive deformation. Atlas seismicity is moderate and the most active tectonic structures penetrate and deform the Ouarzazate basin, in the southern foreland of the High Atlas. The semiarid climate and the presence of stepped fluvial terraces above active structures make this area as an ideal case to analyze recent deformation in a slow tectonic setting. Before this study, recent tectonics had been documented but poorly constricted. A recently obtained terrestrial cosmogenic nuclide surface exposure ages of Quaternary deposits provide a framework to estimate the shortening rates for two main fold-thrust structures, belonging to the South Atlas frontal system, in 0.13-0.21 mmy-1 for the last 250-278 Ky, since MIS-9c. Moreover the reflection seismic profiles show two tectonic styles acting simultaneously within the Ouarzazate basin; thick-skinned at west and thin-skinned at east. This difference is also reflected on the deformation geometry of the Quaternary markers.
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Mapping Regional Deformation Bands Zones Using an Aerial Photographs and Field Data – A Case Study from SW Libya
Authors M. Koprianiuk and M. KlosStructural field mapping as well as high resolution aerial photos interpretation revealed that deformation bands and zones of deformation bands are the most common tectonic structures in the Contract Area 113 (block 1 & 2), SW Libya. These structural features occur mostly in porous sandstones of the Carboniferous Assedjefar Formation. Two major conjugate sets of the deformations bands and the zones of deformations bands were mapped. Their geometrical and kinematical characteristic clearly indicate that they were formed as a result of W-E striking tectonic compressive stress. Deformation bands zones can be traced over hundreds of meters in the studied area. Occurrence of dense network of deformation bands zones in the Contract Area 113 (block 1 & 2) has great impact on modeling of shallow reservoirs, because in most cases deformation bands act as significant barriers for fluid flows during the HC production phase.
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Procedure for Oil- and Gas-bearing Reservoir Prediction in the Black Sea Area
Authors M. V. Gubarev, N. Kondratiev, V. Gayduk and S. ProshlyakovDevelopment of hydrocarbon resources in the sea area of oil-and-gas-bearing provinces is considered nowadays as the most promising trend of growth of the mineral resources base and it is one of the basic investment trends for leading oil and gas companies of the world. In this context it is quite challenging to develop the southern regions of Russia, water areas of the Black sea in particular, where geological exploration is carried out actively at the moment.
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Seismo-stratigraphic Study of the Plio-pleistocene Deposits of the Central Adriatic Sea, Italy
Authors L. Lipparini and R. TinterriAn integrated 3D Seismo-Stratigraphic Study was carried out on a portion of the Central Adriatic Sea (Italy), offshore the coast of the Abruzzo region, aimed to define and understand in detail the Plio-Pleistocene stratigraphic succession, the evolution of this area through this specific geological time, and the implication from and E&P perspective. The study is based on good quality 3D data, wells and regional 2D seismic lines. The stratigraphic succession of the foredeep Plio-Pleistocene deposits presented in this work, shows a general shoaling up trend in which the vertical evolution from deep water deposits into deltaic and nearshore strata is related to the progressive displacement of the main depocentres eastward produced by thrust propagation toward the outer margin of the foredeep basin. In this note, in particular, the Middle/Upper Pliocene and Pleistocene part is described in its main seismo-stratigraphic characteristics. A detailed 3D seismic facies analysis has infact allowed to identify, interpret and understand from a depositional point of view several interesting geological “objects” at different scale: in particular, possibly for the first time in this area, well developed sediment drifts, related to bottom currents and associated to deep water channel complexes, were described.
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Paleo-thermal and Structural Indicators for Unraveling Burial – Exhumation Paths in the Peloritani Mts., NE Sicily, Italy
Authors L. Di Paolo, L. Aldega, S. Corrado, R. Somma, M. L. Balestrieri and R. ManiscalcoWe used vitrinite reflectance and mixed layered clay minerals to investigate levels of diagenesis of the Oligocene-Miocene basin developed on the nappes of the Alpine orogen in the Peloritani Mts. (NE Sicily). Paleothermal indicators were integrated with stratigraphic-structural analyses and apatite fission-track and (U-Th-Sm)/He ages to define the late evolutionary stages of the Peloritani Mts. The reconstruction of the paleogeothermal gradient in Oligocene-Miocene times was performed to constrain the burial-thermal evolution. In the southern area, thermal parameters increase with depth suggesting that their evolution is ruled by sedimentary burial. They recorded a decrease in paleogeothermal gradients which marked the evolution of the basin from a fore-arc to a thrust-top setting during convergence-collision. In the northern edge of the basin, higher vitrinite reflectance values indicate that thermal evolution was controlled by tectonic burial related to late Langhian-early Serravallian out-of-sequence thrusting. This overburden was removed by extensional tectonics and/or erosion since late Miocene. The short time span at maximum temperature (<2 Ma) elapsing between thrust stack emplacement and the beginning of its removal have allowed only vitrinite reflectance and thermo-chronological indicators to record this compressive reactivation.
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Modeling WAG Experiments with Three-phase Hysteretic Fractal Model
Authors J. P. Duquerroix, S. Sygouni, S. Bekri, O. Vizika and E. Fernandez RighiWater Alternating Gas (WAG) processes promise optimized results in applications such as CO2 storage in reservoir rocks, enhanced oil recovery or soil remediation. In this kind of processes, hysteretic phenomena take place due to imbibition/drainage processes or to varying wettability affecting the three-phase relative permeabilities. The optimization of WAG process requires improving the predictive capabilities of current three-phase relative permeability models. In order to emphasize the impact of relative permeability hysteresis on the numerical simulation of WAG injection a series of experiments were performed : injection of nitrogen at residual oil saturation, WAG experiment at ambient conditions, WAG experiment at reservoir conditions. The experiments were then simulated with three available methods : Carlson's hysteretic model and Stone2, Killough's hysteretic model and Stone1 and the three-phase hysteretic fractal model (SPE 65127). The three models were applied and compared with the experimental results and the three-phase fractal hysteretic model which solely applies to both WAG ambient and WAG reservoir conditions was successfully used.
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IOR Technologies Using Thermotropic Inorganic Gel for High-viscosity Oil Pools at Thermal-steam Treatment
Authors L. K. Altunina, V. A. Kuvshinov and S. O. UrsegovAt present high-viscosity oils are considered as the main reserve of world oil production. High-viscosity oil pools are usually developed using thermal treatment. To increase efficiency of thermal-steam treatments of high-viscosity oil pools we proposed to combine them with physicochemical methods using gel-forming systems to increase reservoir coverage by steam injection. The results of laboratory research and pilot tests of IOR gel-technologies for high-viscosity oil pools developed by thermal-steam and cyclic-steam treatments are presented. To optimize gel-technologies involving thermotropic inorganic gel-forming GALKA-Ñ solutions based on aluminum salt – carbamide – water system we investigated rheological properties, effects of the amounts of systems and steam slugs, sequence of their injections on efficiency of thermal-steam treatment. Pilot tests carried out in Permocarbonic deposit of Usinskoye oilfield proved the efficiency of gel-technologies, their availability for IOR from high-viscosity oil pools at thermal-steam and cyclic-steam treatments. Thermotropic inorganic gels increase reservoir coverage by steam injection, decrease water cuttings of well production by 3-45%, increase oil production rate by 11-33% and decrease liquid flow rate by 14-25%. Gel-technologies are environmentally safe and economically effective.
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Effects of Wettability and Composition on Tertiary Gas Injection in Fractured Carbonate Rocks
By H. KarimaieThe purpose of the four experiments described in this paper is to investigate the efficiency of oil recovery by CO2 and C1 in fractured carbonate rock having different wettability state after tertiary gravity drainage in reservoir condition. Samples with different type of wettability have been selected and gas injection experiments were performed on 20 cm long and low permeable outcrop core surrounded with a fracture established with a novel experimental set-up. A mixture of live oil (C1-C7) with a known composition has been selected and PVT properties of the sample such as density, bubble point pressure, interfacial tension between the phases were measured in reservoir condition prior to experiment. The matrix block was saturated using the live oil, while the fracture was filled with a sealing material to obtain a homogeneous saturation. The sealing material was then removed by increasing the temperature which in turn creates the fracture surrounding the core. Water was injected into the fracture at pressures above the bubble point to measure oil recovery by imbibition. Oil recovery as a function of time was monitored during the water injection. After reaching to final oil recovery equilibrium gas was injected to the fracture in two successive stages where interfacial tension was reduced from 0.5 mN/m to o.15 mN/m in order to measure oil recovery by gravity drainage. Non-equilibrium gas (CO2 and C1) were then injected in the last part of the experiment to study the effect of composition on final oil recovery. Results from tertiary gas injection experiments show that additional oil recovery could be obtained by injection of non-equilibrium gas, where diffusion and gravity drainage were the main elements of the displacement mechanism. Results also reveal that CO2 injection is a very efficient recovery method while injection of C1 can also improve the oil recovery.
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Planning of Complex Cyclic-steam and Physical-chemical Treatment of High-viscosity Oil Pools
By I. KuvshinovTwo approaches for cyclic-steam oil wells work prediction are presented in this paper. First approach is for oil wells with steam-cyclic treatment history of several cycles, with Liaohe oilfield, China, as an example. Second is for oil wells with no cyclic-steam history, where such treatment is at a planning stage only, presented for permo-carbon pool of Usinsk high-viscosity oil field, Republic of Komi. The planning of complex steam and physical-chemical well treatment with gel-forming and oil-displacing composition of Institute of Petroleum Chemistry, and its efficiency prediction, are considered. There are specialized computer programs created for all calculations described in the paper.
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Viscous and Gravity Effects at CO2 Injection
Authors G. Calderon and L. SurguchevScaling groups (1) gravity-viscosity ratio and (2) reservoir aspect number (RL) and their effects on CO2 injection under miscible and immiscible gas injection were evaluated by numerical simulations using data from performed laboratory experiments. Results of immiscible and miscible CO2 injection demonstrate transition from viscous towards gravity dominated flow. There was also observed an optimum corresponding to maximum oil recovery for different values of vertical permeability and viscosity ratios. At immiscible CO2 injection oil recovery was increasing with decreasing viscosity ratio, as a function of effective aspect number, RL,. On the contrary, as the RL increases, the total oil recovery decreases at constant viscosity ratio. It is observed that gravity effects dominate the flow behaviour above RL =5. At CO2 miscible injection two regions with a limiting curve were identified for values of RL < 3.6. For the reservoirs with RL > 3.6, three regions are suggested with two separating limiting curves. The region located between these two limiting curves is identified as the transition zone.
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Numerical Laplace Inversion Methods – Calculation of the Water Influx from Aquifers Connected to Petroleum Reservoirs
More LessAquifers are rocks fully saturated with water that can be found associated with petroleum reservoirs. Because of the large volume of the water reservoirs, from 10 to 100 times oil zone volume, aquifers play an important role in pressure maintaining of oil reservoirs in production, making them achieved high recovery factors in function of the water influx supplied to each reservoir pressure drop that is transmitted to the aquifer. Given the importance of that water influx, its correct calculation is important in order to increase the accuracy of the forecast of fluid production from the hydrocarbon reservoir. Thus, this study: (a) compared four Laplace inversion techniques applied to functions in Laplace domain, obtained as solutions of an analytical model to calculate the water influx; and (b) confirmed the Stehfest method as a method that produces accurate and precise results, besides presenting fast numerical convergence.
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An Experimental Investigation of Three-phase Flow Through Water-wet Rocks
Authors M. Masihi and L. JavanbakhtPetroleum production often involves simultaneous flow of three immiscible fluids through porous rock formations. The objective of this work is to experimentally measure two and three phase relative permeabilities and to evaluate the existing relative permeability prediction models. We used typical Berea sandstone with refined mineral oil, distilled water and nitrogen gas. The measurements were carried out at temperature of 23°C and pressure of 800 psi. Two and three phase relative permeability measurements were obtained using the steady state technique. The three-phase experiments are conducted in the imbibition mode. The flow rates of brine and gas were increased gradually and the oil rate was decreased to simulate the reservoir behavior during primary oil production. Several different flow rate ratios were selected to cover a wide range of saturations on the ternary diagram. The three-phase experimental results were compared with the prediction from two relative permeability prediction models. Finally the limitations of the methods were discussed. The analysis has shown that Blunt’s model can be a better choice to predict the three phase permeabilities.
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How an Innovative Adaptive Fine Calculation Can Help in Coning Simulation
Authors R. D. Darvishi, A. D. Dastyari, A. M. Mojdeh and M. H. HaghighiConing phenomenon is an unfavourable experience and should be prevented by the predicting of controlling parameters. The large grid model in conventional reservoir simulation is not able to predict this phenomenon. Large pressure and saturation changes and high velocity near wellbore cause numerical instability and dictate for using fine grid model. Reservoir simulation with fine gridding is not practical because of the need for large CPU time. In this work, we have developed new software using critical region approach to solve this problem. In this approach, for each time step of simulation, the saturation and pressure of each phase are first calculated for all grids globally. Then, in the defined region around the wellbore, each time step is divided to very small time steps and the saturation and pressure of phases will be calculated again with this new small time steps. Our software based on this technique is using triangular irregular grids and finite volume method for the simulation of heterogeneous reservoirs. We used IMPES method for solving the pressure and saturations. The software has been tested by the comparison of water cut between our software and the fine grid model with satisfactory results.
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Joint Interpretation of Rapid 4D Seismic with Pressure Transient Analysis
Authors H. Hamdi, P. W. M. Corbett and A. Curtis3D Seismic data interpretation has been traditionally used in reservoir modelling to pick the reservoir top structure and fault detection. Well testing, on the other hand, been mainly used to provide the well /reservoir dynamic properties and the reservoir structures. However there is limited literature published addressing the joint interpretation of the well testing and seismic. Based on synthetic seismic modelling we can delineate the volume of the reservoir affected by well test interpretation and potentially visible in the seismic volume. In this study the architectural framework of a heterogeneous commingled reservoir is illuminated based on the rapid time-lapsed seismic information (4D signals). The methodology discussed in the extended abstract, helps deconvolve the effects of stratigraphic discontinuities and generate a sector-composite map, providing the necessary geological and geophysical constraints, which is then used as a structural framework to be filled with mobility and diffusivity ratios via inverse and forward approaches. This work leads towards the joint testing and seismic imaging to provide improved reservoir description.
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Permeability Modeling Using ANN and Collocated Cokriging
More LessObtaining a reliable reservoir permeability map that is consistent with all available data is of great important for reservoir engineers. However, there is not enough core from existing wells to estimate the reservoir permeability directly but Well log data are more widely available. This study aims to model permeability within the reservoir while there is no enough data. In particular, we use artificial neural networks to estimate permeability using four input logs of sonic, gravity, porosity and neutron logs in six existing wells. In order to eliminate the correlated data, we have done Principal Component Analysis on selected input logs. Collocated cokriging is considered as a valuable alternative to full cokriging while there is no adequate amount of primary variable to use univariate geostatistical methods like kriging and SGS. We used this in the framework of the sequential simulation to produce various realizations. As the permeability was overestimated in the shaley layers, a shale correction had to be performed on the estimated permeability logs. Then acoustic impedance with a good correlation to the permeability was used as covariable to do 3D modeling of permeability. The underlying statistics, histograms and cross validation confirms the degree of exactness of the presented model.
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Extracting and Unfolding a Stratigraphic Unit to Update Property Population
Authors J. F. Rainaud, S. Horna, C. Bennis, T. Crabie and S. PeltierWith the wide usage of geo-modelling tools, users could have the need to enhance their previous geostatiscal population without rebuilding an entire stratigraphic model In this paper we explain how we can extract non explicit information from a stratigraphic model (reference iso-chronological surfaces, faults used to constraint the model), and then, use this information to realise 3D flattening on iso-chronological surfaces prior to geostatiscal population. Three methods were presented here: traditional by topological correspondence, vertical shear and an original isometric unfolding process based on the minimization of the elastic tensor deformation. These methods could be applied for every type of deposit: Horizontal, Parallel to Top, parallel to Bottom, Proportional. Then, we compare the application of these methods on several case studies and develop the advantages to reengineer a stratigraphic model and repopulate it after flattening Even if the “traditional” and vertical shear methods could be applied on certain situations, following multiple test bed as the ones presented in this paper, we are thinking that the isometric unfolding presented here is much reliable. As a consequence, we will exploit more and more this isometric unfolding method in the next future and process each lithostratigraphic unit independently than the others.
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Ensemble-based Reservoir Characterization Using Time-lapse Seismic Waveform Data
Authors O. Leeuwenburgh, J. Brouwer and M. TraniAssisted history matching methods are beginning to offer the possibility to use 4D seismic data in quantitative ways for reservoir characterization. We use the waveform data without any explicit inversion or interpretation step directly in an ensemble-based assisted history matching scheme with a 3D synthetic reservoir model. For this purpose a seismic simulator was developed to simulate the full waveform response to reservoir changes due to production. We discuss the iterative ensemble methodology, including additional steps that were found to be helpful in obtaining an ensemble that is properly conditioned to the initial base survey and maintains sufficient and reliable spread during the model updating process. The strength of combining the information contained in the waveform data with the prior information contained in the initial ensemble is visualized by means of ensemble covariances. The results of two history matching experiments show that more detailed features of the true permeability field can be reconstructed when production data are combined with time-lapse seismic data.
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Improved Convergence in Seismic History Matching Combining Experimental Design with a Divide and Conquer Approach
Authors F. Sedighi and K. D. StephenHistory matching is performed by changing parameters in reservoir models to reduce the difference between observed dynamic data and predictions. Time-lapse (4D) seismic offers spatial information in the inter-well region and acts as additional constraints to more conventional production data from wells. Finding appropriate models can be a slow process even with additional seismic constraints. In this study we speed up convergence of history matching using experimental design to firstly set up a proxy regression model and then analyse this to identify sub-domains of the parameter space. These can then be searched very efficiently to find models that predict production and seismic data. We apply the approach to the Schiehallion field and show a factor ten speed up in convergence with no loss of match to observations of 4D seismic and production data.
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Semivariogram Parameters for Carbonate Reservoirs – Geological Variability and Potential Impact on Dynamic Modeling
More LessThe stochastic algorithms that are used to populate reservoir models typically use the semivariogram as a measure of spatial continuity. A survey of published porosity semivariogram model parameters from carbonate reservoirs with abundant, high quality, porosity well logs was used to investigate the variability of the range parameter and to determine if the observed variation could be attributed to reservoir age, depositional setting, or carbonate type. The results summarized in the table and figures above show the following: (1) the semivariogram areal (XY) range parameter is typically 1000-2000 m with little anisotropy; (2) the overall variation of semivariogram parameters between reservoirs is similar to the stratigraphic layer variation within reservoirs; (3) there is no significant correlation of the range parameter with depositional age and only a slight correlation with depositional setting; and (4) limestone-dominant or dolomite-dominant reservoirs have similar values for the range parameter. Models generated using short semivariogram ranges show higher recovery (as compared to models with same conditioning data but longer semivariogram ranges). Model grid size also impacts results - larger grids yield more optimistic recoveries.
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Optimising the Sweep Generation and Emission for Portable Vibratory Sources
Authors A. Kosecki, B. Piwakowski and L. Driad-LebeauThe use of lightweight portable vibratory source for shallow high-resolution seismic is obviously of big interest and provides many advantages. However, there is a lack of universal solutions that could be helpful for an operator to optimise the signals used to pilot those sources as a function of given site parameters in order to optimize the seismic image quality. In this paper we present an approach proposed to solve such a problem. The emitted sweep is automatically frequency compensated in order take into account the ground coupling characteristic of the vibrator. The optimisation procedure enables to obtain best parameters of seismic record via adequate choice of the emitted sweep parameters. This procedure is based on parametric optimisation and is quite universal - it can be used with any vibratory source. The field tests of the proposed vibrator control system are presented and discussed.
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On the Spectral Analysis of Rayleigh Waves for the Shear Wave Velocity Evaluation in the Shallow Section
Authors V. Bardan, P. Cristea, V. Manj and C. NiticaMain aspects of the phase velocity evaluation method of the Rayleigh waves are presented. It is shown that the results of the phase velocity analysis can be improved if it is used information from the 2D power spectrum of the considered Rayleigh events. The method is illustrated by synthetic examples and then it is applied on real data to obtain the distribution of shear wave velocities with depth in the shallow section.
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Detection of Geological Structures Ahead of the Tunnel Construction Using Tunnel Surface-waves
Authors S. Jetschny, T. Bohlen and A. KurzmannTo improve the performance and safety of tunnel constructions, seismic predictions methods can be used to detect relevant geological structures ahead of the tunnel face (e.g. faults, lithological boundaries). We present a simple and robust processing method that can automatically calculate the distance of such a geological inhomogeneity from the seismic response of only a few receivers mounted on the tunnel wall. The method works fully automatic and does need much computational resources which is ideal under tunneling conditions. Our approach has been develop on 3D synthetic finite difference and tested on real tunneling data. In both cases, the distance of a fault zone has been determined accurately and without any a priori information.
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Time-lapse Cross-borehole Electrical Resistivity Tomography Monitoring in an Urban Tunnel Site
Authors A. Marcuello, F. Bellmunt, J. Ledo, P. Queralt, E. Vázquez Suñé, J. Carrera, E. Falgàs and V. VelascoThis paper describes how wells drilled during the geotechnical investigation of an urban tunnel into Holocene delta sediments can be employed to complete the geological information and to monitoring drilling processes with low cost experimental electrodes and cables for single-hole (SHERT) and cross-hole (CHERT) electric resistance tomography measurements. A low cost experimental electrodes and specific cables for SHERT and CHERT measurements were produced and fixed during PVC tube equipment as potential/current electrodes every 1 m around the PVC pipe directly. The high electrical conductivity of the sediments of the test site made it difficult to obtain a very large contrast between the tunnel shaft and the background, but inversion of resistance ratios allows to track time variations of resistivity as small as a few tens percent with respect to the background value. NG borelog and SHERT have been efficient to detect minor changes in clay content, and they can be used to refine the available geological information.
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Electrical Resistivity Tomography as a Tool in Geological Mapping
Authors S. Ostrowski, M. Lasocki and G. PacanowskiElectrical resistivity tomography (ERT) is widely used geophysical method in civil engineering surveys and common deposit researches in Poland. Most of the previous ERT surveys were limited to simple glacial and fluvioglacial geological settings. PBG Exploration Geophysics Service Ltd. implemented ERT surveys for purpose of geological mapping in complex settings recently. This paper presents three case studies of ERT surveys, aiming to detail geology of the Andrychów Klippen Belt, Muszyna area and Przeczyce dam basement.
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Correlation of Thermal Conductivity and Electrical Resistivity of Soil – For Near Surface Geothermal Applications
Authors G. Fragkogiannis, G. Apostolopoulos and S. StamatakiSoil thermal conductivity (k) is a critical parameter in various engineering applications, where heat transfer takes place and depends on numerous factors such as mineralogical composition, grain size of soil and physical properties (moisture, dry density, saturation). Same factors have also an influence on the electrical resistivity of soil (ρ). This work presents an experimental determination of soil thermal conductivity and electrical resistivity, in various soil types with different grain size and mineral composition, in terms of variable moisture content and dry density. The change of thermal (k) and electrical (inverse of resistivity, ρ) conductivity values in terms of the increasing saturation is interpreted with the increasing presence of water over the air in the pore space that facilitates heat and current transportation. The study of thermal conductivity and electrical resistivity variation according to the fluctuation of physical properties of soils, can lead to the qualitatively and quantitatively correlation between kand ρ. Such an empirical correlation can be used to estimate the thermal conductivity of subsurface, by applying electrical resistivity tomography in combination with geotechnical data. At the present time, it is a subject of further research exploiting various models of k and ρ.
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GPR Resolution – Lab Data Compared to NDT Evaluations of Structures
Authors V. Perez-Gracia, L. G. Pujades, D. Di Capua, R. González-Drigo, O. Caselles and V. SalinasGround penetrating radar has been converted in one of the most common non-destructive geophysical surveys applied to civil engineering and the evaluation of structures. However, required resolution in these kind of studies use to be elevated. In this paper, experimental measurements under controlled lab conditions and in plain media are presented. Using these data, values of the possible resolution obtained with a high-frequency antenna are provided. Notwithstanding, in civil engineering studies, resolution must be enough to determine the most important features, but it is also desirable not detect small and unimportant anomalous targets that only produce noise in the radar data. Several measurements in different structures provides information about the resolution obtained in real studies. Results are compared to those obtained in laboratory, and seem to indicate that even radargrams from the structures evaluations are highly complex and provide less resolution than radargrams from plain media studies, GPR data is enough revealing to be used as main preliminary information about the structural elements in buildings and other civil engineering constructions.
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Urban Geophysics
By Z. M. SlepakThe paper describes a new geophysical technique to be used under modern urban conditions. Time variations in physical fields allow the study of the impact of active geological processes on buildings and structures to proactively prevent their possible consequences. Some engineering and geological applications successfully implemented in the historic centre of Kazan are reviewed.
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Chemostratigraphy of the Middle Triassic, Central Iberian Basin – An Analogue for the Triassic Central Graben, North Sea
Authors T. Morgan, S. Jones, J. Morris, N. Meadows and M. ButlerThe distal continental deposits of the Triassic Skagerrak Formation (North Sea Central Graben - Goldsmith et al. 1995) form important hydrocarbon reservoirs, but erecting a detailed stratigraphy for this formation proves difficult, despite some recent advancements. These successions typically lack biostratigraphic markers and their E-log correlation is hampered by the thick repetitive nature of the sandstone - shale successions. However, over the last fifteen years, North Sea Triassic successions have been correlated successfully using chemical stratigraphy, or chemostratigraphy, which involves the characterisation and correlation of strata using whole rock inorganic geochemistry. The technique is now an effective method for correlating the Skagerrak Formation and has also been widely applied across much of the Central Graben, North Sea - many of the chemostratigraphic studies are proprietary and only limited amounts of onshore studies have been published (Pearce et al. 2008). This paper attempts to redress the shortage of published chemostratigraphic datasets from non-marine successions. The research has focused on the Central Iberian Basin, where outstanding quality of outcrops allows a three-dimensional study of the fluvial systems to be undertaken.
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The Apulian Chain, Buried Below the Southern Apennines Allochthonous Units (Italy)
Authors P. Esestime, W. Paltrinieri and F. CalamitaThe structural setting of the buried Apulian Chain, below the allochthonous units of the Southern Apennines, shows several analogies with the outcropping fold-thrust belt of the Central Apennines, that implicates a same evolution of the Central and Southern Apennines foreland fold-thrust belt during the Pliocene-Quaternary shortening.
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Multi-scale Fracture Networks – Combining Subsurface Reservoir and Analogue Field Data
Authors G. Strijker, J. Klaver, J. K. J. van Koppen, B. Geiss, S. M. Luthi and G. V. BertottiData from a subsurface productive sequence in the North Sea and a representative analogue outcrop in Jordan are studied to investigate the degree of fault sealing and fracture cementation, deduce the compatibility of the data and to access the potential of this strategy to improve the hydrocarbon production from a reservoir with fracture induced compartmentalization issues. Re-interpretation of PSDM seismic data in the North Sea gas reservoirs reveals a set of faults with limited throw that separates pressure differences in excess of 200 bars. An extensive Shale Gouge ratio study, combined with dynamic reservoir simulations, and detailed evaluation of borehole data are used to determine the fault sealing potential of clay smear and fracture cementation . The field outcrop data, obtained from high-resolution satellite data and digitized field measurements, provides the spatially continuous statistics that can help to predict the inter-well fracture population. A clear relationship between the different orders of fractures in both sites is found, with orientations being similar across several length scales, but increased fracture densities in the fracture corridors.
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Application of Pyrenean Fractured Carbonate Outcrops for Subsurface Reservoir Characterisation
Authors J. C. Gutmanis and L. Ardevol i OroAppraisal and development of fractured hydrocarbon or geothermal reservoirs including tight carbonates, sandstones and basements remains a significant challenge because of the generally high degree of heterogeneity in the intensity and distribution of the open fracture system. Well penetrations are 1-dimensional samples of a complex system. Seismic attribute mapping offers hope for defining domains of high open fracture intensity (‘sweetspots’) but remains a tool in development and may never fully characterise the sub-seismic fracture domain. This presentation describes how outcrop observations in the Catalonian Pyrenees support and extend the interpretation of well and seismic data with respect to fracture typing, scaling, attributes and distributions.
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Quantitative Interpretation of Multi-dimensional Seismic Models of Turbidite Channels from the Ainsa-1 Quarry, Spain
Authors A. Jardin, P. Joseph, M. Koochak Zadeh and O. LeratIn deep offshore clastic environments, turbidite systems can constitute productive oil and gas reservoirs. The description of small scale heterogeneities is important to improve reservoir simulation and hydrocarbon production but these heterogeneities are usually below seismic resolution. As seismic data play an important role in reservoir characterization, seismic modeling of channel systems can be used to better understand the links between interpreted seismic data and individual channel recognition. We have simulated multi dimensional seismic traces based on the description of the multi-channel system of the Ainsa-I quarry (Spain) viewed as an analogue of deep offshore turbidite reservoirs. Even in case of models, interpretation of seismic data to delineate the limits between channels is not easy to do and might often lead to erroneous channel architecture. In the 1D study, gradual simplification of very fine geological description is applied in order to quantify the seismic amplitude variations at each step and link them with facies changes. We have also studied which seismic attributes such as amplitude variations with angle and how impedances estimated by stratigraphic inversion can be used in order to improve the seismic interpretation for a better characterization of these turbidite channels.
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A Three Dimensional Representation of the Fracture Network of a CO2 Reservoir Analogue (Latera Caldera, Central Italy)
Authors A. Alemanni, M. Battaglia, S. Bigi, E. Borisova, A. Campana, M. Loizzo and S. LombardiThe Caldera of Latera (western central Italy) is characterized by a high geothermal gradient and continuous production of CO2 that migrates to the surface along faults and fractures. Because of these characteristics, the area can be considered a natural, exposed analogue of a CO2 reservoir. We investigated the spatial and dimensional properties of fracture and discontinuities (pressure solutions, joints, veins, slip surfaces, etc.) of the outcrop in an abandoned quarry within the caldera boundary. Spatial data were collected using several sampling windows of appropriate dimension on adjacent rock faces of different, and where possible, orthogonal orientation. The interpreted fractures from a 3.5 x 3 x 2.5 m zone were incorporated into a CAD to create a three dimensional fracture network. The aim is to build a three dimensional representation of the fracture system that could be used to model the flow of CO2.
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3D Reconstruction of the Cotiella Extensional Listric Growth Fault System (Southern Pyrenees of Spain)
Authors B. Lopez, J. A. Muñoz and J. Garcia-SenzIn the Cotiella Massif (southern Pyrenees of Spain), a late Cretaceous extensional fault system has been interpreted to be formed by gravity-driven extension in a manner similar to that proposed for the South Atlantic passive margins. The internal structure of the Cotiella basin has been reconstructed in 3D by manual structure map contouring, showing characteristics which could not be understood via cross-sections construction and are more suited for 3D modelling. The listric faults show a concave upwards spoon shaped geometry with southward dipping convex onlapping growth strata in their hanging walls. It is a 4–10 km long fault system and involves 2–5.5 km of cumulative growth section. The inferred total volume contained by the faults is about 37km3. This extensional episode generated significant thickness changes in the postrift succession in the Pyrenees and explains the along-strike changes in thrust-sheet structural styles.
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Tectonic Versus Climatic Controls on Basin-margin Alluvialfan/fan Delta Complex Development, Montserrat, NE Spain
Authors M. López-Blanco, M. Gómez-Paccard, E. Costa, M. Garcés, E. Beamud and J. C. LarrasoañaNew Magnetostratigraphic data from the Montserrat alluvial fan and fan-delta system led to an unambiguous correlation to the GPTS and provided the basis for a quantitative estimate of its tectonosedimentary evolution. Local isostatic backstripping analysis has been performed. Tectonic pulses in the basin margin during the initial synsedimentary folding episode, expressed by unconformities and forelimb rotation rates, correlate to tectonic subsidence which shows a trend similar to the forelimb rotation rates. Three different frequency scales of sequential arrangement have been analysed on the fan-delta. The lowest frequency megasequence (3.2My) resulted from a combination of different factors (local subsidence-related architecture, long-term eustacy and regional basin configuration). The intermediate frequency Composite sequences (457±70ky) can be tied to astronomical cyclicity that controlled accommodation. Lack of periodicity (15 to 125ky) at higher-order sequential arrangement indicates that autocyclic processes were the main control. In tectonically active basin margins, sediment supply and subsidence are usually considered as major controls on sedimentary arrangement. In our study this assumption has been confirmed only for large-scale sequences. However, at intermediate scale sequences tectonics results in high accumulation rates favouring the development and preservation of astronomical-related cycles.
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Extracting the Signal from the Noise in Marine EM Measurements
Authors E. G. Flekkøy, T. Holten, E. Håland and K. J. MåløyUnderwater measurements of electric fields are a key component in most methods for marine hydrocarbon exploration based on electro-magnetism. Often these fields are very weak and their measurements highly challenging. We discuss the physics of a selection of the relevant noise sources in marine EM measurements and the technology designed to deal with them. These noise generating mechanisms include electronic noise in the receivers, electrode drift, noise induced by mechanical motion of the antennas, noise caused by the hydrodynamics of surface waves or the turbulent motion around antennas due to tidal currents, surface charges that move with the surface of the waves, atmospheric EM noise, and signal distortions due to ill-controlled antenna orientation. We address both the questions as how measurement design may be improved to deal with internal noise sources and how the effect of external noise sources may be reduced.
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Classification of Induced Polarisation Anomalies Using Relaxation Time Attributes
Authors P. Legeydo, P. C. H. Veeken, Y. Y. Davidenko, S. Ivanov and S. GarinaNew algorithms are used to determine a classification of induced polarization anomlies as registered by the DNME geoelectric investigation method. Using time filters during the inversion of the measured data is of great significance. Small relaxation time τ values are suited for the exploration of hydrocarbon prospects. Comparison of temporal and amplitude of the IP field characteristics allow to determine with more confidence IP anomalies caused by HC accumulations. The calculation range of τ relaxation time is a good indicator for the occurrence of destroyed or breached oil and gas traps. In this case, the pyrite crystals at a shallow level are submitted to an oxidizing environment and their oxidized rim causes a change in resistance that can be detected in the electric discharge behaviour when the power is turned off.
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Transient Electromagnetic Imaging of Thin Resistive Targets – Applications for Gas Hydrate Assessment
Authors A. Swidinsky and N. EdwardsGas-hydrates are a solid ice-like mixture of water and low molecular weight hydrocarbons. Hydrates are found in two regions: under the permafrost and beneath the seafloor, along continental slopes and margins. Over the years, interest in gas-hydrates has dramatically increased due to their potential as a future energy resource, their possible role in climate change, and their presence as a geohazard. In marine settings, the controlled source electromagnetic (CSEM) method using an electric dipole-dipole configuration has shown great promise in assessing gas-hydrate deposits through modelling and real marine field tests. The technique is valuable because hydrate is electrically insulating and replaces the more conductive seawater in the sediment pore space. As an aid in the three-dimensional interpretation of these structures, we describe a numerical method of transforming marine CSEM data into a form suitable for seismic-style processing. Our approach uses Linear Programming to produce reflection wavelets that show strong similarities to those found on seismic sections. Current work is focused on applying the transform to real marine CSEM data obtained above resistive gas-hydrate structures, in addition to CMP stacking and migration of transformed synthetic data from various hydrate models.
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CSEM Survey over the Frigg Gas Field, North Sea
Authors M. P. Hamilton, G. Mikkelsen, R. Poujardieu and A. PriceA Controlled-Source Electromagnetic (CSEM) survey was conducted over the produced Frigg gas field aiming to locate any remaining stranded gas. This is an innovative application for CSEM, which has traditionally been used for exploration or in particular prospect ranking. A survey such as this contains some additional challenges such as pipeline effects that may not normally be present in exploration CSEM surveys. For a survey of this nature, the collection of CSEM data in a grid fashion with all receivers recording azimuthal data has a clear advantage over 2D acquisition. This paper provides an introduction and overview for this project and its unique application of CSEM, and discusses some of the challenges faced.
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Detecting Favorable Oil and Gas Targets with Time-frequency Electromagnetic Method – Case Studies
More LessArtificial source and axial dipole are used for time-frequency electromagnetic (TFEM for short hereinafter) acquisition. TFEM data in both frequency domains and time domains are simultaneously acquired and studied. TFEM method is based on physical property differences between hydrocarbon-bearing reservoir and non-hydrocarbon-bearing host, in other words, TFEM technique makes use of the characteristic that hydrocarbon-bearing traps cause resistivity anomaly and polarization anomaly, as well as that resistivity and polarization are sensitive to variation on porosity and permeability. High-power artificial source is used to excite underground layers to produce the EM responses, through which resistivity and polarization anomalies caused by reservoirs can be directly detected. TFEM technique has been used for thousands of kilometers’ profile survey and verified by dozens of exploration wells. Extensive attention has been paid to TFEM survey from oil companies. In this paper, we compare our study on different reservoir types (porous-reservoir, fracture-reservoir, blocked-reservoir) and on different trap types (structural traps, stratigraphic traps, lithologic traps) with TFEM technique, providing references for better application of the method.
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Onshore Hydrocarbon Exploration in Brazil Using Non-seismic Methods
Authors P. de Lugao, E. F. La Terra, B. F. Kriegshaeuser, P. Romero and L. RochaWe present the first hydrocarbon exploration project in Brazil which relies completely on non-seismic methods. First, we performed a high-resolution land magnetic and gamma-spectrometry survey with the objective of identifying micro-seepage anomalies, the first in Brazil with this purpose. A total of 120 km along 26 profiles of High Resolution Ground Magnetic (HRGM) and gamma-spectrometry data were acquired. The data were jointly interpreted and five anomalies were preliminarily interpreted and related to the location of hydrocarbon micro-seepages. These anomalies were also related to fault structures as observed in the residual magnetic anomaly map. Based on the microseepage anomalies, we designed a CSAMT/MT/TDEM survey aimed at better delineating structure and targets at depth. These data show the presence of anomalies that can be related to exploration targets. These anomalies will be tested by drilling later this year.
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Geoelectric Structure of the Rybachy Peninsula from Data of Winter Amt Survey
Authors A. K. Saraev, A. B. Nikiforov, N. E. Romanova and R. V. DenisovInvestigations of geoelectric structure of the Rybachy Peninsula located in the northern part of the Kola Peninsula (the Barents Sea shore) have been carried out by the audiomagnetotelluric (AMT) sounding method using a new technology with ungrounded lines for electric field measurements. The deep structure of the Rybachy Peninsula up to 8-10 km was investigated, basement mapping and fault zones localization were fulfilled. The AMT results have allowed adjusting essentially the concept about the geological structure of the Rybachy Peninsula in comparison with data of previous seismic works. The AMT data about the basement depth were confirmed by the subsequent drilling.
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Capabilities and Results of Reservoir Studies via TEM in the Conditions of High-resistivity and Conductive Environments
Authors Y. A. Agafonov, S. V. Kompaniets and A. V. PospeevComparative assessment of the feasibility of applying electromagnetic soundings in contrast geological environments is given. A technology is offered that enables one to solve a wide range of geological problems in oil-and-gas exploration in high-resistivity media. Practical examples of TEM are given. Based upon mathematical modeling and field works, capabilities of EM methods are evaluated under low resistivity of host sedimentary rocks. In the paper a detailed analysis is furnished of the influence of induced polarization on TEM signals.
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Using Seismic Full Waveform Inversion to Guide 1D Marine CSEM Inversions for Resolving Multiple Resistive Layers
Authors V. C. Brown, K. Key and S. SinghIn order to study the physical processes occurring inside the earth we require accurate images of the subsurface. Two of the most successful methods for doing this are seismic and electromagnetic sensing, but no current single method is entirely sufficient for building a complete picture. This problem is especially acute in industrial applications such as hydrocarbon reservoir permanent monitoring, where some changes in reservoir fluid properties are near impossible to detect with conventional acoustic seismics. Electromagnetic methods can detect the fluid properties of interest however the resolution is poor. We present a method which uses the resolution at depth of full waveform seismic inversion to guide a controlled source electromagnetic inversion. The result of combining the techniques in this manner on synthetic examples allows us to model multiple layered structure to within a few percent of the true values.
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Fast Analytical Method for Frequency to Time Domain Conversion in CSEM Application
Authors A. M. Tehrani and E. C. SlobIn this paper comparison of a quasi analytical method to transform frequency domain control source electromagnetic data set back to the time domain with a numerical transformation is discussed. The quasi analytical method exploits the fact that the kernel of the integral equation has a known behavior as a function of frequency and that the solution to the integral equation can be written as a sum of repeated applications of the kernel to the incident field. A set of expansion functions is found, which have analytically known time domain counterparts that need only a few frequencies for the transformation back to the time. We compare this quasi analytical method so called diffusive expansion function in CSEM application with Gaver-Stehfest method and also a numerical method carry out by combination of fast Fourier transformation and the cubic hermite interpolation. As a result diffusive expansion function gives a reliable, accurate and fast method for time domain scattered electric fields conversion and performs well on a sparse set of frequency domain data in CSEM application.
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Solving Spatial Sampling Problems in 2D-CSEM Interferometry using Elongated Sources
Authors J. W. Hunziker, Y. Fan, E. C. Slob, K. Wapenaar and R. SniederWith interferometry by multidimensional deconvolution (MDD), all effects from the air-water interface in marine Controlled Source Electromagnetics (CSEM) data can be removed. Unfortunately, to apply interferometry byMDD, a very dense receiver sampling is necessary. We show, that the critical sampling distance is equal to the larger of the two parameters: source height and source length. Consequently, by using an elongated source, the sampling criteria can be relaxed also for small vertical source-receiver distances.
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