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74th EAGE Conference and Exhibition incorporating EUROPEC 2012
- Conference date: 04 Jun 2012 - 07 Jun 2012
- Location: Copenhagen, Denmark
- ISBN: 978-90-73834-27-9
- Published: 04 June 2012
101 - 200 of 948 results
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Fracture Characterization through Rate Correlation Analysis (SPE 154429)
By K.J. HefferFurther developments have been made in analysing the readily available fluid production histories from existing wells to develop statistical correlations in rate fluctuations. Results of the application of this novel technology to naturally fractured and other fields in the North Sea will be presented. The results reveal surprising characteristics: many of the correlated well pairs are very long-range; they also appear to be stress-related and fault-related. The postulated mechanism is that faults and fractures are reactivated due to the stress perturbations brought about during field development. In one field, comparison with independent data, particularly microseismic recordings, provides very encouraging calibration. A reservoir mechanism that explain both these results and earlier correlations between preferred flowpaths and stress state in secondary and tertiary flooding schemes will be discussed. Identification of major reservoir pathways is of substantial advantage to efficiency in reservoir management, leading to benefit for practical issues of well placements and configurations, injectivities, productivities, sweep efficiencies, short-term and longer-term forecasting. The techniques can be used in a time-lapse fashion in order to monitor changes in reservoir behaviour and provide real-time updating of reservoir models. The proposed mechanism has far-reaching implications for all reservoir engineering.
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Vector Scanning - Hydro-fracture Monitoring with Surface Microseismic Data (SPE 152913)
More LessFor monitoring hydraulic fracture (HF) in oil/gas fields the most reliable seismic method to avoid the adverse effect of strong surface noises is using downhole microseismic surveys . Nevertheless, downhole measurement is more expensive and limited by the availability of suitable boreholes in the vicinity of the hydro-fracture site. By all means seismic surveys conducted on land surface bear the largest flexibility and are more economic than downhole measurements. As a significant progress in hydro-fracture monitoring Duncan et al developed a surface monitoring system using seismic arrays centered at the hydro-fracture point. This monitoring method requires large-scale and prolonged operations; thus the cost-effectiveness is still less than ideal. In this paper we present a novel approach for land monitoring of hydro-fractures that uses only sparse seismic stations far from fracturing vehicles; and the total number of seismic stations is much less than previous approaches; so that the cost-effectiveness is significantly improved. With a small-scale seismic array on land surface we have monitored the hydro-fracture processes using a vector scanning technique for imaging hydro-fractures and determining rupture focal mechanisms. The applications of this technique to a synthetic data set based on numerical modeling and the real-world field data show that it is able to trace the tempo-spatial development of hydro-fractures even when the signal to noise ratio (S/N) is lower than 0.5. The vector scanning technique significantly shows the fracture imaging quality, and provides us a cost-effective approach for monitoring flow-enhancement hydro-fracture processes.
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Determining Gas Flow Rate and Formation Thermal Conductivity from Pressure and Temperature Profiles in Vertical Well (SPE 152034)
Authors P. Bedrikovetsky, I. Abbasy, E. Barrett, C.R. Wu and Z. YouDescription The problem of determining the gas rate in the well from temperature and pressure profiles along the column is considered. The model mathematical developed allows determining flow rate and one extra parameter from the temperature and pressure profiles assuming that other coefficients are known. We discuss determining the overall heat exchange coefficient between the well and the reservoir, thermal conductivity of the earth, geothermal gradient in the reservoir and gas-column friction factor. Different field situations where one of these four parameters is chosen as the second unknown parameter are discussed. Application The proposed approach was applied for determination of well gas rate and geothermal gradient from the acquired well pressure and temperature data in 3 well from field A (Australia, Cooper Basin). Results and conclusions The detailed analysis has been performed on the physical effects that influence the flow rate in gas well. The most significant effects are: friction, gravity, thermal expansion and gas-reservoir heat exchange. Solving the inverse problem determines the flow rate and geothermal gradient by matching the gas pressure and temperature distributions with measured profiles. Good agreement between the measured and predicted temperature and pressure profiles along 3 wells has been achieved (field A). Sensitivity study shows that the most important parameters are the friction factor and the overall heat transfer coefficient. The friction factor exposes the higher sensitivity with respect to small perturbations of initial data. Significance Determination of rate profile along the well is important for reservoir characterisation, since it allows distinguishing the production rates from different layers. The temperature and pressure sensors in the well are small and cheap chips, while flow meters are cumbersome and expensive, and affect the flow in the well. The present method shows its significance in prediction the gas rate from temperature and pressure data.
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Estimating Statistical Parameters from Travel Time Fluctuations of Non-gaussian Media
Authors D. Varilsuha and A. KaslilarIn this study a ray theoretical method is used to estimate the medium statistical parameters of a random medium from traveltime fluctuations of diving refracted waves. In the method, the formulas for estimating the medium statistical parameters have been derived by considering Gaussian Autocorrelation Function (ACF). It has been a question whether the studied medium is Gaussian or not, and whether the formulas derived by considering Gaussian random medium will give successful estimations for media having non-Gaussian ACF’s such as exponential and von Kármán. For this purpose random refractive media are prepared by considering Gaussian, Exponential and von Kármán ACFs and the formulas are used to estimate the medium parameters: the standard deviation of the medium fluctuations, the covariance function and the characteristic scale lengths of the scatterers both in horizontal and vertical directions. It is shown that in case of sufficiently smooth random media and sufficient medium realizations, the medium statistical parameters are reasonably well estimated with Gaussian ACF based formulas, although the medium is not represented by a Gaussian ACF.
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Preconditioning the Helmholtz Equation via Row-projections
Authors T. van Leeuwen, D. Gordon, R. Gordon and F. J. Herrmann3D frequency-domain full waveform inversion relies on being able to efficiently solve the 3D Helmholtz equation. Iterative methods require sophisticated preconditioners because the Helmholtz matrix is typically indefinite. We review a preconditioning technique that is based on row-projections. Notable advantages of this preconditioner over existing ones are that it has low algorithmic complexity, is easily parallelizable and extendable to time-harmonic vector equations.
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Multi-block FD Method for 3D Geophysical Simulation with Explicit Representation of Sub-horizontal Interfaces
Authors I. L. Sofronov, N. A. Zaitsev, A. Daryin, O. Voskoboinikova and L. DovgilovichPrediction of elastic anisotropic full wavefields is required in reverse-time migration, full-waveform inversion, borehole seismology, seismic modelling, and other processes. We propose a novel finite-difference algorithm based on solution of the Navier wave equation using a multi-block methodology. In the current implementation the blocks are sub-horizontal layers. A curvilinear adaptive hexahedral grid in blocks is generated by mapping the original 3D physical domain onto a parametric cube with horizontal layers and interfaces. These interfaces correspond to the main curvilinear physical contrast interfaces of a sub-horizontally layered formation. The top boundary of the parametric cube handles the land surface with a smooth topography. Free surface and solid-solid transmission boundary conditions at interfaces are approximated with the second-order accuracy. Smooth medium in the layers is approximated by second to sixth spatial order schemes. All expected properties of the developed algorithm are demonstrated in numerical tests using correspondent parallel MPI code.
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Efficiency Comparison for Continuous Mass-lumped and Discontinuous Galerkin Finite-elements for 3D Wave Propagation
Authors S. Minisini, E. Zhebel, A. Kononov and W. A. MulderThe spreading adoption of computationally intensive techniques such as Reverse Time Migration and Full Waveform Inversion increases the need of efficiently solving the three-dimensional wave equation. Common finite-difference discretization schemes lose their accuracy and efficiency in complex geological settings with discontinuities in the material properties and topography. Finite-elements on tetrahedral meshes follow the interfaces while maintaining their accuracy and can have smaller meshes if the elements are scaled with the velocity. Here, we consider two higher-order finite-element methods that allow for explicit time stepping: the continuous mass-lumped finite-element method (CMLFE) and the symmetric interior penalty discontinuous Galerkin method (SIPDG). The price paid for the ability to perform explicit time stepping is an increase in computational cost: CMLFE requires a larger number of discretization nodes to preserve accuracy, whereas SIPDG needs additional fluxes to impose the continuity of the solution. Therefore, it is not obvious which one is more efficient. We compare the two methods in terms of accuracy, stability and computational cost. Experiments on a three-dimensional problem with a dipping interface show that CMLFE and SIPDG have similar stability conditions, accuracy and efficiency, the last being measured as the computational time required to reach a given accuracy of the result.
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Acoustic Anisotropic Wavefields through Perturbation Theory
More LessSolving the anisotropic acoustic wave equation in a conventional manner (i.e. finite difference implementation) introduces a number of problems, and sets media restrictions, and it rarely contributes to our ability to resolve the anisotropic parameters. Utilizing perturbation theory in developing the solution of the anisotropic acoustic wave equation allows us direct access to the desired limitations-free solutions, that is solutions perturbed from the elliptical anisotropic background medium. It also provides a platform for parameter estimation as we can isolate the wavefield dependency on the perturbed anisotropic parameters. As a result, I derive approximate phase operators for a spectral domain wavefield extrapolation in transversely isotropic media based on perturbations in the anisotropic parameters. The solutions of the perturbation equations represent the coefficients of a Taylor's series type expansion of the wavefield as a function of the perturbed parameter, which is in this case the anellipticity parameter and the symmetry axis. The accuracy is relatively high in even inhomogeneous media.
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Volume Estimation of the Carbonate Fracture-cavern Reservoir - A Physical Model Study
More LessThe carbonate fracture-cavern reservoir is the main target for petroleum exploration and development in the Tarim basin located in western China. The volume of fracture-cavern reservoir is difficult to calculate due to the seismic resolution and these reservoirs’ scale. For this, a simple physical experiment is conducted in which the main step and theory of how to estimate the volume of fracture-cavern reservoirs is presented. Furthermore, a complex physical model is constructed, a wide azimuth seismic data is acquired and processed, and a set of calibration template for reservoir volume estimation is obtained and applied to the field seismic data.
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Fracture Characterization from Elastic Waves - An Ultrasonic Experimental Approach
Authors J. J. S. de Figueiredo, J. Schleicher, R. R. Stewart and N. DyaurThe main goal of this work was to estimate the preferential fracture orientation of a cracked medium based on cross-correlated S-wave seismograms analysis and Thomsen parameters. For this purpose, we analysed ultrasonic measurements of elastic (P and S) waves in a physical-modelling experiment with an artificially anisotropic cracked model. The solid matrix consisted of epoxy-resin, and small rubber-strip pieces simulate weakly-filled cracks. The anisotropic cracked model has three regions with three different fracture orientations. We used rotation of S1 and S2 polarizations for a cross-correlation analysis of the orientations, and P and S-wave measurements to evaluate the anisotropic parameters gamma and epsilon. The shear-wave source has a dominant frequency of 90 kHz, which corresponds to low wavelengths as compared to to the crack aperture, ensuring effective-media behaviour. Integrating the results from cross-correlation with anisotropic parameters analysis, we were able to estimate fracture orientation in anisotropic cracked model. The anisotropy parameter gamma showed good agreement with the cross-correlation analysis and, beyond that, provided additional information about the crack orientation that cross-correlation alone did not resolve.
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Seismic Geobody-driven 3D Controlled-source Electromagnetic Modeling
Authors A. Lovatini, E. Medina and M. PezzoliIn this paper we present a possible way to incorporate seismic data in EM modeling, using tools developed to extract and analyse seismic attributes feeding this information into EM inversions. This approach provides a restricted subset of solutions to ease the interpreter in geological plausibility assessment and his contribution to guide EM data modeling.
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CSEM Inversion in CMP Domain Using Analytical Derivatives
Authors J. L. Crepaldi, M. P. Buonora and I. FigueiredoThe employment of marine controlled-source electromagnetic method (mCSEM) to reduce risks in the exploration of oil and gas has being gradually growing; however the interpretation of the rendered data is still a challenge for the oil industry. Methodologies for generating geological profiles or maps are often unsatisfactory as well as purely 1D inversion. On the other hand, the algorithms of 2D and 3D inversion require complex implementation and high computational costs. This work presents the needed parts to implement a work-flow of mCSEM inversion, that inverts the data in common mid point (CMP) domain as a set of 1D models, which correspond to their respective CMP cells. Including the analytical derivatives of the responses for 1D models with respect to the resistivities. These techniques allows to recover a section, corresponding to an mCSEM line, in few minutes, which in association with seismic data, can provide very useful results for exploratory works.
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Salt Flank Exploration - 3D CSEM Imaging in the SEAM Model
Authors J. P. Morten and K. KumarWe have simulated a salt flank hydrocarbon reservoir imaging case using the 3D controlled source electromagnetic data from the SEAM phase I model. The complication due to the dominant EM response from the salt body is tackled by a structural constraint. In our simulated exploration scenario, we assumed that seismic imaging provided information to construct an approximate salt structural model but with three types of errors: 1) Limited information below salt overhangs and no base salt, 2) inaccurate lateral and depth positioning, and 3) incorrect salt resistivity. A modeling study and our imaging results demonstrate that the applied workflow is robust against these errors, and the 3D inversion results in a reconstruction that agrees well with the true model reservoir laterally and in depth.
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The Effect of Topography on ZTEM Inversions
Authors V. Kaminski, D. Sattel and K. WitherlyZTEM is an airborne passive source electromagnetic system surveying in frequency domain (30 Hz - 720 Hz). In this paper we study the effect of topography on 2D and 3D ZTEM modelling and inversion results. In the synthetic study, the 3D model is introduced and the predicted data are calculated considering the 3D topographic feature (hill) on the Earth’s surface. Then the predicted data are inverted using MTZ3D (developed at Geophysical Inversion Facility, University of British Columbia) with and without topography consideration. The inversion results are compared to the true model. In the field study, ZTEM observed data are compared to data predicted for 100 Ohm m halfspace with considerable topography. The modeling is done in 2D. The 2D response over uniform half-space should be zero, however due to the presence of the topography the amplitude of the predicted half-space response becomes dominant, compared to the response of conductors. It is further shown that when topographic features are neglected, the inverse models recover false geoelectrical structures. These false electrical structures include near-surface electrical conductors consistent with the positive topographic features (hills) and electrical resistors, consistent with the depressions. The effect is increasingly notable with greater volume of the topographic inhomogeneity.
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Continuous along the Trace Measurements of Seismic Attenuation - Further Improvements, Synthetic and Field Data Tests
Authors Y. Tyapkin and O. ShaduraAccurate estimates of the seismic quality factor Q enable seismic images with a better resolution and a more correct positioning of events to be obtained. Also, Q can successfully be utilized for lithology discrimination and reservoir characterization. We introduce further improvements of our method for continuous in time measurements of seismic attenuation along the trace. The method operates in the time domain and enables the corruptive impact of the reflectivity to be compensated in a straightforward two-step way. The efficiency of the method is demonstrated with synthetic data from a finely layered attenuating medium and with field data from a productive area in Ukraine.
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Bandwidth Enhancement - Inverse Q Deconvolution or Time-varying Wiener Filtering?
More LessBoth dispersion and attenuation corrections can improve the resolution of seismic data. This significantly facilitates interpretation. In principle, both inverse Q deconvolution and time-varying Wiener filtering can achieve this. Inverse Q deconvolution is a deterministic process that requires knowledge of the quality factor Q, whereas time-varying Wiener filtering is a statistical approach based on the estimation of the nonstationary propagating wavelet. Dispersion corrections based on phase-only inverse Q deconvolution is an inherently stable method that is robust in the presence of noise. Attenuation corrections via amplitude-only inverse Q deconvolution on the other hand is likely to lead to noise amplification as well as bandwidth enhancement. Dispersion corrections via time-varying Wiener filtering are challenging since this requires estimation of a nonstationary, frequency-dependent, nonminimum-phase wavelet. Fortunately attenuation corrections via Wiener filtering need only estimation of a zero-phase time-varying wavelet for which robust methods exist. The optimum procedure for combined dispersion and attenuation correction is thus comprised of first applying dispersion corrections using phase-only inverse Q deconvolution, followed by zero-phase time-varying Wiener filtering.
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Image Enhancement by CIG Multi-parameter Characterization
More LessThis study presents an innovative approach for seismic image enhancement using multi-parameter CIGs. During the imaging, summation-free CIGs are generated and analyzed as constant depth slices at every image location. The signal’s coherency is measured by semblance coefficient for different dip-angles across these depth slices in order to detect the specular directions of the model. The enhanced migration image is achieved by partial stacking of the gathers along these directions only. The ability to analyze the structural parameters of each image point allows us to better handle cases of complicated wave propagation and to improve the image quality at poorly illuminated areas or near complex structural geometry. The proposed method and its practical benefits are demonstrated for synthetic and real datasets.
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Consistency of Orientation Azimuth Calibration of Borehole Geophones
Authors P. G. Gagliardi and D. C. LawtonRaw borehole geophone data, taken from a 3-line walkaway vertical seismic profile (VSP) acquired in the Pembina oil field in Alberta, was examined for orientation azimuth consistency. Data were recorded using a 16-level VSP tool placed at three different levels in a deviated well. An algorithm was developed that dealt with the added complexities of a deviated survey. Orientation azimuths, using all three lines, had an average standard deviation of 4.39; consistency was poorest for the mid-level tool position, and best for the shallow-level tool position. Most interestingly, orientation azimuths calculated using sources from Line 1 were, on average, 3.7 higher than Line 2 and 3.0 higher than Line 6. This was judged to be related to geological properties of the area, particularly azimuthal anisotropy.
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Estimation of Surface Impulse Response Data from Walkaway VSP Measurements
Authors A. K. Soni, X. Staal and D. J. VerschuurVSP imaging suffers from poor illumination and imaging artifacts away from the well trajectory. Imaging of the downgoing surface multiples is one of the approaches suggested in literature to increase the illumination area for the VSP data. We propose a new method to image the 2D walkaway VSP data, which includes estimation of the full surface impulse response from the 2D VSP data. The method utilizes both the upgoing and downgoing wavefields to reconstruct a pseudo-surface impulse response using a hybrid convolution-sparse inversion approach. The two-step method contributes in reconstructing the complimentary images: one near the well and the other one away from the well. This new method suffers from relatively little crosstalk compared to interferometric redatuming. Also, it will give us the full surface impulse response, including surface and internal multiples. This means that all existing tools for multiple removal and imaging surface seismic data can be applied to our result.
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Uncertainties in Local Anisotropy Estimation from Multi-offset VSP Data
Authors M. Asgharzadeh, A. Bona, R. Pevzner, M. Urosevic and B. GurevichWe have quantified the errors associated with VTI parameter estimation using multi-offset VSP data. Two common methods, P-wave slownesses only and slowness-polarization are investigated. Estimation errors are expressed in terms of the magnitude of the earth anisotropy, uncertainties related to first break pickings and maximum available source offset. For homogeneous overburden, P-wave slownesses technique can be used to estimate VTI parameters. We demonstrate that estimation errors of using only P-wave slownesses are significantly decreased as longer source offsets are included in the inversion algorithm. Larger offsets involve P-waves which propagate near horizontal at the receiver level and enhance the method's efficiency. An example synthetic VSP is presented next where P-wave slownesses technique successfully recovers VTI model parameters. In case of heterogeneous overburden, P-wave slowness-polarization technique seems to be a solution as there is no need to compute P-wave horizontal slownesses. However, we demonstrate that the errors of VTI parameter estimation using this technique are small only where the anisotropy is very weak (below 5%) and they are not improved by increasing the offset. Furthermore, wave interference effect on polarizations makes the method impractical even on noise free synthetic data.
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Up/Down Wavefield Decomposition by Sparse Inversion
Authors J. van der Neut and F. J. HerrmannExpressions have been derived for the decomposition of multi-component seismic recordings into up- and downgoing constituents. However, these expressions contain singularities at critical angles and can be sensitive for noise. By interpreting wavefield decomposition as an inverse problem and imposing constraints on the sparseness of the solution, we arrive at a robust formalism that can be applied to noisy data. The method is demonstrated on synthetic data with multi-component receivers in a horizontal borehole, but can also be applied for different configurations, including OBC and dual-sensor streamers.
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Model Dip-guided Imaging Condition for Reverse-time Migration in VSP Scenario
Authors I. L. Sofronov, V. Baidin, I. Borodin, L. Dovgilovich and K. LinWe propose a new imaging condition aimed at eliminating swing artifacts, and also balancing the amplitude of the migrated features in RTM images with particular application to VSP data. It uses both the Umov-Poynting vector-based obliquity filter and a model-guided dip filter with several control parameters having a clear physical sense and permits the suppression of imaging artifacts. The quality and improvement of VSP images are demonstrated with two realistic synthetic data examples.
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Improving the Precision of Surface Seismic Data Processing by Walkaway VSP
More LessWalkaway-VSP data has a uniquely superior at extracting geophysical parameters. Applying the extracted parameters to surface seismic data processing can make the processing procedure quantifiable and greatly enhance image fidelity, resolution and precision. Based on the need to improve the characterization of a fractured vuggy carbonate reservoir in the studied oilfield of western China, we extracted geophysical parameters like velocity, true amplitude recovery (TAR) factor, Q factor and anisotropy estimated from zero offset VSP and Walkaway-VSP data, and applied them to high density surface seismic data processing. The result shows that the resolution and precision of imaged surface seismic data have been improved significantly; moreover, the accuracy of geobody characterization has been enhanced. Our study indicates a promising application of the VSP technique in this field.
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Time-varying Sea Surfaces from 3D Dual-sensor Streamer Data
Authors O. C. Orji, W. Sllner and L. J. Geliusthat resolution is compromised leading to misinterpretation and mislocation of events. Realistic time-varying sea surfaces can be modeled based on Pierson-Moskowitz sea surface spectrum and Hasselmann’s directivity correction. Imaged sea surfaces are obtained by applying an imaging technique that is based on decomposed wavefields from dual sensor streamers. The speed and direction of the moving sea surface are obtained by performing spectral analysis on the imaged sea surface. A first imaged sea surface result from 3D field data acquired offshore Brazil is shown.
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Joint Estimation for P-P and P-S Residual Statics
Authors D. Le Meur and G. PoulainThe estimation of residual static terms for the multi-component land dataset is a challenge. The P-P and the P-S residual statics are usually estimated through a two-pass process. In this paper, we propose to simultaneously compute all residual statics terms. The Joint Estimation is the way to guarantee more reliable static terms due to the use of a joint cost function. The Joint Estimation appears to be a simpler and more consistent solution in computing the common P-P source residual statics and both P-P and P-S receiver residual statics.
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Five-dimensional Vector Data Interpolation
Authors A. Stanton and M. D. SacchiFive dimensional interpolation and denoising of multicomponent seismic data is carried out using the quaternions and Projection Onto Convex Sets (POCS). The method is able to reconstruct up to four components of data simultaneously. A real data example is shown for a converted wave dataset acquired over a heavy oil reservoir in the Western Canadian Sedimentary Basin that displays the effects of shear wave splitting. Vector reconstruction is compared with traditional component-by-component reconstruction and is shown to give an improved reconstruction result while preserving the vector relationship between components.
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A Velocity Tomography Inversion Method of Elastic Vector Wavefield
Authors N. Qin, Z. C. Li, F. Q. Chen and K. ZhangWe have derived velocity tomography equation and transformation between traveltime residual and depth deviation under the framework of elastic vector wavefield, proposed a traveltime tomography method which updates velocity of P and S wave based on ADCIGs (angle domain common imaging gathers) by elastic Gaussian beam migration. This method can combine the advantages of the traveltime tomography and ADCIGs to improve the inversion precision and calculation efficiency. Example from the synthetic dataset shows this method is feasible and valid, but its precision is restrained by the resolution of ADCIGs, and prestack data with low S/N may make impact on inversion results.
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Separation of Blended Data by Sparse Inversion Utilizing Surface-related Multiples
Authors P. Doulgeris, D. J. Verschuur and G. BlacquiereBlended surveys have recently appeared in production environments. This underlines the need for processing tools that will either process the recorded data directly or perform the separation into single source data (deblending). An inversion technique for the separation of such data is described here. The problem parameterization utilises the surface-related multiples in order to regularise the inversion. In this way, the separation and surface-related multiple elimination are performed in one step. Also, the physical meaning of the model space is exploited during the inversion by formulating the problem as a Basis Pursuit Denoise problem. The method has been applied on a synthetic dataset and it produced promising results.
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Only Dither - Efficient Simultaneous Marine Acquisition
Authors H. Wason and F. J. HerrmannSimultaneous-source acquisition is an emerging technology that is stimulating both geophysical research and commercial efforts. The focus here is on simultaneous-source marine acquisition design and sparsity-promoting sequential-source data recovery. We propose a pragmatic simultaneous-source, randomized marine acquisition scheme where multiple vessels sail across an ocean-bottom array firing airguns at — sequential locations and randomly time-dithered instances. Within the context of compressive sensing, where the choice of the sparsifying transform needs to be incoherent with the compressive sampling matrix, we can significantly impact the reconstruction quality, and demonstrate that the compressive sampling matrix resulting from the proposed sampling scheme is sufficiently incoherent with the curvelet transform to yield successful recovery by sparsity promotion. Results are illustrated with simulations of “purely” random marine acquisition, which requires an airgun to be located at each source location, and random time-dithering marine acquisition with one and two source vessels. Size of the collected data volumes in all cases is the same. Compared to the recovery from the former acquisition scheme (SNR = 10.5dB), we get good results by dithering with only one source vessel (SNR = 8.06dB) in the latter scheme, which improve at the cost of having an additional source vessel (SNR = 9.44dB).
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Blended Acquisition with Optimized Dispersed Source Arrays
Authors A. J. Berkhout and G. BlacquiereUntil now, blended source arrays are configured with closely spaced source units, such as broadband airgun arrays (marine) and broadband vibrator arrays (land). In the latter case the source units are equal. We refer to this concept as homogeneous blending. In this paper the blending concept is extended to inhomogeneous blending, meaning that a blended source array consists of different source units that may be far apart. We propose for these units simple narrowband sources with different central frequencies.
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Separation of Blended Data by Iterative Denoising
Authors C. Q. Tan, L. G. Han, Y. H. Zhang and W. B. DengSeismic acquisition is a trade-off between economic and quality. Conventional acquisition surveys are designed such that the time intervals between shots are sufficiently large to avoid the interference of different source response. Recently a great change of mindset in seismic acquisition has occurred and much attention has been drawn to blended acquisition, where different sources are shot in an overlapping fashion, so that both efficiency and image quality can be significantly improved. Deblending is the procedure of recovering data as if they were acquired in the conventional way. A simple least-squares procedure is only able to get pseudodeblend results, which cannot removed the blending noise. We already know that this noise is coherent in the common source domain, but incoherent in other domains. For this character, deblending using coherence-pass filter was proposed. However while dealing with high source density ratio blended data, separation results are usually not satisfactory. Based on the previous research, a new method to separate blended data by iterative denoising is introduced. When applied to a numerically blend field dataset of high source density ratio, both separation results and calculation efficiency are largely improved.
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Simultaneous-source Acquisition in the North Sea – Prospect Evaluation
Authors B. Szydlik, C. J. Beasley and I. MooreThis paper outlines a method for quantitative evaluation of marine simultaneous-source separation processes. The method doesn’t require acquiring the simultaneous-source data beforehand. Instead, it generates simulated simultaneous-source from available sequential-source data to emulate as close as possible desired simultaneous-source dataset. We demonstrate how this method enables quantitative assessment and show results for undershoot data from the North Sea.
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A Parallel 3D Front Propagation Algorithm for Simulation of Geological Folding on GPUs
Authors T. Gillberg, Ø. Hjelle and A. M. BruasetA 3D front propagation algorithm for the simulation of geological folding is presented. The algorithm is implemented on multicore and GPU architectures. Numerical experiments based on OpenMP show an almost perfect scaling. Using the automatic code translator Mint, Cuda code is created from seqential C code. On a GPU the Cuda code runs 67-95 times faster than sequential code, and allows large 3D grids to be computed at interactive times.
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Application of GPUs in Seismic Depth Migration
Authors C. Lin and H. Q. WangReverse Time Migration (RTM) has already applied for the high image precision. Aiming at speeding up RTM, we use CUDA to take advantage of the GPUs computational power which is different from CPUs, share memory could minimize global memory traffic. The application of random-v boundary and wavefield decomposition can improve the image of RTM result effectively.
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Acceleration of 2.5D Elastic Anisotropic Modelling
Authors V. G. Tulchinsky, R. A. Iushchenko and Y. V. Roganov3D modelling can be simplified if the medium properties are fixed along some direction. Such type models are called 2.5D ones. One source line computed in 2.5D model can be replicated to produce full 3D survey. 2.5D elastic anisotropic method of finite-difference forward modelling can generate realistic 3D synthetic seismograms for geometrically simplified but detailed models with arbitrary 3D TTI anisotropy and fracturing. The method is based on space frequency decomposition along the direction of fixed parameters. Despite its computational complexity is almost the same as in 3D case GPUs accelerate 2.5D modelling much better than full 3D. Efficient memory decomposition which reduces 2.5D problem to a set of independent quasi-2D problems is a key to the GPU efficiency. 2.5D method runs GPU calculations in the most favourable mode: without data reload, using single floating point precision and local calculations only. Both high level and low level GPUs provide high performance for 2.5D. Additional 3-4 times acceleration of 2.5D over full 3D can be obtained for simple models by random undersampling with spectrum interpolation (for the cost of about 1% noise). 2.5D complements 3D ray tracing in investigation of benefits from multi-component surveys, quasi-anisotropy effects, processing resolution, etc.
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A 3D Tetrahedral Mesh Generator for Seismic Problems
Authors A. Kononov, S. Minisini, E. Zhebel and W. A. MulderFinite-element modelling of seismic wave propagation on tetrahedra requires meshes that accurately follow interfaces between impedance contrasts or surface topography and have element sizes proportional to the local velocity. We explain a mesh generation approach by example. Starting from a finite-difference representation of the velocity model, triangulated surfaces are generated along impedance discontinuities. These define subdomains that are meshed independently and in parallel, honouring the local velocity values. The resulting volumetric meshes are merged into a single mesh. The approach is flexible, efficient, scalable and capable of producing quality meshes.
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Parallel MR-RCGA Based FWI for Building Velocity Model
Authors R. Rastogi, A. Srivastava and K. KhondeWe present a parallel algorithm for distributed-memory platform to perform Full-Waveform Inversion (FWI) of pre-stack seismic data in time domain that can be used for building velocity model. Our code is written in C and uses Message Passing Interface (MPI) and OpenMP for parallelization. This non-linear and non-unique inverse problem is solved by using Multiple Realization of Real Coded Genetic Algorithm (MR-RCGA); a stochastic search approach. For validation of algorithm, we applied it on realistic synthetic test consisting of an intersection point of dip and strike lines of the SEG/EAGE Overthrust data. Inverting two differently recorded data on the intersection point of two lines should yield the similar velocity model: it is done to demonstrate that the algorithm works with a very little start-up information and can give good estimate of compressional wave velocity (Vp) at each inverted CDP point. It is proposed to run this method on several CDP locations and interpolated in between, to get a good reliable starting velocity model. This method is developed and demonstrated on parallel clusters of PARAM Yuva. The results and benchmarking performance of the algorithm are presented and discussed.
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Efficient Implementation of 3D Surface-related Multiple Elimination for Large-scale Compute Clusters
Authors E. Kurin, M. Denisov and E. MuzichenkoSuppression of multiple reflections is an important step in processing the offshore seismic data, since such reflections seriously complicate the data interpretation. SRME is often the method of choice for eliminating multiple reflections related to the free surface. Application of the method to the 3D data demands for a huge amount of computations and data traffic, and scalability for a large number of cluster nodes is a serious problem. In the present work, we suggest an efficient 3D SRME algorithm providing high scalability of computations on Linux clusters with thousands of compute nodes. The main idea is that of organizing a quasi-sequential stream of data from the storage to compute nodes. Implementation details for both CPU-only and hybrid CPU+GPU systems are considered. Performance measurements taken on a high-end supercomputer are presented and discussed.
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Upscaling Routines for Thin Layers with Non-uniform Pressure and Temperature Changes
By P. A. FokkerDifferent demands for reservoir engineering and geomechanical meshes have led to a new upscaling technique. This technique uses the well known Backus averaging method for material parameters, with a new method to also upscale pressure and temperature changes. It assumes pressures and temperatures are not uniform over the formation or that formation contains (impermeable) non-pay zones. The method has been tested successfully in geomechanical upscaling of meshes and is intended to be used to upscale reservoir engineering meshes and results as well, allowing direct coupling of results.
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Building 3D Geomechanical Models - Some Practical Aspects of Mesh Generation and Boundary Conditions
Authors K. Fischer and A. HenkThe optimal exploitation of conventional and unconventional reservoirs is strongly affected by the tectonic stress field. Amongst others, wellbore stability, orientation of hydraulically induced fractures and - especially in fractured reservoirs - permeability anisotropies depend on the recent in situ stresses. This state of stress in a reservoir can be substantially modified by faults as well as lithological changes and contrasts in rock mechanical properties (e.g., Zoback, 2007; Fjaer et al., 2008). In some fault-controlled reservoirs, for instance, local stress orientations differing by up to 90 from the regional trend have been reported for individual fault compartments (Yale, 2003). Any robust prediction of stresses and fracture networks in a reservoir has to incorporate the specific reservoir geometry, the ambient stress field and the mechanical properties of lithologies and faults. An appropriate numerical technique to account for complex reservoir geometries and inhomogeneous material distributions is the Finite Element (FE) Method. The improved workflow presented can be used to build 3D geomechanical FE models and is applicable to both large-scale regional as well as detailed submodels of the reservoir. It allows to maintain the full geometrical complexity of the reservoir and to study stress perturbations in relation to faults and lithological changes.
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Application of the Damage Theory to the Modeling of Hydrofracture-associated Microseismicity
Authors A. Guest and A. SettariIn this paper, we present a numerical model of geomechanical response of the reservoir to the propagating hydraulic fracture. The model includes the effect of the main fracture, poroelasticity, and new-forming fractures, and is capable of predicting microseismic activity. The paper has two parts. In the first one, we investigate how to model deformation of fractured poroelastic media using the damage theory by comparing the numerical results with analytical solutions of fracture opening in impermeable, porous, and jointed media. In the second part, we apply the damage theory to a simple case of unfractured wellbore to assess and understand the behaviour under simple conditions. The tests show that a continuous fracture can be modelled assuming the damage parameter D=1 in the fracture, and that the poroelasticity can be modelled using the damage parameter D=0 in the medium. The damage parameter of fractures that do not fully open, such would be shear fractures or fractures on a small scale, is smaller the damage of the open fracture. The new fractures have influence on the opening of main fracture such that more fracturing (microseismic events) tend to decrease opening of the main fracture.
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Multiscale Modelling of Formation Alteration around Wellbores
Authors L. Grande, Ø. Johnsen and F. CuisiatMechanisms of formation damage have been evaluated in order to explain the size and depth of the “altered zone” close to a borehole, as observed from advanced well logs. It is found that one possible mechanism for formation alteration is tensile failure of the formation caused by radial stress release, pore pressure increase by mud-fluid flowing into the formation close to the borehole tip and temperature reduction due to colder mud-fluid. In this paper numerical modelling is performed at two scales based on data from two field cases. First a global model for calculation of average (continuum) stress changes during radial stress unloading and mud flow into the formation and temperature changes. Then in a second stage the stress changes from the global model are applied at the boundaries of a micro FEM model of a realistic micro-scale grain structure. The 2D micro FEM model is closer to explain the observed potential stiffness reduction based on the difference between the mud temperature and the formation temperature. However, there are limitations in the 2D model and extension to 3D model and dedicated laboratory tests are required to more accurately quantify formation damage and further investigate the physical processes of formation damage.
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Fracture Pattern of Borehole Breakouts in Shale - Comparison of Physical and Numerical Experiments
Authors T. Backers, C. Gruehser, T. Meier and G. DresenIn this numerical study the influence of different fracture propagation criteria on the evolution of breakouts around an isostatically loaded borehole is discussed. The material properties are reflecting those of a shale material. The simulation results are compared to fracture patterns as generated in laboratory experiments on borehole breakout formation in Posidonia shale (Meier et al., 2012). Comparing the fracture patterns as observed in the laboratory experiments of borehole failure in Posidonia shale to the numerical simulation results shows general similarities of fracture pattern attributes in case of fracture propagation based on the maximum shear stress criterion. This criterion assumes the fractures to grow in the direction of local maximum shear stress. In contrast, the simulations based on a tangential stress criterion, which assumes extension fracture propagation, shows borehole parallel fracture growth; this is not observed in the shale material. From these observations it may be concluded that the fracture growth in the laboratory experiments in shales is shear dominated; this was also concluded from microstructural observations by Meier et al. (2012).
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Evaluation of Methods to Quantify Pore Pressure Uncertainty from Geophysical Well Logs
Authors P. Tesch and S. Wesslingn’s equation and porosity indicating logs (e.g., resistivity and acoustic slowness) can be used to calculate pore pressure, presuming overpressure was generated by undercompaction. Pore pressure uncertainty is considered a valuable attribute to the pore pressure model, especially in challenging drilling environments. This study evaluates three different approaches to predict pore pressure uncertainty from variations in the normal compaction trendline. One statistical and two geometrical approaches yield slightly different results for the calculated uncertainties. It is best to incorporate all results in an integrated analysis to produce the most reliable interpretation of pore pressure uncertainty. As the uncertainties are well below 0.2 g/cm³ equivalent mud weight in the undercompaction zone, the methods prove their applicability to challenges like drilling in narrow pressure windows.
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Time Dependent Deformation and Failure in Reservoir Rocks - Experimental Data and Micromechanical Modelling
Authors P. Baud, M. J. Heap, N. Brantut and P. G. MeredithThe characterization of time-dependent brittle rock deformation is fundamental to understanding the long-term evolution and dynamics of reservoir and aquifers. Conventional creep experiments have shown that differential stress exerts a crucial influence on both creep strain rate and time-to-failure in porous sandstone. They have also demonstrated that a critical level of damage needs to be reached before the onset of accelerating tertiary creep. Our experimental data has demonstrated the fundamental characteristics of brittle creep in sandstone, such as sensitivity to temperature, as well as the contribution of variables such as effective pressure (Peff). Data derived from our stress-stepping experiments have been shown to compare favourably with those from conventional creep experiments. Stress-stepping creep experiments have shown that an increase in Peff inhibits the process of stress corrosion. We suggest that the most likely cause is a decrease in water mobility due to a reduction in crack aperture at a higher Peff. The sliding wing crack model of Ashby and Sammis (1990) has been coupled to Charles’s description of subcritical crack growth to explore the behaviour of rocks subjected to constant differential stress in a overall compressive stress state. The model successfully reproduces the qualitative behaviour observed in the experiments.
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Sustainable Architecture for Production Data
Authors I. Zulfiqar and N. LalaniData Management is key element of any E&P activity starting from exploration, drilling, completion to production. E&P companies design various data sources to accumulate these data flowing at various stages of any asset life. Available historical data provides key insights in decission making. However, many organazations face challange due to unavalibility of relevant data in single repository. E&P companies are increasingly trying to adapt a solution that can help them with correlation of data across all existing data sources and to provide long term data archive and retrieval mechanism without affecting their daily operational activities. However, real benefit of such solution would be to able to feed the engineering applications on real-time basis to support trend analysis, reservoir surveillance and studies, data reporting, inquiry & data export. This paper discusses Eni Pakistan’s experience regarding its execution of production data management. It examines usage of business objects as integrating factor across multiple repositories and how different technologies are utilized to create a holistic view of production data. Furthermore, it also highlights available approaches towards the management of repository and how this repository was integrated with OFM, Eclipse, Petrel & IPM suite of applications to achieve production optimization and quick recovery.
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Collaboration Dynamics in Megaprojects in the Canadian Oil Sands Industry
Authors O. A. Abbink, D. W. Faber and A. H. MarrewijkIn the Canadian oil industry, many large scale projects, so-called megaprojects, are undertaken to produce oil sands. However, megaprojects are notorious for their cost overruns and schedule slippages. This study describes the key success factors and key challenges in megaproject collaboration through an ethnographic approach. In total, 17 in-depth interviews with project managers at 7 major oil companies and contractors were recorded. The results show that the main challenge relates to the interaction between the oil companies and the contractors. Furthermore, there is a general hesitance to introduce new, innovative technologies. In addition, external contingencies, i.e. the state of the economy, public acceptance, and, specific for the Canadian oil sands, the climatic conditions have a significant impact on the collaboration dynamics. This would argue that a change in the relationship between the oil industry and contractors creates more effective megaprojects. Partnership-types of collaboration with shared risks may generate a more sustainable relationship resulting in more robust, more resilient, more innovative and, in particular, more on-target projects. Considering these factors, megaprojects can be realized with more efficiency.
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Seismic Attribute Database for Time Effective Literature Research
Authors J. Amtmann, C. G. Eichkitz and M. G. SchreilechnerWhen we deal with seismic attributes we are often overwhelmed by the amount of attributes available in commercial software packages and described by literature. For interpreters of seismic data it is often hard to keep track of the attributes, their capabilities, and their application. If we just look into commercial available software packages we will see that one kind of attribute comes under different names. Over time we have collected numerous papers and abstracts dealing with seismic attributes and their application. These papers needed to be sorted by their attribute categories. Therefore we have decided to create an attribute database containing all necessary information on these papers. For the sorting we have developed a keyword-system that is divided into main and minor attributes. With this database it is now possible to generate queries for specific applications or attributes.
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Pass on the Message - Recent Insights in Large-scale Sparse Recovery
More LessData collection, data processing, and imaging in exploration seismology increasingly hinge on large-scale sparsity promoting solvers to remove artifacts caused by efforts to reduce costs. We show how the inclusion of a ``message term`` in the calculation of the residuals improves the convergence of these iterative solvers by breaking correlations that develop between the model iterate and the linear system that needs to be inverted. We compare this message-passing scheme to state-of-the-art solvers for problems in missing-trace interpolation and in dimensionality-reduced imaging with phase encoding.
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Seismic Data Interpolation by Orthogonal Matching Pursuit
Authors Y. Hollander, D. Kosloff, Z. Koren and A. BartanaWe present a multi dimensional interpolation method for the regularization of seismic data. The method operates in frequency slices where in each slice the data is represented by a Fourier expansion. The algorithm operates iteratively where in each step one Fourier component is selected from an overly redundant space. The coefficients of all previously selected Fourier components are recalculated at every step and in this the present algorithm differs from most algorithms presented in the geophysical literature. The regularization method is tested in two examples of pre stack data.
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Permanent Downhole Electrical Resistivity Tomography in the Focus of Long-term CO2 Monitoring at the Ketzin Pilot Site
Authors C. Schmidt-Hattenberger, P. Bergmann, T. Labitzke, C. Rücker, D. LaBrecque and H. SchüttThe permanently installed vertical electrical resistivity array (VERA) as part of the multi-disciplinary surveillance concept of the Ketzin pilot site represents an interesting object for long-term monitoring and verification studies. A practical workflow has been established to qualify the acquired data considering site specific, operational and technical circumstances. An independently performed electrode test was carried out in order to investigate the behaviour of the individual borehole electrodes. In the present stage, consolidated data sets are available from which preliminary CO2 saturation maps have been derived.
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Recognizing New Exploration Traps beyond Well-defined Structures in North Umm Gudair, Kuwait
Authors N. C. Banik, H. Ammar, M. Ahmed, H. Al-Owihan and S. K. BhuktaExploration focus over the last decade has shifted to challenging frontiers and subtle traps in Kuwait, which were previously considered to be of high risk. Such targets are generally characterized by poorly defined reservoir facies or the absence of well-defined traps. In south west Kuwait, the main productions from Jurassic reservoir are achieved from Umm Gudair, Abduliya-Dharif and Minagish fields. The areas beyond the main structures are assumed and also reported to be non-prospective for a prolong time owing to apparent absence of suitable traps. To investigate new exploration interests in the area, seismic expression of sub-seismic scale lineaments are generated through the understanding of structural, fault and shear systems by way of detailed mapping and robust attribute analysis. The resulting map with detailed fault framework helped to identify several compartmentalized fault bounded closures that opened up a vast area for exploration. The present paper discusses an integrated study with emphasis to north Umm Gudair area where a comprehensive structure and fault mapping led to identification of new exploration interest in the area.
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Preliminary Assessment of the Geothermal System of the Tiris Volcanic Area, East Java, Indonesia
Authors F. Deon, I. Moeck, T. Sheytt and M. S. JayaIndonesia, with 15 % of the world´s active volcanoes, hosts a total estimated geothermal potential of 27000 MW, where only 800 MWe is installed. Exploration of magmatic remote areas is therefore important. Our investigation area is located at the volcano Lamongan, Tiris East Java, Indonesia, which is part of the modern Sunda arc region, characterized by extensional regime. Warm springs (temperature 35-45 °C) are the evidence of geothermal potential of the area. Numerous maars and cindered cones have been located and studied here, some of them with a NW –SE lineament similar to the Tiris fault (only observed in satellite images). In this first exploration stage we characterized the geochemistry of the springs and investigated the petrology of the rocks. The cation and anion concentration suggests that the fluids derive from sea water intrusion. The high permeable pyroclasites, overlain by low permeable basalt – andesitic basalt, may have channeled the sea water from the coast to the Tiris area. A structural lineament, NW – SE, may control the water intrusion as the lineament of the springs confirm. The high HCO3- concentration has probably a magmatic source, as no carbonate rocks are known in the area.
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Using Basin Modeling for Geothermal Energy Exploration in the Netherlands
More LessGeothermal energy in the Netherlands can be used for a number of applications. The exploration for successful locations for geothermal energy calls for a good estimation of temperature and porosity/permeability of the target aquifer. At present, this is done using interpolation between measured values from wells. We use basin modeling to include the geological history including phases of uplift and erosion in the estimation. Especially areas affected by burial anomalies, past maximum burial exceeded present-day burial, show differences in temperature and porosity/permeability when calculated with and without erosion, highlighting the value of basin modeling for this type of exploration.
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Improving Subsalt Imaging by Incorporating MT Data in a 3D Earth Model Building Workflow - A Case Study in Gulf of Mexico
Authors E. Medina, A. Lovatini, F. Golfré Andreasi, S. Re and F. SnyderIn this work we present the simultaneous joint inversion of seismic and EM data in WalkerRidge area, Gulf of Mexico. The deep-water Gulf of Mexico can be a difficult geologic and imaging environment due to the diverse and repeated salt tectonic episodes that have resulted in complex allochthonous salt formation. Accurate salt body characterization and careful earth model building are key objectives for properly assessing the exploration potential of the area. Seismic methods alone, cannot always properly image the subsalt reflectors. The inclusion of non-seismic data, such as magnetotelluric (MT) is very useful in complex salt provinces where the method can leverage the differences between salt and sediment resistivity as well as between seismic velocity.
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Multi Measurement Imaging Using Seismic CSEM MMT and FTG Data for Salt Dome Evaluation in the Nordkapp Basin
Authors F. Ceci, A. Lovatini, L. Masnaghetti, K. Hokstad and V. AntonsdottirIn this paper is presented an integrated workflow using non-seismic methods (magnetotellurics, controlled source EM, gravity and full tensor gradiometry), showing how the inclusion of the information obtained by all these methodologies led to a better understanding of the geological settings over a salt diapir in the Nordkapp Basin, Offshore Norway. Single domain and joint inversions of the EM methods were both carried out, and the results validated using gravity and FTG forward modelling on a step-wise approach.
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Broadband Seismic for Sub-basalt Exploration
Authors C. Spjuth, P. B. Sabel, S. K. Foss, P. Dromgoole, C. Friedrich, J. Herredsvela, A. Day, P. E. Dhelie, S. Hegna, T. Hy and K. KochSub-basalt imaging is challenging for a number of reasons. There is the large absorption of energy which particularly affects the high-frequency seismic signals. In addition, the large impedance contrasts associated with top and base and internal layering of the basalts, are generators of severe multiples and finally inhomogeneities within the basalts, and the sediment-basalt interface, further scatter the energy. In recent years the most common approach has been to focus on low frequencies because frequencies above approximately 40 Hz will be lost for sub-basalt signals. With standard marine acquisition this can be achieved by towing sources and streamers deep. However, this also results in losing the higher frequencies and consequently resolution in the data. Broadband seismic acquisition avoids this trade-off. In this paper we compare 2D data acquired using broadband technology to conventional deep-tow data previously acquired in the same locations over basalt in the Faroe Shetland Basin. We will demonstrate that both the signal and de-noise benefit from broadband acquisition. With a broadband signal the character of the sub-basalt signal and the noise / multiples is clearly different, potentially enabling new ways of dealing with noise and multiples.
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Variations in Seismic Properties of Flood Basalts from Shallow Refraction Seismic Analysis
Authors U. K. Petersen, R. J. Brown and M. S. AndersenThis work aims to contribute to the overall objective of a better understanding of the seismic properties of basalts and the development of better velocity models for basalts. The objective of this work was to establish the applicability of shallow surface-seismic travel-time tomography in basalt-covered areas. We tested many inversion sequences while varying the inversion parameters. Modelled travel times were verified by full-waveform modelling. Zero-offset VSP, VP, VS and density logs, downhole-geophone recordings and previous geological mapping in the area provided good means of control. We show that the method relates detailed seismic properties to different types of basaltic rock and we provide inversion parameters for shallow tomography in a basalt-covered area with high velocities and high velocity contrasts.
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Seismic Imaging and Interpretation of Salt-trapped Prospects in the Dnieper-Donets Basin, Ukraine - Case Studies
Authors O. M. Tiapkina, O. I. Okrepkyj and V. G. KolisnichenkoLarge hydrocarbon deposits are associated with the presence of salt structures in the Dnieper-Donets Basin, one of the deepest in Europe and located in Ukraine, due to favorable conditions for accumulation and trapping of oil and gas. With examples from an area in the central axial part of the basin, which comprises several salt diapirs and associated productive fields, we show how integration of high-quality depth processing with seismic structural and stratigraphic interpretation can improve both hydrocarbon trap delineation in the vicinity of the salt diapirs and subsequent well planning.
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Joint Inversion for Improved Sub-salt and Sub-basalt Imaging with Application to the More Margin
Authors M. Jordan, J. Ebbing, M. Brönner, J. Kamm, Z. Du and P. EliassonThe simultaneous joint inversion of different geophysical datasets has proved to be a technique which results in better imaging in geologically complex areas like sub-salt and sub-basalt. Different approaches of joint inversion have been presented during recent years. We chose a structure based cross gradient approach (e.g. Gallardo and Meju, 2004) for the joint inversion of seismic and non-seismic methods, including gravity, magnetics and CSEM. The resulting models are consistent with all data sets, with each other and with structural and specific a priori information. We present our multi-parameter approach and examples of the application of the joint inversion method to synthetic data sets based on sections of the SEG salt and the Mre Margin.
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Full Wavefield Migration - Utilization of Multiples in Seismic Migration
Authors A. J. Berkhout and D. J. VerschuurThe next generation migration technology considers multiple scattering as vital information, allowing the industry to generate significantly better images of the subsurface. The proposed full wavefield algorithm (FWM) makes use of two-way wave theory that is formulated in terms of one-way wavefields. We show that the current migration algorithms for primary reflections can be easily extended to handle multiple scattering as well.
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Combined-harmonic Analysis of Seismic Data Acquired with Two Vibrators Driven at Different Frequencies
Authors X. H. Campman, B. N. Kuvshinov and T. H. J. SmitThe presence of hydrocarbons cannot be verified directly with current linear seismic relection methods. However, several studies suggest that third-order elastic moduli in reservoir rocks are anomalously large. This presents an opportunity to directly detect hydrocarbons by investigating nonlinear seismic responses. Although the existence of nonlinear seismic signals is well established, their generating mechanism is not known. Nonlinear seismic experiments are difficult to interpret. Vibrators are nonlinear targets and under the influence of a vibration at a different frequency, they may also emit combined harmonics. Hence, the observation of combined harmonics alone doesnot prove nonlinear generation in the subsurface. However, the presence of growing nonlinear responses is a characteristic signature of intrinsic nonlinearities in the medium. By observing this growth, medium nonlinearity can be discriminated from nonlinearities introduced by the source. We theoretically estimate the growth of nonlinear harmonic. Next we discuss an experiment in which two vibrators were driven at different frequencies in order to understand the source and propagation characteristics of nonlinear harmonics. We observe nonlinear harmonics. Comparing their amplitude decay with the theoretically estimated behaviour of nonlinear harmonics, we conclude that they are most likely generated by the sources and not in the medium.
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LWD Quadrupole Dispersion Characteristics of a Prestressed Formation - Numerical Simulation and Field Data Example
Authors C. Hei, Y. D. Su and X. M. TangDetermination of horizontal formation stress is critical for evaluating wellbore stability and predicting formation pressure in the logging while drilling (LWD) environment. This study provide the acoustoelastical equations in the LWD theory model. We analyzed the dispersion characteristics of LWD quadrupole wave in prestressed formation and compared it with that of wireline logging. The results of numerical simulation and field measured data processing both show that in a prestressed formation the phase velocity of LWD quadrupole wave is close to the original formation shear wave velocity at the cut-off frequency, and, at high frequencies, is controlled by the near-borehole formation shear wave velocity that is sensitive to stress concentration. Velocity variation of formation shear waves outside the well caused by imbalance formation stress can be indicated by the difference between the measured LWD quadrupole dispersion data and the theoretical dispersion curve calculated using the homogeneous formation model.
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Hydrocarbon Sand Detection through Prestack Elastic Inversion
Authors L. Plouman Jensen, I. Escobar, A. J. Cherrett and D. H. ChedburnThis paper demonstrates the value of prestack elastic inversion and Bayesian facies classification, compared to the statistically-based technique of coloured inversion. Coloured inversion can be easily biased, either through its implicit assumptions on the spectral character of the Earth, or by incomplete well coverage. The example shown, taken from a North Sea clastic field with complex reservoir geometries, stacked sand bodies and injectite features, illustrates the potential improvement in reservoir characterisation by using a more complete inversion technique. Bayesian facies classification transforms the elastic inversion results into readily-interpreted attributes, such as hydrocarbon sand probability, which integrate the information across the full range of recorded reflection angles.
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Petrophysical Seismic Inversion over an Offshore Carbonate Field
Authors T. Coleou, F. Allo, O. Colnard, I. Machecler, L. Dillon, G. Schwedersky, C. Nunes, E. De Abreu, A. Colpaert and A. J. van WijngaardenThe main objective of this project was to evaluate the ability to derive petrophysical properties like porosity from seismic data in a carbonate environment. A special attention has been given to the possibility of characterizing the geometry of the pore space directly from the pre-stack seismic data. We apply a direct petrophysical inversion technique to a carbonate reservoir offshore Brazil. Starting from an initial geological model in depth and a number of carefully conditioned seismic angle stacks, we derive a detailed 3-D model of the porosity and hydrocarbon saturation matching the observed seismic data. We use a well-calibrated Petro-Elastic Model (PEM) to link the petrophysical properties to the seismic velocities. We compare inversion results obtained using the Xu-Payne and T-matrix PEMs which both account for carbonate pore geometry, lithology, porosity and fluid content but have different elastic sensitivity to fluid saturations. The inverted results provide detailed images of the spatial variations of porosity and fluid content across the reservoir interval. Obtaining estimates of absolute saturations values is more difficult, as saturation estimation is strongly dependent on the choice of PEM.
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Detailed Lithology and Fluid Mapping of the Asterix Gas Discovery Using Bayesian Inversion Methodology
Authors O. Riise, J. Elgenes, J. M. Frey-Martinez, Ø. Kjøsnes and A. BulandConventional AVO methods are in general effective for mapping the gas filled part of good reservoirs, while prediction of several other lithology and fluid classes (LFCs) may be much more challenging. For the Asterix gas discovery (Norwegian Sea), mapping of both the gas and the water-wet part of the reservoir (the aquifer) is important in the production planning. Standard AVO attribute cubes highlighting hydrocarbon presence are usually based on a kind of weighted stacking of the prestack data and represent deviation from a background trend for the water-bearing sediments. We define a set of multiple LFCs with elastic properties based on well logs and geological knowledge, and then predict the probability for each LFC simultaneously using a Bayesian inversion methodology. The approach is ideal for settings with limited well control, since the inversion does not require an accurate level of the elastic background model. Instead, it utilizes the relative elastic differences between the different LFCs. The results are presented as probability cubes for the different LFPs which simplify inter-disciplinary discussions and are easy to interpret for non-geophysicists. For the Asterix discovery, the results have impacted both the volume estimates and the production strategy.
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Pitfalls of AVO Analysis and Elastic Inversion Responses in the Presence of Thin Reservoir Units
Authors R. T. Manafov and J. StrømmenAVO analysis and elastic inversion are techniques extensively used today to differentiate between various lithofacies and fluid fills in both clastic and carbonate rocks. In this study we have used synthetic seismic data to understand behaviour of AVO parameters and elastic inversion data in the presence of thinning layers and varying net-to-gross of reservoir. We also demonstrate how this may create pitfalls where prospective reservoirs are not recognized, illustrated with a real seismic data example.
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Multiple Scenario Inversion of Reflection Seismic Prestack Data
Authors T. M. Hansen, K. S. Cordua and K. MosegaardInversion of prestack seismic data is a highly non-unique inverse problem. Many elastic models exists that fit seismic data observations equally well within the data uncertainty. In a probabilistic formulation of the inverse problem, a full description of such variability is described by the a posteriori probability distribution. Local inversion algorithms quantify the local variability of the a posteriori probability distribution around a ‘best’ model related to a local (or global) a posteriori likelihood maximum. However, many clusters of models centered around local points of maximum a posteriori likelihood may exist. To locate such local maxima, that may reflect models that fit data within their uncertainty, global inversion algorithms are needed. We present an inversion algorithm, based on Metropolis sampling, that will perform a search in the space of possible model solutions, to identify such different clusters of models. All models will fit data within its uncertainty and obey a possibly complex prior model. We make use of a non-linear forward model, and the inversion does not rely on a known smooth background velocity model.
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Statistical AVO Classification in Areas with Diagenesis and Tectonic Uplift - Case Example from the Barents Sea
Authors I. L. Lehocki, P. A. Avseth, H. B. Buran and A. J. JørstadPresent day rock physics properties and associated seismic signatures are controlled by burial history, tectonic events and temperature changes, diagenetic alterations and pressure modifications. Hence, in order to fully understand the seismic signatures of a prospect, we should not only relate rock properties to present day geologic factors (porosity, clay content, mineralogy, in situ pressure, etc.), but honour the geologic processes through time (Avseth and Drge, 2011). There are very few studies documenting the effect of complex tectonic and uplift on rock physics and seismic properties (e.g., Brevik et al., 2011). Taking into account diagenesis and tectonic events, we can predict compaction trends and associated seismic velocities in areas with more complex burial history involving both mechanical and chemical compaction, as well as uplift episodes and corresponding erosion. The resulting rock physics trends help us to better constrain AVO inversion and classification under such circumstances. We propose a methodology for statistical classification of fluids and facies in uplifted areas. The robustness of the method was validated by comparing the results to the information obtained from newly drilled well situated near the Loppa High in Barents Sea.
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Shear Waves in Streamer Data via Non-geometrical Conversions
Authors G. G. Drijkoningen and N. AlloucheIn this paper we show that when an airgun source and a hydrophone streamer are situated in the vicinity of the water bottom, shear-related events are generated via the evanescent part of the P-wave in the water. The shear-related events are not only the often-used surface/Scholte waves but also body S-waves which can be reflected/refracted in the subsurface. The gain of this approach that neither source nor receiver is making any contact with the water bottom itself, making it possible to do shear-wave surveys on water in an efficient manner. We show that such shear-wave events are observed in real data, and can be reproduced by modelling. The results are further validated via real measurements in a borehole.
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On the Significance of Viscoelasticity in a 2D Full Waveform Inversion of Shallow Seismic Surface Waves
Authors L. Groos, M. Schäfer, T. Forbriger and T. BohlenWe perform two tests to investigate to which degree viscoelastic modeling is relevant during a full waveform inversion of shallow seismic surface waves. Firstly, we compare field data with synthetic elastic and viscoelastic data. We show that the optimized source time function acts as a low pass filter in the case of elastic wavefields and can compensate a significant fraction of the residuals between elastically and viscoelastically modeled data. However, the viscoelastic data can explain the recorded data better in some aspects like the amplitude decay with offset of the fundamental mode and the near offset traces. Secondly, we run inversion tests for simulated viscoelastic observations (Q=20) using both elastic as well as viscoelastic forward modeling with Q=20, 25, and 10 during the inversion. The results show that it is not possible to infer the steep gradient in the shear wave velocity model in the topmost meter using an elastic inversion. Using a slightly wrong Q factor in the inversion produces very similar results compared to the results obtained by an inversion using the correct Q factor. If we use Q factors that are too far away from the Q factor of the observed data the inversion result becomes worse.
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2D Multi-scale Cell Tomography for Near Surface Velocities
Authors P. M. Li, Z. H. Yan, Z. Y. Feng, Q. P. Ma and H. W. ZhouTraveltime tomography has become an effective means for solving statics problems. However, traditional single-scale tomography (SST) does not obtain the best velocity values for model cells with low ray hit counts, making smoothing or interpolation of the velocity field after inversion a common practice even though it often reduces the accuracy and resolution of the solution model. Multi-scale tomography (MST) can address the above drawback by simultaneously inverting for velocity components of many overlapping SST models with different cell sizes. The final MST model is a superposition of inverted solutions of all overlapping cells. Here the MST method is demonstrated using 2D field datasets from western China.
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Simultaneous Joint Inversion for Surface-consistent Amplitude and Deconvolution
Authors K. Garceran and D. Le MeurThe surface-consistent amplitude and deconvolution step is one of the main millstones of land processing. The amplitude scalars and the deconvolution operators are usually estimated through a cascading process. In this paper, we propose to simultaneously estimate both surface-consistent terms. Simultaneous Joint Inversion is a way to get more reliable surface-consistent attributes that obey the same general equations and result from a common inversion scheme. Simultaneous Joint Inversion also proves to be the simplest flow to estimate surface-consistent amplitude scalars and deconvolution operators.
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Solution to the 3D Complex Near Surface Problem by Estimation of Propagation Operators
Authors Y. Sun and D. J. VerschuurA two-step method is proposed in this paper to solve the 3D complex near-surface problem. Based on estimating velocity-independent 3D near-surface redatuming operators, we first propose a revised 3D travel time operator that treats the average static time shift and the static time shift jitters separately. In order to make it possible to optimize these travel time operators on realistic-size 3D field data, we propose a new genetic algorithm, the Self-Adjustable Input Genetic Algorithm (SAIGA). After travel time operators are optimized by SAIGA, we propose to run another genetic algorithm optimization to fix the static time shift jitters at every source and receiver point in the field data. This two-step method has been successfully applied to a 3D land field data containing 2.4 million traces, and the results obtained are very promising.
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Elastic Impedance Equation based on the Incident-angle Approximation and Inversion
Authors C. Li, X. Y. Yin and G. Z. ZhangThe use of elastic impedance data contributes to the development of seiemic inversion and improves the understanding of the geology. However, when the Aki-Richards approximation is used to calculate the PP wave reflection coefficient, the incident angle is usually used as the angle parameter of the equation instead of the average of the incident and refracted angle. This calculation brings errors not only to the result of the PP wave reflection coefficient, but also to the Connolly Elastic Impedance which is derived from the Aki-Richards approximation, especially when the difference between the elastic parameters of the sand and shale layers is large. The Incident-Angle approximation is the function of the incident angle, which significantly reduces the errors. This paper proposes a method, named the Incident-Angle Elastic Impedance based on the Incident-Angle approximation to make the inversion of elastic impedance more accurate. Test of a 2D model and the application of real data in East China show that the elastic impedance equation based on the Incident-Angle approximation is feasible and precise.
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Azimuthal Anisotropy Analysis to Determine Stress Regimes from a Reprocessed Full Azimuth 3D Seismic Survey
By S. R. BrewIn 2000 a full azimuth 3D seismic survey was acquired over an undeveloped coal seam gas field in order to determine detailed structure, seam thicknesses and fracture regimes. In 2010 this survey was reprocessed to determine whether it was possible to get reliable ‘sweet spot’ and stress indicators from the seismic. In the intervening 10 years several wells have been drilled with varying levels of production and hydraulic fracturing success. A few even had casing collapse during drilling as a result of extreme stress with a resultant loss of drill stem. Consequently, if seismic could identify localised stress azimuth and magnitude through seismic anisotropy then it would have a significant impact on any future development; particularly with the need for horizontal drilling for both environmental and production purposes. Wells drilled on the field, subsequent to the 3D acquisition, had image logs recorded and processed, thus it was possible to calibrate azimuthal anisotropic seismic attributes with those logs and quantify the results. The presentation discusses the acquisition geometry and the approach taken in the processing and analysis. Various comparisons are made to assess which attributes are key indicators of stress. Finally the results are reviewed and quantified
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Joint Acoustic Inversion of Seismic Reflection and High Density RMS Velocity Data
Authors P. Baron and A. J. CherrettWe present a joint, coupled velocity-density formulation of the acoustic seismic inversion problem, adapted from a previously-published deterministic geostatistical inversion scheme. This formulation allows the simultaneous inversion of both seismic reflection data and high-density RMS velocity picks, without the need to impose a fixed velocity-density relationship. A realistic synthetic test case, strongly based on a North Sea chalk field, is used to demonstrate the characteristics of the method. The resulting model shows not only improved resolution and bandwidth recovery compared to inversion of reflection data alone, but also may be used for high-resolution time-to-depth conversion.
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Effectiveness Study of Azimuthal Amplitude Preserved Migration for Fracture Inversion via Physical Modeling Data
By Z. SunTo obtain correct image in the fracture medium, anisotropic migration which depends on anisotropy parameters is needed. However, the anisotropy parameters are difficult to be extracted, and the migration is quite sensitive to these parameters. To overcome this problem, a compromise scheme using azimuthal amplitude preserved migration is developed and applied to a set of data acquired on a fractured physical model. Three different types of gathers are generated, including CMP gathers from NMO, CRP gathers from conventional Kirchhoff migration and CRP gathers from azimuthal amplitude preserved migration. These gathers are used for fracture inversion and the results are compared. Additionally, the AVO features in the two types of CRP gathers are compared with that on the synthetic gathers. The azimuthal amplitude preserved migration is proven to be effective.
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Geoelectric Investigations for the Assessment of the Rock Massif in the Neighborhood of Excavation
By J. J. JirkuIn this paper we present an investigation of the hard-rocks using the electrical resistivity tomography method. This relatively cheap and simple geophysical technique shows significant changes in the apparent resistivities. We try to describe a repeatibility of the measurements and possible causes of the 4D changes in the resistivities. Knowledge of these time-changes will be crucial for the proposed building of the deep nuclear waste repository. We hope that ERT (and seismic potentially) could be a good indicator of the time changes in the massif.
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Geophysical High-resolution Characterisation of Granitic Dimension Stone Volumes
Authors P. J. Saksa, E. Heikkinen, A. Vuento and S. KurkelaEfficient and integrated geophysical measurement set-up has been created and tested for granite quarry production planning comprising magnetic and electromagnetic measurements. Development was based on an earlier geophysics development project some years ago in Finland. Rock volume models and quality classifications are the results to be used in rock block extraction. Surveys are applicable in various scales: from formation size to subareas and in primary block scale (1000 m3). Automated interpretation is allowed by dense measurements (GPR)with associated 3-D processing. Preparatory site works can improve significantly measurement conditions and rock volume coverage.
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Geophysical Investigations of Seepage and Settlement Effects at Mornos Dam
Authors V. K. Karastathis and P. KarmisA combined application of the Multichannel Analysis of Surface Waves (MASW), electrical resistivity tomography (ERT) and crosshole seismic tomography between crest and tunnels successfully provided crucial information about seepage and differential settlement effects in the Mornos dam, central Greece. The Mornos dam is an 816 m long and 139 m high earthen dam. The dam is exclusively used for the water supply of the capital city of Athens. The seepage through the dam foundation was found to be related with the efficiency of the grout curtain. The weak zones were mainly detected at places, where the jet-grouting has not been absolutely effective due to problematic geological setting, sliding zones, faults etc. In the interior of the core, MASW detected a weak zone along the crest, probably originated by a differential settlement. At its deepest part (at the centre of the dam) this zone had also been detected in the past by the monitoring instruments of the dam. The geophysical survey and particularly the methods of MASW and refraction tomography also revealed the existence of tensional zones at the two edges of the crest.
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Characterization of Glacier Ice with GPR and Reflection Seismic at Mount Isua, Greenland
Authors R. Wisen, A. Almholt, U. T. Nielsen and J. RingaardDuring the summer of 2011 Rambll performed a survey of a glacier at Mount Isua in the south of Greenland, a location where there are plans to realize a large iron mine. The location of the mine is such that parts of the glacier will need to be removed in order to get access to the minerals. A combination of reflection seismic and ground penetrating radar (GPR) was used to map the position of the bedrock interface under the ice. In addition the survey provided a snapshot of the surface level of the ice, and also features within the ice, such as moraine bodies. The combination of these methods proved to be a valuable tool. One advantage of GPR is the high productivity in contrast to that for a seismic survey. For a homogeneous ice body the GPR data show a strong continuous horizon. In case of stones, water or moraine within the ice body, the GPR results are more uncertain. In this case, the seismic results show more robustness and they also penetrate much deeper into the ice than the radar data.
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Reflection Seismic Processing for Imaging the Upper 100m of Bedrock at the Forsmark Spent Nuclear Fuel Repository Site
Authors C. Juhlin and T. LehtimkiRefraction seismic data with a dense receiver and source spacing were acquired at the future site for the Swedish repository for spent nuclear fuel. Data were recorded on two lines simultaneously, allowing some 3D information to be obtained. Reflection seismic processing of the refraction seismic data reveals a sub-horizontal reflection at about 20-25 ms (c. 60 m) that can be traced under much of the survey area.
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The Signature of a Small-throw Fault Affecting Unconsolidated Sediments in S-wave Reflection Seismic Data
Authors J. P. Carvalho, R. Ghose and A. LoureiroThe definition of appropriate places for the development of paleoseismic studies is extremely important in earthquake engineering site investigations. The seismic reflection method is routinely used to locate shallow fault segments where these do not outcrop, like in low slip-rate areas where faults identified in Quaternary sediments have vertical throws less than 2 m. The Lower Tagus Valley (Portugal), covered by 50 m of alluvium sediments, is one of these areas. To find fault segments in this geological environment is a daunting task. Any displacement in the seismic data can be a velocity anomalies and/or statics effect. To illuminate the presence of a fault in Holocene sediments, we acquired an S-wave seismic reflection profile at V. F. de Xira and modelled the response of a fault segment in order to recognise it in our data. The signature of a fault segment can be a change in the shape/attitude of the reflection hyperbolae but reflections from the fault plane are rather weak. These are controlled by fault width and velocity contrast between damaged zone-adjacent sediments. The resemblance between the modelled and field data of V. F. Xira supports the conclusion that the fault affects the Holocene alluvium and is still active.
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An MASW Survey at a Site with High Velocity Uncontrolled Fill - A Case History
More LessLandfill material is not often documented and its thickness and physical properties are largely unknown. The fill materials from general refuge are commonly known to be loose and its S-wave velocity is lower than the natural ground. However, the fill material can vary and there is no guarantee of such common knowledge to be always true. A Multi-Channel Analysis of Surface Waves (MASW) is a seismic survey method used for near-surface investigation. An MASW survey was applied to a proposed construction site with an uncontrolled fill. The survey covered the car park area with 1729m of seismic data collected in two days with a 24-channel landstreamer. A correlation of the result with the borehole data revealed the fill material has a higher S-wave velocity than the natural ground. The MASW method successfully profiled the original ground surface as an interface from high to low S-wave velocity. As this sort of velocity inversion is impossible to detect by more commonly used refraction method, the MASW is perhaps the only way to map the original surface under this environment.
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Seismic Methods in Mineral Exploration - A Case Study from Flin Flon Mining Camp, Canada
Authors M. Malinowski, D. J. White and E. SchetselaarGeophysical techniques become more and more important in looking for new deep-seated ore deposits. Due to the depth limitation of the most commonly used EM techniques, seismic methods become an alternative tool for ore targeting. Here we report on the comprehensive seismic program for ore exploration that has recently been carried out in the Flin Flon mining camp in Canada. We provide an overview of the most important results from Flin Flon project with the aim to provide guidelines for planning future exploration projects in other mining camps.
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Recent Experience with Use of High Definition Seismic Reflection for Nickel Sulphide Exploration in Western Australia
Authors P. KWilliams, M. Urosevic, A. Kepic and M. WhitfordNickel Sulphide ore systems in Western Australia are generally small, but very high value. They are typically found in complex geological settings at depth that is beyond the reach of potential geophysical methods. Only seismic methods can be expected to help prospecting such systems. Indeed petrophysical properties of the nickel ore environment in Kambalda region indicated that the ore is likely to cause detectable events. Consequently several experimental 2D and 3D surveys were undertaken by Centre for High Definition Geophysics. In all cases, especially exploring in the volume of rock below about 500m depth high quality seismic images were produced. 2D seismic was mainly used to test seismic response over complex deposits of Yilgarn Craton but also helped refine existing geological models. Subsequent experimental 3D seismic surveys produced high quality images of potential massive sulphide (MS) deposits. In the last two years several of these targets were verified in the Kambalda region. We show several case histories documenting successful application of seismic methods over MS deposits. Despite the success, the high cost of seismic surveys is still an issue for mineral exploration companies.
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Ultra High-resolution Reflection Seismic Imaging of Quick-clay Landslides in South-West Sweden
By A. MalehmirResults from two nearly perpendicular high-resolution reflection seismic lines over a quick-clay landslide scar are presented. The site is located on the shoreline of the Gta river in the southwest coast of Sweden. The Gta river is the source of drinking water for about 700,000 people. It follows an approximately 4 km wide fault zone. The site is known for its quick-clay formations and landslides. The data show excellent quality and help to image bedrock topography and internal layering above it down to about 100 m. The shallowest reflection is observed at about 20-30 m below the surface, it on-laps the bedrock, and is interpreted to originate from the contact between clay formations above and a sandy layer below. The continuity of the reflection becomes loosely defined at where the landslide scar occurs. This maybe an indication that there is a link between the reflection and landslides in the area; however, this requires further investigations. Reflections from the bedrock suggest a depression zone with its deepest point below the landslide scar. Deeper reflections are also observed in the data and may suggest a deeper depression zone or fault systems for which the Gta river is formed.
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Monitoring Hazardous Open Pit Mine Slope
By J. MrlinaWe performed geophysical measurements, mainly in the monitoring mode, to control landslide hazard in deep open pit mines. We introduced high resolution tilt measurements inside an exploration gallery. Tilt data indicated high risk periods of low slope stability that were caused mainly by mine blasts or hydrological processes, including flood period. Tilt data were supported by hydrological observations in nearby wells, inclinometry in wells, precise leveling, direct deformation measurements and geodetic scanning of the mine edge. An example of a major landslide on the mine slope is given with tilt data of precursory character. Significant changes of tilt vector trend and tilt velocity preceded and followed the landslide. Tilt observations proved the ability to monitor slope stability.
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Iterative Development of Stress Models for Deep Geothermal Reservoirs
By I. MoeckModern geothermal technology, especially EGS (Engineered Geothermal System) technology involves reservoir stimulation to enhance a geothermal reservoir from initially non-commercial to commercial status by increasing reservoir permeability, hence well productivity. These technologies require the quantification of the regional and local stress field. Moreover, exploitation of geothermal systems differs to hydrocarbon systems because production and injection rates from geothermal wells are much larger than from oil and gas wells. This specific operation in geothermal reservoirs has significant effects on the in situ stresses. Therefore, the understanding of the stress field is a key element in geothermal field development, and ultimately the acceptance of overall geothermal projects is affected if stress changes evoke fault reactivation and induced seismicity as an effect of massive reservoir stimulation or large injection rates. This article shows how the stress field of deep geothermal reservoirs can be derived by iterative steps, adapted to the specific data generated by the typical project phases of geothermal plays. Methods are described, and an iterative concept of stress field determination is developed based on the lessons learned from the prominent EGS site Gro Schnebeck in the NE German Basin.
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Geothermal Exploration of Paleozoic Formations in Central Alberta, Canada
Authors S. Weides, I. Moeck and J. MajorowiczThis study explores Paleozoic formations in the Central Alberta Basin with regard to their usability as geothermal reservoirs. A 3D geological model is developed based on stratigraphic picks of more than 7000 wells from the Alberta general well data file. Spatial distribution and thickness of deep formations is analysed by the 3D model. Porosity and permeability distribution is mapped in four Devonian carbonate formations–Cooking Lake, Leduc, Nisku and Wabamun –by data from about 50,000 core analyses. Since logging data of the promising Cambrian Basal Sandstone are rare, porosity and permeability are measured with probe permeametry and helium pycnometry on cores. First results give an average porosity of 11.1 % and an average permeability of 1.4 mD. Formation temperature of Cambrian and Devonian strata is estimated by a newly calculated geothermal gradient and the reservoir depth range derived from the 3D model. Temperatures in the Cambrian Basal Sandstone formation range from 62°C in the shallower northeast to 121°C in the deeper southwest, surface temperatures in the Devonian strata are between 19° - 87°C. Especially for district heating this temperature range seems sufficient to exploit but also industrial applications for oil sands extraction can be an option for geothermal use in Alberta.
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Utilizing SMTI to Characterize the Behavior of Fractures During Hydraulic Stimulation of Naturally Fractured Reservoirs
Authors T. I. Urbancic, A. Baig and S. Goldsteinrom the sites provided corroborative evidence that the moment tensor derived fracture orientations are in-line with the outcrop defined discrete fracture network, suggesting that in shale gas plays the preferred mode of failure during stimulations is the re-activation of pre-existing fractures and joints. It can be further suggested that the presence of sub-horizontal fractures are locally responsible for the transfer of stress resulting in failure along sub-vertical fractures and in the development of a well connect fracture network, required for effective proppant transport. The observed modes of failure can generally be categorized as being dominated by mixed–mode failures, representative of shear-dilatational failures. The opening–closure behavior of observed events, particularly for the sub-horizontal fractures can be related to surface roughness and the presence of asperities. The nature of fracturing appears to be fractal, following a power law distribution. It suggests that when stress levels are sufficiently high, fractures with similar orientations coalesce and develop longer fractures.
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Comparing Energy Calculations - Hydraulic Fracturing and Microseismic Monitoring
Authors N. Boroumand and D. W. EatonIn this paper we compare the input and output energy during a hydraulic fracture treatment to evaluate microseismic efficiency – the fraction of total input energy that is radiated as high-frequency seismic waves. We use three approaches to compute energy. “Injection energy” is the total energy input into the system. “Fracture energy” is an estimate of the work done during the deformation process to open a fracture. Finally, “radiated seismic energy” is the sum of all the energies for each high-frequency microseism, after converting the reported moment magnitudes into an energy based scale. We attempted to correct the seismic energy for missing data by estimating the Gutenberg-Richter b value and determine the contribution each event makes from a magnitude of -3 up to the maximum recorded magnitude. To our knowledge, such a correction has not been previously attempted, but it is very significant for determining the seismic energy. Injection, fracture and radiated seismic energy were calculated for 10 stimulated stages. Fracture energy was found to be 12-41% of the total injected energy, whereas the ratio of radiated energy to fracture energy ratio was consistently less than 1% for all stages.
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Crack-tip Stress Field, Coulomb Failure, and the Spectral Characteristics of Tensile Rupture
By D. W. EatonA simple geodynamical framework has been developed for simulation of frac-induced microseismicity. Subject to exceedance of a threshold value of time-dependent Coulomb failure stress, microseismicity is postulated to occur at random locations and with event magnitudes that satisfy the Gutenberg-Richter magnitude-recurrence relation. Simulations using this approach have many characteristics of observed microseismic clouds. Walter-Brune source spectra are considered for both tensile and shear events, which are parameterized by P- and S-wave corner frequencies and DC displacement factors. Pure tensile events may be distinguished from shear slip events based on low S/P amplitude ratios. Finally, a crack that opens and closes very quickly is characterized by periodic resonance and spectral notches similar to observed spectra of some low-frequency events.
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Distribution of the Vp/Vs Ratio within the Basel 1 Geothermal Reservoir from Microseismic Data
Authors J. Kummerow, A. Reshetnikov, M. Hring and H. AsanumaWe estimate the spatial distribution of the Vp/Vs ratio within the Basel 1 geothermal reservoir from arrival time measurements of micro seismic data. High-precision P and S arrival time differences are calculated by an automatic, iterative, correlation-based procedure for pairs of 2149 multiplet events. The Vp/Vs values in the stimulated volume of the Basel reservoir range from about 1.45 to 1.90 at a depth interval between 3.8km and 4.8km. The average value of 1.70 is close to the characteristic value of the reservoir, 1.72, which was independently determined from sonic log measurements. Also, the depth distribution of Vp/Vs correlates well with the low-pass filtered sonic log measurements in the vicinity of the borehole. Vp/Vs values are less than 1.70 at the top of the seismicity cloud at <3.9km depth, close to average at 4.0-4.4km depth, and exceed the value of 1.70 at larger depth (4.4-4.6km), consistent with the sonic log data. This supports the validity of our results and suggests that using micro seismic data to determine the Vp/Vs ratio of a reservoir may be a competitive alternative or complement to prevailing tools such as sonic log or AVO inversion.
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Simultaneous Microseismic Event Location and Anisotropic Velocity Model Building in HTI Media
Authors S. V. Yaskevich and A. A. DuchkovPassive seismic monitoring is a conventional technique used for mapping hydraulic fracturing treatment assuming that microseismic events occur due to fracture development. These events are usually located using a velocity model derived from sonic logs or perforation shots. Instead of fixing the model we make it also a parameter of inversion while locating the events, and also make it anisotropic (HTI). Such model could be the simplest one for description of azimuthally anisotropic formations. We show advantages of applying such an idea on synthetic data set for homogeneous HTI model and show failure of using isotropic models in this case. Use of isotropic model can lead to biased event locations that shift apparent fracture geometry away from its true position. Used approach not only makes it possible to more accurately predict traveltimes of the recorded waves but it also results in a better event locations. All anisotropic parameters of HTI model appeared to be well constrained by the inversion including accurate estimate of the symmetry axis azimuth. Estimated anisotropic HTI parameters can provide an engineer some additional valuable information as these parameters are usually related to rock physics, lithology, internal fractures etc.
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Microseismic Elastic Full Waveform Inversion for Hydraulic Fracture Monitoring
Authors A. B. Droujinine, J. Winsor and K. SlauenwhiteSimultaneous microseismic inversion for event locations and full source moment tensors enables a greater understanding of reservoir behaviour and can help optimize hydraulic fracture effectiveness. We develop an elastic full waveform inversion algorithm that is applied to 3C multi-well microseismic data. This is a single-stage downhole hydraulic fracture monitoring experiment from an unconventional play in North America. The algorithm minimizes least squares differences between complete observed and synthetic elastic P+S vector waveforms (after Q compensation) in order to determine event coordinates and the full moment tensor. Finite-difference Green’s functions for the VTI medium are used to compute the radiated seismic waves for the arbitrary force system. We utilize the Hudson’s source plot to analyze both the best fit double-couple (DC) solutions and departures from the DC model due to tensile failures. The final inversion workflow addresses uncertainties due to an inaccurate velocity model, a mislocated source and noisy waveforms. We demonstrate both the robustness of the full waveform inversion and the reduced bias of our results when compared with conventional inversion methods based on traveltimes and amplitudes. This leads to increased knowledge and reduced uncertainties of microseismic fracture monitoring that help maximize production and reservoir drainage in unconventional plays.
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Integrated Numerical Modeling of the Southern Brazilian Continental Margin
Authors R. Zuehlke, J. Contreras, S. Bowman and T. BechstaedtIntegrated numerical modeling indicates highly specific rift and sag/post-rift basin developments in the Santos (SB), Campos (CB) and Pelotas Basins (PB) of the southern Brazilian margin. Late Barremian to Late Aptian depth-dependent continental stretching generates sag basins with evaporite deposition in the CB and SB. The PB features volcanic crust, controlled by long-term post-rift thermal contraction and differential accommodation. The subsidence development does not follow a simple trend of progressive thermal relaxation with decreasing subsidence rates. In the CB, total subsidence starts to increase in the Late Cretaceous and reaches a major peak in the Eocene. The PB shows a similar development, but subsidence remains relatively high until today. The SB shows the best match to an exponentially decreasing subsidence trend. Progradation, aggradation and retrogradation differ significantly in the three basins and are controlled by changes in sediment flux. The CB, SB and PB are connected to different continental source areas with individual periods of uplift. Plate-tectonic and structural reconfigurations control accommodation space only during the rift to early drift development. After the Eocene, the flexural subsidence component exceeds the thermo-tectonic component, and therefore primarily controls total subsidence and basin architecture.
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Episodic Burial and Exhumation along Atlantic Margins - Implications for Hydrocarbon Prospectivity
Authors P. Japsen, J. A. Chalmers, P. F. Green and J. M. BonowIt is a common assumption that elevated passive continental margins (EPCMs) have remained high since rifting and breakup. Absence of post-rift sediments in the highlands is often taken as evidence of non-deposition, and the presence of high-level plateaux along many EPCMs is unexplained in many studies. However, the post-rift stratigraphic record in the adjacent sedimentary basins often contains significant unconformities and in some cases, post-rift, marine sediment crop out at high elevation. We present evidence of post-rift vertical movements along Atlantic margins and discuss how these movements affect the hydrocarbon prospectivity of these margins. We maintain that folds, reverse faults, reactivated normal faults and strike-slip faults that are typical of EPCMs, are a result of post-rift compression that leads to the formation of EPCMs, and that the necessary forces build up during changes in plate motion. One episode of uplift results in erosion of the region to produce a low-relief surface and a second (or more) episode(s) raises the plateau to its present elevation, after which fluvial and possibly glacial erosion dissects the plateau. Failure to realize that EPCMs are post-rift features have far-reaching implications for understanding basin development, hydrocarbon systems and the properties of the lithosphere itself.
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New Approach for Building a Tectonic Model of the Black Sea Depression
Authors N. Amelin, I. Gabriel, B. Horn, S. Kadurin, S. Kakaranza, N. Kaymakсi, A. Khortov, E. Kozhuharov, M. Leonchik, M. Ozkaptan, E. Petrov, B. Senin and A. VasilevIn 2010, the International Scientific Consortium was set up. The key objectives of the Consortium included: development of a new tectonic model of the Black Sea Depression and adjacent territories, identification of the major milestones of the basin development in the Para-Tethys System of the pre-Cenozoic era and study of the modern geodynamics of the Black Sea Basin as a whole. The Scientific Consortium was chaired by JVC Soyuzmorgeo, Russia, the internationally recognized Marine Analytical Center. The key Consortium participants included major specialized research centers from various countries of the Black Sea Region: Institute of Oceanology of the Bulgarian Academy of Sciences (Bulgaria), Geoecomar Institute (Romania), Black Sea State Regional Geological Enterprise (PrichernomorGRGP), Ukraine, Middle East Technical University, Turkey (METU). Among the members of the Consortium there were also some regional marine survey companies and a number of oil companies. The investigations of scientific Consortium and geologists from different countries were combined together for creation of Black Sea geological model. The first researches were done 30 years ago and certainly the new obtained data allow to improve Black Sea basin model with new tectonic elements and modern geodynamics.
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