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77th EAGE Conference and Exhibition 2015
- Conference date: June 1-4, 2015
- Location: Madrid, Spain
- Published: 01 June 2015
921 - 940 of 980 results
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The Theory of Pore-type Seismic Quantitative Inversion Method for Carbonate Reservoirs and Its Application
More LessSummaryPore-type is a very important factor influencing the rock physics properties of carbonate reservoirs, which plays an important role on studying storage performance and the connectivity of fracture-cave system in carbonate reservoirs. At present, pore types are identified mainly by utilizing well logging data, rarely conducted with seismic data. On the basis of DEM theory and Gassmann equation, particularly taking the influence of fracture on seismic wave’s velocity into consideration, this paper proposes a new pore-type seismic quantitative inversion method based on improved dual-pore system. Firstly, elastic parameters are obtained by pre-stack seismic inversion, such as Vp/Vs, density, porosity; secondly, based on the improved dual-pore system, reservoir space models with different proportion of cave-pore-fracture are established by Berryman 3D special pore theory, and quantitative relationship template between pore types, P wave velocity and porosity is figured out through theoretical calculation; finally, pore types can be identified in seismic scale. A case of the ZG8 area in Tarim Basin shows this method can not only figure out three secondary pore types and their proportion in carbonate reservoir successfully, but also can predict the distribution of different pore types in the underground medium, which demonstrate the method’s feasibility and practicability.
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Sweet Spot Prediction of Tight Dolomitic Oil of Fengcheng Formation in Wuxia Area, Junggar Basin, NW China
More LessSummaryWidespread thick-bedded tight dolomite has been developed in Fengcheng Formation with fine source-rock in Wuxia area, Junggar Basin of China. The development of Sweet Spot is mainly controlled by lithology, porosity and oil-bearing possibility, while porosity is restricted by lithology, and oil-bearing possibility is restricted by porosity. Lithology, porosity and oil-bearing possibility, can be predicted in order, based on core analysis data, well logs, seismic and test data. We propose to use impedance inversion to predict the distribution of dolomitic rocks, since dolomitic rock is characterized by high impedance. We also propose to use stochastic simulation inversion to predict the porosity, since fine dolomitic reservoir is characterized by low impedance in the background of high impedance, based on the negative correlation between porosity and impedance. We use seismic spectral decomposition to detect hydrocarbon, since oil-bearing reservoir is characterized by high-frequency attenuation. Finally, we summarize the prediction of lithology, porosity and oil-bearing possibility, the favorable areas of Sweet Spot are the places where the oil-bearing possibility is high and the reservoir with lager porosity is thick, inside the distribution of dolomitic rocks.
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A New Method for Sedimentary Microfacies Analysis Named MVF
More LessSummaryThis paper proposes a new method for predicting sedimentary microfacies named MVF (Microfacies Versus Frequencies) that means the relationship between the microfacies and tuning frequencies. The method is based on the logging interpretation, electrofacies analysis and spectral decomposition, combined with the crossplot analysis to do RGB geologically. Firstly the tuning frequencies were calculated by Discrete Fourier Transform (DFT) and Maximum Entropy Method (MEM), and then the relationship TVF (Thickness Versus Frequencies) was established. Secondly by the application of electrofacies considering the geological background, the relationship MVT (Microfacies Versus Thickness) was obtained. At last, we use crossplot technique which integrates microfacies, reservoir thickness and the tuning frequencies to study MVF to guide the selection of fusion frequencies for RGB. It is geologically reasonable for predicting the sedimentary microfacies. The examples for meandering river microfacies are predicted clearly.
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Internal Multiple Study on Åsgard Fields Smørbukk and Smørbukk Sør
Authors A.C. Ramírez, A. Antal and L.T.W. SigernesSummaryNew plays, both onshore and offshore, are once again highlighting the problems associated with internal multiples. Because most of our imaging techniques do not focus multiple energy, internal multiples can be a serious problem towards structural and quantitative interpretation, and can have a negative influence in velocity estimation and Q-estimation/compensation. These multiples mostly cannot be dealt with in a simple manner (e.g., moveout and periodicity attributes do not allow to discriminate them from near-by primary events). The industry has made much progress on developing tools to predict internal multiples, however the application of these tools to real data remains challenging.
We present two efforts to model internal multiples with the purpose of minimizing structural interpretation uncertainty. We analyze two (wave-equation based) internal multiple prediction algorithms; and show how the inverse scattering method can be used as a fast feasibility tool for data evaluation.
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Surface-related Multiple Elimination for Blended Data
More LessSummarySurface-related multiple elimination technique is applied on blended data directly in this paper. It is demonstrated that as long as the blending operator is known, the surface related multiple can be predicted by a formula similar to SRME. The output is the blended multiples. An adaptive subtraction is then applied to obtain the blended primary. The calculation of this method, comparing with EPSI on blended data, is smaller. And the output can be further processed using blended data based algorithms. Two synthetic data examples are given to illustrate the method.
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General Surface-related Multiple Prediction with Model-driven MCG Aperture Determination
More LessSummaryThe surface-related multiple elimination is one of challenging tasks in marine seismic data processing. It has been proven that 3D SRME is a highly effective method to attenuate both of in-plane and out-of-plane surface-related multiples. However, the conventional 3D SRME requires seismic data regularization and interpolation prior to multiple prediction, so the corresponding multiple prediction workflow is very tedious. In addition, the conventional 3D SRME is a highly memory-bounded algorithm in terms of multiple prediction, that limits its application to large seismic gathers. Combined general surface-related multiple prediction and model-driven MCG aperture determination, an improved SRME is introduced in this paper. The real data examples show that the proposed method can greatly improve the efficiency and reduce the memory requirement of multiple prediction without obvious loss of multiple prediction accuracy.
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SRME - Reducing Prediction Cost by a Dip Angle Criteria
Authors Y. Nae, R.R. Lopes and J.M.T. RomanoSummarySurface Related Multiple Elimination (SRME) is composed of two steps: prediction and adaptive subtraction. On the first step, we estimate the multiple contribution traces by convolving every two seismic traces that bounce on a common point at the free surface. This set of traces is called the Multiple Contribution Gather (MCG) and its size depends on the acquisition fold. The larger the fold, the larger the MCG, the more multiple data we have per single trace and hence the more costly the complexity of SRME prediction. Moreover, when using reciprocity, the MCG grows up to twice the fold size per single trace. Therefore, the complexity of SRME prediction is a crucial issue.
In this paper we show how the number of traces, used for multiple prediction, can be controlled. We study the MCG from a multiple travel-time point of view which allow us to estimate the reflector angle on the MCG panel. Then, we establish a relation between regions in the MCG and the angles of reflectors from which they emerge. We show that by limiting the aperture in terms of angle, we can reduce the cost of SRME with negligible impaction on the results.
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Adaptively Matching and Separation for Multiples Using Complex-valued Curvelet Transform
Authors X.W. Huang, P. Deng and D. ZhangSummarySurface-related multiple attenuation consists of predicting multiples and adaptively subtracting multiples model from original data with matching filters. Despite major advances made by surface-related multiple elimination (SRME), errors in the predicted multiples remain a problem.The matching filters are always got by minimizing the residual between the original data and the filtered multiples in a least-squares sense with the assumption that primaries have minimum energy and are orthogonal to multiples. In practice, the energy contrasts and orthogonality between primaries and multiples always vary as a function of offset, time and dip, which will pose a serious challenge for conventional least-squares(LS) matching. We propose an adaptive method that corrects those misfits, which vary smoothly as a function of scale (frequency band), angle and location. With this method, the predicted multiples can be adaptively macthed with the real ones in original data under LS sense by using an complex-valued curvelet transform. Instead of subtaction of the matched multiples, we estimate primaries by primary-multiple separation with curvelet-domain soft-thresholding. Synthetic data show great improvements over conventional least-squares matching with better attenuation of multiple energy and better preservation of estimated primaries.
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Internal Multiple Prediction - A New Approach Based on Seismic Interferometry and Marchenko Autofocusing
Authors G.A. Meles, K. Löer, M. Ravasi, A. Curtis and C. da Costa FilhoSummaryStandard seismic processing steps such as velocity analysis and reverse time migration (imaging) usually assume that all reflections are primaries: multiples represent a source of coherent noise and must be suppressed to avoid imaging artefacts. Suppressions methods are relatively ineffective for internal multiples. We show how to predict and remove internal multiples using Marchenko autofocusing and seismic interferometry. We first show how internal multiples can theoretically be reconstructed in convolutional interferometry by combining purely reflected, up- and down- going Green’s functions from virtual sources in the subsurface. We then generate the relevant up- and down-going wavefields at virtual sources along discrete subsurface boundaries using autofocusing. Then, we convolve purely scattered components of up- and down-going Green’s functions to reconstruct only the internal multiple field which is adaptively subtracted from the measured data. Crucially, this is all possible without detailed modelled information about the Earth’s subsurface. The method only requires surface reflection data and estimates of direct (non-reflected) arrivals between subsurface sources and the acquisition surface. The method is demonstrated on a stratified synclinal model and is particularly robust against errors in the velocity model used.
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Measuring Fracture Complexity with Time-lapse Shear Waves
By T.L. DavisSummaryFracture complexity occurs due to interaction of the hydraulic fracture with the natural fractures in the near well bore region. Measuring and monitoring that complexity and changes over time can aid in shale reservoir exploration and development. Shear wave splitting is an important technology for shale reservoir exploration and development.
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A New Operator Anti-aliasing and its Influence on Fracture Detection Based on Full-azimuth Anisotropic Migration
More LessSummaryIndependent from data and image aliasing, operator aliasing occurs when the input data spacing is too coarse and the frequency is too high for the steep migration operator summation trajectory. In past years, many researches focus on the problem about operator anti-aliasing but most of them are only available for isotropic media. In this paper, an operator anti-aliasing is proposed for anisotropic migration. Moreover, it is applied to fracture detection based on full-azimuth anisotropic migration. Physical model application turns out that fracture detection results are in well agreement with the real situation of the designed model. Meaningfully, compared with the obtained fracture results based on the method without operator anti-aliasing (fracture strike and density seem to be in a disorder), accuracy of fracture detection based on the method with operator anti-aliasing is improved. In the end, the method with operator anti-aliasing is applied to real data in Ha7 area. The fracture detection results are proved to be reliable and in highly agreement with the FMI interpretations, which suggests that this method is applicable and effective.
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The Optimal Design of Point Source Air-gun Array in Marine and its Application
More LessSummaryThe far-field signature for conventional marine air-gun array varies with azimuth, which makes it difficult to meet spatial omni-directional energy distribution requirement of 3D wide-azimuth seismic acquisition with streamer or OBC. Based on the stacking principle of seismic energy in space, we analyze the quantitative relation between the far-field signature and spatial distribution of the air-gun units and individual volume elements. An azimuth-invariant point source array is proposed with symmetrically distributed air-gun units. On this basis, the optimal design for point source array with staggered asymmetric distribution is carried out and applied for actual wide-azimuth seismic acquisition in marine. The seismic profile shows that the reflected energy is significantly increased, reflected events are relatively continuous, the breakpoints of faults are clear, and the resolution is improved.
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Determination of Adequate Reservoir Locations and Operation Using Spatial Approach
Authors S. Sirsant and Y.B. KatpatalSummaryRaipur City, the capital of Chhattisgarh, which is located in the fertile land of Mahanadi River basin, is located in central India. The water supply for the entire city is from Kharun River, which is one of the tributaries of Mahanadi River by constructing large number of anicuts throughout the river and from the groundwater resource. In this study, a methodology is proposed wherein suitable reservoir locations have been proposed based on land use/cover, topography, proximity to drainages, and urban sprawl. The satellite image of the area has been projected and land use classification has been done. The topography of the area has been generated by preparing the Digital Elevation Model (DEM) and the drainages have also been analyzed in reference to the land use of Raipur city. In addition to the rater based classification, a vector classification of the built up areas has also been done to generate the population count and thus determine the total water demand as well as to visualize the urban sprawl of the city. Suitable reservoir locations have then been proposed by performing overlay analysis on all the above mentioned factors.
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An Integrated Wellbore Trajectory Planning Approach Using Volume Based Visualization
Authors M. Ramfjord, A. Aqrawi and H. LudvigsenSummaryA clear, mutual understanding of the field is an important part of well planning. The wellbore position is also important in well planning and especially in collision avoidance management. An overview in the form of a three-dimensional volume of the possible drilling space serves as a facilitator for well planning. Great value is gained by combining disciplines in well trajectory planning in that geoscience interpretations combined with drilling risk and uncertainty handling gives a more robust and complete overview of options. Using a semi-automated drilling trajectory planning algorithm that handles drilling limitations, geological hazards and anti-collision has proven to better facilitate minimizing risk and field development plans.
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Development of Digital Techniques for Mapping an Open Pit at Coolgardie, Western Australia
Authors H.A. Bangash, S. Micklethwaite, P. Bourke and P. KovesiSummaryThis work focuses on the applications of photogrammetry for digitally mapping outcrops or complete open pits.
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Viscoacoustic Full Waveform Inversion for Spatially Correlated and Uncorrelated Problems in Reflection Seismics
Authors A. Kurzmann, R. Shigapov and T. BohlenSummarySeismic attenuation plays an important role in real Earth and contains valuable information about the subsurface. To recover spatial distributions of both velocity and quality factor Q, in this work we investigate the applicability of 2D viscoacoustic full waveform inversion (FWI) to synthetic marine reflection data. Viscoacoustic FWI is a multiparameter inverse problem, and suffers from the cross-talk between different parameter classes. Based on the 2D Marmousi model, we investigate the cross-talk using spatially correlated and uncorrelated models of velocity and attenuation. Our results show a good reconstruction of the velocity model and satisfactory recovery of Q only in the shallow areas. With increasing depth we observe a stronger footprint of the velocity model. Nevertheless, the fit of synthetic and recorded seismograms is excellent. This can be interpreted either as low sensitivity of the synthetic data to attenuation properties in deep parts or as cross-talk with explanation of attenuation-related data misfit by the velocity model. We find that the investigation of multiparameter inverse problems with (highly) spatially uncorrelated parameters has to be considered as a necessary step to verify the reliability of inversion strategies.
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A Combined Elastic Waveform and Gravity Inversion for Improved Density Model Resolution Applied to the Marmousi-II Model
Authors D. Wehner, D. Köhn, D. De Nil, S. Schmidt, S.A. al Hagrey and W. RabbelSummaryIn recent years the elastic full waveform inversion (FWI) was successfully applied to synthetic and field data to compute high resolution velocity models. While seismic velocities are derived from recorded phase information, density models can be estimated from the amplitudes. However, due to the complexity of the inverse problem a long wavelength initial model is required for a good reconstruction of the density. The inclusion of gravity data into the FWI concept can solve this problem.
In this study a two-step hierarchic joint inversion of seismic waveforms and gravity data is tested using the Marmousi-II model. In step 1 FWI is performed for all elastic parameters. Gaussian filtered velocity models of the true model and a constant halfspace density model (CDH) are used as initial models. While the velocities can be reconstructed well, the density shows large deviations from the true model. In step 2 joint inversion is applied to optimize only the density model, while the velocity inversion results of the first step and the CDH are used as initial models. The results of this combined approach show a significant improvement of the density model compared to the results of a pure FWI.
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A Two-stage Elastic FWI Strategy for 2D VTI Elastic Media to Improve c13 Structure
More LessSummaryTo enhance the feasibility of the multi-parameter full waveform inversion (FWI) for field data, including various types of seismic waves, we introduce a new 2-stage elastic VTI FWI strategy. Because the influence of S-waves on FWI is dominant due to its strong amplitudes in partial derivative wavefields, some parameters may not be recovered well. In the elastic VTI FWI, c13 is a parameter that reverses direction in early stage of inversion due to reversed motions of S-S waves with strong amplitudes. To solve this problem, instead of the virtual source for c13, we use the virtual source for λ in isotropic parameterisation, which includes the Lamé constants and density. This approach is based on the fact that radiation patterns of P-P scattered waves for λ and c13 are similar to each other and that the virtual source for λ generates P-P dominant scattered waves. This approach allows us to enable the inversion process for c13 to behave as if we only use P-P scattered waves to invert c13. Next, we perform the multi-parametric elastic FWI again with original virtual source to compensate for the errors caused in the 1st stage and to conduct the FWI for c13 with full wavefields.
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Elastic Versus Viscoelastic Full Waveform Inversion of Near-offset and Wide-angle Data in the Presence of Attenuation
Authors T. Belahi, N. Fuji and S.C. SinghSummaryFull Waveform Inversion (FWI) has proven to be a powerful tool to quantify the Earth’s subsurface. In geological settings, such as gas clouds, gas sand, where attenuation is important, the application of FWI is still very challenging. We have developed a viscoelastic FWI in the time domain. In this paper, we investigate the need to properly account for attenuation when inverting long offset seismic data by comparing the results of elastic FWI applied to viscoelastic data and fully viscoelastic FWI. We carried experiments for short and long offset geometry of acquisition. The effect of attenuation could be divided into two parts: during wave propagation and during reflection. We find the presence of attenuation has a significant effect on wide-angle reflection data, both for reflection and propagation, but it has little or no effect on near-offset reflection data, suggesting that the elastic approximation is only sufficient when inverting pre-critical reflections and the attenuation should be taken into account while inverting wide-angle reflection data.
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Robust Source-independent Elastic Full Waveform Inversion in the Time Domain
Authors Q.C. Zhang, H. Zhou, H.M. Chen, Y.H. Yang and Y.Q. LiSummaryHow to obtain a correct source wavelet is not easy for practical seismic explorations. We define the convolution-based hybrid-norm objective function for the time-domain elastic FWI. We use the synthetic data of Marmousi2 model with Gaussian and spike noise to verify the correctness and feasibility of our method. The inversion results show that our method can not only eliminate the artifacts caused by the incorrect source wavelet, but also improve the anti-noise ability. In addition, due to the filter role of the objective function, we adopt the multi-scale strategy to reduce the sensitivity of FWI to the initial models and to improve the quality of the inversion results.
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