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76th EAGE Conference and Exhibition 2014
- Conference date: June 16-19, 2014
- Location: Amsterdam, Netherlands
- Published: 16 June 2014
61 - 80 of 1028 results
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Compensating Attenuation Due to Gas Cloud Through QPSDM, a Case Study from Offshore Brunei
Authors K.H. Teng, J. Zhou, X. Wu, Y. Zhou, T. Brothers, S. Bergler and C. GibsonSummaryMarine seismic broadband solutions, as e.g. variable-depth streamer acquisitions, have shown great potential in providing high resolution seismic imaging and better low frequency penetration compared to conventional data ( Lin et al., 2011 ). The increased low frequency content as well as signal to noise ratio play an important role in velocity model building, especially in the presence of gas. It benefits the PreSDM with absorption compensation technology (QPSDM) as low frequency energy may penetrate better through gas clouds ( Xie et al., 2009 ). In this paper, we will show the methodology to compensate for Q absorption effects for a case study offshore Brunei. The step change in image quality shows that it is a viable solution to improve imaging through gas clouds by combining broadband acquisition and advanced depth imaging technology (Q tomography and QPSDM).
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Pre-salt Imaging Beneath Volcanic Intrusions in Brazils Santos Basin
Authors J. Langlois, Z. Yuan, H. Li, R. Kumar and B. BaiSummaryRecent offshore deep-water discoveries in the Santos Basin have drawn attention to pre-salt targets; however, seismic imaging in this area has proven to be challenging due to the complex geology and the depth of the pre-salt targets. Volcanic intrusions can also add intricacies to an already complicated geologic setting, creating very complex velocity profiles and limiting the effectiveness of typical tomographic solutions. For this survey in the Santos Basin, we found that even identifying the top of salt (TOS) can be challenging without first evaluating the velocity between the top of volcanic intrusion and the sediments below. Utilizing the improved bandwidth and imaging capabilities of variable-depth streamer acquisition, a new iterative tomographic approach has been developed to image beneath volcanic intrusions, providing a better understanding of the pre-salt targets.
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High Fidelity Imaging with Least Squares Migration
Authors B. Salomons, M. Kiehn, J. Sheiman, B. Strawn and F. Ten KroodeSummarySeismic acquisition is never perfect, and sparsity and irregularity issues lead to suboptimal images when using standard seismic imaging schemes. The remedy of Least-Squares Migration has been topic of research since the early eighties, but the take-up in the industry has been limited so far. This paper describes the experiences obtained for a number of real data cases, which show that the method does deliver and is worth the extra cost and effort.
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FWI-driven High-fidelity Depth Imaging of a Large 3D Arctic Seismic Survey, West Greenland
Authors B. Du, S. Perrier, H. Roende and J. AndersenSummary3D pre-stack depth imaging was conducted for an 1800 km2 narrow-azimuth streamer survey in the Baffin Bay, West Greenland. The survey area is characterised by a hard, shallow and rugose sea bed as well as a high-velocity Quaternary layer immediately beneath. The seismic data are therefore plagued with serious multiple contamination and degraded signal-to-noise ratio. The velocity model building of the Quaternary layer with the conventional tomographic approach is challenging due to the lack of offset coverage and poor data quality on the whole. To tackle these challenges, the high-fidelity depth imaging presented here focuses on three key components: (1) enhanced multiple attenuation with the Shallow Water Demultiple (SWD) technique; (2) incorporating 3D Full Waveform Inversion (FWI) in the velocity model building flow to effectively resolve the details of Quaternary velocity variations - and (3) high-end imaging with the amplitude-preserving Controlled Beam Migration (CBM) to mitigate migration artefacts and further improve signal-noise ratio in the image domain.
We demonstrate the effectiveness of the methodology and show the step change in the resulting image quality, which contributed to robust and optimal structural interpretations throughout the survey area.
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Rock Mechanics template In a Shale Oil Play, Vaca Muerta Fm, Argentina and Their Impact in the Exploratory Strategy
More LessSummaryLocated in the Argentinean Neuquén Basin, the geological formation Vaca Muerta (Thitonian age), became in the last few years a unit that holds a huge potential as an unconventional resources play. Rock mechanics and reservoir characteristics in the Vaca Muerta Fm are extremely heterogeneous. This is due to the differences in depositional environment, petrophysical features and thickness of the unit along the whole basin. In the study area, the thickness of the Thitonian section consists of more than 350 m of marls with variable content of carbonate, quartz and clays. The TOC average in the upper section of the unit is 3.5% and in the lower section is among 6%. In order to understand the productivity behaviour within this formation, a shale rock mechanics template has been developed and implemented. This is done by estimating Lambda-rho/mu-rho for different scenarios, together with the estimation of pseudo brittleness and basic mineralogical characteristics of Vaca Muerta Fm. This work shows a successful integration between wells and seismic data for a shale oil play. The use of rock physics templeate, in an exploration phase, helps improving the understanding of the reservoir mechanical characteristics, optimizing the selection of well location and well completion.
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Improved Prediction of Source Rock Maturity in Liquid-rich Unconventional Plays with 3D Basin Modeling
Authors A. Hartwig, D.J. Jacobi, G.M. Walters and P.J. PerfettaSummaryThe recent unconventional exploration in North America has shown that the viable liquid-rich zone of most source rock plays is a narrow band. Accurate 3D basin modeling studies can be used to predict these in onshore basins with complex burial histories. This requires a rigorous quality checking of multiple thermal maturity indicators and the erosion estimates. The thermal maturity predictions and calibration to kerogen kinetics can be improved by integrating historic production data (API and GOR) and correcting erroneous thermal maturity measurements. This 3D basin modeling approach is shown on an example from the Permian Basin, USA.
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Accurate Velocity Estimation Through the Curvelet Domain
Authors R. Alai, G. Nyein, M.N.B.M. Isa, M.S.B. Sulaiman, B. Chowdhury and M. YusupSummaryWe present significant improvements in pre-migration seismic velocity estimation through the use of Curvelet transform in prestack noise attenuation. Seismic data is decomposed using the Curvelet transform, which has the capability of separating events having differing frequency, dipping angle and location. Curvelet transforms decompose data as a weighted sum of “Curvelets”, where each Curvelet is localised in both the f-k and t-x domains, and each weight consists of both amplitude and phase. The data are processed in the Curvelet domain by manipulation of these weights. Noise suppression via the Curvelet transform on prestack gathers has contributed to significantly improved pre-migration velocity estimation.
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Fluid Flow in Unconventional Reservoirs - Modelling and Implications
Authors V.M. Yarushina, Y.Y. Podladchikov, N.S.C. Simon and D. BercoviciSummaryA new fully coupled model of fluid flow through deformable viscoelastoplastic porous rock is developed. Constitutive evolution equations for porosity and densities of the solid matrix and the fluid are derived using effective media theory. Deformation and porosity-dependent permeability in the model lead to a strong pressure dependence of leakoff during hydraulic fracturing. Predicted rates of fluid loss are higher than those suggested by classical models. The model also allows investigation of the preferred upward flow pathways during fluid injection operations as observed in CO2 injection operations without invoking the hypothesis of a pre-existing fracture network. The model is applicable to soft and unconventional reservoirs whose mechanical behavior cannot be captured by simple elastic laws.
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Evaluation of Formation Permeability Using Minifrac Pre-closure Data - Case Study
Authors V.Y. Guk, M.N. Bychina and M.A. TuzovskiySummaryHydraulic Fracture Design relies strongly on formation permeability. For the fixed quantity of proppant, higher formation permeability will lead to higher optimal fracture width and lower optimal half-length. Low permeability and tight formations, however, in many cases would not flow without fracturing and thus cannot be tested for permeability using conventional techniques such as Pressure Transient Analysis. This is why a practical way to determine permeability for fracture design in such formations is Minifrac, or, Diagnostic Fracture Injection Test (DFIT).
Conventionally, Minifrac pre-closure data is used for determination of leak-off coefficient and fluid efficiency. After-closure data is in turn used for formation permeability evaluation. Low permeability formations, however, exhibit radial flow only after a considerable time after shut-in. This makes permeability evaluation using after-closure data not practically applicable in many cases.
In this study we propose a new approach to DFIT design and evaluation using pre-closure data for determination of formation permeability. The approach is based on the fact, that if water is used as an injection fluid, the dominant leak off mechanism will be reservoir fluid compressibility. This enables to explicitly relate permeability and leak-off coefficient. The leak-off coefficient can be determined using pre-closure data, which reduces required minifrac time considerably.
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Understanding Net Pay in Tight Gas Sands - A Case Study from the Lower Saxony Basin, NW-Germany
Authors B. Koehrer, K. Wimmers and J. StrobelSummaryWe present an integrated workflow to describe and characterise Upper Carboniferous tight gas sands by systematically integrating core-based macroscopic geologic elements (depositional rock types), microscopic observations (post-depositional diagenesis) and pore-scale properties like capillary pressure and nuclear magnetic resonance data.
Our workflow integrates multiple data sets and scales from a Wintershall-operated tight gas field in the Lower Saxony Basin of Northern Germany. The reservoir is of Westphalian C to Stephanian in age and consists of thick successions of fourth-order coarse- to fine-grained tight sandstone cycles separated by siltstones and in party by anthracite coal seams. The tight sandstones are intensely compacted and cemented with quartz, clay minerals and carbonate cements and generally characterized by low matrix porosities (< 10%) and very low permeabilities (<0.1mD).
A hydraulic rock-typing approach was selected to better define net pay of tight gas sands. In contrast to conventional petrophysical net pay criteria (porosity and water saturation log cut-offs), our approach makes use of the calculated pore throat radius (using Winland R35 equation) and relative permeability measurements (“mobile gas”). Our multi-scale rock typing study enables a better understanding of tight gas sand recovery factors and sweet-spot identification especially for new field development/appraisal projects.
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The Role of Geoscience and Engineering in Securing Social License to Operate in Europe
By S.W. GarrettSummaryExploration for Naturl Gas from Shale resources in Europe is at an early stage and it takes many years for these activities, if successful, to mature into pilot tests and full production.
As European Geoscientists and Engineers there is an emerging and increasing duty upon us to link our science and technology through communication to public dialogue and policy making. Companies, governments, trade associations, universities, national institutes, professional societies and scientific societies must to work together in partnership. Information must be disclosed transparently. For peer-review science to be trusted and impartial, it is critical to separate from industry funding and scientific governance. Findings must be communicated clearly to inform reporting to and dialogue with a wide range of press, public and policy-making stakeholders, many of whom may not have a technical background.
These will be increasingly important tasks as our profession helps in meeting the energy challenges of the 21st Century.
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Results of Deconvolution with Sparseness Constraints
Authors A. Guitton and J. ClaerboutSummaryWe tackle deconvolution within an inversion framework using the hyperbolic function for our data (i.e., reflectivity) misfit, thus enforcing sparse solutions.
This “sparse” deconvolution overcomes the minimum-phase assumption and converts the commonly seen three-lobed Ricker wavelet into an impulse. In addition, sparse deconvolution reveals the polarity of seismic events. Three datasets illustrate our findings.
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Seismic Reflectivity Inversion by Curvelet Deconvolution – A Comparative Study and Further Improvements
More LessSummaryCurvelet deconvolution refers to seismic deconvolution for reflectivity inversion based on curvelet transform. Curvelet transform is a multi-scale and multi-directional transform, and thus can provide a sparse representation for seismic reflectivity. When using it to model the reflectivity, the signal is represented effectively by large coefficients and random noise is represented by small ones. In this paper, we conduct a comparative study in the context of reflectivity inversion, to investigate the performance of curvelet deconvolution, the least-squares method and Lp-norm deconvolution. It is shown that by using curvelet deconvolution, the inverted reflectivity profiles have better noise suppression and higher resolution than those obtained by the least-squares method. On the other hand, its results excel those which are obtained by Lp-norm deconvolution in terms of the lateral continuity. Since curvelet deconvolution offers a good trade-off between the lateral continuity and the sparseness, the result obtained by this method can be used as the initial model to enhance the conventional Lp-norm deconvolution. Numerical results show that the lateral continuity of the inversed reflectivity profile has been further improved by the proposed method.
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Surface-consistent Residual Phase Corrections
By K. GarceranSummaryNear surface variations not only create time delays but can create a more complicated frequency dependent phase distortion. The estimation of surface-consistent residual statics can be generalized to the phase, with the same attempt to maximize the stack power. The method presented in this paper, based on cross-spectral analysis, allows performing surface consistent residual phase corrections. This approach has the advantages to avoid the phase unwrapping and to use the full phase spectrum. Used after a first pass of surface-consistent residual statics or not, the proposed algorithm shows very encouraging results.
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Robust Surface-consistent Phase Estimation
Authors P.W. Cary and N. NagarajappaSummaryWe have developed a robust method of estimating surface-consistent residual wavelet phase that is based on the simultaneous maximization of stack-power as a function of both statics and phase. Real data examples show that stack-power and image quality are improved in a robust fashion with the simultaneous estimation of statics and phase corrections. We typically apply the process after residual statics are applied, and we observe that the algorithm comes up with statics and phase corrections that are strongly anti-correlated. We explain the observed anti-correlation by the fact that previous residual statics steps in the processing flow were improperly trying to correct residual phase errors with statics corrections. Maps of phase errors often show good correlation with features of the surface topography. In addition, phase differences between different source types are reliably estimated with the new algorithm when compared with a standard method of phase estimation at overlapping CDP stack locations. These observations lead us to believe that the phase errors that are estimated with this method are real and are being robustly estimated.
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Comparison of Two Semi-automatic Techniques for Seismic-to-well Tying
Authors R.H. Herrera, M. van der Baan and S. FomelSummaryTying well logs to seismic data is a highly subjective task that relies on the interpreter’s experience and the similarity metric used. Automated alternatives could help reduce this degree of subjectivity by making the tie reproducible. In this paper we compare two automated techniques: the dynamic time warping method and the local similarity attribute based on regularized shaping filters. These two methods produce superior tying in a guided stretching and squeezing framework. Results using a real well log example validate both approaches. Automated seismic-to-well tie algorithms can greatly aid in seismic interpretation. It is important to emphasize however that they are based on goodness-of-fit criteria and do not measure correctness of a fit. Best practices in well-tying have to be followed for their results to be meaningful.
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Improved Plane Wave Destruction for Iterative Local Slope Estimation
By K.J. HellmanSummaryThe estimation of local slopes has been an important topic for numerous seismic processing applications. Many local slope algorithms are based on the plane wave destruction approach, using the time derivative of the seismic trace along with a horizontal gradient trace to generate estimates of the dip. Differentiation increases high frequencies in the data, limiting the accuracy of these dip estimates. Alternatively, the plane wave destruction equation may be recast in terms of integration. In this case the original seismic trace is used along with the causal integration of the horizontal gradient trace. Since there is no differentiation to boost high frequency noise, and since numerical integration is itself a smoothing process, this approach leads to better-behaved dip estimates. In both cases, the finite difference approximation of the gradient leads to a biased estimate. However, as long as the local event slopes are not aliased, the dip estimates will be of the correct sign, and an iterative application of the algorithm will lead to accurate local slopes.
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Further Application of Frequency-diverse Filtering - A New 3D Deghosting Algorithm for Streamers
By Y.J. JiSummaryFrequency-diverse filtering is a method that combines array responses at several frequencies in order to overcome spatial aliasing. The method was recently introduced for simultaneous source separation. As a further application example, we present the formulation and results on synthetic data for 3D deghosting of marine streamer data.
We use a set of basis functions that include the ghost term and determine model space parameters (local frequency, slowness, time) using a one-norm (l1) optimization procedure. We illustrate the potential of the method with synthetic data from the SEM model, showing effective removal of receiver-side ghosts in a 3D sense for data acquired with coil acquisition.
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Premigration Ghost Wavefield Elimination on Different Cable Configurations - A Case Study in the Gulf of Mexico
More LessSummaryPremigration Ghost Wavefield Elimination (GWE), or premigration deghosting, has emerged as a key preprocessing step for broadening the bandwidth of marine streamer data. We apply a tau-p domain premigration bootstrap approach to eliminate the ghost wavefield on 2D data sets acquired using four different cable profiles in the Green Canyon planning area of the U.S. Gulf of Mexico. The effectiveness of the approach for all cable configurations is demonstrated, in particular in improved subsalt imaging and free-surface multiple attenuation.
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Full Waveform Inversion for Kinematic Equivalence
Authors J.K. Washbourne, K.P. Bube, K.T. Nihei, S.T. Kaplan, J.P. Stefani, N.K. Shah, G. Hampson, C. Manuel and D. BevcSummaryWe present an approach to 3D full waveform inversion that can handle noisy data deficient in refracted energy. We use time domain modeling and monochromatic inversion, and obtain excellent kinematic agreement of modeled data with observed data for a narrow azimuth towed streamer dataset from the northwest shelf of Australia. We describe how we apply regularization and preconditioners to obtain a robust solution with respect to an imperfect starting model and various sources of noise in the field data. Even though we employ very simple isotropic constant density visco-acoustic wave propagation, we obtain near kinematic equivalence of the data modeled using the inverted velocities with the field data. We discuss how this kinematic equivalence in the framework of robust norms and regularized nonlinear optimization may imply that non-uniqueness comes also from the choice of physics used for wave propagation.
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