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79th EAGE Conference and Exhibition 2017
- Conference date: June 12-15, 2017
- Location: Paris, France
- Published: 12 June 2017
81 - 100 of 1073 results
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High-Resolution Reservoir Architecture Modelling of Thin-Bedded Fluvial Terminal-Splay Sandstone in the Rotliegend Feather-Edge Area
SummaryRotliegend aeolian and fluvial sandstones are prolific gas reservoirs throughout the Southern Permian Basin (SPB). Exploration and research efforts concentrated on the sand-dominated southern flank of the SPB, where the major gas fields are located. The reservoir potential of the Rotliegend feather edge in the central part of the SPB, i.e. the area where the south-derived sands pinch out towards the Silver Pit salt lake, has long been underestimated. The sand-starved, claystone-dominated and evaporite-bearing lithology in the central part of the basin hampered the detectability of thin-bedded, potential reservoir sandstones with conventional well logs. The present study uses high-resolution well correlations in a sequence-stratigraphic framework. The employed methodology is a combination of pattern analysis (trends and trend changes) in gamma-ray (GR) logs, and maximum entropy-based (MEM-based) spectral trend curves of GR to graphically evaluate the validity of the pattern analysis. This allowed for the correlation of at least twelve individual thin-bedded sheets (1–2m thick) a 20–25m thick reservoir interval over distances larger than 20km. Core analysis has identified the sheets as unconfined fluvial terminal-splay sandstone. The facies characteristics and sedimentary architecture were corroborated in an outcrop analogue study of a present-day river system in the Altiplano Basin (Bolivia).
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Multidimensional Gravity Gradient Modeling for 3D Salt Delineation in the Nordkapp Basin
Authors S. Panepinto, I. Guerra, M. Mantovani and L. MasnaghettiSummaryWe present an alternative and cost-effective approach for 3D salt delineation in frontier exploration areas. Our integrated multi-physics workflow combines the vertical tensor components of FTG data, anomaly enhancement techniques, interactive interpretive 2D modeling and 3D forward modeling for salt mapping. The benefit of the proposed approach is the ability to build a first-order 3D salt distribution over a wide area to assess salt volumes. The method was applied to a large FTG survey acquired in the Nordkapp Basin, Norway. Finally, the integrated multi-physics solution can be exploited for 1) Defining the sediment vs. salt ratio in salt basins, 2) Delineating areas of particular interest in terms of exploration prospectivity, 3) Identifying areas of broad salt overhangs, and 4) Ranking salt volumes for more refined 3D seismic acquisitions.
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Gravity Inversion By The MHODE Method: Application To A Salt Dome Case
Authors M.S. Chauhan, M. Fedi and M.K. SenSummaryWe present a new method involving the inversion of the scaling function, a quantity that is calculated along the ridges in 3D space. The inversion is based on the Multi-HOmogeneity Depth Estimation (MHODE, Fedi et al., 2015 ) and enjoys the important feature of not being dependant on density, but only on the source geometry. In order to perform the inversion, it is necessary first to compute the scaling function directly from the data in 3D space along the ridges ( Fedi et al., 2009 ; Florio and Fedi, 2014 ) and this step can be done by computing the field at different levels. We used 2D Talwani’s formula as forward problem ( Talwani et al., 1959 ). A set of non-linear equations is then formed, where the unknown quantities are the source coordinates. We used the Very Fast Simulated Annealing (VFSA) algorithm ( Ingber, 1989 ; Sen and Stoffa, 2013 ) to solve such a system. We will show the application of our approach to the synthetic example of a salt dome like structure having an inhomogeneous density contrast and a real case of the Mors salt dome (Denmark).
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Estimating the Curie Point Depth Using Magnetic Field Data to Assess the Geothermal Potential
Authors J. Drolet, B. Giroux and C. BouligandSummaryNew technologies that allow geothermal energy production in colder conditions result in interest for geothermal exploration in low heat flux regions. The Province of Québec, eastern Canada, is such a case. Mapping the Curie point depth (CPD) is appealing as an exploration tool due to the scarcity of the direct data. We have revisited a methodology to estimate the CPD using a fractal source distribution model and aeromagnetic data. Our methodology relies on a statistical model of crustal magnetization having a constant magnetization direction and random magnetization amplitude. The shape of the radial average of the logarithm of the power spectrum of magnetic anomalies is predicted using this model. The model parameters (thickness and depth to the top of the magnetic layer, the fractal exponent β and the constant C’) are obtained by calculating the best fit between the theoretical and observed radial power spectra using a non-linear least-square algorithm. Rather than using a constant value for the fractal exponent β, we propose a new calibration workflow based on heat flux measurements and lithology. This workflow includes the use of normal kriging of heat flux data. Mapping the CPD will help identifying potential areas for further detailed exploration programs.
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3D Potential Field Data Using L0 Norm Constraint Via Compressive Sensing
More LessSummaryI introduce sparse constraints into potential field data inversion to obtain the sparse inversion results. The sparse constraints have now been used in many types of geophysical domains, such as geophysical data processes. The new stabilized is a common practice, which should be minimized in the inversion method. This new inversion method mainly obtains the sub-surface nonzero density contrast, and the gravity data produced by the nonzero density contrast must fit the observed residual gravity data. Emphasizing L0 norm sparse constraints ensures that the inverse results are simple, and no unnecessary structures are expected as required by the potential field data. Minimizing the quasi-norm tends to penalize smooth variations, and it promotes a more blocky character in the solution. It is well known that the minimization of the L0 norm is an NP-complex problem in combinatorial optimization, which indicates that optimization algorithms solving the problem cannot be completed in polynomial terms. There are several methods to solve this NP-complex problem. In this paper, this sparse-constraints norm has been imposed on the gravity data inverse problems to obtain the density contrast distribution.
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SOM Clustering Analysis in the Discrete Wavelet Transform Domain for Filtering Noisy Magnetotelluric Data
Authors R. Carbonari, L. D’Auria, R. Di Maio and Z. PetrilloSummaryDespite the magnetotelluric method (MT) is one of the most prominent geophysical technique for deep subsoil exploration, it is not yet completely reliable when applied in urban or industrialized areas due to the presence of anthropic electromagnetic noise. The latter, indeed, may severely affect the MT recordings and, as a consequence, the impedance tensor estimates, which allow to retrieve the apparent resistivity values describing the underground electrical behaviour. In this work, a new filtering approach for MT data denoising is proposed. The procedure is based on the clustering of the impedance tensor estimates by using the Self-Organizing Map (SOM) neural network model. The clustering is performed in the time-frequency domain by a discrete wavelet transformation of the MT signals. In addition, a criterion for selecting, in each wavelet scale, the clusters that lead to the most reliable apparent resistivity estimates has been suggested. The application of the proposed filtering approach to synthetic MT signals has shown that the SOM clustering is very sensitive to the presence of noise and that it is possible to get consistent apparent resistivity curves.
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Controlled Source Boat-Towed Radio-Magnetotellurics for Site Investigation At Äspö Hard Rock Laboratory, Southeastern Sweden
Authors S. Wang, M. Bastani, T. Kalscheuer, A. Malehmir and L. DynesiusSummaryThe radio-magnetotelluric (RMT) method has traditionally been used for land investigations. However, with the development of the boat-towed RMT system, this method is used on shallow water. The lowest frequency of the RMT method is about 14 kHz and in addition water resistivity is quite low in some cases, therefore controlled source measurements is naturally considered for data acquisition. In order to resolve a fracture zone under a brackish water body, the controlled source boat-towed RMT (CSRMT) approach was tested. CSRMT and RMT one-dimensional inversions were carried out separately to analyze galvanic distortions and source effects in our dataset. Serious distortions observed in both inversions as well as the two-dimensional (2D) structure observed in our previous study made us consider 2D inversion for modeling the data. Due to the sufficiently large distance between transmitter and receivers, the CSRMT data were inverted using a 2D inversion code originally designed for plane-wave RMT data. Occam and damped Occam schemes were used in our 2D inversions for CSRMT and RMT data. The results show that CSRMT can better resolve the fracture zone than RMT. This study further illustrates the use of the boat-towed RMT system and particularly when combined with controlled source.
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First CSEM Surveys with a Newly Designed Receiver
Authors S.L. Helwig, W. Wood and Ø. FrafjordSummaryA new receiver design for marine CSEM, mainly intended to be used in vertical-vertical CSEM, where both the transmitter and the main receiver component are oriented vertically, was operated in two field surveys for the first time. The design differs strongly from other CSEM receivers and is based on a central vertical pole hinged in a tripod frame. It overcomes previous restrictions in receiver count and operational efficiency in vertical-vertical CSEM.
In combination with a vertical 5000A source dipole, 3D data acquisition with 72 receiver positions and 77 pulse positions was performed.
Noise levels from acquisition in the Barents Sea and in the Norwegian Sea were close to each other with a slight advantage in the Norwegian Sea. Data from the Barents Sea shows a stronger 12h noise period in the frequency range from 3 to 4Hz. This is in agreement with stronger tidal motions in the Barents Sea.
As more receivers are used at the same time the new data sets benefit from additional longer offset data not available in previous data sets. It allows for new ways of processing. Influences from induced polarization for example are offset dependent and can be analyzed in more detail.
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The Next Generation Electromagnetic Acquisition System
Authors A.K. Nguyen, P. Hanssen, R. Mittet, H.R. Jensen, L.T.T. Fogelin, M. Skarø, M. Rosenquist and P. van der SmanSummaryWe have compared field test data from a next generation node based CSEM acquisition system with data from a reference conventional system in a shallow water environment. The next generation system with much higher transmitter dipole moment and more sensitive receivers provides a step change improvement in the data quality, with clean data for all source frequencies out to 20 km offset compared to around 10 km offset for the reference system. The high data quality also provides clear improvements in the inversion results. This was demonstrated by improved imaging of a hydrocarbon accumulation under challenging conditions. We expect a maximal imaging depth, relative to the seabed, of up to 4500 m in future surveys with a commercial version of the next generation acquisition system.
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Why You Should Take Caution in Using Rock Physics Model Approximations for Time-lapse Analysis
More LessSummaryRock physics models are used as a method of modelling the influence of production-related stress change on seismic velocities. Many different models exist, however, almost all require either stress-velocity core data or complex laboratory techniques (e.g. X-ray diffraction) to calibrate. This becomes an issue when core data is not available, which is often the case for non-reservoir rocks. In these circumstances, approximate rock physics models may be applied, which use simplified formulae derived from best-fit parameters to constrained core datasets. However, in this study we show why you should take caution in using such relationships. Although they may provide good approximations of the absolute magnitude of the rock velocity, they are limited in predicting time-lapse changes in seismic velocity due to stress. This is because of the difficulty in relating parameters that govern the shape/curvature of the nonlinear relationship to best-fit constants or abundant rock properties. Although we use only simple isotropic relationships in this study, the conclusions remain applicable to all models, including anisotropic ones. This study also demonstrates the important of an accurate rock physics model in time-lapse monitoring scenarios. We show that just small discrepancies in model parameters can lead to large differences in predicted time-lapse velocities.
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Pressure Effects on the Joint Elastic-electrical Properties of Shaly Sandstones Based on Clay Distribution
Authors N. Aladwani, L.J. North and A.I. BestSummaryThe effect of pressure was tested on to a joint ultrasonic and resistivity datasets for 67 shaly reservoir sandstones classified into four groups according to clay distribution. We investigated the role of pore-filling and load-bearing clay on the pressure-sensitivity of the relationships between resistivity and velocity (G1), resistivity and attenuation (G2), and velocity and attenuation (G3).The results give useful information for joint property model development for improved hydrocarbon reservoir characterization.
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Dispersions and Attenuations Phenomena on Sandstones Poisson’s Ratio
Authors L. Pimienta, J. Fortin and Y. GuéguenSummaryWhen acquiring and interpreting seismic data at the field scale, one aims to gain insights on the rocks travelled through as well as the saturating fluid. One interesting property for such studies is the Vp/Vs ratio that allows insights independently of the density effects. Assuming the media to be isotropic, this ratio directly relates to Poisson’s ratio, an intrinsic property of the rock. Over the last decades, dispersion and attenuation effects were shown to occur on Vp and Vs, but Poisson’s ratio is often assumed to be independent of the measuring frequency.
In this study, provided that dissipation phenomena are observed on the elastic constants, it is shown theoretically that the same is expected for Poisson’s ratio. Moreover, measurements on a viscoelastic material and a poroelastic rock confirm this observation. For the rock sample, the measured dispersion/attenuation phenomena are large when fluid pressure is high or confining pressure is low. At the field scale, Vp/Vs ratio would indeed be a clear proxy of a high fluid pressure, and the ratio in attenuations could be a very interesting asset.
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Effect of Incident Angle on Wave Scattering in Fractured Media - A Numerical Experiment Using an Integral-based Approach
Authors H. Liu, M.K.S. Sen and K.T.S. SpikesSummaryIn this work, we numerically simulate seismic wave propagation in realistic fractured media to investigate characteristic scattering patterns. The linear slip model is used to describe the displacement discontinuity across the fracture. An integral approach, based on an element-level of discretization, is implemented to simulate elastic wave propagation. We used two typical incident angles, 0 and 90 degrees, to investigate their effects on scattering patterns, quantified by their scattering indices. The results show significant variations in wave scattering with different incident angles. More specifically, scattering indices are symmetric for both incident angles. However, the scattering index for the 90-degree incident angle displays a much more spatially distributed pattern than does the index for 0 degrees.
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Experimental Investigation of Clay Content on Brittleness of Synthetic Shale
More LessSummaryIt is important to understand that the brittleness of shale is a combined response of minerals composition, pores, fluids in pores, and micro-structure of rock at certain temperature and pressure. However, clay content as a key parameter that affect the brittleness of shale, has not yet been well studied and understood. In this paper, we focus on impact of clay content on the brittleness of synthetic shale with different clay content. To reduce the number of unknown factors caused by multiple minerals, we made 8 samples each with a different weight percent of mineral: 20%, 25%, 30%, 35%, 40%, 45%, 50%, 55%, instead of natural shale. The results indicate that with the higher clay content, samples show higher Young’s modulus, higher brittleness and lower Poisson’s ratio, which may be attributed to the increase of amount soft component (clay mineral). Besides, bedding plane has a significant impact on mechanical properties, E11 is always larger than E33 and B11 is always larger than B33. For the anisotropy of mechanical properties, ΔE and ΔB increase with the increase of clay content, contrarily, Δv decrease with the increase of clay content.
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Optimization of Brittleness Estimation Using Rock Physics Templates
More LessSummaryThe absence of a universally accepted definition and measurement of brittleness in shale gas plays has led to various methods or models for its quantification. To enhance the reliability of brittleness for evaluating reservoir quality, the paper proposes to optimize the brittleness estimation using rock physics templates. It begins with constructing a rock physics workflow to link the elastic properties of shales to complex constituents and specific microstructure attributes, followed by calibration with well log data, the constructed rock physics template could be used for geophysical prediction of porosity and lithology. Last, the brittleness index defined in terms of mineralogy and different geomechanical parameters based on the template is investigated. Consistent with the well-derived brittleness analysis, the constructed templates show great potential for deciding a better brittleness indicator in practice and enhancing the applicability of well log and seismic data for the estimation of brittleness.
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Estimating Anisotropic Brittleness of Shale Based On a New Rock Physics Model
More LessSummaryIt is widely known that shale often shows high anisotropic property. Ignoring shale anisotropy can induce errors in brittleness estimation. However, in oil industry, the common way to evaluate the brittleness of shale is based on using isotropic parameter (i.e. Young’s moduli and Poisson’s ratios), since it can be easily calculated based on measured elastic wave velocity from geophysical data. Anisotropic shale rock physics modeling offer us a new way to estimate the brittleness of shale from anisotropic aspect. Our studies firstly introduce a new rock physic model for shale. Based on our anisotropic shale model. The relationship between physical properties (like pore geometry, TOC, shale lamination and dip angle of shale formation) and elastic parameters (like anisotropic YM and PR) are established. Our modeling results coincide with the real data points of shale. The prediction shows the vertical/horizontal YM always below 1 while the vertical/horizontal PR can be either over or below 1. We find different extent of shale lamination may be the reason to explain the random distribution of Vani. And the brittleness of shale can vary significantly while drilling due to the strong anisotropy of shale formation.
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Random Noise Attenuation by Planar Mathematical Morphological Filtering
More LessSummaryImprovement of the signal-to-noise ratio (S/N) of seismic data is necessary in many seismic exploration areas. The attenuation of random noise is an important subject in improving the S/N. Geophysicists usually utilize the difference between signal and random noise in certain attributes, such as frequency, wave number, or correlation. In this paper, we have proposed a novel method utilizing the planar morphological attribute of seismic data to separate signal and random noise. The extraction of the morphological attribute is implemented by the planar morphological operations. The attenuation of random noise is achieved by removing the energy in the smaller morphological scales. We have named our proposed method planar mathematical morphological filtering (PMMF). Application of PMMF on synthetic and field seismic data demonstrates superior performance compared with the 2D median filtering and the singular spectrum analysis (SSA) method.
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Adaptive Seismic Random Noise Attenuation Using Curvelet Transform
More LessSummaryThe sparse inversion based random noise elimination methods utilize the soft threshold operation to realize denoising on the basis that seismic signals have sparsity expression in a transformed domain. The threshold values are very crucial for the final inversion results, they should match the energy of noise. However, the energy of noise is hard to achieve, the popular method to get proper threshold values is try many times manually which will cost much computation resource and labor. This paper proposed an adaptive random noise elimination method without any a priori information using the curvelet transform as the sparse transform, the inner relation between the sparsity of solution and residual with the iteration can be used to decide a proper threshold value, thus suitable denoising results can be provide based on this idea. Numerical experiment demonstrate that the proposed method can protect valid signal, eliminate random noise, render the events clear and improve signal-noise-ratio and resolution of seismic data.
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Curvelet-transform-based Random Noise Attenuation Using Energy Mean Scanning in f-k Domain
More LessSummaryThe curvelet denoising method has been successfully applied to seismic random noise attenuation. However, The conventional curvelet denoising method based on thresholding algorithm fails to preserve weak reflected signals in seismic events which have complex geometric structure. In this paper,we propose a novel curvelet denosing algorithm that applies the curvelet transform to 2D Fourier-transformed data in the fk domain instead of original data in the tx domain. In f-k domain in which the energy of the events with similar moveouts and diverse amplitude is located closely. Thus, we can take advantage of the energetic aggregation to preserve the weak reflected signals. Furthermore, an energy mean scanning algorithm based on the energetic statistical difference between effective signal and noise is proposed to perserve effective signal. The application on synthetic shot record and real imagration data demonstrates the feasibility and effectiveness of our proposed method.
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Adaptive Empirical Wavelet Transform for Seismic Noise Reduction
More LessSummaryDenoising is of great importance in seismic data processing. A variety of denoising methods have been proposed in the past several decades. However, it remains a longstanding problem to effectively separate noise and useful signal in the 2D/3D data set. In addition, seismic denoising is often performed trace by trace and the lateral continuity is usually not taken into consideration. To solve these two problems, we propose a novel method named adaptive empirical wavelet transform (AEWT) for seismic random noise reduction. In the AEWT, we take advantage of the outstanding denoising performance of EWT and the lateral continuity of multidimensional seismic data. When dealing with 2D data sets, the AEWT considers the spatial lateral continuity between the traces using the dominant frequency criterion (DFC) method, which selects the intrinsic mode functions by adaptively judging the dominant frequency of each trace. Both 2D synthetic and field data examples show successful performance of the proposed AEWT.
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