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77th EAGE Conference and Exhibition 2015
- Conference date: June 1-4, 2015
- Location: Madrid, Spain
- Published: 01 June 2015
1 - 20 of 980 results
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Total-variation Based Seismic Imaging with Bregmanized Operator Splitting Algorithm
Authors T. Zand, A. Gholami and M.D. SacchiThe Born approximation of wave equation provides the possibility of determining the Earth velocity model from pre-stack seismic data. But ill-conditioning of the linearized problem is a major challenge. In this paper, in order to solve the problem and find an appropriate velocity model the total variation (TV) regularization is used to force the velocity model to have sparse gradient. Such a constraint allows selecting a model that has sharp boundaries between adjacent layers. We employ the Bregmanized Operator Splitting (BOS) algorithm to solve the problem. Numerical examples show high performance of the proposed method for velocity model building.
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Verification of Bright Spots Using Fluid Factor Attribute in Miocene Deposits of the Carpathian Foredeep (SE Poland)
Authors K. Cichostepski and M. KasperskaThe Miocene deposits of the Carpathian Foredeep are known for its lithological variability and uneven compaction. These circumstances often cause occurrence of many bright spots which are not connected with gas accumulations. Standard seismic reservoir interpretation using only post-stack attributes can lead to wrong conclusions in such area. That is why it is very important to find a valid method for verification of these bright spots. In this paper we propose the Fluid Factor attribute for validation of bright spot anomalies in the Miocene deposits of the Carpathian Foredeep. The application of pre-stack attributes significantly reduced ambiguity of reservoir interpretation.
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Geochemical Characteristics of Crude Oils, their Asphaltene and Related organic Matter Source Inputs from Fula Oilfields
Authors Y. Makeen, W. Abdullah, M. Hakimi, Y. Hadad, K. Mustapha and O. ElhassanThe oils were derived from alga organic matter, which was sourced from sediments deposited in a lacustrine environment under suboxic to relatively anoxic conditions and were generated from mature source rock with a wide range of maturity ranging from early to peak oil window. This is indicated by biomarker compositions based on saturated and aromatic fractions and bulk geochemical characteristics. Previous work by Makeen et al. (2013) on the Abu Gabra shales in the basin shows similar organic matter characteristics, palaeo-depositional environment and maturity, suggesting that the Fula oils are derived from the early Cretaceous Abu Gabra shales. This genetic relationship is also confirmed by the similarities in the structural moieties of the Fula oil asphaltenes and Abu Gabra shale kerogens (Makeen et al., 2015).
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A New Edge-detection Method of Potential Field Based on Discrete Shearlet Transform
More LessIn the potential field explorations, edge detection occupancies the crucial role in the interpretation of geological structure, geological mapping, delineating the mineral range and so on. In this paper, it proposes a new edge-detection method of potential field Based on the combination between Discrete Shearlet Transform theory (DST) and the Mathematical statistics theory. And a combined synthetic model is tested by the proposed method, the experiment presents that the method is very effective in the edge detection with simple algorithm, meanwhile, it shows the more details are retained and the more accurate location is detected with the comparison to three other edge-detection methods.
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Aquatic Oil Spill Remediation by CSASSBs- Cork Sorbent Carrying Automated Sub-Surface Boats
Authors M.D. Imtiaz, A. Aggarwal, J. Chhateja and S. DeiOil spills are environmental catastrophes, which not only lead to major economic losses, but also lead to the destruction of marine ecosystem and loss of aquatic life. These can happen as a result of simple dumping of crude by tankers to spilling of oil in major accidents. The paper briefly discusses the present trend in removal of slick, and puts forward a revolutionary methodology for the same in the form of CSASSB,Cork Sorbent carrying Automated Sub-Surface Boats. The paper is divided into two parts; the first part discusses the effectiveness of the use of CSASSBs, and compares it with the currently used counterparts. The second part discusses the suitability of Cork as the appropriate adsorbing material. The CSASSB has several advantages over the ships that are currently being used, they are more fuel efficient, and also have a larger sorbent bags is to base area ratio. The use of Cork as a sorbent has its own advantages,it is organic and does not cause harm to the environment. The combination of these two revolutionary techniques gives rise to a new comprehensive method for remediation of oil spill sites.
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Prediction with Geostatistics (in free software) of Aluminum Soil Concentrations in a Forest in Southeast of Ecuador
Authors X. Buenanio and G. ChicaizaGeostatistics is a discipline that deals with the statistical analysis of regionalized variables. In this case study, geostatistics is used to determine high values of Aluminum, from a soil sampling done in a forest in the southeast of Ecuador. Free statistical software R and mainly gstat and RGeostats libraries were used. RGeostats is the Geostatistical Package (under R platform) developed by the Geostatistical Team of the Geosciences Research Center of MINES ParisTech. First, exploratory data analysis (EDA) was performed. The second step was the review of a probable presence of drift or trend in the data through the analysis of directional clouds: East and North. Geostatistical tools such as: variogram cloud and variogram surface were used to detect outliers and anisotropy, respectively. An automatic model fitting by Iterative Least Squares was employed to fit the variogram. Finally, Kriging with moving neighborhood was used to get a detailed map of Aluminum soils concentration. The standardized error was reached in the interval [-2.5; +2.5]. The highest values obtained in estimation map belong to the central area. For additional conclusions in relation with toxicity of Aluminum is required to develop a multivariate analysis that includes variables such as pH and average plant growth.
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First Results of 4D Monitoring from the Deepwater BC-10 Life of Field Seismic (LoFS), Brasil
Authors M.A. Galarraga, K. Wang and H.G. FarmerThis paper presents the first results of the time-lapse monitoring from the full field ocean bottom life of field seismic system (LoFS) deployed by Shell at the deepwater BC-10 Argonauta field offshore Brasil, the deepest deployment of this technology in the world. The base survey was completed November 2013, shortly after start of production and the first monitor survey was obtained during June 2014, only 3 months after first water injection. The interpretation of high quality fast-track 4D data volumes identified some key 4D anomalies (softening, hardening, time-shift) that show excellent correlation with the production and injection performance of the field, providing timely input to reservoir management decisions that are essential to enhance and maximize the oil recovery in this field.
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Imaging an Incoherent Wavefield without Cross-correlations - Chaotic Wavefield Gradiometry
Authors S.A.L. de Ridder and B.L. BiondiWe propose a new technique for passive seismic imaging via the direct application of operators to noise recordings. We propose a time-domain 2D scalar wave equation to describe the propagation of surface waves within a narrow frequency range. Outside the source region, this scalar wave equation relates the second-order spatial and second-order temporal derivatives of the wavefield with the local velocity. Different from seismic interferometry, this technique does not rely on cross-correlations to reveal the statistical coherence of a chaotic wavefield at two locations. Rather, it relies on the local measurements of velocity obtained directly from the ratio between temporal and spatial derivatives of the wavefield. The new method allows us to do passive imaging with much shorter passive recording. We apply this technique on ambient seismic recording made at a large and dense array installed over Ekofisk oil field, in the Norwegian North Sea. We are able to image a subsidence-induced geomechanical imprint on the Scholte wave velocities over Ekofisk.
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Improving Repeatability of Land Seismic Data Using Virtual Source Approach Based on Multidimensional Deconvolution
Authors D. Alexandrov, J. van der Neut, A. Bakulin and B. KashtanWe present a new redatuming workflow developed for improving the repeatability of seismic data and designed specifically to account for changes in the source signatures or variations in downgoing fields in general. The new approach is based on the virtual source method with the same potential for reducing non-repeatability, associated with acquisition geometry changes and variations in the near surface. To correct for changes in the source wavelet between surveys, we suggest deconvolving the virtual source gather of the monitor survey with the point-spread function (PSF) of the same survey, and immediately convolving with the PSF of the base or reference survey. The PSF governs the radiation pattern of the virtual source. Trying to completely deconvolve the effects of individual PSFs on each virtual source response may degrade repeatability due to possible amplification of noise. Instead, we try to equalize radiation patterns of the virtual sources across all repeat surveys by reassigning a new reference PSF to all surveys. We apply the deconvolution-convolution method to a field 4D dataset with buried receivers and demonstrate significant improvement in repeatability.
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Quantifying Model Based Uncertainty Using Seismic Uncertainty Analysis – Case Study Danish North Sea
Authors O J Lewis, L. Letki, C. Hidalgo and C. MogensenThis work presents a case study of the application of Seismic Uncertainty Analysis (SUA) in the Danish North Sea where uncertainty in the lateral positioning of faults posed a significant drilling hazard. 500 equivalent models were generated and used to reposition nine key structural objects. Statistical analysis and displays of the repositioned objects were generated to reveal the structural uncertainty and provide quantifiable estimates of the model based uncertainty for use in drilling risk mitigation planning. Structural uncertainty in the pre-stack depth migrated seismic image used for interpretation and well planning is a consequence of the non-uniqueness of the Earth model built by tomography. There are several possible models which will satisfy our data and lead to the same overall gather flatness, but each will result in a different image and different depths of the reflection events. The objective of the Seismic Uncertainty Analysis was to quantify the structural uncertainty of target events in the final seismic image via the derivation of many equivalent TTI Earth models.
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Truncated Gauss-Newton Method with a Modified Scattering-integral Approach for Multi-parameter FWI in Acoustic Media
More LessDensity is difficult to reconstruct in multi-parameter full waveform inversion, due to the cross-talk effects between velocity and density. In this study, we implement the truncated Gauss-Newton method to multi-parameter FWI in acoustic media, in which we incorporate the inverse of the approximate Hessian where the off-diagonal blocks reflect the trade-off effects between different parameters, to decouple the velocity and density during the reconstruction procedure. The model update is computed through the matrix-free conjugate gradient (CG) solution of the Newton linear system. We adopt a modified scattering-integral approach to calculate the gradient of the misfit function with respect to the model parameters and the Hessian-vector product instead of the widely accepted adjoint-state method. The numerical examples prove the feasibility of our method.
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General Optimization Framework for Robust and Regularized 3D FWI
Authors S.R. Becker, L. Horesh, A.Y. Aravkin, E. van den Berg and S. ZhukScarcity of hydrocarbon resources and high exploration risks motivate the development of high fidelity algorithms and computationally viable approaches to exploratory geophysics. Inverse problem formulations for large scale imaging and full waveform inversion have proven very valuable over the past two decades. While initial approaches considered minimizing least squares, recent developments have emphasized the importance of robust formulations, as well as formulations that allow disciplined encoding of prior information into the inverse problem formulation. We propose a generic, flexible optimization framework capable of incorporating a broad range of noise models, forward models, regularizers, and reparametrization transforms. This framework covers seamlessly robust noise models (such as Huber and student’s t), as well as sparse regularizers, projected constraints, and Total Variation regularization. The framework is also expandable - we explain the adjustments that are required for any new formulation to be included. We conclude with few numerical examples demonstrating the versatility of the formulation.
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Use of Low and High Noise Models for Land Surface-seismic Data
Authors W.P. Kimman and P.L. VermeerIn land surface-seismic acquisition ambient noise levels can vary significantly both during a survey and from one survey to another. We show that, for a relatively quiet survey, the addition of increasingly strong realistic noise levels progressively damages the data, especially in the high frequencies. To mitigate such damage, the planned survey effort must offer robustness in the prevailing variable noise conditions. The robustness also renders the data impervious to sensor/system noise in state-of-the-art acquisition systems. In global seismology, Low and High Noise Models are used to describe the range of noise levels encountered on Earth. Models specific to land surface-seismic are not openly available. This may be partly due to the historical use of geophone arrays. High-channel count acquisition systems using broadband digital point-receivers, which have been in operational use in many different areas for more than ten years, provide a new and reliable source of data on acquisition noise levels. From broadband point-receiver ambient noise recordings around the world, we compiled models of the median and extreme values of the noise spectral density. More analysis will be required, but once established, the land surface-seismic noise models can serve as reference for survey and system design.
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Benefits of Blended Acquisition with Dispersed Source Arrays (DSA)
Authors M. Caporal and G. BlacquièreIn blended data acquisition, the recorded wave field is incoherent. Nevertheless blended source units in the arrays are historically chosen to be equal. We propose to abandon this constraint. This allows us to suggest the exploitation of inhomogeneous blended sources, together representing a Dispersed Source Array (DSA). Each source unit involved in the survey might be dedicated to a narrow and arbitrary frequency bandwidth, without the need to satisfy the wideband requirement. Inhomogeneous blending with DSA has several attractive potential advantages. The design of such sources is potentially simpler. In addition, the DSA concept opens the possibility to use tow depths and spatial sampling intervals that are optimum for specific sources. The whole inhomogeneous ensemble of sources incorporated to the array is designed to cover the entire seismic bandwidth of interest.
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Application of High-efficiency Nodal Seismic Acquisition in Niger
Authors Y.L. Huang, W. Wang, M.G. Zhang, X.F. Liang and C.H. WangAs a high-productivity and cost-effective acquisition system, cableless node is widely accepted and deployed in recent years. This paper gives the highlights of some key techniques of cableless node system applied in Niger G&B 3D survey, including multi-fleet vibrators stakeless guidance, high efficiency operation, field QC, and mega data management and processing. We demonstrate that the overall data quality of major geology target and deep formations has been improved through the implementation of the new acquisition in this project, which has proved wide azimuth, high density nodal acquisition is a scientific and cost effective approach in G&B desert area.
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The Role of Interfacial Impedance on Poroelastic Reflection Coefficient
Authors Q. Qi, T.M. Müller and B. GurevichThe characteristics of the seismic P-wave reflection coefficient can depend on the properties of the interface separating two dissimilar poroelastic half-spaces. This interface behavior can be characterized by an interfacial impedance which is associated with various petrophysical scenarios. We study the effects of the interfacial impedance on wave propagation across the interface between gas- and fluid-saturated media as well as a fluid/porous-medium contact. We obtain the reflection coefficient accounting for the interfacial impedance for all frequencies and angles by solving the corresponding boundary value problem. The interfacial impedance shows small influence on the P-wave reflection coefficient for the gas/water contact at seismic frequencies. However, it substantially changes the amplitude and phase angle of the reflected P-wave for a fluid/porous-medium contact.
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Taking Advantage of Hydraulic Fracturing to Improve Gas/condensate Recovery - A Case Study
Authors M. Sheydaeemehr, B. Sedaee sola and A. VataniHydraulic fracturing is one of the most proposed methods to overcome the condensate banking problem around a gas condensate well. This paper investigates the effects of hydraulic fracturing on gas/condensate recovery in one of the world's largest gas condensate fields located in the Middle East. Accumulation of the condensate around a few numbers of wells of this field has resulted in severe deliverability loss. In this study a single compositional well model was constructed and well test data were used to validate the model. The fracture was described as a thin vertical layer positioned symmetrical at the center of the model and the properties of fracture were assigned to this thin layer. A vast number of simulation runs were performed in order to investigate the effects of different parameters on the well production performance. The results showed that hydraulic fracture can significantly improve productivity of this giant field wells and the permeability-width product must be maximized and increasing fracture length would not result in much benefit and the optimum half-length of hydraulic fracture is 125m. Also the effects of negative inertia and positive coupling are dominant in the matrix and the fracture, respectively.
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Micro-CT Pore-scale Analysis of Low Salinity Recovery from Reservoir Sandstones
Authors M. Shabaninejad, R. Marathe, J. Middleton and A. FogdenThe mechanisms of low salinity recovery were investigated by micro-CT imaging of the pore-scale distribution of residual crude oil in clay-rich reservoir carbonates after secondary recovery by high salinity flooding and tertiary recovery by low salinity flooding. A workflow is presented for preparing small mini-plugs (5 mm diameter, 19 mm long) in a holder/flow cell and performing restoration, flooding, imaging and image processing and quantitative analysis. In tomograms of one such sandstone mini-plug after high salinity flooding, the half closest to the inlet was well swept with around 20% residual oil, as disconnected blobs contacting pore walls. The half closest to the outlet had much greater residual due to a substantial capillary end effect, reinforced by the close proximity of the mini-plug walls. Low salinity flooding did not change the oil saturation in the inlet half, while that in the outlet half was greatly reduced by lessening of the end effect. Analysis of interfacial areas in the tomograms showed that oil selectively detached from clay in the inlet half, but remained too disconnected for additional recovery. Oil detached equally from clay and grain in the outlet half, where oil-brine interfacial tension lowering was probably responsible for the artificial extra recovery.
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Forward Stratigraphic Modeling at Appraisal Scale - A Tool to Reduce Facies Uncertainty Distribution in Carbonate Fields
Authors C. Pellan, D. Granjeon, M. Zen and F. BenardCarbonate ramps are usually very good carbonate reservoirs and could be found all around the world, in South-East Asia and Middle-East. Stratigraphic architecture of these reservoirs is a key feature controlling hydrocarbon occurrence and behaviour. Detailed outcrop studies have been performed during the last decade to understand better the structure and facies distribution of carbonate reservoirs, and have led to a considerable improvement of the sequence stratigraphic conceptual models A full stratigraphic parameter set including subsidence map, eustatic curve, production law for the three carbonate sediments, supply of the two clastic sediments, and transport parameters was configured for each sediment. After design of an initial stratigraphic parameter set, a first simulation was performed using DionisosFlow. Once a best-fit simulation was reached, a series of extreme tests was then performed on each stratigraphic parameter to estimate the sensitivity of the numerical simulation, and in particular of the sediment proportions near wells. This stratigraphic forward modelling approach allowed us to understand better the impacts of sedimentary processes on the large-scale carbonate reservoir architecture and thus reduce uncertainties on the appraisal-scale reservoir characterization
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Models and Controls on Sequence Stratigraphy of the Miocene Zhujiang Formation in the Northern Pearl River Mouth Basin
More LessThe Pearl River Mouth Basin is located at the passive continental margin of the northern South China Sea. During the Early Miocene, it was converted from a rifted basin to a down-warped basin and deposited the Zhujiang Formation. Influenced by shelf break migrations, inherited paleo-uplifts, mixing of siliciclastic and carbonate sedimentations, fault breaks and so on, characterizations of sequence stratigraphy of the Zhujiang Fm is different from that of a typical passive margin basin. The study in this paper shows that five third-order sequences in the Zhujiang Fm are recognized and categorized to three types of sequence models. Controls on sequence architectures are characterized by variety and variability in time and space.
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