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78th EAGE Conference and Exhibition 2016
- Conference date: May 30, 2016 - June 2, 2016
- Location: Online
- Published: 30 May 2016
941 - 960 of 1034 results
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Inversion-based t-x Domain Signal-preserving Random Noise Reduction method
More LessSummaryRandom noise attenuation is a persistent problem in seismic exploration. There are many methods to attenuate random noise, among which the prediction filtering method is one of the most classical methods. However, prediction method is model-inconsistent and reduces the amplitudes of the signals. To overcome the shortcomings of the prediction method, we propose a novel approach to attenuate random noise in t-x domain through an inversion procedure. In this approach, a prediction error filter (PEF) is calculated from the noisy data. Then we use this filter as a constraint to the seismic data in order to get the denoised data by inversion. Since the PEF is calculated from the noisy data, it should be recalculated from the denoised seismic data. The process of calculating signal, then getting a new PEF should be iterated a few times. Besides, how to select the two trade-off parameters efficiently also has been discussed. Both synthetic and field data examples demonstrate excellent performance of the proposed approach.
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Statistical Modelling of Pre-injection Noise Recorded at the Aquistore Carbon Storage Site
Authors C. Birnie, K. Chambers and D. AngusSummaryNoise is a persistent feature in seismic data and so poses challenges in extracting increased accuracy in seismic images and physical interpretation of the subsurface. A previous noise analysis on the passive seismic dataset collected on a permanent surface array at the Aquistore carbon storage site identified individual noise signals, broadly classified as stationary, pseudo non-stationary and non-stationary, providing a basis on which to build an appropriate spatial and temporal noise field model. We introduce a novel noise modelling method based on a statistical covariance modelling approach created through the modelling of individual noise signals. This modelling method provides a significantly more accurate characterisation of real seismic noise compared to noise models created using conventional methods. Furthermore, we have developed a workflow to incorporate realistic noise models within synthetic seismic datasets providing an opportunity to test and analyse detection and imaging algorithms under realistic noise conditions.
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Random Noise Attenuation in Reflection Seismic Data Using Adaptive Neuro-fuzzy Interference System (ANFIS)
Authors A. Hajian, R. Kimiaeefar and H.R. SiahkoohiSummaryThis research introduces a method for background random noise attenuation in seismic data giving priority to the preservation of coherent seismic events and automation of algorithm. Since statistical characteristics of random noise are different than those of coherent events, in the proposed method, after defining a few statistical features, fuzzy C-Mean clustering was carried out on some randomly selected data samples from the seismic section. Then, the resulting membership functions along with the output of the adaptive Wiener filter were used so that automatic training of ANFIS could take place. Then, the acquired weights of the ANFIS were generalized to the whole data set based on the calculation of the statistical features. The proposed method was applied on both synthetic and real data sets and the results were compared to those of the conventional methods. The research findings revealed that the method was of a considerably higher performance in random noise attenuation as well as preserving the coherent events.
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Mapping the Basal Tertiary Maureen Fm. at the Mariner Field with Isometrix Broadband Data
Authors P.J. McFadzean and N. McArdleSummaryA case study is shown where high quality broadband Isometrix data is utilised in the structural seismic interpretation of the basal Tertiary Maureen Formation sandstones, one of the two principal Paleocene reservoirs constituting the Mariner field. Combining well tie results with detailed structural mapping at Tertiary, Cretaceous and Devonian stratigraphic levels reveals clear depositional and structural controls on reservoir development and quality and potentially also on compartmentalisation.
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Integrated Post-stack Acoustic Seismic Inversion Case Study to Enhance Geological Model Description of Upper Ordovician
More LessSummaryThe Upper Ordovician Formation in Algeria is a complex reservoir, characterized by high lateral variability in lithology, ranging from fluvio-glacial to near-shore marine environments. Increased understanding of the depositional setting, allowing improved tracking of the associated sand bodies (paleovalleys and associated fans and lobes) is a key objective to derisk this play. Dedicated studies have been performed in the South-East Illizi exploration concession (SEI) incorporating a Post-Stack acoustic seismic inversion, combined with detailed wells correlations, cores and FMI analyses. The result has been to refine the geological model of the Ordovician IV Unit, improving volumetric assessment of known accumulations and better defining the location of forthcoming appraisal wells.
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Interpretation of Complex Reservoirs - From Outcrops to Superresolution Imaging
Authors T.J. Moser, S. Johansen, B. Arntsen, E.B. Raknes and S. SangeslandSummaryOutcrop models are an invaluable help to calibrate seismic imaging techniques and assess their impact on interpretation of exploration and production targets. We investigate reservoir models based on an outcrop at Kvalhovden, east-Spitsbergen, and evaluate images obtained by regular migration and diffraction imaging. Diffraction images demonstrate the potential to enhance image resolution to beyond the traditional Rayleigh criterion and reveal considerable more structural detail. The use of high-frequency and high-resolution data modeling makes these investigations relevant for both production and exploration. The objective of this paper is to increase the awareness of the interpretation community of enhanced resolution capabilities of seismic imaging.
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Application of bandwidth extended seismic attributes to aid trap definition in Paleocene reservoir, Faroe-Shetland basin
Authors T. Fukano, S. Pugliese and M. HibbertSummaryReducing the uncertainty on trap risk is a key challenge in Paleocene aged stratigraphic prospects within the Faroe-Shetland Basin, UK. In this paper, we demonstrate how a BE® Bandwidth Extension (BE) workflow can be applied to conventional full stack seismic data to yield a high resolution, BE volume that significantly helps reduce uncertainty in trap definition. Similarity and relative impedance attributes derived from this volume have been used to better understand both the pinch out edge and fault geometry defining the prospect. The resulting interpretation has then been used as an input to fault seal analysis, which has allowed a better evaluation of lateral seal risk on the prospect.
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The Method on Accurate Description of Central Volcanic Conduits
Authors Z. Y. Zhen and Z.J. HanSummaryIn igneous rock area, the volcanic conduits occupy reservoir space and influence the reserves calculation and well location decision. So, accurate description of volcanic conduits becomes an important part of the oil field reserves evaluation and oilfield development. In this paper, we propose a new method to make accurate description of volcanic conduits by forward modelling and seismic attribute analysis. Firstly, we establish the principle of accurate description by forward modelling and pre-stack time migration. Then, we analyze the sensitive seismic attribute such as steered similarity and fracture density to enhance the difference of volcanic conduits and sedimentary rocks. Lastly, we make 3D accurate description of the central volcanic conduits based on the principle of accurate description and seismic fracture density in practical application.
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Morphogenetic Classification of Carbonate Buildups in the Northern Donets Basin Using Seismic Data - Case Study
By I. KhabanetsSummaryCharacteristics of carbonate buildups in the northern Donets Basin are analyzed using recently acquired seismic data. A methodology of delineation and classification of these buildups is suggested. This methodology allows the morphology, depositional characteristics and patterns of areal distribution of carbonate buildup structures in this region to be determined.
Characteristics of carbonate buildups in the northern Donets Basin are analyzed using recently acquired seismic data. A methodology of delineation and classification of these buildups is suggested. This methodology allows the morphology, depositional characteristics and patterns of areal distribution of carbonate buildup structures in this region to be determined. The results of this research will promote successful exploration of buildup structures in this and other areas of the northern Donets Basin.
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Study on the Feasibility and Stability of Zero-crossing Time Slices of Seismic Attributes in Identification of Thin Sand
Authors X.C. Zhang, J.S. Shen, P.L. He, Z.M. Zhu and P.C. WangSummaryIdentification of the interbedded thin bed has become a topical issues of the seismic exploration. The zero-crossing time slices technique is a new method which has the great advantage of depicting sand body. In this paper, we discuss the stability of this method by using different forward modeling. We test the influence of the prime frequency and phase of wavelet to the ZCTs intervals.Then we discuss the solution of the staggered finite-difference method to this model and inspect the feasibility of the ZCTs to real data. The result we got has proved that the method is generally applicable.
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Multi-scale Sequence Stratigraphy - Extending Well-analyses to 3D Seismic
Authors M. Morosini, J.D. Sanchez Mendoza, F. Qayyum and V. RomanovaSummaryA new workflow for seismic sequence stratigraphy has been developed by the authors. The workflow relies on a quick yet robust semi-automated seismic interpretation and allows to move easily from 1D well based sequence stratigraphic interpretation to 3D seismic derived thickness maps for the identified system tracts.
The methodology behind such workflow is illustrated in detail and results from a deepwater setting are presented.
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Estimation of Interval P Wave Orthorhombic Parameters from VSP Walkaway and Walkaround Data Using Differential Evolution
Authors A. Padhi, R. Zhou, M.E. Willis and J. ZhuSummaryFractured subsurface formations with anisotropic backgrounds, such as in shale layers, can be effectively modeled as orthorhombic media in many cases. Extracting interval orthorhombic parameters from seismic data (surface or VSP) is, however, a non-unique and nonlinear problem. The extraction is further complicated by the presence of local extrema in the error functional that needs to be optimized. Such parameters, however, can help characterize the formations better, and hence it is necessary to develop a robust methodology for such parameter extraction. In this work, we developed an inversion scheme for obtaining interval orthorhombic parameters from VSP walkaway and walkaround direct P-wave travel time data. We combined a layer (3D planar/non-planar) based anisotropic ray tracer with a global optimization algorithm called Differential Evolution to estimate P-wave anisotropic parameters along with principal stress orientations. We further applied the developed algorithm to a field dataset and demonstrated that it can help obtain orthorhombic media parameters that could be potentially related to geology, in the presence of noise and suboptimal acquisition design.
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Calibration of Distributed Acoustic Sensing (DAS) VSP Data
Authors M.E. Willis, A. Ellmauthaler, X. Wu, D. Barfoot, C. Erdemir, O.A. Barrios-Lopez, D. Quinn and S. ShawSummaryThe usefulness of distributed acoustic sensing (DAS) VSP data to map reservoir structures and extract rock properties is limited only by our understanding of the fidelity and characteristics of the measurement. In order to calibrate both the kinematics and dynamics of DAS VSP products, we document the correspondence of the DAS and geophones measurements for extracted slowness values, corridor stacks, amplitudes, linearity with source effort, and response to incident angle. The DAS slowness values match very well with the corresponding geophone slowness and up-scaled sonic log. The arrival times and amplitudes of the corridor stacks show a very good agreement. The average earth attenuation extracted from the first break amplitudes are nearly identical for the DAS (Q=86) and geophone (Q=88) data sets. Tests varying the source effort confirm that the DAS measurement performs linearly with seismic amplitude. We also confirm the cosine squared response of the fiber to the incident angle of the seismic wave field. These tests show that properly acquired DAS VSP data sets can be trusted for both travel times and amplitude information.
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Depth Calibration of Fibre-optic Distributed Vibration Sensing Measurements
Authors T. Dean, T. Cuny, A. Constantinou, P. Dickenson, C. Smith and E. HamoucheSummaryDepth calibration for conventional vertical seismic profile (VSP) tools is relatively straightforward. For fibre-optic distributed vibration sensing (DVS) measurements, however, depth calibration is more problematic and has been identified as a particular drawback.
In this paper we describe four different methods for calibrating the depth of DVS recording channels. The end-of-fibre and freeze methods can be applied to both permanent and temporary fibre installations whereas the downhole source method is primarily applicable to permanent installations. Methods based on the raw backscatter measurements are more likely to be accurate because they do not involve any effects from the processing stages required to extract the phase. The freeze and downhole source methods both suffer from problems associated with picking an amplitude peak that has been smoothed by the gauge length. If a permanently installed fibre must be depth calibrated at a variety of depths, the downhole source appears to be the most promising method. The error associated with the hammering technique is significantly larger than the other techniques and thus we do not recommend its use.
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Learnings from Distributed Acoustic Sensing Data Processing for Seismic Applications - A Case Study from the North Sea
More LessSummaryUse of Distributed Acoustic Sensing (DAS) fibre-optic technology for acquisition of vertical seismic profile (VSP) data is increasing rapidly. Since 2012 BP has carried out and participated in several field studies using DAS across different basins. These tests have included acquisition on land, in deep and shallow water, with sources deployed as a walk-above spread and shot patches of 60,000, using pre-installed fibre in producing wells and highly deviated wellbores. This paper will discuss the results and experience gained from acquisition and processing of the dual-well 3D DAS VSP over the Valhall field in the North Sea in 2015. This survey had a larger shot patch than previous trials, was acquired in shallow water and one of the wells remained on production throughout; a scenario presenting various challenges and opportunities. Successful imaging of the data confirmed the technical utility of DAS in achieving a targeted subsurface image and results indicate that recording data acceptable for imaging may be possible in producing wells.
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Walkaway VSP Using Multimode Optical Fibres in a Hybrid Wireline
More LessSummaryA Walkaway and a Walkaround Vertical Seismic Profile (VSP) data were acquired with an iDAS system. The survey took place in a CNPC formerly producing well in northeastern China, near Tangshan, Hebei. A standard VSP data pre-processing workflow was applied, followed by prestack Kirchhoff time migration. The DAS pre-processing step was faced with additional and special challenges: strong coherent noise due to cable slapping and ringing along the borehole casing. The final pre-processed DAS data rendered a vertical aperture the height of the well that resulted in a much wider lateral image than customary from a single well. This single well DAS Walkaway and Walkaround VSP image provided a good result with higher vertical and lateral resolution than the surface seismic in the objective area.
The vertical well environment without the ability to effectively clamp the sensor to the borehole casing wall creates a unique set of challenges. This paper reports on lessons learned in the handling of the wireline cable and subsequent special DAS data processing steps developed to remediate some of the practical wireline deployment issues. Optical wireline cable as a conveyance method for VSP in vertical wells will open the use of the DAS system to much wider applications.
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Low-frequency Data Acquisition from High-frequency Source Using Half-cycle Pseudorandom Sweep
Authors Y. Nakamura, M. Takanashi, M. Nakatsukasa, Y. Kunishi, J. Sakakibara and A. TagoSummaryThe importance of low-frequency acquisition is widely recognized as it contributes to illumination of deeper targets and estimation of quantitative properties by the use of full waveform inversion. We introduce an approach of low-frequency acquisition using half-cycle pseudorandom sweeps. The waveform is characterized by continuous half-cycle sine curves with constant frequency (carrier frequency), which polarity changes randomly. Auto-correlation of the half-cycle pseudorandom sweep is close to side-lobe free delta-function, which makes it possible to obtain broad-band seismic data. We performed a field test for a crosshole seismic survey using piezoelectric source with various carrier frequencies. Each pseudorandom sweep has the same number of “half-cycles”, and therefore, the total sweep time is shorter with increasing carrier frequency. The field results demonstrated that low frequency component is not dependent on the carrier frequency, although high frequency component increases with it. Thus, half-cycle pseudorandom with higher carrier frequency can provide broadband seismic data with shorter acquisition time, which is related to flat frequency property of the piezoelectric source. This approach should provide low-frequency data acquisition from piezoelectric or other high-frequency instruments and may be a significant contribution to low-frequency data acquisition.
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Feasibility of Azimuthal Anisotropy Determination Using P-wave Reflection Amplitude from a Walkaround VSP
Authors R. Zhou, K. Green, J. Peron and W.S. LyonsSummaryA walkaround vertical seismic profile (VSP) survey offers full-azimuth seismic measurements for fracture or stress-field characterization near a well. Since downhole geophones may be placed close to a target zone, high quality P-wave reflection data can be obtained to study seismic amplitude anisotropy or provide key parameters for possible calibration of surface seismic amplitude versus offset and azimuth (AVOAz).
This paper explores the feasibility of using a zero-offset and walkaround VSP to determine azimuthal anisotropy in P-wave reflection amplitude. The case study in the paper shows evidence of azimuthal anisotropy in the reflection amplitude observed from a fractured reservoir. A workflow is developed to extract and analyse the AVOAz data from the walkaround VSP. The results demonstrate that the walkaround VSP can provide a quantitative measure for the orientation and magnitude of fracture-induced azimuthal amplitude anisotropy. It can also provide a key data set to calibrate surface seismic amplitude, including P-wave reflection coefficients, offset-to-angle conversion, and amplitude gradients.
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Insights on the Robustness of Event Locations from Analysis of Acoustic Emissions Observed in a Triaxial Experiment
Authors I. A. Vera Rodriguez, S. Stanchits and J. BurghardtSummaryThis work compares acoustic emission raw-location results for a hydraulic fracture experiment performed under triaxial stress conditions. The observed acoustic emissions were located using two different homogeneous velocity models. One of the models considers only compressional velocities derived from the measurement of transmission signals. The second model uses the same velocity for compressional waves but also incorporates an estimation of shear wave velocity. Both, compressional and shear wave velocities, present errors that in the case of compressional waves are known to be in the range from 1.5% to 5%. The acoustic emission raw-clouds obtained with both models are compared with the surface of the created hydraulic fracture, which was laser-scanned over the open rock sample. The raw-location results highlight robustness in the location algorithms to the errors in the velocity models and place more importance in the incorporation of shear wave information for the determination of accurate hypocentre locations.
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Locating Passive Seismic Sources Location with Cross-correlation Migration
More LessSummarySeismic sources location is a crucial step in the engineering of unconventional shale reservoirs. The accuratly locating hydraulic fracturing is the critical for microseismic monitoring, which can contribute for the source mechanism analysis and enhance oil/gas recovery. More difficult than processing with the active seismic data, the passive seismic data usually is recorded with the unknown source initiation time. Conventionally, the energy-focusing method and the migration-type location method are used for locating the sources. However, the energy-focusing methods lead to an unreliable estimate of the source location. The cross-correlation migration (CCM) algorithm is proposed, based on the concept of the seismic interferometric method. The method has the following steps: 1. generate the correlated gathers by correlating each trace with all the other traces in the original passive data; 2. migrate each correlated gather to get an image of the source location; 3. stack all these images together and get the final estimate of the source location. Than, a real hydraulic-fracture stimulation case is processed with the cross-correlation migration method and shows a reasonable and acceptable result compared to the reference fracture location.
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