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81st EAGE Conference and Exhibition 2019 Workshop Programme
- Conference date: June 3-6, 2019
- Location: London, UK
- Published: 03 June 2019
1 - 50 of 93 results
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A Brief Overview on Seismic Attenuation
More LessSummarySeismic waves decay due to geometrical spreading (in 2D and 3D) and scattering (energy is conserved), and anelastic -- or intrinsic -- attenuation (energy is lost to heat). Amplitude decay in the last two cases is accompanied with wave-velocity dispersion, by which each Fourier component of the signal travels with a different phase velocity (Kramers-Kronig relations). Attenuation can be described by a phenomenological (non-predictive) theory, as the Burgers mechanical model -- composed of springs and dashpots --, or with predictive models, such as the scattering theory, and the Biot and related models of poroelasticity (wave-induced fluid-flow attenuation). Another phenomenological approach is the use of temporal or spatial fractional derivatives, e.g., Kjartansson and Cole-Cole models. In the following, I present a brief overview on the various attenuation mechanisms, where most of the material refers to Carcione (2014) .
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Seismic Attenuation Mechanisms in Fractured Fluid Saturated Media – Numerical and Field Examples
Authors E. Caspari, N.D. Barbosa, M. Novikov, V. Lisitsa, J. Hunziker, B. Quintal, G. Rubino and K. HolligerSummaryA number of different mechanisms can cause attenuation of propagating seismic waves in a fractured fluid-saturated porous medium, notably geometrical spreading, displacement of pore fluid relative to the solid frame, and transmission losses and scattering. In this study, we examine these attenuation mechanisms using numerical forward simulations and a field example. The numerical methods include a quasi-static upscaling approach and wave propagation simulations. They are based on Biot's equations of poroelasticity and, hence, fractures are modeled as soft, highly porous and permeable features. The field examples include full-waveform sonic data from the Grimsel Test Site underground laboratory situated in a granodioritic rock mass, which exhibits both brittle and ductile deformation structures at various scales.
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Use of the General Fractional Zener Model to Represent Attenuation in Poro-Viscoelastic Numerical Modeling
Authors X. Liu and S. GreenhalghSummaryTo approximate seismic wave propagation in double porosity media we use the governing equations of effective Biot theory with complex phase velocity and attenuation dispersion characteristics. To upscale them and extend to shear waves we use the poro-viscoelastic modeling approach of multiple fractional Zener elements and apply a frequency-space domain mixed grid finite difference simulation method to calculate wavefields for solid particle velocity, fluid flux and pore pressure.
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Dispersion and Attenuation of Wave Velocity in Fluid-Saturated Rocks : Experimental Investigations
Authors J. Fortin, J. Borgomano and S. ChapmanSummaryFor fluid-saturated rocks, comparing ultrasonic measurements (1 MHz) in the laboratory and seismic (100 Hz) or logging (10 kHz) measurements in the field is not straightforward due to dispersion of the elastic-wave velocities. If there are several theoretical models, there is a lack of data. We developed an apparatus for measurements over a large-frequency range, by the combination of forced oscillations (0.004 to 100 kHz in apparent frequency) and ultrasonic measurements (1 MHz) at various effective pressures. Our experimental results typically show two cut-off frequencies: i) one related to a drained/undrained transition; and ii) one related to squirt flow.
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Attenuation From Passive Seismic Monitoring
More LessSummaryMeasurements of attenuation from passive seismic monitoring datasets increase in number. We provide an overview of methods that are used to determine attenuation factors using detected microseismic events. We discuss applications and advantages of using passive monitoring to characterize medium -in particular hydrocarbon reservoirs.
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Q Compensation: From Nice to Have to Mandatory But…
Authors P. Charron, B. Duquet, C. Agut and A. LaframSummaryAttenuation is a well-known phenomenon in seismic. For tens of years, this has not been compensated or partially compensated with an inaccuracy that would not be accepted for any other processing steps. Most often, only a phase de-absorption with a constant Q value was applied and the amplitude absorption was compensated with spectral enhancement. This was considered as acceptable until today since the frequency bandwidth was limited to around 2 octaves and the effect of this de-absorption was not clearly observed as an improvement or adrawback. Today, the market has moved forward and the broadband seismic has become a standard. The consequence is that the bandwidth may now be spread over up to 5 octaves depending on the area and the burial of investigation. This wider frequency bandwidth is naturally unbalanced according to the magnitude of the absorption. In order to deliver the promises of the broadband (resolution), compensating the absorption is not an option anymore. It has become a processing step of a major importance that will impact the resolution, the phase and the overall “aspect” of the final result that the end-user will interpret or use to extract some attribute through AVO analysis or inversion processes.
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Q-Tomography: Status and Challenges
Authors Fatiha Gamar-Sadat, Alessandro Pintus, Patrice Guillaume and Andrew WrightSummaryAlmost all current time or depth seismic studies need to go through a correction process to recover energy lost by absorption phenomenon. The so-called Q factor is responsible for dissipation of high-frequency seismic energy, which decreases seismic amplitudes and causes velocity dispersion. For general background Q, a post-migration inverse Q filtering ( Wang, 2002 ), using smooth or even constant Q, may be sufficient for data with gentle geology. In areas with more absorptive heterogeneities such as unconsolidated materialor gas, theneed for a morecomplex Q model is necessary for an accurate correction. Brzostowski and McMechan (1992) have been pioneers for addressing this problem, adapting Q-Tomography from fundamental to applied seismology. Over the last decade, it has resulted in an industrial solution ( Cavalca et al., 2011 ; Valenciano and Chemingui, 2013 ; xin et al., 2014 ; Gamar et al., 2015 ) using VSP or surface seismic data.
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Viscoelastic Full Waveform Inversion of Wide-Angle Data: Application to Ultra-Long Offset Data from Mentawai Basin, Indonesia
More LessSummaryFull Waveform Inversion (FWI) is a powerful tool to quantify the Earth's subsurface structure. However, most of the FWI applications have been limited to acoustic media. In geological settings, such as gas clouds, gas sand, melt lens, where the attenuation becomes important, one must use a viscoelastic FWI. Here we present the theory and application of a viscoelastic FWI in the time domain. First, we carried out sensitivity analyses for back-scattered, reflected and transmitted waves. We find that the presence of attenuation has a significant effect on post-critical reflections, but it has little or no effect on near-offset reflection data, suggesting that the inversion of port-critical reflections can help to reduce the cross talks between attenuation and velocity contrast or propagation effects. We have first tested the method on synthetic data and then applied to 15 km long offset data acquired by CGG Offshore central Sumatra, Indonesia. Apart from the recovery of attenuation parameters, the viscoelastic inversion provides sharper P-wave velocity image as compared to the elastic FWI.
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Effect and Reconstruction of Attenuation in Acoustic FWI - Method and Field Data Application
Authors N. Kamath, R. Brossier, L. Metivier and P. YangSummaryOur contribution is divided into two parts: in the first we discuss the mechanism (based on generalised Zener body) used to incorporate attenuation into our forward modelling engine, and the manner we manage the efficient building of the FWI gradient in 3D. The second part deals with the application of mono- and multi-parameter (velocity only in visco-acoustic media, and velocity-attenuation joint inversion, respectively) FWI to a 3D OBC dataset from the Valhall field.
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A Hybrid Inversion Strategy for Visco-Acoustic Full Waveform Inversion: Application to the Marmousi Model
Authors H. Jiang and H. ChaurisSummaryVisco-acoustic full waveform inversion aims at retrieving the velocity and attenuation models, but suffers from cross-talks between parameters. Attenuation dispersion leads to equivalent kinematic velocity models, as different combinations of velocity and attenuation have the same kinematic effects for band-limited seismic waves. We propose a hybrid inversion strategy: we incorporate the kinematic relationship to guide the non-linear inversion. The hybrid inversion strategy includes two steps. It first updates the kinematic velocity, and then retrieves the velocity and attenuation models for a fixed kinematic velocity. This hybrid inversion strategy is tested on the Marmousi model dominated by reflections, and compared with the conventional simultaneous inversion strategy. It proves that the hybrid inversion strategy mitigates the cross-talks without involving the Hessian matrix.
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Joint Estimation of Velocity and Attenuation by Frequency-Domain TV-Regularized Wavefield Reconstruction Inversion
Authors H. Aghamiry, A. Gholami and S. OpertoSummaryFull waveform inversion (FWI) is a nonlinear waveform matching procedure which can provide high-resolution subsurface models. However, viscous effects must be taken into account in attenuating media to exploit the full potential of FWI. In the frequency domain, attenuation is implemented in the time-harmonic wave equation with complex-valued velocities. During the inverse problem, the real and imaginary parts of the velocity are generally processed as two independentreal-valued parameters. In this study, we process instead the velocityas a complex-valued parameter using derivative of real functions of complex variables. Moreover, we implement visco-acoustic frequency FWI with search space extension in the framework of the wavefield reconstruction inversion (WRI) method. We implement WRI with the alternating-direction method of multiplier (ADMM), which makes the parameter-estimation subproblem linear thanks to the bilinearity of the wave equation and provides a suitable framework to cascade nonsmooth regularizations and bound constraints in the objective function. In this study, we review ADMM-based WRI for complex-valued parameters and show preliminary results of joint velocity and attenuation reconstruction when inversion is performed without and with total variation (TV) regularization. We show the key role of TV regularization to decrease the ill-posedness of the velocity-attenuation reconstruction.
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Accounting for Heterogeneous Attenuation in Full-Wavefield Inversion
Authors M. Lacasse, H. Denli, L. White, V. Gudipati, S. Lee and S. TanSummaryThis talk presents a numerical approach for including attenuation in forward seismic viscoacoustic simulators in the time domain using a generalized Maxwell body (GMB). We discuss how to select the proper number of relaxation mechanisms and the values of the parameters of the GMB. We also present a few synthetic case studies determining the feasibility of performing full-wavefield inversion of viscoacoustic media, and the aperture requirements. Finally, field examples are shown where attenuation needs to be accounted for in order to perform a successful inversion.
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Integrated Visco-Acoustic Model Building: a Case Study Illustrating the Challenges and Benefits for Large Scale Exploration
Authors T. Martin, M. Barbaray, G. Venfield and V. ChavdaSummaryThe seismic character of Early and Late Cretaceous plays in deep water Côte d'Ivoire data are affected by Late Cretaceous and Paleocene channel and canyon systems. Unresolved, these create structural uncertainty and impacting amplitude fidelity. Using an integrated visco-acoustic model building sequence we resolve the impact of complex Late Cretaceous and Paleocene channel systems on deeper targets. A full wavefield FWI approach creates an accurate velocity model removing the structural uncertainty when used in the imaging step. Viscoacoustic effects were determined using tomography. Fully integrated into the sequence, this method calculated measures of log spectral ratio in demigrated space, mitigating stretch and tuning effects. The resulting combination of the complete visco-acoustic model building flow compensated for the structural complexity of the area, whilst significantly improving the amplitude fidelity of the dataset.
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Seismic Inversion for Near Surface Applications and the Derivation of Geomechanical Properties
By A. FoggSummarySeismic inversion methods broadly fall in to two categories; conversion of seismic event amplitudes in to reflectivity or the analysis primarily of seismic event arrival times (and waveform shape) to derive a velocity model. These are generically referred to as Acoustic Impedance (AI) inversion and Full Waveform Inversion (FWI) respectively, the former typically working from processed seismic reflectivity data and the latter being derived during the processing phase. Both procedures have application in the characterisation of the rock properties of shallow stratigraphic sections, indeed FWI is specifically designed (and limited to) no deeper than approximately 1500m below the mudline (though this depth is dependent on seismic acquisition parameters; notably cable length, water column height and subsurface velocity). This paper will review several different approaches to AI inversion, which can be calibrated to derive rock mechanical properties, and discuss their application to the near surface. The paper will also demonstrate how FWI can yield a high resolution image of near surface velocity which improves the seismic image and thus enhances AI inversion results. Case studies will be used to demonstrate the procedures and contrast the advantages and disadvantages of different methods.
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A Request for Quantitative Seismic Solutions for Drilling Hazards Assessment
By G. WoodSummaryIn this paper, we focus on the need to provide a quantitative approach to drilling hazard assessment and the benefits such an approach would have to reducing uncertainty and risk while potentially releasing marine real estate for drilling or developments that has previously been considered unuseable
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Towards QI for Site Investigation in Orsted
Authors K.H. Karkov and S. HviidSummaryA recently concluded Ørsted R&D project successfully demonstrated the possibility of extracting quantitative information on soil composition from 2D UHRS data by leveraging the acoustic inversion method.
Our contribution to the workshop will include an introduction to Site Investigation in Ørsted, a presentation and discussion of our identified key challenges related to acquisition, processing, calibration, interpretation and integration as well as our perceived status on these.
Examples from recent advances will be presented providing the status on commercial scale QI for site investigation purposes in Ørsted.
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Seismic Inversion for Geotechnical Problems
SummaryFor foundation design the geotechnical analyses and interpretations often rely on isolated 1D boreholes and the geophysical data is only used to confirm horizontal layering. The great amount of information capture in the geophysical data, not only related to layering but also related to soil parameters, are therefore not used. Geophysical data are collected in 2D lines and/or 3D volumes and therefore provides the natural link to re-populate geotechnical properties found in the 1D boreholes onto a larger area and thereby build a consistent and robust ground model. There is therefore a great potential in using this data in a quantitative way during all phases of a project.
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A Review of Seismic Attenuation Mechanisms, Measurements, and Inversion Strategies
By E. MorganSummaryThis segment of the Seismic Inversion for Marine Overburden Characterization workshop discusses the physical mechanisms responsible for intrinsic and scattering attenuation, rock physics models for intrinsic attenuation, common methods for measuring attenuation from seismic reflection surveys, and inversion strategies to estimate soil and fluid properties from attenuation measurements.
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Using Vs Measurements in Shallow Marine Sediment to Guide Vp Matrix Velocity Assessment for Seismic Inversion
By A. FoleySummaryMeasuring seabed velocities by transmission surveying, as opposed to those measured by reflection surveys, gives key, unambiguous results. By determination of Vs, which only responds to the sediment matrix, a more useful value of Vp can be found. Geotechnical engineers refer to this as the “drained” velocity. This value for Vp allows practitioners to calibrate inversion results and derive meaningful values for several engineering parameters of seabed soils.
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A Deep Learning Approach to Quantitatively Characterising the Marine Near-Surface
Authors M. Vardy and T. DarnellSummaryIn this paper, we present a Deep Learning workflow developed specifically for inverting marine site investigation data, comparing and contrasting it against the results obtained using traditional stochastic inversion algorithms with both synthetic and field data. In particular, we assess its potential for rapidly deriving a range of subsurface parameterisations, including geotechnical engineering properties of direct interest for various site investigation problems.
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Porosity Prediction from Shallow Subsurface Seismic Investigation - A Rock Physical Model Approach
Authors Guillaume Sauvin, Maarten Vanneste, Park Joonsang and Madshus ChristianSummaryIn this paper, we present a rock physical model to estimate the porosity from the seismic velocities and compare it with existing rock physical models. A parameter sensitivity analysis is also conducted and the various models are validated with lab data. We also propose a workflow to predict the porosity from seismic velocities at field scale and apply it to a case study.
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Time-Lapse Imaging of the Shallow Subsurface at Decimetre Scale Resolution
Authors M. Faggetter, M. Vardy, J. Dix, J. Bull and T. HenstockSummaryHigh-resolution seismic data provides information for many applications including offshore engineering work, where an accurate characterisation of the shallow marine subsurface is essential. However, single 3D volumes only provide a temporal snapshot and do not fully capture the highly dynamic nature of shallow water environments. Although changes at the seabed can be interpreted from repeat bathymetry, only very limited information about the substrate below. Here, we discuss the application of multiple, collocated, ultra-high-resolution (kHz-range) 3D seismic surveys as a tool to investigate changing processes in the marine subsurface. Examining data acquired with the 3D Chirp sub-bottom profiler, two case study examples will be presented. Results illustrate the capability for quantitative mapping of subsurface differences at decimetre-scale resolution using bin sizes of 0.25 cm and smaller.
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High Resolution Imaging and Quantitative Analysis of HV Cable and Pipeline Trenching in the Marine Environment
Authors Justin Dix, Mark E Vardy, Michael Faggetter, David White and Peter AllenSummaryThe life time performance of both HV cables (ORE inter -array and export cables and cross-continental shelf interconnectors) and oil and gas pipelines are limited by the physical properties of the sediment in which the cable/pipeline is buried. In the case of HV cables the burial material and burial depth have implications for heat dissipation from the cable, which in turn plays a primary role in cable rating and its lifetime operation and maintenance. For a pipeline changes in the density and strength of the overburden material can impact on buckling potential once in operation. Our current understanding of the key physical parameters of the sediment (e.g. grain size, porosity, permeability, thermal conductivity, relative density and strength) are based on in situ measurements of the ambient condition and rarely take account of physical property changes during the trenching process. We provide initial acoustic inversion results from high resolution 3D Chirp volumes from both a prototype scale, CPT calibrated, tank experiment and in situ trenched cables in a range of substrates. We shall demonstrate the potential of acoustic inversion to non-destructively quantify trench disturbance in this critical engineering scenarios.
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Sub-Surface Imaging at the Rockall Basin, Using Travel Time Tomography and Full Waveform Inversion
More LessSummaryThe geological structure beneath the Rockall basin and the nature of the crust are largely undefined because of the sill intrusion, lack of the seismic data coverage and deep well data penetration. The basaltic rocks prevent the seismic waves from travelling underneath them and make it hard to image below these high velocity layers. Here, we perform travel time tomography on long streamer data sets along a 80 km long profile to get a smooth P-wave velocity model using the first arrival travel time. The 2D seismic lines were acquired in 2013–14 using 10 km long streamers. We pick first arrival travel time from the shot gather after cleaning the data set. The velocity model obtained here, indicate the velocity from 1.6–4 km/s for the sediments and we also observe very high velocity ~ 6–7 km/s just 3 km below the sea-floor. This high velocity structure could be the lower crust pinching out at the Rockall high. This velocity model is used as a starting model for full waveform inversion (FWI) to get a higher resolution velocity structure.
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Opportunities and Challenges in Multi-Component Processing
More LessSummaryThis talk gives an overview of the opportunities for a wider use of multi-component data and the requirement for the processing which needs to be met in order to ensure that the full value of the data are realized.
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Multi-Component Processing on Land for Complimentary PP and PS Imaging and Characterisation
Authors R. Johnston and A. AyreSummaryThe use of multi-component seismic data has risen steadily since the ‘pure’ shear-wave acquisition activity onshore of the 1980s, through the converted-wave ‘revolution’ offshore in the 1990s and beyond. To benefit the most from multi-component seismic we hope for a situation where data quality of the entire elastic wavefield is similar which allows the complimentary information from compressional and shear waves to contribute together. Where either of these waves are compromised, the combined potential will necessarily be sub-optimal. To respond to Canada's Northern Alberta shallow unconventional reservoirs and provide high resolution imaging and characterisation, the industry has developed using point source and multi-component point receiver seismic. We describe the challenges addressed in processing for high resolution PP and PS imaging which deliver improved images and complimentary PP and PS attributes for characterisation. In this heavy oil unconventional reservoir setting, PS images are revealing new details about the geology not previously seen on P-wave data alone. The multi-component data have positively influenced an appraisal drilling program and subsequent pad layout, to take advantage of the geological variations and high grade the reservoir development plan.
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Extraction of Acquisition and Processing Attributes from a Time-Lapse Ocean-Bottom Seismic Elastic Finite-Difference Study
Authors R. Whitebread, P. Kristiansen and M. BranstonSummaryObserving changes of seismic amplitude and event timing over time within recorded seismic data are a well-established path to understanding the subtler changes to reservoir properties during injection and production phases of reservoir development. To understand the impact of acquisition tolerances and factors such as noise, ghost, and multiple energy on these reservoir changes, we must move away from real recorded seismic data and look at key issues in isolation with synthetic data.
We created a small four-component ocean-bottom seismic (OBS) data set using elastic finite-difference modelling where we have full control of the physical changes at the reservoir as well as free-surface effects and deviations from nominal acquisition geometry.
We chose elastic finite-difference modelling to include interface waves into PP and VZ data as well as to allow full modelling VX and VY components to infer 4D response from the subsequently derived radial component.
Our results confirm that geometry errors rapidly degrade the observed 4D response, but that the cumulative effect of geometry deviations, tidal statics, and water velocity corrections could also mask expected reservoir changes.
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Multi-Component Seismic Data Processing of a 3D 3C Dataset for Sand Filled Channels and Rock Property Identification via PP/PS Joint Inversion : A Case History
More LessSummaryMulti-component seismic data processing of a 3D 3C dataset for sand filled channels and rock property identification via PP/PS joint inversion: A case history.
In this case history, we present improvements in sand filled channel identification and associated fracture detection, including fracture density and orientation. This was achieved by performing seismic data processing of vertical component (PP) and converted wave (PS) data for a 3D 3C dataset.
A superior quality image of the P-wave using 3D 3C data will be demonstrated by the robustness of the applied processing sequence and consistency of the utilized processing and Q.C. tools. In addition, we will demonstrate in detail the converted wave measured from the horizontal component processing.
Incorporating the interpreter's geological knowledge into the processing workflow is extremely crucial where intermingling of the data processing sequence, algorithms and geological knowledge plays a major role in obtaining successful final PS data results. Integrating PP / PS images by introducing both components in one processed solution should alleviate the interpretation challenges at the target reservoir interval, due to the added precision in elastic properties derivation through the PP/PS joint inversion process.
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Multi-Component Seismic Data Processing of a 3D 4C OBC Dataset for Lithological Identification Through PP/PS Joint Inversion: A Case History
More LessSummaryIn this case history we present the advantages and improvements in lithological discrimination and identification by implementing a robust seismic data processing workflow of vertical component (PP) and converted wave (PS), for a 3D 4C dual sensor OBC dataset.
The image quality of the P-wave using dual sensor data will be demonstrated by the robustness of the applied processing sequence and quality control tools. We will demonstrate in details the converted wave measured from the horizontal component processing, where the interpreters geological knowledge, incorporated into the integration of processing applications, plays a major role in the success of the final PS data results.
Integrating PP / PS images and introducing PP, PS processed data in one solution should enhance the interpretation resolution at the target interval. Improved Vp/Vs for prominent markers and more accurate AI through PP/PS joint inversion is continuously evaluated throughout the processing workflow. Eventually, our main objective is the utilization of PP/PS processed data in joint inversion to produce accurate lithology discrimination maps.
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Anisotropy processing of multi-component seismic data – Part 1: Theory and Implementation
More LessSummaryAn oil-gas reservoir can be treated as an orthorhombic medium which can be considered as a combination of VTI and HTI media. It means, for a given azimuthal direction, that an orthorhombic medium can be treated as a VTI medium. To process the seismic reflection data acquired from such a medium (the reservoir), the common practice is to separate the processing into two stages: anisotropy processing for a VTI medium and anisotropy processing for a HTI medium. In the first stage, we can ignore the HTI features and apply VTI anisotropy processing to this data, from which we can estimate the velocity and anisotropy parameters and obtain seismic images. Actually, the results are the average results for the whole dataset. Then we use the estimated velocities and anisotropy parameters as an initial model for HTI processing. In HTI processing, we need to separate the seismic data according to the azimuthal direction of the offset. Then we can carry on VTI processing for each set of azimuthal data. The results will be dependent on the azimuthal direction. The azimuthal dependence of velocity and anisotropy parameters can be used to estimate the fracture direction and strength of anisotropy of the reservoir.
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Anisotropy Processing of Multi-Component Seismic Data – Part 2: Processing Demonstration Based on CXtools
More LessSummaryIn Part 1, I introducted the theory for anisotropic processing in VTI and HTI media and CXtools, a processing package which implements the theory. In this part, I will show how to use CXtools to carry out anisotropic processing based on a 3D multicomponent seismic dataset. During the demonstration, I also show how to adjust the velocity and anisotropy parameters to improve the results. This live demonstration is separated into three sessions:
- How to run the CXtools
- Anisotropic processing for VTI media
- Anisotropic processing for HTI media
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Anisotropy Processing of Multi-Component Seismic Data – Part 3: Pre-Stack Time Migration
More LessSummaryPrestack time migration is an efficient imaging method for processing seismic data due to its input/output flexibility and target-orientation, and has recently become a routine step in the seismic data processing flow. Prestack Kirchhoff time migration can produce high-quality migrated images from real seismic data with the correct velocity models. Important issues in applying prestack time migration are how to obtain the correct velocity model, and selecting suitable travel time formulae for different wave types (PP and PS) in different media. In this part, I will introduce the theory for prestack time migration in a VTI medium, and a method for obtaining the optimal velocity model for prestack time migration from seismic data.
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How High Can We Go? Pushing Limits of Lateral and Vertical Resolution in Deepwater Seismic
Authors P. Hatchell, P. Dutta, S. Bakku and Z. YangSummaryWe acquired low-cost high-resolution 3D (HR3D) streamer seismic surveys using the P-Cable system with a small air-gun source array (300 in3) over deepwater fields with water depths ranging from 900m to 3000 m. The P-Cable HR3D streamer system employs multiple short streamers (100 m) connected to a cross-cable. In our surveys we deployed 18 streamer cables with each of the 100 m streamer cables having 16 hydrophone groups spaced at 6.25 m intervals. With shot intervals spaced every 12.5 m, the nominal bin size of this configuration is 6.25 m × 3.125 m and the fold is four. In the Shallow sections, we achieved migrated images with frequencies up to 200 Hz. The lateral resolution of the images is found to be superior to that from high-resolution processing of conventional data (streamer and OBN). In the deeper section, the frequencies dropped to much lower values indicating that the earth has more control on the high frequency end than the geophysicist.
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Imaging with Near-Field Hydrophones
Authors Pete Nevill, Kevin Davies, Shanice Mohammed, Krzysztof Ubik, Richard Jupp, Ed Kragh and Philip ChristieSummaryNear Field Hydrophone (NFH) data are routinely collected during marine acquisition and historically these data were used to QC air-gun timings and/or other air-gun-related issues. More recently (last 10–15 years), these data were recorded and employed during processing to aid both 1D and 2D source-signature deconvolution. The results presented here demonstrate it is possible to obtain a high-resolution image (greater than 100 Hz) of the near subsurface (0–1 s) using passive NFH array data. Similar results are also achieved with the active NFH array although noise handling in processing is more difficult. NFH data for imaging, can be a natural by-product of conventional marine seismic acquisition, with minimal additional processing cost. Potential uses could include: replacing requirements for a high-resolution 2D acquisition for site surveys, utilizing a source-only vessel for localized overburden and reservoir 4D monitoring, as well as improved deghosting and integration with distributed acoustic sensor vertical seismic profile data.
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Broadband De-Signature for Air-Gun Arrays
Authors R. Telling and S. GrionSummaryDe-signature processing of broadband seismic data demands reliable signature estimation in the band 2–200 Hz. Here we discuss estimation of signatures via inversion of near-field hydrophone data. This uses a model for the propagation of energy from each source point to each hydrophone in the array, incorporating bubble motion and ghosting at the sea-surface. In the standard approach we solve for a set of notional sources, assuming a simple model for the ghost, with rough sea effects treated statistically using a frequency and angle varying reflection coefficient corresponding to the observed sea-state.
We discuss the successes of this standard approach and observed problems, specifically with predicted ghost amplitudes, that in practice leads us to parametrize the model using effective sea state parameters often larger than observer logs suggest. The physical reasons for this are linked to onset of cavitation in the water column. We then present results for an alternative approach, employing additional hydrophones, that solves directly for the down-going part of the signature without need for ghost model parametrization. We assess the quality of signatures estimated via this approach, their application to de-signature processing and examine sensitivity of this inversion to noise compared to the standard parametrized approach.
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New Wave Seismics
More LessSummaryThis talk will focus on the field of seismic oceanography. Seismic oceanography exploits acoustic energy reflected from temperature and salinity boundaries in the water column to map oceanic structure at unprecedented horizontal resolutions. New insights into four-dimensional ocean dynamics that marine seismic data has to date provided, along side potential future applications, will be reviewed. In addition, the challenges and opportunities presented by processing water column seismic reflection data, as opposed to sub-surface datasets, will be discussed. Advances include: estimating temporal changes in the water column during seismic data collection; quantifying noise, water turbulence and wave energy from seismic data; and inversion techniques to extract the high resolution temperature and salinity structure with precision uncertainty. Such non-conventional approaches to seismic data processing, alongside better quantifying the influence of the water column on the quality of marine seismic data, will be of interest to this community. Finally, the integration of autonomous systems into the acoustic mapping of oceanic thermohaline structure will be considered.
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Finite Difference Modelling Including Dynamic Speed of Sound in Water
Authors K. Davies, J. Stefani, L. Zhuo and T. JohnsenSummaryIdentifying and implementing fit for purpose Earth complexity in synthetic modelling is an important part of testing the ability to recover broadband signal. Effects of dynamic speed of sound in water Vw(x,y,z,t) have widely been recognized in 3D marine processing, although 4D often highlights the complexity and requirement for adequate measurement and correction. Corrections are applicable to conventional 3D and VSP marine applications, even if the effect is not immediately obvious. In 2013 Chevron in conjunction with WesternGeco investigated, quantified and ranked the effects of Vw(x,y,z,t) in streamer 4D using finite difference modelling. However, modelling with Ocean Bottom Node data presents additional challenges. In 2015, Chevron built a complex 4D dynamic water column model closely based on Vw(x,y,z,t) observation. The model was specifically designed for evaluation of 4D OBN data. Processing in conjunction with CGG demonstrated the significance of no-correction, after typical correction and with alternative methods, including Up-Down deconvolution, the latter demonstrating a remarkably good efficient solution. Furthermore, Up-Down deconvolution enables efficient source signature deconvolution for enhanced bandwidth. Including the complexity of Vw(x,y,z,t) in modelling has enabled estimation of 4D signal to noise and design of mitigation measures in both acquisition and processing.
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Why 4D Broadband is the Next Standard for Reservoir Monitoring Studies?
Authors D. Lecerf, B. Caselizt and C. ReiserSummaryFor the last ten years, the seismic industry has been offering broadband 3D seismic. Broadband acquisition and processing technologies are appealing for 4D time-lapse surveys. As for any 4D requirement, they must deliver seismic signal repeatability for an extended frequency range to be qualified as a 4D broadband solution. Multisensor streamer systems offer an optimum platform for acquiring 4D broadband data in an efficient way. Deeper tow depths give a better signal-to-noise ratio and allow an improved acquisition weather window. In addition, multi-sensor recording provides receiver ghost-free data insensitive to the sea state.
We will discuss the different options for introducing a new broadband dataset into the 4D reservoir cycles. In a genuine 4D broadband acquisition context, we will describe how the repeatability of broadband streamer data can compete with the repeatability of 4D OBN and why an extended bandwidth 4D signal allows to better characterize the seismic image variations due to reservoir production. Finally, we conclude that 4D broadband acquisition, processing and interpretation can complete the challenge of quality and efficiency improvement.
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Multi-Parameter Waveform Inversion Using Broadband Data from the North West Shelf of Western Australia
Authors C. Manuel, J. Washbourne, D. Sibley, L. Duranti, M. Merino and B. BoulahanisSummaryWe present a multi-disciplinary approach to determine overburden anisotropy on the North West Shelf of Australia. Beginning with a synthetic dataset we demonstrate the significance of incorrect overburden anisotropy in seismic imaging and develop a workflow for solving the problem. This is followed by application of our workflow to a field case study involving the use of geological inference, log-based rock property relationships, and surface seismic data. Comparisons are made between applying the workflow using conventional and broadband streamer datasets acquired over the same area.
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High-Frequency Full-Waveform Inversion: Just How High Should You Go?
Authors A. Ratcliffe, S. Bretherton, B. Xiao and R. HaackeSummaryWe pose the question, “how high a frequency should you go to in FWI?” The answer depends on your objective: the traditional processes of imaging, reservoir characterization, and interpretation, or as a potential complete replacement for these. In this paper we discuss and demonstrate the impact of the maximum frequency in the FWI velocity model on these processes, using data sets from the North and Norwegian Seas.
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Low Frequencies Unlock Visco-Acoustic Full Waveform Inversion Capability in Trinidad
Authors C. Theriot, T. Fox and S. BarronSummaryA large Ocean Bottom Node (OBN) survey acquired off the east coast of Trinidad has allowed Shell the opportunity to deploy another application of its visco-acoustic Full Waveform Inversion. The setting is ideal, with pervasive shallow gas covering the area resulting in dispersion and attenuation. A proper and accurate earth model including the Q anomalies in this area is more accurately determined with visco-acoustic FWI over tomographic methods given shallow water depths resulting in incoherent shallow images and migrated gathers. In addition to the Q-field, the inversion will also derive the velocity field including the resulting slow-downs from these gas zones and ultimately improve image quality. The higher quality low frequencies recorded by the OBN has resulted in a more accurate and geologically reasonable model where previous Full Waveform Inversions using streamer data have left inaccuracies. And from this more accurate model, we present a substantial image uplift.
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Broadband FAZ Land Data: an Opportunity for FWI
Authors O. Hermant, A. Sedova, G. Royle, M. Retailleau, J. Messud, G. Lambare, S. Al Abri and M. Al JahdhamiSummaryThere are very few applications of full waveform inversion (FWI) on land data. This is commonly attributed to data-specific challenges. However, modern broadband full-azimuth (FAZ) land surveys offer an extraordinary opportunity for applying FWI. They have dense surface and offset sampling X and Y directions, and contain very low frequencies down to 1.5 Hz. We demonstrate in this study and in other real data examples from the Sultanate of Oman that it is possible to benefit from the broadband spectrum of modern land acquisitions to obtain a high resolution velocity model reliably using FWI.
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Does Broadband Address the Cycle Skipping in Complex Areas?
By D. VighSummaryFull-waveform inversion (FWI) is a high-resolution model building technique that uses the entire seismic record content to build the earth model but have struggles with cycle skipping . Conventional FWI usually utilizes diving and refracted waves to update the low-wavenumber in other words the background components of the model; however, the update is often depth-limited due to the limited offset range acquired. To extend conventional FWI beyond the limits of the transmitted energy, we must use reflection data as well with broad band preprocessing.
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Towards Lateral Broadband
Authors R. Soubaras and B. GratacosSummaryNew acquisition techniques and the evolution of broadband processing in the past ten years have enabled the extension of the frequency bandwidth from the conventional three octaves bandwidth [10Hz–80 Hz] to a six octaves broadband bandwidth [2.5Hz–160Hz]. Despite this impressive achievement, some problems still remain:
- The broadband processing sequence has become very complex.
- This processing sequence makes a heavy use of sparse tau-p transforms in steps like receiver deghosting and regularization. However, the underlying assumption that a shot point can be locally decomposed in a few linear events can be questionable.
- The lateral resolution has not increased in the same proportion as the vertical resolution.
In order to solve these problems, we show that we can obtain a significant increase in lateral resolution by using for the final imaging a least-squares migration with ghost and multiple modeling, allowing the deghosting, regularization and multiple attenuation being handled by the inversion. This is assessed on a real 3D dataset with depth-slices showing an increase in wavenumber bandwidth similar to the increase already obtained in frequency bandwidth.
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Imaging Including Internal Multiples: Influence of Broadband Acquisition
By E. VerschuurSummaryNowadays there is a strong trend towards considering multiples as genuine part of the seismic response and, therefore, including this in the imaging process.
For surface multiples, this has already shown successful in various applications over the last decade.
For the correct imaging of internal multiples, there is a debate whether removing internal multiples can be more fruitful than trying to image them. In this paper we will show the added value of properly including internal multiples in the imaging stage, where the transmission effect is also being accounted for. In this way the imprint from a multiple-generating overburden is also minimized.
Finally, it will be demonstrated that acquiring data with a broadband acquisition set-up, the effect of internal multiples is already greatly reduced, which inceases the abilities to treat them properly in the imaging stage.
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Thermal Modelling of Magmatic Geothermal Systems: the Role of Deep-Seated Heat Sources
Authors G. Gola and A. ManzellaSummaryWe present the results achieved in the framework of different research projects, i.e. the Geothermal Atlas of Southern Italy, the Image, the Descramble and the Gemex Projects, mainly focussing on the thermal aspects of four geothermal fields developed in magmatic setting. We applied an integrated method in order to set-up numerical models able to simulate the conductive-convective thermal structure of the Ischia Island (southern Italy), Long Valley Caldera (eastern California), Acoculco caldera complex (eastern Mexico) and Larderello-Travale (central Italy) geothermal systems. We propose a numerical approach implemented in a Finite Element environment capable to evaluate the contribution of the main variables that characterize the magmatic heat source and the geothermal reservoir. The final 3D thermal models were achieved via the optimization of the available temperature measurements in deep boreholes tacking into account the thermal effects of the interplay between the free convection and the topographically driven groundwater flow, the reservoir permeability and the thermal load released by the parametrized heat source. Our results contribute to better understand the relationship of magmatism to geothermal resources in continental settings.
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Laboratory Studies of Organic and Inorganic Geothermal Tracers at Superhot and Supercritical Conditions
Authors Muller Jiri, Sissel Opsahl Viig and Helge StraySummaryLaboratory studies have been performed at testing stability of organic and inorganic tracers at super-hot and supercritical conditions. Both static and dynamic tests have been performed at specially constructed equipment which can tolerate such hard conditions. In some cases these tests indicate no rapid thermal degradation of the tested tracer candidates within the time frame of the performed stability test (2 months). In other cases the experiments indicate interactions between the rock material and the tracer candidates.
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Seismic AVO Inversion for Geothermal Reservoir Characterisation
Authors E. Dalgaard, K. Bredesen, A. Mathiesen and N. BallingSummaryA field case is demonstrated to show how 2D seismic AVO inversion together with well log analysis can aid reservoir characterization of a geothermal play in the northern Zealand of Denmark. From the seismic inversion it is possible to interpret different lithologies and estimate porosities via links established at well logs. Several connected high porosity sands were predicted, and with an expected temperature of around 50C in the target zone this gives room for a potential good geothermal reservoir. With this specific field case it is demonstrated how seismic AVO inversion can be applied where geothermal reservoir characterisation is needed in order to obtain a better understanding of potential geothermal plays.
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Geothermie 2020: Exploration and Development of Geothermal Energy in Geneva
More LessSummaryThe deployment of renewable energy sources for both power and heat production is accelerating in Switzerland, a trend that will continue, thanks to the 2050 Swiss Energy Strategy that aims at gradually phasing out nuclear power by reducing the energy consumption and increasing heat and electric power generation from renewable energy sources. Geothermal energy will be an important resource to supply heat and power for industrial, agricultural and domestic use.
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Exploration of Geothermal Reservoirs: an overview and future opportunities
By P. JoussetSummaryAn overview of geophysical exploration methods for geothermal reservoir is proposed. Focus is made on the integration of seismic attributes and resistivity structures, with examples from Iceland and Mexico. Future targets include magma chambers and urban environment.
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