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77th EAGE Conference and Exhibition - Workshops
- Conference date: June 1-4, 2015
- Location: Madrid, Spain
- Published: 01 June 2015
1 - 50 of 128 results
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4D Forward Modelling to Optimize a Closed-loop Seismic Reservoir Monitoring Work-flow
Authors D.I. Hill, D. Lowden, S. Sonika, M. Paydayesh, V. Dimova, K. Westeng and K. EggenbergerSummaryThe historic closed-loop seismic reservoir monitoring workflow is redefined to incorporate the geologic, reservoir simulation, and geomechanical models into an integrated full-field coupled Dynamic Integrated Earth Model (DIEM) to surface. From which elastic parameters for a range of reservoir simulations can be derived via the petro-elastic rock-physics model for input into the field-wide finite-difference forward-modelling with realistic calibrated noise, imaged to produce a high-fidelity prediction of the 4D signal. The Chimera geologic, reservoir, and geomechanical models were integrated into a DIEM. The Chimera turbidity type reservoir model has a maximum sand porosity of 0.25 and a maximum permeability of 200 mD with light oil and an initial gas cap supported by an aquifer from the bottom, accumulated within a structural trap segmented by normal faults. Production scenarios are simulated at the reservoir pressure corresponding to the baseline date, and four future realisations. These are transformed into elastic properties for the finite-difference forward-modelling. The modelled data with calibrated noise for each scenario is imaged, and differenced to quantify the type, magnitude and location of the 4D signal. Hence we determine if the base-line or an alternative geometry will measure the 4D signal at the required time-step and consequently if the reservoir is a candidate for seismic reservoir monitoring.
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Monitoring Changes in the Overburden – Some Observations from Using Various 2D and 3D Seismic Time Lapse Data Sets
More LessSummaryIn 1989 a major underground blow out developed when well 2/4-14 was drilled into a target reservoir at 4.5 km depth in the North Sea. 2D seismic data was acquired both prior to and during the underground blow out. In addition to these data, we use two 3D seismic data sets, one acquired 2 years after the blow out, in 1991 and another acquired in 2005. By comparing various data, we can analyse both short term and especially long term movements of hydrocarbon flows in the overburden. Since there is significant amount of shallow gas in the area, it is a challenge to discriminate between in-situ shallow gas and gas originating from the underground flow. We find that the combination of slightly dipping shallow glacial sand layers and ice berg plough marks serve as a trap for shallow gas. This can be mapped from the 3D seismic data, as well as flow of gas due to the underground blow out.
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Estimating Overburden Velocity Changes from Pre-stack Time Shifts Using Linear Tomography
Authors J.A. Edgar and T.D. BlanchardSummaryProduction from oil and gas fields induces velocity changes and strains in the subsurface, which create time shifts between vintages of time-lapse seismic data. Recovering these time shifts can be useful for reservoir management, particularly through calibration of geomechanical models. Rickett et al. (2007) and Williamson et al. (2007) have shown that these shifts can be estimated using non-linear inversion of poststack time-lapse seismic. These existing inversions of post-stack data assume that the seismic ray paths in all vintages are vertical. However, examining pre-stack time-lapse data shows that the recorded time shifts are offset dependent. To estimate the true subsurface changes we must invert pre-stack time-lapse seismic, which requires more accurate modelling of the seismic energy propagation. This abstract introduces a new tomographic inversion of pre-stack time-lapse seismic which aims at estimating the velocity changes that explain all pre-stack time shifts. We retain the assumption of the existing post-stack methods that the ray paths do not change between vintages, but discard the assumption that they are vertical. This allows a linear tomography system to be set up and solved for velocity change. We test this method on synthetic data and compare the results with an existing post-stack approach.
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3d and 4D Imaging Using a Non-destructive Ambient Noise Seismic Interferometry
Authors N.M. Shapiro, S. Singh, A. Mordret and G. TomarSummaryIn recent years there has been increasing interest in the study of so-called ambient noise seismic interferometry. This method is used to extract meaningful information from long recordings (hours to days) of ambient seismic noise. This meaningful information is extracted in the form of wavefields propagating between those receiver positions at which the noise was recorded, i.e., as if a source had been placed at one of those locations - a so-called “virtual source”. The method has found most success in global/regional seismology where low-frequency (sub-1 Hz) fundamental mode surface waves are extracted by cross-correlating months of ambient noise recorded on two or more receiver stations. Whereas the most successful applications of the method have been in recovering surface waves propagating between receiver locations, other successful applications have seen the recovery of body waves. Another very appealing aspect of the ambient noise interferometry is the possibility to use it for time-lapse or continuous un-invasive monitoring of the subsurface properties.
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A Well-to-seismic Interpretation of Interwell Connectivity Using Well Behaviour Data and 4D Seismic Surveys
Authors Z. Yin, C. MacBeth and R. ChassagneSummaryA technique is proposed to quantitatively measure inter-well connectivity by correlating multiple 4D seismic monitors to historical well production data. We make use of multiple 4D seismic surveys shot over the same reservoir to generate an array of 4D seismic differences. Then a causative relationship is defined between 4D seismic signals and changes of reservoir fluid volumes caused by injection and production activities. This allows us to correlate seismic data directly to well data to generate a “well2seis” volume. It is found that the distribution of the “well2seis” correlation attributes reveals key reservoir connectivity features, such as the seal of faults, inter-reservoir shale and fluid flow pathways between wells, and can therefore enhance our interpretation on inter-well connectivity. Application of our proposed technique proves that the well2seis attribute agrees with geological interpretations better than conventional well connectivity factors based on engineering data only. Additionally, combining with a conventional inter-well study method, this multiple 4D seismic method is found to support the conventional inter-well approaches and can provide more robust and detailed interpretation.
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Effective Imaging of Reservoir Fluid Changes
Authors O. Salako and C. MacBethSummaryMonitoring of changes in brine chemistry (salinity and temperature), during water-flooding is important for injector optimisation, understanding efficiency, detecting early water breakthrough, locating bypassed hydrocarbons or detecting scaling in the heterogeneous reservoir. It is already known that water injection into the oil-leg of a hydrocarbon reservoir can be monitored by both seismic acquisition and also CSEM methods. The problem of an interfering pressure signal for seismic impacts quantitative evaluation for time-lapse analysis, whilst with EM there are the counterbalancing effects of salinity and temperature. CSEM becomes favoured when the pressure effects on seismic are dominant, or heavy oil is present with similar acoustic properties as the formation and injected waters. The quality of measurement for both methods is influenced by reservoir facies variations, acquisition repeatability and overburden heterogeneity. Time-lapse seismic is unlikely to detect brine distributions injected into the water-leg or aquifer, although it may detect associated pressure up effects. However our calculations show that it may be possible for time-lapse CSEM to distinguish the inter-mixing of different brines in the subsurface hydrocarbon reservoir. Specifically, low salinity injection or injection into a highly saline formation can clearly be detected with this technique.
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Measurement and Potential Applications of Time-lapse Attenuation
Authors T.D. Blanchard and J.A. EdgarSummaryCan we use other time-lapse seismic attributes to compliment our measurements of travel-time and reflectivity changes? In this paper we have measured attenuation changes in a seismic reservoir undergoing depletion and in some locations water injection. We will discuss these measurements in three sections, covering:
1.Potential uses of time-lapse attenuation measurements. What can we use them for? Time-lapse inverse Q? Interpretation? For this we will show an example of trying to separate water and gas saturation effects.
2.Real signal or an artefact? Could we just be looking at an apparent effect from, for example, migration using the same velocities for all vintages? Is a dedicated workflow necessary to extract what might be very subtle signals?
3.What are the underlying mechanisms controlling attenuation? What could we learn if we made these time-lapse measurements in other reservoirs?
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Application of Full Wavefield Inversion to 4D Seismic Data - Workflow and Field Data Examples
Authors G. Chen, P. Routh, X. Lu, M. Helgerud, S. Lazaratos and D. JohnstonSummaryAdvances in full wavefield inversion (FWI), 4D seismic technology, and depth migration of seismic data have led to the application of FWI to 4D seismic data in which time lapse changes of velocity model can be directly obtained from the data. It has been shown that correcting for velocity changes due to production in depth migration improves 4D imaging repeatability. In this paper, we present a detailed workflow to correct for large acoustic velocity changes due to production using the FWI 4D results. Through FWI 4D application, we achieved seismic processing cycle time reduction in a recent 4D seismic project. We have also tested the FWI 4D methodology in areas of poor seismic repeatability due to production facility obstruction to seismic data acquisition.
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Full Elastic Non-linear Inversion the Key to 4D
By A. GisolfSummaryUsually great emphasis is placed on the repeatability of seismic acquisition for time-lapse purposes. However, the non-linearity of the relationship between seismic time-lapse data differences and time-lapse property changes is usually ignored. In this paper it is demonstrated that ignoring the non-linearity can cause serious errors in time-lapse interpretation, whereas application of full elastic non-linear inversion to base-line and time-lapse surveys separately, fully accounts for the non-linearity and gives quantitatively very accurate results. In addition, it is well understood that full elastic non-linear inversion is less sensitive to noise and acquisition imprint. The method is illustrated with the help of a synthetic time-lapse example based on real logs.
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An Engineering-consistent Bayesian Scheme for 4D Seismic to Simulator Inversion
Authors S. Tian and C. MacBethSummaryA workflow is designed to integrate simulator to seismic predictions into the process of 4D seismic inversion using a coupled Bayesian scheme, and honouring the concept of reservoir engineering consistency (EC). The proposed approach is demonstrated by an application to a West Africa dataset. The results show the benefits of being EC when working across domains during a “close the loop” exercise.
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Engineering Consistent Constraints for the Inversion of Changes in Pressure and Saturation on Ekofisk
Authors M.Y. Wong, C. MacBeth and A. BertrandSummaryA high resolution, time lapse seismic inversion into pressure and saturation changes is performed. This provides insights into well performance and pressure distribution within a geo-mechanically active chalk reservoir (Ekofisk). The inversion is constrained by reservoir engineering concepts and predictions to reduce the non-uniqueness involved, and to maintain consistency with the physics of flow. At the heart of this inversion scheme is the effective union of engineering data and different seismic products such as reservoir time strain, percentage changes in elastic properties to influence the inversion. Quantitative interpretation on this field using the inversion results shows good agreement with well production data and helps to explain strong localised anomalies in both the Ekofisk and Tor formations. Analysis shows that the hardening signals around producers are due to lack of pressure support and reservoir compaction; whereas softening signals are attributed to high pressure flooding around injectors.
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4D Reservoir Analysis beyond 1D Convolutions
Authors A. Khalil, H. Hoeber, A. Jafargandomi and S. de PierrepontSummaryAnalysis of time-lapse data is performed on migrated seismic images, which represent the spatial and time-lapse variability of the medium’s reflectivity. The process of migration effectively rotates the wavelet so that it is normal to the imaged reflectors. Processes used in 4D reservoir analysis such as deconvolution, inversion and warping need to follow the structure of the data. The traditional 1D (vertical) convolutional approach does not honour this directivity. For this reason, we introduce a wave equation based approach which provides an effective platform for structurally consistent reservoir analysis. This includes applications such as wavelet extraction, warping and 4D time-strain inversion.
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Quantifying Time-lapse Seismic Signal Detection for the Otway Project Using Prestack Migration
Authors M. Alajmi, A. Bona and R. PevznerSummaryDuring Stage 2 of the Otway CCS Australian project it is planned to inject a small, up to 15,000 tonnes of gas, into a saline aquifer located at depth of 1500 m. In CO2 sequestration, the ability to detect CO2 plumes is one of the main purposes of using time-lapse seismic imaging. The detectability of CO2 in seismic time-lapse surveys relies on two main factors: a sufficiently strong signal and sufficiently small noise. Therefore, to model time-lapse seismic records, we need to model not only the seismic response of the geology and the plume but also the time-lapse noise. Because plume detection is determined by the S/ N, the ability to model realistic time-lapse noise is crucial in any feasibility study. In this work, we propose a more realistic approach by adding band-limited random noise to the pre-stack data (shot gathers) to match the S/N of field data. Using these noisy gathers we then compare the detectability of CO2 plume by using pre- and post-stack Kirchhoff migrations.
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Intra-survey Pressure Variations - Implications for 4D Seismic Interpretation
Authors V. Omofoma and C. MacBethSummaryDuring the time taken for seismic data to be acquired, reservoir pressure and saturation may fluctuate as a consequence of field production and operational procedures. This has consequences for the quantitative analysis of 4D seismic data and particularly for understanding of the pressure signal that diffuses rapidly into the reservoir over a time-scale of hours or less. A modelling study using actual acquisition data (permanent seabed sensors and also towed streamers), reveals that the signature of pressure variations in the pre-stack domain is complex, and thus the resultant post-stack image is not representative of the true reservoir mechanisms that caused the pressure changes. This is of particular concern when trying to accurately resolve small pressure changes away from wells with post-stack data. It appears however that larger signals closer to the well may still be detected adequately. Our results have implications for post-stack quantitative 4D seismic analysis, as well as processing and acquisition workflows for detailed seismic time-lapse studies.
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The Implementing Geological Disposal of Radioactive Waste Technology Platform
More LessSummaryAfter decades of bilateral and multilateral cooperation, several European waste management organizations decided, under the auspices of the EC, to join their forces to tackle the remaining research, development and demonstration (RD&D) challenges associated with the implementation of their respective geological disposal programs. The main objectives of the Implementing geological disposal of radioactive waste technology platform (IGD-TP) are to initiate and carry out collaborative actions in Europe to tackle the remaining research, development and demonstration (RD&D) challenges with a view to advancing the implementation of geological disposal programmes for high-level and long-lived waste in Europe. This paper presents the organisation of the work and the main Joint activities and projects to date, initiated by the IGD-TP members and supported for some of them by the European Commission under the FP7 framework programme.
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Microseismic, Acoustic Emission and Ultrasonic Monitoring in Radioactive Waste Disposal and Feasibility Studies
Authors J.M. Reyes-Montes, W.S. Pettitt, J.R. Haycox, M. Lopez-Pedrosa and R.P. YoungSummaryConstraining the volumetric extent of excavation damage zones (EDZ) around engineered structures has benefitted from the application of remote, scaled seismic studies that passively monitor the medium using microseismic (MS) and acoustic emissions (AE) techniques combined with active ultrasonic surveys. By mapping AE/MS locations, fracturing and rock deformation can be correlated with the different operations in a working repository, e.g. gallery excavations, pressurization of containment holes and thermal stresses from the waste. These technologies provide a unique means of monitoring in real time the evolution of the EDZ and rock volumes surrounding a disposal facility and particularly the potential for creation of paths for fluid communication between the facility and its environment.
This paper present presents a series of case studies where these methodologies have been applied for the imaging of damage development and containment capability of repositories excavated both in crystalline and plastic rocks.
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Near Field Characterization of Hard Rock Spent Nuclear Fuel Repository by Seismic Reflection
Authors C. Cosma, N. Enescu, E. Heikkinen, A. Joutsen and P. KosunenSummaryPosiva and SKB conduct RD&D activities for the safety assessment and to test disposal techniques in real deep-seated conditions. Brittle deformation zones and large fractures are considered to pose a potential risk for the mechanical integrity of the spent fuel disposal canisters. These are to be avoided in positioning of the deposition holes that will host the canisters, and they need to be identified during construction of the deposition tunnels and ultimately the deposition holes. Results from two high resolution seismic surveys carried out in ONKALO and Äspö HRL in 2013 are presented here, providing continuity information for several large fractures identified through geological mapping to cut the tunnels and/or boreholes. These were recognizable in transmission and reflection images produced from the seismic data sets.
We show that reflection seismic surveys are relevant to the detailed characterisation of crystalline bedrock. Relatively small-scale features, even single fractures, can demonstrably be detected. On the other hand, the detection of some distinctive features, even large-scale, can be uncertain if the survey layout is spatially constrained. Combinations of borehole and tunnel measurements using measuring arrays with diverse orientations helped reducing the location ambiguities and should be used in the future wherever possible.
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High-resolution Seismic Characterization of the Shallow Subsurface Applied to Civil Engineering
Authors D. Martí Linares, I. Marzán, J. Sachsenhausen, J. Alvarez-Marrón, I. Cienfuegos and R. CarbonellSummaryThe construction of the future Centralised Temporary Storage facility (CTC), a surface infrastructure built to manage and storage the nuclear waste for a lengthy time, needs the characterization of the near surface to assure the suitability of the construction and operating process. In this sense, a seismic characterization to regional and local level was carried out to understand the structure and the 3D geometry of the main stratigraphic units that can be related to a safe location of the CTC. Ten
kilometers of normal incidence seismic reflection data were acquired to understand the regional context, whereas a high-resolution 3D tomographic survey were carried out around the CTC location to obtain a detailed pictures of the shallow subsurface were the main buildings have to be built. Basically the main objective was to obtain the most detailed image of the geometry of the contact between the upper shallow lutites and the gypsum units that outcrop at the Eastern part and gently dip to the West. This information is very valuable from the engineering point of view during the design and construction of the main buildings of the CTC.
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Application of Diffrction Imaging and Steered Migration to 3D Seismic Data from the South West Hub CCS Project
Authors K.V. Tertyshnikov, S. Ziramov, A. Bóna and R. PevznerSummaryThe assessment of subsurface architecture and location of faults is key information in CO2 geosequestration projects. The 3D seismic survey has been acquired as a part of the SW Hub CCS project in vicinity of potential future CO2 injection sites. The acquisition was carried out within the Harvey and Waroona Shires about 150 km south-east from Perth, Western Australia. In order to support the fault detection and decrease uncertainties on the structural framework two additional imaging techniques have been applied to the 3D seismic volume. One is a diffraction imaging algorithm, the other is an alteration to the post-stack Kirchhoff migration – the steered migration. The application of these methods to the seismic volume enhanced the signal to noise ratio of the final migrated images and supported the understanding of fault distribution in the study area.
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Application Seismic Multiattributes Fuse Method in Shale Play
By W. LiuSummaryShale gas "sweet spot" usually refers to an area that contains high total organic carbon content (TOC) and has high brittleness, relatively developed fractures and thick favorable shale, high core pressure. High TOC ensures a high gas content of shale gas, and high brittleness and fracture development guarantees that an effective stimulated reservoir volume (ESRV) can form after fracturing, thus achieving fracture network communication. In this paper,we using seismict attribute to identify shale sweet spot.By elastic parameters crossplots analysis,we established the relationship between the TOC, brittleness and elastic parameters, and extrapolated to a three-dimensional block, we can getting the brittleness and TOC distribution.we can defined different sweet spots by how much the content of TOC&brittleness& pore pressuer.finally,we jointed all parameters by seismic attributes fuse method to identify shale sweet spot.
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Construction of Synthetic Shale Based on Physical Simulation Method
More LessSummaryIn this paper, a construction method of synthetic shale sample is proposed. Fine particles (3000–5000 mesh), brittle mineral, clay, carbonate, organic carbon and cement powder are mixed together in different amounts and then cold-pressed the mixture to obtain solid synthetic samples. And basic measurements of the finished samples are conducted in the laboratory to verify whether they are able to meet the requirements of relevant studies by simulating natural shale. The final sample similar to real shale cores in aspects of mineral composition, pore structure, seismic characteristics, etc. is constructed. The biggest characteristic of synthetic shale samples can be simply summarized as controllability, i.e., their mineral composition, diagenetic pressure, cementation degree, porosity, permeability, etc. can all be set according to experiment requirements, and an arbitrary combination of different factors is possible to meet multiple research needs.
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Decline Curve Analysis for Low Permeability Gas Condensate Reservoirs - Effect of Fluid Richness, Inertia and Coupling
Authors C. Johnson and M. JamiolahmadySummaryDecline curve analysis has been proposed as an efficient approach for estimating reservoir and well parameters especially in unconventional gas reservoirs where the use of conventional pressure-transient analysis is often technically and economically challenging. This study investigates the applicability of the widely accepted Fetkovich type curves to low permeability gas-condensate reservoirs under various operating conditions. A synthetic reservoir model based on one of the Fetkovich et al. (1987) case histories was first constructed and validated. Then the impacts of condensate gas richness, different rock types, relative permeability (kr) including coupling or capillary number (increase in kr as flow velocity increases and/or interfacial tension decreases) and inertia (decrease in kr as flow velocity increases) on estimated parameters were examined. The results show that the quality of match (and parameter estimates) between the generated decline curve and type curves is dependent on the condensate saturation level around the wellbore and the nature of the kr curves. In those cases where non-Darcy effects are strong enough to affect the results, use of Fetkovich type curves in the presence of inertia (coupling) results in pessimistic (optimistic) estimates of permeability, and higher (lower) skin estimates than the non-rate-dependent values input into the simulations.
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Towards a Joint Programming on Geological Disposal – The Joprad Project
More LessSummaryThe goal of The JOPRAD project is to prepare the setting up of a “Joint Programming on Radioactive Waste Disposal” that would be established to coordinate at the European level, national research programmes and the associated research and development (R&D) activities on geological disposal for high activity long lived radioactive waste. This action includes reviewing of all strategic aspects linked to a stepwise move towards a Joint Programming in this field. This project will involve organisations that are active in the safety, management and disposal of radioactive waste and research entities. The first step of this project will be to engage in discussion with Member States representatives in order to clarify the organisation of their national R&D consistent with the implementation of the Council Directive. The second step will be to identify existing research programmes that could contribute to the identification of common scientific objectives and activities as well as specific aspects that the organisations would like to develop in the Joint Programme. The third step will be to draft the joint “Programme Document” that should be the technical background of the Joint Programming. This action will lead to the further integration of the interested research community and hence help to maintain and develop the EU leadership in knowledge and expertise for innovative radioactive waste management solutions that effectively matches public expectations. Moreover, it will further reinforce and make the interaction at EU level between WMOs, TSOs, industry, policy makers and the research community more effective.
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How Rift-related/Plate-forming Processes Control Structure and Shortening in Fold-thrust Belts
More LessSummaryFold-thrust belts (FTBs) are archetypical tectonic features adjacent to collisional orogens, where structural traps account for 14% of discovered oil reserves. After decades of field and seismic surveys, detailed geological interpretations have emphasized their high degree of structural complexities. This has dampened academic research interest and impetus towards the understanding of larger scale geodynamic processes related to their development.
FTBs express processes by which plate convergence in collisional orogenic belts is accommodated by accretion within the continental lithosphere. Two dominant tectonic modes are observed in FTBs, thin-skinned and thick-skinned. Thin-skinned style characterized regions dominated by underthrusting, suggesting simple-shear subduction of the underlying crust. A recently discovered relationship between structure of FTBs and plate forming processes ( Mouthereau et al., 2013 ) shows that styles of tectonic deformation at the front of orogenic belts are controlled by age-dependent, deep-seated, properties of the crust and sub-continental mantle. More generally, the role of inherited thermo-tectonic properties of the lithosphere and the architecture of former continental margins is increasingly being shown to be a major driver in the evolution of mountain belts. This research should stimulate novel R&D integrated efforts on both rifted margin and thrust belt.
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Integrated Workflow for Risk Assessment in Fold-and-thrust Belts
By F. RoureSummaryOur understanding of sedimentary basins and thrust belts has greatly benefited from recent improvement of imagery techniques, accounting for a renewed interest for hydrocarbon exploration in fold-and-thrust belts.
This paper describes, using various case studies worldwide, the integrated workflow developed at IFP-EN to reconstruct the kinematic and thermal evolution of fold-and-thrust belts (foothills) and adjacent forelands, and the way numerical modelling and analytical work can improve our predictions in terms of energy resources, hydrocarbon potential and reservoir risk assessment.
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Coupling Tectonics and Surface Processes in Fold and Thrust Belts - Insights from 30 Years of Analog Modeling
More LessSummaryThrough a rapid overview of 30 years of analog modeling studies, we outline the role of the primary mechanisms and processes that exert a strong control on fold and thrust belts evolution. Following this general approach, we address major open questions regarding the global and local responses (i.e., at orogenic scale and at the scale of faults or ridges) of a fold and thrust belt under the impact of tectonic or climatic forcing at different time scales. Insights from analog models are used to: a) characterize the behavior of wedges subject to different geometric, kinematic and rheologic boundary conditions and b) show how the interactions between surface and tectonic processes influence the structures, kinematics of deformation, exhumation mechanisms, and long-term evolution. Impact of first order parameters such as the initial tectonic setting, material transfer in the wedge, structural inheritance (OCT and inherited extensional structures), and their role on the tectonic evolution of fold and thrust belts will be successively reviewed. Several case studies of active or fossil orogens (Taiwan, the western Alps and the Variscan belt) representative of first order tectonic processes are presented in the light of field observation and analog experiments comparison.
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What are the Limits of Balanced Sections in Fold and Thrust Belts
By J. VergesSummaryIn this paper the limits of the geological cross-sections are explored as well as their validity depending on the used datasets and multidisciplinary approaches. Selected cross-sections from different orogenic belts are discussed and framed within plate tectonic reconstructions. The Pyrenees formed during convergence between Iberia and Europe producing the inversion of the relatively narrow basin system between the two plates. Contrarily, the Zagros fold belt is a more complicated orogenic chain produced by an initial obduction phase and a later collision between Eurasia and Arabia. The uncertainties and variability of published balanced cross-sections through these orogenic systems need further constrain to solve problems that cannot be interpreted only with existing structural information.The integration of multidisciplinary studies at different scales of work might help constraining the evolution of the orogenic events and might provide solutions for regions that cannot be addressed solely by the construction of the balanced cross-section using structural information.
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Apatite (U-Th)/He Thermochronology Data Interpretation in Fold and Thrust Belt - New Insights from Physical Point of View
Authors C.G. Gautheron, D. Mbongo-Djimbi, C. Gerin, J. Roques, C. Bachelet, E. Oliviero and L. Tassan-GotSummaryThe apatite (U–Th)/He (AHe) system has rapidly become a very popular thermochronometer to constrain burial and exhumation phases in a variety of geological contexts, including fold and thrust belt. In this particular case, detrital apatite crystals come from different sources and are characterized by different pre-deposit ages and grain chemistry. However the actual He diffusion models are not well constrained and do not fully explain the mechanism of He retention. This is particularly true for detrital apatite crystals and AHe age interpretation can be tricky. In order to have a deeper insight on this issue, multidisciplinary studies on apatite combining physical studies were performed. We propose new He diffusion coefficient, so closure temperature and a physical He diffusion model. We will propose a new way of interpreting AHe datasets on fold and thrust belt samples more particularly, because of their own apatite characteristics. Two examples from Peruvian Subandean zone and south Pyrenean foreland will be given. We will show how a better interpretation of He diffusivity will improve significantly AHe data and thermal histories obtained by data inversion.
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Balanced Cross-sections, Thermochronology and Unexplored Plays - The Peru Case Study
Authors P. Baby, Y. Calderon, C. Hurtado, N. Espurt, M. Louterbach, A. Eude, S. Brusset, M. Roddaz, S. Brichau and R. BolanosSummaryIn the Peruvian Subandean fold and thrust belt, the construction of 4 serial balanced cross-sections from a good set of structural data and an extensive knowledge of the stratigraphy and geodynamic evolution allow a more refined definition of the unexplored plays, as sub-thrusts, duplexes or pre-Cretaceous structures. Sequential restorations are proposed by coupling thermochronologic analyses with growth strata studies. The results show significant north-south variations in the geometry, the timing and the rate of the deformation. This latitudinal variation is related to the pre-Andean basins inheritance, but also to the Andean slab geometry. Thermochronologic ages correspond to the most recent tectonic uplifts and cannot be disassociated from the study of growth strata that might have recorded oldest events. North of the Peruvian Subandean zone, the thrusts propagation seems continuous since the Late Cretaceous. In the south, two stages of Cenozoic deformation are clearly indentified.
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From Andes to Zagros - Variations in Structural Styles and Seismic Data from Two Processors’ Perspectives
Authors R.W. Vestrum and J.M. GittinsSummaryAn overview of data examples from a variety of settings illustrates the similarities and differences in structural style, velocity structure, and acquisition conditions. We have observed that younger rocks typically show lower velocities and the lower compressibility of these strata results in velocities more sensitive to depth of burial. Velocity gradients need more testing in younger basins with lower velocity rocks. Another observation is that more topsoil with wetter surface conditions appear to offer better coupling for seismic sources and receivers, which could explain why we see better signal-to-noise ratios on seismic data from rainforest versus desert environments. Desert outcrops may read like a geology textbook, but visual clarity at the surface comes at a cost of clarity in the subsurface.
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Broadband Seismic Imaging of Thrust Belt along the Outer Banda Arc in Indonesia
Authors M. Fujimoto, Y. Sasaki, Y. Guo and M. OharaSummary3D broadband seismic technique and appropriate PrSDM imaging technique provided us significant improvements in seismic imaging for both thrust complex and sub-thrust structures. Broadband 3D seismic imaging contributed better recovery of seismic energy from deep sections where conventional seismic imaging could not reveal any reflections. Pre-migration deghosting technology provided us the stable phase of wavelets and desired broadband frequency spectrum in the seismic image. The velocity model constructed from the combination of Kirchhoff PrSDM and Controlled Beam Migration provided better resolution and continuity of seismic images under thrust complexes and large fault surfaces by overcoming the poor illumination issue. These technologies contributed to revealing subtle fault displacements, reducing depth structure uncertainty below thrust complex and increasing the understanding of petroleum systems and risk elements of exploration target in a frontier region.
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Fast-track 2D Seismic Processing While Drilling to Ameliorate Foothills Exploration and Optimize Side-track Trajectory
Authors F. Sapin, H. Allouche, G. Sterbecq, B. Chevallier, G. Guerin, B. Eriksen and P. RochatSummaryThe petroleum exploration in foothills domains remains challenging in terms of positioning a well in an optimal manner to target different objectives in places where there are several mechanical discontinuities in the stratigraphy separating them and inducing often shifted structural tops. In consequence, seismic imaging, as well as a good geological knowledge, is mandatory to predict a well trajectory suited for all the targeted objectives. In Kurdistan Region of Iraq, the mechanical stratigraphy is rather simple but the tightening of the structures often leads to the activation of internal mechanical discontinuities and a shift of the main objectives tops. In consequence, and as in any foothills environment, side-tracked wells have to be carefully planned.
After drilling the first leg of a well, and finding out that we were clearly out of our predictions in terms of structural positioning and in the evidence that the deepest objective cannot be drilled with the first leg, the decision to drill a side-track came quickly. Meanwhile, we performed a fast-track processing on the closest 2D line in order to image the high dips of the drilled formations. The output allowed us to help optimizing the side track trajectory and to ahead with better constraints.
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Inversion, Detachment Folds, and Out-of-sequence Thrusts in the Papua New Guinea Fold Belt
Authors K.C. Hill and R. WightmanSummaryAnalysis of structural profiles through oil- and gas-fields of the Papuan Fold Belt indicates that the preexisting configuration of basement played a significant role in the compressional deformation. The Moran-Paua structures overlie upthrust basement and comprise small asymmetric detachment folds subsequently decapitated by out-of-sequence thrusts, causing shearing of the forelimb. Interpretation of reflection seismic data in the Agogo area suggests a 10° regional dip in basement and a thick syn-rift sequence in which a large detachment fold was formed, probably associated with early basement thrusting at Moran. The forelimb of the fold was then cut through by low-angle thrust faults creating oilfields in both the gentle hangingwall and steep footwall-forelimb. Along strike at Usano, in contrast, seismic interpretation suggests that the basement is shallower dipping and rift sediments appear to be thinner. There, the detachment folds were not developed and early basement thrusting/inversion resulted in a shear zone. Subsequent thrusting along Jurassic and Upper Cretaceous décollements created duplexes and cut through the shear zone such that it was oversteepened creating the Usano oilfield in the hangingwall. Understanding these relationships is important in defining new hydrocarbon plays.
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Plio-pleistocene Thrusting in the Eastern Amazonian Orogenic Wedge (South Peru)
Authors M. Louterbach, M. Roddaz, P. Baby, S. Brichau, J. Bailleul and Y. CalderónSummaryQuantifying interactions between uplift, climate, deformation and exhumation processes remains difficult, mainly due to a paucity of data relevant to all processes. Central Andes are a prime example to study the respective role of climate forcing and tectonic activity on mountain building. In this study we propose new data (thermochronology, biostratigraphy, field observations and seismic interpretations) focused on the Eastern Cordillera (EC) and the Sub-Andean Zone (SAZ) of southern Peru between 12ºS and 14ºS, in order to i) constrain the timing of deformation, and to ii) demonstrate that contrary to recent studies, our new data outline that the Plio-Peistocene uplift and erosion of the Andes are more likely related to thrust induced exhumation than to a climate forcing. Low temperature thermochronological results obtained for the EC and the SAZ, as well as the growth strata documented in seismic and on the field allow to determine two main deformation periods: i) from the Oligocene to Middle Miocene (~25-14 Ma), and ii) from the Late Miocene to Pleistocene (~10-2.8 Ma). The Plio-Pleiostocene cooling induced by the erosion of the EC in southern Peru is not controlled by climatic change, but better by the development of duplex in the Andean front.
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New Exploration Concepts in Zagros Fold Thrust Belt and Persian Gulf, Iran
Authors S. Jahani, I. Abdollahie Fard and S. SherkatiSummaryAfter more than 100 years hydrocarbon exploration, The Zagros Fold-Thrust Belt (ZFAB) is still remained as one of the most talented regions for future hydrocarbon discovery. Three main hydrocarbon structures originated from the Neogene folding, inherited deep-seated faults and buried salt diapirs. Remained many complex and small structures with potential prospect in the ZFTB which has not completely studied yet. They could be categorized in: (1) Fault related structures as subtle traps, which formed in response to intermediate detachments during Zagros folding or formed below the thrust faults, (2) Long time halokinesis prepared suitable small traps around the diapirs or under the salt sheets, (3) Inherited deep-seated fault movement and see-level changing formed stratigraphic-structural traps towards the palaeohighs, (4) Results of few drilled wells in pre-Permian sediments (Faraghan Formation) proved new gas reserves (5) and oil rings developed in some of onshore folded anticlinal. Consequently for future oil and gas exploration has to take two strategies. For oil exploration focuses more on the complex and small structures including subtle traps, stratigraphic-structural traps around salt diapirs and Palaeohighs. Whereas, for gas exploration remained many huge anticlines to the eastern part of ZFTB which has not been investigated in details.
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Analogue Modelling of the Papua New Guinea Fold and Thrust Belt
Authors R. Darnault, K.C Hill, J.M Mengus, J.M Daniel, J.P Callot and J.C RingenbachSummaryIn the PNG Fold Belt the jungle-covered mountains limit data acquisition so that the internal geometry and evolution of the large anticlines are poorly understood. It is postulated that the anticlines formed above old normal faults in basement, which has been tested by analogue modelling and 3D computerized X-ray tomographic scanning. Layers of corundum, sand, silicone and sand/silicone mixes were used to represent the PNG stratigraphy of 2 km of molasse, 1 km of carbonate, 1 km of mudstone, 500m of sandstone and shale reservoirs and 0.5-3 km of syn-rift clastics. The thicknesses, strengths and velocities of deformation were all scaled appropriately and erosion/deposition was modelled by adding or removing ‘molasse’. It was found that the carbonate deformation was often detached from that of the underlying reservoirs and that the structural style was critically dependent upon the strength of the intervening mudstone and of the basal detachment. Structural style was also strongly correlated to deformation rate, in that slower convergence rates yielded a single large fold, whereas optimum rates yielded more realistic detachment folds. It was observed that the development of an overturned detachment fold was greatly enhanced when the basement fault was first partially inverted.
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Development of Detachment Folds on Syn-orogenic Sequences Including Salt Layers
Authors O. Pla, J.A Muñoz, O. Ferrer, E. Roca and O. GratacósSummaryThe southern Pyrenean foreland basin is formed by a thick syn-orogenic sequence that includes several evaporitic layers with salt that are involved in the fold-and-thrust belt. The Oliola anticline is a detachment fold probably developed at the southern pinch-out of the syn-orogenic Cardona salt unit that also involves younger syn-contractional evaporitc unit (Barbastro Fm.).
Based on this natural analogue and using an experimental approach (sandbox models) we propose a new kinematic model for the development of detachment folds with multilayered evaporites in the Ebro basin. Analogue modelling of detachment folds suggests a new scenario for diapirs formation in compressional tectonic settings.
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Genesis and Tectono-thermal Evolution of the Altiplano (Central Andes), from the Basin to the Orogen
Authors A.M.M. Robert, P. Baby and M. RoddazSummaryWe would like to present our project that aims to investigate the tectono-thermal evolution of the Altiplano in the Central Andes from the basin to the orogenic scale and to study the interplay between Earth's deep and surface processes in convergent context.
We aim to unravel the sedimentologic, structural and thermal evolution of the hinterland basins of the Altiplano in order to provide critical evidences for the history and style of the deformation in that region. In fact, these basins remain attractive frontier basins for petroleum exploration.
At the orogenic scale, this study projects to compare regional cross-sections at different latitudes. According to the available seismic and seismologic data, we propose to produce 2 regional lithospheric-scale cross-sections mainly based on detailed balanced cross-sections and geophysical modeling.
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Algorithmic Aspects of Extended Waveform Inversion
By W. SymesSummaryExtended waveform inversion uses inference of an extended model, depending on non-physical parameters, to extract velocity information directly from waveform data. It has been observed that fitting data at all stages of velocity updates, a possibility offered by model extension, appears to be important to assure reliability of algorithms of this type. An analysis of the modeling operator derivative provides an explanation for this observation, and reveals the link between extended waveform inversion and traveltime tomography.
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Inversion Velocity Analysis - The Importance of Regularisation
Authors H. Chauris, C.A. Lameloise and E. CocherSummaryInversion Velocity Analysis has been recently proposed as an alternative to Migration Velocity Analysis. Under the Born approximation, it consists of first determining the optimal reflectivity model such that the synthetic data set nicely fits with the observed data set. Then, a standard velocity analysis is applied to the inverted reflectivity. The main differences with respect to the classical approach is the use of iterative migration versus standard migration. We propose here an alternative way to compute the gradient of the objective function and demonstrate the importance of the regularisation term introduced to determine the optimal reflectivity model.
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Optimizing the Input Model for Waveform Inversion Using Image-domain Wavefield Tomography with Illumination Compensation
Authors E.F. Diaz Pantin and P.C. SavaSummaryImage domain wavefield tomography exploits focusing characteristics of extended images for updating the velocity field. In order to make good use of this information, we must understand how such images behave if the migration velocity is accurate. This is not trivial since focusing depends on the acquisition setup, as well as on illumination variation caused by the geology separating the acquisition array from the imaged structure, the data bandwidth, etc. We address this problem using a combination of migration/demigration to construct penalty functions that characterize focusing by incorporating acquisition parameters and data bandwidth. Moreover, instead of sampling the extended images at preset distance along the surface, we sample the image by constructing common image-point gathers, which are also much more economical from a computation point of view. Coupled with image residuals exploiting illumination-based penalty functions, we obtain robust wavefield tomography in areas of poor or uneven illumination. Models obtained with this type of methodology are good starting points to more sensitive, but less robust waveform inversion methods.
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Migration Velocity Analysis Combining Reflected and Direct Waves in a Crosswell Configuration
Authors C.A. Lameloise and H. ChaurisSummaryMigration Velocity Analysis is classically restricted to reflected wave fields. In Crosswell Seismic Profiling (CSP) configuration, transmitted waves are usually considered. Here, in a CSP configuration, we combine direct and reflected waves in order to perform a Migration Velocity Analysis. The idea is to take advantage of the different illuminations of the subsurface provided by these different wave fields. The velocity update shows that the part related to reflected waves mainly emphasizes zones around reflectors, whereas transmitted waves illuminate the subsurface in a more homogeneous way. We discuss in a heterogeneous faulted model an automatic velocity method, based on different waves, separately or combined.
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Is Image-warping a Robust Tool for Image Domain Tomography?
Authors F. Perrone and P. SavaSummaryMigration Velocity Analysis in the subsurface-domain measures velocity errors via (extended) imagedomain residuals with respect to an ideal reference image and then updates the velocity model in order to minimise those residuals. Because of the similarity between images with similar extension parameter (shot number, offset, incidence angle, etc.), image-warping presents a robust approach to compute image residuals in different subsurface domains. However, since similarity measures cannot in general distinguish between signal and coherent noise, kinematic artefacts that contaminate the migrated images in certain extended domains can lead to strong and spurious events in the image perturbations and hinder the robustness of the tomographic inversion.
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Utilization of Multiples in Simultaneous Image Building and Velocity Estimation
Authors A.J. Berkhout, D.J. Verschuur, X.R. Staal and M. DavydenkoSummaryIn the past the seismic industry has made large investments in the removal of multiples from the seismic response ('data linearization'), with the purpose to make the data suitable for our linear velocity estimation and linear migration algorithms. Now we are beginning to understand that multiples contain most valuable information that should not be removed.
Instead they should be utilized, making velocity estimation and migration fully consistent with the underlying physics. In this presentation it is shown that velocity estimation can function as an integral part of the nonlinear migration process: Joint Migration Inversion (JMI).
It is also shown that JMI is insensitive to the initial velocity distribution.
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Affordable Full Subsurface Image Volume - An Application to WEMVA
Authors T. van Leeuwen, R. Kumar and F. J. HerrmannSummaryCommon image gathers are used in building velocity models, inverting for anisotropy parameters, and analyzing reservoir attributes. In this paper, we offer a new perspective on image gathers, where we glean information from the image volume via efficient matrix-vector products. The proposed formulation make the computation of full subsurface image volume feasible.
We illustrate how this matrix-vector product can be used to construct objective functions for automatic MVA.
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3D RTM-based Wave Path Tomography Tested at a Realistic Scale
Authors P.M. Bakker, S. Gerritsen and Q. CaoSummaryA new method of 3D RTM-based Wave Path Tomography is presented. Input of the method are RMO picks from wide-azimuth RTM angle gathers. The depth sensitivity of picked events to a velocity perturbation is derived by Born approximation of the associated wave fields and the images. For reasons of efficiency, this is done only for the stationary shots, pertaining to selected picks at certain angle slots in the gather. In the sensitivity kernel calculations, the corresponding recorded data are restricted to those in the vicinity of the estimated stationary receivers. Each branch of a sensitivity kernel, linking stationary shot or receiver to the picked event, is computed by RTM imaging. The method is successfully tested at a realistic scale for a wide-azimuth synthetic example, and for a case with real data from an OBS survey.
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Application of Plane-wave Extended Waveform Inversion to an Onshore Seismic Dataset
Authors Y. Liu, W.W. Symes, C.H. Zhu, Y.Q. Chen and M.Q. LuoSummaryExtended waveform inversion (EWI) fills the gap between migration velocity analysis (MVA) and waveform inversion (WI). It’s less prone to local minimum when the starting velocity is inadequate for conventional WI. To improve the efficiency of EWI, we extend the velocity model in the plane-wave source domain. To weaken the absolute amplitude information and make plane-wave encoding applicable in the real data processing, we use normalized wavefields in the data-misfit term of objective function. Numerical tests show that EWI can successfully and efficiently build a high-resolution velocity model for the onshore seismic dataset.
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Strength and Limitation of FWI - What Can Tomographic Approaches Bring?
Authors G. Lambare and T. AllemandSummaryFull waveform inversion is now well established for velocity model building in areas investigated by recorded diving waves. At larger depths, significant limitations appear associated with a lack of resolution in the long vertical wavelengths of the velocity. To remedy this, new wave equation based approaches have been proposed. They reveal strong connections with migration velocity analysis and tomographic techniques. In the new context of an overlap between the resolution of velocity analysis and of imaging (created by the progress of migration velocity analysis and of low frequency acquisitions) the challenge is to combine these approaches with full waveform inversion in order to get high-resolution structurally conformable velocity models. We review and analyze the proposed methods.
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Joint Full Waveform Inversion of Diving Waves and Reflected Waves for Velocity Model Building
Authors W. Zhou, R. Brossier, S. Operto and J.M. VirieuxSummaryAt depths where there is no sampling by diving waves, FWI behaves as a least-squares migration of the short-spread reflections, hence providing a reconstruction of the short-scale reflectivity at the expense of the long wavelengths of the velocity. Recently, it has been proposed to modify the FWI formalism such that the long wavelengths of the velocity can be updated from reflected waves using some prior knowledge on the reflectivity and an explicit scale separation between the velocity macro-model and the reflectivity. This scale separation allows one to emphasize the forward-scattering regime in the sensitivity kernel of the FWI, referred to as reflection FWI (RFWI). The drawback of the RFWI is to discard the valuable information on the shallow subsurface carried out by diving waves. A new FWI formalism, referred to as joint FWI (JFWI) is proposed and takes advantage of the long-wavelength information carried out by both diving waves and reflected waves to build a smooth velocity model. This formalism leads to a workflow which iteratively cycles the update of the smooth velocity model by JFWI and the update of the short-scale impedance model by classical FWI of short-spread reflections. Application to a synthetic Valhall model illustrates the performance of JFWI.
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An Auxiliary Bump Functional to Overcome Cycle Skipping in Waveform Inversion
Authors P. Bharadwaj, W.A. Mulder and G.G. DrijkoningenSummaryTo overcome the local minima problem in FWI, we propose to use an auxiliary data-domain objective function during inversion. It reduces the data to a simpler form by squaring, followed by blurring to ensure that events that are too far apart can still interact during the inversion. As it effectively replaces seismic arrivals by bumps, we call it the bump functional. This objective function is less sensitive to cycle skipping. Its rôle is to guide the inversion towards the global minimum by pulling the trapped solution out of the local minima associated with the least-squares functional whenever necessary.
Waveform inversion cannot be performed with only the auxiliary objective function because it is insensitive to the polarity of the arrivals and the source signature. Therefore, we alternate between minimization with this and the classic least-squares functional. We confirm the validity of the approach using a simple numerical example with reflection data.
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