- Home
- Conferences
- Conference Proceedings
- Conferences
77th EAGE Conference and Exhibition - Workshops
- Conference date: June 1-4, 2015
- Location: Madrid, Spain
- Published: 01 June 2015
61 - 80 of 128 results
-
-
A Practical Approach to Vector-acoustic Imaging of Primaries and Free-surface Multiples
Authors M. Ravasi, I. Vasconcelos, A. Curtis and A. KritskiSummaryFree-surface multiples travel different paths and illuminate different volumes of the subsurface than primaries. When used jointly with primaries to image the subsurface by means of forward and backward extrapolation of separated down- and up-going wave components respectively, free-surface multiples have been shown to improve the continuity of shallow parts of the subsurface image by suppressing acquisition related footprints.
We show that by carefully combining the full pressure and particle velocity data by means of newly developed, vector-acoustic boundary conditions, wavefronts can be forward and backward propagated without ambiguity in their propagation direction. Wavefield decomposition is thus naturally incorporated within the extrapolation procedure.
Moreover, ocean-bottom acquisition geometries generally present source coverage that is wider than the receiver array. A strategy is proposed to incorporate in our imaging scheme energy of primary events whose direct source illumination lies outside of the receiver aperture. This is achieved by combining a directly modelled source illumination with the recorded (down-going) data.
-
-
-
Complete Wavefield Imaging Using Broadband Dual-sensor Streamer Data
SummaryWhen considering shallow water towed streamer data, developing an accurate velocity model using primary reflections alone is challenging and often only allows an average velocity of the near surface interval to be defined. For robust reservoir imaging, it is essential to resolve near surface velocity heterogeneity, thus the conventional VMB approach, which uses data acquired with standard streamers, is compromised.
A methodology for VMB utilising the complete wavefield has been presented. The foundation of the method is dual-sensor towed streamer data which allows separation of the recorded wavefield and is thus the technology enabler for an advanced imaging workflow. Complete wavefield imaging delivers a highresolution velocity model of the near surface which in a conventional approach typically remains unresolved. The more accurate near surface velocity model and subsequent imaging improves the accuracy and confidence of the imaging at reservoir levels.
-
-
-
Causality Aspects of the Elastodynamic Marchenko Method
By K. WapenaarSummaryWith the acoustic single-sided Marchenko method it is possible to retrieve the Green’s function of a virtual source in the subsurface from the single-sided reflection response of the medium and an estimate of the first arrival of the Green’s function. Important ingredients of the Marchenko method are the so-called focusing functions. One of the underlying ideas of the acoustic Marchenko method is that the Green’s functions and focusing functions reside in different time intervals in the time domain. We call this the causality condition. The only overlap of the Green’s functions and focusing functions occurs at one time instant, namely at the time of the direct arrival of the Green’s function.
In this paper we analyze the causality condition for the elastodynamic extension of the single-sided Marchenko method. It appears that the overlap of the elastodynamic Green’s functions and focusing functions occurs in an extended time interval. The parts of the focusing functions that overlap with the Green’s functions cannot be retrieved with the Marchenko method, and must therefore be specified separately. It appears that these overlapping parts are defined as the inverse of the forward-scattered part of the transmission response of the medium.
-
-
-
Reliable Depth Imaging - A Matter of Selective Integration of Subsurface Knowledge
Authors D. Sineva, Q. Liao Yang, W. Harmony and G. GonzalezSummaryDuring the last few years significant improvements have been made in all branches of geophysical technology, from acquisition and processing all the way to depth imaging. The diversity of existing technology and variety of methodologies that can be applied for depth imaging make it difficult to choose the right technology that will result in a “perfect” image. In order to find that perfect combination of rapidly evolving technologies we need first to understand the environment: regional geology, the possible target, the known geological and geo-mechanical scenarios and all other possible challenges that will be reflected on our seismic data.
Although today we are able to acquire high resolution, high density, Multi or Wide azimuth seismic data, without proper understanding of geology and careful integration of all related geo-disciplines the final result will not be satisfactory.
The knowledge integration should happen at every stage from seismic acquisition planning to delivery of the final image. Thus what to integrate becomes a very critical question.
-
-
-
Decoupled TTI P-wave Poststack RTM and Demigration Using Pseusdo-spectral Operators
Authors J. Jiao, Q. Zhang, X. Ma, P. Stoffa and G. GonzalezSummaryThe pure P-wave equation for tilted transverse isotropic reverse-time migration is free of shear-wave artifacts unlike the widely used coupled TTI equations. A new hybrid pseudo spectral and finite-difference algorithm has recently been developed to solve the TTI pure P-wave equation for prestack RTM. This algorithm applies part of the wave propagation in the wave number domain and part in the space domain and is inherently parallel improving its computational efficiency. Here we extend this hybrid algorithm to 3D post-stack de-migration. De-migration of stacked images is the reverse process of migration and generates un-migrated seismograms compatible to seismic data with zero offset. We have tested the proposed de-migration on both field and synthetic seismic data and we have also used the proposed demigration to establish a workflow to validate or build anisotropic models. After de-migration is performed with the models used in the previous migration, we select a series of anisotropic models to re-migrate the seismograms generated by the de-migration. The new models may be derived from seismic-well ties, perturbation of anisotropic parameters, perturbation of locations of interpreted horizons. By investigating a series of re-migrated images, an experienced interpreter can identify which model is the most geologically plausible.
-
-
-
Cost Effective Improvements for Seismic Survey Planning Using Remote Sensing
By W.M. BaughSummarySignificant new capabilities for remotely sensed material and mineral identification were enabled with the launch of the WorldView-3 (WV-3) commercial remote sensing satellite on 13 August 2014. Most noteworthy (for material/mineral identification) are the addition of 8 high resolution super-spectral bands in the shortwave infrared (SWIR) range of the electromagnetic spectrum.
The SWIR imaging bands are collected at a native 3.7 m resolution, and cover a range of diverse and unique absorption features for materials of interest to geophysical exploration. In addition, there are 8 bands of WV-2 heritage spanning the visible through near-infrared (VNIR) range. The VNIR bands are collected at a higher 1.2 m resolution. A panchromatic band at 0.31 m resolution reveals unprecedented spatial details from space.
WV-3 is a sensor for geophysical applications. Its new capabilities look beyond the image pixels, and into materials, minerals, moisture content, and disturbance. For example, surface material information provides a natural extension to the seismic survey risk mapping proposed in the article “Satellite Sensing: Risk Mapping for Seismic Surveys” ( Oilfield Review, 2009 , v. 20, n. 4). Improved knowledge about surface characteristics benefits both seismic vehicle logistics as well as understanding of near-surface velocities.
-
-
-
Surface Microseismic Imaging - Influence of High Velocity Layers
Authors D. Price, D.A. Angus, K. Chambers and G. JonesSummaryImaging artifacts due to the influence of high velocity layers on the reduction of effective array aperture and the presence of increased multiples in the microseismic data are examined. FD full-waveform microseismic synthetics were generated that mimic a typical surface monitoring array for a range of 1D velocity models. Microseismic event locations using two different imaging techniques were compared: standard diffraction imaging (SDI) and moment tensor microseismic imaging (MTMI) algorithms. The results confirm that the presence of high velocity anhydrite layers reduce the overall aperture of a surface array, which results in poor resolution of imaged events, and a reduction in accuracy of event locations and effective monitoring area. The presence of high velocity lithological units also increases the amount of multiple and converted waves in the seismic data, resulting in an increase in coherent noise following the primary arrivals. Comparison of the two imaging procedures conclude that MTMI produces a much cleaner, less noisy image domain with more accurate and precise location estimations for similar monitoring scenarios, but both MTMI and SDI are equally affected by the presence of high velocity layers and recorded event frequency. For settings where high velocity lithological units are expected, the results of this study suggest that larger aperture arrays be deployed and the application of novel/advanced processing techniques be incorporated into the pre-processing of microseismic data to reduce multiple and converted wave noise.
-
-
-
Analysis and Interpretation of Induced Micro-seismicity by Flooding of the Gardanne Coal Basin (Provence – Southern France)
Authors E. Matrullo, I. Contrucci, P. Dominique, M. Bennani, H. Aochi, J. Kinsher, P. Bernard and P. BigarréSummaryMining activity in Provence has left many underground voids that can cause land subsidence or collapses in areas of high population density. In the abandoned coal basin of Gardanne, the flooding of mine voids and fluctuations in the groundwater level induced many seismic events that have been recorded since the beginning of operational monitoring. An example is the seismic crisis of November 2012, where magnitude events > 2.5 were felt by the population.
In this context, the objective is to understand the mechanisms of the observed seismicity. This will clarify the relationships between seismicity and rising waters in old mine working, geology and local tectonics. This general aim will be pursued, thanks the availability of the high quality dataset of recording from the dense arrays managed by INERIS and BRGM.
We will focus on the spatio-temporal distribution of the seismicity, which allows to monitor the dynamics of faulting and to estimate the extension and mode of rupture of the fracture system. The present work is based on the observation and the characterization of the microseismicity in terms of the accurate hypocentral locations, local and moment magnitudes and focal mechanisms determination in order to characterize the status of the abandoned mine.
-
-
-
Induced Seismicity in Underground Gas Storage - The Case of Castor, Offshore NE Spain
Authors R. del Potro and M. DiezSummaryOil and Gas operations have the potential to induce earthquakes, and this is becoming an increasing concern for operators and regulators. Here we present the case of the Castor Underground Gas Storage (UGS), offshore NE Spain, where seismicity was induced during the first phases of gas injection. The microseismicity that occurred during the injection period, and which was not felt, evolved into magnitude 4 events almost two weeks after the end of the injection. The largest earthquakes of the sequence were weakly felt by coastal populations (EMS-98 Intensity III) and, in spite of posing no risk, pressed the authorities to halt all activity in the UGS. Here we compile the results from the major studies of the Castor seismicity: earthquake relocations and source mechanisms, and use new tools to characterise the seismicity and its relation to the gas injection. Cases of induced seismicity, such as Castor, where the external forcing is known, can contribute significantly to our understanding of the response of the crust to stress perturbations caused by fluid movement and the associated rupture events.
-
-
-
Production-induced Fault Reactivation and Seismicity in The Netherlands - From Quick Scan to 3D Geomechanical Modelling
Authors B.B.T. Wassing, L. Buijze, P. Fokker, B. Orlic, K. Van Thienen-Visser and J.D. van WeesSummaryRecent induced seismic events in the giant Groningen gas field have raised concern on the safety of gas production and the risk of induced seismicity in the Groningen gas field in The Netherlands. Statistical analysis of past seismic events in the Groningen Field reveals that seismicity is non-stationary and seismicity rates are increasing, which leads to the conclusion that the maximum possible magnitude of seismic events, related to gas depletion, may be significantly higher than estimated before on the basis of statistics of past seismic events alone. The non-stationarity of seismicity may have implications for the seismic hazard of the small gas fields in The Netherlands as well.Formerly the maximum magnitude for these small onshore fields was estimated via the frequency magnitude distribution of the combined seismicity for all these fields, which resulted in an estimate of ML 3.9 for the maximum magnitude. However, as seismicity is non-stationary, only a small fraction of the gas fields is seismically active and the number of seismic events associated with them is generally small, past seismicity and related statistics cannot be used very well to study the future response of those fields and implications for fields with no recorded seismicity are unclear. In this presentation we show methods to assess the seismicity potential of these fields, which are based on techniques other than statistical analysis of past seismicity alone.
-
-
-
Case Studies of Depletion Induced Seismicity Using Rate & State Modeling for Probabilistic Discrimination and Hazard
More LessSummaryEarthquakes with magnitudes M>4 have occasionally been observed close to depleted reservoirs after longer periods of production. Events of this size can be felt and pose a significant hazard for population and infrastructure. Key questions are whether such events can be associated as depletion induced, how reliable they can be discriminated against natural but rare tectonic events, and whether we can assess their seismic hazard.
We suggest a probabilistic approach based on the relative rates of natural and induced seismicity. We employ a rate and state seismicity model combined with modelled rates of Coulomb stress. The quantitative model is able to forecast the relative increase of earthquake probability during depletion as a function of space and time. We use this estimate to define a trigger potential function for the earthquake. In addition, the human induced question can be considered if a fault smoothing filter is applied to the trigger potential function.
The method is applied to different earthquakes in Europe, showing that some of the significant earthquakes were human-induced, human-triggered or caused by natural tectonic stresses. We discuss possible extensions to earthquakes occurring during the re-filling of depleted reservoirs for gas storage facilities and the assessment of time dependent hazard.
-
-
-
InSAR for Induced Seismicity Monitoring
Authors A.R. Rucci, A.F. Ferretti and A.T. TamburiniSummaryWhenever fluids are injected or extracted from a reservoir, pore pressure and stress field change both in the reservoir and in the overburden. According to geomechanics, such variation in stress or pore pressure can produce a reservoir compaction, trigger pre-existing faults or even generate new ones. Al these events will translate into surface deformation which turns to be a valuable information to better understand the subsurface phenomena.
In the last few years, the analysis of multi-temporal SAR data sets represents an important layer of information, for reservoir monitoring and management.
The possibility to provide an high spatial density of accurate measurement points make InSAR an additional information to be integrated with subsurface data to calibrate geomechanical models, to identify fault/fracture reactivation providing also information about the fault geometry and mechanism.
-
-
-
Geomechanical Assessment of Seismic Potential from Hydraulic Fracturing
Authors S.C. Maxwell, F. Zhang and B. DamjanacSummaryThe impact of hydraulic fracturing on a Horn River Basin fault was examined to quantify seismic potential or hazard. A geomechancial model was designed to investigate the mechanism of fault activation and the impact of fracturing at different locations around the fault. The model is used to simulate hydraulic fracture growth through a discrete fracture network, examining the pore pressure diffusion and associated fracture dilation and shearing. Based on the geomechanical deformation, the seismic activity can be predicted and used to compare with the actual seismicity monitored during the fracture treatment. The microseismic geomechanics study indicated that the stimulated fracture network had to grow directly into the fault in order for the injection pressure front to trigger fault slip. Geomechanical assessment of absolute seismic potential can be used to modify the engineering design prior to operations to minimize the seismic hazard including the placement of the well, and modifiy staging along the well to avoid fracturing in the regions likely to lead to fault activation. In scenarios where induced seismicity occurs during the treatment, the method can also be used to examine operational changes to lessen the relative seismic hazard.
-
-
-
Real Time Forecasting of Maximum Expected Induced Seismicity
Authors J.P. Verdon, M.J. Werner, A.L. Stork and J.M. KendallSummaryFluid injection into the subsurface is performed for a variety of reasons, such as hydraulic fracturing, and waste storage. It is well established that fluid injection can trigger seismic activity of sufficient magnitude to be felt by local populations. The industry wishes to avoid such events. We develop a statistical model to forecast the largest event that might be induced by a given injection operation. The model is continuously updated as microseismic data is processed in real time. We use this model in a prospective sense, updating our forecasts through the injection period. We apply our model to two case studies: a hydraulic fracture stimulation in a tight gas reservoir; and at the In Salah CCS project, Algeria. In both cases, our model is capable of forecasting the largest event prior to its occurrence, providing an early-warning for the operator.
-
-
-
Fracture Corridors in Carbonates
Authors S. Chatelée, J. Lamarche and B.D.M. GauthierSummaryAmong fractures, Fracture Corridors (FC) are anomalous structures made of highly persistent fracture clusters having a strong effect on multi-phase fluid flow in subsurface. The aim of this study is to reveal the genetics factor for FC development, their global geometry and internal morphologic variations, but also to clear the impact of fracture corridors on diffuse fracture. For that, we studied fractures in a 400×300 m wide quarry (Calvisson, SE France) dug in homogeneous marly limestones of Hauterivian age. The quarry exhibits diffuse fractures and FC. we measured >2500 fractures (strike, dip, spacing, filling, aperture, etc.) and studied microstructures in 80 thin sections. We calculated fracture density and acquired LiDAR data with >90 million points with a resolution of 4 to 15mm.
The LiDAR acquisition allows to visualize the 3D lateral continuity of corridors with a minimal extension of 30m. We also distinguished several internal morphology types of FC.Fracture density study shows that diffuse fracture increase around FC.
FC growth and variability was not dependent on facies variations, as they are inexistent in the quarry. The result of this study allows to interpret geomechanical behaviors and geological history of fractures and fracture corridors in carbonates.
-
-
-
Fracture Modeling in a Complex Carbonate Reservoir - The Lubina-Montanazo Field, Offshore Spain
Authors O. Fernandez, M. Masini, R.M. Aguilar, M. Victoria, A. Briceño and P. CalderónSummaryThe Lubina-Montanazo field is a carbonate reservoir producing from Tertiary clastics and Cretaceous limestones. An outcrop analogue study has been integrated with subsurface data (image logs, well test interpretations, seismic attributes) to characterize the static and dynamic behavior of the fracture network and its interplay with diagenetic facies.
-
-
-
The Kurdamir-Topkhana Field of Kurdistan - Modelling Clinoforms, Dolomitisation, Porosity Distribution and Fracturing
Authors R.B. Owens, J. Hsieh, D. Nolan and B. VeilleuxSummaryThe Kurdamir-Topkhana reservoir consists of carbonates deposited in a passive margin ramp setting during the Oligocene. Six principal facies types have been identified that differentiate between inner, middle and outer ramp facies, as well as differing degrees of dolomitisation. Subtle evidence of most of these features can be identified on seismic inversion (AI) data, which also provide good indications of porosity distribution throughout the reservoir. In addition, multiple fracture sets have been identified in image log data and a discrete fracture network constructed for the field. It presents a considerable challenge to construct a geocellular model that successfully intergrates all of these differing reservoir characteristics and which can be used for history matching and overall reservoir management purposes.
-
-
-
Seismic Full Waveform Inversion for Characterizing Near-surface Structures - Potential Problems and Solutions
Authors H.R. Maurer, A. Nuber, E. Manukyan and S.A. GreenhalghSummaryFull waveform inversion (FWI) of seismic data has great potential to image the shallow subsurface, but the specific nature of the associated data sets requires that several problems be first addressed. One problem is the predominance of high-amplitude surface waves, which enforces changes primarily in the shallowest part of the subsurface model when matching observed and predicted data. A more uniform model update over the full depth range of interest can be obtained using Jacobian matrix scaling techniques. A further issue with FWI concerns the occurrence of local minima in the model space. We demonstrate the use of joint inversion of travel times and waveforms to alleviate this problem. Finally, we address the problem of variable source and receiver coupling and propose an estimation procedure that allows such variations to be accommodated and subsequently determined during the inversion.
-
-
-
Towards Robust Acoustic Full Waveform Inversion
Authors E. Manukyan, H. Maurer and A. NuberSummarySeismic full waveform inversion (FWI) is a powerful method for obtaining high resolution subsurface images, but the objective function of FWI algorithms typically contains many local minima, which may lead to erroneous solutions. This can be avoided by choosing an initial model that is close to the true model, and by incorporating only low frequencies at an early stage of an inversion run. Here, we demonstrate that the local minima problem can be mitigated by removing, at each iteration, all data that have more than half a cycle mismatch in the traveltimes compared with those predicted for the current model. Using a simple two parameter example, we show that filtering waveform data by this traveltime criterion can successfully circumvent local minimum trapping. Inversions of synthetic 2D acoustic data show that our novel traveltime-directed FWI approach is more robust and far less dependent on having an accurate starting model.
-
-
-
Alternative Multicomponent Observables for Robust Full-waveform Inversion - Application to a Near-surface Example
Authors R. Valensi, R. Brossier, D. Leparoux and P. CôteSummaryIn this study, using the framework of the Full Waveform Inversion (FWI) method we compare three different multicomponent cost-functions : the conventional multicomponent cost-function, a cost-function based on the normalized particle motion and a cost function only sensitive to the particle motion polarization.
With a synthetic test, it is showed that even if the attenuation model is poorly estimated the normalized particle motion misfit function and the polarization based cost functions are able to accurately recover the shear wave velocity parameters whereas the conventional multicomponent misfit function fails. Furthermore in context of near surface imaging, the proposed polarization based cost-function has the advantage to have a great sensitivity to the near-surface and to be independent of the knowledge of the source wavelet.
-