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77th EAGE Conference and Exhibition - Workshops
- Conference date: June 1-4, 2015
- Location: Madrid, Spain
- Published: 01 June 2015
1 - 20 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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