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76th EAGE Conference and Exhibition - Workshops
- Conference date: 16 Jun 2014 - 19 Jun 2014
- Location: Amsterdam, Netherlands
- ISBN: 978-90-73834-90-3
- Published: 16 June 2014
81 - 100 of 142 results
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Utilizing Impressed Current Cathodic Protection as the Source for Electromagnetic Exploration
More LessCentral Europe is criss-crossed by pipelines to transport water, gas and oil. Metal pipelines are routinely protected against electrochemical corrosion with a coating supplemented with an impressed current cathodic protection (ICCP) system. For pipeline integrity tests, the rectified injection current is temporarily switched on and off. The switching scheme effectively generates time-varying electrical currents and induces secondary electric and magnetic fields in the subsurface, which decay spatially and temporally as a function of subsurface electrical resistivity. Here, we describe our first attempts to measure and to analyze the induced electromagnetic fields generated by switched cathodic protection currents in order to determine the subsurface electrical resistivity structure in the upper (few) kilometers depth range. This approach is closely related to controlled source electromagnetics. It may provide a cheap complement to existing electromagnetic geophysical sounding techniques, which is applicable in noisy environments without facing the logistical challenge of the installation a strong current source in the field. The methodology can aid in geophysical subsurface reconnaissance addressed in the exploration and monitoring of resources, reservoirs and geological storages.
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Assimilation of Time-lapse CSEM Data for Fluid Flow Monitoring
Authors M. Lien, T. Mannseth and R. AgersborgThe feasibility of marine CSEM for reservoir monitoring is supported by several model studies suggesting that there may be a detectable time-lapse signal in CSEM data. However, the detectability of these signals for field cases will depend on careful acquisition design and reliable inversion methodology. To mitigate the inherent non-uniqueness associated with these large scale geophysical problems, the integration of additional data types is required. Constraining the solution space by including different data types in the model calibration process can help reducing the model uncertainty and lower production related risk. In this talk, the use of statistical ensemble based methods (EnKF) for the integration of CSEM data and other geophysical data types (i.e. gravimetric data) will be discussed. By the utilization of a statistical inversion method, an assessment of the uncertainty in the estimated flow patterns is obtained as part of the solution.
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Hydro-frac Monitoring Using Ground Time-domain EM
Authors G.M. Hoversten, M. Commer, E. Haber and C. SchwarzbachThis paper explores the sensitivity of surface based time domain electromagnetic systems for monitoring hydraulic fractures. The steel well casing of the frac well acts primarily as a DC current path that charges the conductive fracture zone during the transmitter on-time. This increases the current density in the fracture zone several orders of magnitude above that without the steel well connection. The background resistivity for production environments range from Bakken shale (30 Ohmm) to West Texas carbonates (500 Ohmm). The transient decay response from fracture zones with steel casing produces anomalies between 5% (30 Ohmm background) and 150% (500 Ohmm background) for Ex-Ex coupled surface systems for a 1500 bbl injection (a small frac stage) at 3km below the surface when a conductively enhanced proppant is used. An adequate characterization of hydraulic fractures will no doubt require the integration of multiple disciplines, including production/injection data and other geophysical techniques. EM methods can play an important role because they can sense where fluid and conductively enhanced proppant actually go.
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Non Stationary, Broad-band Waveforms for CSEM - An Analysis with Synthetic Data
Authors M. Neukirch and X. GarciaControlled source electromagnetic (CSEM) methods are sensitive to the subsurface conductivity structure and thus had led to its use in resource exploration. Since the frequency for peak sensitivity and the exact location of an exploration target is normally unknown prior exploration, it is desirable to acquire the transfer functions for a broad range of frequencies and in a wide area. Investigations in both directions have been driven by optimising properties of the Fourier transform in order to enhance the frequency range and the source-receiver distances. Recent research on non-stationary (NS) time series analysis tools significantly enhanced processing of NS time series. This work assesses the possibility of NS source waveforms by presenting a chirp source that is highly customisable in amplitude and frequency range in order to accommodate any frequency range in combination with virtually any amplitude for each frequency (e.g. in order to counter attenuation by decreasing power from low frequencies to increase high frequency power assuming constant energy supply). A numeric example illustrates the NS waveform and that robust NS time series processing may lead reliably to the transfer functions of a 1D conductivity model. Lastly, the advantages of a freely customisable waveform design are discussed.
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The Prospecting Potential of Frequency and Pulse CSEM
Authors P. Barsukov and E. FainbergThe depth of exploration, sensitivity and resolution of two methods of marine electromagnetic soundings using a horizontal electric dipole as a field source are investigated. An inline dipole-dipole setup measuring a horizontal electric field in the frequency domain and the vertical electric field in a pulsed mode (time domain) in the near-field source are analysed. It was found that the sensitivity of the pulse method in shallow water is higher than that of the frequency approach. In water depths exceeding 800 m, the sensitivities of both methods are approximately the same. The horizontal resolution of the pulse method is higher throughout the range of depths studied. A new approach to the inversion of sounding results is demonstrated on a model of the geological section.
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The 3D Forward of Vertical Current Source Electromagnetic Method
More LessA special CSEM in frequency-domain method, using a vertical current source place on the wall of a borehole and measures the horizontal electric fields on the surface, is named Vertical Current Source Electromagnetic (VCSEM) method is introduced in this paper to study the feasibility of the method. The 3D responses calculated using finite difference simulation scheme to analyze the 3D responses in case of the source being buried different depth. The results show that the multiple information about the object can be obtain using the observation data of the different depths of the VCS. Therefore, the vertical CSEM method is a high-precision electromagnetic method and have the potential to be applied in prospecting minerals, predicting water inflow or mapping reservoir boundary and monitoring the variations of oil-gas contact, and so on.
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A Scalable Parallel Edge 3D Finite-lement Approach to Marine Controlled Source Electromagnetic Using a Multifrontal Sol
More LessWe present a Scalable Parallel edge 3D Finite-Element Approach to marine controlled source electromagnetic using a multifrontal solver.By using domain decomposition of METIS grid partition technology,we make the most of each MPI processors.In orde to decompose the matrix system and solve right sides for different sources we use a massive parallel multifrontal solver implementation (MUMPS). The result of 3D CSEM matches very well with the 2.5D CSEM.
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CSEM Monitoring of a CO2 Reservoir Imaged by MT
Authors V. Puzyrev, P. Queralt, J. Ledo, E. Vilamajo, A. Marcuello, J. de la Puente and J.M. CelaDuring the last years, different studies based on numerical simulations have shown the potential of CSEM for CO2 monitoring. In this study, we carried out a set of simulations for CSEM monitoring of CO2 realistic deep saline reservoir in a 3D dome anticline structure. We perform numerical simulations in different scenarios (emission frequencies and surface-to-borehole configurations) in order to investigate the effect on the resolution when the simulations are done considering a baseline geoelectric model resulting from the inversion of MT synthetic data.
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Future Applications for CSEM - Shales and Monitoring
By K.M. StrackCSEM has become again of interest for land applications because of emerging markets such as reservoir monitoring and shale applications. They are sufficient high value to justify dealing with the complexity of a grounded dipole source, necessary to resolve both the resistors (oil reservoirs) and the conductors (host rock) equally well. For shale application, three key applications are: Reservoir depletion, fracture monitoring and geosteering. Since increased accuracy is required at different field development stages, borehole measurements need to be added as depth and accuracy requirements increase. For monitoring, one starts with surface only measurements. Since in more mature fields have borehole data, they should be added for a realistic 3D solution. In all cases, feasibility studies are essential to guide the fieldwork. To estimate the risk correctly, one should acquire noise data as oilfield are likely to have pipes and corrosion protection installed. With that noise data and bounding it by the 3D seismic reservoir boundaries we can illustrate the success chance of CSEM. Because EM responds to fluid contrast, we see more cases where EM is likely to work than not. As in these cases there is often no seismic signature it is likely to track fluid movements even better than seismic.
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Seismic-EM Integration Tackles Deep Water E&P Challenges
Authors A. Zerilli, M.P. Buonora, P.D.L. Menezes, J.L. Crepaldi and T. LabruzzoDeep water is a complex high-risk environment with no shortcuts to success. Joint interpretation of seismic and deep reading electromagnetics (EM) can provide a powerful tool for the risk mitigation process. This work focuses on the advances and challenges in seismic-EM integration and gives case examples of imaging improvements that are consistently proving to lower exploration risk while maximizing knowledge of the prospects in the deep Brazilian offshore where challenges, logistics, and costs can be formidable.
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Industry Adoption and Use of the CSEM Technology
Authors S. Fanavoll and P.T. GabrielsenAfter more than ten years of acquisition of EM data, it is widely accepted that the technology has a significant potential for improving exploration efficiency. However, despite the fact that there is a convincing track record of EM results correlating with well results and some oil companies incorporating EM technology into their workflows, adoption of the technology in the industry overall has not come a long way. This paper discuss some of the challenges faced by the petroleum industry in the interpretation of EM data, as well as necessary improvements of the technolgy in order to enhance the value of incorporating EM data into decision workflows. the current use of EM is illustrated by two examples, one unsuccessful and one successful
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Development of a 3D velocity Model for Improving the Location of Potentially Induced Earthquakes in the Gulf of Valencia
Authors B. Gaite, A. Ugalde and A. VillaseñorOn September 2013, unusual seismic activity was detected around an underwater gas storage plant in the gulf of Valencia (Spain). According to the reports by the Spanish National Geographic Institute, more than 550 occurred during two months, the strongest having a magnitude of Mw=4.2, which took place after the gas injection activities halted. The low magnitude of the events (only 17 earthquakes had magnitudes greater than 3), their long event-to-station distance, and the inhomogeneous station distribution, made the location problem to be a great challenge. Here we present a preliminary relocation of this earthquake sequence using absolute and relative methods. We also present a new 3D shear-wave velocity model estimated from inversion of Ambient Noise Tomography data which will serve to obtain more accurate seismic-wave travel times to improve the earthquakes location in this area. The interpretation of the results in terms of the tectonic structure of the region is in progress.
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Surface Microseismic Monitoring of Hydraulic Fracturing of a Shale-Gas Reservoir Using Low-Frequency Sensors
More LessIn this study, we report results from a surface microseismic monitoring of a 21-stage hydraulic fracturing of a shale gas reservoir along a horizontal well. The depths of hydraulic fracturing range from 2500m to 3020m. A surface array consisting of 45 sensors was deployed around the well, with 27 L22E short-period and 18 CMG-6TD broadband seismometers. For analyzing the continuously recorded microseismic data, we adopted the following steps: (1) event detection, (2) event location, (3) event focal mechanism determination, and (4) microseismic imaging. The double-difference seismic tomography method of Zhang and Thurber [2003] is applied to determine the Vp and Vs anomalies due to the fracturing process. In total, more than 700 events were detected. The events can be categorized into two groups: group I near the wellbore and group II about 500 meters to the east of the wellbore. The group II events are likely induced by the pore pressure increase directly caused by fluid migrated from the fracturing spot or the pressure perturbation caused by undrained response of fluid injection. The velocity tomography shows that the fracturing process causes lower Vp and Vs anomalies around the fracturing zone.
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Small Microseismic Surface Acquisition System Case Study
Authors G.N. Erokhin, V.D. Baranov, A.N. Kremlev, D.N. Gapeev, I.I. Smirnov and S.V. RodinSmall Microseismic Surface Acquisition System for oilfield monitoring is presented. Algorithms for data processing are based on the mathematical theory of inverse problems and the using of the supercomputer calculations. A distinctive feature of the suggested system is high mobility, compactness and universality. The technology based on the this acquisition system is intended not only for hydraulic fracturing monitoring but also for long-duration passive monitoring of fluid injection, for hydrocarbon drainage area estimation and for oilfield block structure mapping. Case Study has more than 50 examples.
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Diffraction Stacking - The Role of Source Mechanisms
Authors O. Zhebel, D. Gajewski and C. VanelleLocalization of seismic events provides us valuable information about structures activated by tectonic stresses, geothermal or volcanic activity, reservoir stimulation, and other subsurface activities. In the last few years automatic stacking-based localization techniques that do not require any picking of phases, have become popular and widely-used localization tools. Localization results obtained by such techniques are influenced by various factors. In this work we illustrate that source mechanisms directly influence the form and resolution of a resulting image function. For this purpose, two numerical examples are presented. The first considered source type is a so-called compensated linear vector dipole source, which is typical for geothermal and volcanic areas. As the most seismic events can be best characterized by a combination of explosive, double-couple (DC) and compensated linear vector dipole (CLVD) components, localization of such a source mechanism is also illustrated.
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The Application of the Microseismic Monitoring in Natural Fracture Detection
More LessMicroseismic monitoring (MSM) is one of the effective and real-time evaluation techniques for the fracturing. The results from in-field real-time MSM always provides the valuable benefits that help us gain an insight into the changes in the reservoir and the status of the fracturing operation. Sichuan area has a complex structure characteristic and many natural fractures are activated by the fracturing.The paper describes the different fracturing responses between the shale and tight sand, reveals its special characteristic of the natural fracture which activated by fracturing and probably provides the method (Relative magnitude), suitable analysis (Radiated pattern, Linear distribution), and interpretation (Integrated fracture interpretation) to detect the natural fracture through MSM and prevent induced fracture propagation towards fault zones.
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Accounting for Seismic Energy Release and Fracture Surface Area Development Associated with Hydraulic Fractures
Authors T.I. Urbancic, A. Cochrane and A. BaigHydraulic fracturing in naturally fractured reservoirs is known to generate seismicity due to the interaction of injected fluids with the pre-existing fracture network. Typically, the observed moment magnitudes for such operations are small, usually with Mw < 0. To map the seismicity during these injections, geophones (typically consisting of only 15 Hz elements) are deployed in arrays in nearby wells. From such configurations information on the relative stimulation volumes and overall fracture dimensions can be obtained. However, the ubiquity of these high-frequency instruments has profound implications for the reliability of magnitude estimates for the largest events associated with these treatments. To address this concern, accelerometers and lower-frequency geophones can be installed to characterize events over a wider magnitude band. Furthermore, these sensors can be combined with the high-frequency downhole geophones to monitor (hybrid sensor network) the full bandwidth of activity that can occur during fracture stimulation programs.
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Auxiliary Media - A Generalized View on Stacking
Authors B. Schwarz, C. Vanelle and D. GajewskiStacking still plays a fundamental role in seismic data processing. While the summation helps to decrease data redundancy and leads to a first interpretable time image with a high signal-to-noise ratio, the estimated stacking parameters form the foundation of many important subsequent processing steps, including depth imaging. Current multi-parameter stacking techniques aim to include higher order terms in the traveltime moveout surface. Without increasing the number of parameters, this goal is commonly achieved by assuming a certain reflector geometry and straight raypaths. In the presence of heterogeneity, as a consequence, moveout is described in an auxiliary medium. Although modern methods are usually based on the same set of parameters, we show that they can be divided into two types of approximations, one assuming an effective medium, the other describing the optical analogue in a medium of constant near-surface velocity. Based on ideas of de Bazelaire and Höcht, we provide a simple but general recipe to transform operators from the effective to the optical medium. As an example, we investigate the optical representation of a nonhyperbolic effective medium operator currently in use. In addition, we clarify the unique role of the multifocusing method and point out distinct advantages of both approaches.
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3D Common Offset CRS for Data Pre-conditioning
More LessCommon Offset CRS allows to enhance S/N and to regularize pre-stack data, to be used for pre-stack migration algorithms, both in time and depth domain
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Prestack Signal Enhancement by Multi-parameter Common Offset MultiFocusing
Authors E. Landa, M. Rauch-Davies, K. Deev and A. BerkovitchImaging in complex areas is of great importance in seismic imaging. First of all it is connected to the ability to extract valuable information from the raw seismic data and to use this information for constructing of a reliable velocity model, which is a crucial step in depth imaging. In such case, time processing is a necessary step to improve signal to noise ratio in the raw data. Moreover, results of time imaging can significantly help to create reliable velocity models and consequent depth images. Improving the quality of prestack data always stays in focus of intensive research. In this paper we follow an approach presented by Berkovich et al. (2011) which proposes using a local COMF approximation for traveltime stacking surface description. It allows for an arbitrary common offset adequately approximate traveltimes of seismic events in the vicinity of a CMP position. The paper presents application of the proposed procedure on synthetic and real data including imaging using the improved seismic data.
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