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78th EAGE Conference and Exhibition 2016
- Conference date: May 30, 2016 - June 2, 2016
- Location: Online
- Published: 30 May 2016
21 - 40 of 1034 results
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A New Method for Field-wide Real-time Subsidence Monitoring with Sub-centimeter Accuracy
Authors H. Ruiz, R. Agersborg, B. Fagerås, L.T. Hille, M. Lien, J. E. Lindgård and M. VatshelleSummarySeafloor subsidence is an observable effect of reservoir compaction, and hence provides important information for the management of offshore reservoirs. In some extreme cases, seafloor subsidence can compromise the safety of the installations and even cause well failure.
This abstract proposes a new, patented system for real-time monitoring of subsidence over large areas with sub-cm accuracy. The system consists of two main elements. The first is a grid of pressure sensors permanently deployed on the seafloor. The sensors can be integrated in a full-scale permanent reservoir monitoring system or a smaller caprock integrity monitoring system.
The second element is a periodical surveying that provides the calibration of the seafloor sensors, by means of the comparison of the real-time seafloor measurements with the subsidence measured between the baseline and the repeat surveys.
This abstract describes first the method used for the periodical surveying, traditionally used for measuring both 4D gravity and subsidence. Then, the challenges related with the integration of pressure sensors in a permanent monitoring system at the seafloor are introduced, and the need for an in-situ correction for the drift of the sensors is motivated. The new method for solving this problem is described in the last section.
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CO2 Reservoir Monitoring Using a Permanent Electrode Array - The Ketzin Case Study
Authors C. M. Schmidt-Hattenberger, D. Rippe, T. Labitzke, P. Bergmann and F.M. WagnerSummaryAt the Ketzin pilot site (Germany), a permanent downhole electrode array is accompanying the geological CO2 storage operation from June 2007 until December 2016. Electrical resistivity tomography (ERT) results provide images about relevant operational stages of the storage reservoir. The presented geoelectrical downhole system displays a very promising long-term behavior, and its technical effort and cost has been amortized by its continuous application during the complete injection history. The experiences drawn from the Ketzin site yield strong arguments for the application of the ERT method as part of a multi-disciplinary monitoring concept.
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The CO2CRC Otway Project deployment of a Distributed Acoustic Sensing Network Coupled with Permanent Rotary Sources
Authors B.M. Freifeld, R. Pevzner, S. Dou, J. Correa, T.M. Daley, M. Robertson, K. Tertyshnikov, T. Wood, J. Ajo-Franklin, M. Urosevic and B. GurevichSummaryWe have deployed a novel permanent monitoring system at the Australian CO2CRC Otway Site that includes a surface and borehole distributed acoustic sensing (DAS) network with orbital vibrator (rotary) surface seismic sources. DAS is an emerging technology for performing seismic acquisition based on optical interferometric techniques, which allows for data collection with a wide spatial aperture and high temporal resolution using commercially available telecommunications fibres. DAS sensitivity currently lags behind conventional discrete geophone and hydrophone sensor technologies. Our implementation of surface rotary seismic sources is based on open-loop controlled asynchronous motors. This avoids the complexity of feedback loops for phase control, instead using deconvolution of the source function as measured by a shallow source-monitor sensor. Initial data analysis shows that the amount of energy available from long source sweeps overcomes limitations in DAS sensitivity. The combination of relatively inexpensive but powerful permanent surface sources with permanent DAS deployment in an areal array provides a new paradigm for time-lapse seismic monitoring. The methodology we describe has broad applicability for long-term reservoir surveillance, with time-lapse change sensitive to many subsurface properties.
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Correlating Frequent InSAR Deformations with Reservoir Pressure for Areal Conformance in Thermal EOR at Peace River
Authors C. Didraga and J.L. LopezSummaryWe present a preliminary analysis of the InSAR data acquired over the Pad 31 thermal EOR development area, located in the Peace River Oil Sands, Alberta, Canada.
While InSAR is often viewed as a technology for reservoir containment monitoring, we demonstrate that it may be very effectively used for conformance monitoring if data are acquired frequently.
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How Permanent DTS Installation Could Improve Well and Reservoir Knowledge
Authors AL Leone and G.G. GALLISummaryThe paper describes, by means of real and blind example, how the continuous thermal profiling provided by permanent DTS is useful for many extra application than the pure fluid allocation purposes. For an unconventional reservoir a permanent and continuous monitoring tool represents the key point to provide a correct management of the reservoir and hence to maximize the recovery factor of the field. The proposed case is based on a horizontal producer drilled in gas shale located in North America. In order to evaluate which are the possible issues that could affect the overall monitoring system, DTS analysis already started before the production phase, directly during the installation. This was the occasion to test and bring the technology to the next step: a proper analysis of the data taken during installation provides additional informations about wellbore conditions whereas the warmback dataset, that followed frack job, increased knowledge about the dynamic attitude of the fractures just created, providing a qualitative forecast about the expected production profile. The final result is that the continuous update in temperature profiling given by DTS could improve significantly well efficiency knowledge and the reservoir performances evaluation even when no further investigations are feasible in the wellbore.
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4D Using Non-repeated OBS Acquisition Systems on the Njord Field
Authors M.S. Guttormsen, S. Ng, Ø.H. Solbu, H. Westerdahl, J. Oukili and T. HøySummarySeismic monitoring has been challenging on the Njord field. The rather weak 4D responses related to production have been difficult to detect due to the noise level in the streamer 4D seismic data and due to dominant overpressure effect after injection. The streamer seismic data was replaced by Ocean Bottom Seismic (OBS) in 2010 and the first repeat was performed in 2014. The 4D noise level is expected to improve using Ocean Bottom Seismic (OBS) due to repeated receiver positions and better coverage closer to installations. However the sensor technologies and the seismic source were not repeated and we show how we accommodated for this. In addition, we will show how the lack of shallow overburden illumination through the OBS acquisition was compensated for using streamer seismic data and imaging with multiples.
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Angle-dependent Water Column Statics Correction through Sparse TauP Inversion
Authors R. Huang, P. Wang, K. Nimsaila and M. VuSummaryWater column statics caused by tidal variation and water velocity change during seismic surveys is one major source of noise in marine 4D projects. Correction of this statics effect is a key step in any marine 4D processing. Applying water column statics correction requires a good knowledge of the distance or surface take-off angle when waves travel through the water column, which conventional methods such as ray tracing are not able to obtain accurately when the subsurface velocity is complex.
We propose a new method to apply water column statics correction through progressive sparse TauP inversion. This method does not need prior inputs of subsurface velocity and reflector dips, as required for ray-tracing methods, and benefits from the progressive sparse TauP inversion engine that can properly handle spatially aliased marine seismic data and mitigate energy leakage in the TauP domain.
We demonstrate the effectiveness of this new method using synthetic ocean bottom seismometer (OBS) data derived from a SEAM velocity model and using real OBS data from 4D surveys over the Atlantis field in the Green Canyon area of the Gulf of Mexico (GOM).
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Simultaneous Time-lapse Imaging via Joint Migration and Inversion
Authors S. Qu and D.J. VerschuurSummaryWe propose a simultaneous Joint Migration and Inversion (SJMI) method for time-lapse migration/ inversion, which combines a joint time-lapse data processing strategy with the Joint Migration and Inversion (JMI) method, and also extend it to include an L1-norm sparsity constraint on the reflectivity model-difference in a suitable transform domain and a total-variation (TV) edge-preserving constraint on the velocity model-difference. We tested the proposed method with two synthetic examples, from which it is shown that our method is effective, even when the datasets contain strong noise, are generated by different acquisitions, and also contain a strongly scattering overburden.
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Time-lapse Repeatability Evaluation of a Multimeasurement Towed-streamer System - A North Sea Case Study
Authors C. Ocampo, P.A. Watterson, C. Cunnell, L. Hodgson and D. DaviesSummaryWe present a case study comprising a time-lapse seismic (4D) repeatability test in the North Sea using a broadband multimeasurement towed-streamer acquisition system. Repeat acquisition with unchanged parameters and minimal time-lapse enabled various wavefield separation techniques to be evaluated, additionally providing a rigorous test for 3D capabilities. Wavefield separation approaches comprised both dual-sensor (PZ) and full multimeasurement (PZY) approaches. The results show consistently higher spatial resolution in the multimeasurement prestack depth migrated volumes, particularly in the shallow section, but also slightly elevated noise levels, especially in the higher-frequency bands. The 4D difference plots are consistent with respect to the elevated noise, but higher 4D signal leakage is observed on the dual-sensor (PZ) data, also within the main signal bandwidth at the reservoir level. This demonstrates a subtle but consistent uplift in the full multimeasurement data set, extending from shallow to reservoir level, suggesting that processing steps including multiple attenuation and migration benefit from dense spatial sampling, even at depth.
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4D Feasibility Case Study in a Mature Oilfield
More LessSummaryFeasibility study is an essential component for 4D seismic projects. It includes rock physics modelling, seismic forward modelling, 4D difference calculation and feasibility study. Among them, rock physics modelling is very important because it links the attributes of reservoir fluid-flow simulation model with elastic properties such as P-wave and S-wave properties, and the measured data of cores in the laboratory are required. However, these data are lack of for some oilfields. But well logging data are available. We propose a method of rock physics modelling using well logging data, based on which 4D feasibility is carried out. It is applied to a mature oilfield where a seismic survey was shot more than ten years ago, which is different from what we usually do, to an undeveloped oilfield. The subsequent 4D case study proves the proposed method is practical, and it is the first 4D project offshore in China.
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A Regularization Algorithm Optimized for Time-lapse Processing
Authors A. Khalil, H. Hoeber, B. Deschizeaux, M. Ibram and D. DaviesSummaryIn time-lapse processing, independent regularization of each vintage is the typical approach. This disregards any geometrical limitations imposed by different surveys. Here we recast the regularization process as a minimization problem with model-space constraints. These constraints couple geometrical relations between surveys to improve repeatability. We also demonstrate how to solve the minimization problem using a practical and pragmatic approach. Results from a North Sea dataset show overall reduction of 4D noise, especially around less repeatable parts of the surveys including the undershoot zone.
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A Novel Approach for Cost Effective PRM Seismic Operations at Snorre
Authors M. Thompson, A.S. Pedersen, M. Andersen and S.M. SkoglandSummaryThe Snorre Permanent Reservoir Monitoring system has a receiver area encompassing approximately 200 km2, and aims to monitor, seismically, the reservoir twice a year; through autumn and spring seismic campaigns. In order to acquire two seismic surveys during a single seismic season in the North Sea, while still maintaining enough separation in time to allow for monitoring of the production effects in the reservoir requires consideration of a novel technique to ensure that both surveys are effectively acquired. Since the seismic sensors are stable from one survey to another, and in the case of no production effects outside the receiver area, shots from outside the receiver area can be borrowed from earlier surveys and used to pad out the repeated surveys during the processing of the seismic. This enables a managed reduction in the annual source effort, while ensuring good time-lapse data quality, and contributes to acquisition of two monitoring surveys per year.
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Measurement and Dynamic Wavefield Correction for Time-dependent Water-velocity Changes
Authors R. Zietal and R.R. HaackeSummaryChanges in water velocity produce significant 4D noise in time-lapse images. To be addressed accurately, the water-velocity problem requires two major ingredients: 1) water velocity must be estimated accurately at all acquisition times and for all shot/receiver locations, 2) time-variable corrections to the data must be dynamic to treat the full wavefield accurately. We present a new approach to parameterization of water-velocity changes which minimizes sensitivity to water depth, allowing data redundancy to be exploited to increase robustness and precision of water velocity estimation. Dynamic correction of the wavefield is then achieved by designing 3D time-variable phase-shift operators that extrapolate data through the water column with a time-variable water velocity and re-extrapolate back to the acquisition datum with a stationary (reference) velocity. This is applied in a tau-px-py least-squares modeling process. Application of the method to deep-water OBN data shows significant improvements in data repeatability, decreasing 4D noise and increasing focus and clarity of the 4D signal.
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High Resolution Model Building and Broadband Imaging in Deep Water Offshore Angola
Authors A.A. Shmelev, A. Cooke, O. Zdraveva and J. PenwardenSummaryWith increased interest in pre-salt hydrocarbon exploration in Kwanza Basin offshore Angola, reliable and accurate information from surface seismic data is critical to successful imaging. This area, however, presents many challenges to the geophysicist, being characterized by complex salt geometry, high velocity carbonate layers, a faulted tertiary section and limited well control. In such an environment the desired seismic would have long offsets, rich azimuthal coverage and be broadband by design. Using the latest data-processing techniques, including deghosting and high-resolution model building, a combination of reflection tomography and full-waveform inversion (FWI) we add significant value to existing, conventionally acquired, narrow-azimuth datasets, ultimately leading to improved imaging and interpretation confidence in pre-salt structures.
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Full Waveform Inversion and Ambiguities Related to Strong Anisotropy in Exploration Areas – Case Study Barents Sea
Authors Ø. Korsmo, S. Marinets, S. Naumann and G. RønholtSummaryIn this case study from the Barents Sea, we have used refraction based Full Waveform Inversion (FWI) in an extreme anisotropy regime without the support from well information. We reveal our observations for decoupling the vertical and horizontal velocity, which enables us to achieve good data matching as well as flat gathers, focused images and a geological consistent model. Our frequency cascaded FWI flow results in a high resolution velocity model to the depth of interest, following the faulted crest in great detail, as well as low velocity zones correlating with the bright spots in the seismic image.
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TI Anisotropy Calibration with Sonic and Walkaway VSP
Authors R. Guerra, E. Wielemaker, F. Miranda, M. Ferla, F. Pampuri, S. Gemelli and V. MattonelliSummaryVelocity anisotropy calibration using Walkaway VSPs or sonic data has been shown to deliver net quality improvements in seismic imaging. Nevertheless, common industry workflows still do not take full advantage of all available data. In this study, advanced borehole sonic and Walkaway VSP data acquired in a single presalt vertical well were combined to estimate continuous depth profiles of Thomsen parameters. These parameters were successfully propagated away from the well in the surface seismic velocity model, in order to minimize the Walkaway transit time residuals.
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RTM Imaging Conditions and Image Enhancement via Optical Stacking
Authors I.F. Jones, M. Kobylarski and J. BrittanSummaryThe final stage of a migration process is usually the imaging condition, which brings together elements of the upcoming and downgoing wavefields for each shot gather in order to form an image contribution. This procedure suffers limitations due to the approximations made in representing the physics of the system, but in addition to that, the final summation of all shot contributions necessarily assumes that the subsurface parameter model was perfect, such that all image contributions align perfectly for summation (within a Fresnel zone), as well as having recorded data that are noise free and adequately sampled. In this work, we assess the effect of unresolvable velocity errors on the final image, and present a case study example of a technique for compensating for these errors via techniques borrowed from astronomical image processing applied to each of each of the many thousands of elemental traces that contribute to the final image.
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Integrating Geophysical and Geological Models for De-risking Hydrocarbon Exploration – a Rio del Rey Basin Case Study
Authors P.G. Wilson, J. Wanstall, M.P. Jameson, M. Nuzzo, P. Nguema and S. TamfuSummaryThis paper presents a case study outlining key technical developments and the integration of geophysical and geological models that have advanced our understanding of the hydrocarbon plumbing in the Agbada Formation in the Rio del Rey Basin, offshore Cameroon. Geophysical techniques including extended elastic impedance and seismic fluid classification were developed using elastic log data and modern 3D seismic data. These techniques were shown through the drilling of the Oak wells to aid the prediction of presence and hydrocarbon phase in exploration targets. Gas composition analysis in the wells combined with seismic interpretation has resulted in an understanding of how the different oil and gas reservoirs have been sourced. Integrating the geophysical and geological models means there is a coherent approach to de-risk the presence and phase of hydrocarbons in the prospects.
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A Successful Geophysical Prediction of Fractured Porous Basement Reservoir - Rolvsnes Oil Discovery 2015, Utsira High
Authors J.E. Lie, E.H. Nilsen, E. Grandal, K. Grue and R. SørlieSummaryThe Southern Utsira High in the Norwegian North Sea was explored on and off for more than 40 years before Lundin Norway made the Edvard Grieg breakthrough discovery in 2007 (186 million bbls of recoverable oil). This discovery opened up for the giant Johan Sverdrup 16/2-6 discovery in 2010 (reserve range of 1,7-3,0 billion bbl of oil). Triassic to Cretaceous clastic sandstones are here the main reservoirs.
The most recent oil discovery on the Southern Utsira High was made by the 16/1-25 S, Rolvsnes, well. This well targeted and found oil in fractured porous granitic basement. In this paper, Lundin Norway will present this basement discovery and the geophysical methods used to distinguish between tight and fractured/porous basement which allowed for a successful placement of the Rolvsnes well.
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De-risking Drill Decisions - A Case Study on the Benefit of Re-processing Conventionally Acquired Seismic data
Authors E. Knight, J. Raffle, S. Davies, H. Sherazi-Selby, E. Evans, M. Johnson and I.F. JonesSummaryAcquiring and processing a new vintage of seismic data can often fall outside the time frame of ongoing field development, In this case, careful and detailed reprocessing of vintage seismic data can be a practical and timely way of de-risking any imminent drilling decisions.
Here we consider one such case study over the Thistle field, in the Northern Sector of the North Sea, demonstrating how contemporary de-ghosting of conventional marine streamer data, combined with refined demultiple techniques and iterative non-parametric tomographic preSDM model building facilitate more reliable well-track planning.
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