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72nd EAGE Conference and Exhibition incorporating SPE EUROPEC 2010
- Conference date: 14 Jun 2010 - 17 Jun 2010
- Location: Barcelona, Spain
- ISBN: 978-90-73781-86-3
- Published: 14 June 2010
41 - 60 of 797 results
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A Marine Broadband Case Study Offshore China
Authors T. J. Bunting, B. J. Lim, C. H. Lim, S. W. Pei, S. K. Yang, Z. B. Zhang, Y. H. Xie and L. LiThe effect of the sea surface ghost on marine seismic acquisition is well understood. Shallow tow geometries recover high frequencies at the expense of attenuating low frequencies and deep tow geometries recover low frequencies at the expense of attenuating high frequencies. In recent years two dual streamer tow depth solutions (Over-Under and Sparse-Under) have been deployed, both of which use two streamers which are towed at two different depths. A 2D survey was acquired offshore China, in August 2009, utilizing three separate streamer depths (5, 17 and 23 m). This three streamer depth configuration allows for the benefits of the two broadband solutions to be evaluated against each other and against a shallow streamer single depth seismic measurement. This paper will review the theory behind the two combination techniques, compare the seismic datasets, and finalize with some conclusions on the relative benefits both in terms of seismic imaging and acquisition efficiency.
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First 3-D Dual-sensor Streamer Acquisition in the North Sea – An Example from the Luno Field
Authors B. Osnes, A. Day, M. Widmaier, J. E. Lie, V. Danielsen, D. Harrison-Fox, M. Lesnes and O. El BaramonyIn 2009, the first 3-D dual-sensor towed streamer survey in the North Sea was acquired over the Luno field. This field presents a challenging area for seismic imaging that requires the best possible resolution to image the complexity of the reservoir, together with maximum signal penetration due to the presence of an overlying chalk interval. Dual-sensor technology is therefore attractive due to its ability to remove the receiver ghost, thereby increasing the usable bandwidth, which further permits increased towing depth to improve the low frequency signal-to-noise. In this paper, the acquisition and processing of this dataset will be reviewed. It will be shown that, in addition to the data quality benefits, deep towed dual-sensor acquisition has a number of operational advantages over conventional acquisition. In particular, dual-sensor streamer operations are less susceptible to weather-related noise and seismic interference.
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Mitigating the Environmental Footprint of Towed Streamer Seismic Surveys
Authors P. M. Fontana and C. P. ZickermanThe environmental risks associated with marine towed streamer seismic surveys can be categorized into four main emission components; solid, fluid, gaseous, and acoustic. Sources for each component can be identified with respect to the maritime technologies incorporated into the design of the seismic survey vessel and the seismic acquisition technologies and methods applied to specific geophysical objectives. To facilitate this analysis, we introduce the concept of an emission risk matrix. Within this matrix the potential risk level of each emission component associated with the survey vessel and the seismic equipment can be assessed. Once the primary risks have been identified, mitigation measures can then be identified which, when applied, can significantly reduce the environmental footprint of the towed streamer survey effort.
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Recon 3D – A Fast and Cheap 3D Acquisition Approach to Large Scale Exploration
Authors M. D. MacNeill and J. F. McNuttIn deep-water environments, energy companies are exploring increasingly subtle plays, in ever shorter time frames, to discover commercial hydrocarbon volumes. Advances in deep-water drilling and completions, subsea equipment and facilities technology underpin many of the recent commercially successful deep-water developments; exploration seismic advancements lagged those in engineering. In deep-water frontier environments, seismic stratigraphic and structural interpretation, in addition to hydrocarbon system and regional analyses, obviously are key components of prospect evaluation and risking leading to successful exploration and development programs. Clear business need provides an opportunity for more cost effective seismic acquisition technology. This paper introduces the novel RECONnaissance 3D marine seismic acquisition method that provides the spatial and temporal resolution of conventional marine 3D seismic, but at a significantly reduced cost. RECON 3D is an ideal method for acquiring deep water seismic data to explore large areas, to upgrade separately or previously acquired azimuthally restricted data, or to acquire fast-track data covering numerous fields, prospects, or leads.
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First Wide-azimuth Time-lapse Seismic Acquisition Using Ocean Bottom Seismic Nodes at Atlantis Field – Gulf of Mexico
Authors G. J. Beaudoin, M. D. Reasnor, M. Pfister and G. OpenshawThe world's first ocean bottom seismic (OBS) node-on-node time-lapse monitor survey was acquired at Atlantis Field in the Gulf of Mexico in 2009. The baseline survey, acquired in 2005-2006, was the first large-scale deepwater OBS survey employing autonomous nodes (Beaudoin and Ross, 2007). Following first oil in October 2007, studies were initiated for a time-lapse survey to monitor production changes in the Atlantis reservoir. The baseline survey demonstrated that remotely-operated vehicles (ROVs) could deploy and recover autonomous nodes with high positional accuracy even in the presence of severe bathymetric challenges. This capability underpinned the design, planning and execution of a highly repeatable monitor survey. For the monitor survey, an ROV deployed 500 nodes to a subset of the original 1628 baseline node locations. These 500 monitor locations were chosen to image the expected area of reservoir changes after careful analysis of image quality as baseline data were progressively decimated. The ROV deployed 91% of the nodes to within 5 meters of their respective baseline locations and 98% within 10 meters. This remarkable geometric repeatability within a producing field has laid the foundation for highly repeatable monitor surveys even in challenging seafloor environments.
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A Case Study of a High Latitude Towed Streamer 3D Seismic Survey
Authors A. Ross, S. Hildebrand and S. ViceerIn the summer of 2009, CGGVeritas collected a towed seismic streamer survey in the Canadian Beaufort Sea for BP. This was the highest latitude (>71 degrees) towed streamer 3D survey collected by either company. The presence of first-year and multi-year sea ice dominated the operation and taught both companies a great deal about high latitude seismic operations.
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Randomized Sampling Strategies
More LessSeismic exploration relies on the collection of massive data volumes that are subsequently mined for information during seismic processing. While this approach has been extremely successful in the past, the current trend towards higher quality images in increasingly complicated regions continues to reveal fundamental shortcomings in our workflows for high-dimensional data volumes. Two causes can be identified. First, there is the so-called "curse of dimensionality" exemplified by Nyquist's sampling criterion, which puts disproportionate strain on current acquisition and processing systems as the size and desired resolution of our survey areas continues to increase. Secondly, there is the recent "departure from Moore's law" that forces us to lower our expectations to compute ourselves out of this curse of dimensionality. In this paper, we offer a way out of this situation by a deliberate randomized subsampling combined with structure-exploiting transform-domain sparsity promotion. Our approach is successful because it reduces the size of seismic data volumes without loss of information. As such we end up with a new technology where the costs of acquisition and processing are no longer dictated by the size of the acquisition but by the transform-domain sparsity of the end-product.
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Acquisition Design for Incoherent Shooting
Authors G. Blacquiere and A. J. BerkhoutIn blended seismic data acquisition, the blended source wavefield should be designed in such a way that it has a large spatial bandwidth without notches. This corresponds to using blended source arrays with a high degree of incoherency. The three-dimensional (x,y,t) autocorrelation function of the blended source wavefield at the surface is proposed as a surface-related, quantitative measure of incoherency. In this assessment the subsurface is not involved. A second measure is proposed that does include the propagation effects of the near- and subsurface on the illumination by the blended source wavefield. For each subsurface gridpoint the autocorrelation function of the incident blended source wavefield - being represented by a dispersed time series - is judged for its whiteness. This result can be extended to angle-dependent illumination by computing the cross-correlation function as well.
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Time-lapse Refraction Seismic Monitoring
Authors F. Hansteen, P. B. Wills, J. C. Hornman, L. Jin and S. J. BourneA novel seismic technique for reservoir monitoring has been developed and tested in a resent field trial at the Peace River heavy oil field in Alberta, Canada. By measuring time shifts on first arrival head-waves from a refracting layer below the reservoir, the method aims to produce high-resolution areal maps of reservoir time shifts at a much lower cost than conventional 4D seismic. Good lateral resolution is achieved by numerically redatuming the wave field recorded at surface to a datum just above the reservoir. Preliminary results show plausible one-way time-lapse time shifts in the reservoir of the order of 2 ms, caused by variation in reservoir fluid pressure in the vicinity of active steam injectors.
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Benefits of Hydrophones for Land Seismic Monitoring
Authors E. Rebel and E. ForguesCGGVeritas has conducted for Shell Canada a 4D project based on a network of buried mini-vibrators associated with buried sensors. This paper shows a comparison of signal and noise recorded on different types of sensors (surface DSU, buried geophones and hydrophones). We conclude that buried hydrophones provided the best data quality: (i) they are free of shear wave, (ii) they present a better Signal to Noise ratio (20dB gain), (iii) they show better repeatability. Therefore, hydrophones are well adapted for permanent seismic land acquisition used in 4D monitoring.
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A New Approach to Efficient 4D Acquisition
Authors P. B. Sabel, L. Fenstad and S. DarlingTo acquire good 4D it is important to repeat acquisition parameters and especially the baseline’s source and receiver positions. If one cannot compensate for feather one will have to shoot 4D infill, which adds to the cost of the monitor survey. We present a novel approach to pre-plot planning and positioning QC during acquisition. From analysis of the baseline’s post-plot data for unique coverage contribution of each source-receiver pair and using a field specific tolerable positioning error we derive uniqueness criteria. Lines not matching these criteria will be removed from the pre-plot. From analysis of the baseline data we define how much feather deviation we can tolerate and introduce a robustness criterion, the feather aperture. All pre-plot lines for the monitor survey will now have an associated, line specific, feather aperture value. The feather aperture concept assists in choosing lines with a wide feather aperture for periods of unpredictable currents and can also help to reduce time spent waiting on unnecessarily tight feather matching criteria. This paper shall demonstrate a technique that should change 4D QC and also significantly improve acquisition efficiency.
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Time-lapse Acquisition With a Dual-sensor Streamer over a Conventional Baseline Survey
Authors A. Day, M. Widmaier, T. Høy and B. OsnesThis paper describes an experiment to validate the use of a dual-sensor streamer for time-lapse acquisition. Dual-sensor streamer data was acquired at an acquisition depth of 15m over five adjacent sail lines that had been acquired using a conventional streamer that records the pressure wavefield at 8m depth some months earlier. The dual-sensor streamer data were processed to obtain the total pressure field at 8m depth. Both these data and the conventional data were then taken through a state-of-the-art time-lapse processing flow. The difference in the final images is very small, as would be expected for two surveys conducted only a few months apart in an area where there is no production. The repeatability is shown to conform to industry requirements, thereby demonstrating that a dual-sensor streamer can be used to perform time-lapse acquisition in areas where earlier surveys have been acquired using conventional streamers.
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The Correlated Leakage Method – It's Application to Better Quantify Timing Shifts on 4D Data
Authors P. Paramo, D. N. Whitcombe, N. Philip, A. Toomey, T. Redshaw and S. LinnWe present a new methodology for estimating time shifts between 4D surveys, the Correlated Leakage Method (CLM). Its ability to provide accurate estimates of time shifts for a wide range of window size makes it an attractive alternative to existing algorithms. Timing shifts are calculated from the gradient of a line fitted to a cross plot of: the amplitude difference between baseline and monitor against the amplitude difference between the baseline and monitor survey average and a time shifted version of this average. The nature of the fitting process of the CLM suppresses the time shift noise and makes it stable. Additionally the CLM calculations can be implemented in 1D, 2D and 3D and can be easily modified to estimate vertical or lateral shifts between time lapse surveys. Here we review the CLM theory and discuss the advantages and limitations of this method.
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Simultaneous Multi-vintage Multi-parameter Time-lapse Matching
Authors E. Zabihi Naeini, H. Hoeber, G. Poole, F. Buker and M. van Schaack4D matching is an important processing step which is repeatedly used within a time-lapse processing sequence in order to remove residual amplitude, time and phase differences between vintages of seismic data. In this paper we introduce a new matching algorithm that minimizes the global NRMS between an arbitrary number of vintages and thus automatically achieves the best possible overall repeatability in one single matching step. The algorithm can work in the time- or frequency domain and simultaneously finds all matching parameters for all vintages. By using constraints a unique solution to this non-linear optimisation problem is found without the necessity to define an upfront reference vintage. This minimises the risk of propagating artefacts which may be present on one of the vintages to all other datasets. We show two example applications of the new algorithm. Firstly, we use the new algorithm for pre-imaging sail-line consistent removal of acquisition related artefacts (destriping) of multiple vintages. Secondly, we present examples of multi-vintage matching, as applicable to 4D residual local matching on imaged data.
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Retrieving 4D Signal in Complex Media Using the Full Waveform Inversion Paradigm
Authors P. Thore, H. Allouche, P. O. Lys and I. TarrassVarious 4D processing techniques are based on 1D approximation and their applicability is limited in the case of dipping reservoirs. In this paper we present a synthetic case study with dips up to 40° and superimposed reservoirs where data have been generated using full waveform modelling. New processing, based on full waveform inversion technique has been applied to the data in order to extract the 4D signal. Our results show that even in a complex environment seismic monitoring can be considered.
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Time Lapse Monitoring of the Elgin HPHT Field
Authors A. Grandi, O. Rahmanov, V. Neillo, F. Bourgeois, C. Deplanté and L. Ben-BrahimMonitoring is essential in understanding HPHT fields and extending their life. The high cost of infill drilling requires minimising risks of well failure, improving understanding of compartmentalisation, flow connectivity and reservoir quality away from control wells. Time lapse seismic when fully integrated with other geosciences disciplines can bring essential information to help achieving these aims. Using a dedicated warping inversion, a new and more stable 4D signal has been inverted at the reservoir level. This signal is well correlated with compaction patterns predicted by the reservoir model and brings essential information on compartmentalisation and vertical connectivity within the reservoir. Both 4D attributes and the 4D-calibrated geomechanical model are used in various operational studies targetting the reservoir and the overburden, confirming 4D as a key source of information to improve the understanding of the Elgin Field.
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Coil Shooting on Tulip Discovery – Processing Challenges and Results
Authors M. Buia, R. Vercesi, D. Nikolenko, A. T. Waluyo, M. Tham and S. L. NgThe circular (Coil) shooting geometry, when compared with conventional 3D marine data, introduces several differences and a number of new challenges in the whole modeling, acquisition and processing workflows. This paper describes the positive seismic processing experience made on Tulip Coil data in Indonesia. After an ad hoc sequence, aimed both at overcome challenges and at taking advantage from the opportunities given by circular shooting, the results demonstrated to be far superior to vintage seismic data in the area
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Multi-azimuth High-resolution Tomography – Application to Offshore Nile Delta
Authors D. W. van der Burg, S. Lin, C. Zhou and J. JiaoMulti-azimuth acquisition has been shown to be beneficial for attenuating multiple diffraction energy and improving illumination. In this case study on a multi-azimuth dataset from the Nile Delta we demonstrate that multi-azimuth reflection tomographic inversion is able to resolve smaller scale velocity variations than narrow-azimuth inversion, and hence enables more accurate velocity model building in depth. Multi-azimuth inversion is capable of resolving these small scale velocity heterogeneities because of the azimuthal diversity. The gathers obtained from multi-azimuth inversion are flatter and the stack is improved compared to narrow-azimuth inversion. The resolved small scale velocity variations correlate very well with geology.
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Exploring Oligocene Targets Using Multi-azimuth Acquisitions – Application of Non-linear Slope Tomography
Authors J. P. Gruffeille, P. Guillaume, G. Lambaré, H. Ladegaard, A. Spedding and A. El FattahNon-linear slope tomography offers an accurate and efficient way of combining dip and residual move-out information from several narrow azimuth acquisitions. We present an application of non-linear slope tomography to a multi-azimuth acquisition in West Mediterranean Sea. We demonstrate the improved resolution obtained in the velocity model thanks to the complementarities and redundancy of the azimuths.
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The Benefits of Multi-azimuth Depth Migration over the Tidepole Field, North West Shelf, Australia
Authors D. Dickinson and T. Ridsdill-SmithThe Tidepole gas field, located in WA-5-L on the North West Shelf, Australia was discovered in 1971. The field is covered by the high-resolution Demeter 3D seismic survey acquired over the central North West Shelf in 2003, but further appraisal of the Tidepole field remained difficult due to poor seismic data quality. The successful results from model studies led to the acquisition in 2007 of two additional azimuths over the Tidepole field to complement the existing Demeter data. The two new datasets were acquired at azimuths 60 and 120 degrees apart from Tidepole to maximize the azimuthal coverage. Time domain processing of the multi-azimuth data revealed the existence of strong localized velocity differences in the different acquisition directions. To resolve these differences multi-azimuth anisotropic pre-stack depth migration was proposed. During the model building process the conventional residual moveout from all three azimuths was used to perform a multi-azimuth tomography. Initially an isotropic model was used to solve for heterogeneity. Then anisotropic layers were introduced where residual moveout remained. The resulting single model was used to migrate all three azimuths to the same depth. This paper demonstrates the benefits of multi-azimuth depth migration.
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