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First EAGE Workshop on Borehole Geophysics
- Conference date: 16 Jan 2011 - 20 Jan 2011
- Location: Instanbul, Turkey
- ISBN: 978-90-73781-95-5
- Published: 16 January 2011
21 - 40 of 44 results
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3DVSP and cross-well surveys for deep EOR target imaging in South Oman.
Authors A.S. Al-Maamari and D. KiyashchenkoA geophysical surveillance pilot was started to identify the best monitoring solution for field-scale deployment. The field is being developed using steam-injection EOR methods. Baseline surface seismic, 3DVSP and cross-well surveys have been acquired and processed. Surface seismic is very challenging in the area due to complex near-surface conditions, multiple contamination and weak target formation reflectivity. On the other hand, 3DVSP and cross-well surveys allow us to get clear images of the target reservoir after application of the experimental processing approaches. For cross-well data, the use of sources and receivers below the targets and down-going reflections delivered the image of the interval of interest, whereas there was almost no use in sources and receivers above the targets. This was not expected originally and highlighted the importance of considering ’illumination from below’ as an option in pre-survey modeling. The extensive multiple presence in the field impacted the 3DVSP images created with the use of space-domain Deconvolution of up-going signal with a filter derived from downgoing waves. In order to suppress multiples more efficiently, we developed and applied ’interferometric deconvolution’ in the wavenumber domain. This deconvolution approach led to a cleaner image of the target.
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Application of 3D VSP's to Tight Gas Reservoir Characterization
Authors P. Mazumdar, T.L. Davis, J. Liu and R. BansalExploration and development of tight-gas sandstone reservoirs relies heavily on understanding the distribution of sandstone bodies in the subsurface. Shear-wave sourced 3D vertical seismic profiling (VSP) data are used for sandstone detection and fractured interval delineation. Anisotropic Kirchhoff 3D prestack depth migration was applied to the shear-wave reflection data. A geologically-constrained migration-velocity model was created by integrating the results from the virtual source method, well logs, interval velocity derived from surface seismic and the Dix-differentiation of the fast and slow shear-wave NMO ellipses. The resulting common image gathers (CIG) are flat, indicating that the reflection events can be stacked reliably. The depth migrated images tie with the well logs and the surface seismic data. The VSP images show subtle stratigraphic features involving sandstone intervals in the Williams Fork Formation and pinchouts in the coal beds within the Cameo Coal interval. Structural features, especially faults, previously unnoticed on surface seismic data are now clearly visible. The shear-wave VSP data can now be used as a complementary dataset to other commonly acquired data such as surface seismic, well logs and core data and microseismic information to improve reservoir characterization.
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A new Well-Seismic method to help Seismic-to-Well ties in complex environments. Example on the deep-offshore, Angola
Authors C.C. Cheyron, V.M. MARTIN, P.T. THORE and A.P. PAREThe development of PSDM processing enables interpreters to work in the depth domain. But as PSDM velocity is not the same as actual velocity, we wonder then whether the drilling trajectory is compatible with the PSDM data. The answer is certainly affirmative if the PSDM velocity is close enough to the actual subsurface velocity and negative if is not. To circumvent this difficult problem of the PSDM velocity, we devised a new method for computing a well trajectory that is fully compatible with the PSDM volume. Thus, even if the PSDM is biased, the relocated well trajectory will be shifted consistently. The events seen while drilling the well will be really crossed on the PSDM by the relocated trajectory and this way, even if the PSDM velocity volume is not clearly established, interpreters will be able to tie their PSDM more successfully. In this paper, we describe the principle of this new well-seismic method, called Multi Offset Relocation (MOR), which consists in intersecting wave fronts shot from several different VSP offsets. We show how to use it in practice, and present an example of its application in the deep-offshore subsalt domain in Angola.
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Optimization approach to automatic first arrival picking for 3C 3D VSP data
By E. BliasA new adaptive optimization method for accurate estimation of the 3C 3D VSP first breaks is proposed. It uses combination of different criteria to estimate first breaks through an objective function with adaptive parameters. First we pick first breaks manually for the first gather of the 3D VSP set, and adjust several coefficients to describe close-to-first-breaks wave-shape parameters. We calculate an objective function for a moving trace window and minimize it with respect time shift and the slope. This function combines four main properties that indicate first breaks on 3-C VSP data: linear polarization, signal/noise ratio, similarity in wave shapes for close shots and their stability in time interval after first break. We adjust coefficients as a combination of current and previous values, so this approach uses adaptive parameters to follow smooth wave-shape changes. The method utilizes three components by calculation objective function for the direct P-wave projection. Using adaptive multi-criteria optimization approach for several traces and three components makes this method very robust even for the data contaminated with high noise.
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3DVSP from interpreter's perspective
Authors M.C. Schinelli, E.A. Thedy, R.C. Sansonowski, O.F. Keller and P.R.S. Johann3D-VSP has clearly become a borehole seismic technique with strong impact over seismic reservoir characterization activities. Much attention has been given to operational aspects, new equipments and processing techniques, but the opinion of their interpreters is usually only superficially explored. We discuss here the interprets point of view, covering their experience in the use of three different 3D-VSPs surveys, one in marine and two others on land areas. Basic aspects of survey planning, acquisition and processing are revisited, with focus on interpretation by the perspective of learned lessons, highlighting benefits and obstacles in the use of those 3Ds, with suggestion to the future projects.
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3D VSP Processing Issues for Detailed Reservoir Characterization
Authors C.B. Barberan, E.C. Crouzy, A.M. Michot and P.W. WillemsenVertical Seismic Profile (VSP) was originally designed and is still primarily used to give us time-to-depth relationship for seismic-to-well ties. But the inherent 3D nature of the earth and a desire to obtain 3D reservoir information near the well has led to interest in acquiring 3D VSP data. Over the past few years, and with the development of long receiver arrays, an increasing amount of 3D VSP data have been acquired as a cost-effective technique by possibly giving a 3D high-frequency seismic volume around the well, and as an alternative to OBC acquisition. However the processing of large array 3D VSP remains a challenging issue. Not only 3D VSP images often suffer from limited acquisition aperture and limited fold, but processing techniques, including VSP migration, initially designed for 2D imaging have not evolved much. The consequence is to make the VSP images often difficult to interpret. We present a case study from a 3D VSP acquired offshore, where a workflow different than the conventional 3D VSP processing route has improved the results. Preserving fine interpretable details was finally obtained by improving the processing workflow, reducing the migration aperture and using a 3D mapping technique.
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Planning, Acquisition, and Processing with Modern Borehole Seismic Tools
Authors B. N. Fuller, L.A. Walter and J.M. SterlingNew technologies, such as large borehole seismic receiver strings challenge practitioners to explore and find new ways to optimize their use. Methods that have proved valuable in improving the outcome of 2D VSP, 3D VSP, and microseismic surveys are discussed.
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Large-Array 3D-VSP and Full-Azimuth 3D Surface Seismic Simultaneous Acquisition Survey Design
Authors C.W. Liu, G. Xu, Y.P. Li, K. Kang and H.L. LiangAlong with the VSP technique developing ceaselessly, especially with the advancing of manufacturing engineering of downhole geophone and the data processing level, 3D-VSP survey has become feasible. As a strong support for performing 3D-VSP survey, application of large-array downhole geophones will form a tendency. BGP and Daqing Oilfield Company in CNPC have performed a large-array 3D-VSP and full-azimuth 3D surface-seismic simultaneous acquisition test jointly aiming at the volcanic geologic body, through which, a study has been made in the view of geophysical parameter extraction, high-resolution imaging and reservoir description. This paper illustrates the design of this method taking the Xushen 21-1 in Daqing as an example.
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Downhole seismic sources for Reverse 3D-VSP surveys
Authors C. Naville, R. Ásmundsson, S. Thorhallsson, G. Asgrimur, J. Kolle and E. GillotAcquisition of Reverse 3D-VSP with Downhole seismic sources and large amount of surface seismic sensors is desirable in many instances. A non exhaustive overview of existing powerful prototype downhole seismic source devices is presented, as well as the main results obtained in a recent past, as well as the emerging technology which can contribute to industrialise the Reverse 3D-VSP method. Discussion with industry is welcome
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Vp/Vs ratio estimation from joint PP-PS inversion of 3D VSP seismic data
Authors T.L. Tonellot, J. Fitzmaurice, S. Khater and S. RahatiA workflow to derive Vp/Vs and acoustic impedance volumes from joint PP-PS inversion of seismic data is applied to 3D VSP data. PP and PS depth migrated VSP volumes, converted to PP time, are first sequentially inverted for acoustic and PS elastic impedance respectively. In a second step the main reservoir horizons are interpreted for each volume. The PS volume is then transformed in time so that the picked horizons coincide in the PP and PS datasets. The resulting data are jointly inverted for acoustic impedance and Vp/Vs. This workflow was applied to two 3D VSP datasets, recently acquired in the Arabian Gulf, to improve the delineation of thin sand stringers for optimized horizontal well placement. The 3D VSP inversion results were compared to the conventional elastic inversion of PP OBC data. When OBC data are good, no significant resolution improvement was observed on the 3D VSP results. In an area where the OBC data quality was low, the 3D VSP provided a superior image in the proximity of the well.
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A VFSA Method of Travel Time Inversion for Layer Interval Anisotropy Estimation Using Walk-away VSP
Authors D. Pei, B. Cornish, R. Zhou, D. Quinn and R. WilliamsonWe developed a new implementation of VFSA as an alternative method of travel time inversion for Thomsen’s parameters using walk-away VSP data. Velocity along the symmetry axis and TTI axis orientation must be known. Two synthetic tests show that the inverted parameters are within 10% of their true model values. The sensitivity analysis shows that ε is more dependent on ray paths in the horizontal direction or group angles close to 900 , while δ is more affected by ray paths with 550 incident angles. This implies that walk-away surveys designed for this purpose may require longer source-receiver offsets, e.g. the ratio of offset to depth may be equal to or greater than 1. Consequently, head and / or guided waves may interfere with accurate first arrival time determination and care is required in picking the proper event.
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3D VSP data RTM
More Lessit can accurately image the reflectors beyond 90o dipping angles. RTM uses the full wave equation to extrapolate the wave field. And a key issue is that it creates the low-frequency imaging noise if the Claerbout’s (1971) correlation imaging condition is employed. The modified imaging condition is that at reflection points, the arriving time of the incident wave equals to the taking-off time of the reflection wave. The imaging condition is suitable to be implemented in the local angle domain, which can completely attenuate the imaging noise. The high-order or compact finite-difference is commonly used to solve the full wave equation. The hybrid GPU/CPU high-performance computer system can rapidly finish the RTM of one shot gather. However, the absorbing boundaries are not suitable to be used on the platform because their finite-difference computation violates the GPU’s character. Therefore, the random scattering boundary condition is adapted (Robert, 2009). Reverse phase of the reflectivity at the same point on a reflector and Dependence on the high-wavenumber components in the migration velocity if multiples are imaged are two important issues for 3D VSP data RTM.
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Constrained viscoelastic full waveform inversion of North Sea offset VSP data
Authors M. Charara and C. BarnesFull-waveform inversion of VSP data requires simulation of the wave propagation in complex media in order to account of the complexity of the wavefield and therefore to extract more information from the data; the drawback is the increase of the number of the degree of freedom for a problem already underdetermined. Constraints consistent with the least squares formalism, i.e. through covariance matrices, on the data space and the model space can be introduced to significantly reduce the number of the degree of freedom. The data covariance matrix can be filled by using the polarization analysis to describe the multi-component data uncertainties and the model covariance matrix can be filled with spatial correlation functions. A visco-elastic full-wave inversion of offset VSPs data from the North Sea illustrates the impact of multi-parameter inversion when constraints help to regularize the inverse problem.
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Borehole seismic monitoring of CO2 storage within a saline aquifer at Ketzin, Germany
More LessThe borehole seismic monitoring in the in situ laboratory for saline aquifer CO2 storage (Ketzin, Germany) comprises crosswell tomography, offset-VSP, walkaway-VSP, and single level 3D-VSP. Time-lapse measurements of the crosshole tomography indicated a decreased P-wave velocity of the rock units affected by CO2 injection, the walkaway-VSP observed increased reflectivity from the sandstone layers of the formation. The offset-VSP and 3D-VSP provide structural geometry and characterization in the vicinity of the site. A particular challenge will be the time-lapse processing of surface-to-borehole data.
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Walkaround VSP for Fracture Detection in Northern Saudi Arabia: A Case Study
Authors D.C. Weber, K. Al Dulaijan and J.C. OwusuThis paper documents anisotropy analysis for fracture detection using data from a walkaround VSP that was acquired in a gas well in Saudi Arabia. The results are compared to dipole sonic, image log data and core analysis. Results from another walkaround VSP in a nearby well are included. Also covered is the VSP modeling and acquisition design process.
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A Brief History of Microseismic Mapping in Unconventional Reservoirs
By R.J. ZinnoMicroseismic monitoring has played a critical role in the success of oil and gas production from unconventional reservoirs over the last ten years. Several surveys spanning that period, including the first survey in a shale gas field, describe the evolution of that success. These case histories illustrate important lessons learned about influence of fine geologic structures on the fracture behaviour of these reservoirs during stimulation. These stimulation mapping examples chronicle the evolution of modern completion techniques to address and exploit these reservoir complexities; and describe the economic impact of applying microseismic monitoring to these operations.
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Elastic gaussian beam imaging of walk-away VSP data.
Authors M.I. Protasov and V.A. TcheverdaThe approach to true amplitude seismic imaging for walk-away Vertical Seismic Profile (VSP) multi component data is presented and discussed. This approach is migration procedure based on weighted summation of prestack data. True amplitude weights are computed with application of Gaussian beams (GB). The couple of beams is used in order to compute true amplitude selective image of the rapid velocity variation. The total true amplitude image is constructed by superposition of selective ones being computed for a range of available dip angles. Shooting from the bottom overcomes difficulties due to multi arrivals of seismic energy which are common for complicated velocity models (in particular salt intrusions). In addition, the global regularity of Gaussian beams permits one not take care of, is the ray field regular or not. The use of P- and S-wave Gaussian beams provides the possibility to handle raw multi component data without of their preliminary separation to PP and PS waves. The true amplitude selective images computed for a variety of opening angles gives possibility to implement AVO analysis.
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High-resolution seismic exploration system in boreholes - Seismic Prediction While Drilling (SPWD)
More LessSeveral borehole seismic methods are in use while drilling. Because the sought-after small-scale structures like thin local layers or faults encountered more and more in deeper regions the focus of exploration has shifted to methods with higher resolution. Combining a seismic source and receiver in a common device in the drill string would increase the seismic resolution. Within the project (S)PWD a first prototype of such a Seismic Prediction While Drilling (SPWD) device has been designed and tested in dry horizontal boreholes. With source signal frequencies up to 5000 Hz a resolution of about one meter is feasible. By focusing the seismic waves the energy can be maximized in desired directions. An increased radiation of seismic wave energy in direction of the borehole axis allows the view in areas to be drilled. If applied while drilling such a tool allows adjusting the drill path to minimize risks and costs of drilling. The next step in the project (S)PWD will be in 2010 the development of a wireline SPWD prototype for vertical boreholes with depths to 2000 m.
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Coda-wave interferometry analysis of Synthetic time-lapse VSP data at CO2SINK project site, Ketzin, Germany
More LessThe CO2SINK project is the first on-shore pilot CO2 storage study in Europe and Address a number of the Key Aspects related to geological storage of CO2 . Different Seismic Surveys Have Been Carried Out in the project , Such as time-lapse Seismic and surface moving source profiling ( MSP , Also known as walk -away VSP ) Surveys . We Have investigated the feasibility of coda -wave Interferometry Analysis for Monitoring of CO2 Injection Using time-lapse VSP synthetic data based on a project site CO2SINK elastic model . Our studies Suggest That coda -wave Interferometry Analysis Could Potentially Be A Reliable and Effective tool for monitoring Geological Carbon Sequestration .
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Borehole Hydrophone Aquisition - Some pitfalls and solutions
Authors A.J. Greenwood, J.C. Dupuis, A.W. Kepic and M. UrosevicHydrophones are highly sensitive broadband pressure sensors. They are slim-line, lightweight, rapidly deployable and do not require clamping. Strings of 24 – 48 receivers can be manufactured for the same cost as a single slim-line 3C shuttle. The passive hydraulic coupling and suspension within the water column employed by the hydrophones lead to specific acquisition issues due to noise sources related to cable and borehole seismic modes. With the use of a 24 channel hydrophone string, over several surveys in predominately mineral exploration boreholes, we have investigated suppression of these noise sources. Improvement of hydrophone coupling to the formation is achieved through higher viscosity drilling fluids. It is also encouraging that very high quality converted shear waves can be recorded with hydrophones. We show that due to easy deployment and rapid acquisition time it is possible to utilise very fine hydrophone increment of just 1m which enables a proper registration of tube waves and hence their effective removal. Finally we test our hydrophone array in a complex hard rock environment. Using a known geological model, through extensive elastic modelling we prove the validity of an ultra-high resolution VSP image constructed from hydrophone data.
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