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Fourth EAGE Borehole Geophysics Workshop
- Conference date: November 19-22, 2017
- Location: Abu Dhabi, United Arab Emirates
- Published: 19 November 2017
1 - 20 of 29 results
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3D Reflectivity-Guided Joint Migration Inversion of Multi-Well Borehole Data
Authors B. El Marhfoul and D.J. VerschuurSummary3D borehole-related seismic data has superior quality and higher-frequency content compared to surface seismic data. These unique properties make it possible to produce high-resolution images and accurate velocity models especially around the borehole. However, using conventional imaging algorithms, that assume primary reflection energy, will retrieve only a limited area around the borehole. This problem can be overcome by including surface-related and internal multiples in the imaging algorithm to enhance the illumination of the. In addition, on-the-fly the velocity model can be updated using the so-called Joint Migration Inversion (JMI) process, which explains the full wavefield seismic data in terms of reflectivity and a propagation velocity model. To augment the results, datasets from different wells in the area can reinforce each other by simultaneous inversion to assure the consistency and improve the quality of the results. To steer and constrain the velocity estimation, the estimated reflectivity in the JMI process can be used as additional constraint for the velocity updating process.
In this paper we have deployed the full wavefield of the 3D borehole data, from two different wells, containing all orders scattering, both up- and down-going wavefields, in one integrated inversion-imaging process as proposed by the JMI methodology. The final result is a smooth accurate background velocity model along with a true amplitude reflectivity image with high resolution and maximum lateral extent.
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Interferometric VSP Multiples Imaging: A Case Study from Saudi Arabia
Authors A. Aldawood, S. Alsaadan and N. PalaciosSummaryWe utilized interferometric datuming to convert VSP first-order surface-related multiples into virtual surface-seismic primary reflections. These reflections are subsequently imaged using a Kirchhoff-based migration to obtain representative subsurface structures. Tests on both synthetic and field datasets demonstrate the ability of imaging with VSP multiples to extend the spatial resolution of the migrated images. We concluded that imaging with VSP multiples could potentially provide a wider subsurface illumination compared with conventional imaging with VSP primaries.
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Characterization of a Fractured Reservoir Using DAS VSP—A Model-Based Reflection Amplitude Study
Authors R. Zhou, M.E. Willis, D. Cheng and K. GreenSummaryDistributed acoustic sensing (DAS) technology offers the time-lapse capability of monitoring hydraulic fracturing and reservoir depletion processes. This paper uses a model-based study to explore the feasibility of using DAS vertical seismic profiling (VSP) to detect and characterize fracture-induced azimuthal variation in P-wave reflection amplitude. The study particularly focuses on seismic amplitude vs. offset and azimuth (AVOAz) to answer two questions. First, which fracture-induced seismic responses can be detectable by a three-dimensional (3D) DAS VSP survey. Second, how shots can be arranged to detect such seismic responses and image the extent of the fractures. Waveform data were simulated for two types of fractured reservoir models using full-elastic anisotropic algorithms. P-wave reflection amplitude was mapped in incidence angle intervals for the top of each reservoir model. Analyses of the amplitude variation with AVOAz revealed distinctive patterns for the two fracture models. These patterns of amplitude variation can be used to detect fractures, if the fractures have uniform density and similar orientation around the well.
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VSP Anisotropic NMO Correction and Its Application to Attenuate Noise
Authors M. Lou and H. SimpsonSummaryNormal moveout (NMO) correction is an important data processing step for VSP CDP transform and other applications. Most of the previously used VSP NMO correction methods are valid for isotropic media, but can cause significant errors in multi-layered and/or anisotropic (VTI) media. We present a new methodology to accurately and efficiently perform VSP anisotropic NMO correction for walkaway VSP (WVSP) or 3DVSP data. We adapt the Fomel and Stovas’ NMO correction formulation originally developed for surface seismic data, to NMO correction for WVSP or 3DVSP data in multi-layered VTI media. We employ a simulated annealing (SA) algorithm to automatically search for four parameters in the Fomel and Stovas’ formulation. In the SA algorithm, we use semblance coherence analysis in the VSP common receiver gather domain as an object function. That is, after a correct NMO correction, a reflection event is aligned and its semblance coherence coefficient is maximized. To attenuate both coherent and incoherent noise in the reflection wavefield of VSP data, we utilize a three-step processing flow consisting of NMO correction, median filtering, and reverse NMO correction. We demonstrate a significant improvement in the image quality of a field WVSP data after attenuating noise by this new methodology.
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From VSP Optimum Imaging to Reservoir Characterization
Authors N. El Yadari, A. Suleiman, C. Planchart Marquez, S. Saadan and M. AhmedSummaryThe past twenty years have witnessed significant developments in the way that seismic data are used in oil and gas exploration and production. Arguably, the most important has been the use of surface seismic, not only to map structures in detail but also to infer reservoir properties from an analysis of seismic amplitude and other attributes. Improvement in seismic amplitude fidelity coupled with advances in the understanding and application of seismic inversion and rock physics have made quantitative description of the reservoir and risk evaluation not only a possibility but an expectation in certain geological contexts. To benefit from the superior quality of the VSP image over the surface seismic one, we extend the reservoir characterization workflow to borehole data and show its application to a 2D walkaway VSP data recorded in Saudi Arabia.
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Imaging Salt Flank by a Rig-source VSP
By M. LouSummaryAccurately delineating a salt flank or base is critical to evaluate the extent of reservoir rock and to successfully place development wells in many salt-trap oil reservoirs. Due to the severe distortion and obstruction of seismic waves by the salt body, surface seismic imaging often fails to clearly define the salt flank or base boundary. Borehole seismic salt proximity surveys (SPS) have historically played an important role in delineating and mapping the salt flank/base adjacent to a borehole by either calculating the salt exit points from first break travel times or directly migrating the first arrival waveforms. In a conventional SPS, a seismic source is positioned above the salt body. In an offshore environment, deploying a source boat adds significant cost for the acquisition of a conventional SPS. Through modelling a real case of rig-source VSP survey, this paper suggests for certain salt-trap reservoirs such as those in Gulf of Mexico (GOM), a rig source VSP can also serve as a salt proximity survey to delineate the salt flank as done by a conventional offset source SPS. By removing the need to deploy a source boat, a rig-source SPS is more efficient and cost-effective than a conventional offset-source SPS.
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Subsalt Imaging Using Walkabove and Walkaway VSP in the Transition Zone of the Red Sea
Authors C. A. Planchart, M.J. Vega, J. Jiao, N. El Yadari and Y. K. FadolalkaremSummaryThe transition zone in the Red Sea contains challenges for seismic imaging related to the complex bathymetry and presence of reefs. Also, the presence of salt bodies overlying the potential reservoirs causes weak illumination due to the defocusing of the energy and the weak reflectivity.
While drilling a well, it was necessary to drill a side track due to operational reasons. Some unexpected lateral variations at the same depth were found between both wells separated by only 130 ft. As part of the exploratory efforts, several VSP surveys were acquired. We present a case study where several migration algorithms were evaluated to perform subsalt imaging. The image from walkaway VSP found the cause of the unexpected lateral variation. We also used the VSP data to explain the possible reasons of the poor imaging of the 2D surface seismic data.
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Estimation of Maximum Horizontal Stress Direction using a Walkaround VSP dataset: A Case Study from the Red Sea, Saudi Arabia
Authors N. Palacios, C. Planchart and M. VegaSummaryA Walkaround VSP (WARVSP) dataset has been acquired and analyzed to estimate the principal stress direction at the target formation, using various methods such as shear wave splitting analysis, Alford rotation analysis, and azimuthal amplitude analysis. As results of these analyses the different methods for determining the maximum stress direction concurred in the results and confirming the maximum stress direction in the field. WARVSP data also provided a qualitative characterization of the salt body shape around the well. This study recommend to combine different techniques to measure the principal stress directions and achieve characterization of a known presence of irregular salt bodies in geological complex fields.
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Vertical Cable Seismic (VCS) Processed Using VSP Methods
Authors J. Bailey, E. Asakawa, M. Humphries and K. TaraSummaryA VCS case study for the shallow marine imaging of seafloor massive sulphides. The processing workflow, using borehole seismic techniques, will be discussed. An interpretation and examination of the final 3D imaging results will be presented.
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DAS Versus Geophones: a Quantitative Comparison of a VSP Survey at a Dedicated Field Laboratory
Authors J. Correa, L. Van Zaanen, K. Tertyshnikov, T. Dean, R. Pevzner and A. BonaSummaryDistributed Acoustic Sensing (DAS) is a novel technology to acquire acoustic data. DAS is noticeably promising for Vertical Seismic Profiling (VSP) applications as it offers highly sampled data, acquired simultaneously at all levels, at relatively low cost. In this study, DAS data is acquired using two different cable deployments: cemented behind the casing, and deployed suspended in the well. Both datasets were compared to conventional 3-component geophone VSP. DAS acquired with cemented cable presented similar quality and signal to noise ratio as geophone data, although it suffers from loss of high frequencies. The suspended cable presented predominantly tube noise, however reflections can still be recognized. We hope the results from this study contribute to a broader use of DAS for VSP acquisition.
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The Merits of DAS Acquisition on Multimode Optical Fiber
Authors A. Constantinou, A. Hartog, P. Dickenson and G. LeesSummaryCollecting Distributed Acoustic Sensing (DAS) data with multi-mode (MM) optical fiber is a challenge but not impossible. This paper presents the effect of MM fiber on DAS data for several oil and gas applications. These include borehole seismic surveying and downhole flow monitoring. The business need to acquire DAS on MM is high given the considerable installed base of MM fiber. This MM fiber was originally installed for Distributed Temperature Sensing (DTS) and communications. However, it is now possible to re-purpose this fiber for DAS acquisition, making a considerable saving over the installation of a new fiber. We present promising results acquired using this approach.
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Offset VSP for the Reservoir Monitoring
Authors K. Tertyshnikov, A. Egorov, R. Pevzner and A. BonaSummaryOffset Vertical Seismic Profile (VSP) is often used for time-lapse seismic monitoring in oil/gas exploration or CO2 geosequestration. Standard offset VSP processing technologies allow the imaging and qualitative interpretation of time-lapse changes in the medium. However, quantification of the observed time-lapse anomalies is often needed. We suggest using Full Waveform Inversion (FWI) for quantitative interpretation of the offset VSP data. We apply conventional time-lapse processing and time-lapse FWI to the offset VSP dataset acquired in the Otway field and compare the results. We observe a match in the images of the CO2 plume obtained by both methods and suggest that using FWI increases the value of offset VSP data.
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Application of 4D VSP for Monitoring Of Small-Scale Supercritical CO2 Injection: Stage 2C of CO2CRC Otway Project Case Study
Authors H. AINasser, R. Pevzner, K. Tertyshnikov, D. Popik and M. UrosevicSummaryTime-lapse VSP seismic can be used in addition to land seismic to increase the repeatability in reservoir characterization. As a part of the monitoring program within the Stage 2C of the Otway Project, CO2CRC conducted the acquisition of offset Vertical Seismic Profile (VSP) data before injection (baseline) and three monitoring surveys after injection of every 5kT of CO2. The objective of this study is to evaluate the repeatability of 4D VSP onshore seismic and compare the results with surface seismic data. To this end, we develop an optimal workflow for VSP data processing of the CRC-1 well 2015 baseline and the 2016 monitor surveys to produce 3D migrated images of the subsurface.
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Elastic Anisotropy Estimation in the North Sea from Walkaway VSP and Sonic Data
Authors C. Mogensen, M.L. Khaitan, R. Guerra, L. Dahlhaus, S. Leaney, J. Jocker and E. WielemakerSummaryThe Hejre oil and gas field is located in the Danish Central Graben, a shallow water part of the central North Sea. The reservoir lies at depths below 5 km in a high-temperature (172°C) and high-pressure (1 kbar) environment. Seismic resolution is relatively poor due to absorption in the overburden, multiples and distortion from a complex structure. Anisotropic depth processing improved the seismic quality but the anisotropy uncertainty remained high.
In order to measure elastic anisotropy in-situ, reduce the velocity model uncertainties and allow improvements in anisotropic surface seismic processing, comprehensive Walkaway VSP and modern wireline sonic logging surveys were planned in a new deviated production well drilled in 2016.
This project represents a first step in the velocity model calibration workflow and highlights the importance of integrating measurements taken at different scales: cores, sonic, borehole and surface seismic, in order to understand the elastic anisotropy of the rocks drilled and allow reducing the uncertainties in the seismic velocity models used for depth imaging.
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High Resolution Imaging Using Crosswell Seismic with Complex Stratum in Western China
Authors J. J. Wu, Y. P. Li, Q. H. Zhang, J. H. Huang, Y. Z. Chen, C. Chen, Y. H. Wang and Z. D. CaiSummaryThe crosswell seismic has the characteristics of high frequency and high resolution. It can provide more accurate velocity information because of its depth domain data. The crosswell seismic is known as the link of well logging, conventional 3D seismic and reservoir geology. Because the shot and geophone of crosswell-seismic are both inside the well, seismic waves avoid be attenuation of propagating through the surface with low velocity. So we can get higher quality data theoretically. In the other hand, the source of crosswell seismic usually radiates high frequency wave, which is typically several times higher than surface seismic. These features make the reflected imaging can obtain more insider information. Then we can get small sand group, which surface seismic hardly resolved. Multi-attribute parameters were extracted based on amplitude preserving imaging. Comprehensive analysis of a variety of attribution information can achieve fine structure interpretation and reservoir cognition. In this paper, we acquired three pairs of crosswell seismic data in a western China oilfield. And then data processing and corresponding geological interpretation give us good results.
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Application of Walkaway-VSP Technology in Volcanic Rocks
More LessSummaryVolcanic rock, as a kind of special reservoir, has gradually become an important target for oil and gas exploration. Because of the complex geological conditions in the volcanic rock exploratory area, the poor layering of rock mass, irregular development of rock mass, and quick changes of thickness, the conventional seismic methods can not to satisfy the requirements for fine exploration and development for volcanic rock, due to the low data resolution and the uncertain velocity information. This paper gives an application of Walkaway-VSP data processing and interpretation in Tuha Oilfield Malang Sag Santanghu basin, with high resolution, high fidelity of Walkaway-VSP longitudinal wave imaging, the volcanic rock of M68 well area is described exactly, based on the imaging, vertically the lithologic interface of volcanic rock reservoir and source rock reservoir is carefully identified, horizontally the shape and distribution range of volcanic rock are fine described,which achieves very good application effect.
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Utilizing the Uniqueness of Vertical Seismic Profiling (VSP) for Deepwater Exploration
Authors M.L. Khaitan, P. Ranjan, S. Chandrasekhar and B. KumarSummaryWe plan to present two case studies from deepwater drilling wherein we performed look-ahead VSP inversion. The cases elaborated in this paper are unique in the sense that these are examples wherein look-ahead VSP was the only possible alternative that could lead to viable planning of risk mitigation associated with the drilling and aid decision making in the drilling program in the deepwater environment for avoidance of major financial losses
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3D VSP Processing and Imaging: A Case Study in Eastern China
Authors Y. Z. Chen, Y. H. Wang, H. Y. Zhao, Y. P. Li and J. H. HuangSummaryComplex structure, fault development and thin reservoirs are three main characteristics of Liaohe oilfield in Eastern China. And the development is difficult due to the low resolution of surface seismic data in this area. To accurately evaluate and predict the reservoir, identify small faults and implement the micro structure, as well as predict the distribution range of the oil sand body, a 3D VSP survey was conducted. In this paper, the 3D VSP project in Liaohe oilfield is taken as an example to demonstrate the 3D VSP technology and its application in structural imaging. After interpretation and fault recognition, small faults which were not seen on surface seismic data are shown up on VSP image. Analysis shows that the 3D VSP has a good impact on oil and gas exploration and development.
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Characterisation and Imaging of a Near-vertical Fault Zone in Crystaline Rock from Hydrophone VSP Data
Authors A. Greenwood, E. Caspari, J. Hunziker, L. Baron, T. Zahner, D. Egli and K. HolligerSummaryA shallow near-vertical hydrothermally active fault zone embedded in fractured crystalline rocks of the central Alps has been drilled and geophysically explored in view of its potential analogies to planned deep petrothermal reservoirs in the Alpine foreland. Hydrophone-based zero-offset vertical seismic profiling (VSP) data were found to be highly effective for detecting open fractures and determining seismic velocity changes due to deformation. Walk-away hydrophone VSP data were acquired with a 45-degree crooked-line survey geometry with respect to the borehole plane, which requires 3D processing methods for seismic imaging. For imaging purposes, a laterally changing velocity cube was generated from the ZVSP velocities and projected along the strike of the fault. The subsequent, pre-stack-depth-migration imaging has been successful in delineating vertical structures, the target fault core, and an as of yet unknown, and correspondingly enigmatic, sub-horizontal structural feature.
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Application of Far Field Shear Wave Reflection Imaging To Identify The Precise Location Of A Horizontal Well In A Formation
Authors T. Bradley, A. Przebindowska and N. AarsethSummaryIn recent years imaging of near wellbore structures using reflected shear wave energy from full waveform wireline acoustic logging tools has become an accepted technology in formation evaluation.
The technique enables imaging and identification of geological features up to approximately 30 metres from the borehole axis on a scale and resolution between those of borehole images and vertical seismic profiles, so filling the resolution gap between these two techniques. High resolution borehole images resolve features located millimetres to centimetres from the borehole wall, whereas vertical seismic profiles image geological features on a metre to tens of metre scale and located between tens and hundreds of metres from the wellbore.
In this extended abstract we present the application of single well imaging using shear energy to visualize the location of a horizontal well in a formation, and a technique to easily visualize the data. We then present a case study where the location of a horizontal well in a formation has been precisely identified using the technique.
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