Previous studies performed in Abu Dhabi oilfields, United Arab Emirates, revealed the direct link of seismic wave attenuation to petrophysical properties of rocks. However, all those studies were based on zero offset VSP data, which limits the attenuation estimation at one location only. This is due to the difficulty of estimating attenuation from 3D seismic data, especially in carbonate rocks. To overcome this difficulty, we developed a workflow based on the centroid frequency shift method and Gabor transform which is optimized by using VSP data. The workflow was applied on 3D Ocean Bottom Cable seismic data. Distinct attenuation anomalies were observed in highly heterogeneous and saturated zones, such as the reservoirs and aquifers. Scattering shows significant contribution in attenuation anomalies, which is unusual in sandstones. This is due to the complex texture and heterogeneous nature of carbonate rocks. Furthermore, attenuation mechanisms such as frictional relative movement between fluids and solid grains, are most likely other important causes of attenuation anomalies. The slight lateral variation of attenuation reflects the lateral homogeneous stratigraphy of the oilfield. The results demonstrate the potential of seismic wave attenuation for delineating heterogeneous zones with high fluid content, which can substantially help for enhancing oil recovery.

Volumetric maximum curvature attribute computed from 3D ocean bottom cable (OBC) seismic data, production logging tool (PLT), inorganic chemical tracer data, and fractures observed from core and full-bore formation microimager (FMI) logs were integrated to characterize fractured carbonate reservoirs of an offshore oil field in Abu Dhabi, United Arab Emirates (UAE). The extracted maximum curvature anomalies are predominantly orientated in NNE-SSW and NE-SW, a trend perpendicular to the dominant fault direction in the oil field and similar to the dominant strike directions of fractures measured from core data and FMI logs. Because the fracture strike directions of well data mimic the strike directions of curvature anomalies at corresponding reservoir levels, we interpreted the maximum curvature anomalies to represent dilatational fractured zones or fracture corridors. Integration of dynamic data, such as PLT and chemical tracers, and maximum curvature anomalies demonstrate that the inferred fracture zones can determine water breakthroughs as well as inter- and intrareservoir communications. As a result, this study highlights possible fracture zones and their internal architecture, as well as their potential flow capabilities. These results play a key role in reservoir management and monitoring of water movement through structural pathways.

Two-dimensional elastic full waveform inversion was applied to two lines extracted from a spiral three-dimensional vertical seismic profile data acquired in an oilfield offshore, Abu Dhabi, in the United Arab Emirates. The lines were selected to be parallel and perpendicular to the plane defined by the deviated borehole. The purpose of the inversion was to derive high-resolution elastic properties of the subsurface. After pre-processing, the data were band-pass filtered with a minimum frequency of 3.5 Hz and a maximum frequency of 30 Hz. A sequential inversion approach was used to mitigate non-linearity. The pre-processing of the data consisted in the removal of bad traces, followed by amplitude and phase corrections. High-resolution P- and S-wave velocity models that show good correlations with the available sonic logs were obtained. The results of the inversion suggest that the oilfield consists of a stack of layers with varying lithology, porosity and possibly fluid content.

Summary Seismic wave attenuation Q−1 is directly related to fractured rocks through scattering and fluid-related mechanisms, which are caused by fractures and pore fluids. This makes seismic attenuation a good parameter for studying fractured reservoirs. However, getting an accurate estimate of Q−1 from 3D surface seismic data is challenging. This is due to the immaturity of the methodology which is mainly suitable for zero offset seismic data. In this study we established a new workflow to overcome such limitation. The seismic attenuation profiles estimated from geophone data acquired in an oilfield located in Abu Dhabi an emirate of the United Arab Emirates, show a sensitivity to oil-saturated zones.

PreviousNext No AccessProceedings of the 13th SEGJ International Symposium, Tokyo, Japan, 12–14 November 2018Potential of intrinsic and scattering attenuation for the investigation of a fractured reservoirAuthors: Fateh BouchaalaMohammed Y. AliYoucef BouzidiJun MatsushimaEric M. T TakougangWeining LiuAala A.I. MohamedAkmal A. SultanFateh BouchaalaThe Petroleum Institute, part of Khalifa University of Science and TechnologySearch for more papers by this author, Mohammed Y. AliThe Petroleum Institute, part of Khalifa University of Science and TechnologySearch for more papers by this author, Youcef BouzidiThe Petroleum Institute, part of Khalifa University of Science and TechnologySearch for more papers by this author, Jun MatsushimaThe University of Tokyo, Frontier Research Center for Energy and Resources, JapanSearch for more papers by this author, Eric M. T TakougangThe Petroleum Institute, part of Khalifa University of Science and TechnologySearch for more papers by this author, Weining LiuThe Petroleum Institute, part of Khalifa University of Science and TechnologySearch for more papers by this author, Aala A.I. MohamedThe Petroleum Institute, part of Khalifa University of Science and TechnologySearch for more papers by this author, and Akmal A. SultanThe Petroleum Institute, part of Khalifa University of Science and TechnologySearch for more papers by this authorhttps://doi.org/10.1190/SEGJ2018-150.1 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract Intrinsic attenuation of seismic waves results mainly from the presence of fluids in pore spaces and fractures of rocks. Therefore, intrinsic attenuation can be a valuable seismic attribute for obtaining information from fluid saturated media, such as reservoir zones. However, getting accurate and high resolution attenuation estimates is challenging. This is due to the high sensitivity of the estimation methods to signal-to-noise ratio and the difficulty of isolating intrinsic attenuation from elastic losses, such as scattering. In this study, we used a novel method to accurately separate intrinsic and scattering attenuations for zero-offset Vertical Seismic Profile (VSP) data. This method is based on the assumption that the intrinsic and scattering attenuations are frequency independent and frequency dependent, respectively. We applied this method to zero-offset VSP data acquired from an oilfield located in the emirate of Abu Dhabi, United Arab Emirates (UAE). We obtained a high depth resolution intrinsic and scattering attenuation profiles. The intrinsic attenuation is high in the reservoir zones, which are characterized by high oil saturation, low velocity and high porosity. However, in the presence of fractures surprisingly the reservoir zones display low intrinsic attenuation. Even though the scattering is usually considered as an unwanted and as a source of noise, our results show that it can be used positively for reservoir investigation. Indeed, the frequency dependence of the scattering can be helpful to define the frequency ranges at which the heterogeneities and fractures affect the seismic wave propagation. Therefore, the combination of intrinsic and scattering attenuations can greatly improve studies of fractured reservoir zones. Keywords: attenuation, fractures, reservoir, VSPPermalink: https://doi.org/10.1190/SEGJ2018-150.1FiguresReferencesRelatedDetails Proceedings of the 13th SEGJ International Symposium, Tokyo, Japan, 12–14 November 2018ISSN (online):2159-6832Copyright: 2019 Pages: 588 publication data© 2018 Published in electronic format with permission by the Society of Exploration Geophysicists of JapanPublisher:Society of Exploration GeophysicistsSociety of Exploration Geophysicists of Japan HistoryPublished Online: 29 Apr 2019 CITATION INFORMATION Fateh Bouchaala, Mohammed Y. Ali, Youcef Bouzidi, Jun Matsushima, Eric M. T Takougang, Weining Liu, Aala A.I. Mohamed, and Akmal A. Sultan, (2019), "Potential of intrinsic and scattering attenuation for the investigation of a fractured reservoir," SEG Global Meeting Abstracts : 581-584. https://doi.org/10.1190/SEGJ2018-150.1 Plain-Language Summary KeywordsattenuationfracturesreservoirVSPPDF DownloadLoading ...

PreviousNext No AccessProceedings of the 13th SEGJ International Symposium, Tokyo, Japan, 12–14 November 2018Characterization of small faults and fractures from 3D VSP data in a carbonate reservoirAuthors: Eric Takam TakougangMohammed Y. AliYoucef BouzidiFateh BouchaalaAala A. I. MohamedAkmal A. SultanEric Takam TakougangThe Petroleum Institute, part of Khalifa University of Science and TechnologySearch for more papers by this author, Mohammed Y. AliThe Petroleum Institute, part of Khalifa University of Science and TechnologySearch for more papers by this author, Youcef BouzidiThe Petroleum Institute, part of Khalifa University of Science and TechnologySearch for more papers by this author, Fateh BouchaalaThe Petroleum Institute, part of Khalifa University of Science and TechnologySearch for more papers by this author, Aala A. I. MohamedThe Petroleum Institute, part of Khalifa University of Science and TechnologySearch for more papers by this author, and Akmal A. SultanThe Petroleum Institute, part of Khalifa University of Science and TechnologySearch for more papers by this authorhttps://doi.org/10.1190/SEGJ2018-149.1 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract 3D Vertical Seismic Profile (3D VSP) data were acquired over a carbonate reservoir, offshore Abu Dhabi, in the United Arab Emirates, to obtain seismic images for structural characterization. The area of acquisition is part of a giant oilfield which is a large anticlinal with very gentle dips, that was formed during the Late Cretaceous and Neogene times. A high resolution seismic volume was obtained after reverse time migration of the 3D VSP data and was used for the extraction of fractures and small faults; i.e. lineaments whose vertical displacement are beyond the seismic wavelength. The main processing step prior to the extraction of small faults and fractures consisted of removing acquisition footprint from the migrated volume that would otherwise influence the results negatively. The acquisition footprint, recognizable in the wavenumber domain by spiral patterns that mimic the source acquisition geometry, was removed using a carefully designed Notch filter. The filter uses a function to scale down regional maxima that mimic the source pattern geometry. Fractures and small faults were then extracted from the migrated volume using an algorithm based on semblance seismic attribute. The algorithm provides fracture orientation by comparing the similarity between neighboring traces and provides the likelihood of a point being part of a fault surface. A binary filter was later used to enhance the results and remove structures with small size that could be related to noise. We found that the extracted small faults and fractures are orientated in various directions, with a majority orientated in the NNE-SSW and NE-SW directions at a reservoir depth range. These orientations are in good agreement with interpreted strike azimuths of fractures from available core data at the same reservoir level, and with previous studies in the area based on seismic anisotropy and FMI (fullbore formation microimager). Keywords: 3D VSP, fractures, faultsPermalink: https://doi.org/10.1190/SEGJ2018-149.1FiguresReferencesRelatedDetails Proceedings of the 13th SEGJ International Symposium, Tokyo, Japan, 12–14 November 2018ISSN (online):2159-6832Copyright: 2019 Pages: 588 publication data© 2018 Published in electronic format with permission by the Society of Exploration Geophysicists of JapanPublisher:Society of Exploration GeophysicistsSociety of Exploration Geophysicists of Japan HistoryPublished Online: 29 Apr 2019 CITATION INFORMATION Eric Takam Takougang, Mohammed Y. Ali, Youcef Bouzidi, Fateh Bouchaala, Aala A. I. Mohamed, and Akmal A. Sultan, (2019), "Characterization of small faults and fractures from 3D VSP data in a carbonate reservoir," SEG Global Meeting Abstracts : 577-580. https://doi.org/10.1190/SEGJ2018-149.1 Plain-Language Summary Keywords3D VSPfracturesfaultsPDF DownloadLoading ...

We present a workflow for the extraction and characterization of fractures and faults using a Reverse Time Migrated (RTM) volume from 3D Vertical Seismic Profile data (3D VSP) acquired in an oilfield offshore Abu Dhabi in the United Arab Emirates. The workflow consists of: preconditioning of the input RTM volume, which involves removal of acquisition footprints; extraction of faults and fractures using a semblance based discontinuity attribute; binary filtering and clustering for characterization and interpretation using prior geological information, as well as removals of unwanted features such as those related to stratigraphy; and finally interpretation. Complex networks of lineaments were extracted after application of the workflow. The location of lineaments with length greater than 200 m and orientated WNW-ESE to NW-SE correlates with a known flower structure which has a trend similar to that of the Proterozoic Najd Fault System that cut the Arabian Peninsula. Lineaments with strike directions ENE-WSW and NE-SW are interpreted to be related to reactivation of basement faults and correspond to the Hormuz Salt basin's major trend in the Arabian Gulf. Dominant strike directions of lineaments at three reservoir levels correlate with dominant strike directions of interpreted fractures from Fullbore Formation Microimager (FMI) and core data; thus implying that they are likely related to fractures or fracture corridors. Lineaments with orientation NNE-SSW correlate with closed fractures while lineaments with orientation NNW-SSE correlate with open fractures. Zones with relatively high fracture intensity are generally located north and north-west of the VSP well in the reservoir zones. The good correlation of the results with interpreted fractures from core and FMI data shows the robustness of the workflow and gives confidence to the results.

Three-dimensional vertical seismic profiling data acquired from an oilfield located in Abu Dhabi, United Arab Emirates, were used to obtain a high-resolution multioffset azimuthal estimate of compressional seismic wave attenuation. On the basis of the assumption that the fracture strike corresponds to the azimuthal direction [Formula: see text] at which the attenuation is minimized, fracture orientations were obtained in three reservoir units. Two approaches were used to determine [Formula: see text]: first from the variation of the absolute attenuation [Formula: see text] with the azimuth and second from the variation of the relative attenuation [Formula: see text] with the azimuth. The rose diagrams of [Formula: see text] estimated from the [Formula: see text] variation indicated better agreement with those showing the strikes of open and cemented fractures obtained from core interpretation than with either of those showing the two types of fractures separately. However, the rose diagrams of [Formula: see text] estimated from the variation of [Formula: see text] were more similar to those showing the strikes of open fractures obtained from core and Fullbore Formation Microimager data. This observation can be explained by the fact that in the first approach, all types of fractures contribute to the scattering and fluid-related mechanisms of [Formula: see text]. However, in the second approach, [Formula: see text] is obtained from a least-squares fitting of the variation of [Formula: see text] with the azimuth, which is based on the squirt flow mechanism that is caused by the movement of fluid between grain pores and fractures. Therefore, a comparison of the orientations obtained using these two approaches can be an efficient way to separately determine the orientations of open and cemented fractures.

Summary Fractures and faults were extracted from a reverse time migrated 3D Vertical Seismic Profile (VSP) data acquired over a carbonate reservoir offshore Abu Dhabi in the United Arab Emirates. A specific workflow was used for the extraction of fractures and faults. The workflow was based on data preconditioning (i.e. noise attenuation), semblance based seismic attributes, binary filtering, and clustering. A complex network of fractures was extracted. The dominant strike direction of the extracted fractures showed a good correlation with the dominant strike direction of interpreted fractures from FMI (Fullbore Formation Microimager) and core data at three reservoir zones. A known fault in the area was also detected. The extracted fracture network was then used to compute fracture intensity maps. Fracture intensity maps give indications of zones with high fracturing that may be associated with greater porosity and permeability.

The dense geometry of a 3D VSP survey which was carried out in an oilfield located in the Emirate of Abu Dhabi, United Arab Emirates, enables us to perform high resolution azimuthal study of seismic wave attenuation, in order to investigate a fractured reservoir in the oilfield. We obtained the orientation of fractures in three reservoir units by using the concept suggesting that the strike direction of fractures corresponds to the azimuth of the minimum attenuation ϕ0. We defined ϕ0 as the azimuth of the minimum attenuation Q-1 that we estimated at several azimuths and offsets by using the spectral ratio method. The rose diagrams gathering ϕ0 obtained at several offsets, are in agreement with those gathering the strike direction of open and cemented fractures, obtained from cores interpretation. This is due to the fact that the attenuation Q-1 is caused by a combination of scattering and fluid-related mechanisms. It is physical evidence that fractures, regardless their type, are an important source of scattering mechanism, and also of fluid-related mechanisms if they are open. Another way to define ϕ0 is by using a cosine least square fitting of azimuthal variation of the relative attenuation ϕQ-1, that we estimated at several azimuths and offsets by using a modified spectral ratio method. In this case, the rose diagrams gathering ϕ0 defined at several offsets, are in agreement with those gathering strike direction of open fractures obtained from cores and Full-bore Formation Microimager interpretation. This agreement is due to the fact that the cosine least square fitting is based on the squirt flow mechanism that is caused by fluid movement between grain pores and fractures. Accordingly, comparison between the rose diagrams of ϕ0 estimated by using the two approaches, can be a good way to separate between open and cemented fractures. Such, finding is very interesting for petroleum industry and can help in Enhanced Oil Recovery (EOR) studies. Presentation Date: Monday, September 16, 2019 Session Start Time: 1:50 PM Presentation Time: 3:55 PM Location: 217D Presentation Type: Oral

High-resolution seismic velocity was obtained using acoustic full-waveform tomography of walkaway vertical seismic profile (VSP) data from an oil field dominated by carbonate rocks, offshore Abu Dhabi in the United Arab Emirates. The data were collected in a deviated borehole with receivers located from 521 to 2742 m depth. The inversion was performed in the frequency domain. The success of the inversion was determined by three important factors: the starting model, the preconditioning of the input data, and the inversion strategy, which included an appropriate selection of a damping term [Formula: see text] in the Laplace–Fourier transformation. The inversion was performed between the frequencies of 4 and 50 Hz, and a logarithmic data residual was used. The extracted 1D velocity profiles from the final high-resolution velocity model correlate well with the sonic log, and estimated vertical incidence VSP velocities. The predicted data obtained by the final velocity model indicate a generally good fit with the field data, thus confirming the success of the inversion. A reverse time migrated section derived by the final velocity model provides additional structural details. The velocity model indicates anomalous zones of low-velocity values that correlate with known locations of hydrocarbon reservoirs.

The aim of this study is to understand the distribution of fractures in a carbonate reservoir zones in a giant offshore oilfield in Abu Dhabi. We integrated faults and lineaments interpreted from 3D OBC seismic attributes (pre-stack and post-stack data) with fractures observed in cored (Well “A”) and in Ultra High Resolution Image - UHRI (Well “B”) wells drilled in the area. We found that the maximum curvature attribute is the most suitable attribute in predicting the presence of faults and fractures in this case. The orientation of the extracted fractures is consistent with fracture orientations observed in the core and image log interpretation. The maximum curvature attribute highlights anomalies in NE-SW and NNE-SSW directions which are nearly perpendicular to the dominant fault directions. These anomalies may represent concentration of fractures in the area. It is noted that the dominant fault orientation interpreted from 3D seismic in the study area is NW-SE. The strike of the fracture orientation from the cored well is NE-SW at shallow reservoir level whereas it is in NNW-NNE and NNE-SSW directions at deeper reservoir levels. The fracture strike direction from the cored well data correlates well with the direction of dominant maximum curvature-ant tracking co-rendered attribute anomalies at these reservoir levels. Similarly the strike of the fracture orientation from the high resolution image log is NE-SW and correlates very well with the dominant direction of anomalies interpreted from maximum curvature and anisotropy attributes. The orientation of the extracted faults and fracture lineaments from maximum curvature and azimuthal anisotropy (AVOaz) at different reservoir zones are displayed in stereonet and rose diagrams and compared with the rose diagrams computed from fracture orientation observed in the cored well and in image log at different reservoir levels and a good correlation is observed between them. Presentation Date: Wednesday, October 17, 2018 Start Time: 8:30:00 AM Location: 210A (Anaheim Convention Center) Presentation Type: Oral

PreviousNext No AccessRDPETRO 2018: Research and Development Petroleum Conference and Exhibition, Abu Dhabi, UAE, 9-10 May 2018A fractured reservoir in the light of seismic wave attenuation attributeAuthors: Fateh BouchaalaMohammed Y. AliYoucef BouzidiJun MatsushimaAala A.I. MohamedEric M. Takam TakougangAkmal A SultanFateh BouchaalaThe Petroleum Institute, part of Khalifa University of Science and Technology, Abu Dhabi, UAESearch for more papers by this author, Mohammed Y. AliThe Petroleum Institute, part of Khalifa University of Science and Technology, Abu Dhabi, UAESearch for more papers by this author, Youcef BouzidiThe Petroleum Institute, part of Khalifa University of Science and Technology, Abu Dhabi, UAESearch for more papers by this author, Jun MatsushimaThe University of Tokyo, Frontier Research Center for Energy and ResourcesSearch for more papers by this author, Aala A.I. MohamedThe Petroleum Institute, part of Khalifa University of Science and Technology, Abu Dhabi, UAESearch for more papers by this author, Eric M. Takam TakougangThe Petroleum Institute, part of Khalifa University of Science and Technology, Abu Dhabi, UAESearch for more papers by this author, and Akmal A SultanThe Petroleum Institute, part of Khalifa University of Science and Technology, Abu Dhabi, UAESearch for more papers by this authorhttps://doi.org/10.1190/RDP2018-41274720.1 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract In this paper, we investigate a fractured reservoir zone in an oilfield located in the Emirate of Abu Dhabi, United Arab Emirates, by using seismic wave attenuation attribute. The dense geometry of a 3D VSP walkaway spiral survey carried out in the oilfield, permits to perform a high resolution (15° spacing) azimuthal estimation of the attenuation at different offsets. By assuming the azimuth of the minimum attenuation as the strike direction of fractures, we obtain this direction in the three reservoir units, R1, R2 and R3 at several offsets. The comparison between the estimated directions and those based on core data interpretation is quite satisfactory. This is a good indication about the potential of seismic wave attenuation attribute for fracture characterization. Our results show that the effect of fractures on seismic wave attenuation is frequency dependent. By modifying the frequency range, the dominant orientation of fractures changes. This is related to scattering and intrinsic attenuation mechanisms that are strongly dependent on frequency. More investigation on this dependence can be useful to provide information about fracture sizes and their fluid content. This a great advantage of attenuation attribute, compared to the classical seismic attributes, such as curvature and ant tracking, which are widely used to extract fracture orientations from seismic data. Keywords: attenuation, attributes, VSP, scatteringPermalink: https://doi.org/10.1190/RDP2018-41274720.1FiguresReferencesRelatedDetailsCited byStudy of a fractured reservoir by using the anisotropy of seismic wave attenuationFateh Bouchaala, Mohammed Y. Ali, Jun Matsushima, Youcef Bouzidi, Eric. M. Takam Takougang, and Aala A.I. Mohamed10 August 2019 RDPETRO 2018: Research and Development Petroleum Conference and Exhibition, Abu Dhabi, UAE, 9-10 May 2018ISSN (online):2159-6832Copyright: 2018 Pages: 233 publication data© 2018 Published in electronic format with permission by the Society of Exploration GeophysicistsPublisher:Society of Exploration Geophysicists HistoryPublished Online: 28 Jun 2018 CITATION INFORMATION Fateh Bouchaala, Mohammed Y. Ali, Youcef Bouzidi, Jun Matsushima, Aala A.I. Mohamed, Eric M. Takam Takougang, and Akmal A Sultan, (2018), "A fractured reservoir in the light of seismic wave attenuation attribute," SEG Global Meeting Abstracts : 24-27. https://doi.org/10.1190/RDP2018-41274720.1 Plain-Language Summary KeywordsattenuationattributesVSPscatteringPDF DownloadLoading ...

Data from a magnetotelluric survey along a 2D transect across the basin-scale Badaminna Fault zone in the northern Central Perth Basin was used to augment the information from a limited number of monitoring wells across the fault zone. The magnetotelluric method was employed to provide continuous spatial information of the subsurface electrical resistivity for hydrogeological interpretation from the near surface to depths exceeding 2 km, where hydrostratigraphic units are offset by vertical fault displacement. Unconstrained 2D inversion resulted in a somewhat compartmentalized subsurface structure consistent with the known shallow hydrostratigraphy from borehole information, seismic and airborne EM. At larger depths broad conductive structures can be linked to increasing salinities.

Frequency domain visco-acoustic waveform inversion is applied to multi-offsets vertical seismic profile data acquired over a carbonates reservoir in an oil field offshore Abu Dhabi in the United Arab Emirates, to produce high resolution seismic velocity and attenuation structures. The starting velocity and attenuation models are obtained from traveltime tomography, and from the centroid frequency-shift method, respectively. Waveform tomography is performed between the frequencies 4 and 50 Hz. To reduce coupling between velocity and attenuation parameters during model updates, a two stage inversion strategy is adopted. During the first stage, only the velocity model is recovered and, during the second stage, velocity and attenuation models are recovered. The density is estimated from empirical correlation derived from sonic and density logs at the borehole location. A judicious selection of the time-damping constant [Formula: see text], used to suppress late arrivals in the Laplace-Fourier domain is critical to mitigate nonlinearities. Prior to the inversion, data preconditioning is done to transform the data in a form convenient for the visco-acoustic wave equation. High resolution final velocity and attenuation models are obtained. Extracted 1D profiles from the final models generally correlate well with the sonic log and estimated clay content from the gamma-ray log. These observations give confidence to the results. A comparison of the synthetic data generated from the final models and the field data shows a high degree of similarity. The high resolution of the results enables us to readily identify layers and provide a geologic interpretation from Quaternary to Late Jurassic. The inverted models show a stack of layers with alternating relatively high and low velocity values associated with relatively high- and low-attenuation values defining anticlines, as we progressed deeper into the subsurface. The two main reservoirs units in the Lower Cretaceous are clearly identified.

Waveform tomography and reverse time migration were used to derive a high resolution seismic migrated section with walkaway VSP data from an oil field in Abu Dhabi, United Arab Emirates. A high resolution velocity model that correlates well with the sonic log was obtained from waveform tomography and used for reverse time migration. A specific workflow, based on dip estimate, structural conditioning, noise attenuation, similarity/coherency attributes and binary filtering was used for the extraction of faults and fractures from the reverse time migrated section. Complex networks of lineaments were obtained and interpreted using rose diagrams. The lineaments associated with large throw in seismic section correlate well with manually interpreted faults from seismic, and the dip angle of lineaments with little to no throw correlate with the dip angle of interpreted fractures from FMI data, thus suggesting they might be related to fracture zones or fracture corridors.

2D visco-acoustic waveform tomography was applied to walkaway VSP data acquired over a carbonate reservoir in the United Arab Emirates, to form high resolution images of P-wave velocity and attenuation structures. The waveform tomography algorithm was implemented in the frequency domain, and the field data were inverted between the frequencies 4-50 Hz. The preconditioning of the input data, the inversion strategy and the starting models were all critical for the success of the inversion. A specific inversion strategy was used to decouple between updates in velocity and attenuation parameters during the inversion. A high resolution velocity model that correlate with the available sonic log was obtained, confirming the reliability of the results. Zones with anomalous low velocity values associated with relatively high attenuation values at known locations of hydrocarbon reservoirs were identified. Presentation Date: Tuesday, September 26, 2017 Start Time: 3:55 PM Location: 361F Presentation Type: ORAL