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.

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.

Intrinsic attenuation is mainly caused by the frictional movement induced by seismic waves during their passage between fluids contained in subsurface pores and solid grains. In contrast, scattering attenuation is due to small reflections caused by subsurface heterogeneities. Since porosity and fractures are important sources of heterogeneity and fluids, scattering and intrinsic attenuation are suitable seismic attributes for investigating porous and fractured subsurface zones, such as oil and gas reservoirs. In the present study, we accurately estimated scattering and intrinsic attenuation from zero-offset vertical seismic profiling (VSP) and sonic data acquired from three wells that cross a reservoir zone of an oilfield located in Abu Dhabi in the United Arab Emirates. In addition, we properly separated scattering and intrinsic attenuation. The attenuation profiles show high variation with depth. Furthermore, the scattering is frequency dependent and has a significant contribution to the total attenuation. This is due to the high heterogeneous property of carbonate rocks, which dominate the lithology of the reservoir zone. This means that the variation of attenuation can be used as an indicator of the heterogeneity degree of reservoir zone. The VSP and sonic intrinsic attenuations exhibit high anomalies in oil-rich zones, and the ratio of the compressional sonic attenuation to the shear attenuation exhibits a high anomaly in gas-rich zones, but not in oil-rich zones, because the presence of oil influences the compressional and shears attenuations in a similar fashion. However, the presence of gas attenuates compressional waves much more than the shear waves. Therefore, can be used to distinguish oil- and gas-rich zones. The highly fractured reservoir units display negative VSP intrinsic attenuation anomalies and strong scattering, which reveals a strong interference phenomenon. This phenomenon leads to an increase in amplitude of the downgoing wave versus depth, which results in negative attenuation. Hence, strong negative intrinsic attenuation accompanied by strong scattering can be an indicator of a highly fractured zone. The VSP and sonic intrinsic attenuations in such zones have a large discrepancy, which might be due to the squirt flow mechanism due to the inter-crack fluid flow due to the compressional stress induced by seismic waves on the fractures. This mechanism attenuates the waves propagating at low frequencies less, because the fluid pressure has sufficient time to reach equilibrium, which is not the case at high frequencies. This explains why the VSP intrinsic attenuation is much smaller than the sonic attenuation in highly fractured zones. As such, a large discrepancy between VSP and sonic intrinsic attenuations also indicates a highly fractured reservoir.

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 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 ...

In this paper, we present a case study of fracture characterization by integrating borehole data with a variety of seismic attributes in a carbonate reservoir from a giant offshore field, United Arab Emirates. The objectives are to determine to what extent seismic data may be confidently used for mapping spatial distributions of subtle faults and fracture corridors in the reservoirs and to better understand the distribution of overburden anomalies (karsts, high impedance channels) for field development planning. Borehole data used in our study include information from core descriptions (fracture density and orientations), image logs, cross-dipole shear-wave anisotropy analysis, and dynamic data (well testing, PLT, tracer, and mud-loss). The seismic attributes include standard and advanced post-stack geometrical attributes; pre-stack seismic azimuthal AVO attributes, and recently developed pre-stack diffraction imaging. We find that there are common features that can be identified in different attributes, and the differences may indicate different scales of fractures. We also observe a qualitative correlation in the area of history match challenges and high anisotropy magnitude, where seismic anisotropy can identify relatively high fracture intensity regions/zones instead of pinpointing individual fractures and complements other attributes as differences do exist between seismically identified fracture zones and well data due to overburden anisotropy, resolution and sampling issues (which are addressed using the synthetic modeling approach). Diffraction attributes have revealed more detailed geological features in overburden (e.g. karsts) and reservoirs (e.g. lineaments) than in reflection data and a comparison with mud loss data in the shallow zones looks promising with a good correlation between mud loss and collapsed features. This work has provided an improved understanding of the applicability of the using multi-seismic attributes for fracture characterizations in carbonate reservoirs.

Abstract We present a case study of fracture characterization by integrating borehole data with a variety of seismic attributes in a carbonate reservoir from a giant offshore field, United Arab Emirates. The objectives are to determine to what extent seismic data may be confidently used for mapping spatial distributions of subtle faults and fracture corridors in the reservoirs and to better understand the distribution of overburden anomalies (karsts, high impedance channels) for field development planning. Borehole data used in our study include information from core descriptions (fracture density and orientations), image logs, cross-dipole shear-wave anisotropy analysis, and dynamic data (well testing, PLT, tracer, and mud-loss). The seismic attributes include standard and advanced post-stack geometrical attributes; pre-stack seismic azimuthal AVO attributes, and recently developed pre-stack diffraction imaging. We conclude that (1) there are common features that can be identified in different attributes, and the differences may indicate different scales of fractures; (2) There is a qualitative correlation in the area of history match challenges and strong anisotropy, where seismic anisotropy can identify relatively high fracture intensity regions/zones instead of pinpointing individual fractures and complements other attributes as differences do exist between seismically identified fracture zones and well data due to overburden anisotropy, resolution and sampling issues; and (3) diffraction attributes have revealed more detailed geological features in overburden (e.g. karsts) and reservoirs (e.g. lineaments) than in reflection data and a comparison with mud loss data in the shallow zones looks promising with good correlation between mud loss and collapsed features. This work has provided an improved understanding of the applicability and limitations of the using multi-seismic attributes for fracture characterizations in carbonate reservoirs.

PreviousNext No AccessSEG Technical Program Expanded Abstracts 2011Role of high quality seismic data in field development and production through case studies from a giant offshore carbonate field, Abu Dhabi, UAEAuthors: Akmal SultanJie ZhangH. Ewart. EdwardS. Ahmed HageKhaled ShahataKamran JanAkmal SultanZakum Development CompanySearch for more papers by this author, Jie ZhangZakum Development CompanySearch for more papers by this author, H. Ewart. EdwardZakum Development CompanySearch for more papers by this author, S. Ahmed HageZakum Development CompanySearch for more papers by this author, Khaled ShahataZakum Development CompanySearch for more papers by this author, and Kamran JanZakum Development CompanySearch for more papers by this authorhttps://doi.org/10.1190/1.3627396 SectionsSupplemental MaterialAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract A recent reprocessing of a large Ocean Bottom Cable (OBC) seismic dataset of an Offshore Carbonate Oilfield in U.A.E. resulted in significant seismic imaging, signal/noise ratio, and detectability improvements of faults and horizon geometries, which included new fault system sets never previously detected. In addition, seismic amplitude fidelity was improved significantly, confirmed by better well‐ties and subsequent acoustic impedance inversion, which made seismic quantitative analysis possible (Zhang et al., 2010). This paper will focus on the description of successful applications of the seismic data in pre‐ and post‐drilling analysis, understanding anomalous water production, and variability in production along boreholes through case studies. In the first example , in case A, the new seismic data was used to identify faults and structural lineaments (such as subtle faults, possible sub seismic fracture corridors, etc.) for pre‐drilling analysis: this was an input considered in drilling design and, on well execution, the identified lineament correlated with mud loss increase, deduced by the post drill analysis. The second example, in case B, is for a well with anomalously high water breakthrough (80%) in a relatively low permeability part of a reservoir: this was observed in a lower section after about 6 years of production. To understand this unusual and uncommon observation, production data and RST logs were integrated with seismic data: it was found that in this instance fault juxtaposition could explain the observed effects. Finally in case C, a single water entry point was identified on PLT and temperature logs. After tying to seismic, the water conduit was mapped on seismic data as a small throw fault. The diversity of the three examples cited attest to the value generated on a day‐to‐day drill well planning, execution and review basis by the reprocessed seismic. In recent years seismic has provided major input to well delivery and understanding of apparent anomalous behavior in ZADCO and with newly reprocessed data the seismic is utilized beneficially for reservoir understanding (examples here) and for drilling of karstified, channeled and faulted overburden.Permalink: https://doi.org/10.1190/1.3627396FiguresReferencesRelatedDetailsCited byFracture characterization from seismic attributes and anisotropy through core and image log integration in a giant offshore oil fieldAkmal A. Sultan, Mohammed Y. Ali, Youcef Bouzidi, Eric M. Takam Takougang, Fateh Bouchaala, and Aala A.I. Mohamed27 August 2018Improved Fracture Characterization by Utilizing Seismic-Derived Attributes including Anisotropy and Diffraction Imaging in a Giant Offshore Carbonate Field, UAE9 November 2015 SEG Technical Program Expanded Abstracts 2011ISSN (print):1052-3812 ISSN (online):1949-4645Copyright: 2011 Pages: 4424 Publisher:Society of Exploration Geophysicists HistoryPublished Online: 25 May 2012 CITATION INFORMATION Akmal Sultan, Jie Zhang, H. Ewart. Edward, S. Ahmed Hage, Khaled Shahata, and Kamran Jan, (2011), "Role of high quality seismic data in field development and production through case studies from a giant offshore carbonate field, Abu Dhabi, UAE," SEG Technical Program Expanded Abstracts : 1103-1107. https://doi.org/10.1190/1.3627396 Plain-Language Summary PDF DownloadLoading ...

PreviousNext No AccessSEG Technical Program Expanded Abstracts 2010Seismic constrained reservoir property prediction — example from a Middle East carbonate field Offshore Abu Dhabi, UAEAuthors: Jie ZhangRaed El‐AwawdehZyg J. ShevchekNaeema KhouriAkmal SultanChristopher E. HarrisJoe M. ReillyJie ZhangZakum Development CompanyExxonMobil Upstream Research CompanySearch for more papers by this author, Raed El‐AwawdehZakum Development CompanyExxonMobil Upstream Research CompanySearch for more papers by this author, Zyg J. ShevchekZakum Development CompanyExxonMobil Upstream Research CompanySearch for more papers by this author, Naeema KhouriZakum Development CompanyExxonMobil Upstream Research CompanySearch for more papers by this author, Akmal SultanZakum Development CompanyExxonMobil Upstream Research CompanySearch for more papers by this author, Christopher E. HarrisZakum Development CompanyExxonMobil Upstream Research CompanySearch for more papers by this author, and Joe M. ReillyZakum Development CompanyExxonMobil Upstream Research CompanySearch for more papers by this authorhttps://doi.org/10.1190/1.3513084 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract A recent reprocessing of a large Ocean Bottom Cable (OBC) seismic data set of a Middle East Offshore Carbonate Oilfield in U.A.E. resulted in significant seismic imaging, signal/noise ratio, and detectability improvements of faults and horizon geometries which included new fault system sets never recognized before. In addition, seismic amplitude fidelity was improved significantly and it has been confirmed by better well‐ties and subsequent acoustic impedance inversion, which enabled seismic quantitative analysis possible. This paper will focus on the description of a successful application of porosity prediction based on the data and a workflow that consists of four major steps: rock property analysis, acoustic impedance inversion, porosity prediction from multi‐attribute analysis, and validation based on well data. Hundreds of regular wire‐line and/or cross dipole sonic logs were acquired and dozens of ultrasonic measurements from core samples were performed across the field. Data was conditioned and analyzed to understand the porosity versus impedance and other rock physics trends. A relatively narrow porosity versus impedance trend was observed in the data set, which laid the foundation for our subsequent analysis. Acoustic impedance inversions were performed in a commercial software package by 1) well‐to‐seismic tie and wavelet estimation, 2) earth model building based on interpretation and well data, 3) band‐limited impedance inversion and total impedance derivation. The inversion results and seismic stacks were loaded into a seismic attribute analysis software package where seismic multi‐attribute analysis was performed and porosity versus impedance and other attribute relationship was established. The porosity volume was then generated across the entire field based on the established relationships. The resulted porosity volumes based on the inversion results and other attributes were validated with well data where high consistency was observed. These volumes are layered properties rather than reflectivity tied to interfaces; therefore they can be very easily used for integration between geological and engineering data. Also higher frequency was observed within the volumes. Examples of application of the impedance and porosity volumes for thinner reservoir mapping, well planning, and input for geological models will be shown.Permalink: https://doi.org/10.1190/1.3513084FiguresReferencesRelatedDetailsCited ByFracture characterization from seismic attributes and anisotropy through core and image log integration in a giant offshore oil fieldAkmal A. Sultan, Mohammed Y. Ali, Youcef Bouzidi, Eric M. Takam Takougang, Fateh Bouchaala, and Aala A.I. Mohamed27 August 2018Role of high quality seismic data in field development and production through case studies from a giant offshore carbonate field, Abu Dhabi, UAEAkmal Sultan, Jie Zhang, H. Ewart. Edward, S. Ahmed Hage, Khaled Shahata, and Kamran Jan25 May 2012 SEG Technical Program Expanded Abstracts 2010ISSN (print):1052-3812 ISSN (online):1949-4645Copyright: 2010 Pages: 4453 publication data© 2010 Copyright © 2010 Society of Exploration GeophysicistsPublisher:Society of Exploration Geophysicists HistoryPublished: 21 Oct 2010 CITATION INFORMATION Jie Zhang, Raed El‐Awawdeh, Zyg J. Shevchek, Naeema Khouri, Akmal Sultan, Christopher E. Harris, and Joe M. Reilly, (2010), "Seismic constrained reservoir property prediction — example from a Middle East carbonate field Offshore Abu Dhabi, UAE," SEG Technical Program Expanded Abstracts : 1312-1316. https://doi.org/10.1190/1.3513084 Plain-Language Summary PDF DownloadLoading ...

We have carried out 4D seismic research on two giant carbonate fields in Abu Dhabi, UAE, employing an integratedapproach. Our work process started from fundamental rock physics analysis. The Xu-White rock physics model, originallydesigned for clastic rocks, was extended to carbonates. With this model, we characterized the reservoir interval by different(geophysical) pore types, related them to petrophysical (sedimentalogical) pore types, and performed log conditioning toimprove well to seismic ties. Laboratory ultrasonic measurements of core plugs and log analysis were conducted incombination with the rock physics model to examine the fluid and pressure sensitivities.

Abstract Structural analysis of 3D seismic data over an offshore field in Abu Dhabi, involving a detailed study of the early Cretaceous reservoir sequence, the shallow cover and the deeper stratigraphy of the area, has shown that spatial fault patterns change subtly through the different stratigraphic packages present. This relates to the rheological properties, but consistency is shown in both the fault locations and in the resolved tectono-kinematic signature of the fault systems. The main fault system present comprises a rhombohedral array of NW-SE to WNW-ESE zones intersected by a broadly NE-SW system, at ∼100-130° to each other. Elements of these faults controlled depositional facies in the early to late Cretaceous (e.g. Thamama depocentres, Mishrif edge, Salabikh basin) though often only structurally soft-linked at the time of deposition. Hard linkages characterize the later Oman orogenic event as flower zones generating the Fiqa channels. Fewer of the faults continue up through the Tertiary sequence, where most of the breaks reflect fold-related arching of the cover sequences, but many coincide with locations of linear features and intersections at deeper levels. Within the reservoir sequence the dense-reservoir alternations are fractured in a manner that responded to the mechanical layering. On a seismic sequence scale the faults display a similar effect whereby their geometry, density, connectivity and style within the damage zones display a brittle-ductile contrast, and where fault branches, tip zones or nucleation sites indicate structural linkage and deformation of a multi-layer rheology. A distinct effect is illustrated by changes in fault orientation, style and linkage across the fine-grained Nahr Umr seal sequence. From the seismic structural analysis a basement-influenced faulting model, whereby localized readjustment of elements within a chequer-board of steep, deep faults occurred during Mesozoic-Cenozoic tectonic events, linked to distal mountain building episodes (Oman Mountains, Zagros event), is proposed. Repeated use of the antecedent framework is reconciled with a highly linked, low-offset, strike-slip dominated system that propagated into cover sequences as variably hard to soft-linked architectures: Hard linkages exist across stronger, stiffer carbonate sequences Soft linkages prevail through more ductile shale-rich sequences Within the offshore area many of the structures are salt-cored, particularly the smaller, tight dome-shaped fields and piercements. Large fields define broader, very open folds, each envisaged to be underlain by a deep ‘salt pillow’, postulated to be governed by the intersection of basement lineaments: they do not show distinct alignment/asymmetry typical of onshore fields. Initial growth of such traps during the Oman obduction event was largely by upward-propagating foreland-reactivated faulting, however, the later growth of these structures, when the trap amplification occurred, is viewed as a response to mild salt pillowing at depth above fault intersections triggered by Zagros-related events. Flattening of the seismic surfaces in the Tertiary sequence illustrate the timing of this fold modification coupled with the tilting of the fields to the northeast, with an effect to relocate the trap crests. This can be reconciled with the distribution of bitumen zones at reservoir levels that exhibit components of (i) NE-wards tilting, (ii) amplified doming of the crest of the structure, and (iii) activity on fault-controlled panels adjacent to the major lineaments under the field.

Abstract Recent mapping of fault patterns from picked surface attribute analysis (‘difference’ maps, spectral decomposition, isochron maps) and time slices over a giant offshore field in Abu Dhabi has recognized a complex multi-set pattern of faults at reservoir level. As well as providing additional seismic scale faults, linear features (proposed subseismic faults and fracture systems) have been identified. These patterns are best described in terms of strike-slip geometries; however, many display components of both dip-slip and strike-slip over their movement history. In different parts of the field dominant fault directions displaying dextral transtension, dextral transpression, trapdoor hinge faulting and oblique-slip keystone graben generation are observed. Fault throw statistics and segment growth history in the most important mapped zones typify components of strike-slip along with local shear and segment termination at cross-fault zones. The prevalent fault trends are roughly orthogonal NE-SW and NW-SE systems that dissect the field. Superimposed on this geometry is an array of distinctly en-echelon WNW-ESE and WSW-ENE structures that link to steep zones at deeper levels. Within sub-regions of the field other trends are also present, including NNE-NNW to N-S, NNW-SSE and E-W. These sets do not form a radial pattern; they are distributed spatially within field domains and involve complex systems and layer-related rheologically controlled deformation. Comparison of the mapped lineament pattern with core-derived fracture orientation data shows that all sets identified in the field from seismic are present within the overall fracture strike system within the wells. Field-wide, domains where transtension and transpression dominate, as well as more dip-slip dominated areas can be mapped out. Core scale fractures tend to display a component of strike-slip within the bulk strain field-wide, as evidenced by steep or sub-vertical fracture intersections. Newly identified lineament zones allow better understanding of high intensity fractured wells previously mapped distal to known faults

From structural analysis of 3D seismic data over a giant field, offshore Abu Dhabi, a complex pattern of intersecting, broadly conjugate, strike-slip dominated en-echelon fault systems are observed from 'basement' levels up to latest Cretaceous horizons. Over geologic time these fault systems exerted fundamental controls on depositional patterns within the study area. Use of new attribute techniques, isochron mapping, flattening on key intra-Cretaceous horizons, cinematic time-slice 'movies' and a review of the available vertical seismic sections has indicated that many apparent velocity anomaly zones are controlled by deep-seated fault systems developed as strike-slip dominated 'flower structures'. Spatial continuity of these fault zones, the most prominent of which trend ~NE-SW, exhibit a linear nature on a scale of several kilometers to tens of kilometers; have flower-zone geometry in cross-section but with increasingly en-echelon nature at Upper Cretaceous levels; low apparent normal offsets on long fault segments; anastomosing, convergent and divergent, patterns at different stratigraphic levels; wrench offset with respect to other deep fault systems; throw terminations with rapidly decreasing displacement gradients along en-echelon zones into the crossover zones with other fault systems. There are four prominent fault systems that exert control on the depositional systems: (1) NE to NNE trending 'Fiqa' direction, also delineating local depositional highs/lows and Mishrif 'reef' margin; (2) NW-SE zones defining depositional areas of step-wise thickening/thinning; (3) Conjugate WNW-ESE and WSW-ENE en-echelon strike-slip zones, and (4) NNW-SSE fault zones displaying local control on thinning or thickening. Temporal fault activity on these zones is linked to sedimentary thickening and thinning patterns, though deeper level faults provided only 'soft' links to the sedimentary sequences of early Cretaceous age. By late Cretaceous times the transtensional / transpressional fault systems provided 'hard' links to the deposition systems (e.g. Fiqa channel system).