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EAGE/SPE Subsalt Imaging Workshop
- Conference date: January 31-February 3, 2016
- Location: Dubai, United Arab Emirates
- Published: 02 May 2016
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Decoding the Seismic Signal: A Comprehensive Approach for Carbonate Buildup Imaging in the Red Sea
By L. EscalonaSummaryThe seismic data set provides geological information from stratigraphic boundaries. Commonly, different responses are reflected in terms of amplitude, phase and frequencies changes. The bandwidth of the seismic signal and processing approximations restrict the subsurface resolution. Several techniques such as seismic inversion, spectral decomposition, coherency processing has been developed to extract geological information from the seismic data, to reveal the subsurface geology and evaluate reservoir targets. This work summarizes different workflows to improve seismic imaging and provide better reservoir characterization of carbonate buildups in the Red Sea.
The process started in terms of whether the seismic attributes below the salt are robust enough to enable a seismically driven carbonate characterization. Extensive gather analysis, velocity corrections and data conditioning was performed at pre and post stages. Employing HD spectral decomposition, elastic inversion, interactive geobody extraction and integration of well data (core analysis) a successful qualitative and quantitative reservoir characterization was reached.
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New Marine Acquisition Technologies for Subsalt and Pre-salt Seismic Exploration
Authors N. Moldoveanu and C. CunnellSummaryMost of the developments in marine acquisition technology in the last decade were triggered by the challenges that oil industry faced in exploration and development of subsalt and pre-salt oil reservoirs. These challenges can be divided in three categories: reservoir illumination, limited vertical and horizontal seismic resolution, difficulties encountered in accurate imaging of the seismic data.
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Improving Subsalt Imaging with a New Seismic Acquisition System
Authors L. Haumonte, L. Velay and M. ManinSummaryTraditional marine seismic acquisition methods (streamer, OBC) struggle to address the combination of high data quality and large survey areas needed to image sub-salt reservoirs and prospects. This article will describe a completely new seismic acquisition system that delivers higher quality data within an acceptable time frame, and the key advantages it delivers for sub-salt and other challenging geological settings. Test results will illustrate some benefits of the system.
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Miocene to Present Tectonics in the Levant Basin (Lebanon) and the Role of the Messinian Evaporites Regional Seal
Authors B. Montaron, L. Montadert, W. Chbat, I. Dupin and V. TestelinSummaryThe Levant Basin is characterized by the presence of a regionally continuous layer of Evaporites of Messinian age. About 2000 m thick, they pinch out on the margins of the deep basin. Upslope they pass to the Messinian Erosional surface (MES) known in the whole Mediterranean and linked to the 1500m sea level drop of the Messinian.
The regional continuity of this seal and the high rate of sedimentation particularly in the Oligo-Miocene impeded a normal compaction of the pre-Messinian sediments and generated overpressures. The combination of these particular characteristics and of the regional Lower-Middle Miocene tectonic stress produced faults and folds constituting traps for Exploration.
In the whole basin, seismic data show the existence of a dense fault system oriented N110–120°. It is characterized by a fault spacing of few km and a limited fault length (about 2 to 10km). Their vertical throw component formed a series of discontinuous horsts and grabens. They have a strike-slip component associated with the Lower-Middle Miocene shortening of same orientation, a consequence of the initiation of the Dead Sea transform Fault.
They stop downward generally at the base of the Oligocene in under compacted sediments and stop upward in the Messinian ductile Evaporites. In some parts of the NE offshore Lebanon they lose their preferred orientation and display a typical polygonal fault pattern. It shows that these faults were linked to the compaction of the sediments but under a NW-SE oriented tectonic stress since the Lower-Middle Miocene. Associated strike slip faults at 60° of their orientation and elongated N20° positive flower structures at 80–90° of their orientation are observed.
Along the continental margin of Lebanon, other traps are linked to transpressive flower structures of also N20° orientation, but contrary to the folds in the basin they are rooted in the deepest horizons.
Other SW-NE oriented elongated anticlines with a senestral strike slip component are present in the deep Levant basin along the Latakia Ridge which bounds the Cyprus Arc. They are linked to the motion of the Anatolia microplate since the Late Miocene towards the SW.
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Sapropels in the Mediterranean - What Caused the Difference Between East and West?
By E. RohlingSummaryI will go through the environmental processes behind organic deposition in the Mediterranean, and their relationship to climate. I will then address why there is a difference between organic-rich deposition between the eastern and western Mediterranean basins, which I relate to the different straits connecting these basins. Basin isolation turns out to be a major control on organic burial potential.
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Allochthonous Salt Sheet Growth: Implications for Thermal Maturation & Hydrocarbon Prospectivity in the Deepwater Burgos & Perdido Basins, Mexico
By I. DavisonSummaryThis study uses numerical modelling to understand the thermal history of allochthonous salt sheets using a case study of the Burgos and Perdido Fold belts in Mexico.
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Seismic Depth Imaging In Oman: Building up the Ladder of Learnings Toward a WAZ PreSDM Workflow
Authors J. Al-Riyami, A. Al-Mamari and M.J. van de RijzenSummaryPDO has experienced a steep learning curve in depth imaging processing since the delivery of its first WAZ data from south Oman in 2008, then considered then the largest PSDM project. Subsequently many various larger WAZ and NAZ data has been the subject of PreSDM processing.
In this paper we intend to share the PDO journey of developing the standard workflow for PreSDM, showing step by step additions to workflow; from south Oman intra salt objective addressing the intra salt velocity variation, central Oman challenges, and north Oman faults imaging.
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The Value of Re-processing for Intra/Pre-salt Exploration - A Case Study of the Sultanate of Oman 1st WAZ Survey
Authors J. Al-Riyami, MJ van de Rijzen, B.V. van der Kooij and A.A. BulushiSummarySince seismic processing and velocity model building is an evolving business, a re-processing project generally is worthwhile to execute. In this paper the results will be presented of a re-processing project done on the first PDO WAZ survey, shot in 2008 in the South of the Sultanate of Oman.
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Magnetotelluric and Gravity Subbasalt Imaging: Case Studies from Ethiopia and Djibouti Republic
More LessSummaryComplex geology, large volcanic provinces and remoteness makes the exploration difficult and expensive. A major problem is the imaging of sedimentary basins masked by volcanics. Relatively inexpensive geophysical exploration techniques such as magnetotelluric (MT) are used for preliminary investigations in order to provide an accurate geological background of possible oil&gas prospects prior extensive seismic surveys. The reason to use MT in sub-basalt imaging is that in general volcanics are electrically resistive and as a result are relatively transparent to electromagnetic fields. Additionally old basements are also resistive. In contrast, sediment basins are often electrically conductive and this good contrast of properties provides informations on the thickness of the hidden basin. This information is difficult and expensive to obtain otherwise.
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Subsalt Imaging: Challenges and Practical Solutions
Authors H. Rynja, H. Vocks and G.J. OuwerlingSummarySub-salt imaging is key to exploring remaining hydrocarbon opportunities. Due to a large velocity contrast at the top salt, ray-based methods often fail to provide the best image and also cannot be used for velocity model updating. Wave-equation based approaches such as Reverse Time Migration (RTM) are often preferred for sub-salt imaging.
Sub-salt imaging requires more effort in model building and applying more advanced wave-equation based techniques. Optimal stacking can provide a significant uplift in imaging quality for sub-salt targets within a shorter time frame.
Other case histories for sub-salt imaging will be presented at the workshop including an update on sub-salt imaging in Offshore Gabon as presented at the 2014 EAGE/SPE Subsalt Imaging Workshop in Cyprus.
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Waveform Inversion for Complex Salt Models: The Basic Objective, the Challenges and the Opportunities
More LessSummaryFull waveform inversion (FWI) provides us with the opportunity to utilize the full wavefield to build a high-resolution velocity model with very limited human intervention or bias. For complex salt bodies, it implies high-resolution description of the salt body free of top and bottom of the salt picking and salt body flooding. High velocity contrasts in the Earth (like those given by salt bodies) pose an inherent problem to the Born-approximation based gradients of waveform inversion. These gradients, even if properly preconditioned with the Hessian, are based on small perturbations with small support. Delineating the bottom of the salt is especially challenging in waveform inversion as it relies on the wavefield transmission through the salt. This induces incredibly high nonlinearity of the wavefields with respect to the perturbations in the salt or subsalt regions of the model, which requires very large number of FWI update iterations imposing a top-to-bottom strategy. The cost is exacerbated by the necessity to invert high frequencies (at the large cost of fine sampling) to develop the salt bodies sharp boundaries. Alternatively, salt body flooding within FWI have been utilized over the years to handle salt bodies, however, it requires massive manual intervention including salt body picking. In our lab, we recast the problem from inverting for velocities and impendences to inverting for velocity variations. This allows us to have a better definition of large vertical variations, and as a result, the linearized relation to these changes are better equipped to handle the large contrasts. This is accomplished by utilizing the source-shift wave equation developed by Alkhalifah (2010). We also utilize multi-scattered energy in the inversion, as the majority of the waves penetrating the salt experience multi scattering from the salt edges. The presentation will include an overview of such approaches with numerical examples that demonstrate the effectiveness of the proposed approaches.
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