EAGE touches range of technologies
Gene Kliewer, Technology Editor, Subsea & Seismic
The European Association of Geoscientists and Engineers (EAGE) held its annual convention and exhibition recently in Rome and Offshore was there. The following are excerpts from several of the presentations and papers given at the meeting.
Realistic 3D Modeling Based on Advanced Interpretation and Geomodeling Techniques
F. Pivot, A. Price, and J.N. Ferry of Total
Marine control source electromagnetic (mCSEM) surveys have a level of maturity that requires it to be integrated into the 3D exploration workflow. To build realistic models for feasibility testing, including all the information available from seismic and geological interpretation, methods must be incorporated to map the complexities of the subsurface, and to measure impacts of topology or scale changes. This paper describes such a methodology and its application to a case study in a turbiditic deep offshore environment.
The prospective target has average burial of 900 m (2,953 ft) for a water depth of about 1,100 m (3,609 ft). High quality seismic data are available with multi-angle cubes to allow generation of detailed images of the sandy fairways.
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3D red geobody is obtained by extraction in a lithoseismic cube, and shows the envelope of the amalgamated prospective sands. A part of the CSEM 3D “sugar-box” model is also displayed for showing how geomodeling tools allow to paint the cells (in red) concerned by the prospective object.
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Moreover, AVO analysis increases the probability of mapping particular fluids. However, detailed sedimentological interpretation underlines high risk for the sealing of the trap, as possible leakage points are identified. Additionally, no target is identified by flat-spot or any other direct hydrocarbon indicator.
By combining geomodeling tools, recent advances in seismic interpretation, and 3D mCSEM modeling tools, it is possible to create and fill a very realistic mCSEM “sugar-box” model and to compute CSEM responses of a set of probable scenarios covering uncertainties identified in a prospective area. The procedure is fast and allows rapid development of understanding what additional information can be brought by an mCSEM acquisition. A proposed workflow spelled out in the paper gives a method to integrate mCSEM in the suite of interpretation tools.
Improved Marine 4D Repeatability Using an Automated Vessel, Source and Receiver Positioning System
J.O. Paulsen & G. Brown of WesternGeco
A new automated and integrated, vessel, source, and receiver control system has been developed to improve the accuracy and repeatability of 4D surveys. The new control system replaces operator intervention with automated updates to vessel, source, and streamer steering devices using positioning information from in-sea equipment. This has lead to an increase in the accuracy of source repeatability (2.5-m repeat accuracy for 95% of shotpoints), and also has improved the ability to repeat receiver positions.
The dynamic spread control (DSC) system provides accurate feather match for lines with dynamically changing feather, provided that the current strength is less than the operating capability of the streamer steering devices. The DSC system improves source position accuracy. A major part of this improvement comes from the automation which takes the place of operator intervention.
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Source positioning results showing 4-m error or less for 95% of observations with the DSC system, and 14-m or less error without the DSC system.
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Volume 68 Issue 8
August 2008
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