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EAGE workshop on Developments in Land Seismic Acquisition for Exploration
- Conference date: 17 May 2010 - 19 May 2010
- Location: Cairo, Egypt
- Published: 18 May 2010
21 - 40 of 73 results
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Near-Surface Characterization Using Point Receiver Data
Authors L. Velasco, C. Strobbia and A. LaakeThe effect of near-surface perturbations is still one of the key problems in land seismic surveys. Elastic near-surface characterization can provide a robust solution for the compensation of the effects of the shallow geology on surface seismic data. Seismic point receivers provide densely sampled data that enable the use of high-resolution methods for near-surface characterization. Near-offset refractions and surface wave inversion allow generation of shallow 3D depth models for P-wave and S-wave velocity. The two models reveal near-surface geological layers and lateral heterogeneities. A case study from the Gulf of Suez gravel planes demonstrates that lateral heterogeneities in shallow P-wave and S-wave velocity horizons map shallow faults. The results are validated by fault outcrop maps from remote sensing. For the first time the elastic near-surface model is being estimated from surface seismic data. Point-receiver technology provides geological information in a domain that is usually not accessible for seismic investigation. The approach to attenuate shallow seismic data in conventional acquisition is replaced by a method that focuses specifically on the extraction of shallow seismic data for geological mapping.
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How Can We Use Cross-Spreads for Near-Surface Model Building?
Authors F. Ernst, G. Baeten and X. CampmanIn on-shore exploration, an adequate near-surface model is often crucial for a proper image at depth. Shallow velocities can be inverted from dispersion curves of surface waves and guided waves (`coherent noise'). This requires small arrays and dense sampling, as also short wavelengths of the coherent noise need to be sampled. However, properly sampling ground roll is often not cost effective. By staggering shots or receivers in a cross-spread acquisition geometry, and jointly transforming multiple gathers, we obtain adequate sampling in absolute offset. This allows the use of small arrays without introduction of aliasing. The increase in acquisition effort and the decrease in spatial resolution is only marginal, while a significantly larger bandwidth for the dispersion curve is obtained and hence shallower velocities can be resolved.
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Cablefree Systems, are They Just Faking it?
Authors R.G. Heath, S. Savazzi and U. SpagnoliniCablefree systems have been available to the land industry for decades but have only ever managed to be used in acquisition niches. The land indsutry is desperate to have viable and universal alternatives which are cablefree. This paper looks at the technologies which are now available in second generation cablefree recorders which will allow them to dominate the acqusition market and take land land exploration forward.
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Land Cableless Systems: Use & Misuse
By D. MougenotIt is a fact that there are more cableless than cable systems on offer today. In this abstract which is from a paper published in the February issue of the First Break we provide a tentative analysis of the reasons for the emergence of these cableless systems and of their real advantages compared to cable architecture. Cable systems have significantly improved in compactness, flexibility and reliability. They represent and will continue to represent the bulk of the land system market. The suggested approach is not to try to replace an architecture with the other (the misuse), but to facilitate their complementary application (the right use) in order to adapt to various terrain conditions and spread configurations.
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Digital Accelerometers: Expectations and Practical Achievements
By D. MougenotWith the dawn of this century came a new generation of seismic sensors. These are 1C or 3C MEMS based accelerometers integrated with electronics to deliver a well calibrated digital signal. Contrary to arrays of geophones, they must be recorded individually as point receivers. Since noise is only filtered during processing, the interval between receivers must be reduced to avoid spatial aliasing of the noise and to increase fold coverage. The benefits provided by digital sensors are both operational (weight, power consumption, integration with the line…) and geophysical (amplitude & phase response, vector fidelity, tilt detection…). Early 2D-3C tests as well as 3D production surveys, including those performed by the highest channel count crews (35,000+), confirm the benefits of these new sensors: immunity to pick-up noise due to full digital transmission; increase of the frequency bandwidth of the signal and of the associated vertical resolution; well calibrated amplitude suitable for AVO and inversion.
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Ultra Large 100,000+Channels Cable-Less Data Acquisition System with Easy Logistics
Authors G. Nemeth, T. Szabo, Z. Csizmadia and C. AstonThe current, predominant trend of leading instrument provider companies (e.g., ION, Sercel, and OYO) has been to remove the heavy bulk of extensive cabling in acquisition systems by using a wireless node for each channel. These one channel per recording node based wireless acquisition systems have great flexibility and are an ideal fit for medium-sized surveys. However, the latest trend of the major oil companies is to use dense spatial sampling surveys in the 100,000+ channel range. The subsequent increased number of batteries and data downloads can create a logistic nightmare and make it very difficult to use systems with one channel per recording node in these ultra-large surveys. Seismic Instruments, Inc.’s hybrid cable-less data-acquisition system enables the use of 1-96 channels per autonomous recording node. Using multiple of these nodes ultra large 100,000+ channel number data acquisition systems can be formed with very simple and easy logistics. This system technology drastically reduces the number of batteries and data download tasks, simplifying survey logistics even with a channel count greater than 100,000.
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Cable-less Seismic - Multiple Real-World Experiences
By J. Caldwell4 projects (conducted in Turkey, Libya, Malaysia, and Chile/Argentina) demonstrated that a wireless
system was cheaper to operate, provided improved HSE benefits, was more flexible in laying out and
handling obstacles, and was more mobile, than a wired system could have been.
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Vibroseis: Is "Close enough for Seismic" Still Good Enough for Today
Authors R.G. Heath and M. MorrissAlthough Vibroseis is the source-of-choice for modern acquisition, even simple research into vibrator performance demonstrates that this industry makes too many assumptions about the technique itself and about source behaviour. Either of these may lead to poorer data and less productivity than otherwise might be the case. This paper, therefore, addresses two closely related aspects of modern Vibroseis control and documentation that need improvement: • Accurately measuring and improving the energy transmitted into the ground and, • Improving quality control functionality of Vibroseis source control systems.
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Quality Control of Seismic Vibrator Output Force
More LessThere are many quality control methods used to monitor the output force from seismic vibrators. These quality control tools are used to provide what is normally expected to be a flat amplitude spectrum. However, rarely do amplitude spectrums of the QC data look similar to actual recorded seismic data. The purpose of this paper is to demonstrate how vibrator designs often degrade the accuracy of the QC data and how more rigid actuator designs improve QC data quality.
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