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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
1 - 50 of 73 results
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Surface-Subsurface Integration Reveals Faults in Gulf of Suez Oilfields
Authors A. Laake, M. Sheneshen, C. Strobbia, L. Velasco and A. CuttsReservoir mapping in the Gulf of Suez petroleum system is challenging because rifting broke up the reservoirs by transform and cross faults. We have developed a technique which integrates fault outcrop mapping using satellite image interpretation, seismic near-surface characterization techniques such as Rayleigh wave velocity mapping and rayparameter interferometry as well as ant tracking of faults and geobody extraction on a PSTM cube. The technique utilizes a combination of GIS and Petrel for surface-subsurface integration. The joint analysis of Rayleigh wave data with satellite imagery provides a near-surface structural geologic model, which is interpreted for shallow drilling risks. The suite of near-surface geological products is enabled by the acquisition, processing and interpretation of point receiver seismic data acquired by Q-Land. For the first time detailed structural geology could be imaged in the near-surface, a data regime, which is conventionally contaminated by the footprint of the seismic acquisition.
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Making the Seismic Hydraulic Vibrator Better
Authors M.A. Hall, Z. Wei and T. PhillipsThe results of improvements to the physical design of a seismic Vibrator are shown. These improvements lead to improved low and high frequency energy levels, improved Vibrator control under variable ground conditions and an improvement in the weighted sum signal such that it better matches the ground force, or source signature, of the Vibrator. These improvements will lead directly to significantly better seismic data in a variety of terrains.
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Making the Seismic Hydraulic Vibrator Better
Authors M. Hall, J. Wei and T. PhillipsSummary not available
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Making the Seismic Hydraulic Vibrator Better
Authors M. Hall, J. Wei and T. PhillipsSummary not available
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Improving the Performance of Seismic Vibrators can be the Key to Break Through the Limits of Vibroseis Data Quality
Authors Z. Wei, T. Phillips and M. HallVibroseis is the principal source of seismic energy in land seismic exploration. It seems that this method has been extended to its limits as we continue the search for energy resources. The vibroseis method uses the vibrator to generate a controlled force at the source point. It has been recognized that the hydraulic vibrator is not perfect and does not perform exactly as we expect. In spite of significant success using vibroseis technology in land seismic exploration, many practical issues arising from field operations have remained theoretically unexplained. Many people believe that these problems are attributed to the nonlinearities in the complex system involving the vibrator and the ground. This paper will focus on a few such examples.
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BP's (ISSTM) Technique for High Quality, Fast, Efficient 3D Vibroseis Acquisition in Challenging Desert Terrain
More LessIn October 2008, BP awarded a large 3D Seismic Survey in Blocks 230 and 231, Algeria, to Global Geophysical Services. The objective of the survey was to acquire 2560 Sq Km of high fold seismic (495 at 4km offset) in 8 months using a technique called ISS which had never been previously deployed full scale in Algeria. A further requirement of the survey was that the recorded seismic data would be fast track processed in the field, up to and including post-stack time migration and delivered periodically to the interpreter’s workstation in a reduced time frame to enable a strategic drilling program. This paper describes the ISS technique and its implementation in Algeria where data acquisition was completed in October 2009 after just 8 months of recording operations at productivity rates some ten times greater than those previously achieved in Algeria , with a fully processed data volume delivered within 30 days of last shot point. The paper demonstrates that BP’s ISS seismic method is a viable and commercially feasible technique which enabled a large, high quality, very high fold seismic survey to be acquired in difficult terrain, and fast-tracked data delivered for Well Planning
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Distance Separated Custom Slip-Sweep - A New High-Productivity Method
Authors P.I. Pecholcs, Y. Zhang and S.K. LafonA new method has been derived such that two simultaneous custom Vibroseis sweeps can be decoupled free of cross-talk noise at a distance equal to or great than the source line interval. The only limitation is Vibroseis sweep repeatability. Synthetic and real data examples are used to demostrate the method.
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Iterative Deblending of Land Seismic Data
Authors A. Mahdad, G. Blacquière and A.J. BerkhoutSeismic acquisition is a trade-off between economical and quality considerations. Generally seismic data is recorded with large time delays between illuminating sources in order to avoid interference in time. The consequence is a poorly sampled shot domain. However, in the concept of blended acquisition, the time delay between sources is reduced significantly. Moreover, the sources may transmit encoded signals. Depending on the acquisition objectives, blended acquisition significantly improves the economics or quality or both by adding additional degrees of freedom in the acquisition design. By a deblending procedure, the individual source responses are retrieved. However, the deblended result contains residual noise due to the interference from other sources. The level of this noise depends on the choice of blending parameters. E.g., in the case of a simple code like linear phase encoding (i.e., applying time delays), it is larger than in the case of a more sophisticated code like transmitting sweeps as in vibroseis technology. In this paper an iterative approach is proposed for deblending, based on the estimation and subsequent adaptive subtraction of the interference noise. The type of coding that is applied is one of the factors that determines the required number of iterations.
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Distance Separated Simultaneous Sweeping: Efficient 3D Vibroseis Acquisition in Oman
More LessDistance Separated Simultaneous Sweeping (DS3) is one of a number of techniques developed by BP for efficient land seismic operations. DS3 relies on the Vibroseis source separation distance being chosen to allow sufficient travel time such that the first break noise, or reflection signal, will reach the midpoint crossover later than the time of interest for target horizons. The DS3 records are thus uncontaminated by simultaneous source noise for all levels down to, and including, the target horizon. Implemented at field wide scale across Block 61 in Oman, the DS3 technique achieved world record acquisition production rates and produced excellent data quality.
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Dithered Slip-Sweep Acquisition
Authors Y. Ji and C. BagainiThis paper describes a high-productivity vibroseis acquisition and separation method termed dithered slip-sweep acquisition. It combines two techniques, slip-sweep and dithered acquisition, that have been previously, but individually, used in land vibroseis and marine acquisition, respectively. The constraints on the start time of the sweeps keep the interference noise under control such that the separation algorithms can attenuate the interference more effectively than when the vibrators sweep without synchronizing their activities. An example of dithered slip-sweep acquisition generated from a conventional dataset demonstrates the method.
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Sparse Inversion of Simultaneous Sources
Authors R.L. Abma, T. Manning, J. Yu, M. Tanis and M. FosterNoise caused by the interference of seismic sources in simultaneous shooting is a barrier to the acceptance of this type of seismic acquisition. This paper presents a method that produces pre-stack data from blended acquisition data that are comparable to data from conventional acquisition. While filtering interference noise from the shots and the subsequent stacking of the data are effective in attenuating the interference on high fold wide azimuth ISS(TM) surveys, a high-quality separation of the interference from the pre-stack data would make the data more suitable for amplitude dependent analysis such as amplitude-versus-offset, time-lapse measurements and fracture detection. The high quality interference attenuation method presented here is achieved by using a sparse inversion process that solves a modified version of Berkhout’s matrix system, accurately separating source responses for good quality amplitude measurements. This produces seismic records in which the interference is attenuated to the point that it is well below the background noise. The success of this source separation step in the data processing of blended simultaneous source acquisition therefore further improves the data quality while retaining the lower cost and higher productivity of ISS(TM) acquisition compared with conventional acquisition.
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Deharmonics, a Method for Harmonic Noise Removal on Vibroseis Data
Authors F.D. Martin and P.A. MunozWith the advent of slip sweeps to increase Vibroseis acquisition productivity, the need for harmonic noise removal became more critical to preserve the data quality compared to conventional “flip flop” vibroseis data. Several methods for harmonic noise attenuation are available such as HPVA, Jeffryes, Bagaini, Ziolkowski, Sicking et al. and others. Most of the methods are based on the recording of the vibrator ground force signal to design the operator. However, in some cases the signal is lost or not representative of the vibroseis array. Some of the methods require using uncorrelated data that implies handling of a large amount of data every day. We have successfully implemented a method to remove the harmonic noise without the ground force signal. The method is based on collapsing the harmonic noise by adding the pilot fundamental phase on a correlated record and subtracting the theoretical harmonic phase to be collapsed followed by a deterministic surgical edit of the first breaks. Transformation back to the original noise free correlated record is trivial by applying the inverse phase operation, which is adding the harmonic phase and subtracting the fundamental. The method is demonstrated with synthetic and real data from a slip sweep acquisition
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High Productivity Without Compromise - The Relationship between Productivity, Quality and Vibroseis Group Size.
Authors T. Dean, P. Kristiansen and P.L. VermeerIt has been shown that reducing the source line interval can significantly improve the acquisition footprint of land data. To achieve this reduction without impacting acquisition rates requires the use of high-productivity techniques such as slip-sweep and ISS, typically utilising single vibrators with extended sweeps. These techniques result in a decrease in shot record quality as the sweeps from different vibrators overlap. This paper discusses an altogether more tractable solution: vibrator groups with short sweeps. High productivity can be achieved without interference between different sweeps.
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Meeting the Challenge of Mesozoic Exploration
Authors A. Laake, J. Quigley, C. Strobbia, L. Velasco, P. Vermeer, P. v. Baaren, M. Cogan, A. Zaghloul and A. ShabrawiThe Western Desert of Egypt challenges the exploration for oil and gas both from the reservoir as well as from the surface. The reservoir rocks are often intensely faulted and fractured. Mapping these reservoirs requires high quality 3D seismic data of broad bandwidth with frequencies above 40 Hz to provide sufficient vertical resolution and lateral discrimination of reservoir features. This paper addresses the challenges of the Western Desert through the introduction of point-receiver based seismic technology. Conventional receiver arrays, which attenuate surface waves and high frequency signal, are replaced by point-receivers. Coherent noise attenuation can be carried out on point-receiver traces, whilst additional signal enhancement is taken care of in subsequent steps. The result is often a substantial increase in high frequency content of the desired signal. Reducing multiple contamination is one of the greatest challenges in land seismic processing. Demultiple algorithms and innovative workflows are presented, specifically designed to handle 3D land geometries and attack multiples in a 3D sense. In practice, these methods, relating to both surface and interbed multiples may be combined and cascaded to obtain the optimum solution. We will illustrate the benefits of point-receiver technology through examples from Egypt and the Middle East.
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How to Acquire Even Fold Distribution in A Converted-Wave Seismic Geometry
More LessThis paper proposed a new strategy for designing even converted-wave geometries with binning, calculating fold and selecting roll distance. Through analysis by the surface stacking charts, the projection positions of conversion points on horizontal direction regularly shift with two kinds of period. One is Common-Shot-Conversion-Point Interval (CSCP Interval) and the other is Common-Receiver-Conversion-Point Interval (CRCP Interval). If the two periods have common divisors and the bin size is several multiples of the maximal common divisor, the fold distribution will be even. Otherwise, a parallelogram consists of the conversion points on the surface stacking chart. One side is the total length of conversion points of the common receiver gather and the other is that of the common source gather. Based on the magnitude relationship of the two sides, converted-geometries can be divided into two kinds of pattern. Each kind of pattern has its special formula for calculating fold and roll distance. If the fold is not even, several certain parameters with the fixed velocity ratio must be changed according to the proposed method. Furthermore, the new strategy for converted-wave geometries can be also used for primary wave geometries.
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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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Onshore Seismic Acquisition: Updating an Efficient QC on Increasing Seismic Data Volume
More LessThis article describes the evolution of TOTAL best practises in terms of seismic data QC during the last 15 years. This evolution takes into account the big increase of data volume acquired onshore, and most specifically in vibroseis acquisition. Task automation, standardization of QC, homogeneous database between different surveys & countries are the key words of this evolution.
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Quantitative Evaluating Offset and Azimuth Uniformity Based on Entropy
More LessThe paper introduced entropy as the information function for quantitatively evaluating the offset and azimuth uniformity of each bin and the whole geometry. It is uniform offset and azimuth rather than high-density sampling to be caught more attention while imaging the object events, especially in the complicated structure areas. The bigger the information functions is, the more uniform the offset and azimuth. Otherwise, under the same maximum values of the information function, which is determined absolutely by the numbers of the offset sections and the azimuth bins from the method of the paper, the geometry with the smallest sampling density and field costs is the optimum. Consequently, the information function can not only quantitatively evaluate the offset and azimuth uniformity but also the ratio about the acquired data quality with the field costs. It will be a promising quantitative tool for the seismic acquisition geometry as long as the correlation between the seismic imaging quality with the offset and azimuth uniformity in the near future.
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What if I...? - The Use of Vibroseis 'Energy Tests' as an Aid in Parameter Choice
Authors P. Kristiansen, J. Quigley, T. Dean and D. HolmesA core component in planning a land seismic survey is the choice of source and its parameters. Parameters tests are often performed as part of the survey start-up, but Interpretation of the results from these tests is frequently subjective, particularly when a complete line or swath is not acquired and processed. The typical instinct is to err on the side of caution and this may result in the application of an excessive amount of source energy, thus negatively impacting survey efficiency and cost. However, the effect from different sources and source parameters on signal-to-noise ratio and other key quality indicators can be tested and analyzed in a systematic way. This will allow comparison of a much wider variety of source options than is possible through the acquisition of a very limited number of costly and time-consuming test lines. We can also identify possible efficiency improvements resulting from acquiring data with equivalent signal-to-noise ratios, but different parameter combinations. A suite of such tests has been developed within WesternGeco and are referred to as energy tests. Within this paper, we will describe the results from such tests and its interpretation.
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Digital Crew Management – An Integrated Approach to QC for Large Scale, High Production Onshore Seismic Operations
Authors D. Pavel, A. Bull, G. Hofland and G. HauerThe concept of Digital Crew Management focuses on three primary areas; advanced planning, integrated crew operations and intelligent, automated field QC. Tighter integration of survey planning systems with field operations and automated trace QC from intelligent cable-less acquisition nodes are presented as methods to mitigate some of the challenges resulting from the trend toward greater receiver density and high productivity Vibroseis operations.
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Quality Control in Modern Recording Systems, Benefits Beyond Comtract Compliance
By M. LansleyQuality control (QC) has generally been considered by the seismic data acquisition industry to simply be a method to determine if the recording system is performing within the tolerances of the instrument manufacturer’s specifications and that the geophysical specifications of the survey design are being matched. With today’s modern recording systems there is a large amount of information that is being recorded that can provide significant benefits beyond the normal QC perspective. Much of this information is frequently ignored or misunderstood and may never be reviewed after being recorded. There are system capabilities available today that can even improve the ability of the geoscientists from the oil companies and contractors to interact with the field crew in recording parameter determination. This paper will discuss this information and how it may be utilised to assist the field crew in improving their operational performance and the data processing geophysicists their understanding and analysis of the data.
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