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EAGE Workshop on Marine Seismic - Focus on Middle East and North Africa
- Conference date: 22 Feb 2009 - 25 Feb 2009
- Location: Limassol, Cyprus
- ISBN: 978-94-6282-068-5
- Published: 22 February 2009
32 results
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Marine Wide-azimuth Seismic for Signal to Noise Enhancement and Multiple Suppression
Authors R.G. Williams, R. Wombell and L. TwiggerWide azimuth marine surveys have been successful in the deep water Gulf of Mexico at imaging beneath mobile salt. They have also shown that wide azimuth surveys can have benefits for multiple and noise suppression. Therefore, we should ask if these effects will be of benefit in other parts of the world with multiple and noise problems – do they still apply in shallower water, or in provinces with faster sedimentary velocities. The simplest answer is yes, but sampling criteria are likely to mean we will need to use different recording geometries for different geological settings – just as we do for conventional surveys.
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Multi-azimuth Streamer Seismic in the Nile Delta
Authors W.E.A. Rietveld, J. Keggin, M. Benson, B. Barley and T. ManningSince 2003 BP has been acquiring Multi-Azimuth (MAZ) Streamer Seismic in the Nile Delta. Other these last 5 years the total unfold MAZ data covers 25,000 sqkm, over a total surface area of about 6000 sqkm. The initial results showed that MAZ data greatly improves general image quality, signal-to-noise ratio and lateral resolution, as well as suppresses diffracted multiples effectively. Since those early results MAZ data has been taken to more difficult areas. This paper will give a short historical overview on MAZ in the Nile Delta and will focus on some of the new technologies that have been applied to get more value out of the MAZ data.
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Full Azimuth Modelling at Heidrun
Authors M. Houbiers, B. Arntsen, M. Thompson, E. Hager, G. Brown and D. HillA simulation study was initiated to investigate whether or not a marine full azimuth acquisition geometry improves the image of the subsurface at Heidrun. Full azimuth shot data was modelled with finite difference and one-way wave equation modelling, and images obtained from full, wide, and narrow azimuth survey geometries were compared with each other. The study shows that a full azimuth geometry leads to better suppression of noise, less migration artefacts, more consistent amplitudes along horizons, and sharper fault planes than a narrow azimuth design. Attenuation of multiple energy is present, but less than expected. The improvements in image quality can be obtained with a realistic 4-vessel wide azimuth design and a coil geometry, but the coil geometry has a smaller acquisition footprint in the shallower part. Based on the modelling results, a field trial with coil design was carried out at Heidrun.
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Full-azimuth Marine Acquisition Using the Coil Shooting Technique
More LessWide-azimuth (WAZ) marine acquisition using towed-streamer technology has seen dramatic growth in recent years: mainly in the Gulf of Mexico. To date, the WAZ technique typically requires the use of multiple vessels. We report here on Coil Shooting*; a method of collecting full-azimuth (FAZ) data using one vessel. In this paper, we discuss survey designs for coil acquisition focusing on survey efficiency. We also show results of extended field trials and review data processing challenges such as noise removal and multiple attenuation.
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A Multi-level Source Design Improves Seismic Imaging Below Highly Reflective Layers
Authors G. Cambois, B. Osnes, A. Long, G. Parkes, A. Mattsson and T. LundstenThe multi-level source is a new airgun array design that attenuates the effects of ghosting in the low frequency range. This design does not remove the source ghost but shifts energy around to favor low frequencies. It is therefore useful in area with poor seismic penetration due to highly reflective layers such as salt, basalt or carbonates.
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Geophysical Benefits and Operational Characteristics of Steerable Marine Seismic Streamers
More LessMulti-streamer marine acquisition is possibly the most successful application of 3D seismic. However, the method has problems and short-comings. Cables are influenced by tides and currents, and precise control of streamers is not possible. In order to prevent tangling the streamer separations are high, so that the high-fold acquisition is difficult to achieve. Streamers are affected by the dynamics of the towing vessel, leading to phenomena such as 'fantailing'. Time-lapse surveying is now commonplace, to monitor production-induced changes in the reservoir. 4D effects are subtle, so it is essential to remove sources of error that could mask the actual differences. Repeatability is a measure of how well the original survey has been emulated by the monitor surveys, by replicating source and receiver positions. This is difficult with existing technologies. The solution is to control the lateral behaviour of the streamers. Vertical control of seismic cable positions is achieved using 'birds'. This concept can be used to control horizontal motion, i.e. employing a a vertically mounted fin. This enhances streamer control so that cable separations can be reduced, enabling higher density acquisition. Results will be shown based on modelled data and case studies.
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Dual-sensor Streamer Increases Data Bandwidth Leading to Improved Penetration and Higher Resolution
Authors G. Cambois, B. Osnes, A. Day and A. LongThe use of a dual-sensor streamer allows the exact removal of the receiver ghost. The bandwidth of the seismic data is consequently increased, providing better penetration and greater resolution. In addition, seismic velocities and earth attenuation are estimated more accurately. These results are illustrated with case studies from basins worldwide.
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Regularisation for Wide Azimuth Datasets
Authors G. Poole, D. Trad, R. Wombell and G. WilliamsWide-azimuth datasets allow us to incorporate more dimensions into data regularisation. Using a multi-dimensional Fourier transform that handles irregular data we can either output traces on a regular grid or interpolate additional source and receiver lines. This allows us to fill holes more effectively and regularise in the offset and azimuth directions whilst preserving AVO and AVAz. Data examples show an improvement in continuity and accurate reconstruction of missing data.
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Simultaneous Source Separation – A New De-blended Approach via Multi-directional Vector-median Filter
Authors S. Huo, Y. Luo and P.G. KelamisA new approach aiming in the de-blending of seismic data acquired by simultaneous sources is presented based on Multi-Directional, Vector-Median Filtering.
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Simultaneous Source Separation Using Wave Field Modeling and PEF Adaptive Subtraction
Authors S. Spitz, G. Hampson and A. PicaThe acquisition of n-shots, more or less simultaneously, increases acquisition efficiency and collects a wider range of information for imaging and reservoir characterisation. Its success relies critically on the ability to separate n-shots from one recording. Using a difficult data example we show that a PEF-based adaptive subtraction of the estimated wavefield due to a secondary source provides an effective separation of the sources.
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True-azimuth 3-D Multiple Prediction – A Step Change in Multiple Elimination – Method and Examples
Authors R.G. van Borselen BV, S. Barnes, R.F. Hegge and P. AaronThe paper shows the application of a new true-azimuth 3-D multiple prediction method capable of removing the most complex 3-D multiples from a Mediterranean data set, known for the challenging diffracted multiples that hamper interpretation.
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Complex Multiple Attenuation Using 3D General Surface Multiple Prediction (GSMP) – A Case Study from Offshore Egypt
Authors A. Cooke, M. Abdelaty, E. Shady, T. El Melegy, B. Broussard, H. El-Meligy, M. Sheath, J. Høyen, D. Renshaw, Ø. Skinnemoen and M. HårdeIn this case study, we show how a new implementation of 3D surface-related multiple elimination (3D SRME) can be used to successfully predict and attenuate complex multiples, including diffracted multiples, on a dataset from Egypt’s Mediterranean Sea.
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Reverberation Attenuation Strategy for an Arabian Gulf 3-D OBC Survey
Authors A.P. Shatilo and J.M. ReillyWater-column related reverberations are well pronounced in a 3D OBC data from Arabian Gulf. Effective removal of the reverberations is critical for obtaining a reliable seismic image. The reverberation mitigation is complicated by substantial noise in the data. The data processing strategy includes a deterministic source-side de-reverberation filter and post-stack 2C OBC combination. Effectiveness of the reverberation attenuation strategy is demostrated.
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3D Seismic Data in Shallow Waters of Arabian Gulf – Acquisition and Processing Challenges
Authors R. Pedersen-Tatalovic, M. Wendorff, B. Myhre, P. Christian, P. Walshe and M. EmangA large shallow-water seismic survey offshore Qatar was acquired for targets at 2000-4000ft. The main processing challenges in this environment are complete multiple removal and detailed velocity analysis in the presence of velocity inversions.
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3D OBC Seismic Survey Parameters Optimization for a Carbonate Field Offshore Abu Dhabi, UAE
Authors T. Ishiyama, D. Painter, K. Belaid, H. Ikawa, A.S. Al-Suwaidi, J. Karwatowski, D. Barwick and M. KanekoA 3D OBC pilot seismic survey was conducted in a carbonate field of offshore Abu Dhabi, United Arab Emirates with the main objectives: (1) to demonstrate imaging of the Upper Jurassic Arab formation; and (2) to optimize survey parameters for future seismic surveys. In this highly-specified pilot seismic survey, two orthogonal 3D datasets were acquired, and one swath 3D dataset was simulated by sampling shot-points parallel to receiver-lines. Twenty-three cubes were generated from these datasets by decimating the full data. The relationship between data quality and operational effort was determined by analyzing twenty-three cubes qualitatively and quantitatively from the structure interpretability point of view. The pilot seismic survey confirmed expected results that higher operational effort lead to higher data quality in general. However, the results also indicated that extremely high operational effort is poorly rewarded with little improvement of data quality. The methodology and results will be used to assist in establishing and optimizing survey parameters for future seismic surveys offshore Abu Dhabi, United Arab Emirates.
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4C OBC for Imaging the Pre-Messinian Offshore Nile Delta, Egypt
Authors C.H. Henke and D.R. LangtonRWE Dea began exploring in 2006 using two seismic crews to span a very difficult transition area. A conventional land operation using a dynamite source was used in the agricultural areas of the Nile Delta while a 2C-OBC crew was utilized shoot all areas offshore and up to the beach. To ensure a seamless image these crews used a master/slave configuration to maintain consistent offsets and azimuths throughout the transition area. More recently a 4C-OBC was acquired directly west of the original survey and this was designed to merge directly with the previously acquired data. Unlike the first survey the 4C operation needed to be capable of operations in water depths up to 250m while maintaining sufficient positioning accuracy as to not degrade the image quality. The acquisition environment was also significantly more difficult than the initial OBC as the survey area spanned the shipping lanes for Alexandria Port and numerous platforms and fishing vessels operated in the area The decision to proceed with a wide-azimuth OBC in favour of streamer operations was driven by the desire to optimize the image quality and provide a comparison product to existing streamer and MAZ-streamer surveys.
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3D Seismic Data Acquisition in TZ/Shallow Water Area of Hendijan-Bahregansar Oil Fields – North West of Persian Gulf
More LessThe OBC method was one of the main phases of 3D seismic data acquisition project in Hendijan-Bahregansar oil fields in Northwest of Persian Gulf. Using OBC method in TZ/Shallow water area, lead to acquire high quality and high resolution reflection data with broadband. This is evident in the generated brute stacks and preliminary 3D cube slices.
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Permanent Fibre-optic Seismic System for Increased Hydrocarbon Recovery
Authors J. Langhammer and H. NakstadPermanent seismic installations at the sea-floor have emerged as a potential tool for oil companies in their work to actively monitor oil/gas flows and injection processes in order to increase hydrocarbon recovery and optimize production. The passive nature of fibre-optic sensors, embedded into 4C receiver station, is an advantage since the in-sea sensor equipment is not prone to electrical noise, leakage and short circuit, in addition to that the life-time of the buried sensors may be longer compared to electrical systems. Fibre-optic based permanent seismic monitoring systems represent a great opportunity for the field engineers, in a cost effective way, to optimize production and increase the hydrocarbon recovery rate from existing fields.
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Permanent Reservoir Monitoring Using 4C Fiber-optic Sensors in Seabed Cable
More LessAdvances in fiber optic technology provide a system for 4D reservoir monitoring. Successful pilot demonstrations in the Gulf of Mexico and North Sea shows the optical system meets the requirements for permanent reservoir monitoring. Advances in the optical technology, have turned this system into a practical tool for 4C permanent reservoir monitoring. We have demonstrated the optical systems capabilities in deepwater with high channel count over many kilometers while maintaining high dynamic range, low crosstalk and low distortion. The optical system is an excellent fit for and a preferred solution for permanent reservoir monitoring systems.
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New Seabed Cable Technology for EM and Seismic Applications
Authors R. Smedal, K. Kristiansen and G. PotterA new exploration technology has been developed which combines the strengths of both seabed seismic and EM sensing into a single seafloor cable to locate and identify the content of hydrocarbon reservoirs. While conventional seismic methods offer the best means to map the sub-surface structural geometry, EM waves have the ability to identify reservoir fluids better than seismic P-waves. Therefore EM data acquired in combination with seafloor seismic (P- and S-waves) are considered the best way of determining hydrocarbon probability. The technology was first tested out in the Sognefjord and extensive field trials were performed in 2008 over the North Sea Peon discovery.
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Challenges of Marine Seismic Project in Block 15, Sudan Red Sea
More LessDuring 2007 marine seismic survey, RSPOC’s contracted 2D seismic vessel equipped with 6-km length streamer cable faced several technical and operational challenges. It is quite a challenging task to process Pre-Stack Time Migration (PSTM) seismic data due to complicated seismic wave ray paths and velocity trends from two different exploration objectives. Additionally, seismic interpretation using 2D seismic dataset requires exceptional interpretation skill with sound-geological model to ensure the result represent an acceptable geological model of Red Sea rift tectonics. The latest Pre-Stack Depth Migration (PSDM) processing sequence has provided better definition of complicated Pre-Miocene Salt Formation fault pattern. With better PSDM seismic velocity dataset, bore hole formation pore pressure trend at the proposed prospect drilling locations could be estimated and predicted in effort to assist the planning of offshore high-pressure and high-temperature (HPHT) wildcat drilling campaign.
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Marine Seismic Data Acquired over the Libyan Offshore Area – A Case History
Authors J.A. Martin, S. Bowman and S. WaddinghamDuring 2004 and 2005, over 38,000km of 2D non-exclusive data were acquired in the waters offshore Libya in cooperation with NOC and NAGECO. This consistent dataset provides regional correlation from the existing developed western fields into the largely un-explored offshore Gulf of Sirt and Cyrenaica regions. It provides a unique resource for reviewing the potential of some of the world’s most prospective acreage and complements NOC in their efforts to boost Exploration in Libyan waters.
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2D Marine Seismic Acquisition for Sub-salt Objectives in the Red Sea
By J.A. MusserSAUDI ARAMCO recently acquired a very large regional 2D reconnaissance marine seismic program in the Red Sea. The objectives of the project were to identify and map potential leads both above and below salt bodies in the Red Sea basin. Streamer length and depth were tested for their impact on low frequency data recovery and imaging of deep objectives. Prestack depth migration results show improvement in deep imaging as the maximum offset is increased from 7200 meters to 10,330 meters. The greatest improvement in depth image quality occurs when offsets of up to 9200 meters are included. New solid streamer technology proved valuable for acquiring the long offsets required by this project while maintaining continuous operations.
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Velocity Model Building and Depth Imaging Challenges – Red Sea 2D Marine Case Study
More LessSaudi Aramco acquired an extensive 2D marine seismic program in the Saudi Arabian portion of the Red Sea during 2007 and 2008. Acquisition utilized a 10 km long solid streamer cable with 816 active hydrophone channels spaced 12.5 meters apart and towed at a 10 meter depth. Shots were taken every 25 meters using an airgun array comprising 25 guns and a total array volume of 4060 cubic inches at a tow depth of 7 meters. This survey was part of an initial exploration phase, and is being used to find leads for 3D acquisition. The geology in the region can change rapidly from younger sediments to complex non-homogeneous salt bodies, anhydrites, limestones, and igneous rocks. We present the challenges encountered in processing a large (20,000+ km) 2D dataset through prestack depth migration (PreSDM), and techniques used to generate the depth images within the project timeline.
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Acquisition and Integrated Interpretation of Controlled Source Electromagnetic (CSEM) Survey Data with Other Geophysical Data Types
By A. GreerControlled source electromagnetic sounding (CSEM) is now becoming a mainstream exploration tool in a wide range of geological environments; and to date the technique has been primarily used on a standalone basis. It is recognised that by accurately integrating CSEM data with other geophysical data types, such as rock physics and seismic, that significant improvements in subsurface understanding can be gained throughout the E&P process.
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Marine Transient EM Surveys
Authors A.M. Ziolkowski and D. WrightWe describe transient electromagnetic (EM) surveys in water depths of about 100 m, where conventional Controlled Source EM (CSEM) has great problems with the air wave. Our proprietary method recovers the complete Earth impulse response, optimising signal strength with offset-dependent coded signals. Air wave removal is straightforward and our new method for removing magnetotelluric (MT) noise increases the low-frequency signal-to-noise ratio by about 20 dB. We demonstrate the techniques on real data from the North Sea.
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Porosity Prediction in Carbonates – Learnings from the North Sea Chalk Applied to Platform Carbonates
Authors A. Uldall and R. Pedersen-TatalovicPorosity can be predicted from seismic data when seismic impedance is correlated with porosity. One of the problems is that the correlation between impedance and porosity can be to a large degree determined by the low-frequency component of impedance, which is not present in seismic data. We explain how to overcome this problem and show the method which we developed while working on North Sea chalk. In addition to broad-band impedance data, the impedance - porosity transforms should be derived separately for different facies, in order to apply the same workflow to platform carbonates.
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AVO Application in a Carbonate Offshore Oil Field, U.A.E.
Authors H. Ikawa, G. Mercado and A. SmithWe will present fluid substitution well log modeling results based on Gassmann's equation and application of conventional AVO and other techniques such as Elastic Impedance and Simultaneous Inversion followed by lambda-rho mu-rho (LMR) techniques in a pilot area of interest. The results of the pilot study were validated with the known well fluid status in the pilot area. Mapping of the different water-oil-gas fluid response using the LMR technique shows a reasonably good agreement with currently known well saturations. It is, however, difficult to discriminate reservoir sub-layer water-cut percentages due to data resolution limitations. Generally, the results of the analysis indicate potential to identify hydrocarbon to water fluid contents, with the above constraints.
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3D-2C OBC Multi-azimuth Seismic Data Processing and Its Applications for a Carbonate Field Offshore Abu Dhabi, UAE
Authors T. Ishiyama, D. Painter, K. Belaid, H. Ikawa, T. Matarid, A. Al-Hendi, A. Mouaki Benani Chebihat and T. SalehA 3D-2C OBC multi-azimuth seismic data processing was conducted in a test area in a carbonate field offshore Abu Dhabi, United Arab Emirates with the main objectives: to demonstrate improvement of imaging; and to detect any HTI response. Three processing flows were designed to generate (i) conventional, (ii) full-azimuth and (iii) multi-azimuth cubes. The output cubes were evaluated qualitatively and quantitatively: (1) overall imaging analysis; (2) fault imaging analysis; and (3) HTI analysis. The results demonstrated improvement of imaging compared to traditional processing and detection of a certain HTI response. These encouraging results will be the incentive to apply multi-azimuth seismic data processing in carbonate fields offshore Abu Dhabi, United Arab Emirates.
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Detailed Velocity Model of the Nile Delta Using Multi-azimuth (MAZ), Multi-Parameter Reflection Tomography
Authors D. Baptiste and T.A. ManningIn the Nile Delta, a complex and dipping water bottom, shallow gas filled channel systems and the evaporitic Messinian interval have prevented the creation of an accurate velocity model in depth using conventional 3D data. By designing a workflow that combines the Multi-Azimuth data in a multi-parameter reflection tomography approach, we have built a detailed velocity model that shows variations that correspond very well to the geology interpreted from the seismic, and which yields improved images at depth.
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Interval Velocity Analysis in Complex Areas – What About the Azimuth?
More LessThree dimensional interval velocity analysis must deal with the problem of lateral velocity variations along different azimuths. Traditionally, when this azimuth dependency is treated, the analysis refers to the acquisition azimuth. The main idea presented in this study is that in complex geological regions, the acquisition azimuth may not be the optimal domain for analyzing velocity errors. We suggest here to define the azimuth in the image domain. Together with the scattering angle and dip, all parameterized in the depth image domain, accurate CIG analysis method can be designed.
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