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- Volume 23, Issue 10, 2005
First Break - Volume 23, Issue 10, 2005
Volume 23, Issue 10, 2005
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How PGS is taking care of business
By A. McBarnetPGS boss Svein Rennemo talks to Andrew McBarnet about how his company returned to financial health and retained its key position in the geophysical services marketplace. Svein Rennemo never doubted that Petroleum Geo-Services (PGS) would survive the financial troubles which nearly swept it away on a tide of debt less than three years ago. He was brought in as president and CEO as part of the rescue effort mounted in the fall of 2002 by Jens Ullveit-Moe, one of Norway’s star entrepreneurs and investors. ‘My feeling,’ Rennemo recalls, ‘was that the finances were in a mess, but operationally and competence-wise, PGS was a great company. Fortunately this has proved to be the case. With the financial problems behind us, PGS is once again a very profitable operation in the industry with a bright future ahead.’ In fact Rennemo, now 58, says that he doesn’t intend to quit until PGS is substantially bigger and more profitable. But you can be sure that any major initiative in the future will bear the Rennemo hallmark of prudence which brought PGS back from the brink.
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The Lower Paleozoic succession in the Tassili outcrops, Algeria: sedimentology and sequence stratigraphy
Authors R. Eschard, H. Abdallah, F. Braik and G. DesaubliauxThe EAGE Conference held in Algiers in April 2005 was the opportunity for 23 attendees to participate in a post-conference field-trip organized in the Tassili N’Ajjer outcrops in southern Algeria. The stratigraphic succession from the infra-Cambrian to the Middle Devonian is exposed in these exceptional outcrops, desert conditions favouring continuous exposure. The field trip started in the city of Djanet in the Infracambrian granites and shales and ended five days later in Illizi in the Lower Devonian Emsian sandstones (Figure 1). During the trip, these outcrops were described in terms of sedimentology, fracturation, and sequence stratigraphy. The outcrops of this area are of particular interest for petroleum geologists as the same sedimentary succession produces hydrocarbons in the nearby Illizi and Berkine basins and in the Hassi- Messaoud area. The Cambrian, Ordovician, and Devonian sandstones observed in the Tassili outcrops have an equivalent in the reservoir units in the subsurface. The Silurian hot shales are also the prolific source rock of the petroleum system in these basins. The succession presented in the outcrops can then be directly compared with the subsurface data of the Illizi and Berkine basins. The area was first surveyed by Killian (1922) who described the sedimentary succession of the region. Then, the lithostratigraphy and the Siluro-Devonian succession in the outcrops were established by Dubois et al. (1967). The reference study of the Lower Paleozoic outcrops in Algeria was published by Beuf et al. (1971). These authors proposed a lithostratigraphic nomenclature for the Lower Paleozoic and a sedimentological description of the formations. They also identified and interpreted the main unconformities in the Lower Paleozoic with a modern approach, discussing the relative role of tectonics and climate during sedimentation. A detailed mapping of the area was also performed by Sonatrach and Beicip under the supervision of the Ministère de l’Industrie of Algeria. However, since these pioneer studies, little has been published about the outcrop geology although hydrocarbon exploration and development has been very active in the nearby Illizi and Berkine basins. The objective of this paper is to propose a reference section for the Lower Paleozoic in the western Tassili with an updated sedimentological interpretation. An interpretation in terms of sequence stratigraphy will also be proposed. We then summarize the lithostratigraphy in use in the outcrops and propose a correspondence with the sub-surface.
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What it’s really like on a field trip
More LessAnton van Gerwen, EAGE executive director, joined a field trip to the Tassili N’Ajjer, southeast Algeria, after the successful 2nd North Africa & Mediterranean Petroleum and Geoscience Conference in Algiers last April. This is his report along with photos from the field trip. In five days the group of 27 participants travelled from Djanet to Illizi, a virtual trip from the infra Cambrian unconformity to the lower Devonian via the Cambrian, Ordovician, and Silurian. The Tassili N’Ajjer offers geological sections, which represent structures similar to those found in a large part of North Africa. The Tassili Plateau offers a variety of geological formations and scenic interest, but is also a place of great historic value. For example, the national park contains one of the most important groupings of prehistoric cave art. Over 15,000 drawings and engravings show the migration of animal life and human life over a period of more than 6000 years before our calendar. The Tassili is also important for its wildlife with 28 national plant rarities, one internationally threatened plant species. and five endangered mammal species. Besides that, the area is a key resting station for migrating Palaearctic birds. Given this rarefied background, it is no wonder that the Tassili N’Ajjer National Park is included in the UNESCO World Heritage Sites list.
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The changing face of reservoir modelling
More LessDavid Hardy, product manager, and Andres Hatløy, VP Technology, Roxar Software Solutions, provides an overview of developments in reservoir modelling with a peek at what future challenges lie ahead for geoscientists and reservoir specialists. A brief look back will show how radically things have changed for reservoir professionals over the last decade and a half. Many geologists will still remember hand contouring maps and calculating the reservoir volumes with a planimeter and some graph paper. Computer based mapping changed this dramatically, enabling geoscientists to build better reservoir models, with more data and faster. Today many asset teams now rely on 3D geological models for their field development planning and reservoir modelling. Today’s tools enable interdisciplinary workflows to be executed by multidisciplinary teams. Whilst not quite commonplace worldwide, it is fair to say that 3D geological modelling has gone mainstream and is a now a central part of many peoples daily work. The impetus for change was really driven by a realization that traditional 2D map-based approaches to geological reservoir modelling were grossly oversimplifying the reservoir. Whilst geophysicists and reservoir engineers were now working in a 3D world, geologists were still producing crude 2D models. The models were often so poor that reservoir engineers commonly applied arbitrary, non-physical corrections to try and get a history match. This added up to not just a poor understanding of the reservoir but a complete failure to accurately estimate field reserves and predict future production. Poor reservoir models meant poor decisions and poor development plans which had the potential to cost millions. Early applications of these techniques were in the North Sea where complex, heterogeneous geology combined with a high cost environment led to the development of much of the technology which is now common place.
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Advances in seismic interpretation using new volume visualization techniques
Authors L. Castanie, F. Bosquet and B. LevyLaurent Castanie, Fabien Bosquet, and Bruno Levy discuss new techniques in volume rendering to improve the visualization of 3D seismic structures. As the use of 3D seismic interpretation continues to become part of the main stream work process with the industry, visualization techniques also continue to evolve as software and hardware improves. In the past 10 years, volume rendering tools have been progressively adopted by the geophysical community as the emergence of high-end graphics workstations with 3D texture capabilities made real-time volume rendering possible. Many interactive volume rendering packages are now available for seismic interpretation. However, interpretation is still mostly done in 2D. Using classical volume rendering with high spatial frequencies of seismic data make it very difficult to produce meaningful volume images and often results in cluttered useless images. Volume rendering tools are now part of most seismic interpretation packages. However, most do not provide better insight into the 3D structures of seismic data because the noise and high spatial frequencies in the data prevent classical volume rendering from capturing relevant information. As an improvement, we propose more suitable high quality volume rendering algorithms based on a pre-integration of the transfer function (i.e. colour map) that use the capabilities of the recent programmable graphics processing units (GPUs) of new graphics cards. This results in a versatile multimodal (multi attributes) volume rendering system. This system is dedicated to the efficient combined visualization of several volumes. Coupled with high quality volume rendering algorithms, it makes it possible to visualize isosurfaces interactively and paint them with another attribute. This is done without explicit extraction of the surface. By this way, isosurfaces of distance maps to faults or well paths can be interactively extracted and painted with the seismic data. In this article, we adapt high quality volume rendering algorithms from the computer graphics industry to improve the imaging. We have found these algorithms more suitable for seismic data analysis than classical ones. They use the capabilities of the recent programmable graphics hardware. In addition, we will present a versatile multimodal volume rendering system that enables the efficient co-visualization of several volumes. .
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More vertical resolution and accuracy with less uncertainty in reservoir characterization
Authors A. Contreras, C. Torres-Verdín and T. FasnachtArturo Contreras and Carlos Torres-Verdín, University of Texas at Austin, and Tim Fasnacht, Anadarko Petroleum Corporation, present a new reservoir characterization method using a model-based inversion technique which claims superior results to traditional approaches. A new technique for reservoir characterization has proven effective in significantly improving accuracy and vertical resolution in the modelling and simulation of reservoirs. It combines pre-stack seismic amplitude data and well logs to construct high-resolution models with reduced uncertainty. As a result, development and production risks are substantially reduced. The approach is based on Markov-Chain Monte Carlo (MCMC) statistical updates both vertically in seismic time and in lateral location. It combines the Gauss random field conceptual model underlying traditional geostatistics with iterative local updates inherent to non-linear optimization. In addition, the inversion implements transformed Gaussian covariance matrices and efficient projection operations via Fast Fourier Transforms. Pre-stack seismic amplitude data are used to yield more degrees of freedom for the interpretation of petrophysical properties of rock formations. Unlike post-stack seismic amplitude data, pre-stack are sensitive to p-wave impedance, s-wave impedance, and density, enhancing the differentiation between lithology types, porosity, volume of shale, and fluid type. In addition, by relying on a statistical range for controlling the stochastic simulation, residuals are consistent with the assumed noise-to-signal ratios in the seismic amplitude data. The technique has the ability to construct accurate, highresolution models of reservoirs. By making use of these models, companies can assemble more efficient drilling programmes and production plans.
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Next-generation modelling workflows improve reservoir management decisions
Authors S. Gorell, T. Smart, K. Narayanan, P. Sabharwal and S. BassettSheldon Gorell, Tom Smart, Keshav Narayanan, Pom Sabharwal, and Sarah Bassett of Landmark Graphics discuss the development of better, more economic reservoir management through the use of enhanced workflows that can be carried out multiple times in practical timeframes. In today’s global business environment, exploration and production (E&P) asset teams are making increasingly challenging and costly development and production decisions earlier in the life of a reservoir. These decisions are being driven by a number of factors including more complex reservoirs, more complex and expensive wells, costly facilities, smaller targets requiring better strategies for optimal multi-reservoir development, high oil and gas prices, and the need to minimize risk. The ability to accurately model field development scenarios before making significant capital investments can optimize oil extraction and yield tremendous business savings. Historically, reservoir simulation and associated workflows have been time- and compute-intensive, often forcing asset teams to choose between a more thorough analysis and acceptable turnaround times. Typically, a majority of complex reservoir situations have been solved by methods of approximation, in which some degree of fidelity was sacrificed within one or more of the domains being modelled. Examples of such trade-offs range from simplified tank models for reservoirs with sophisticated surface network models to loosely coupling sophisticated high-resolution reservoir models with approximate or iterative methods for coupling them together with surface network modelling. Traditional reservoir engineering/management workflows have consisted of linear processes in which each discipline hands off its version of the model to the next specialist. Fine-scale earth models that capture all the complexities and heterogeneities of the subsurface can be constructed using seismic, well, and geologic data. Often, these earth models are up-scaled to a resolution that can be used effectively in conventional flow simulation where they become the basis for reservoir simulation. At this point, a number of ‘what if’ scenarios are run for different uncertainties and development options. Then there is yet another hand-off to the facilities engineering and economics domains. The key problem with this methodology is that each domain often produces its results in a ‘siloed’ manner, tossing them over the wall to the next person in the chain. This familiar process has been especially cumbersome due to the difficulties in transferring digital data and models. The tools and technology available within each of the disciplines enables a high degree of rigor but there has been limited support for integration between disciplines. The focus is often on building the best model possible in each of the silos instead of optimizing the asset to deliver on a core business objective. As a multi-step process (very much analogous to the old game of ‘telephone’ where a message gets passed from one person to the next), the original objective often gets lost, producing a suboptimal result. The linear process has also prevented asset teams from evaluating multiple development scenarios prior to capital investments, creating greater risk. Additional downsides from this process include the lack of a repeatable process, no audit trail, and unnecessary constraints. Inaccuracies often creep in because each step fails to fully capture the interdependencies in the reservoir development value chain.
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Populating a PSDM created earth model with PSTM predicted seismic properties
Authors A. Huck, M. De Rooij, P. de Groot, Chr. Henke and S. RauerArnaud Huck, Matthijs De Rooij, Paul De Groot, Christian Henke, and Stephan Rauer address a key issue in quantitative seismic prediction. When an earth model is constructed from depth migrated seismic data and porosity is predicted from time migrated data, we are confronted with spatially inconsistent information. To use the predicted porosities in the earth model the data needs to be converted to depth and re-positioned. In this case study, we present a pragmatic approach in which porosity trace positions were shifted after depth conversion to their correct x/y positions followed by a vertical depth-to-depth transformation to correct the remaining misfit. The x/y shifts were calculated by image ray map migration in the earth model. Porosity was predicted from 3D time migrated data by acoustic impedance inversion followed by pseudo-well modelling and neural network inversion. With the increasing popularity of pre- and post-stack depth migration more and more earth models are constructed from horizons mapped on depth migrated data. Populating such models with seismically derived (reservoir) properties is not a trivial task, because properties are usually predicted from seismic data in two-way time. Seismic inversion and forward modelling techniques require a seismic wavelet. In depth, the concept of a seismic wavelet does not exist, as the wavelet is distorted by the time-depth transformation. This problem is often solved by changing the depth migrated volume back to time by a vertical depth-to-time transformation and using the resulting time volume for further quantitative analysis. Transforming the predicted properties back to depth is the way to populate the earth model. However, this procedure assumes that amplitudes have been preserved by the depth migration and subsequent depth-to-time transformation processes. This is questionable, which is why many quantitative interpretation specialists prefer to predict seismic properties from conventional time migrated data. Using the predicted seismic properties in a depth migrated earth model poses another problem: the properties are not predicted at the correct spatial positions, hence need to be corrected before they can be used to populate the earth model.
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Slope failure, mass flow and bottom current processes in the Rockall Trough, offshore Ireland, revealed by deep-tow sidescan sonar
Authors B.M. O‘Reilly, P. W. Readman and P. M. ShannonThe margins of the Rockall Trough, currently the focus of oil and gas exploration interest, incorporate an environmentallyimportant and lightly studied shelf region. To address the paucity of information within this region an extensive high resolution sidescan sonar survey was carried out in the Irish sector of the Rockall Trough in June/July 1998. This valuable natural laboratory contains information on slope stability, sediment transport, nutrient upwelling, bottom current, and biological activity at a shelf/slope/basin-floor transition. Detailed information on the nature of many of these processes can be provided from shallow geophysical techniques. The TRIM (TOBI Rockall Irish Margins) project (Shannon et al., 2001), funded by the Irish Petroleum Infrastructure Programme (Rockall Studies Group), acquired 3100 line-km of TOBI sidescan sonar and 3700 km of 3.5 kHz profiler data along the margins of the Rockall Trough (Figure 1). This project followed on from the earlier reconnaissance AIRS (Atlantic Irish Regional Survey) survey conducted over the entire southern Rockall Trough region, using the lower resolution surface towed sonar side-scan system known as GLORIA (Unnithan et al., 2001). The TOBI sidescan system, developed at the Southampton Oceanography Centre (Flewellen et al., 1993), is deep-towed at 300-400 m above the seafloor. It transmits at a frequency of 32 kHz and samples the acoustic response of the seabed and shallow sedimentary structure to a centimetre to metre depth scale. This acoustic response therefore reflects not only the backscattering properties of the seabed but also the shallow detailed structure of sediments formed by recent sedimentological processes.
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West of Shetland exploration unravelled – an indication of what the future may hold
By N. LoizouExploration west of the Shetlands began in 1972, but it was not until the 17th exploration well in 1977 that the first discovery, Clair, was made. Although a number of commercial discoveries have been made since then, the overall exploration success rate of approximately one in five has been generally disappointing. This is a consequence of a number of factors that are reviewed below. Loizou (2003a) concluded that the majority of the failed wells with Palaeocene objectives from 1995 were due to invalidity of the trap. This paper reviews the historical exploration success history and provides an analysis of all 138 exploration wells from 1972 to the end of 2004.
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Volumes & issues
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Volume 42 (2024)
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Volume 41 (2023)
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Volume 40 (2022)
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Volume 39 (2021)
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Volume 38 (2020)
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Volume 37 (2019)
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Volume 36 (2018)
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Volume 35 (2017)
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Volume 34 (2016)
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Volume 33 (2015)
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Volume 32 (2014)
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Volume 31 (2013)
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Volume 30 (2012)
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Volume 29 (2011)
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Volume 28 (2010)
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Volume 27 (2009)
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Volume 26 (2008)
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Volume 25 (2007)
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Volume 24 (2006)
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Volume 23 (2005)
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Volume 22 (2004)
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Volume 21 (2003)
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Volume 20 (2002)
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Volume 19 (2001)
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Volume 18 (2000)
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Volume 17 (1999)
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Volume 16 (1998)
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Volume 15 (1997)
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Volume 14 (1996)
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Volume 13 (1995)
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Volume 12 (1994)
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Volume 11 (1993)
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Volume 10 (1992)
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Volume 9 (1991)
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Volume 8 (1990)
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Volume 7 (1989)
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Volume 6 (1988)
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Volume 5 (1987)
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Volume 4 (1986)
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Volume 3 (1985)
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Volume 2 (1984)
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Volume 1 (1983)