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75th EAGE Conference & Exhibition - Workshops
- Conference date: 10 Jun 2013 - 13 Jun 2013
- Location: London, UK
- ISBN: 978-90-73834-49-1
- Published: 10 June 2013
101 - 120 of 138 results
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Combining Velocity Model Building and Interpretation Techniques to Reduce Uncertainty in Pre-salt Imaging
More LessThere is ever increasing interest in exploring pre-salt provinces across the South Atlantic Conjugate Margin The 2006 discovery of the Lula (Tupi) field in the Brazil Santos Basin and more recent discoveries such as the 2012 Azul Field in the Angolan Kwanza Basin in the Lower Cretaceous, have proven that there is a working hydrocarbon system across the South Atlantic Conjugate Margin. The key to evaluating the prospectivity of these pre-salt provinces is generation of an accurate seismic image using pre-stack depth imaging methods. However, it is not possible to obtain a useable image below allochthonous salt using an approach entirely dependent upon algorithms to construct the PSDM velocity model. The introduction of geological understanding through seismic interpretation, basin modelling and the (limited) available well data can aid PSDM velocity model accuracy and reduce uncertainty of the pre-salt image obtained (Merry, 2012). This paper reviews an approach taken to resolve the pre-salt image using data examples from Angola Blocks 24 and 25.
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Improving Seismic Salt and Subsalt Imaging by Jointly Interpreting Non-Seismic Data
Authors M.H. Krieger, C. Müller, R. Ballesteros, H. Salazar and O. GeislerWithin the scope of multi-technology interpretation projects in Mexico and the Gulf of Mexico, gravity, gravity gradient and magnetic data are jointly modelled and inverted. This iterative seismic and non-seismic interpretation process improves the geological depth model, focusing on salt features as main imaging problem zones. Analysing well logging data results in regionally valid, layer specific density-velocity relations which enable an independent gravity-based control of the seismic velocity model. This results in a final increase of seismic imaging quality.
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Keynote 2: Cretaceous Plate Restoration, Palaeo-geography, and Salt Deposition in the South Atlantic
By J. HossackThe South Atlantic was restored in GIS using Moulin et al (2010) rotation poles to various pre-, syn-, and post rift palaeo-geographies. Particular attention was paid to pre-rift tectonic piercing point structures that could be correlated from Africa to South America as a test of the veracity of the restorations. Adjustments were made to the restorations to ensure a better alignment of the piecing points. Then, the appropriate tectonic, stratigraphic, topographic, and geomorphological data were plotted on the restored maps to create palaeo-geographies in a series of time slices that track the development of the salt basins.
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Sedimentary Model of Upper Cretaceous and Paleogene Deposits within South Part of Western Siberian Plait
Authors O. Shelukhina and E.M. KhabarovNew findings of research Upper Cretaceous and Paleogene deposits are presented in the article. The question behind the investigation was to interpret the sedimentary environments. The basin of South part of Western Siberian plate could be divided into seven stages through this period of geological time, which defined by the trend of first order and all of them indicate the unique phase of evolution of the shelf.
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Facies versus Seismic Facies: Case Studies
By E. MalyshevaThe presentation will touch upon the comparison of well based and seismic interpretation models on the example of two hydrocarbon fields in Pechora oil and gas basin. It shows that the latter provides much more accurate lateral distribution of reservoirs in the inter well space. On the other hand in complicated polyfacial successions only apriori depositional models provide accurate and geologically reasonable interpretation of seismic data
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Interpreting between the Lines
More LessAfter three years of intensive R&D efforts, a novel approach is proposed in seismic interpretation to exploit the three dimensionality of the seismic data throughout the seismic volume. Instead of interpreting individual seismic events this method enables interpreters to build a stack of horizons that follow every event. User intervention is still needed, for example, to ensure that the correct jump correlation is made between horizon patches on opposite sides of a fault. Once an interpreter has identified the correlations, the method will then automatically make an updated and optimized stack of chronostratigraphically indexed horizons. Such technology reduces time cycles, helps in the identification in the geological prospects and minimizes risk for drilling decisions in the E&P process. It has been tested on various case studies to quickly leverage information contained in seismic data at different scales. This approach is ideal when you need to rapidly evaluate a new area from top to bottom.
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Resolution from an Alternative Dimension
By G. PatonSeismic data contains a wealth of information, but it is often hard to get the complete picture by viewing a single attribute. Multi-attribute colour blending is an established technique that uses high resolution visualisation techniques to improve the way that information obtained from analysis of seismic data is presented to the interpreter. Multi-attribute colour blending can aid both stratigraphic and structural interpretation and this paper illustrates the improvements in understanding of facies heterogeneity and fault composition by using colour blending techniques. Stratigraphic variability is more easily identified using RGB colour blending models, whereas fault composition is most effectively viewed using a CMY blending scheme.
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Do Our Thought Processes in Geology and Geophysics Stifle the Extraction of Information from Our Data?
By D. DalleyGeophysicists and Geologists think differently! One thinks in depth but, with the 3D seismic process, samples the subsurface best in breadth. The other thinks in breadth but, by drilling, samples the subsurface well in depth. The first tends to disregard the excellent lateral sampling and strives to make seismic look like well traces, the second would like to drill multiple wells to look like seismic. Seismic is cheap, while wells are expensive. So how can we make most use of the resolution we already have through better, more thorough, interpretation of relatively cheap seismic data that we have or can easily acquire? This paper will introduce and present some of the geological information that can be highlighted in our 3D seismic by exploiting the resolution available in the lateral domains and in the extra resolution available by the use of colour to represent amplitude and frequency in the data.
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High Resolution Stratigraphic Architecture of the Cretaceous Chalk of the Danish Central Graben
Authors F. van Buchem, F. Smit, I. Schmidt and B. TrudgillThe lithological composition of the Cretaceous Chalk of the North Sea Basin is homogenous and consists essentially of nannofossils (coccoliths and nannoconids), with only locally admixtures of clays and coarser bioclasts. Traditionally exploration strategy in these homogenous rocks was guided by acoustic impedance volumes that showed the location of high porosity units. With increased maturation of fields and the search for remaining hydrocarbon occurrences, it is now essential to better understand the high resolution stratigraphic architecture. We will show how high resolution three-dimensional geo-model interpretation of the seismic volume helped to document the change from a post-rift phase into a violent inversion phase and its impact on sediment distribution. This three-dimensional seismic approach allows for interpretation of previously poorly understood seismic features in the context of the geological evolution of the area, and helps to better understand the porosity distribution in the chalk.
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Limitations of Seismic Pore Pressure Prediction - What Is the Alternative?
Authors R. Swarbrick, R. Lahann, S. O‘Connor and E. HoskinPore pressure prediction is becoming even more critical to successful drilling as conditions for exploration and exploitation of oil and gas reserves move into more hostile environments. Rock property relationships (including seismic interval velocity) tend to under-predict pore pressures when temperatures exceed about 120oC. Understanding of the geological setting (tectonic stress history) and lithology control on pressure mechanisms provides the basis for a geology-model based approach, which can yield more realistic predictions in these high-temperature settings.
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Do Operations Geologists Have the Competence To Do Pore Pressure Predictions?
By G. HolmThis paper will review the post-Macondo requirement for competancy in planning well design. It discusses the pore pressure prediction, which is the starting point for a safe well design and reviews the requirements for Operations Geologists to make Pore Pressure predictions.
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HPHT Campaign in West Baram Delta: Successful Alternative Approached in Pre-drill Pore Pressure Prediction & Real-time Pore Pressure Monitoring
Authors C. Anwwar Ibrahim, F. Wijnands, J. Ismail, M.A.M Ariff, M.A. Wahab and L. LightRecent HPHT campaigns have successfully tested deep seated overpressures plays at depths over 4500m below mudline and subsurface pressure more than 14000psi/96.5MPa. Regional overpressure model identified under-compaction as the predominant overpressure mechanism within this region. Furthermore, inflationary overpressures are also inferred in some wells where significant overpressure increases are observed beyond the under-compaction trend. A primary concern during pre-drill was the possibility of encountering inflationary overpressures (also termed late overpressures) where prediction is difficult. Wells that have encountered inflationary overpressure are characterized by a lack of clear inversion in sonic and resistivity log profiles, with abrupt pressure increase, however with considerable variation in magnitude. This rapid pressure increase has resulted in early TD of previous wells. Successful development of alternative way in incorporating all available well and seismic data has proved to underpin the prediction of overpressures in exploration prospects. Utilizing pre-drill pore pressure prediction result from this method has successfully helped drilled both wells safely. Throughout these HPHT campaign, monitoring various gas trends was found to be a reliable key indicator for real-time pore pressure estimation. Small increases in event gas peak amplitudes were flagged and interpreted to signal increased pore pressure, with mud weights raise accordingly.
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Well Planning outside of the Gulf of Mexico - NCT’s, Overburden and Fracture Gradient
Authors S. O‘Connor, R. Swarbrick and R. LahannThe use of empirical relationships derived in the Gulf of Mexico to predict shale pore pressure and fracture pressures will lead, potentially, to inaccurate definition of the drilling window and future well control problems in wells in other basins. A more robust and defensible approach is to use/derive relationships based on rock properties under-pinned by understanding the geology of the basin.
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Pore Pressure Prediction in Frontier Exploration - The Before, the During and the After. How Well Did We Do?
By T. SinclairIn a frontier exploration basin, determining the pore pressure for an upcoming well is very challenging where the primary objective is for the exploration well to be drilled in a safe and cost efficient manner. Where minimal offset data exists, seismic interval velocities along with an interpretation of the geological depositional system is often the primary data used to construct the pore pressure model for the basin. From this a pore pressure ‘base case’ is determined for the prospect location which is then used in the pre-drill well design process. During the operational phase of the 1st well, the pre-drill ‘base case’ becomes a secondary guide and it is the wellbore and drilling parameters that is the primary data source for dictating the ‘base case’ while drilling. The focus shifts again in the post wells analysis and planning phase of the next well where the primary data for the ‘base case’ pore pressure profile for the 2nd well is now the hard offset geological and geophysical data gained form the first well. The secondary data sources (seismic interval velocities & geological interpretation) then help to form the pore pressure envelope around the base case.
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Challenges and Uncertainty in Seismic Velocity Analysis Based Geopressure Prediction and the Application of Geostatistics
Authors C. Ryan, M. Igoe and A. ColhounOnly by understanding the geological aspects of overpressured systems can we hope to predict pore pressure accurately in frontier basins. Prediction of pore pressure is critical at several stages in the exploration and development process. Geophysical technologies play a central role in almost all aspects of hydrocarbon exploration, and geopressure prediction is no exception. Seismic velocity analysis techniques provide our most powerful method of geopressure prediction in underexplored basins, yet these techniques should not be used in isolation. Every effort should be made to enable any seismic-based prediction to be driven by available geological data, information, and experience of analogous basins. This paper investigates the potential improvements that can be made in geopressure analysis via intelligent use of log and seismic velocity analysis coupled with geological interpretation. We focus on basins where we have both reasonable and poor well calibration to examine how different velocity data sets predict geopressure in shale sequences. The key to building a geophysical framework that reflects nature is an understanding of the geology. Recognition of the challenges associated with the seismic experiment and imaging will allow more accurate velocities to be picked.
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Drilling the Undrillable Well - An Introduction To Managed Pressure Drilling and The Acquisition of Additional Sub Surface Pressure Data While Drilling
By C. HillsThe presentation will give a brief introduction to the technique of closed loop ‘managed pressure drilling’ (MPD). Field examples and lessons learned from recent campaigns will be discussed including examples of acquiring new pore and frac downhole pressure data
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Uncertainty and Cognitive Biases - Limitations of the Human Mind
By M. BondThe purpose of this talk is to make the listener aware of cognitive biases and their impact on judgment and decision making, and offer some solutions to counter their influence.
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The Most Significant Faction in Decision Making and Uncertainty Management? People.
By J. CarterAs scientists and engineers, we grow up with the idea that things are knowable. If we want to know something, we can measure it, model it and find out what it is. In the geoscience world, this paradigm does not apply. There are many things we are uncertain about and we are also uncertain about how uncertain we are. People’s reaction to uncertainty and the way they deal with it varies widely. It is shaped by their personalities, their attitudes and their education. It can be influenced by members of the groups they belong to and affects decision makers as much as geoscience professionals. In this talk, I shall discuss the various factors that affect people’s attitude to uncertainty and the impact this has on attempts to address uncertainty rationally and systematically.
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Decision Focused Assessment of Opportunities Including a Case Discussion of Unconventional Evaluation Principles
By B. HaskettA fundamental solution path involves the creation of decision centric models that incorporate chance, uncertainty, dependency, and correlation. Throw out the precision/calculation approach and embrace the uncertainty. Typical model objectives of “calculating the answer” fall flat. A better approach is to create threshold, indifference, and confidence models that truly provide management with decision context as opposed to a sometimes baffling array of discrete output.
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Decision Driven Modelling Strategy
By T. WoodheadReservoir modelling capability has grown significantly over the last twenty years and data fidelity has enabled ever-increasing detail for certain reservoir parameters. This has led to a modelling workflow in which a single complex and detailed full field model is typically the focus. Sub-surface modelling is however, carried out to underpin field development or reservoir management decisions and these often require the understanding of geology and fluid flow at a range of different scales and uncertainties. Another danger in full field modelling is the tendency to focus on a sub-set of the full range of uncertainty in the outcome of a development decision. This is aggravated by the requirement to construct, calibrate and validate large numbers of full field model realisations, which is time and resource consuming. Working with a large complex model additionally leads to a linear workflow in which there is often limited time to revisit modelling assumptions and evaluate their impact on the business decision at hand. A decision driven modelling strategy based on multiple models at different scales offers a flexible solution to these issues. A broader description of the uncertainties at each scale is facilitated by the ‘big loop’ approach in which the integrated model is described completely by a single set of the ‘model parameters’. The ranking of uncertainties and the identification of low, expectation and high decision outcomes is then an output of the model rather than an assumed input.
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