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74th EAGE Conference and Exhibition - Workshops
- Conference date: 04 Jun 2012 - 07 Jun 2012
- Location: Copenhagen, Denmark
- ISBN: 978-90-73834-28-6
- Published: 04 July 2012
141 - 156 of 156 results
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Frameworks for Modeling and Inversion
More LessInversion combines modelling with optimisation, two computational domains with quite different concepts and requirements. I suggest a few simple principles that help to organize software for these two types of tasks into linked frameworks. Code libraries based on these principles minimize the work involved in construction of modelling and inversion applications, and maximize the reliability of the end product. This paper presents example libraries constructed by the author’s research group, the principles on which they are based, and some examples of their use.
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Python for Geophysical Data Processing and Visualization
Authors Didrik Pinte, Eric Jones, Robert Kern and Pietro BerkesThe Python language excels as a tool for processing and visualizing scientific data. The array processing tools in NumPy handle multi-dimensional arrays and provide convenient representations for common geophysical data types such as well logs (1D), horizons (2D) and seismic volumes (3D). SciPy provides a wealth of efficient algorithms (interpolation, statistics, signal processing, etc.) common in processing such data, and matplotlib, chaco, and Mayavi provide plotting and 3D visualization capabilities. For those interested in harnessing the powers of the GPU, libraries such as CLyther, PyOpenCL, and PyCUDA offer a convenient bridge to these technologies. This presentation will provide an overview of these Python tools and demonstrate how to apply them to geophysical problems. We will provide examples of how these open source tools can be used for academic research as well as incorporated into commercial applications.
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Challenges Facing Open Source Software Developers and Users
More LessUsing open source E&P software for the first time or, in particular, becoming a developer has always meant that we have to put in an enormous effort in learning the ins and outs of the desired open source package. This requirement has, over the years, limited the number of potential users of open source software or has scared off new users. Addressing the reasons behind the big effort required to learn an open source E&P software will be the subject of this panel discussion.
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A Redeposited Chalk Reservoir (Upper Maastrichtian–Danian) in the Oseberg Field, Northern North Sea
More LessSetting and Stratigraphy The northern limit of the Upper Cretaceous chalks in the North Sea occurs at 60–61°N where carbonates interdigitate with mud-rich siliciclastics. This facies transition, coinciding with marked submarine palaeotopography descending from the Horda Platform to the Viking Graben, is recorded primarily by well-log data which demonstrate the temporal shifts in the position of the chalk:mudstone facies boundary. The Oseberg Field, 130 km west of Bergen (Norway), straddles this regional facies front; declining production from the primary Jurassic reservoirs in this field has focussed attention on hydrocarbon-bearing carbonates in the uppermost Shetland Group, mainly in the south of the field. Of particular interest is a 10–30 m thick chalk-rich section that caps the upper Campanian–Maastrichtian Hardråde Formation; a thin Danian carbonate unit (equivalent to the Ekofisk Formation farther south) is also recognisable locally, resting on a hiatal surface spanning the latest Maastrichtian (nannofossil subzone UC20d) and early Danian (subzones NNTp1–4E).
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Comparison of Fracturing Techniques for Unconventional Reservoirs
Authors Klaasvan Gijtenbeek and Markvan DomelenDue to their extremely low permeability, unconventional (UC) reservoirs such as tight sandstones, shale formations, and coal seams nearly all require hydraulic fracturing to maximize production. With marginal economics often at the forefront of the decision process to proceed with a field development project, successful fracture stimulation is critical for helping to de-risk these types of projects. Over the years the industry has used many different approaches in an effort to determine the “optimum” fracturing and completion design in different UC reservoirs. Using a variety of evaluation techniques that help to define success, one common theme emerges from the extensive amount of literature published: UC reservoirs respond most favourably to fracturing methods that are tailored to the specific reservoir conditions. This presentation will focus on some of the key factors that must be considered when designing hydraulic fracturing treatments for three different types of reservoirs; 1) low permeability sandstone formations, 2) shale reservoirs, and 3) coalbed methane (CBM) reservoirs, with a specific emphasis on comparing and contrasting the fracturing objectives between these different reservoir types.
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An Inversion Approach to Separating Sources in Marine Simultaneous Shooting Acquisition
Authors Roaldvan Borselen, Rolf Baardman, Bedanta Goswami and Eivind FromyrIn seismic exploration, there is continuous drive towards more dense data sampling to better image complex geological structures. Recent advances in acquisition such as Wide-Azimuth, Multi-Azimuth or Rich-Azimuth acquisition can deliver a more diverse range of source, azimuth and offset sampling. To collect such data, multiple source and receiver vessels are deployed, thereby increasing the costs of the survey significantly. In conventional acquisition, there is zero time overlap between shot records, and data are recorded discontinuously. The source domain is often poorly sampled, leading to aliasing. In simultaneous acquisition, data can be recorded continuously, and temporal overlap between shots is allowed. Consequently, more sources are fired during the same period of acquisition, which greatly enhances the flexibility in survey geometries. As a result, a more densely sampled data set in terms of source spacing, but also azimuth and offset distributions can be obtained. In terms of efficiency, simultaneous acquisition can contribute by reducing survey times, which is of particular value in critical situations where small acquisition timewindows dominate due to severe safety, environmental or economic restrictions. As such, from an acquisition point of view, simultaneous acquisition holds the promise of both efficiency and quality improvements. However, unless source separation can be achieved to a sufficiently high degree, the enormous potential benefits of simultaneous sources remain unrealized. Two approaches are currently utilized by the industry to achieve source separation: methods based on random noise attenuation and inversion-based methods. By regarding the energy from secondary sources as incoherent noise, after sorting the acquired data into an appropriate domain, the interference noise appears as random spikes which could be attenuated using well-known random noise removal procedures. Alternatively, inversion-driven methods aim to construct the separated sources through the minimization of a cost function that describes the “data misfit”. In such methods, incoherent energy is no longer regarded as noise that is to be removed. Instead, this energy is recognized as a representation of coherent events belonging to (one of) the interfering shots. An inversion approach aims to distribute all energy in the blended shot records by reconstructing the individual unblended shot records at their respective locations. In this abstract, an inversion-driven method is utilized that uses coherency measures to reconstruct the individual shot gathers from the blended data. The method is demonstrated to be capable of separating sources, even in the presence of strong diffraction energy. The method can be used in conjunction with other methods, resulting in so-called hybrid solutions. A simultaneous source wide-azimuth 3D data set from the Gulf of Mexico is presented.
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A Land Example of Full Waveform Inversion and Distance Separated Simultaneous Sweeping
Authors R.É. Plessix, G. Baeten, J. W.de Maag, F.ten Kroode and R. J. ZhangSimultaneous or blended shooting has been developed to reduce the acquisition cost while keeping a dense coverage. The processing and imaging are complicated by the cross-talks between the simultaneous sweeps. A compromise can be achieved with distance separated simultaneous sweeping when we are primarily interested in reflected events since by design, the interferences at the target are avoided and the shots can be easily separated. At large offsets which are relevant when full waveform inversion is used to construct the background velocity, cross-talks occur. Based on the single shot, single receiver land data set recorded in Inner Mongolia, China, we simulated a 2D distance separated simultaneous sweeping acquisition. We then carried out several full waveform inversions to evaluate the effects of the cross-talks. By adapting the offset weighting traditionally applied, a multi-scale full waveform inversion of the blended data produces a background velocity model that is very similar to the model obtained with the original unblended data.
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On the Relation between Seismic Interferometry and the Simultaneous-source Method
Authors Kees Wapenaar, Joostvan der Neut and Jan ThorbeckeIn seismic interferometry the response to a virtual source is created from responses to sequential transient or simultaneous noise sources. In the simultaneous-source method, overlapping responses to sources with small time delays are recorded. Seismic interferometry and the simultaneous-source method are related. In this paper we make this relation explicit by discussing deblending as a form of seismic interferometry by multidimensional deconvolution.
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Blended Acquisition with Optimized Dispersed Source Arrays
Authors Guus Berkhout and Gerrit BlacquièreUntil now, blended source arrays are configured with equal source units: ‘homogeneous blending’. We propose to extend the blending concept to inhomogeneous blending, meaning that a blended source array consists of different, narrowband source units with different central frequencies.
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Waveform Inversion Overview: Where Are We? And What Are the Challenges?
More LessSince at least forty years, mathematicians and geophysics have studied seismic waveform inversion. Its computational cost and its ill-posedness (i.e. the presence of local minima and the non-uniqueness of the solutions) make its use difficult with real-sized problems. Nevertheless, with the improvements in data quality and in acquisition and the increase in computer power, several real data examples have been reported. In the literature, waveform inversion has been formulated either in the data domain or in the model domain. In this presentation, I shall discuss the data-domain formulation, where we minimize the misfit between the observed data and the computed data that are direct solutions of the wave equation. I shall consider three main applications. In the first group of applications, waveform inversion is solved with a global optimization and a simple 1D forward modeling. The objective is, generally, to derive some petrophysical parameters from the seismic reflection traces. In the second group of applications, waveform inversion is solved with a local optimization assuming a known background velocity, the objective is to retrieve reflectivity or impedance maps from reflection data. In the third group of applications, waveform inversion is solved with a local optimization and a multiscale approach. The goal is to estimate the background velocity mainly from low-frequency and long-offset data. While reviewing these waveform inversion applications, I shall discuss the challenges we are still facing. The focus of the presentation will be the applications of waveform inversion for macroscopic (background velocity) model building.
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Integration of Dispersion Curve and Full Waveform Inversion Techniques for Onshore Velocity Model Building – Inner Mongolia Study
Authors Alexander Droujinine, Ren-douard Plessix and Fabian ErnstWe develop an integrated velocity model building workflow for prestack depth imaging in onshore settings with a complex shallow subsurface. This workflow incorporates dispersion curve inversion and full waveform inversion into a single framework to optimize the advantages of each. An accurate near-surface velocity is derived using the dispersion curve inversion technique that overcomes limitations of traditional traveltime tomography. This velocity is then incorporated into layer-stripping full waveform inversion. We illustrate the workflow on an experimental data set from Inner Mongolia, whose long-offsets and low-frequency content provide the necessary input for both the dispersion curve and full waveform inversion techniques.
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Microseismic Geomechanics – Complexity Simplified
Authors Alexander Droujinine, Joel Ita and Steve OatesAdopting the Kostrov methodology we determine a strain rate tensor for any grid area in 4D by summing source moment tensors of microseismic events. The predicted strain rate tensor is used to provide a priori constraints on the style and direction of the observed deformations. This is a hybrid method that is shown to reduce uncertainties of geomechanically modeled displacement field in a depleting reservoir during the monitoring period. The improved microseismic-to-geomechanics link is seen as a key step to reservoir modeling and to the future realization of reservoir management value from this technology.
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Microseismic Geomechanics – Complexity Simplified
Authors Alexander Droujinine, Joel Ita and Steve OatesAdopting the Kostrov methodology we determine a strain rate tensor for any grid area in 4D by summing source moment tensors of microseismic events. The predicted strain rate tensor is used to provide a priori constraints on the style and direction of the observed deformations. This is a hybrid method that is shown to reduce uncertainties of geomechanically modeled displacement field in a depleting reservoir during the monitoring period. The improved microseismic-to-geomechanics link is seen as a key step to reservoir modeling and to the future realization of reservoir management value from this technology.
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Shallow Shear Wave Reflections: What Can the Amplitude Tell Us and How?
More LessShallow shear-wave reflection method at present is entirely restricted to the use of reflection time information. The average velocity is estimated from the travel time, whether in stacking velocity analysis, tomographic inversion, or in other processing schemes. Use of reflection amplitude has remained challenging primarily due to source and receiver effects camouflaging geologically meaningful amplitude perturbation. We have found ways to improve amplitude fidelity and reduce the effect of source and receiver coupling variations. When tested on real field data, shear-wave reflection amplitude as a function of incidence angle is found to provide useful near-surface interfacial information. Moreover, when frequency-dependent reflection amplitudes are looked at using the pertinent theories of poroelasticity, we find that those reflection amplitudes seem to contain even further information about the flow properties and the state of stress in the near-surface. These information are crucial to diverse practical applications.
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The Road to Open Source: Sharing a Ten Years Experience in Building OpendTect, the Open Source Seismic Interpretation Software
By Hlne HuckOpendTect is a complete Open Source seismic interpretation system, available for already ten years. We demonstrate that Open Source as a business model can be successful in the oil and gas industry provided you pay extra attention to a few key points. We discuss the importance of the Freemium business model and use our experience to list important topics to consider when going Open Source. It covers a wide range of issues going from communication with the users’ community and stimulation of research and development to the architecture of the software code itself.
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Estimating thermal conductivity from geophysical well logs: Selected boreholes in Danish sedimentary basins
Authors Thue S. Bording, Niels Balling and Søren B. NielsenEstimating temperatures in sedimentary basins and geothermal reservoirs requires knowledge of heat flow, thermal conductivity, heat production, and the surface temperature history. Contrary to heat flow, thermal conductivity typically shows large local variability, both on vertical and horizontal scale, resulting in large variations in temperature gradients. Accurate estimates of thermal conductivity are thus of paramount importance.
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