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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
101 - 120 of 156 results
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Geothermal Exploration – Ensuring an Optimized Utilization of Geothermal Energy in Low-enthalpy Sedimentary Settings
Authors Ben Norden, Sven Fuchs, Simon Weides, Inga Moeck and Andrea FrsterAn adequate comprehensive understanding of the subsurface geology is a pre-requisite for a precise planning and successful operating of geothermal applications and reduces the financial risks considerably. An exploration concept is needed which is tailored for the geological setting to be evaluated and the level of exploration performed prior to the geothermal exploration. We present examples from ongoing geothermal exploration projects encompassing, for example, studies on the geological structure, including the stress field, on the hydraulic and thermal properties of geological formations, and on the temperature prognoses for target reservoirs.
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Improved Inversion of Needle Probe Data for the Determination of Rock Thermal Properties
Authors Thue S. Bording, Sren Bom Nielsen and Niels BallingHeat flow, thermal conductivity and thermal diffusivity are essential properties in subsurface temperature modelling. We present initial results of a novel inversion approach for laboratory measurements of rock thermal conductivity and thermal diffusivity by the needle probe method. Instead of analytical expressions, we use a numerical finite element procedure for the forward temperature response. A Markov Chain Monte Carlo Metropolis Hastings inversion procedure produces estimates of rock thermal parameters with uncertainties.
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The Thermal Properties of the Subsurface – Key Parameters for Geothermal Energy Utilization
Authors Ben Norden, Thue S. Bording and Niels BallingOften the investigation of petrophysical properties is far behind the capabilities of sophisticated modelling techniques applied in basin and geothermal modelling and for which these data serve as an input. Therefore, more in-depth investigations especially of thermal properties are requested. We evaluate different methods and devices for measuring rock thermal properties including thermal conductivity and thermal diffusivity and will compare the results to assure a high quality of these important key parameters.
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Porosity and Permeability Depth Trends, Examples from the Danish Upper Triassic−Upper Jurassic Gassum Formation
ty-depth and permeability-depth trends, established for all cored intervals of the Gassum Formation. The porosity-depth and permeability-depth trends represent sandstones alteration during burial due to mechanical compaction and diagenesis. The focus of this study is on the Gassum Formation, which has the largest potential and is the main target for planned geothermal wells in Denmark, as it is widely distributed and generally occurs within the depth interval of 800-3000 m, thereby reaching sufficient high temperatures and still assumed to maintain the required porosity and permeability. The Gassum Formation occurs with thicknesses of 50–150 m in central and distal areas of the Danish part of the Norwegian−Danish Basin, thickening locally in association with salt structures and major faults (up to 300 m in the Sorgenfrei−Tornquist Zone) and thinning or being absent on the structural highs, such as the Skagerrak−Kattegat Platform and the Ringkøbing−Fyn High (Fig. 1). The Gassum Formation consists of shoreface, fluvial, estuarine, lacustrine, lagoonal and marine facies (Nielsen 2003).
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Deep Saline Pre-Rhaetian Triassic Aquifers in the Hllviken Halfgraben, Stratigraphy, Distribution, Petrology and Petrophysical Properties with Respect to Their Geothermal Potential
Authors Mikael Erlstrm and Sofie LindstrmThe pre-Rhaetian Triassic sequence in the Hllviken Halfgraben contains several sandstone layers, which have been investigated concerning their potential as geothermal aquifers. Two geothermal projects managed by E.ON Sverige AB, DONG (Danish Oil and Natural Gas) and HGS (Hovedstadens Geotermiske Samarbejde) resulted in the early 2000s in the completion of four deep wells in Copenhagen and Malm. The wells penetrate an up to 700 m thick pre-Rhaetian Triassic sequence at depths between 1800 m and 2650 m. The geological information from these wells and data from 15 older wells and one cored borehole constitute the main database in this study. The incentive has been the need for a comprehensive characterization of the Triassic aquifers regarding their distribution, lateral extension and petrophysical properties as to assess their geothermal potential on a regional scale.
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Geothermal Energy Production Assessment from Premature Reservoir Evaluation
Authors Carsten M. Nielsen and Lars KristensenAssessment of the geothermal energy production potential, in an early decision stage of a development project, is subjected to great uncertainty due to the often sparse data coverage. By using all available data i.e. wireline logs, core analysis data and seismic interpretations to construct a preliminary geological model for the area of interest, the basis for decision is strengthen. The geological model forms the basis for subsequent reservoir simulation, where the uncertainty in water flow rates from the various input parameters can be quantified. Different production strategies can be examined and optimized. Furthermore, any identified faults or geological baffles potentially constraining fluid flow may be incorporated and evaluated. The present paper illustrates the construction and use of a subsurface model to address uncertainties in early decision making for geothermal energy production projects.
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Regional Geothermal 3D Modeling in Denmark
Authors Sren E. Poulsen, Niels Balling, Thue S. Bording and Sren Bom NielsenWe present first results of a 3D model of the subsurface temperature in Denmark. Updated temperatures are contoured for the Gassum formation which is currently utilized for geothermal energy production. The Gassum formation of Upper Triassic/Lower Jurassic age is present in most of Denmark with sufficient net sand thickness and temperatures between 50oC and 80oC in large areas. This makes this formation of particular interest for further geothermal exploration. The regional geothermal model is expected to aid decision makers in future prospecting of geothermal resources in Denmark.
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Risking Seismic Amplitude Anomaly Prospects Calibrated to an Industry-Wide Database
Authors Rocky Roden and Mike Forrest and Roger HoleywellOver the past decade, a consortium of oil companies in the US and Europe has developed a work process to interpret and risk seismic amplitude anomalies on exploration and development prospects. Over 175 prospects have been reviewed and documented in a database where the geology risk factors, seismic and rock physics data quality and amplitude anomaly characteristics have been analyzed to calculate the probability of geological success (Pg - flowable hydrocarbons). The drilling results for each prospect were compared to the calculated Final Pg, a function of the Initial Pg (geology) and the DHI Index which is the impact of the anomaly characteristics modified by data quality. The Final Pg and DHI Index compared to drilling result trends indicate a DHI Threshold Effect on prospects at the high end of the risk spectrum and a low Pg Threshold Effect at the low end of the spectrum. In other words, on the upper end of the spectrum there is a point at which a significant amount of the risks have been reduced to dramatically increase the Final Pg and DHI Index. On the lower end of the spectrum there is a threshold below which essentially all the wells are dry holes. Using these database trends, Pg can be calibrated to a wide range of 5% to 95% Final Pg. Therefore in DHI prospects, geoscientists should be more optimistic in analyzing the prospect risk if Final Pg and DHI Index are above certain threshold levels. Conversely, the low end of the risk profile prospects in the portfolio should probably be farmed out or not drilled with an overall goal of upgrading the exploration portfolio.
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Bayesian Risk Modification for Seismic Anomalies and Multiple Segment Prospect
More LessIt is well understood that anomaly information such as a flat spot, conformance, AVO, boosts the chance of success (COS) of an exploration target. Similarly, lack of anomaly information, when expected, attenuates the COS of the target. However, what happens when a prospect is composed of multiple targets (zones, compartments) with differential anomaly information? This paper presents a methodology that captures the intuitive notion that the aggregate effect of anomaly indicators at the target level depends on the degree of risk dependency between the discrete targets in the prospect. If the targets are relatively risk independent, then the prospect level COS will be a direct consequence of risk modification at the target level. On the other hand, if there is significant risk dependency, then the aggregate effect can be a relatively stronger boost or a significant attenuation depending on whether the signatures are consistent or mixed.
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Seismic Rock Physics, Sherlock Holmes and DHI Risking
By Rob SimmWe have been chasing ‘amplitude plays’ in earnest for over 20 years in this era of rock physics, AVO and seismic hi-fidelity. The published statistics and our own experience tell us that it pays off; exploration success rates are higher in plays where DHI technology is applicable. So, where to now?, more of the same presumably. We have all the checklists we need to ensure that procedures are followed together with systematic risking processes that help rank prospects around the globe. But oil and gas is found by the creative mind not committees, and filling in forms is no substitute for experience. The challenges faced by E & P companies requiring rigorous and consistent risking of amplitude supported prospects are not insignificant. Education, discipline integration and technology transfer from ‘experts’ to asset teams are significant issues, but the encouragement of a seismic rock physics mindset in seismic interpreters is the key to success.
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Amplitude Preservation for PSDM Processing
Authors Alfonso Gonzalez, Everett Mobley, Charles Wagner, Xiang Du, Robin Fletcher and Craig TophamAs seismic exploration moves to more complex and challenging geologic environments, Anisotropic Prestack Depth Migration is becoming the standard imaging technology. At the same time, there is high interest to use seismic amplitudes in these complex environments for risk assessment and reservoir characterization, objectives that require accurate amplitude preserving prestack depth migration. In this paper we review recent advances made to ensure depth migration algorithms maintain the quality of relative amplitudes. We verify with simple synthetics the amplitude response of Reverse Time Migration, Adaptive Beam Migration and Kirchhoff Migration algorithms, and demonstrate how these can be used successfully, under controlled circumstances, for AVO/AVA and Absolute Acoustic Inversion in media with lateral velocity variations.
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Fast Amplitude Analysis from Geo-Model Horizons
Authors Sebastien Lacaze and Fabien Pauget and Ingelise SchmidtIn this paper, we propose a new workflow, based on a global approach in seismic interpretation, to better analyze seismic amplitudes in a new horizon framework. This method seeks to overcome limitations in seismic such as wavelet polarity changes and amplitude drops and allows for building a continuous geological model for detailed understanding of the different reservoir levels of the survey. The amplitude extraction on numerous horizons in a short vertical window enables the delineation of geological prospects and therefore minimizes risks for drilling decisions. In this paper, we will describe the proposed workflow, its background technology and some case studies where amplitude extractions on horizons computed from the geo-model enabled to identify unseen events with classical approaches and facilitated fast modeling for forward modeling.
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Use of Quality and Anomaly Indicators in the QC of Seismic Inversion
More LessQuantifying the capability to repeat measurements of a signal or repeatability analysis is essential in geophysics and particularly for 4D seismic studies. Traditionally, it relies on statistical measurements like correlation coefficients and NRMS. We introduce two new repeatability indicators called “Quality” and “Anomaly” which allow the identification and quantification of inconsistencies inside a large amount of data. These indicators can also be used for AVO studies or after a seismic inversion to evaluate the match between the synthetic response of the inverted model and the observed seismic amplitudes. For prestack and 4D seismic inversion, the amount of data to analyze is significant. These indicators provide data reduction and quantify the ability of a given elastic model to reproduce seismic data. They are therefore useful to find the optimal parameterization of the inversion and to identify areas where further analysis and interpretation is needed. It is also used for qualifying different processing options for inversion purpose.
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Tricky DHIs for a Successful Exploration History in West Africa Deep Offshore
More LessDHIs have definitely become a crucial factor at steering the exploration activity in a mature block of the deep offshore of West Africa. Eni has drilled here many wells to test so far some thirty target levels. Many examples will be reviewed to show how the really tricky AVOs and DHIs have gained reliability and prediction power along the four year of exploration history in the block.
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Development and Utilization of an S-wave Type Land Streamer for High-Resolution Reflection Surveying
More LessHigh-resolution S-wave reflection surveying has been conducted on the paved surface utilizing Land Streamer which was originally developed by the author. The Land Streamer is featured by nonstretch towing member on which geophone units are mounted or hooked. The geophone units are coupled with paved surface without being planted to the ground. Since 1997, we have conducted production surveys using S-wave type Land Streamer at 27 sites, 46 lines, in Japan, and successfully delineated detailed near-surface structure down to 100 m. Especially, the tool has been utilized to active fault survey, because it is capable to discriminate vertical displacement of sediment layers less than 1 m owing to shorter wavelength of S-waves in the near-surface sediments compared with that of P-waves.
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Shear Wave Reflection Seismic by Combining Vibratory Sources and Land Streamer Receiver Setups
By Ulrich PolomSeismic imaging of the shallow subsurface to about 100 m in depth in high-resolution got a push on the demand in the last decade. The range of requests to image subsurface structures and also to assign shear wave velocities with respect to dynamic shear modulus analysis spread from very shallow targets in the first 10 m for e.g. building ground investigation for foundation to continuously increasing depths of more than 100 m for a wide range of shallow subsurface investigations. A special target in that frame was the subsurface investigation in urban environments, on paved surfaces and also below existing buildings, which can hardly be carried out by other geophysical methods. The performances of shear waves compared to P-waves allow new insights in this scale of subsurface investigations, if the method and the tools are adapted to these specific requirements. Beside only a few other research groups worldwide, LIAG research focussed to this demand since 2001 in developments of the shear wave reflection method, including research in tool development, acquisition operation, data processing, imaging, and interpretation. Over the years, a wide range of case studies led to continuously increasing experiences using this method. Since 2006 the achieved results and improvements also led to first breaks through to the commercial market.
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Is the Vila Franca de Xira Fault Still Active? A Shallow Seismic Reflection Shear-wave Study in an Intraplate Environment
The V. F. Xira fault (VFXF) is considered to be the most probable source of several destructive earthquakes that caused significant damage and loss of lives in Lisbon, Portugal and surrounding cities. The fault outcrops in Miocene sediments but is not seen to affect Quaternary terrains. The combination of low slip-rates in the area with erosion/sedimentation rates prevents the identification of active faults in the region. Our goal is to confirm if this fault has been active and to improve seismic hazard assessment in the LTV area. Previous P-wave seismic reflection data indicated the possibility of two shallow fault segments affecting the Holocene alluvium close to the VFXF outcrop. Due to the lack of resolution of this data to detect a small throw (< 2m) fault, the site was revisited with a high-resolution shallow S-wave reflection profile to confirm the fault segments but results were not completely conclusive. Here, we present reprocessed S-wave data and results of full-elastic seismic modelling to confirm the presence of the suspected faults. Clear indications of faulting were found: change of the shape and the amplitude of the reflection hyperbolae, discontinuities in the reflectors in the stacked section, shear-wave velocity dropping in anticipated the damage zones, and weak fault plane reflections. The results are analyzed further through seismic modeling. We conclude that the shallow fault segments affect the entire thickness of the Holocene alluvium and that the VFXF is active.
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Integrating High-resolution Shear Wave Seismics and Outcrop Data:A Case Study from Northern Germany
Authors Christian Brandes, Ulrich Polom and J. WinsemannShear wave seismic surveys allow a detailed assessment of the facies architecture and structural style of the Emme Delta in northern Germany. We combine outcrop and seismic data. The individual architectural elements that form the delta body were defined on the basis of their external geometry and the internal reflector pattern. Outcrops and borehole data were used to relate the seismic facies to the sedimentary facies. Special emphasize was placed on identifying faults, based on the reflector pattern. Faults are imaged as transparent lines that offset the reflectors. Syn-sedimentary faults can be indentified based on the wedge-shape of the growth strata. The faults have planar to slightly listric geometries and show vertical offsets in a range of 2 to 15 m. They form small graben and half-graben systems, which locally show roll-over structures. The fill of the half-grabens has a wedge-shaped geometry, with the greatest sediment thickness close to the fault.
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Seismic Reflection Surveys Using an SH-wave-type Vibrator Across Active Faults
Authors T. Kurahashi and Tomio InazakiThis paper describes the results of seismic reflection surveys conducted using a horizontally polarized shear (SH) wave-type vibrator. In the study, post-migrated CMP profiles of seismic reflection processing were produced to characterize subsurface structures across both the Asahiyama flexure and the Kozu-Matsuda fault. The throw of the top reflector enabled estimation of the cumulative vertical offset in the bedrock across the fault, and refraction tomography processing also revealed the SH wave velocity structure across it. The velocity structure in the subsurface around the fault decreased to 300 or 500 m/s. This was considered to be the result of unfavorable geological conditions with a low shear modulus. Against this background, SH-wave seismic reflection surveys are strongly expected to be very useful for acquiring images of bedrock across active faults, approximating the depth of bedrock, and identifying dataset signal anomalies that may indicate unfavorable geological conditions. These benefits are owed to the lower speed and shorter wavelength of SH waves.
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S-wave reflection profiling: Applicability and demonstrated use in Denmark at site and regional scale
Authors Kerim Martinez, Jos A. Mendoza and Andre PuginMulti-component reflection methods have gained acceptance for near surface mapping during recent years. Two case studies from Denmark employing shear wave reflection at different survey scales are presented. The first case study is a small site scale investigation to image the near surface lithology of a contaminated site. Here the S-wave reflection mapping was employed to update the Conceptual Site Model. The second application is a regional scale investigation with the aim to supplement mapping of unconsolidated sediments in buried valley structures as the mapping of these geological units is a primary objective in the hydrogeological mapping in Denmark. In both cases the method was utilised to obtain more detailed information on structures at the very near surface. Continuous advances in shear wave acquisition and processing methods contribute to increased applicability of shear wave reflection profiling in near surface characterisations.
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