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68th EAGE Conference and Exhibition incorporating SPE EUROPEC 2006
- Conference date: 12 Jun 2006 - 15 Jun 2006
- Location: Vienna, Austria
- ISBN: 978-90-73781-00-9
- Published: 12 June 2006
1 - 100 of 462 results
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Lambda-Rho Processing - A tool to Reveal Full Hydrocarbon Potentials
Authors T. H. Larsen, C. Ojo, S. Gemelli, P. Licalsi and M. AtkinsRegional analysis of a 5,716 well log database from the Gulf of Mexico allows prediction of AVO response, as well as prediction of velocities useful to processing geophysicists. Regional trends are derived from depth profile plots of well sand / shale velocity histograms.
Four major sub-regions were delineated, based on these profiles:
1.Lower and Middle Miocene Shelf,
2.Upper Miocene through Pleistocene Shelf,
3.Upper to Middle Slope, and
4.Lower Slope.
Strong velocity inversion is common in the geopressured Miocene in the deep Lower and Middle Miocene Shelf region. The present deep water areas shows a slower velocity increase with depth throughout the lithologic section than is seen on the shelf above geopressure, but has a much narrower range in variation than is seen on overpressured rocks on the deep shelf. The Lower Slope appears to have a greater spread in sand and shale P-wave velocities than are seen in the Upper to Middle Slope areas.
This analysis also allows prediction of the velocities which should be seen by the processing geophysicist. Some features of the velocity functions seen are those usually associated with multiple reflections, and as such, often discounted by the processor.
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AVO and Seismic Processing Implications from a Regional Database of Velocity and Other Acoustic Rock Property Trends
Authors H.R. Nelson, S.D. LeRoy, L.R. Denham, P.J. Desai, M.E. Guthrie and M.A. DunnTo better understand the physical characteristics of sedimentary deposits in Lake Geneva, we acquired and processed very high resolution seismic reflection data. Accurate amplitude measurements were obtained after correction for the frequency response of the hydrophones which were individually calibrated. In a first part, we present the acquisition and the pre-processing done on these data to correct the amplitude. In a second part, we migrate the data using a preserved amplitude pre-stack depth migration, and then apply a post-migration processing in order to correct for residual move-out. Finally, AVA analysis enables to differentiate sedimentary unit boundaries.
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AVA Analysis of Very High Resolution Seismic Data for the Study of Sediments in Lake Geneva, Switzerland
Authors D. Hammami, A. Egreteau, F. Marillier and P. ThierryThis paper continues the studies presented in this conference by Loizou et al. (2006), where we have compared the AVO analyses from four wells in the west of Shetland: Foinaven oil well (204/24A-2); Laggan gas well (206/1-2) and two prospect wells (204/17-1 and Assynt 204/18-1). In this study, we apply the spectral decomposition to the data from these four wells and provide further evidence that there are also differences in the spectral characteristics between the four wells. While Foinaven and Laggan Class III AVO anomalies are consistent theoretical predictions for frequency-dependent AVO behaviours. However, the results from the Assynt prospect 204/18-1 and another prospect 204/17-1 show rather complicated behaviour in the iso-frequency sections that cannot be fully explained. In summary, though the amplitude anomalies seen in the two prospects were originally interpreted as to be similar to the Foinaven, but our study indicated they are different in both the AVO behaviour and the spectral characteristics.
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AVO Analyses from Four Wells in the West of Shetland - Spectral Decomposition
Authors E. Liu, M. Chapman, N. Loizou and X.Y. LiGeological models are currently used to aid AVO-analysis, usually thick-layered. In an actual thin-layered sub-surface medium, the AVO has some specifics, ignoring which may lead to errors in predicting hydrocarbon reservoirs. In the resonant frequency range periodic thin-layered stack, AVO inversion on the basis of the linearized Shuya formula produces an estimate of the effective Poisson coefficient much lower than one of a separate gas-saturated layer. Also, in the low-frequency range an effective Poisson coefficient estimate is much higher than one in case of a separate gas-saturated layer. Within a frequency range close to the resonant frequency (tuning thickness) for a thin-layered stack, favorable conditions occur for predicting multi-layer hydrocarbon reservoirs from the AVO-analysis. At the same time, disregarding absorption may lead to interpretation errors. A finite difference solution for the elastic wave equation and the Haskell-Thomson method in its visco-elastic variant were used to perform the investigation.
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AVO for Pre-Resonant and Resonant Frequency Ranges of a Periodical Thin-Layered Stack
Authors N. Marmalyevskyy, Y. Roganov, A. Kostyukevych and Z. GazarianA new method for computation of seismic AVO attributes such as intercept and gradient, is proposed. By combining detailed sedimentological modeling with well logs, we compute alternative net-to-gross and porosity logs. The method is developed for reservoirs consisting of ultra-thin sand-shale layers, as for instance turbidite reservoirs.
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Seismic Modelling from Ultra-Thin Layered Reservoirs
Authors A.M. Stovas and M. LandroAs we are running out of oil, and the oil price is reaching new hights, the oil industry is increasing the focus on exploration and production of heterogeneous reservoirs. In this paper we focus on the rock physics of shaly sands, and how different types of clay configurations will affect the rock stiffness and pore fluid sensitivity.
Laminated sands and shaly sands with pore-filling clays will have different fluid sensitivity. We find that lamination will increase the Vp/Vs ratio for gas saturated sands compared to clean sands, in contrary to sands with pore-filling clay, where the Vp/Vs ratio will be relatively less affected by the clay content. This is related to the reduced shear effect induced by the micro-scale clay lamina.
Next, we study the effect of net-to-gross and scale on fluid sensitivity using the Backus Average method. Here we also observe an increase in Vp/Vs ratio. Gas saturated thin-bedded sands will have Vp/Vs ratios similar to oil-saturated clean, homogeneous sands. This is related to the patchy saturation induced by the geologic heterogeneities. We also study the effect of anisotropy on the fluid sensitivity of heterogeneous reservoirs.
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Seismic Fluid Prediction in Heterogeneous Reservoirs
Authors P.A. Avseth, A.J. van Wijngaarden, T.A. Johansen and G. MavkoAs we are running out of oil, and the oil price is reaching new hights, the oil industry is increasing the focus on exploration and production of heterogeneous reservoirs. In this paper we focus on the rock physics of shaly sands, and how different types of clay configurations will affect the rock stiffness and pore fluid sensitivity. Laminated sands and shaly sands with pore-filling clays will have different fluid sensitivity. We find that lamination will increase the Vp/Vs ratio for gas saturated sands compared to clean sands, in contrary to sands with pore-filling clay, where the Vp/Vs ratio will be relatively less affected by the clay content. This is related to the reduced shear effect induced by the micro-scale clay lamina. Next, we study the effect of net-to-gross and scale on fluid sensitivity using the Backus Average method. Here we also observe an increase in Vp/Vs ratio. Gas saturated thin-bedded sands will have Vp/Vs ratios similar to oil-saturated clean, homogeneous sands. This is related to the patchy saturation induced by the geologic heterogeneities. We also study the effect of anisotropy on the fluid sensitivity of heterogeneous reservoirs.
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Depth Trend and the Characteristics of PS AVO
By H. XuGonzalez et al. (2003) & Xu et al. (2005) showed the application of PS Elastic impedance (PSEI) for lithology and fluid prediction. To understand the effectiveness of this approach in relation to the target depth it is necessary to analyze the typical characteristics of PS AVO in a compaction trend framework. In this paper we will review the typical depth trend of sand and shale properties in a sedimentary basin and discuss the characteristics of PS AVO in several unique depth zones.
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Use of Rock Physics Principles for Inversion of Pre-Stack Seismic Data
Authors A. Mukherjee, H. Xu and N.C. DuttaFull waveform pre-stack inversion of seismic data usually provide a more accurate and reliable estimate of the elastic properties of the earth over conventional AVO analysis, as it can account for the contamination of seismic amplitudes from other wave modes. However as in all other types of inversion pre-stack full waveform inversion is also sensitive to the starting model and other apriori information. Conventionally well logs available in the area are used for this purpose. However, dipole sonic log in most cases is not available due to cost and P-wave sonic and bulk density logs are not available in the shallow parts due to large holes. In this abstract, we present a general rock physics based technique for constructing pseudo logs and then use them to build our initial models for pre-stack waveform inversion of seismic data. The pseudo-shear sonic log calculation is based on the work by Dutta and Wendt (1993). Another set of pseudo-logs are based on mechanical compaction theory and rock physics based velocity porosity relationships. We test inversion results for both the techniques on well log synthetic from deep water Gulf of Mexico.
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Physical Modeling of AVO Responses
Authors B.J. Evans, A. Wandler and C. LinkSeismic amplitude versus offset (AVO) methods are a well established practice for the direct indication of hydrocarbons, and are proven using both numerical modeling and field data. However, from a laboratory stand-point, AVO techniques have not to date been demonstrated in practice. This paper presents a first case of a physical model which was used to practically demonstrate the use of AVO for the separation of a hydrocarbon (oil) from pure water or brine. The physical model was also used to demonstrate how AVO cannot be used to separate water from a brine (30,000 ppm NaCl). A test using dissolved CO2 in water showed that an amount of 0.1 mol% was inadequate for seismic detection. The physical model was also used to demonstrate the complexities of the oil/gas/water mix, where it was possible to show how under certain circumstances, gas bubbles can remain trapped between oil and water.
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Moveout Stretch Implications for AVO
Authors P.R. Williamson and E. RobeinThe Zoeppritz equations for AVO, and their various approximations, apply strictly to a single isolated interface between two half-spaces. In practice this is almost always not the case, and effects known as AVO tuning are observed due to the apparent change in the time-thickness of beds on recorded traces with offset. While NMO or migration should equalise these time thicknesses across all offsets, the tuning effects are maintained by wavelet stretch. This stretch cannot be meaningfully avoided by 'non-stretch' processing, which simply corresponds to the isolated reflector paradigm. Meaningful AVO analysis, can, however, be achieved by effectively equalising the wavelet across all traces.
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Quantitative Calibration of Seismic to Wells and Probabilistic AVO
Authors M.F. Bee, E. Rietsch, D. Pankhurst and J. MagillWe present deterministic and probabilistic methods to quantitatively calibrate pre-stack seismic data to well data before AVO analysis. We then show how to use the calibrated seismic data with probabilistic AVO methods to analyze the prospectivity of a step-out exploration prospect several kilometers away from well control with the goal of identifying and quantifying hydrocarbons.
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Identification of Upper Cretaceous Volcanics Using AVO Attributes; Santos Basin, Brazil
Authors S. Klarner, R. Culpan, R. Fontana and B. BankheadThe deposition of the main reservoir unit in the Santos Basin, the fluvial to shallow marine Upper Cretaceous Ilhabela sandstones, took place during a period of active basaltic volcanism. The volcanic rocks have been partly eroded and subsequently deposited in the reservoir. This has been the cause of a complex diagenetic history. The results are locally occurring sandstones with complex lithologies and elastic properties which differ from the basin trend (Klarner et al, 2005). In order to predict and interpret the amplitudes and AVO behaviour of the Ilhabela reservoir it is essential to map the occurrence of the volcanics as well as the transport direction of their erosional products. We make use of the fact that the volcanic related lithologies display a significantly higher Vp/Vs ratio than the embedding clastic sequences. In this paper, an AVO approach is presented which helps to identify volcanic rocks in the section.
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Improved Seismic Imaging of Deepwater Turbidite Channels - A Case History from Offshore Angola
Authors S.P. McHugo, M.F. Francis, A. Cooke, N. Woods and J. EnglishExisting seismic data and appraisal drilling in the lower Congo basin show evidence of significant sandstone reservoirs in the tertiary section, formed by deepwater turbidite flows. The challenge is to develop and manage these complex reservoirs. To delineate the reservoirs, it is important to identify the fine details of the geometry of the reservoir sands and locate the structural and stratigraphic trapping mechanisms. The cost of drilling development wells in this area and the complex nature of the reservoirs make reflection seismic data a cost-effective tool in reservoir management. Thickness resolution obtained from existing seismic data in this area is in the order of 19 m A new survey was acquired in 2003 in an effort to obtain higher resolution.
In this paper, we describe the planning, acquisition, and processing results of a high-resolution point-receiver seismic survey. The survey was acquired with the objectives of mapping the thin sand units associated with turbidite sand channels, to provide long offset data not present in the existing data and to assess the benefits of point-receiver acquisition.
Results indicate that the objectives of the project have been met through acquisition and high-fidelity processing of point-receiver seismic data.
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Porosity and Shale Volume Estimation for the Ardmore Field Using Extended Elastic Impedance
Authors A.M. Francis and G.J. HicksDeterministic seismic inversion and extended elastic impedance (EEI) have been used to obtain quantitative estimates of porosity and Vshale over the Ardmore Field. The optimum EEI angles corresponding to porosity and Vshale were determined from the well logs, together with a lithology indicator. The prestack seismic data were then projected to the Chi angles corresponding to these three petrophysical indicators and deterministic inversions were performed to obtain three broadband EEI volumes. Three-parameter linear regressions were then performed to estimate quantitative porosity and Vshale volumes from the three EEI volumes. Regions of High porosity and low Vshale have been identified which may suggest possible future drilling locations.
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Prediction of Resistivity Using P and S-wave Properties from Prestack Seismic Inversion
Authors H. Xu and N.C. DuttaIn this paper, we study the prediction of resistivity from seismic data, based on resistivity-velocity relationships calibrated from well logs. Previous efforts in this area have included predicting resistivity from seismic amplitude or seismic-derived P-wave velocity. Here we present the prediction of resistivity from both P and S wave properties (P-impedance and Poisson’s ratio), which can be derived from prestack seismic inversion. The results can be used for identification or upgrading prospects in a mature field where resistivity logs are abundant.
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The Development of Low Temperature Tem Squid Systems for the Geosciences
By C.L. Le RouxSuper-conducting Quantum Interference Devices (SQUIDs) are tiny sensors that detect and measure very small magnetic fields. As part of an ATD-GRG research project, the Institut für Physikalische Hochtechnologie (IPHT) in Jena, Germany, have developed a Low Temperature SQUID (LTS) ground Transient ElectroMagnetic (TEM) system for Anglo to further strengthen the company’s mineral exploration capabilities. A brief history of the technology development is illustrated with results from various field tests. Early field trials conducted in Germany in 2002 showed good promise, but some system problems. Partial redesign and good applied science led to successful field testing and comparison of LTS, HTS and conventional coil receivers in Sweden in 2003. Further field tests on the Western Australian Nickel belt in 2003 and 2004 proved the system’s field-worthiness and that using liquid Helium as a coolant poses no serious logistical problems even in such a harsh environment. Undisputed proof of superior signal-to-noise capabilities over HTS, Fluxgate and coil sensors was again evident as well as the advantages of using LTS sensors for detecting conductive targets at depth or below conductive cover, hitherto a severely limiting constraint on exploration for conductive ore-bodies. Because of the better S/N stacking time is reduced and production is 4 to 10 times faster depending on the environment. Some spurious system response problems were more prominent during tests in resistive terrains in South Africa, but have subsequently been solved. The LTS TEM SQUID system has now been recognized as a major breakthrough with potential to give Anglo exploration teams a significant strategic advantage over competitors. An agreement has been signed with IPHT that provides Anglo with exclusive rights to the project technology for a ten year period following its development. Three systems are being deployed by our base metal exploration teams in Australia and Canada, while a fourth will be delivered later in 2005 for on-going exciting development work in Southern Africa.
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The Interpretation of Potential Field Data Using Continuous Wavelet Transforms
More LessThe continuous wavelet transform has been used with much success in the analysis of non-stationary time series. It has been used much less frequently in the interpretation of magnetic or gravity data, although several approaches have been tried. A simple method of obtaining location and depth estimates of gravity and magnetic field sources is suggested here, For gravity data the method uses wavelets based on the integer-order horizontal derivatives of the gravity anomaly from a point source (the Poisson kernel). For magnetic data the wavelet is based on the integer-order horizontal derivatives of the analytic signal of the anomaly from a step or a horizontal cylinder. The method is compared with Euler deconvolution, and is demonstrated with synthetic models and on gravity and magnetic data from South Africa.
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Contributions to the Gravity Field of Southern Africa from Crustal Thickness and Seismic Velocity Variations
Authors S.J. Webb and D.E. JamesAs a result of the Kaapvaal Project we now have unprecedented coverage of the crustal thickness and details of the seismic velocity variations in the tectosphere beneath southern Africa. By using these data and reasonable density relationships we can calculate the contribution of each of these components to the overall gravity field of southern Africa. These gravity modeling results confirm the suggestion that the high seismic velocity keel beneath southern Africa has a lower density than surrounding mantle material and is consequently highly depleted; a result in agreement with the xenolith data obtained from kimberlites. We estimate that the 1% seismic velocity variation observed between on and off craton leads to a 1% variation in mantle density due to compositional variation. This low density keel is vital to counterbalance the effect of the thinner than average crust that is observed beneath the Kaapvaal and Zimbabwe cratons. Thus in regions where the Archaean craton boundaries may not be apparent from geological mapping, seismic studies and gravity modelling could assist with delineating potentially cratonic regions with diamond potential.
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New Palaeomagnetic Data from the Main and Upper Zones of the Bushveld Complex
Authors S.A. Letts, T. Torsvik, L. Aswal and S. WebbThe Bushveld Complex (BC) has been the subject of many palaeomagnetic investigations since 1959. Despite these studies, systematic inconstancies have been found between the palaeomagnetic findings and well constrained ages determined for the Bushveld Complex. One concern is the large spread in pole positions previously determined for the different zones of the BC. This has been interpreted in prior studies to indicate that the Bushveld was emplaced and cooled below the Curie temperature of magnetite over a time span of 50 Ma. This inconsistency has prompted the current re-investigation of the palaeomagnetic results.
New palaeomagnetic data collected in the Main and Upper zones of the Eastern and Western limbs of the BC, yielded palaeomagnetic poles that eliminated the spread in the apparent polar wander path. This observation is in agreement with precise age data, constraining the time period of emplacement of the BC. Fold tests applied to each zone yielded statistically positive results supporting a primary magnetic signature and indicate that the complex was intruded in a near horizontal position.
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Finding the Edge of Salt Via a Dual-Velocity Flood
Authors J.E. Anderson and C.M. MarcinkovichImaging an overturned salt edge with turning waves often requires large apertures, long recording times and a sediment velocity profile that appropriately increases with depth and that is unobstructed by other salt bodies within the aperture of interest, conditions that may not always be available in practice. In some situations, data that may not meet all of the turning-wave-image criteria can be used to find the salt face via a dual-velocity-model flood technique similar to a vertical-seismic-profile (VSP) proximity survey. In this case, the reflectors that truncate against salt are imaged at their truncation point in the correct position, helping to define the salt face.
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How Many Angles Do We Really Need for Delayed-Shot Migration
By J.T. EtgenWhether you can use a sparse set of source angles in delayed-shot migration, or not, depends on how well your actual set of sources approximates (or can be made to approximate) an unaliased “antenna”. If you have a well sampled source antenna, then sparse angles can be used to create high-quality images since you can transform your data into the equivalent delayed-line-source experiment. If your collection of sources does not satisfy this requirement, then you may have to use a large number of angles to construct artifact-free images.
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Measuring Reservoir Compaction Using Time-Lapse Timeshifts
Authors P.J. Hatchell and S.J. BourneTime-lapse timeshifts refer to the differences in two-way seismic travel times that are frequently observed in the analysis of time-lapse seismic surveys. One source of timeshifts originates inside the reservoir interval as a result of changes in the pore-fluid properties that alter the seismic velocity. Another is from changes in seismic velocity and layer thickness that occur both inside and outside of the reservoir as a result of reservoir compaction and stress and strain redistribution in the surrounding formations. Timeshifts induced by changes in fluid properties are always zero above the top reservoir reflection event and constant below the base of the reservoir. These fluidinduced timeshifts can be significant (for example, when gas is released as an oil passes through bubble point) and are routinely calculated using Gassmann or similar theories and are not the focus of this paper. The compaction-induced timeshifts have opposite gradients on the inside and outside of the reservoir. Within the reservoir, the reduction in layer thickness and the expected increase in seismic velocity will reduce the seismic travel time across these layers. Outside the reservoir, the decrease in reservoir thickness is exactly balanced by surface subsidence and rock expansion. The expanding overburden produces increased layer thickness and slower seismic velocities that increase the seismic travel times. Observations on real time-lapse seismic data over compacting reservoirs show that the positive timeshifts that accrue in the overburden are larger than the negative timeshifts that accrue inside the reservoir (the sign convention chosen is that positive timeshifts result when the seismic travel time increases). The amount of overburden elongation cannot exceed the amount of reservoir compaction. So if the change in velocity were simply proportional to the change in vertical strain, the reduction in travel time through the reservoir would exceed the increase in travel time though the overburden. The net effect would be a negative timeshift below the reservoir. Instead positive timeshifts are observed below compacting reservoir indicting velocity reduction per unit elongation strain significantly exceeds the velocity increase per unit contraction strain. Using simple models of the velocity-strain response it is shown that time-lapse timeshifts are proportional to the stretching of the overburden layers and that this is highly correlated with the reservoir compaction. The net result is that time-lapse timeshifts are a good measurement of the reservoir compaction.
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Definition of Depositional Geological Elements in Deep-Water Minibasins of the Gulf of Mexico Using Spectral Decomposition in Depth Domain
Authors R.H. Tatham, P. Montoya, W. Fisher, R. Steel and M. HudecSubmarine channels, large scours, distributary channel-lobe complexes, turbidite fan complexes and many other components of deep water depositional systems in the central Gulf of Mexico were successfully imaged and mapped using spectral decomposition in the depth domain. When this powerful tool is applied along an interpreted seismic horizon, a better definition of stratigraphic architecture is obtained.
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Natural Perturbations of Shared Earth Models
More LessNatural Perturbations of Shared Earth Models (SEMs) are introduced and demonstrated. SEMs, such as the Compound models developed at Norsk Hydro, contain representations of natural geological entities (compartments, formations, fluids, (geo)logical rules etc). Natural Perturbation of the entities (deformation, translation, rotation etc.) can be performed involving only very few degrees of freedom. Perturbations, exemplified in the paper, are run individually, in series or parallel. A special entity within the Compound model (the perturbation structure) holds the order of the Natural Perturbations to be evaluated and can therefore be used in (global and joint) automatic optimization.
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Geostatistical Impedance Simulation after Prestack Depth Migration
Authors F. Schaub, A. Egreteau, P. Thierry and H. BeucherConventional reservoir characterization using geostatistical techniques to compute facies and porosity distribution usually begins from an estimation of the acoustic impedance. This impedance distribution is obtained using inversion technique as the stratigraphic inversion which works on prestack reflection seismic data [Tonellot & al., 2001]. The aim of this work is to take advantage of Amplitude versus Angle (AVA) inversion done after prestack depth migration to perform a depth domain impedance estimation constrained by AVA attributes. We propose to use geostatistical impedance simulation constrained by the migrated common image gather (CiG) and the skeleton of the structure obtained during the AVA inversion as well as the intercept and the slope sections.
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Neural Modelling of Core Permeability Data
Authors R.K. Fruhwirth and G. MaierIn this paper we show a neural network based method to develop a relationship between core permeability data and a set of other well logs to complete permeability information in well areas that do not contain that information. As an alternative to the common multi layer perceptron we use a special network architecture that has several advantages in approaching the optimal network size. In combination with parallel learning, automatic network growing and sophisticated stopping criteria that architecture allows an efficient and robust estimation of the optimal network for a particular problem. We use resistivity, gamma-ray, density, neutron porosity and the p-wave sonic logs as model input yielding a heuristic permeability model that allows completion of information in the area of interest yielding a synthetic permeability log. In addition convolutional network input in combination with principal component transform enhances the quality of the resulting model.
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Methodology for Integration of Small Scale 3D/4D Seismic Features in Reservoir Simulations
Authors N. Hadj Kacem, P. Berthet, F. Pivot and P. SamierGeological modelling of depositional facies and petrophysics is usually performed with a high vertical resolution and a low lateral resolution due to flow simulation constraints. The 3D/4D seismic may bring a high lateral resolution on reservoir characterization. To handle this fine scale information, the geological modelling requires a direct integration of well and seismic information. The lateral fine scale details of some good quality seismic attributes allow to locate small and meaningful reservoir connectivity. The deterministic method of integration, presented here, preserves seismic connectivity into the flow reservoir model. The method also offers a permanent link from seismic/geologic information to dynamic model. As soon as small heterogeneity is properly transferred into the flow model, the great benefit of this method is to reduce the history matching phase and to ensure more predictive dynamic model. In this paper, we illustrate a three step methodology allowing an automatic integration of geologically coherent seismic information within the reservoir model.
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The EU Research Strategy for Zero Emission Fossil Fuel Conversion
By P. DechampThe research strategy put in place by the Directorate General for Research of the European Commission in the field of the mitigation of CO2 emissions is first placed in the general context of the Commission energy policies. These actions are addressing the climate change issue, the introduction of renewable energy sources, the security of energy supply, the promotion of energy efficiency and the opening of energy markets.
The research policy of the Commission is mainly the European Research Area concept and its number one instrument, the Framework Programmes for research and technological development. The rational and the analysis supporting the ERA will be covered, as well as the structure and the new implementation modalities of the Framework Programme. Initial ideas for the 7th framework programme covering the years 2006-2013 will be debated.
CO2 capture and sequestration projects are organised to fit into the above-mentioned research policy, while contributing to the successful deployment of the Commission energy policies. These projects represent a portfolio of the order of 140 m€ of research and technological development.
Future perspectives, in particular in view of initiatives in the international arena and the Zero Emission Power Technology Platform, are finally outlined, addressing the need for an integrated European approach to develop and demonstrate CO2 capture and storage technologies for the benefit of the European citizens, industry and society.
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The ReMoVe project; Can We Guarantee Long Term Safety of Geological Storage of CO2
By E. ElewautSince 1990, Europe and the European Commission have invested a huge amount of research in the geological storage of CO2, The aim was initially to create an inventory of potential storage sites and volumes, later to build models to study the subsurface behavior of CO2 and the storage matrix and to forecast possible problems, later still to perform risks analysis at all relevant time scales.
Since Statoil started injecting CO2 on an industrial scale off-shore Norway in 1996, the focus has shifted to the monitoring of geological storage. Over the last ten years, experience has been acquired with both large scale projects (Sleipner, Norway; Weyburn, Canada) and more limited in scope, so called “subsurface laboratories” in Germany, The Netherlands and Poland. Two new geological storage projects (In Salah, Algeria and Snøhvit, Norway) now provide the opportunity to build on this work.
The CO2ReMoVe project started on 1 March 2006. It is being carried out under the umbrella and with the support of the European Commission’s Sixth Framework Programme for Research and Technology Development.
For five years, 30 partners from 12 different countries all over the world will invest EUR 15 million in an effort to bring together all relevant research and industry experience and know how in the field of underground storage of carbon dioxide.
The consortium of industrial, research and service organizations proposes a range of monitoring techniques, applied over an integrated portfolio of storage sites in order to develop:
1. methods for base-line site evaluation;
2. new tools for monitoring storage and possible well and surface leakage;
3. new tools to predict and model long term storage behavior and risks;
4. a rigorous risk assessment methodology for a variety of sites and time scales;
5. Guidelines for best practice for the industry, policy makers and regulators.
The recommendations from these international efforts will form an important step towards a worldwide consensus in licensing and certification of the storage activities in a number of geological media. These will include oil and gas reservoirs, coal seams and aquifers.
It can be expected that the project will achieve a better understanding with the policy makers and the public that CO2 can be safely transported and stored in the subsurface and that this storage can at all times be safely monitored. The project will also provide the assurance required for geologically stored CO2 to qualify for credits under the emissions trading mechanism.
It can be expected that the project will lead to greater understanding among policy-makers and the public that CO2 can be safely transported and stored in the subsurface, and that this storage can be safely monitored at all times the project will also provide the assurance required for geologically stored CO2 to qualify for credits under the emissions trading mechanism.
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Climate Change – The Challenge of the 21st Century
By K. RadunskyIssues to be addressed by the presentation:
- Energy scenarios by the International Energy Agency: Business as usual scenario, scenario with enhanced energy efficiency, scenario with additional carbon capture and storage;
- Possible impacts of climate change, worldwide and in Austria: temperature change, cryosphere, hydrology and water resources, terrestrial biological systems (including agriculture and forestry), human health, disasters and hazards;
- Policy responses
· The UNFCCC: its ultimate objective
· The Kyoto Protocol: its added value
· The European Union: its current position on climate change as reflected in council conclusions
· Processes started in Montreal in 2005
o Process linked to Article 3.9 Kyoto Protocol
o Dialogue under the Convention
- Elements of a possible future architecture: Outcome of the Climate Dialogue at Pocantico
- Carbon capture and storage
· Potential contribution: based on the Special report of the IPCC
· Issues for further consideration: based on the outcome of SBSTA24
- The timing challenge: based on recent scientific results (PIK)
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Controlled Source Electromagnetic Imaging in Shallow Water - A Case Study
Authors D. Andreis, L. MacGregor, J. Tomlinson and N. BarkerCSEM surveys have been used successfully in a variety of settings including West Africa, Southeast Asia, The Gulf of Mexico and the North Atlantic. Early surveys concentrated on deepwater areas. However they represent only a small proportion of potential exploration targets. In particular to date the method has been limited to relatively deep water (300m or more). This is because in shallow water, signals that have interacted with the air can have a severe impact on the recorded signals and can dominate the response. This noise (known as the 'airwave') dominates the CSEM response at source-receiver offsets which are sensitive to resistivity structure at the likely range of depths of hydrocarbon reservoirs. Researchers at OHM have been working on extending the operating envelope of the CSEM method into progressively shallower water. The approach adopted centres on characterising the physics behind the airwave phenomenon, and then using this knowledge to design approaches to data acquisition and processing that mitigate its effect. As with many geophysical problems, there is unlikely to be one silver bullet that will solve the 'airwave' problem in all circumstances, and so a range of concepts were investigated.
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Shell's Controlled Source EM Results Show Positive Impact
Authors D.J. Smit, S. Saleh, M. Costello, J. Voon and J. MoserIn this paper an overview will presented of the use of so-called Controlled Source Electro-Magnetic (CSEM) data acquired in deep water areas. Various results in different geologiocal settings will be used to illustrate its impact on a global exploration portfolio. We conlclude with a discussion on some future developments.
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A Fast and Rigorous 3D Inversion of the Marine CSEM Data
Authors M.S. Zhdanov and A. GribenkoMarine controlled source electromagnetic (MCSEM) surveys have become an important part of the offshore petroleum exploration. However, due to enormous computational difficulties of the full 3-D inversion, the practical interpretation of the MCSEM data is still based on qualitative analysis and relatively simple 2-D geoelectrical models of the sea-bottom structures. In this paper we present a new approach to 3-D inversion of the MCSEM data. It is based on the rigorous integral equation (IE) forward modeling and a new IE representation of the sensitivity (Frechet derivative matrix) of the observed data to the variations of the sea-bottom conductivity. This approach requires just one forward modeling on every iteration of the regularized gradient type inversion algorithm, which speeds up the computations significantly. We also use a regularized focusing inversion method, which provides a sharp boundary image of the petroleum reservoir. The methodology is tested on a 3-D inversion of the synthetic EM data representing a typical MCSEM survey conducted for offshore petroleum exploration.
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Anisotropic Depth Migration of Marine Controlled-Source Electromagnetic Data
Authors K. Hokstad and T. RøstenWe present a transversely isotropic depth migration scheme for marine controlled-source electromagnetic (MCSEM) data, based on Claerbout's well-known 45 degree equation from seismic imaging. The proposed scheme is applicable to MCSEM data acquired with a 2-D geometry, and is numerically very efficient. We show examples from field data acquired offshore Norway.
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Contribution to Oil Exploration and Development - A Successful Inductive Multi-Frequency EM Survey On-Shore Brazil
Authors C.A. Dias, O.A.L. de Lima, H.K. Sato and J.A.C. MoraesIn this work we discuss the results of an experimental study performed using a multi-frequency electromagnetic method over a mature oil field in Recôncavo basin, Bahia-Brazil. Five 1.8 km transects, 200 m apart, were surveyed over a selected oil reservoir block. The processed EM data are represented as cross-sections and maps of apparent resistivity and induced polarization parameter, using a consistent plotting procedure. All the sections, controlled by well logging data, allow to recognize the following geological features: (i) the oil sandstone horizons and their trapping shales; (ii) the oil-water interface and some zones of water invasion; and (iii) lateral electric contrasts representing fault zones. These results suggest the real possibility of the use of the spectral EM method in the direct detection of hydrocarbons, as well as for monitoring the efficiency of the artificial fluid injection used for secondary recovery. Also, this experiment brings about a further development in the inductive measurement of IP and introduces, for the first time, the use of this property in oil reservoir exploration and characterization.
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A 3D Near-Wellbore Imaging Algorithm for Triaxial Induction Data
Authors A. Abubakar and T.M. HabashyWe present a rigorous nonlinear inversion method for the three-dimensional (3D) imaging of the near-wellbore region employing multi-array triaxial induction data. The method used is the so-called Multiplicative-Regularized Contrast Source Inversion
(MR-CSI) method. There are two main features of this method. The first is that the method does not require the explicit solution of the full forward problem at each iteration step. The second is that the regularizer is included as a multiplicative constraint that allows the automatic and adaptive determination of the regularization parameter. These two features enable us to robustly solve an inverse problem with 65,536 unknowns using a single-processor present-day computer power.
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Inversion of Multi-Transient Electromagnetic (MTEM) Data
Authors B.A. Hobbs, G. Li, C. Clarke and J. LinfootThe multi-transient electromagnetic (MTEM) technique, for detecting and monitoring hydrocarbons, works by injecting a transient current into the ground (a source) and recording the potential difference between two receiver electrodes (the receiver) some distance, or offset, from the source. Field layout is similar to that of seismics, with many receivers per source and many sources per profile. After processing, the data for each source-receiver pair consist of the earth’s impulse response function and step response function. Two methods of inversion are described in this paper. The first uses a single value from each step response (the late time value) and transforms this to an apparent resistivity. These apparent resistivities are inverted in a 2D scheme to give a cross-section of resistivity versus depth. In the second method the full waveforms of either the step or the impulse response functions, are inverted simultaneously for several offsets at each common mid-point position. The resulting 1D resistivity models are collated to form a 2D resistivity image of the subsurface. The methods are illustrated with data from a demonstration survey over a gas storage reservoir.
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Fracture Imaging in Weathered Granitic Quarries Using GPR Data
Authors M.A.B.B. Barsottelli-Botelho and M.H. HeimerWe study a granite rock quarry, partially covered by a weathering cap, situated at the State of Bahia (Brazil). The aim was to understand the spatial distribution of fracture surfaces inside the rock and distinguish quickly intact marketable granite areas in order to improve quarry management. To interpret the real data, we use a finite-difference scheme to simulate 2D ground penetrating radar data by solving the damped wave equation. The synthetic GPR sections reveals how a conductive clayey overburden (20 mS/m) masks the real position of the fractures in the granite. The algorithm shows clearly the increase in attenuation with the increase of the frequency, and also with the thickness increase of the weathering cover; which is also responsible for the pull-down effect on reflectors below. The results of the modeling have a good agreement with the actual data.
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Normalized ElectroMagnetic Imaging (NEMI) for Controlled Source EM Evaluation of Hydrocarbon Prospects
Authors E.C. Morris, M.C. Sinha, L.M. MacGregor and D.W. OldenburgMarine Controlled Source ElectroMagnetic (CSEM) surveying is a powerful tool for mapping offshore electrical resistivity structure and in recent years has been developed as a DHI tool. Geophysical inversion and forward modeling are currently the standard methods of CSEM data analysis. However, due to non-linearity of the problem, these methods are computationally time intensive. We present a technique for fast imaging of thin resistive layers within a conductive background that enables a ‘first look’ at full CSEM datasets before imaging. The non-linear properties of the electromagnetic fields are used to determine the existence and lateral extent of thin resistive layers that may be associated with hydrocarbon-bearing layers. We present the results of synthetic datasets that show the imaging algorithm is successful at identifying the existence and lateral extent of a hydrocarbon bearing layer.
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Modelling Study of Airwave Contribution to the CSEM Signal
By K.N. MadsenThe Controlled Source Electromagnetic (CSEM) signal received in a three layer model (air, sea and seabed) has been split into contributions from the direct wave, the signal travelling through the seabed and the direct and indirect airwave by means of three modified models run in addition to the full three layer model. The components have been split for various cases of sea depth, seabed resistivity and frequency. The results show that the contribution from the indirect airwave is of the same order of magnitude as the contribution from the direct airwave and may be even larger. It is also shown that the relationship between the airwave and the signal that has travelled through the seabed is very different depending on whether the seabed resistivity is low or high. This may influence the choice of frequency for a CSEM survey.
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Accuracy of Sharp Inversion of CSEM Data Constrained by Seismic
More LessIt is well known that sharp inversion of CSEM data constrained by seismic can produce very accurate resistivity estimation. However frequently asked questions are: is the inversion result still valid if the depth and the thickness of the layers estimated from seismic interpretation are affected by some inaccuracy? How this inaccurate depth/thickness estimation propagates through the inversion of the CSEM data? In this paper we try to answer these key questions through synthetic tests and with application to real data where a well control exists.
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AEM Combined with TDEM - A Good Tool for Mapping the Quaternary in Rugged Areas
More LessOverdeepend alpine valleys are main players in alpine geology, and therefore the main operational theatre for applied geophysicst in Austria. One of the main geological questions to be tackled is the presence and/or size of hydrogeological regimes, mostly harboured in quaternary units. The combination of Air-borne electromagnetics (AEM) and transient-electromagnetics (TDEM) proofed successful as assistance for geological mapping activities in rugged, alpine areas. Hereby the TDEM method is applied to collect deeper information than provides by air-borne systems. The starting models for TDEM inversions are constraint by multi-electrode geoelectric profiles. However, strong anthropogenic noise in alpine valleys reduces the success rate of TDEM surveys to 70%. One case study is presented, showing the thinning out of a clay rich bottom set underneath a glacial terrace.
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Improving Signal-to-Noise Ratio Using Pseudo Random Binary Sequences in Multi Transient Electromagnetic (MTEM) Data
Authors D. Wright, A. Ziolkowski and G. HallWe present multi-transient electro-magnetic (MTEM) data using a step-function and a pseudo-random binary sequence (PRBS) as the source time function. We may recover the earth impulse response from either data set and integrate the result to obtain the corresponding step response. Results show that the PRBS waveform recovers the same result as the step in current but in a much shorter time.
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Modeling Responses of a Wide-Band Drill-Hole FEM Receiver
More LessResults from numerical modeling of a eletromagnetic drill-hole probe SAMPO are presented. The modeled quantities are in-phase, quadrature, amplitude and phase of the axial components of the magnetic field. All quantities are normalized by the value of the reference field. The model used in this study is a thin plate model. The results of modeling are also compared with field data. The interpretation rules derived from numerical modeling were found to be in good agreement with the field data.
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Magnetotelluric Study along a Profile Traversing the Korean Peninsula
More LessMagnetotelluric measurements were carried out along a profile traversing the Korean peninsula, which is an important tectonic link between the continental block of China and the island arcs of Japan, to figure out the mid-crustal structure of electrical conductivity. The 2-D inversion result shows a few highly conductive anomalies and highly resistive anomalies. The highly conductive anomalies are related with the basement rocks of the Cretaceous Kyongsang basin and the sedimentary and metamorphic rocks of the Okchon belt that is a representative orogenic belt in the Korean peninsula, while the highly resistive anomalies are connected with the Cretaceous granite intrusions in the middle part of the Okchon belt and the eastern part of the Kyongsang basin. Another interesting feature is the large phase anomaly exceeding 90° in the Okchon belt. Although a reliable explanation seems to be made by an electrically anisotropic structure, it will be necessary to treat a full 3-D modeling or an anisotropic modeling to understand the complex structure of this region.
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Structure of Flysch Cover as a Result of Detailed and Semi-Detailed MT Survey
Authors M. Wojdyla, M. Stefaniuk, T. Czerwinski and A. Maksymlish Carpathians where the efficiency of reflection seismic survey is poor as a result of complex structure of the flysch cover of the Carpathian overthrust. The main aims of the surveys were recognition of Carpathians structure, but results of them were applied to studying structure and lithological differenciation of flysch cover. The meseurements were applied in two variants. First, MT sites were located separately along profile line with a step 1–3 km. In each sounding site short, 400 m continuous profiling was carried out to eliminate effects of small near-surface resistivity inhomogenities. Second, long (up to 15 km) magnetotelluric continuous profiling was carried out as an EMAP method. The quantitative interpretation was based on 1D Occam inversion and 2D NLCG algorithm. The 1D interpretation based on the least-square inversion was made too. An initial model for LSQ inversion was created based on available geological data and results of other geophysical methods. There were two ways of recognizing resistivity of flysch cover during interpretation. The first one is using the EMAP algorithm, the second one - using 2D inversion. A combination of those two methods gives good geoelectrical model.
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NL Oil and Gas Portal - Your Gateway to Dutch E&P Data
Authors A.T. Ganzeveld, M.R.H.E. Peersmann, G. Remmelts and R.R.L. AllardSince the 1990's TNO has developed POSC-related E&P data repositories. As of 1997, the Dutch government commissioned TNO to develop a national data repository for all geological data of the Netherlands: DINO. In 2001, the first online interface on that database was launched, called DINOShop. The reliability as well as the vast amount of data contained in the DINO system resulted in a steady growing number of customers and system use, improving the overall quality of data and interface.
In order to endure oil and gas production in the Netherlands, the Dutch government tries to endorse independent operators to work in the Dutch area, offshore and onshore. To emphasize the meaning of this policy, the government wants to give new players a head start: effective regulatory framework and efficient licensing procedures, good infrastructure and easy access to E&P data. In Q4 of 2005, a start was made to create a DINO-driven portal dedicated to the oil and gas industry, the NL Oil and Gas Portal. Not only is the portal a gateway to all E&P related data, it contains petroleum province reference information (in a geological atlas) and gives access to interactive stratigraphic maps, profiles and 3D models.
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Integrating Scalable Vector Graphics (SVG) in a Web-Based Seismic Data Portal
More LessAn integrated web-based seismic data portal can effectively support collaborative research in the field of geophysics. In this context, user-perceived performance and usability of the system is of paramount importance. New technologies such as Scalable Vector Graphics (SVG) can improve user interaction, but need to be exploited in a judicious manner. Scope, difficulties and necessary paradigm shifts are considered from the experience of integrating SVG in an open-source web-based seismic data portal.
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Vertical Seismic Pitfalls - Problems in Archiving VSP Data
By E.L. JackVSP (Vertical Seismic Profile) data are the poor relation of the oil exploration industry. They are neither fish nor fowl, neither simply well log data nor simply seismic and because they do not easily fit into a database set up for either of their more famous cousins, they can prove troublesome to archive, or at least troublesome to archive in their entirety. This paper describes some of the problems attached to the archiving of VSP data, by examining the variety of data (calibrated logs, velocity tables and reports, in addition to the seismic data) involved in a VSP archive. The particular problems inherent in the various data types are addressed, with special attention given to the seismic data. A recent feasibility study on loading VSP Data to the Common Data Access (CDA) DataStore is described, with an analysis of some of the problems encountered. Finally recommendations are made for archive procedures and for the media most suited to allow access to all aspects of the VSP.
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Parallel Computers from the Seismic Processing Viewpoint
By E. KurinThe analysis of present-day parallel computer architectures is done in terms of their fit to processing/imaging seismic data. The classification of processing algorithms is suggested based on their demand for computing power, required physical memory, and a number of traces contributing to each output trace. We discuss the dependence of the optimal computer configuration on the algorithms applied, as well as on the given processing sequences.
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UN Framework Classification - Towards Global Harmonization of Fossil Energy and Mineral Resources Classification
Authors P. Blystad, S. Heiberg and J.E. RitterThe UN Economic and Social Council recommended in July 2004 the UN Framework Classification for Fossil Energy and Mineral Resources (UNFC) for worldwide use by UN Member States, international organizations and regional commissions. UNFC is a tool for harmonizing existing classifications and will be helpful in improving Energy studies, Resource management, Business process management and Financial reporting. The basic criteria are Economic viability, Field project maturity and Geological knowledge which are divided into categories and subcategories. A simple codification makes UNFC applicable universally and to meet the demand for a global code for fossil energy and mineral resources. Non-conventional energy resources are emerging as supply sources, some of these blurring the boundary between mineral and energy. Collaboration with the financial community supports the development of an International Financial Reporting Standard for extractive activities. Specifications, guidelines and case studies for the classification are being developed by the Combined Reserves International Reporting Standards Committee (CRIRSCO) and UN experts for minerals and by the Society of Petroleum Engineers (SPE) for petroleum. Aggregated classes of remaining recoverable quantities, like proved, probable and possible reserves are distinguishable in UNFC.
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Re-Developing Europe's Largest Onshore Oilfield - How to Justify New 3D Seismic for Schoonebeek
Authors M.A.M. van Dongen, H. Priebe, K. Pipping, G. Warren and R. TileyThe Schoonebeek Oil Field, is currently being considered for re-development. A critical element for this re-development is an optimal positioning of the horizontal injector and producer wells in the shallow Bentheim reservoir. The original 3D seismic comprises a large structural uncertainty at reservoir level, which is expected to be significantly reduced with new hires 3D seismic. The impact of the (reduced) structural uncertainties on the well performances has been simulated in Petrel and the outcome supported the acquisition of new seismic.
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Play Concepts Based on New Stratigraphic Methods - Two Examples from the Dutch
Authors O.A. Abbink, H.F. Mijnlieff, D.K. Munsterman and R.M.C.H. VerreusselIn the Northern Offshore of the Netherlands 'Upper Jurassic' strata are mostly limited to the Central Graben and Terschelling Basin. Outside the Central Graben and the Terschelling Basin only thin veneers of these strata occur on the fringing highs as the Schill Grund High and the Step Graben. The 'Upper Jurassic' strata are an important target for the oil and gas exploration. The geology of the non-marine to shallow marine strata is complex. The combination of lateral facies changes, repetitive log and facies characteristics in time, sea-level and climate changes, salt tectonics and structural differences hamper straightforward seismic interpretation and log correlation. A tectono-stratigraphic approach has led to the identification of three tectono-stratigraphic sequences. Sequence 1 (Callovian - lowermost Kimmeridgian) comprises the initiation of the Central Graben. Sequence 2 (lower Kimmeridgian - lower Portlandian) comprises the initiation of the Terschelling Basin. During sequence 3 (upper Portlandian - Ryazanian) the Dutch offshore is draped by a regional transgression. In this presentation the enhanced exploration potential resulting from the tectono-stratigraphic approach, is exemplified by two potential play concepts.
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Value of Seismic Information with Multiple Drilling Targets
Authors J.E. Bickel, R.L. Gibson, D.A. McVay, S. Pickering and J. WaggonerPrevious work has focused on valuing seismic information in the context of a go/no-go decision surrounding a single hydrocarbon target. While useful, this scenario fails to address the more common decision situation facing most oil and gas companies: the development of a multi-target drilling program in the face of constrained resources (e.g., capital, rigs, time). In this paper, we quantify the value of seismic information when facing some form of drilling or budget constraint. In so doing, we demonstrate that seismic information is potentially more valuable than has been shown before. We also highlight the importance of quantifying seismic accuracy in different geologic settings.
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Meso-Scale Heterogeneities in Reservoir-Scale Sand Injectite Complexes
Authors M. Vigorito, A. Scott, A. Hurst and J. CartwrightThe mesoscale structures (centimetres up to several metres sized structures) associated with the injection complexes have important effects on reservoir quality and performace. Some the mesoscale structures may act as permeability barriers while others can be preferential pathways for fluid migration with obvious effects on the vertical and horizontal permeability.
Field investigation on reservoir scale analogues demonstrates that these structures may occur in well-defined associations and that their style, geometry and distribution are related to the type and morphology of the architectural elements with which they are associated and, on a larger scale, to the internal and external geometry of the injection complex.
Mesoscale structures are recognisable both at outcrop and in core and provide insights on the main genetic processes. The structures can form or be modified during the injection process and/or during the following compaction and diagenesis of the intruded sands.
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Buried Quaternary Valleys Stand Out - Infill and Implications for Oil and Gas Fields of the North Sea
Authors T.B. Kristensen, M. Huuse, J.A. Piotrowski, O.R. Clausen and L. HambergBuried Quaternary valleys spread out beneath the formerly glaciated North Sea stand out from the surrounding sediments and provide significant challenges for seismic imaging, borehole stability and seabed installations. Through the use of a 1244 km2 3D seismic dataset and a few shallow borehole logs important details about the valley infill are revealed with implications for offshore operations. Two types of seismic infill facies are found in a number of different combinations within 12 buried valleys of very different sizes, and a conceptual model explaining the circumstances under which the valleys are likely to have been filled up are presented.
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Exploring for Stratigraphically Trapped Gas in Deep-Water Channel Deposits of the Austrian Molasse Basin
Authors R. Hinsch and S.M. HubbardGas is produced from deep-water sandstone and conglomerate of the Puchkirchen and basal Hall Formations (Oligocene-Lower Miocene) in the Molasse foreland basin of Upper Austria. The basin is mature, with >2000 wells drilled to date, and an extensive seismic reflection dataset that covers much of the paleo-basin foredeep has recently been acquired in the study area. Seismic stratigraphic analysis has revealed that deep-water sedimentation in the basin was dominated by a channel belt up to 5 km wide that transported sediment derived from the Central and Eastern Alps eastward along the basin axis (Linzer, 2001; de Ruig, 2003; de Ruig and Hubbard, 2006). New exploration models for stratigraphic traps associated with the recently developed channel model are necessary for future success in the basin. Channel abandonment and migration were important processes that resulted in a stratigraphic configuration consisting of coarse-grained sandstone and conglomerate overlain by channel and overbank mudstone. This represents an ideal reservoir architecture, including porous reservoir facies sealed by impermeable deposits, and may be an important play concept for future exploration in Upper Austria.
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Sequence Stratigraphy and Reservoir Architecture of Late Ordovician Glacially-Related Deposits, Murzuq Basin, Libya
Authors S.M. Ghnia and A. AzizThe Upper Ordovician deposits comprise two main stratigraphic units: Melaz Shuqran, and Mamuniyat, of which Mamuniyat Sandstones represent the primary reservoir targets in Murzuq Basin.
Sequence stratigraphic analysis of these deposits using well and seismic data led to the subdivision of the Melaz Shuqran into two third order sequences: Pre-Melaz Shuqran Sandstone - and Melaz Shuqran Seq.#2, and the Mamuniyat into three sequences. The Pre-Melaz Shuqran Sandstone represents the initial massive deposits in the deepest parts of the troughs (Palaeovalleys). The MZseq.2 shale comprises stacked, fining-upward parasequences. The Pusgillian Melaz Shuqran is separated by a stratigraphic break from the Upper Ashgillian Mamuniyat.
The Mamuniyat sequences correspond to a periglacial sediments and exhibit a cut and fill geometry related to successive glacial events during Hirnantian times. The Mamuniyat Sequence#1, interpreted from seismic, incised Melaz Shuqran. Seismic character suggests that it comprises massive deposits, probably coarse grained. The Mamuniyat Sequence#2 started with retrogradational parasequences culminating in Maximum Marine Flooding Surface. This was followed by progradational parasequences of the Highstand System Tracts (HST). The Mamuniyat Sequence#3 initiated with Transgressive System Tracts either very thin or absent. The HST locally displays poor reservoir quality which reflects variations in the energy of the depositional systems.
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Deep Play Exploration in the Mature Niger Delta Basin - An Appraisal of Risks and Challenges
Authors B. Olaleye, R.N. Basorun and R.N. BasorunSome attempts have been made in the past by some of the major operators to explore the deep plays with no exciting results owing to some overwhelming challenges.
A major risk factor in the branding of any deep prospect is the accuracy of the trap imaging. A spectrum of seismic methodologies has evolved over time in response to the issue of enhancing the image resolution of the deep plays.
The quality of reservoir at critical target depths is a fundamental issue in the evaluation of deep prospect for hydrocarbon volumes. The application of high resolution sequence and seismic stratigraphy has allowed the prediction of sand fairways and their environments of deposition. The evolution of petro-acoustic analysis and multi-attributes inversion in seismic stratigraphy has produced tools for the prediction with good probability, reservoir qualities and petrophysical parameters and their distribution within an area/volume of interest.
The primary challenges the explorationists face include the prediction of hydrocarbon presence in terms of type and volumes, pore pressure prediction and issues of completion and production engineering in an intimidating HPHT environment.
These challenges make deep play exploration a high risk venture as at now in the mature Niger delta basin.
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First Gas after 40 Years - The Geophysical Challenges of the Saturn Gas Complex
By S.D. ElamConocoPhillips has held Block 48/10b in the UK southern North Sea for some 40 years. The first gas production from the Saturn field in this block was achieved in September 2005. The main geophysical challenge of this block is to understand the sub-salt wall structure of the Rotliegendes reservoir. A variety of geophysical techniques have been applied, some of the earlier methods are briefly reviewed. The main emphasis of this presentation is the interpretation of the pre-stack depth migrated data and its subsequent depth conversion, including a subjective method of removing the artefact created under the salt wall overhangs. The results of the recent horizontal wells, together with the pre and post drilling interpretations are used to show the limitations of the seismic reflection data to predict the details of the reservoir structure beneath this salt wall. Finally, a brief review will be made of the two previously stranded gas fields that will be developed using these new Saturn facilities.
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Surface Seismic Techniques for the Recovery of Heavy Oil
Authors J.M. Garrity, M. Rajab, I. Al-Hakim, A.S. Smart, A. Shabrawi, A. Laake, W. Gamal El-Din, P.M. van Baaren, D.L. Barge and S.D. GriestThis paper shows the results from a number of experiments conducted using single-sensor and single-vibrator techniques to image heavy-oil sands at a depth of 300 m to 600 m in an existing oilfield in the Partitioned Neutral Zone between Kuwait and the Kingdom of Saudi Arabia. The aim of the experiments was to investigate whether surface seismic techniques can obtain the bandwidth required to be able to image the thick heavy-oil layers in the near surface in the presence of high-amplitude coherent noise that masks most of the reflected energy from the target. Further complications are introduced by the presence of high acoustic impedance layers above and below the heavy oil deposits and the presence of high ambient noise levels from the oilfield infrastructure.
An 800-m x 800-m 3D seismic grid was acquired over an area that will be the site of pilot long-term steam-flood in 200X. This heavy oil (18 API) reservoir currently produces 78,000 barrels of oil per day. For efficient steam injection, knowledge of the heavy oil reservoir is essential.
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Petrophysically-Constrained Simultaneous Inversion and Interpretation of a Deepwater Gulf of Mexico Field
More LessIn an effort to extract reliable density data from pre-stack seismic data, a new seismic inversion process has been developed that simultaneously solves for density (ρ), P impedance (Ip), and S-impedance (Is). Because all three parameters are linked and solved for simultaneously in this process, this type of inversion is referred to as a dependent inversion; that is, each term is consistent with the other two terms. Conventional inversion techniques independently solve for these three parameters, and the resultant density may or may not be internally consistent.
In addition to a better inversion algorithm, this process also utilizes petrophysical data to put constraints on the relationship(s) between velocities and density. The petrophysical data is also used to better constrain the porosity, allowing a more robust estimation of water saturations from the inverted density volume.
This new technique is applied to a deepwater Gulf of Mexico field, where conventional analysis of both pre- and post-stack seismic data proved to be problematic. This analysis allowed for reservoir fluids to be more accurately predicted. However, evaluation of the seismic data also shows the reservoir to be more discontinuous and complex than previously thought.
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Mapping Thin Sandstone Reservoirs - Application of 3D Visualization and Spectral Decomposition Techniques
Authors H. Lal, C.G. Rao, R.C.P. Saxena, J.L. Nangia, A. Sood and S.K. GuptaThe 3-D data of C-37 of Tapti-Daman sub-basin of Mumbai offshore Basin, India, have been evaluated for delineation and mapping of Oligocene Mahuva
pay sands. Post drill analysis of log and seismic data show that low impedance pay sands, embedded in high impedance shales, are separated in thin beds by limestone and/or shale streaks. Delineation of these sands by conventional interpretation methods is difficult because of thin and discontinuous occurrences, abundance of limestone streaks and limited bandwidth of seismic data.
3-D visualization of surfaces and volume attributes, neural network based seismic trace shape classification and spectral decomposition techniques have been applied with integration of well and log data. Amplitude attributes based on full bandwidth data were found more contaminated by thin limestone streaks. Spectral decomposition based iso-frequency sections and slices mapped areal extent and temporal thickness of pay zone. 3-D visualization of selected frequencies from instantaneous frequency volumes and seismic trace shape classification maps provided comparable image of the reservoir sands.
Marine sands near shore-zone areas during continued sea level fall are envisaged depositional system for the pay sands. The sandstones are spread over 90 km2 area in isolated sand bodies.
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Migration Velocity Analysis and Inverse-Ray Imaging of 3D Sedimentary Structures
By T.K. WangMajor horizons from stacked sections and velocity analysis of the time migrated sections along eighteen oblique profiles in the southernmost Ryukyu forearc region are integrated based on the inverse-ray method. Inverse-ray imaging starts from shooting three inverse rays at three non-collinear sources/receivers, propagating through structural layers and arriving at a planar reflector. All possible triangulations of the picked reflection times between neighboring profiles are applied for 3-D inverse-ray imaging of the Ryukyu forearc structures and in a layer-stripping approach. The results show that the top of the oceanic crust subducts deepest near the Nanao forearc basin and the maximum thickness of the accretionary prism south of the Nanao forearc basin is greater than 9 km whereas that south of the East Nanao forearc basin is only greater than 5 km. These may imply the most active subduction in the southernmost Ryukyu forearc region is probably along the Nanao forearc basin which is also supported by the active earthquakes below the Nanao forearc basin.
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Dense, High-Resolution Velocity Model Building Onshore; Application to a Major Fault System in Western Desert - Egypt
Authors M. Emile, R. Saba, A. El-Fiky, G. Bakry, S. Zimine, C. Pinson, P. Mitouard and V. VinjeThe long turnaround of the velocity model building phase in the past has been the main drawback of the depth migration when compared to the time migration. To compensate for this, CGG has recently developed alternative methods to the time consuming layer stripping approach. The method described here is based on dense, volumetric picking of the residual move-out followed by non-linear finite-offset tomographic update. One single layer is updated.
Earlier published cases on similar methodology have been mostly in marine environment. The case test in this paper is onshore, in desert environment and contains a strong lateral velocity variation (up to 1500 m/s) across a major fault induced by a throw reaching 3 km. An important question is whether the new volumetric, tomographic approach is able to represent the complexity of the velocity model needed for pre-stack depth migration. Land data is also typically noisier, which may cause problems for the automated, dense volumetric picking approach described here.
The results from this study show that the new VMB approach may also be feasible onshore. In addition to giving an improved imaging in the vicinity of the problematic fault zone, it is also considerably less work-intensive.
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Time Migration Tomography
By R.J. LeggottThe tomography algorithm presented will generate an optimum velocity model for time migration. The velocity model is computed to flatten every sample on every common image gather, whilst being constrained to be smooth and bounded, and using the correct relationship between residual curvature and velocity update. This avoids the inconsistency of vertical updating which updates the velocity differently from how the velocity is used for imaging. The resulting interval velocity model satisfies all available information and is shown to contain valid high resolution features. Consequently the updated velocity model gives an improved seismic image.
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Gravity and Magnetotelluric Survey of Sub-Zechstein Structures in Northern Poland
Authors M. Stefaniuk, C. Ostrowski, T. Wolnowski, A. Mickholz, P. Targosz, M. Wojdyla and I. KosobudzkaAn integrated geological model was built for the strongly tectonized belt of the Balaton-lineament in the Zala Basin, SW Hungary, to help further exploration and exploitation in this mature hydrocarbon sub-province. Investigation of core samples and interpretation of recently acquired 3D seismic surveys showed that the most important events of the tectonic evolution were Neogene strike-slip movements and a Pliocene/Quaternary basin inversion. Application of the geological model made it possible 1) to explain the peculiar behaviour of reservoirs; 2) to specify the rock volume and the reserves of known reservoirs; 3) to recognize and exclude a non-perspective sub-region from exploration; 4) and to discover a new hydrocarbon accumulation.
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Integrated Geological Model of Balaton-lineament as a Key to Success of Exploration and Exploitation
Authors A. Németh, J. Jósvai, I. Czeller and A. Szuromi-KoreczIn the Transylvanian Basin have been discovered more than ninety gas fields. The gases consist only of biogenic methane reservoired in the Upper Badenian, Sarmatian and Lower Pliocene rocks. The almost all gas structures are dome-shaped and most of them are controlled by salt diapirism of different intensities that suggest more mechanisms of the salt movement. To study the salt flow and the formation of the gas structures we used a simple model considering an elastic plate overlying a viscous fluid. In this model the viscous fluid is the layer of Badenian salt and the elastic plate is represented by the overburden composed of Upper Miocene and Pliocene deposits. The model shows that the early stages of salt movement have been due to folding of the overburden during compression in the Uppermost Sarmatian and Pliocene compressive regime and dragged by the Sarmatian deltaic deposits. The salt buoyancy was the main mechanism in the later stage of diapirism. The results are in agreement with the geological evolution of the basin, gas generation and accumulation.
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Relationships between Gas Accumulation and Salt Diapirism in the Transylvanian Basin
More LessThe Transcarpathian gas-prone sub-basin of the Carpathian and Pannonian petroleum provinces embraces the territory of West Ukraine bordering with Slovak Republic, Hungary, Romania, and the East Carpathians Mts. In terms of geology it is a depression of 20-48 km in width and 147 km in length. Only 3% of the region’s hydrocarbon potential are discovered to the date. Probable reserves of the basin are estimated at 112.3 Bcm of natural gas with specific density of probable reserves varying from 7-8 to 12-13 toe per 1 sq.km for different sedimentary complexes. Proven gas reserves of 4 discovered fields are 2.3 Bcm. According to exploration works there are more than 10 prospects and leads here with probable gas reserves of 23.5 Bcm that requires further seismic exploration and drilling. An economic advantage of this highly immature exploration area is a possibility to use abandoned wells drilled to the pre-Neogene basement as hot water producers to utilize hydrothermal energy and conversion of depleted fields into gas storages on the way of Russian gas to the West.
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Shallow Gas of the Ukrainian Transcarpathian - Its Status Quo and Exploration Perspectives
Authors L.F. Hafych, A.A. Kitchka and O.I. GafychSeismic data interpretation in geologically complex areas suffers from the shortcomings of out-of-date 2D data acquisition technique and time-domain processing, both of which are still predominant in Ukraine. With numerous examples from a variety of structural settings in onshore and offshore Ukraine, we demonstrate that prestack depth migration yields great improvements in seismic imaging and structural positioning as compared to poststack time migration. Because of the absence of any 3D survey in the majority of prospective arias in Ukraine, we are not able to take advantage of this data acquisition technique and have to use a 2.5D migration procedure. With examples from onshore Ukraine, we demonstrate that even such an out-of-data process allows out-of-plane reflection events to be greatly diminished, which favors more confident seismic data interpretation. This study is aimed to justify that a great improvement in exploration success in Ukraine may be achieved in the future by using a combination of 3D seismic acquisition technique and high-quality depth processing.
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Seismic Depth Imaging in Onshore and Offshore Ukraine - Case Studies
Authors A.N. Tiapkina, Z.Y. Voitsytski and R.S. KhomaEmissions of coalbed methane released by mining and related underground hazards are major problems for safe and efficient coal exploitation in the Donets Basin, which mines are among the gasiest in the world. There is a proved potential for coal bed methane capture and utilization as an emerging energy resource. Almost the all coal fields of the Donets Basin excluding most eastern superanthracite regions are characterised by high coalbed methane content in situ (from 8-10 to 25-37 m³/t). Some seams during underground coal mining demonstrate more than 100 m³ per ton of mined coal. In this paper, the catalogues of coal properties and methane content and outburst danger of coal seams in the Donbas were used to establish maps of vitrinite reflectance, methane generation, methane adsorption, and actually observed methane content of coals. These maps allow to understand migration of methane in the basin and to determine the areas that present a high potential for coal mine methane projects and industrial coalbed methane exploitation.
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Seismic Imaging of Imbricate Structures in Southwest China: A Case Study
More LessThe hydrocarbon prospects of the Western China Thrust Belt require solving a most challenging problem in seismic imaging --- irregular topography associated with a rugged terrain, complexity of the near-surface that includes high-velocity layers and outcrops with significant lateral velocity variations, complexity of the overburden, and the complexity of the target imbricate structures themselves. We present a case study that demonstrates a workflow to solve this challenging problem: (1) The near-surface model is estimated by nonlinear traveltime tomography that accounts for topography, and resolves lateral and vertical velocity variations. The near-surface corrections are based on wavefield datuming rather than shot-receiver statics. (2) The subsurface overburden model is estimated by prestack time migration combined with powerful interactive tools to pick rms velocities that are structurally consistent and laterally consistent, and the substratum model is estimated by half-space velocity analysis. (3) The subsurface image is obtained by prestack depth migration of shot gathers from topography.
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Comprehensive Application of Geophysical Techniques to Igneous Rock Study
By D.C. LiPresently, the igneous reservoir has become a new exploration target for hydrocarbon reserves and increased more and more attention from worldwide petroleum and geology experts. The concept of comprehensive application of different geophysical techniques can provide a new and effective approach for igneous reservoir detection and delimitation since it advocates the principle of solving problem by combining multi-technique and comprehensive interpretation.
Comprehensive application of gravity and magnetic data, electric data and seismic data provides a platform for jointed data processing and interpretation, consequently, reduces the interpretation ambiguity, and enhances the ability for special geological body study such as igneous rock distribution and lithology identification. The concept made the research on igneous rock in several large basins in west China extremely successful
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Fe-Chlorite Coating Evolution in Sandstones during Late Diagenesis - Is Temperature a Key Parameter?
Authors A. Ortenzi and E. Previde MassaraIn this paper, we describe a geometrical algorithm to solve the problem of the kinematics at basin scale. Two elementary models of geological deformation are considered: flexural slip and vertical shear. The combination of these models enable us to properly describe mechanical stratigraphy of a sedimentary basin sequence.
The methodology presented is 3D, reversible, simple to implement and fast. Validations are presented on two different examples: one synthetic to validate the algorithm, and a structurally complex model.
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Reversible 3D Structural Deformation for Basin Modelling
Authors M. Thibaut, N. Gibergues, J.P. Gratier and W. SassiWe use seismic tomography at time delays of first-arrival waves in order to solve this problem. Special 2D time fields t(õ,l) of reference waves are used for velocity inversion. It allows us to combine wave-arrival times into a unified system when observed with different details, and also when isolated travel-time curves are not correlated.
The developed technology of seismic tomography is common in different problem-solving in oil and ore geology and in studying deep Earth’s crust of Siberia. These problems are as follows:
- Interpretation of first waves recorded by CDP method in ore regions makes it possible to study the uppermost heterogeneous layer of the Earth’s crust and to forecast new ore knots and investigate their structures;
- Problem-solving in prospecting for oil and gas in West Siberia allows studying structures and compositions (in combination with drilling logs) of the oil-and-gas Paleozoic, which is rather difficult to do by CDP method;
- Illumination of the inner structure of the deep Earth’s crust and disclosure of wave guides, zones of disintegration, deep faults.
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First Wave Seismic Tomography in Ore and Oil Problem-Solving and Studying the Earth's Crust of Siberia
Authors A. Salnikov, V. Kuznetsov, V. Markov and V. TitarenkoAvailable surface and industrial subsurface data provide the basis for a general balanced cross-section from the Sahara platform to the Mediterranean Sea in Central Algeria. This section gives an overview of the whole Maghrebian orogen comprising from south to north: the intra-continental Atlas system; the External Tell system, the Flyschs domain and the Kabylides domain of European affinities. Restoration of the southern segment of the section, comprising the Atlas and External Tell systems, yields a minimum value of 40 km (20%) of horizontal shortening. For this part of the section, a four-step kinematic scenario, illustrates the main stages of the deformation history: 1. late Eocene "Atlas" deformation pulse, 2. early Miocene deposition of a thick flexural sequence, 3. middle-late Miocene emplacement of the Tell nappes and 4. late Miocene to present out-of-sequence thrusting. On this basis, a conceptual geodynamic model is proposed for the Maghrebian orogen. After the Atlas event, which just preceded the roll-back of the Tethyan slab, the model emphasises the role of subduction responsible for: flexuration of the subducting plate (slab pull effect); development of both accretionary prism and back-arc basin and late uplift linked to slab break-off.
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Post Cretaceous Deformation in the Tell-Atlas System in Central Algeria
Authors N. Benaouali-Mebarek, D. Frizon de Lamotte and F. RoureA seismic line is shot over a relatively flat area in North-East India that has a thrust fault in the subsurface. The quality of the seismic data does not allow adequate imaging of the thrust. Also, the surface expression of the thrust is too subtle to be used as a key for interpretation. To aid the interpretation, first arrival times have been inverted using a well-established regularized inversion algorithm and a shallow (~1.5 km deep) velocity-depth model has been developed. The thrust has been interpreted on the velocity-depth model based on the variations of the velocity contours. This interpretation can be converted in time and used to interpret deeper parts of the thrust in the seismic data.
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Velocity Modeling of Naga Thrust, North-East India
Authors P. Jaiswal, C.A. Zelt, A.W. Bally and R. DasguptaThe sedimentary basins of the Alpine-Carpathian mountain belt extend from France to Romania. These basins, some being known hydrocarbon provinces since the mid-XIX century, form important exploration areas in several countries. Although mature, the basins attract considerable interest, following the political changes of the early 1990s and application of new petroleum technologies. During the 2000-2005 period, new concessions were granted, 2D/3D seismic programs recorded, and over 250 exploratory wells drilled, resulting in some 145 successful operations. Bulk of the action was reported from Austria (51 wells), Poland (87 wells) and Romania (about 100 wells). Significant new discoveries of the period are Erdpress, Strasshof Tief (Austria), Jasionka, Terliczka, Trzebownisko, Stobierna (Poland), two Bilca wells and Fratauti (Romania). History of reserves additions (creaming curves) shows that new gas discoveries are generally small and new oil discoveries have been scarce since the mid-1970s. Apart from Poland, the arrival of a diachronous gas plateau is observed for majority of the basins since mid-1980s. The remaining hydrocarbon potential is believed to be principally associated with the prospects at greater depths, sub-thrust plays and stratigraphic traps. Application of 3D seismic is expected to help resolve internal flysch structures.
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Recent Exploration Developments in the Alpine-Carpathian Mountain Belt - Review of Successes and Potential
Authors H.D. Dobrova, P. Gawenda and E. KollyCentral Iran is a tectonically complex and under explored region. Recent seismic, gravity, magnetic and geological field studies allow to understand the tectonic style and the structural evolution of this region during the tertiary. Petroleum system and trapping potential are discussed.
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Structural Evolution and Hydrocarbon Accumulation in Central Iran, Qum Region
Authors J. Letouzey, D. Baghbani, J.L. Rudkiewicz, L. Cuilhe and K. KazemiThe study area covered a segment of eastern Pomerania close to the Gdansk Bay. The region is regarded as prospective for hybrocarbon exploration. The main objective of gravity and seismic survey was to support interpretation of reflection seismic data. The problem of seismic survey in the area includes a highly reflective complex of Zechstein evaporates, which screen the propagation of seismic waves, and locally thick complex of unconsolidated sediments of Pleistocene, which severely attenuates seismic energy. As a result, poor quality data especially from sub-Zechstein complexes were often obtained. Magnetotelluric and gravity measurements were made mainly along seismic profiles. A part of gravity sites were scattered between profiles. Magnetotelluric surwey was made in two ways: as isolated soundings located at crossings of seismic profiles, and continuous profiling covering selected parts of profiles. Results of integrated gravity and magnetotelluric interpretation supplement results of seismic survey in relation to Paleozoic and Precambrian formations screened by very elastic complexes of Zechstein evaporates. A great diversity of density and resistivity in thick Silurian measures was found. Major tectonic zones in Paleozoic and Precambrian rocks were reconstructed. Results of gravity and magnetotelluric data interpretation are generally in agreement.
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Accurate and Verifiable Interwellbore Fracture Attribute Predictions
Authors P. Eichhubl, S.E. Laubach, J.E. Olson and R.H. LanderThe continuity of fracture porosity is of fundamental importance for fluid flow in tight formations. Some authors emphasize the role of in situ stress on determining which fractures are conductive and which are not, where the maximum permeability direction in fractured media is expected to align with the maximum compressive stress for opening mode fractures or with the strike orientation of critically stressed faults. Other work has focused on the role of diagenesis that occurs contemporaneous with or after natural fracturing events. Precipitation of cements in a fracture can prop it open, occlude the porosity, or otherwise affect the stress sensitivity of fracture permeability. In this paper, we examine the potential consequences of the interplay between diagenesis and mechanics in the development of a natural fracture network using diagenetic models that incorporate fracture, geomechanical models of fracture population growth that incorporate diagenesis, and extensive observations of fracture populations in core and in outcrop reservoir analogs. We report patterns of fracture growth and decay that are generally applicable to fractured siliciclastic and carbonate rocks.
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Determination of Permeability Zones and Traps by Means of the Proni Filtration Method
Authors S. Smolin, G. Mitrofanov and L. SlepokurovaPresent investigations concern to processing and interpretation of surface seismic data. It is the new method using for oil-field tasks solution. In particular the Proni filtration method can be applied to a solution of the task of zones detecting with high permeability and fractured which can be conductive to fluids reservoirs and traps of unstructured forms. Possibilities of this approach are demonstrated on the basis of real seismic data processing obtained in Western Siberia.
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Fractured Reservoir Characterization Using Post-Stack Seismic Attributes - Application to a Hungarian Reservoir
Authors A.M. Zellou, T. Royer, G.C. Robinson, P. Zahuczki and A. KiralyEfficient development of fractured reservoirs has been notoriously difficult. This inefficiency arises from the difficulty in locating the fractures in the reservoir. By synergistically combining seismic data, containing the interwell information, with geologic and engineering data at the wells, we develop a fracture model that honors the various datasets and successfully predicts the location of fractures within the reservoir.
The reservoir consists of fractured metamorphic basement, with a hereogeneous distribution of both porosity and fractures. Thirteen wells exist in the field, 5 of which were used in building the reservoir model. Seismic inversion and spectral decomposition were applied to a 3D seismic survey covering the field in order to generate attributes used in the fracture characterization. In addition to the 4 post-stack seismic attributes, gamma ray, porosity, and resistivity models and 9 geomechanical attributes were generated for the fracture modeling. Using these 16 attributes and the fracture intensity at the control wells, a fracture model was built for the reservoir using the continuous fracture modeling (CFM) approach. Validation using the blind wells indicates that the fracture model was able to successfully predict both the highly fractured zones and the relatively unfractured zones within the reservoir.
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Fracture Characterization at Clair - Analysis of P-Wave Azimuthal Anisotropy in 2D & 3D Ocean-Bottom Data
More LessOver the past ten years, there has been a continuous increase in the use of 3D P-wave data for fracture characterization. In this study, we analyze P-wave azimuthal anisotropy in three 2D OBC (Ocean-Bottom-Cable) lines combined with a patch of 3D OBC data from the Clair Field, in the UK continental shelf (UKCS), in order to assess how seismic anisotropy can help improving fracture characterization in this field. The three 2D OBC lines are at 45-degree angle with each other, intersecting at a well position, and overlaps with the 3D survey. Analysis of the P-wave amplitude and velocity at the intersecting point shows significant azimuthal variation. P-wave interval velocities show about 10% variation in azimuth and the orientation is at N94oE, agreeing with previous studies. The 2D and 3D results are consistent at the intersecting point, and the joint analysis of 2D and 3D data increases the spatial coverage and improves the accuracy, further confirming the potential for using azimuthal variations of P-wave attributes for fracture detection.
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Dynamic Characterization of a Karstic Reservoir - A Field Case Study
By F. GouthWell tests are commonly recognized as a valuable source of information for the large scale characterization of the dynamic behaviour of a reservoir. However, when the level of heterogeneity is high, the interpretation becomes complex as the data convolute multi-scale responses. A key to resolving the complexity may be to isolate the wells evidencing a specific flow mechanism.
This paper focuses on a karst reservoir where both emersion & hydrothermal circulation occurred. The static model has been discussed in a previous paper (1) and more specifically the way fractures control karst development. In the present work, we focus on the dynamic data and show how the main features of the karst can be characterized by the use of well test and pressure build up data.
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Detection of Out-Of-Zone Growth in Multi-Stage Hydraulic Fracturing by Microseismic Monitoring
Authors L. Eisner, T. Fischer and J. Le CalvezOut-of-zone growth in multi-stage hydraulic fracture treatments can be detected by analysis of microseismic multiplets. This novel technique allows detection of the out-of-zone growth when we observe a repeated hydraulic fracturing of the part of the reservoir which has been fractured in a previous stage (i.e. cross-stage fracturing). The cross-stage fracturing is detected by automated identification of multiplets, i.e. microseismic events with similar source mechanisms and nearly identical locations. We applied multiplet identification to detect the cross-stage fracturing on two hydraulic fracture monitoring datasets (Canyon Sand and Barnett Shale Formations) one of which is described in this paper. We verified this detection method with the initial microseismic events locations. The cross-stage fracturing was detected only a few minutes after the first microseismic events were detected.
The computation cost of this new multiplet identification method is a fraction of a second per detected microseismic event, thus making this application suitable for real-time monitoring. The identification of the multiplets provides additional information to the locations of microseismic events and can be used to verify or justify change during hydraulic fracturing treatment. The early detection of the cross-stage fracturing could lead to real-time adjustments of the hydraulic fracturing.
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Dynamics of Microseismicity by Hydraulic Fracturing - An Approach to Interpretation
Authors S.A. Shapiro, C. Dinske and E. RothertSeveral basic dynamic processes related to propagation of hydraulic fracturing modify the effective stress in rocks and, therefore, are relevant for triggering of microseismicity. For instance, these are the creation of the new fracture volume, fracturing fluid loss and its infiltration into reservoir rocks as well as diffusion of the injection pressure into the surrounding rocks and inside the fracture.
Here, using real data we show that some of these processes can be seen from features of the spatio-temporal distributions of the induced microseismicity. Especially, the back front of the induced seismicity starting to propagate after termination of the fluid injection seems to be characteristic and informative for the aims of reservoir engineering.
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Statistical Characterization of Rock Strength Using Fluid-Induced Seismicity
Authors E. Rothert and S.A. ShapiroWe estimate the strength of fractured rocks in-situy by analysing fluid-induced microseismicity. Such an analysis is able to provide us with a completely new feature of naturally fractured rocks. The strength corresponds to the value of critical pressure in the pore space that must be exceeded in order to trigger earthquakes. We assume that during hydraulic injection experiments in boreholes, microseismicity is mainly triggered by a diffusive process of pore pressure perturbation. An analytical solution can be applied to find time-dependent pore pressure perturbations in rocks. Characteristics of the spatio-temporal evolution of microseismic clouds can be then used to estimate minimum and maximum pressures necessary to trigger earthquakes as well as the full spectrum of rock strength. We verify the approach using numerical data and apply it to real data of injection-induced microseismicity from Hot-Dry-Rock tests in crystal
line rocks and a hydro-fracturing experiment in sediments. We find that quite low critical pressures are characterising the strength of pre-existing cracks for all data sets analysed. The strength of the rock at sedimentary environment is found to be at least one order of magnitude smaller than for crystalline rocks.
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Multiwave Seismic Survey under Conditions of Salt-Dome Tectonics of the South of Cis-Ural Trough
Considered are results of applying the multiwave seismic technologies based on the use of different types of seismic waves: reflected, scattered waves and waves of infrasonic seismic emission of hydrocarbon beds to solution of basic problems of prospecting HC reservoirs under complicated conditions of salt-dome tectonics. The use of multiwave seismic technologies allows solve such problems as building a detail structural plan, mapping fractured zones and identifying oil and gas saturation of reservoirs. By way of example considered is solution of these problems for the south of Cis-Ural Trough, particularly for the Akobinsk area.
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The Use of X-Ray Tomography in Complex Research of Rock-Collectors of Oil and Gas in Residual Soil of Carbonates
Authors E.A. Zhukovskaya and Y.M. LopushnyakThe use of X-ray tomography by complex research of full-size core sample of oil-filled pre-Jurassic bauxite-like and strongly sideritised rocks of Urmansk oilfield (Western Siberia) allows to explain the absence of dependence between their physical and collector properties, and also between the structure of rocks
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Relocation of AE Events from a Compression Test of a Rock Salt Specimen by Coherence Collapsing Method
Authors H. Asanuma, A. Hotta, G. Manthei and H. NiitsumaThe authors combined the concept of the Collapsing method and multiplet analysis, and derived an algorithm that is a variation of the collapsing method (Coherence Collapsing method). In the Coherence Collapsing method, the absolute locations of the multiplets are selectively located to the simplest structure, and the whole AE/MS cloud is optimized in the same manner as in the Collapsing method. Because the multiplets are related to the multiple slip of a fracture/fault, their locations are of importance to interpret the physical phenomenon. In this paper, we describe an application of the Coherence Collapsing method to the AE events from a compression test of a salt rock specimen and compare the locations with the distribution of the fractures in the specimen.
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Use of Reflected and Scattered Seismic Waves to Build Geologic Model of Riphean Reservoirs of East Siberia
Considered are results of applying Side-View Seismic Location method (SVSL), designed for mapping open fracturing based on scattered seismic waves, and structural 2D seismic based on Focusing Transformation of seismic wavefield for refining a geological model of the Riphean complex of East Siberia (Kuyumba oil field) and identifying fractured zones which are promising drilling targets. Proposed is a technique for identifying organogenic reef structures in the interval of Riphean complex. This technique allows materially improve the reliability of geological recommendations for selecting optimal exploratory drilling sites and produce oil at a maximum flow rate. Based on the use of information about a distribution of subvertical tectonic fracturing and location of organogenic structures submitted are recommendations for drilling exploratory wells
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Integrated Study Of Fracture Characterization Using 3D P-Wave Seismic Data in Southwest China
More LessHere, we present a case study of fracture detection using 3D P-wave seismic data from the Sichuan Basin in Southwest China. A major aspect of this study is the integration of outcrop, core and wireline logs with seismic data for reducing the uncertainties in the seismic results. The target is a gas reservoir buried at about 1700m in depth, and the reservoir rocks are tight sandstones with an average porosity about 2% only, and fractures are the main fluid pathways. Analysis of core and log data from 21 boreholes reveals that there are two major sets of fractures in the study area striking northeast and northwest, respectively, with an average linear fracture density about one fracture every two metres. We have processed and analyzed 50 square kilometres of 3D P-wave seismic data in order to evaluate the fracture characteristics between the boreholes. The seismic data is of average quality. Nevertheless with carefully-calibrated processing, the final fracture orientation and intensity maps estimated from the amplitude attributes compare reasonably well with the regional pattern in the area, and the seismic results at the well locations are consistent with the borehole results.
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Spectral Attenuation Analysis in a Mexican Mature Oil Field
Authors L.C. Ramirez, L.C. Ramirez and R. del ValleSeismic attenuation analysis is used to distinguish changes in the spectral and amplitude characteristics of the seismic signal with the purpose of identifying the presence of fluid and fractures within the rock system. The analysis of such chances can be used as a tool for characterizing rock properties and for understanding the behaviour of wave propagation in a complex environment composed by pores and cracks containing fluids. The study is carried out using high-resolution reflection data obtained from a mature fractured carbonate reservoir near the northeast coast of Mexico. Production from this reservoir is declining considerably. For that reason, a horizontally drilling program is considered. The result obtained from in situ measurements indicates that the spectral changes and attenuation anomalies are related to the presence of hydrocarbons on the fractured reservoir rocks; however, such anomalies are also related to the highly fractured areas due to wave scattering. The seismic attenuation patterns associated to productive zones helped to identify new potential areas and in assisting for horizontal drilling targets.
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Benefits of Full-Waveform Modelling and Inversion. A Case Study from the Polish Basin
Authors M. Malinowski and S. OpertoIn this study we present the workflow and results of modelling the 3D wide-offset data acquired in central Poland during the GRUNDY 2003 seismic experiment. Previously those data were modeled using more "conventional" approach, like reflection processing and the traveltime tomography. Here we focus on the application of the frequency-domain full-waveform tomography for the interpretation of such kind of seismic data. We consider this method as a tool for obtaining both the structural image and a detailed velocity field in single step without the need for performing prestack migration or forward ray-tracing modelling. The validity of our results was tested by the comparison with well velocity survey.
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Elastic Parameter Estimation from the 2D Waveform Inversion of a Look-Ahead Walk-Away VSP Survey
Authors M.A. Roberts and S.C. SinghPore pressure in sediments beneath salt in the Gulf of Mexico varies widely creating a potentially dangerous and difficult drilling challenge. The elastic parameters are key to identifying many attributes, but in this paper the elastic parameters are being estimated with the aim of predicting the pore pressure in the sedimentary layer immediately below the salt. The elastic parameters have previously been estimated using an AVO type approach. In this paper we investigate the ability of full waveform inversion to estimate the P-wave and S-wave velocity models from a walk-away VSP in the context of a salt dome. Results demonstrate the ability to further localize the position of the bottom of the salt and extract velocity information beneath the salt.
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Comparison of Regularization Techniques for Waveform Inversion
More LessWe compare different regularization techniques of the steepest-descent directions appearing in waveform inversion using a backpropagation technique. In the waveform inversion using the steepest-descent method, we can have better convergence to a true velocity model by regularizing the steepest-descent directions properly. The regularization can be done by using the diagonal of pseudo Hessian matrix instead of using the approximate Hessian matrix that appears in Gauss-Newton method but is too expensive to calculate. We can apply the regularization to inversion algorithms in two different ways. One is to regularize the steepest-descent direction at each frequency independently. The other is to regularize the steepest-descent direction summed over entire frequency band. The former plays a role of equally distributing a weight to the steepest-descent direction at each frequency. For the conventional waveform inversion, the former gives better results than the latter. We also applied the two regularization methods for the logarithmic waveform inversion, which gives better results than the conventional waveform inversion for the original Marmousi data. Numerical examples showed that the logarithmic waveform inversion is not sensitive to the regularization, because the logarithm makes the steepest-descent direction at each frequency commensurate with each other.
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Conventional vx. Cepstral Full Waveform Inversion
Authors J.B. Bednar and C. ShinConventional vs full wavform inversion is usually a least squares process. In this paper we investigate the use of a logarithm or cepstrum style objective function and show that this approach is vastly superior to the more traditional method.
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Distant Relief Effect and Its Possible Impact on Large-Scale Gravity Interpretations
Authors J. Mikuska, R. Pasteka, I. Marusiak, M. Bielik and M. HajachIn gravimetry, the topography and bathymetry beyond the angular distance of approximately 1.5 degree from the point of calculation (we call it distant relief) is conventionally not accounted for. However, the availability of powerful personal computers as well as satellite digital elevation models, allows us to estimate the effects of those features on the measured gravity and thus also on the values of Bouguer anomalies. Using an approximate spherical Earth model, we have calculated distant relief effect as well as its vertical gradient within the territory of Central Europe. We show that although distant relief effect varies relatively slowly in the study area, it can occasionally be considered in the framework of large-scale gravity studies. On the other hand, vertical gradient of the distant relief effect is practically negligible.
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