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70th EAGE Conference and Exhibition incorporating SPE EUROPEC 2008
- Conference date: 09 Jun 2008 - 12 Jun 2008
- Location: Rome, Italy
- ISBN: 978-90-73781-53-5
- Published: 09 June 2008
401 - 500 of 556 results
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Automatic Velocity Analysis with the Two-way Wave Equation
By W. A. MulderMigration velocity analysis constructs a velocity model by focusing a migration image in terms of a redundant coordinate, for instance surface offset or a shift at depth between forward and time-reversed wavefield. The latter option is considered here in the context of two-way wave equation modelling with a frequency-domain finite-difference code. Gradient optimisation of a focusing cost functional automatically provides the velocity model. An experiment on multiple-free synthetic data confirms the validity of the method, as earlier demonstrated by other authors for one-way wave-equation propagators. In the presence of multiples, results may be less favourable. A variant is proposed that appears to give better results and can potentially be used to construct a starting model for more refined least-squares fitting of the measured seismic data.
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Seismic Modeling for Interpretation Verification and PSDM Workflow Design - A Case Study
Authors Q. Liao, W. Cai, M. La Cruz, L. Benkovics and F. OrtigosaWe used seismic modeling and imaging as effective tools to verify structural interpretation of a seismic section from geological complex area at an onshore field of Venezuela. By analyzing PSTM image problems and combined with a nearby well information we derived a new structure/velocity model, and re-produced the image problems by pre-stack time migration of the synthetic seismic data acquired from this new structure model. The comparison of PSTM images of synthetic data and the real data verified the new interpretation concept and confirmed that the target structure was distorted by the overriding thrust faults in the PSTM images and PSDM has to be adopted to produce accurate structure image. To select an adequate PSDM velocity model building workflow for this specific imaging objective the same synthetic dataset has been used to evaluate different PSDM model building approaches. Both grid and model based tomography workflows have been evaluated. From the comparison between PSDM images of the two different approaches we concluded that grid tomography without structure surfaces constraint is inadequate and model-based velocity update method is suitable to achieve the imaging objective.
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Towards a Unified Imaging Procedure for 2-D Land Multichannel Seismic Data
Authors P. Jaiswal, C. A. Zelt and R. DasguptaWe demonstrate that imaging of 2-D multichannel land seismic data can be effectively accomplished by a combination of traveltime inversion and pre-stack depth migration; we refer to the combined process as "the unified imaging". The unified imaging comprises cyclic runs of joint reflection and direct arrival inversion and pre-stack depth migration. From one cycle to another, both the inversion and the migration provide mutual feedbacks that are guided by the geological interpretation. In every cycle, a coefficient of congruence, j, measures the structural similarity of the interfaces from the joint inversion with their corresponding counterparts from the depth migration within the assigned uncertainties. The depth migration in every cycle is performed with the updated velocity model from joint inversion in that cycle. A value of unity for j implies that the unified imaging has converged. For j values grater than unity, the updated velocity model from the joint inversion and the interfaces from the depth migration in a given cycle are used as the initial model and interfaces for joint inversion in the next cycle. We apply the unified imaging to 2-D multichannel seismic data from the Naga Thrust and Fold Belt, India.
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Using FD Seismic Simulation for 3D Seismic Survey Design Complicated by Salt Dome Tectonics, Case Study
Authors P. Gofman, A. Kharitonov, R. Pevzner, M. Tokarev and K. StarkovThe main objective for the study was the design of optimal 3D seismic survey acquisition technique at Chervonoyarskaya field (Ukraine). The seismic exploration at the area is complicated by salt-dome tectonics and by the presence of a small town in the middle of the area that limits the use of seismic exploration. Case study covers overall survey design technique that was used and achieved results. The technique includes building a priory seismic and geological model and using FD simulation for choosing and proving optimal design.
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Inverse Q Filtering in 3D P-P and P-SV Seismic Data - A Case Study from Sichuan Basin, China
Authors S. Q. Chen and Y. H. WangIn this case study we will review a workflow from post-stack seismic data estimate the quality factor Q value, and do inverse Q filter processing with the estimated Q value. We use this work to successfully to improve the resolution of the three dimensional (3D) P-P and P-SV seismic data sets in the tight-sand gas reservoir in Sichuan basin, China. As the inverse Q filtering method is built on the data driving, we can not only enhance the resolution of the P-P seismic data, but also the P-SV seismic data. According to the interpretation results, we get much higher resolution seismic section and reservoir details.
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Estimating Attenuation by Using Marine Seismic Reflection Data
By A. KaslilarThe attenuation structure, inverse of quality factor (Q), in the sediments is estimated from the multi-channel seismic reflection data by using the wavelet modeling technique based on the constant-Q model. The estimated parameter is the effective-Q which is the sum of the anelastic absorption and the apparent attenuation. The aim is to investigate the existence of fault zones in the sediments by using the estimated effective-Q values. Two intersecting profiles of marine seismic shot data collected in Cinarcik Basin of eastern Marmara Sea, Turkey is used for Q estimation. In the time-migrated section of the N-S profile a local fault zone is observed while at the same location of the NW-SE profile it is not clearly visible. However the estimated effective-Q values of both profiles show local minima at the same location. It is seen that there is a correlation between the local minima of the effective-Q values and the faults and the effective-Q parameter can be used as possible indicator in determining the fault zones.
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Microscale Yielding as Mechanism for Low-frequency Intrinsic Seismic Wave Attenuation
Authors V. M. Yarushina and Y. Y. PodladchikovWe revisit the idea of microscale yielding being responsible for attenuation of small amplitude waves in a wide frequency range. We consider microscopic rate-independent irreversible deformation around cavities causing local stress amplification in pre-stressed porous media as a mechanism responsible for frequency independent attenuation. Following the effective media approach, we consider low porosity material containing non-interacting isolated spherical pores under cyclic loading by isotropic stress field imitating passage of a wave, and evaluate resulting dissipation in terms of quality factor Q. Assuming initial local microscopic stress state around the cavity at the yield, we show that even for small seismic strains attenuation can be high and independent of both frequency and strain amplitude.
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Seismic Signatures of Anisotropic Dispersion Anomalies
By M. ChapmanObservation from VSP data indicates that fractured hydrocarbon reservoirs often exhibit significant anisotropic attenuation and dispersion. It is known that, in the isotropic case, reflections from the interface between an elastic layer and a strongly dispersive are affected by a strongly frequency-dependent reflection coefficient, with the nature of the response being dependent on the AVO class of the interface. In this paper, we extend this analysis to the case in which the dispersion is anisotropic. We show that the frequency-dependence of two parameters, the vertical incidence reflection coefficient and the normal fracture compliance, control the behaviour. Once again, the modeled response depends on the AVO class of the interface. The strongest azimuthal frequency variations are expected for class I interfaces, where we find that the dispersion tends to boost the high frequencies of the reflections perpendicular to the fracture strike. It is hoped that azimuthal frequency analyses could improve our ability to characterize fractured reservoirs.
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An Extension of Linear Inverse Scattering Methods for Absorptive Media to the Case of an Absorptive Reference
Authors K. A. Innanen, J. E. Lira and A. B. WegleinWe cast and present inverse scattering quantities appropriate for the description of a two-parameter (P-wave velocity and Q) absorptive medium given an absorptive reference, and present a tentative procedure for carrying them out on measured seismic primary data. We note particularly that (1) this procedure involves a Q compensation component, and therefore must be expected to require regularization in the presence of noise, and (2) the formalism does not tend to our earlier non-absorptive reference procedure as reference Q goes to infinity; the absorptive, or the non-absorptive reference case must be chosen at the outset. These linear inverse results form part of a developing framework for direct non-linear Q compensation, or data-driven enhancement of resolution lost due to absorptive processes.
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Waveform Inversion with Data Correlation
Authors T. van Leeuwen and W. A. MulderA common way to obtain a suitable velocity model for migration is migration velocity analysis. These methods somehow try to focus the migrated image in the depth-domain. Recently, a method was proposed to perform the velocity analysis in the data-domain. And first tests using the convolutional model and NMO velocities proved successful. In this paper we want to incorporate this method in a waveform inversion scheme. Classical waveform inversion tries to fit the data in a least-squares sence, and it has been shown that it is difficult to get an update of the background velocity this way. By combining classical waveform inversion with the data-correlation method we hope to be able to invert for the background model as well.
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Near Surface Velocity Analysis in the Common Image Cube (CIC) Domain
Authors S. M. Al-Saleh and P. G. KelamisLow relief structures are increasingly important onshore exploration targets. Accurate resolution of these structures and reservoir characterization can be difficult because seismic reflections of these targets are contaminated with distortions due to complicated near surface geology. Downward continuation wave equation datuming techniques offer a solution to the near surface problem but they require a detailed knowledge of the near surface velocity. Near surface Migration Velocity Analysis (MVA) can be quite challenging due to the low fold of the data involved. In this paper, we integrate different MVA methods into the common image cube (CIC) approach. These methods include residual curvature analysis (RCA), depth focusing analysis, and common focus point (CFP). We use the CIC as a domain for near surface velocity analysis to address the low fold problem. For 2D data at a lateral position, instead of invoking the zero-lag imaging condition, we store other lags at each depth level. The result is a cube of data that offers more information than other methods. We illustrate two uses of this cube by applying wave equation datuming to a synthetic dataset, simulated from topography, using correct and incorrect velocity models, respectively.
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Testing Gassmann Fluid Substitution Using Sonic Logs and Core Measurements in a Sandstone Reservoir
Authors M. Grochau and M. GurevichWe have developed a workflow to test Gassmann fluid substitution by comparing saturated P-wave moduli computed from dry core measurements against those obtained from sonic and density logs. The workflow has been tested on 43 samples taken from a 45m turbidite reservoir from Campos Basin, offshore Brazil. The results show good statistical agreement between the P-wave elastic moduli computed from cores using Gassmann equation with the corresponding moduli computed from log data. This confirms that all the assumptions of the Gassmann are adequate within the measurement error and natural variability of elastic properties. These results provide further justification for using Gassmann theory to interpret time lapse effects in this sandstone reservoir and in similar geological formations.
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Synthesis of Realistic Petrophysical Logs Using Truncated Fractal Levy Flights
Authors A. -C. Bon, P. Thore and J. EscodaWe use truncated fractal Levy motion (fLm) to generate synthetic well logs, in order to reproduce more closely well statistics than with the commonly used Gaussian distribution. Four parameters are required to define the truncated fLm: alpha, which determines the shape of the fLm, C which is an equivalent of the standard deviation, H which corresponds to the strength of the spatial correlation, andlambda which is a cut-off value for the Levy distribution. We present a method to estimate these parameters from real well logs and an algorithm to generate realistic synthetic logs with the truncated fLm. An application to real data is shown.
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Scaling of NMR and Mercury Porosimetry Data on the Basis of Reservoir Parameters of Various Rocks
Authors E. Puskarczyk, J. Jarzyna, A. Wójcik and R. SemyrkaInvestigations aimed to calibration on Nuclear Magnetic Resonance (NMR)measurements and Mercury Porosimetry (MP) were performed on a big group of samples of various rocks. Measurements of the T2 relaxation time were done for hydrogen nuclei occurred in the media in pore space of rocks, in the bound water in clay minerals and in the hydroxyl groups in these minerals. Cumulative NMR signals were calculated and used for qualitative description of the porous space in rocks. Mercury porosimetry measurements were also done to obtain cumulative intrusion and cumulative pore area plots vs. pore diameter and incremental intrusion and incremental pore area vs. pore diameter. The results of both methods were correlated to find the corresponding anomalies for the scaling of the NMR outcomes T2 in the pore diameter and fracture widths D. The correlation equations for T2 and D were calculated for the full data file. The result equations were tested for the extreme values of diameter in the mercury porosimeter range. Results proved the significant role of micropores and microfractures in the porous space of the carbonate rocks examined and showed the big diversification of results for the Carboniferous and the Devonian carbonates.
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Influence of Structure and Cracks Distribution on P-wave Velocity Anisotropy in Rocks - Laboratory and Field Study
Authors J. Vilhelm, V. Rudajev, R. Živor, T. Lokajicek and Z. ProsPhysical properties of rocks are often investigated by laboratory methods. The extrapolation of the laboratory results anisotropy of P-wave propagation to larger rock units requires comparison with direct field measurements. The purpose of this contribution is this comparison between laboratory and field measured anisotropy of P-wave. Field measurements and rock sampling for laboratory tests carried out on the outcrop of peridotite massif in the Ivrea zone - north-western Italy. The direct surface seismic measurement of elastic waves velocity was realized by means of shallow seismic refraction method on base approximately 10m. Laboratory tests were realized on spherical samples with diameter 50 mm by using ultrasound velocity measurement in 132 directions under confining stress from atmospheric level up to 150 MPa. The common laboratory and field research can reveal reasons of anisotropy at different scales. Scaling factor is effected dominantly by different sampling size. Laboratory samples contain only microcraks, which represents nearly continuum with regard to ultrasound wave length (11 mm). Rock massif, however, contains beside mickrocraks also cracks with comparable size of applied seismic wave length (10 m).
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Fracture Mechanics - Fracture Toughness Determination
Authors T. Backers and O. StephanssonFracture Mechanics has great potential in solving rock mechanics challenges. Therefore software packages like FRACOD2D which make use of such models are being developed. Input to such codes are e.g. fracture toughnesses. This contribution presents a new laboratory method for determination of the resistance of rock to shear fracturing, i.e Mode II fracture toughness, KIIC, and compares it to Mode I (tensile) fracture toughness, KIC, values. The new testing method, the Punch-Trough Shear with Confining Pressure (PTS/CP) test uses core specimens and a confining pressure representing elevated overburden can be applied separately from the shear load. The experimental data presented gives KIC and KIIC values for some granitic rocks, marble, limestone and sandstones. Emphasis is put on the important influence of confining pressure on the Mode II fracture toughness.
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Fracture Mechanics - Examples of Applications in Rock Engineering
Authors T. Backers, O. Stephansson and I. MoeckRock strength and integrity can be described using fracture mechanics principles. Instead of using empirical relations, the explicit fracture initiation, growth and interaction leads to a fracture network in the rock mass which then defines the mechanical behaviour. These fracture mechanics principles are the basis of modelling software which is applied to different examples in this contribution. Using FRACOD2D, a laboratory compression experiment is modelled, the in-situ stress field is estimated from borehole breakouts, the influence of mud pressure on wellbore stability is analysed and hydraulic fracture growth is simulated. It is shown that fracture mechanics has great potential in solving rock mechanics challenges.
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Mechanically Induced Permeability Damage Due to Rock Proppant Interactions
Authors A. Reinicke, B. Legarth, S. Stanchits, E. Huenges and G. DresenHydraulic proppant fracturing technology is used for a wide range of problems from bypassing drilling induced near wellbore damage to increasing productivity of extreme low-permeable reservoirs. During production the placed proppant pack interacts mechanically with the rock matrix. This causes proppant embedment and grain / proppant crushing and leads to permeability damage at the fracture face. To investigate this mechanically induced fracture face skin (FFS) new laboratory equipment was used to quantify the permeability damage ratio at the fracture face and to locate the damaging events via acoustic emission (AE). High permeable Bentheim sandstone as well as low permeable Flechtingen sandstone was investigated. The tests point out that crushing and fines production starts at low stresses at the fracture face. This effects a permeability reduction at the fracture face up a factor of 67 compared to the initial rock permeability for high permeable rock. For low permeable rock the permeability reduction factor is about 7. The conducted tests give evidence that rock matrix proppant interactions induce a significant permeability reduction and leads to mechanically induced FFS.
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Velocity to Resistivity Transform for the Norwegian Sea
By L. HubertControlled Source Electro Magnetics (CSEM) is promising exploration technology, in that it has the ability to distinguish resistive hydrocarbon reservoirs from conductive wet sands in the subsurface. CSEM data is particularly powerful when combined with seismic and well data. Using seismic and well log data to aid in constraining an inversion of CSEM data may significantly improve the results of the inversion. This paper describes a new model for linking electro-magnetic properties (resistivity) and acoustic properties (p-wave velocity).
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Magnetotellurics in the Rub al'Khali, Saudi Arabia
Authors A. Al-Dulaijan, M. D. Watts and P. van MastrigtMagnetotelluric data were collected as part of a multi-disciplinary exploration program for Paleozoic non-associated gas in the southern Rub al-Khali Basin of Saudi Arabia. Data collection was difficult due to the presence of large sand dunes, but the use of specially developed buffer amplifiers helped to partially overcome the very high contact resistance. Interpretation of data was carried out using 3D inversion, and this images the basement structure well. The post-basement sediments show a local increase in resistivity above a positive basement structure. It is speculated that this might be due to porosity reduction (compaction or facies changes), or to a change in fluid resistivity (salinity reduction or hydrocarbon charging).
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First Application of Marine Magnetotellurics Improves Depth Imaging in the Santos Basin, Brazil
Authors P. P. de Lugao, S. L. Fontes, E. F. La Terra, A. Zerilli, T. Labruzzo and M. P. BuonoraRecent subsalt oil discoveries in the deep waters of the Santos Basin, Brazil, have received considerable attention due to the extent of their reserves and by the challenges in exploration and production in such environment. Recently, electromagnetic methods have re-gained attention and changes in technology are making them a powerful tool for challenging imaging environments. A first large Marine Magnetotellurics (MMT) survey was acquired in Brazil by WesternGeco Electromagnetics in cooperation with Observatório Nacional/CNPq and Petrobras. MMT data were recorded at 96 sites along three profiles. One profile extends approximately 148 km along existing seismic. The MMT data were processed and interpreted using an advanced integrated workflow. The main objectives of the survey were to assess the response and quality of MMT data in a wide range of water depths and test the ability of MMT to enhance seismic depth imaging by providing reliable information that will be used to constrain/improve the resolution of the velocity models. We show that the MMT data can clearly enhance resolution and reduce ambiguities of depth interpretation based on seismic. Work is in progress to enhance the MMT interpretation and apply the enhanced MMT model to develop an integrated depth imaging workflow.
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Contrast Source Inversion of Marine Controlled Source Electromagnetic Data for Hydrocarbon Prospecting
Authors T. Wiik and K. HokstadWe present an inversion scheme for controlled source electromagnetic (CSEM) data to picture anomalies in conductivity on a geophysical scale. The method is based on the scalar diffusion equation corresponding to the approximation of the vector wave equation governing electromagnetic wave propagation in conductive media in the ultra low frequency domain. The scheme is tested numerically with a homogenous background model.
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Gradient Calculations for 3D Inversion of CSEM Data Using a Fast Finite-difference Time-domain Modelling Code
Authors T. Støren, J. J. Zach and F. A. MaaøGradient-based 3D inversion of controlled-source electromagnetic (CSEM) data requires the gradient to a data-misfit functional to be computed within the volume where we seek to find a resistivity model that explains the observed data. Since 3D inversion typically requires more than 100 iterations in order to converge to a good model, fast modelling is important to make 3D inversion a feasible tool in advanced interpretation of CSEM data. We have previously presented a fast finite-difference time-domain (FDTD) modeling code which reduces the computational time of a typical modelling scenario by a factor of 40. In this presentation we show how we use this FDTD modeling to efficiently compute the misfit gradient. A benefit of this approach is that the gradient can be computed for several frequencies in one forward modelling thus saving valuable computational resources when inverting data from a large number of receivers. We present results showing that the gradients obtained are well-behaved. We also present results from inversion of synthetic data based on these gradient calculations showing that, for this specific example, a good result was obtained for the inverted resistivity model after relatively few iterations.
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Scenario Planning for Electromagnetic Surveying
Authors B. A. Hobbs, M. Kemper, M. Westwood and J. RutterThe Multi-Transient ElectroMagnetic (MTEM) technique is used to delineate resistive targets that may correspond to hydrocarbon reservoirs. Prior to actual surveys, feasibility studies are conducted to determine the probable detectability of the target of interest, set in the background resistivity structure where known or postulated. From the 2D model cross-section, resistivity profiles are extracted at positions along a profile. Modelling comprises determining the earth’s impulse responses for appropriate source-receiver offsets and these may be varied in the feasibility process. Two methods are then used to assess detectability. One exploits the amplitude of the impulse responses by plotting common offset sections. Shallow offsets illuminate targets near-surface, if they are addressable, whilst longer offsets see deeper. In an alternative method, the arrival time of the peak of the earth’s impulse response is used to determine an apparent resistivity. Values may be determined for all offsets at all selected profile positions and the result plotted as a 2D resistivity pseudo-section. Detectable targets are those that can be seen to correspond with the target reservoir of interest. Resolvability of individual targets within a sequence of overlapping stacked reservoirs on land and in marine studies will be addressed.
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RTP - A New Algorithm for Generation of 2D Resistivity Sections from MTEM Data
More Less1D inversion of electromagnetic, (EM), data is a fast, effective method for generating reasonable subsurface resistivity models. In order to be interpretable 1D EM inversions are normally collated into a 2D resistivity section. A common method is to place each model at a lateral position associated with the measurement. For Multi-Transient Electromagnetic, (MTEM), data the Common Midpoint, (CMP), of the source and receiver positions is usually used. This works well when we are able to invert the data in CMP gathers, however in the presence of complicated geology this is not always possible. In this case each transient must be inverted singly, resulting in more than one model per CMP. The new algorithm resistive target positioning, (RTP), uses all these 1D models and the array sensitivity of the MTEM acquisition to create a 2D resistivity section. This avoids the artefacts commonly found when generating a 2D section from CMP positioned 1D inversion models, and allows the use of a whole dataset.
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Frequency-domain 3D Borehole-surface Electromagnetic Modeling by the Volume Integral Equation Method
More LessThis paper presents the characteristics of electromagnetic anomalies using borehole-surface 3D modeling. The program used was developed by BGP on the basis of the volume integral equation. The modeling results show that borehole-surface EM method can monitor the variation of resistivity and thickness of reservoir during oil gas production based on the variation of electromagnetic anomalies. Although we have modeled several parameters, only two, resistivity and thickness, are described in the paper.
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Realistic 3D CSEM Modelling Based on Advanced Interpretation and Geomodelling Techniques
Authors F. Pivot, A. Price and J. N. FerryThe mCSEM (marine Control Source Electromagnetic) technique have now reached a level of maturity that it becomes necessary to identify ways to integrate them in the global 3D exploration workflow. As we want to build realistic models for feasibility testing, including all the necessary detailed knowledge generated by seismic and geological interpretation, we must develop methodologies able to map properly the complexities of the subsurface, and able to measure impacts of topology or scale changes. This paper describes such a methodology and its application to a case study in a turbiditic deep offshore context.
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Recovery Factors and Production Technology - An Overview
Authors J. Roelofsen and B. BastianWith an ever increasing demand to increase production it is more than ever important to understand how recovery from existing fields can be improved. A project between the Ecole Polytechnique de Lausanne (EPFL) and the industry has analysed the importance of the various factors controlling recovery, primarily of oil, and the efficiency of different technologies applied to extract hydrocarbons. Some 424 offshore producing fields were selected, representing some 140 billion barrels of oil-in-place. Oil gravity and reservoir characteristics like lithology, trap type and drive mechanism were analysed for different field types to determine common parameters for recovery. Albeit statistical analysis shows significant differences between reservoir types, the applied recovery technology is a more determining factor. Injection of water and gas is the most common recovery improvement method, with water injection being the most important. Drilling technology has evolved over time and examples are provided for two fields offshore Congo to demonstrate the effect of new technology like horizontal wells for production and improved injection schemes.
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Gel-technologies for IOR and Water Shutoff of High-viscosity Oil Pools
Authors L. K. Altunina and V. A. KuvshinovNovel physicochemical gel-technologies have been developed to improve oil recovery of high-viscosity oil pools. Presented are results of laboratory research and pilot tests. Use of gel-technologies employing inorganic and polymer gels at thermal-steam and cyclic-steam treatments in oil fields of Russia and China increases coverage by steam injection, decreases water cut of well production by 3-45%, increases oil production rate by 11-33% and decreases liquid production rate by 14-25%.
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Thermal Recovery in Kuwait - From Potential to Characterization
Authors T. E. H. Esmaiel, A. A. A. Al-Qallaf and F. Y. A. Al-TarkaitA large scale study (Al-Bahar et al. 2004) of Improved Oil Recovery (IOR) potential within Kuwait was performed by a team from Kuwait Oil Company and Kuwait Institute for Scientific Research. The study screened 10 IOR displacement processes in 81 reservoirs in Kuwait. The study comprised of chemical, thermal, and gas injection processes. This paper will highlight some of the findings regarding the thermal IOR processes in the screening study. These 4 processes are Steam Flooding, Cyclic Steam Flooding, Steam Assisted Gravity Drainage (SAGD), and In Situ Combustion. Steam Flooding passed the screening criteria in 6 percent of the reservoirs while In Situ Combustion passed in 16 percent of the reservoirs. The failure of a large number of the reservoirs to pass the screen will be the focus of this paper. An analysis of the critical failure parameters and the potential to overcome these parameters will be discussed.
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Chemical Flood IOR Potential in Kuwait - 10 Year Window
Authors F. Y. A. Al-Tarkait, T. E. H. Esmaiel and A. A. A. Al-QallafA large scale study of IOR potential within Kuwait was performed. The study screened 10 IOR displacement processes in 81 reservoirs in Kuwait. The study comprised of chemical, thermal, and gas injection processes. This paper will highlight some of the findings regarding the technical issues of chemical IOR processes to pass the screening study. These 4 processes are Polymer Flooding, Alkaline / Polymer (AP) Flooding, Surfactant / Polymer (SP) Flooding, and Alkaline/ Surfactant/ Polymer (ASP) Flooding. A highlight of the full study is shown in Table 1. The most glaring result is the failure of all the chemical floods in the 81 reservoirs studied. Following an analysis of the failure of these processes, recommendations on potential future chemical IOR process applications in Kuwait will be discussed. To illustrate the future of chemical floods in Kuwait an unidentified sample reservoir is water flooded for 5 years and then subjected to a Polymer Flood. An ensemble of runs is performed to determine that there is substantial potential for chemical flooding in the near future. Furthermore, a look into the changing landscape of polymers is briefly discussed with their potential future applications in mind.
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Geothermal Exploration Using Integrated 2-D MT and Gravity Surveys in Hungary
Authors H. Tulinius, L. Ádám, K. M. Strack, G. Yu and L. F. HeAll available data were used to outline the most prospective areas for geothermal electrical production and space heating in Hungary. Before locating wells to be drilled for geothermal utilization more data was needed. It was decided to use integrated MT and gravity survey in additional to the existing data in an attempt to further strengthen the possibility of drilling successful wells. Survey lines were proposed on the geosciences data and optimized for the clients concerns. The spacing for the 2-D MT lines was 1000 m, but 250 m for the gravity points. When the surveying was finished for a given line the geological cross section is derived and used for constraints on the MT and gravity interpretation.
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Geophysical Characterization of the Gross Schoenebeck Low Enthalpy Geothermal Reservoir
More LessAbstract The EU funded project I-GET is aimed at developing an innovative strategy for geophysical exploration of geothermal deep water systems. The strategy is to integrate all the available knowledge, from rock physics to seismic and magnetotelluric (MT) deep sounding. The magnetotelluric method is a natural-source electromagnetic method capable of imaging the subsurface electrical conductivity down to depths of several kilometers. Since electrical conductivity depends strongly on the presence of fluids, the magnetotelluric method is a very promising exploration technique for geothermal reservoirs. In this work we present results of MT experiments carried out in the study area which is located approximately 20 km north of Berlin. The MT data was collected along a 40 km-long profile centered on the well doublet and a second 20 km-long profile located 5 km to the east. The 2D inversion results show a good correlation of the resistivity model with tectonic structures. Several zones of high conductivity coincide with structural lows, probably due to sedimentation of more porous material or fluid accumulation. Two distinct conductors located at depths of 4-5 km could be related to a deep, highly fractured anhydrite zone.
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Detection of Tectonic Faults Using In-mine Geoelectric Methods
Authors M. Dobroka, T. Ormos, A. Gyulai, T. Sasvári and S. ZelenakIn-mine geoelectric methods – the geoelectric seam-sounding and geoelectric transillumination – were applied for detection of fault zones in a coal mine. The measured data were inter-preted using geoelectric tomography algorithm. An appreciable agreement were found between the location of tectonic zones predicted by the interpretation and those observed during the mining extraction.
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Experimental Exploration of Geothermal and Ore Mineralized Zones in Sudetes Mts in Poland with the Use of AMT Method
Authors M. Wojdyla, J. Farbisz, W. Klitynski and M. StefaniukThe area of the Sudetes comprising south-western part of Poland is considered to be prospective for geothermal water connected with zones of deep tectonic breaks and granitic massifs. The area is also known for numerous occurrences of lode type ore mineralization that have been exploited since the Medieval time. Taking into account the increasing role of renewable sources of energy and the need for discovering new ore deposits, the experimental geophysical survey were undertaken in the Sudetes. The general aim of the survey was the evaluation of effectiveness of audiomagnetotelluric method in recognising tectonic zones and connected with them geothermal resources and ore mineralisation occurrence. Some examples of application of audiomagnetotelluric continuous profiling in the Sudetes area are presented. Geophysical interpretation was based on 1D OCCAM inversion, 2D inversion and pseudo 2D EMAP transformation. Geothermal zones and zones of mineralization are clearly visible in resistivity cross-sections.
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Seismic Signatures of Temperature-dependent Geothermal Rocks at In-situ Reservoir Conditions
Authors M. S. Jaya, S. A. Shapiro, R. Ciz, D. Bruhn, Ó. G. Flovenz and H. MilschAn analysis of two rock samples, hyaloclastites and basalts, at in-situ reservoir conditions has been done to identify the role of temperature on the seismic velocity and attenuation. The goal is to present the result of using Gassmann equation within the framework of Biot’s poroelasticity for a fluid substitution analysis of geothermal rocks. The analysis of temperature-dependent wave attenuation is shown for hyaloclastites. The results show that P wave velocities decrease with the temperature rise in a systematic way. The general decreasing trend of seismic velocity towards temperature may be related to the fluid characteristics with the temperature. Using Gassmann equation it has been shown that the presence of steam bubbles can reduce the effective elastic property of rocks. The Q factor behaves surprisingly almost in the same way as the seismic velocity with temperature, except in the lower temperature range. The Q factor increase with the temperature is supposed to be a quick viscosity decrease. The later decrease of Q factor may indicate the presence of steam bubbles due to the further temperature increase. This finding demonstrates that the application of Gassmann fluid substitution modelling may be used for the characterization of geothermal reservoir systems.
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Seismic Exploration for VMS Deposits within the Paleoproterozoic Flin Flon Belt, Trans-Hudson Orogen, Canada
Authors M. Malinowski, D. White, C. J. Mwenifumbo, M. Salisbury, G. Bellefleur, D. Schmitt and B. DietikerThe Trans-Hudson Orogen forms the largest Paleoproterozoic orogenic belt of Laurentia. It is particularly known for its world-class volcanogenic massive sulphide (VMS) deposits, including Flin Flon mining camp.A program of seismic investigations has been implemented as part of the Targetted Geoscience Initiative-3 (TGI-3) to provide a basis for constructing a 3D geological model and refine the current conceptual exploration model for the camp, and ultimately to provide new drill targets. Rock property measurements, downhole geophysical logging and vertical seismic profiles acquired in advance of the main seismic survey demonstrated the expected reflectivity of the mining camp geology. The main seismic survey comprised a total of 75 km of high-resolution 2D seismic profiles and a 3D survey covering approximately 10 km2. The results of processing the vertical-component data for P-wave reflections reveal subhorizontal reflectivity associated mainly with the Missi metasedimentary complex and steeply dipping reflectivity associated with the polydeformed volcanic rocks, including the main rhyolite horizon which hosts the VMS deposits. Some important fault zones are also imaged.
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Time-lapse Shallow Seismic Reflection CDP Observations in the Area of the Water Penetration to Potash Mine
Authors T. V. Baibakova, I. A. Sanfirov and G. Y. PriymaResults of surface seismic reflection researches for different stages of the technology catastrophe development in potash mine area were presented. Water penetration place and dissolving directions were main targets. Every survey included observations for some profile lines with using source offset and without it. The equipment, acquisition data and methods of the interpretation were described.
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Geodetic Investigation of Torfajökull Volcano, Iceland (Best of SAGA)
Authors S. E. Scheiber, P. C. LaFemina, E. Sturkell and S. J. WebbCampaign GPS observations made from 2000 to 2006 at the rhyolitic Torfajökull caldera in south Iceland have been processed, using GIPSY-OASIS software, and analysed in an attempt to create a 3-D elastic half-space model of the interior of the volcano. Current seismicity, resistivity and tilt data for the volcano point towards a cooling magma chamber at 8 km depth below the western part of the caldera, and a shallower magma source in the southeast. The horizontal site velocities show a large effect due to the spreading eastern branch of the Mid-Atlantic ridge that passes through Torfajökull. Hekla volcano approximately 20 km to the northwest of Torfajökull, has been inflating since its last eruption in 2000 and is also influencing the site velocities to a small extent. The spreading ridge and inflation of Hekla volcano could be masking any smaller deformation due to the Torfajökull magma sources. Vertical velocity data shows an average uplift of around 15 mm/yr in the caldera. This uplift is most likely due to postglacial rebound, as well as high-temperature geothermal activity within the caldera.
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Sysif, a Low Frequency Seismic Profiler for Near Bottom Marine Geophysics
Authors S. Ker, Y. Le Gall, T. Marsset and P. LeonIfremer has recently developed a deep-towed seismic system designed for High to Very High resolution near-bottom marine seismic surveys. This paper presents this new tool which is dedicated to the study of deepwater geological objects especially geohazards. After a technical description of the system, we expound an overview of the complete workflow from survey design to amplitude preserved processing illustrated by data acquired during sea trials.
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S-wave Reflection Seismic Exploration of a Shallow Sediment Body - A Case Study at Alfbach Valley, Vulkaneifel, Germany
Authors U. Polom and M. PirrungHigh resolution S-wave seismic profilings were done in 2007 to determine the basement and the internal structure of a shallow fluvio-lacustrine Quaternary sediment body in the region Vulkaneifel in Germany. The investigations were done with the aim to explore the capabilities of the S-wave reflection seismic method over small and shallow sediment bodies prior to the definition of new well locations for further sedimentary analysis. The results of these first reflection seismic investigations in the area give detailed insights in the geometry and the internal structure of the sediment body down to 60 m in depth. The application of a small vibratory S-wave source combined with a S-wave land streamer unit leads to an excellent data quality and meets the requirements for successful seismic operation also in residential areas. During data processing, time migration was an important step to image details of the basement and to reduce diffractions near the base of the sediment body. Beyond the primary aims of the investigations, the quality of the raw data and the geometry of the structure enable further testing of other seismic migration methods to shallow S-wave reflection data.
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Hard Rock High Resolution 3D Seismic Investigations at Olkiluoto, Finland
Authors I. Ohman, N. Enescu, C. Cosma, C. Juhlin and E. HeikkinenOlkiluoto was selected as the site for the final disposal of nuclear waste in Finland. Currently, ONKALO, the access tunnel and underground research facility is being built at Olkiluoto. Since 1987, comprehensive geological and geophysical investigations have been performed at Olkiluoto for the detailed characterization of the disposal site area. Various seismic surveys were done, from surface and boreholes (Enescu et al. 2004), over a period of more than 10 years. A pilot high resolution 3D reflection seismic survey was acquired, for the first time in Finland, in 2006. High quality data led to very promising results, hence 3D seismic investigations were continued in 2007, over a larger area (Cosma et al. 2007). The 3D reflection seismic method proved instrumental for determining the geometry of rock features and ultimately building a geometrical model of the investigated rock volume, consistent with previous geophysical determinations in the area. Reflectors ranging from 100 m down to at least 3 km were imaged with accuracies of less than 10 m.
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Robust Use of AVO to Geohazard Assessment - South-east Asia Gas Field Case Study
Authors B. Paternoster, D. I. Knyazev and T. Des-VallieresTo reduce drilling risk around proposed sites during the development of the field complex integrated shallow gas risk assessment is performed. It includes automatic screening of the volume cross-validated by the interpretation followed by an innovative AVO approach to geohazard assessment.
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Water Bottom Channels’ Impact on Pre-stack Depth Migration on Elgin Field, North Sea
Authors J. Arnaud, S. Hollingworth, A. Woodcock, L. Ben-Brahim, C. Tindle and S. VarleyThis paper shows a case study where sea bed glacial channels have a strong influence on the imaging of the tilted blocks constituting the gas field located below 5000m. 2 models were built with the CGGVeritas tomographic software: the first without the channels, the second with the channels in the first 500 meters. The channels were input using a 1D method and then refined by tomography using the residual move-out of depth gathers down to 2000m. As velocity and anisotropy had to be found in those layers, additional iterations were necessary. The final result was a better structural aspect and a better imaging of the faults separating the panels of the field.
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Shot and Receiver Domain Iterative Direct Static Corrections and Their Application
Authors M. Z. Huang, Z. Y. Feng and D. T. ZhouThe near-surface structure in different areas features special complexity. The surface condition in this study area features Gobies, cliffs, gullies and mountains. Elevation static corrections fail in areas with gullies and cliffs due to rapid lateral variation of weathering layer. Refraction static corrections perform poorly due to the difficulty in picking the first break times of vibroseis data. A new method, shot and receiver domain iterative direct static corrections (SRD-IDSC), is proposed and applied in the study area. Compared to elevation static corrections, the proposed method can better resolve issues with mid-high frequency static corrections. The quality of imaged sections has been greatly improved and meets the needs of data processing.
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Study and Application of Tomographic Static Corrections
Authors Z. Y. Feng, Q. P. Ma, Z. H. Yan, Y. F. Zu and X. L. YangIn areas with severe topographic relief, complex near-surface structure, and thick weathered/sub-weathered zones, first break refraction static corrections often do not work properly to meet the needs of data processing. It is necessary to carry out a study of tomographic static corrections in these areas. Conventional tomographic static corrections, however, are mostly used for long wavelength static corrections and therefore do not fully improve the resolution of tomographic models. In this paper, we introduce a novel technique to implement tomographic static corrections by incorporating irregular grid tomography and fat-ray tomography with an attendant quality control method. Theoretical tests and practical data applications presented in this paper suggest that these new approaches solve the issues of static corrections successfully.
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Integrating Frequent Time-lapse Data into the Reservoir Simulation Modeling of the Valhall Field
Authors J. van Gestel, K. D. Best, O. I. Barkved and J. H. KommedalThe frequent time-lapse observations from the Life of Field Seismic (LoFS) system across the Valhall field have provided a wealth of new information. Time-shift and amplitude changes are matched to the predicted responses from the reservoir simulation model and used to reduce uncertainties and validate reservoir properties. Streamlined workflows are implemented to convert the reservoir simulation properties to a synthetic seismic response for any time range. A match quality factor between the observed and predicted responses is calculated based on a correlation function that quantifies the visual comparisons. This match quality factor allows us to quantitatively compare multiple LoFS time ranges, well areas and alternative reservoir models and quickly choose the parameters that best match the seismic observations. Three different case studies are shown where this method has helped us narrow the uncertainty range associated with the reservoir model parameters, which in turn improves the predictive capabilities of the reservoir simulation model. The examples show positive results in a range of different problems.
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High-frequent 4D-surveys for Identification of Subtle Reservoir Property Changes
Authors L. V. Skopintseva and M. LandroThe potential of ultra-frequent 4D acquisition is tested by simple 1-D modeling for a reservoir thickness of 5 meter. By linear changing the reservoir parameters from oil-filled to water-filled situation over 680 days, and assuming that a new seismic dataset is acquired every day, we find that a stacking procedure using data from 80 proceeding days yield a stable result that is close to the noise free result. The random noise level used in the synthetic test is 10 %. Systematic noise sources, such as velocity variations in the water layer, tidal variations and changes in weather conditions over calendar time, are expected to be major challenges for this method. We find that it is possible to correct for velocity changes in the water layer, by a simple estimation of timeshifts of the water layer reverberations.
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Tight Gas Reservoir Monitoring with 4-D 9-C Seismology
Authors T. L. Davis and R. D. Benson4-D 9-C seismic data are capable of monitoring pressure depletion in a tight gas reservoir at Rulison Field, Colorado. This technology can be used to monitor production and to identify depletion zones and bypassed pay.
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Modelling Anisotropy for Improved Velocities, Synthetics and Well Ties
Authors P. W. Wild, M. Kemper, L. Lu and C. D. MacBethThe construction of a new-work flow for deriving well ties from deviated well log data is comprised of three main stages. These are the building of an anisotropic model of the sub-surface; the verticalisation of well velocities measured in deviated wells; and the replacement of isotropic formulations for computing PP and PS reflectivities with anisotropic counterparts, which are then used in extracting wavelets from seismic data and in computing synthetic traces. The development of this work-flow is described, together with field data that underlines its strength in producing well-ties that provide a better fit with observed data than those produced using a conventional, isotropic work-flow.
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Can Image Logs Be Interpreted Using Artificial Intelligence Techniques? A Supervised Test over Two FMI Borehole Logs
Authors R. Di Cuia, D. Ferraretti, L. Tagliavini, G. Gamberoni and E. LammaImage logs held important information of the subsurface sequences. They can provide not only information about bedding and fault/fracture spatial distribution and characteristics but they can also supply insight on the rock texture, textural organisation and porosity types and distribution. In order to reduce the subjectivity of the interpretation and cut the interpretation time we tested a new semi-automatic process for image log interpretation and extraction of the main characteristics of the image/formation. This approach uses image processing algorithms and artificial intelligence techniques to analyze and to classify borehole images. The final results of the process is a series of “image facies” that are identified along the image log and that can be calibrated using cores to sedimentary facies to assign them a geological meaning. In this study the image log from one well was processed using this method to identify different rock facies to be compared with those identified by the log interpreter. The results of this study are encouraging because up to 75% of automatic classes correctly correspond to those identified by the interpreter
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Mud Volcanism in the Po, Italy and South Caspian, Azerbaijan Basins - Differences and Their Possible Origins
More LessIn presentation the results of the analysis on mud volcanism of Po and South Caspian basins” are given. It has been determined that the differences in development density, morphology and activity of mud volcanoes in the Po and South Caspian basins are conditioned by the difference of sedimentation rate, thickness and facial composition of sediments, as well as by total content of OM in mentioned basins.
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Re-exploring the Cretaceous in One Block of the Maracaibo Lake Using Volume Visualization and Geological Integration
Authors C. Olivares, M. Carrillo, C. Zambrano, E. Moreno and N. HambalekA re-exploratory approach has been applied to search for Cretaceous opportunities in one traditional oil field located in the central part of the Maracaibo Lake, with the purpose of getting a ranked cretaceous prospects program. The study was based on Volume Visualization Technologies, together with traditional interpretation and geological integration methods. Surface visualization and conventional seismic interpretation were done on four 3-D seismic surveys (2006Km2). The results show three areas: An structurally complex development area, where the majorities of the cretaceous wells have been drilled and several up dip locations can be proposed; a new exploratory concept area, were the Cretaceous is at the highest position and no well has fully tested the main objective and finally, an exploratory area where a good compartalized structure is present. A geological model was done and provided isochore, isopac, net to gross, porosity and maturity maps to characterize the reservoir, seal and source rock sections. Results and risk analysis have enable the planning of future drilling opportunities in the moderate to high risk ranked Central Block, followed by development locations in the low risk West Block. This re-exploration approach has led to a successful process for efficient future exploration efforts.
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Oil-oil and Oil-source Rock Correlation in the Alpine Foreland Basin Austria
Authors R. F. Sachsenhofer, R. Gratzer, A. Bechtel, H. M. Schulz and A. Smuk37 oil samples from 17 oil fields in the Austrian part of the Alpine Foreland Basin have been investigated with regard to biomarker composition. The differences in the composition of oil are generally minor reflecting a common lower Oligocene source rock (Schöneck Fm.) and homogenization during long-distance lateral migration. Nevertheless a regional subdivision into five oil groups is suggested by biomarker data. Variations in biomarker composition reflect a strong vertical facies zonation within the source rock (e.g. carbonate content) and different maturity of the source rock. Within the distinguished oil groups, the western one is most discrete. In comparison to the others it is characterized by relatively low maturity (0.7-0.8%Rr), low C28-/C29-steranes ratios, low Ts/Tm values, high hopane / moretane ratios and high sulphur contents. Probably, the oil is mainly derived from the middle part of the Schöneck Formation, which yields a sulphur rich oil during pyrolysis.
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Controls on Source and Reservoir Distribution Along the East African Margin
Authors I. Gomez Perez, R. Veiga and F. PallottiniThe geotectonic evolution of East Africa has been investigated using plate and paleogeographic reconstructions. The aim was to understand the distribution and characteristics of Karoo rift depocentres, which influenced both rift and post-rift source and reservoir distribution along the East African margin.
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The Prospects of Deep Horizons Development – by Example of Timan-pechora Basin, Russia
Authors E. Mironcheva, T. Kirjuhina, A. Stoupakova, K. Sitar, D. Norina and N. KirjuhinaTiman-Pechora Basin known as one of the prospective petroleum basins in European Russia is forecasted to be a high perspective in lower horizons located on the depth more than 4 km, were some pools have already been discovered. Structure and geochemical analysis of such fields was done on Geological faculty of Moscow State University as a part of Russian-Norwegian collaboration study.
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HC Prospects of the Western Black Sea, Ukraine
Authors O. I. Khriachtchevskaia and S. N. StovbaExploration activity has been taken in the region for about last three decades. Eight gas-condensate fields have been discovered within Odessa shelf (water depth less 100 m). Last revision of offshore well data with modern technology have allowed to determinate additional prospect reservoirs of existed fields. The productive horizons are located in Upper Cretaceous, Palaeocene, Eocene, Oligocene and Lower Miocene sequences. Present-day exploration activity is focused on inverted structural highs of Odessa shelf. About 40 non-drilled anticline structures are known within Odessa shelf. In addition to anticline traps, stratigraphic traps are distributed within the shallow water. Among them traps that formed by pinching out of Paleocene-Eocene layers as well as valleys of Oligocene paleorivers. The deepwater area (up to 2000 m) has not been studied well yet. Nevertheless, the recent expert appraisal based on interpretation of new regional seismic data carried out by Naftogaz of Ukraine demonstrates very high prospects for discoveries of huge fields in the area. Potential targets are Miocene-Pliocene sandstone bodies of submarine turbidite fans. Numerous gas chimneys are strong evidence of HC. Prospect reservoirs in deep water have a potential to contain hundred million barrels of recoverable HC.
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Reserves Against the Russian, New Russian, and SPE Classifications Based on BS6 Example, Radonezh Field
Authors M. Grechnev, Y. R. Sergeeva and A. M. VagnerIf compared to SPE, New Russian reserves classification meets the international standards and can be accepted for common usage in market economy conditions. The difference in reserves estimation between the two classifications is only 3-4%, which is supported with one of the Western Siberian fields from Russia.
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Seismotomography-based Forecasting of Carbonate Deposits Promising for Oil in the Paleozoic Complex of West Siberia
Authors V. L. Kuznetsov, A. S. Salnikov, V. M. Markov and B. A. KanareikinPresence of oil and gas in the Paleozoic roof under conditions of the West-Siberian plate is associated for the most part with carbonate and carbonate-terrigenous Pre-Jurassic outcrops. We have been discovered a lot of hydrocarbon fields confined to the disintegrated roof of these carbonate units in different areas of the West-Siberian plate. Under conditions of West Siberia the CDP method does not provide the necessary information about the Paleozoic structure. In this connection we used seismic interpretation of CR data processed previously in the region. Processing of previous CR data with two-dimensional seismic tomography can make it possible to get additional geological evidence very important in searching for oil and gas pools in Paleozoic deposits, in particular, to reveal carbonate reservoirs favorable for HC accumulations in them without laborious and expensive field work.
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From the CARG Project (Geological Map of Italy - 1:50,000 Scale) to 3D Geological Modeling – Collection & Dissemination of Multi-scale Geological Data
Authors C. D‘Ambrogi, R. Carta and M. LettieriGeological Survey of Italy (SGI) realizes the national geological map at 1:50,000 scale (CARG Project), in cooperation with territorial organizations, and several research institutions and universities. At present the CARG Project has financed 255 geological maps, corresponding to 40% of the entire Italian territory. One of the achievement of the CARG Project is the realization of a geological database (1:25,000 scale) where digital data are organized in accordance with the logical scheme defined in specific guide lines. Both field data (e.g. geological mapping units; points of geological observations; plicative structures and structural elements) from CARG database and geological data collected in other SGI databases (e.g. borehole stratigraphies and gravity anomalies) are used to build 3D geological models. The full applicability of the CARG database for the creation of 3D models has been tested. SGI has increased its activities in 3D modeling and visualization combining different types of multi-scale georeferenced data into a single 3D environment, soon available also on the WEB.
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Digitising, Geo-Referencing and Web-loading of Public Petroleum Exploration Data in Italy
Authors P. Casero, L. A. Epofani and D. SimonciniThe main Petroleum Exploration and Production Law in Italy was promulgated in 1957. Among several purviews, this law disposes that the Operator of a given Mining Right (Exploration Permit or Exploitation Concession) has to provide the State Mining Authority (UNMIG - Ufficio Nazionale Minerario per Gli Idrocarburi of the Ministry of Economic Development), during the life of the said Mining Right, with periodic reports illustrating the activity being conducted. Such reports must also be accompanied by technical documents (i.e. maps, seismic lines, well logs, etc.). In over fifty years, an important base of documents has been accumulated, all of which are in hard copy paper form. This represents the entire record of the petroleum exploration and production history in Italy. Additionally, the Petroleum Exploration and Production Law stipulates that one year after the cessation of a given Mining Right the provided data be made available in the public domain, nevertheless for researchers, access to this data was quite difficult: This arose as a result of logistical complications (this was especially true for non-nationals) in the first place and in the second place, out of a necessity to know, a priori, the name of the Mining Right(s) which had existed previously and the area of interest, as all information is linked to the file of the permit in which they have been acquired. Knowledge and use of this mass of information is being slowly achieved, particularly in the academic environment, however, in order to surmount this difficulty and provide even greater accessibility to the data, a joint project was promoted by Ministero dello Sviluppo Economico, Assomineraria and Società Geologica Italiana. The operational procedure essentially consists of: - Collection of technical documents of individual permits - Digitisation of documents - Classification of data as per technical categories - Geo-referencing of data - Web-loading of data with the ESRI web-GIS software The first phase of the project was conducted and achieved in 2006: It was decided to give priority to the "raw data", composite well logs and seismic lines. To date, approximately 1,600 composite logs and several thousands seismic lines can be found on the web-sites of the project partners. The second phase commenced early this year, and this phase is expected to take one year to complete. The aims of this phase are to complete digitisation, classification and loading of all remaining documents ( i.e. texts, maps, well velocity data, etc.).
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Research Projects in Seismology within the DPC-INGV 2007-2009 Agreement
Authors D. Di Bucci and D. PantostiThe 2007-2009 Agreement between the Dipartimento della Protezione Civile (DPC) and the Istituto Nazionale di Geofisica e Vulcanologia (INGV) includes, among the others, the execution of a series of Projects in Seismology funded by the DPC with € 5,250,000. These are developed to achieve objectives of specific interest for the DPC in the field of Seismology. The projects are carried out with the contribution of the national and international scientific community, and they are organised as follows. S1 - Analysis of the seismic potential in Italy for the evaluation of the seismic hazard. S2 - Development of a dynamical model for seismic hazard assessment at national scale. S3 - Fast evaluation of parameters and effects of strong earthquakes in Italy and in the Mediterranean. S4 - Italian Strong Motion Database. S5 - High resolution multi-disciplinary monitoring of active fault test-sites areas in Italy.
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Environmental Risk Assessment and Management Methodologies in Oil Production Frameworks
Authors R. Salvati, M. Barlettani, G. Yarwood, R. Morris, A. Carreon and A. CampioniThe most common sources of hydrocarbon emissions in the oil and gas industry are as follows (Picard, 2000): - Fugitive equipment leaks; - Process venting; - Evaporation losses (e.g. tanks and wastewater treatment); - Venting or flaring of disposal waste gas streams; and - Accidents or equipment failures. Fugitive equipment leaks originate from valve stem packings, unions, pipe thread fittings, and hatches (Alberta Research Council, Inc., 2004). Well blowouts, pipeline breaks, tanker accidents, tank explosions, gas migration to the surface around the outside of wells, and surface-casing vent blows are also sources of hydrocarbon emissions, including methane, a potent greenhouse gas ("GHG") (Picard, 2000). Studies conducted during 2007 by the Texas Commission on Environmental Quality ("TCEQ") using Differential Absorption Light Detection and Ranging ("DIAL") indicate that poorly-performing flares may also be large sources of hydrocarbon emissions in petroleum refineries (Clawson, 2007). Emissions from fugitive sources have traditionally been estimated using emission factors, such as those found in the U.S. EPA’s compilation of emission factors known as AP-42. Studies performed in Europe and North America over the past decade reveal that hydrocarbon emissions from refinery and natural gas processing operations may be 10 to 20 times greater than the amount estimated using emission factors (EPA, 2006). In addition to the environmental implications, hydrocarbon losses represent opportunities for significant financial savings. Some companies have reported savings of over $1 million per year by locating and adjusting a single major fugitive leak (Cuclis, 2008). For a large refinery reporting non-methane, non-ethane hydrocarbon emissions of 2,500 tons per year, assuming an economic value of $0.40 per pound of hydrocarbon, the reported emissions represent a loss of US$2 million annually (Cuclis, 2008). If actual losses are 10 to 20 times higher than reported, then the economic value of the lost material increases to between US$20 and $40 million for this same refinery. Unidentified or underestimated emissions may also pose safety risks to workers and to the public. In the presented posters different methodological approaches to evaluation and modeling of hydrocarbon emissions from refinery and natural gas processing operations are described. Particularly the attention will be stressed about the most up to date technical and methodological tools for both the emissions detection, with Optical Remote Sensing technologies, and the emission modeling, with Comprehensive Air quality Model with extensions CAMx. Both tools offer the opportunity to significantly improve our understanding of both the sources and magnitudes of hydrocarbon emissions.
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ANDRILL (ANtarctic geological DRILLing) Drilling System – A Modified UDR1200 Drill Rig for Antarctic Use
Authors F. Florindo and THEANDRILL science teamThe ANtarctic geological DRILLing Program (ANDRILL; www.andrill.org), an international collaboration between scientists, drillers, engineers, educators, and technicians from Germany, Italy, New Zealand and the United States working together in the spirit of the 4th International Polar Year (IPY), successfully completed the drilling phase of its second project in early December 2007. This new drillcore in the western Ross Sea complements and expands the results from ANDRILL’s first successful drilling season. The primary objectives of ANDRILL were to recover and examine stratigraphic records of sedimentary rock from the Antarctic continental margin that document key steps in Antarctica's Cenozoic climatic and glacial history, and reveal events in the development of the Transantarctic Mountains and West Antarctic Rift System(http://www.andrill.org). ANDRILL's two new stratigraphic sections are guiding our understanding of how fast, how large, and how frequent were glacial and interglacial changes in the Antarctic region, and will help establish, through correlation to existing records and integration with climate and ice sheet models, how these local changes relate to regional and global events.
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Early to Middle Miocene Palinspastic Reconstruction of the North-western Part of the Sava Depression
Authors N. Nastasic, Z. Ivkovic and M. MatkovicThe main objective of this paper is to present tectonic deep Sava depression structural events in order to provide information about different sedimentation environments and to point out approach for possible remaining hydrocarbon traps. The 3D area of investigation is settled in Sava depression along the southern margin of the Pannonian basin (Figure 1). This is the area of small but numerous oil and gas fields . Due its position the structural features are mainly due to regional tectonic. The reservoir rocks are mostly Miocene sandstones but some hydrocarbons occur on the uplifted edges and weathered top of the Paleozoic basement. Reservoir rocks in the Lower Miocene (Ottnangian stage) are coarse grained clastics (conglomeratic sandstones and conglomerates). The most frequent reservoirs in the Upper Miocene (Pannonian stage) are coarse-grained clastics (conglomeratic sandstones and conglomerates). The fields were discovered 30 years ago and although a long period of time has elapsed since discovery, because od their geological complexity the area is still the subject of detailed geological studies. According to seismic structural interpretation, palinspastic ,thickness maps construction, and well data incorporation new insight into the Sava Depression is given.
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Spectral Decomposition of Seismic Reflection Data to Detect Gas Related Frequency Anomalies
Authors A. Welsh, F. G. C. Brouwer, A. Wever and W. FliermanA study was conducted into the use of spectral decomposition algorithms for the purpose of direct hydrocarbon detection through frequency anomalies in a geologically and seismically challenging area. A shallow water North Sea seismic data set in an area with well-known geology, with good well control for both water and hydrocarbon bearing formations was used as test set in this study. The correlations found between attribute responses and well results can be used to de-risk leads and prospects. The study included synthetic modeling with two objectives: assessing the relative performance of different spectral decomposition algorithms, and obtaining indications on algorithm sensitivity, especially for changes in rock properties such as porosity and saturation. Subsequently the most promising spectral decomposition algorithms were applied to the real seismic dataset. The results of this step were cross-validated with the synthetic study and interpreted using the geological information in the area as constraints.
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Tectono-stratigraphic Framework of TAL Block, Pakistan Based on Seismic Interpretation
Authors L. Csontos, K. Lorincz, A. Ali and I. CsikiThe studied area is located in the Kohat Plateau in NW Pakistan in a collision zone resulted by N-S convergence of Eurasia and India. It was less explored area until 1999, when the MOL Plc. with Pakistani partners started a hydrocarbon exploration program. A detailed structural analysis was carried out on the basis of integrated interpretation of field, seismic and borehole data. All seismic data (2D, 3D, old and new) were jointly interpreted, seismic attribute analysis and balancing study were also applied. Two different structural levels can be identified which are composed of different formations. Both of them have own detachment surfaces. Two different tectonic regimes created the complexity of the region, older thin skinned fault bend folds and younger wrench tectonics. The same shortening can be found in the structural maps of horizons of different ages, thus presumably the same stress field formed the different tectonic levels. The most characteristic structures are the thrust faults with southward vergence, but eastwards this trend is flexed towards ENE. Secondary en echelon folds with ENE-WSW axial direction are superposed to the general E-W directed structures. Significant oil and gas fields were discovered in several antiforms by the exploration program.
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Analysis of Seismic Attributes for Determination of Reservoir Properties of Jurrasic Sediments, Western Siberia
By I. NagaevaAt modeling of oil and gas reservoirs confined to sedimentary deposits very often there are serious problems to forecast changes of rock properties of productive horizons. Reservoir properties have a sharp variation both on horizontal and vertical directions. For correct interpolation of these properties it is necessary to consider factors which are controlled of theirs variations. Certainly, large influence on rock properties of pores and caverns are rendered conditions of sedimentation as main part of porosity volume is formed at this stage. Goals of 3D seismic interpretation are a reconstruction of sedimentation conditions and a definition of reservoir properties by using significant correlations between petrophysical properties and seismic attributes for a target interval. A number of attributes and 3D cubes (instantaneous amplitude, AVO intercept; acoustic impedance) are calculated from standard seismic cube (after processing) for extraction of the maximal information. Seismic attributes, as we understands them, are generalized quantitative characteristics of a seismic record (Taner, 2001) which are calculated from seismic cube. We use such petrophysical parameters as: effective and general thicknesses and effective and average porosities. These parameters are calculated from the analysis of logging data.
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Seismic Interpretation of Jihar Field
Authors M. P. Pleic, S. G. Gacesa and B. T. TomljenovicThe Jihar gas-condensate/oil field is located in central Syria, about 250 kilometres northeast from Damascus. This paper describes 3D seismic interpretation and attributes analysis of Jihar field. The standard methods of interpretation were used for interpretation top horizons of C2 and D1 reservoir in Kurrachine Dolomites. Studied area is characterized by two differently oriented sets of folds. First, younger set comprises E-W trending folds parallel to structures mapped at the surface. Second set includes NW-SE trend and belong to older fold set. Jihar anticline is formed above the north dipping thrust and thus represents the fault-propagation type of fold The Jihar anticline is overprinted by a younger set of faults. Ant tracking algorithm was used to improve fault interpretation This process resulted with confirmation of conventionally interpreted tectonic settings. Different seismic attributes were extracted from the seismic as well as, structural attributes of horizons, attributes of trace, and attributes of horizon and continuity attributes. Values of seismic attributes were correlated to the available petrophysical parameters and potential relationship was noted. Data resulted in this seismic study presents input data for geological model of the field.
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Multi-spectral Volumetric Curvature Adding Value to 3D Seismic Data Interpretation
Authors S. Chopra and K. J. MarfurtMultispectral curvature estimates extended to volumetric calculations can yield both long and short wavelength curvature images, allowing an interpreter to enhance geologic features having different scales. Tight (short-wavelength) curvature often delineates details within intense, highly-localized fracture systems. Broad (long wavelength) curvature often enhances subtle flexures on the scale of 100-200 traces that are difficult to see in conventional seismic, but are often correlated to fracture zones that are below seismic resolution, as well as to collapse features and diagenetic alterations that result in broader bowls.
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Geological Evolution and Trapping Mechanism of the North-West Barents Sea Continental Margin
Authors P. Golynchik, G. Kazanin, S. Chernicov, A. Stoupakova, T. Kirjukhina, V. Shlykova and P. SafronovaBased on seismic, magnetic, gravimetric, literature data and on geological knowledge main tectonic events which had place in Paleozoic, Mesozoic and Cenozoic history in the Western Barents margin were determined. Seismic stratigraphic method was involved in interpretation of the seismic data. Six seismic stratigraphic complexes were outlined by seismic data. Main tectonic events (uplifts) were tied to regional unconformities traced by seismic. Main thickness of the sedimentary cover in the studied area is represented by Cenozoic deposits. Paleo geological profiles and paleo geographic maps were built for main tectonic events in Cenozoic. It helped to build geological model of the studied area. Perspective reservoirs in the sedimentary cover of the Western Barents margin were outlined in both Paleozoic-Mesozoic and Cenozoic stratigraphic intervals. Main oil and gas potential related to Paleocene – Lower Oligocene and Miocene reservoirs.
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Synthesis of a Virtual Reflector by Processing Recorded Seismic Signals
Authors F. Poletto and B. FarinaWe present a method to process the signals produced by seismic sources and recorded by seismic receivers deployed in suitable locations to obtain new signals as if in the position of the receivers there was an ideal reflector, even if a reflector is not effectively present in the position of the receivers. With this method we obtain the signals of a "virtual reflector". The proposed algorithm performs the convolution and the sum of the real traces, and does not need subsurface model information to process the data. It can be used in combination with interferometry to separate wavefields and process the reflection events. We describe the application with synthetic examples, including stationary phase analysis, and real data in which the virtual reflector signal can be appreciated.
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Multi-component Controlled-source Interferometry by Multi-dimensional Deconvolution Applied to a 1D Elastic Model
Authors J. R. van der Neut, K. Wapenaar and E. C. SlobIn various modern redatuming techniques one cross-correlates registrations at two receiver locations to obtain a Green’s function as if one of these receivers was a source and the other was a receiver. Although these methods have generally been derived by time-reversal arguments or Seismic Interferometry (SI), they can also be interpreted as attempts to solve a general integral equation, evaluated at various shot locations. We show how this integral equation can be solved by multi-dimensional deconvolution and apply the method to multi-component synthetic data generated by a 1D elastic model. We compare retrieved PP, SS and PS converted reflection responses by multi-dimensional deconvolution and cross-correlation-based interferometry in both the space-time and the FK-domain. We show that for one-sided illumination, multi-dimensional deconvolution results in significant improvements compared to cross-correlation, both in terms of kinematics and amplitude.
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Duplex Wave Migration and Interferometry for Imaging Onshore Data without Angle Limitations
Authors N. Marmalevskyi, Y. Roganov, A. Kostyukevych and V. RoganovTwo migration procedures are described which allow a wide range of steep-dip seismic boundaries to be imaged. The first procedure is based on using duplex waves that suffer mode conversion when passing through seismic heterogeneities. Thus, these are transmitted converted waves, which are still not involved in surface seismic exploration. The second procedure is based on interferometric migration both compressional and converted wave fields, continued downward to the points of mode conversion. For imaging, this procedure uses primary reflected compressional and converted waves, as well as duplex reflected and transmitted compressional and converted waves. This assembly of waves allows us to obtain a migration procedure with, practically, no limitations on the angle of inclination of the seismic boundaries. Examples showing both migrations on synthetic data are provided.
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Amplitude Radiation Pattern of a Virtual Source - Estimation and Correction
Authors J. R. van der Neut, A. Bakulin and K. MehtaIn the Virtual Source (VS) method we cross-correlate recordings at two receiver locations to create data as if one of these receivers is a Virtual Source and the other is a receiver. We study the amplitude radiation pattern of Virtual Sources. This pattern can be estimated by autocorrelation of the spatial Fourier transform of the downgoing wave field that is used for the VS creation in the special case of a laterally invariant medium. The generated VS data can be improved by deconvolution with the estimated amplitude radiation pattern in the FK-domain. The methodology is tested on a 1D elastic model, where it is shown that almost perfect amplitude retrieval is possible within a limited aperture of VS radiation. In general heterogeneous media the spatial Fourier transforms are not laterally invariant and the VS amplitude radiation pattern has to be estimated in a different way. We argue that Wigner distribution functions can serve this purpose. We show how these functions can be used for diagnosis of the spatial distributions of the wave fields that are used for VS creation, with a VS synthetic data example generated by the Peace River 2D elastic model.
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Drillbit Seismic Interferometry with and without Pilot Signals
Authors F. Poletto, P. Corubolo and P. ComelliWe process for interferometry purposes the seismic signals generated by a drillbit source in a first well and recorded by seismic receivers located in a second borehole, and at the surface near the well. We compare the standard interferometry results, obtained by using the raw drillbit data without pilot signal, with new interferometry results obtained by using the drillbit seismograms correlated with a reference pilot signal. The analysis of the stationary phase shows that the coherent noise affects the final results, which have different S/N levels. The interferometry methods are compared by using different deconvolution approaches. The analysis shows that the results agree with the conventional drill-bit seismograms, and that using the reference pilot signal improves the quality of the drillbit wavefields redatumed by the interferometry method.
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Sampling and Illumination Aspects of Seismic Interferometry in Horizontally Layered Media
Authors E. N. Ruigrok, D. S. Draganov, J. Thorbecke, J. R. van der Neut and K. WapenaarSeismic Green's function retrieval or seismic interferometry (SI) refers to the principle of generating new seismic responses by crosscorrelating seismic observations at different receiver locations. We consider retrieving a reflection response between receivers at an (approximately) horizontally layered medium. Only transmission responses due to sources that are, in a Fresnel sense, inline with the receivers are needed as an input for the SI relation. The sampling criterion for the sources is much more relaxed than Nyquist. Sources at the edges of the source distribution will cause distortion of the retrieved reflections or even spurious events. Based on a tau-p transform of the transmission responses, a filter can be designed to remove kinematically wrong events from the retrieved results.
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Single Well Imaging in Cased Borehole by Interferometry
Authors F. Poletto, L. Petronio, B. Farina and A. SchleiferWe performed an interferometry experiment to simulate seismic signals in a single well. A seismic vibrator source was used to generate vertical and horizontal components of ground motion along a surface seismic line, and an array of 3C seismic receivers to record the signals in the borehole. The recorded traces are processed to obtain virtual sources in the borehole, and to simulate single well imaging (SWI) gathers with variable offset in the array. We compare results obtained by processing the real data with synthetic signals calculated by numerical simulation, and analyze the signal bandwidth and amplitude versus offset to evaluate near-field effects. The analysis shows that the method provides an approximation of the direct and reflected SWI signals, with results depending on the available coverage for interferometry. Good quality reflections are detectable in the simulated SWI sections.
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Wave Equation Migration Using Isochron Rays
Authors E. Filpo Ferreira da Silva and P. SavaThe migration of a single seismic trace produces an image where the amplitudes are distributed along isochron surfaces. This image can be interpreted as a superposition of snapshots taken from a propagating isochron in an equivalent velocity media, i.e. an isochron-field. We present an isochron-field migration method which is comprised of three steps: equivalent velocity computation, data conditioning, and application of a standard zero-offset wave-field extrapolation migration algorithm. We suggest the term equivalent exploding reflector model for the hypothetical model that theoretically supports our imaging approach. The presented methodology extends the use of zero-offset wave-equation imaging algorithms to finite-offset gathers. We successfully applied the approach for depth migrate a common-offset gather. The methodology presents some features that can facilitate the implementation of parallelized migration velocity analysis algorithms.
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2D Specular Beam Migration - Enhancing Structural Images in Frontier Areas
By I. CockshottThe specular beam migration method has been applied successfully in 3D (Cockshott, 2007). In this paper, the method is shown to also work well in 2D. The speed advantage over the Kirchhoff method is not so great in 2D as in 3D; in 2D, it is the signal enhancement ability of the method which is its strength. Here, the specular beam method is applied to real data examples from the North European margin and the results are compared with those of conventional Kirchhoff migration.
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Pre-stack Sparse Least-squares Migration
By S. T. KaplanWe use least squares migration with a sparse prior to attenuate migration artifacts, and increase resolution. We invert for pre-stack migrated images in the shot-geophone domain, adding a sparse constraint to the LS system by applying a Cauchy norm to pre-stack common shot image gathers.
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A Full-wave Equation Based Seismic Illumination Analysis Method
Authors X. -B. Xie and H. YangWe propose a full-wave equation based method for seismic illumination analysis. The full-wave finite-difference method is used to calculate the waves from the source and receiver to the subsurface target. A time domain local slowness analysis technique is used to decompose the wavefield into angle domain beams. Based on the angle domain information, we formulate the illumination matrix from which different illumination measurements can be derived. Unlike the one-way wave equation based method, the current approach does not have the angle limitation and the reflection/transmission energy can be accurately calculated. The new illumination method can handle turning waves which are crucial for imaging steep structures. Thus, this method is particularly useful for providing illumination analysis in reverse-time migration. A group of numerical examples are calculated to demonstrate the time-domain wavefield decomposition and the creation of different illumination measurements. The illumination in the 2D BP model is investigated. Our special attention is focused on the illumination of vertical and overhung structures.
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Fourier Finite-difference Depth Extrapolation for VTI Media
By B. J. NolteI introduce a Fourier finite-difference method for one-way depth extrapolation in VTI media. The cost of the algorithm is comparable to its isotropic counterpart, i.e. anisotropy is implemented at essentially no additional cost.
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PSDM Velocity Model Building and Application – Case Study in KUCHE Foreland Basin
Authors X. K. Feng and Z. R. ZhuIt is well known that PSDM is the best way to get high quality imaging of complex, steep-dip structures. However, in KUCHE foreland basin (western China) conventional PSDM is seriously challenged because the topography is very complicated, the sub-surface geological structure is severely distorted and lateral strata vary rapidly. The purpose of our study is to set up a suitable modeling procedure, through analysis of the main elements affecting image quality, to derive accurate depth-velocity models in such complicated environments. We accomplish this through a combination of surface and sub-surface information that effectively enhances imaging accuracy.
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Imaging the Slope of the Marine Camamú Basin, Brazil, Using Only Reverse Time Migration
Authors M. A. Barsottelli-Botelho and A. V. M. LimaIt is proposed a scheme using finite-difference Reverse Time Migration (RTM) and two or more common shot gathers which is able to perform as a velocity indicator. The procedure was tested on synthetic and real marine data and allow to define a good velocity model with errors of approximately 5%. The procedure presented here can be used on any data acquired over complex geology. A velocity field was used on RTM of near trace sections and also of stacked sections acquired over the continental break and slope of Camamú Basin (Brazil). The migrated sections were able to reveal the complex structural and stratigraphic framework for the syn-rift and pos-rift successions. This procedure has an advantage over the conventional seismic processing velocity analysis, based on normal move out equation, which is based on the assumption of flat and horizontal reflectors.
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Regularization in Slope Tomography
Authors J. Schleicher, J. C. Costa, F. J. C. da Silva, E. N. S. Gomes, A. Mello and D. AmazonasSeismic imaging in depth is limited by the accuracy of velocity model estimation. Slope tomography uses the slowness components and traveltimes of picked reflection or diffraction events for velocity model building. The unavoidable data incompleteness requires additional information to assure stability to inversion. One natural constraint for ray based tomography is a smooth velocity model. We propose a new, reflection-angle-based kind of smoothness constraint as regularization in slope tomography and compare its effects to three other, more conventional constraints. The effect of these constraints are evaluated through angle domain common image gathers, computed with wave-equation migration using the estimated velocity model. We find the smoothness constraints to have a distinct effect on the velocity model but a weaker effect on the migrated data. In numerical tests on synthetic data, the new constraint leads to geologically more consistent models.
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Traveltime Approximations in VTI Media
Authors R. Aleixo and J. SchleicherAs exploration targets have gotten deeper, cable lengths have increased accordingly, making the conventional two term hyperbolic traveltime approximation produce increasingly erroneous traveltimes. To overcome this problem, many traveltime formulas were proposed in the literature that provide approximations of different quality. In this paper, we give an overview over a number of those approximations and compare their quality. Moreover, we propose some new traveltime approximations based on the approximations found in the literature. The main advantage of our approximations is that some of them are have rather simple analytic expressions that makes them easy to use, while achieving the same quality as the better of the established formulas.
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Non-linear Estimation of Thomsen's Anisotropy Parameters in Dipping TI Media
Authors D. Nadri and B. HartleyIn a dipping transversely isotropic layered medium, the exact offset and traveltime equations have been formulated. A non-linear inverse model using pre conditioning conjugate gradient algorithm has been developed to estimate the Thomsen’s anisotropy parameters from the PP or the joint PP & PS traveltimes. With the assumption of weak anisotropy no prior knowledge of the Thomsen’s anisotropy parameters is required.
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2.5D True-amplitude Diffraction-stack Redatuming
Authors A. Novais, M. F. Pila and J. SchleicherThe purpose of redatuming is to transform seismic data acquired at a certain measurement surface to simulated data as if acquired at a different measurement surface. Based on the chaining of diffraction-stack migration and isochron-stack demigration, we derive a 2.5D true-amplitude diffraction-stack-type redatuming operator and present its specific form for zero-offset data. The operator consists of performing a single weighted stack along adequately chosen stacking lines. For simple types of media, we derive analytic expressions for the stacking lines and weight functions and demonstrate its functionality with numerical examples.
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Prestack Seismic Data Enhancement with CRS Parameters
Authors M. Baykulov and D. GajewskiWe present the results of partial stacking of prestack seismic reflection data based on the kinematic wavefield attributes computed during the automatic CRS stack. The resulting CRS supergathers are more regularised and have better signal to noise ratio compared to original CMP gathers. The improved data can be used in any conventional processing tool instead of the original data, providing enhanced images of better quality. The CRS supergather method is especially suited for low fold seismic reflection data. Application of the new method to synthetic and real low fold data shows a clear improvement of seismograms as well as time and depth-migrated sections.
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Treatment of Conflicting Dips in the 3D CRS Stack
Authors N. -A. Mueller and P. MarchettiThe 3D common-reflection-surface technique (CRS) provides a stacking tool for the simulation of zero-offset sections. For that purpose, the stacking operators, which represent the kinematic reflection responses of specific reflector segments in depth, are parameterised in terms of so-called kinematic wavefield attributes. Implementations of the 3D CRS stack automatically determine the kinematic wavefield attributes by means of coherence analyzes for each ZO location to be imaged. Therefore, coherence values are computed for a set of different stacking operators and the operator and the corresponding wavefield attributes with the highest coherence value are chosen for the realization of the stack. Obviously, this technique assumes that only one reflection event contributes to a specific ZO location. As this assumption is in many cases not fulfilled the stack may show a deteriorated quality and the attributes may be fragmentary. Here, we present a method to overcome this so-called conflicting dip problem. We allow different stacking operators for each ZO location and construct the final stack as a superposition of these operators. Additionally, our approach yields coherent sets of stacking operators for each of the conflicting dips. The applicability of the method is finally demonstrated on a marine dataset.
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Five Dimensional Interpolation
By D. TradMany seismic processing techniques have strict requirements on the regular spatial distribution of traces in seismic data. Datasets that do not fulfill these requirements, such as most 3D land surveys, will suffer from poor processing results when these techniques are used. Although not a substitute for well-sampled field data, interpolation can provide useful data preconditioning that allows these techniques to work better, and hence provide a superior result. Interpolation algorithms that use multiple spatial dimensions have many advantages over one-dimensional methods. In particular simultaneous interpolation in all the five seismic data dimensions has the greatest chance to predict missing data with correct amplitude and phase variations. However, the negative aspects of working in five dimensions are both the difficulty of solving the problem in a numerically efficient fashion and the handling of the large volumes of data. The first aspect is a consequence of the nonlinear increasing cost of interpolation with data size. The second aspect arises because of poor data sampling when considering all five seismic dimensions simultaneously. In this paper, we discuss an approach that has been successful for interpolation of land data and contrast it with narrow azimuth marine interpolation.
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Geo-electric Surveying, a Useful Tool for Hydrocarbon Exploration
Authors S. Ivanov, Y. Davidenko, E. Kudryavceca, P. Legeydo and P. C. H. VeekenThe geo-electric method (GE) allows mapping Induced Polarization effects, often caused by epi-genetic micro-crystals of pyrite. A shallow halo-shaped mineralogical alteration zone is typically formed some distance above a hydrocarbon accumulation. The geo-electric surveying technique (DNME) makes it possible to acquire data in shallow water, where other EM methods are hampered by airwave energy (seabed logging or CSEM). GE method gives encouraging results in deeper water, transition zone and onshore domains. Geo-electric surveying visualizes anomalies in the electric potential response measured in the receiver. Inversion of the registered relaxation curve is done to establish a depth model. Various diagnostic GE attributes are here proposed. Acquisition and processing parameters are adjusted to the target depth, varying from very shallow to 5 km. GE surveys cover different geological settings (e.g. rifts, subsiding cratons, foredeeps). The success ratio for predicting hydrocarbon occurrences is high and some Russian companies incorporate the methodology already in their standard prospect evaluation toolbox. The GE technique helps to reduce risks related to drilling new prospects and allows a substantially better ranking at a reasonable cost.
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Creation of Geophysical Basis in the Scale 1:1000000 in the Region of the Barents Sea
Authors V. Vasilev, N. Fedukhin and T. FedukhinaThe creation of Geophysical Basic Foundation on the shelf of Russia is been conducted by JSC MAGE beginning from 2000 in the frames of State Geological map in the scale 1:1000000. The main aim of this work is regional classification and generalization of the data available, obtained by different geological exploration organizations, correction of the geological structure, including arrangement of basins, perspective in hydrocarbons. The maps of gravitational and magnetic fields, geological-geophysical sections and plots of geophysical zoning are included to the complete set of Geophysical Basic Foundation. This geophysical foundation is based obligatory on the digital database, containing either measurement results at the points of observations and data, translated to the uniform grid.
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Gravity Potential Series Expansion for Homogeneous Polyhedra
Authors H. Holstein, C. Willis and C. AnastasiadesSeries expansion methods in gravity anomaly calculations provide a convenient representation of the local anomaly that do not require the complexity of a full anomaly computation at every evaluation point within a region of interest around the expansion point. We give one approach to obtaining such an expansion, appropriate when the causative body is a homogeneous polyhedral target. We make use of the known gravi-magnetic anomaly formulae for such targets, to obtain computationally stabilised coefficients of the series exansion around an interest point. We develop the formulae for the gravity potential as a the series expansion, and show that the method can have efficiency advantages over gridded interpolation as a means of expressing the local variation in potential.
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Geological Features of Murzuq Basin Area
This paper describes our interpretation of the main structural features of the Murzuq basin area (Lybia), obtained by identifying the geometrical and physical characteristics of the magnetic basement. We also compare gravity and magnetic interpretation results with the geological knowledge of the area, contributing to the definition of small-sized and very localized objects which occur within the sedimentary sequence
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Integraded Geophysical Study of the San Andreas Plate Margin
Authors N. Bundalo and S. A. HallThe goal of this study was to develop a better understanding of structures and plate interactions along the San Andreas continental transform margin using gravity, magnetic and seismic data. Although many geological and geophysical studies have been carried out in the region; most of these have focused on small parts of the plate margin area. Here, an integrated approach is used to investigate the entire transform margin. Because the evolution of continental transforms is reflected in their deep structure, geophysical data have been used to construct 2-D and 3-D models of the crust and uppermost mantle beneath the region. The implications of these models are examined in the context of published geologic evolutionary models for the San Andreas plate margin.
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2D Series Expansion Based Geoelectric Inversion Using Optimized Weights
Authors A. Gyulai, T. Ormos, M. Dobroka and D. DrahosIn the joint inversion of geophysical data measured above 2D or 3D geological structures non-uniqueness and ambiguity problems often occur. An other problem in integrating various data sets in a single inversion algorithm (simultaneous- or joint inversion) is the use of appropriate weights regulating the contribution of the given data set to the solution. In order to reduce non-uniqueness and ambiguity problems in this paper we use series expansion in the discretization of the laterally varying model parameters resulting in a much lower number of unknowns. In the joint inversion of two data sets containing sufficiently different level of noise we apply optimized weights for balancing between the data sets. It is demonstrated in a numerical experiment that the application of optimized weights together with the use of series expansion in discretization results in stable and reliable joint inversion.
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Gravity Survey over Jabal Hafit - Implications for Basement Configuration of the Frontal Fold Belts of Oman Mountains
More LessA gravity survey was carried out in and around Jabal Hafit, south of Al Ain, Abu Dhabi in the United Arab Emirates. Jabal Hafit is a 30 km long and 4.5 km wide asymmetrical, double-plunging, NNW-SSW trending anticline which consists of shallow-marine carbonates of Eocene to Miocene age trending parallel to the Oman Mountains. The area is of tectonic significance because the reactivation of basement faults are believed to control distribution of hydrocarbon traps. Results from the gravity data constrained by outcrop geology, confidential well and seismic data and bedrock density measurements, have been used to determine the subsurface structure of the study area. NNW-SSE trending positive residual gravity anomalies of up to +6 mGal occur on the Jabal Hafit and Al Ain anticlines. These positive gravity highs are attributed to basement horsts as the structural style is considered to have resulted from reactivated deep-seated fault blocks. The residual Bouguer anomaly values decline gradually to the east and west of Jabal Hafit as the basement deepens. A large negative gravity anomaly of <-5 mGal is observed east of Jabal Hafit and coincides with a syncline which caused thickening of the Upper Cretaceous and Tertiary sequences.
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Automated Data-based Relative Bearing Estimation for 3-Component Borehole Seismic Sensors
More LessThis abstract describes an automated way of estimating the relative bearing angles of 3C sensors in a borehole seismic array. The method is based on deriving a weighted global azimuth error function that describes the mismatch between calculated polarization angles and the survey geometry. The relative bearing angle that minimises this azimuth error function is considered to be the optimal one. The use of the method is demonstrated on both synthetic and real data examples, including multi-azimuth, multi-offset VSP and Walkaway VSP datasets. The method may be used on both vertical and deviated wells and is highly automated, requiring minimal user intervention.
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