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68th EAGE Conference and Exhibition incorporating SPE EUROPEC 2006
- Conference date: 12 Jun 2006 - 15 Jun 2006
- Location: Vienna, Austria
- ISBN: 978-90-73781-00-9
- Published: 12 June 2006
201 - 300 of 462 results
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MPI Multiple Attenuation Method in the CMP Domain
More LessThe multiple prediction through inversion (MPI) method is a fully data driven multiple attenuation technique and has been implemented in the shot gathers. In this paper, we attempt to extend the MPI multiple attenuation method from the shot domain to the common mid-point (CMP) domain, so that it can be used to data sets that have poor signal-to-noise ratio in the shot gathers. For the CMP domain version, although it is still a pre-stack application, implemented on CMP gathers instead of shot gathers, the pre-stack multiple prediction process can be carried out on individual CMP gathers by auto-convolution in the frequency-space domain or multiplication in the frequency-wavenumber domain. Real data examples demonstrate the efficiency of this CMP domain MPI method, when the approximation of a low-relief earth is valid and the earth is laterally homogeneous.
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Recursive Transformation of Multiples into Primaries - Data Examples
Authors D. J. Verschuur and A. J. BerkhoutIn most seismic processing flows multiples have been considered as noise and, therefore, are discarded after the removal process. In this paper it is argued that multiple reflections contain a wealth of information that should be used in seismic processing to improve the resolution of reservoir images beyond current capability. The proposed method, multi-channel weighted cross-correlation (WCC), in combination with surface-related multiple elimination (SRME) allows the transformation of multiples into primaries for surface seismic data. The latter means that nonlinear seismic imaging can be implemented by a number of linear steps.
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On the Origin of Source and Receiver Perturbations in Land Seismic Data
Authors R. van Vossen, A. Curtis and J. TrampertNear-surface conditions often vary within land seismic surveys resulting in differences in source strength and signature. Furthermore, discrepancies between closely spaced recordings are also commonly observed. We investigate the origin of these source and receiver perturbations on land seismic data. The source perturbations retrieved show a strong correlation with the moisture content of soil. For frequencies above 40 Hz, explosive sources located in moist-to-wet sediments transmit more than 100 times more energy into the ground than explosive sources located in dry sands. This difference is a result of high absorption rates in the dry sand due to nonlinear deformation in the near-source region, whereas these absorption rates are low for sediments with fluid-filled pores. The receiver terms are determined for vertical component data, and these do not show a significant correlation with the moisture content of the soil. The changes from receiver to receiver are dominant indicating that these are related to the geophone plant itself. However, we could not fit the receiver responses retrieved to the generally accepted damped harmonic oscillator model which describes the geophone-ground coupling. This implies that this model may need to be revised for future land seismic applications.
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2D and 3D Tomography for Near-Surface Statics Corrections
More LessP076 2D and 3D Tomography for Near-Surface Statics Corrections J. Zhang* (GeoTomo) & O. Yilmaz (GeoTomo) SUMMARY If the near-surface velocity structures are complex in land seismic conventional refraction methods for statics corrections often fail. the assumption of "layers" is no longer valid. When this happens traveltime tomography often proves effective for solving statics prob tomography approach that we developed inverts the first-arrival tr reconstructs a near-surface velocity model on a grid basis and t assumption for the shallow Earth. After resolving the near-surfac calculate long-wavelength statics using the velocity model and al short-wavelength residual statics from the refraction traveltimes.
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CRS Stacking Velocity Estimation - A Key to High-Resolution Seismic
Authors G. Gierse and J. PruessmannThe seismic line considered in this case study is a typical example of land data from an arid region. Strong variations of the surface conditions from deep weathering zones to outcrops of consolidated rocks were posing the main problem, and imaging quality primarily depended on the compensation for the surface effects. Static corrections, however, could not completely remove the surface-induced imaging problems. In areas with strong near-surface inhomogeneities, e.g. below deep bottom fills of a wadi, the resolution and event continuity still were much lower than in undisturbed areas. These remaining problems due to near-surface inhomogeneities, however, could be solved by appropriate dynamic corrections that are obtained from CRS processing. The local adaptation of CRS imaging parameters at every point of the image automatically provides very detailed dynamic corrections. These corrections produce a major increase of signal frequency and event continuity, and widely adapt the signal quality in disturbed areas towards the undisturbed signal character. It turns out that the strong surface inhomogeneities induce small-scale variations of the stacking velocities in the subsurface below, that cannot be resolved by manual velocity analysis and by the resulting smooth velocity field.
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Refraction Statics Correction in Sand Dunes
More LessModeling and field studies show that sand dunes exhibit vertical velocity profiles. Ignoring this property in processing seismic data collected over sand dunes can lead to errors. In this study, I present a V(z) function derived from Hertz-Mindlin and Gassmann theories and use it to calculate the refraction static correction in a sand dune. I then compare this static correction to that calculated while assuming a vertically homogenous sand dune. Modeling results show that the absolute error due to ignoring the dune’s vertical velocity profile does not exceed 6% for sand dunes with porosities, water saturations, and thicknesses ranging 0.2-0.7, 0-0.9, and 0-200 m, respectively.
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Imaging of Scattered Surface Waves - Application to Ultrasonic Data
Authors A. Kaslilar and G. C. HermanAn inverse scattering method is presented for determining near-surface heterogeneities from scattered surface waves in a laterally invariant, layered embedding. The scattered wavefield is represented using a domain-type integral representation and the Born approximation. An ultrasonic laboratory data set is used for imaging the near-surface heterogeneity caused by an epoxy-filled hole in the surface of an aluminium block. The results indicate that it is possible to locate the scatterer and also estimate the actual density contrast as well as its depth dependence.
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Elastic Full Waveform Inversion for Near-Surface Imaging
Authors C. Gélis, J. Virieux and G. GrandjeanWe propose here a method for maging near-surface structures although it can nevertheless be applied for deeper areas characterization. We perform the elastic full waveform inversion in the frequency domain in order to recover physical properties of the medium from both body waves and surfaces waves. We first present the forward problem and then the inverse one, mostly based on the (Pratt et al.,1998) formulation, here modified for multi-components and multi-parameters elastic full waveform inversion. After that, we illustrate the method with numerical examples and a real case where data have been acquired for a masonry detection.
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Elastic Full Waveform Inversion of Multi-Component OBC Seismic Data - Application to Shear Wave Statics
Authors T. J. Sears, S. C. Singh and P. J. BartonElastic full waveform inversion of seismic reflection data is an alternative to conventional stack based processing. Both travel-time and amplitude information within shot domain data are used to invert for the sub-surface velocity, from a starting model containing the long wavelength features. Although full waveform inversion is computationally intense, the ability to invert for both P- and S-wave velocity, in a data driven manner, makes the computational burden worthwhile. Building on previous developments in waveform inversion, such as the benefit of wide-aperture data, we consider multi-component ocean-bottom cable seismic data. Synthetic examples show that it is possible to invert for and to quantify both P- and S-wave velocity. Example synthetic work is presented, followed by a summary of work in progress on real data. Inversion for the shallow sub-seabed region is of particular interest. Successful inversion for the shallow region may be used to help solve shear-wave static problems observed in OBC data. This idea is explored in a synthetic example, and acts as an objective for real data application, with results to be presented.
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Mapping Heavy Metal Pollution of Soils Affected by Metallurgical Point-Source Pollution Near Barcelona (Spain)
Authors A. Casas, G. Ferrero, J. C. Tapias, L. Rivero, X. Font and M. ViladevallOne of the most urgent tasks for atmospheric environmental protection is to monitor particle loadings in urban and industrial areas from point pollution sources. This allows the drawing-up of policies aimed at reducing emissions and the appraisal of their long-term effectiveness. Besides, mapping of the spatial distribution of pollution on contaminated surfaces is a primary prerequisite for further remedy and recovery efforts. This study presents results of magnetic mapping around a metallurgical plant near Barcelona. The aim of the study was to delineate highly contaminated areas and to discriminate them from areas relatively unaffected by this source. An enhancement in the concentration of magnetic particles in topsoil through this area has been observed. This fact is originated by anthropogenic magnetite transported through the atmosphere in a form of a plume which travels down-wind along the valley of the Llobregat River.
Optical microscopy on magnetic extracts shows the presence of small spherical particles (less than 20 mm) typical for the anthropogenic magnetic phases from high-temperature industrial processes. The spatial distribution of magnetic susceptibility of soil surface has been compared with the distribution of heavy metals in soil samples. High susceptibility values were found to coincide with increased heavy metal values.
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Subsurface Geophysical Surveys to Civil Engineering, Geotechnical and Environmental Applications
Authors A. Wójcicki, M. Honczaruk and G. PacanowskiThe study presents results of subsurface geophysical works carried out by PBG Geophysical Exploration Company. The results come from final reports of surveys ordered by particular local authorities in Poland. The goal in first case was related to the planned office building foundation and in the second - detecting of leaks produced by old, underground concrete reservoir of gas pitch on an area of old gas works.
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Shear Wave Velocity Inversion from the Seismic Surface Waves Using Data Adaptive Wavelets
Authors A. Kritski, A. P. Vincent and D. A. YuenWe study the dynamic and physical properties (shear velocity, seismic attenuation, stiffness and density) of marine sediments from seismic-acoustic records of surface/interface waves along the water-seabed boundary. Accurate models of the marine sediments properties in the shallow subsurface are critical in many disciplines. For example, in oil and gas exploration knowledge of the sedimentary acoustic properties helps to improve the shear wave static corrections, it provides shear strength modulus in the geotechnical engineering, helps to estimate acoustic loss for sonar operation in the shallow water. Our method relies on using dispersive characteristics of the seismic surface waves which can be further inverted for the shear velocities as function of depth and distance. We use wavelet analysis to separate surface wave modes and extract their group and phase velocities. To improve the accuracy in imaging of the surface wave modes we have developed and applied a new tool - adaptive wavelet which parameters are defined directly from the data. We demonstrate how these wavelets can be employed to provide more accurate shear waves velocities estimates.
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High-Resolution Seismic Reflection Investigations of Dissolution Sinkholes
Authors R. D. Miller and K. MillahnSeismic reflection images of dissolution subsidence features prior to surface expression provide insights into potential growth mechanisms, development rates, and sinkhole risk. Vertical growth of small depressions or drape in reflectors several hundred meters below ground surface and in proximity to major salt dissolution sinkholes appear to be controlled by active dissolution in deeper salt layers and the size and competence of the unsupported span of roof rock. Gradual failure and continued upward movement of voids characterized by reflector drape are confined to the inverted cone geometry defining the stress regime or tensional dome. Time-lapse imaging of these yet-to-emerge sinkholes could provide key parameters for developing empirical-based models of sinkhole development. Ideally, these models would allow reasonable estimations of growth rates and mature sinkhole areal expressions.
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Seismic Imaging of Fractured Reservoirs in the Scansano-Amiata Area, Southern Tuscany, Italy
Authors R. G. Francese, F. Mazzarini, G. Morelli, N. Wardell and A. ZajaFresh water availability has recently become a serious concern in the Italian Apennines as various activities rely on a predictable supply. In southern Tuscany along the Scansano-Amiata ridge the situation is further complicated because of the contamination of the nearby alluvial aquifers.
Locally aquifers consist of thin fractured reservoirs, generally within low-permeability formations, and planning exploitation of resources, based on conventional techniques, could be complicated.
An integrated investigation program, based on remote sensing, structural geology and geophysical exploration, was initiated in 2002 to associate tectonics and groundwater circulation and better define the hydrological model.
After the regional identification of fault and fracture patterns a major structure has been investigated in detail to accurately map the spatial position, and understand the associated aquifer geometry and properties to assess exploitation potentials.
The subsurface around the fault zone was clearly imaged with Ground Probing Radar, 2D and 3D resistivity tomography and more recently with 3D shallow seismic. The vertical and the horizontal contacts between the different geological units of the Ligurian and of the Tuscan Series were resolved with a high degree of spatial accuracy. 3D high-resolution geophysical imaging proved to be very effective in small-scale fractured reservoir characterisation.
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Method Development for Waste Site Characterization Using TAU-Transformation of IP Curves
Authors M. Dobroka, E. Turai and P. VassThe induced polarization method is an effective geophysical method of ore exploration. It is well known that both the time-domain and frequency-domain IP measurements are capable to detect even small amounts of the metallic minerals. On the other hand, the metallic content is not the only factor resulting in polarizability of the medium; filtration- and membrane effects as well as electrochemical (redox) properties can also lead to similar phenomena. Induced Polarization is a very useful geophysical method also in the detection and characterization of environmental spots mainly waste sites. For the interpretation of IP curves the TAU-transform method was introduced by Turai (1985). Combining the TAU transform method and the tools of inverse problem theory a general algorithm for the determination of the time-constant spectrum of the polarizability data is available for the general case of continuous spectra. Some results of the interpretation of field data collected over Hungarian waste sites (Nyékládháza - 1997-2004, Ráckeve - 1997, Kecskemét - 1997, Győröcske - 1999, Pásztó - 2000, Tokaj - 2001, Balmazújváros - 2002, Szerencs - 2003 and Tiszaújváros - 2004) will be presented in lecture and (based on the time-constant spectra) the characterization of the main components of the contaminating material is given.
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Volcanic Rocks-Discrimination and Hydraulic Parameters by Spectral Induced Polarisation (SIP)
Authors N. H. Schleifer and G. MaierThe increasing application of spectral induced polarisation (SIP) in hydrogeophysics is accompanied by petrophysical studies investigating the possibilities to derive the hydraulic conductivity from recorded complex electrical resistivity spectra.
The presented study concentrates on the volcanic rocks of Styria and their spectral behaviour. The Styrian basin in the south-eastern part of Austria is characterised by volcanic activity during Miocene and Pliocene, which can be discriminated by their SiO2-contents. Since especially pyroclastic rocks show large variations in grain size and porosity, we expected significant differences of electrical behaviours in the low frequency range (0.001-1000 Hz). For the laboratory studies seven sites were sampled including mainly basaltic and tuffitic rocks.
Concluding the results three groups can be classified by their electrical properties. This demanded further laboratory investigations showing that samples with a single phase peak are characterized by one single dominant pore throat size diameter. In contrast samples with constant phase angles throughout the spectra show an almost even distribution of pore throat sizes.
As these correlations had been observed in earlier SIP studies on sandstones the existing models relating permeability, pore-throat size and porosity present the possibility to evaluate all relevant hydraulic parameters by SIP.
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Combined Function Inversion Method
Authors R. Kavanda, A. Gyulai and T. OrmosThe geological structures are usually layered and inhomogeneous. We developed an inversion technique to research these structures. This method is the function inversion, which is suitable to determine the vertical and lateral inhomogenity. We do the inversion in two phases. In the first phase we use 1D forward modelling and in the second one 2D. This method accelerates accomplishing the iterative inversion. The 1D forward modeling give an approaching solution (1.5D inversion). So that we get the correct value, have to do the second phase (2D/3D inversion). In the function inversion, one of the main problem is determining of the optimal number of coefficients besides choosing the type of function. In this text first of all we look for the answer, what is the optimum number of coefficients for the estimation of model parameters and we give a scheme to solve this problem.
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Geophysical Investigations within the Cave Field of the Kyiv-Pechersk Lavra
Authors V. Prilukov, S. Levashov, M. Yakymchuk, I. Korchagin and N. DravertGeophysical investigations performed over the cave field of the Near Caves of the Kyiv-Pechersk Lavra by geoelectric, seismic-acoustic and GPR methods allowed: 1) to draw a map of the plots of high moistening of soils over the cave field surface; 2) to define paths of migration of man-caused water flows over the Near Caves; 3) to find and map vertical fractures in the sandstone which serve for vertical migration of the subsurface water flows; 4) to establish the leakages from the subsurface water communications outside the Lavra territory as well as leakages under irrigation with the surface irrigation system caused the arising of man-caused water flow within the cave field ; 5) to reveal anomalous zone of thinning and moistening of rocks, as well as the zones of "subsurface hollow" type in the region of caved gallery; 6) to establish objective causes of the caving of the cave gallery using a complex of obtained geophysical data.
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Structure of Dallackau Landslide on the Refraction Data with Interpretation by Homogeneous Function Method
Authors V. B. Piip, N. M. Orlova and A. N. NaumovInner structure of Dallackau landslide has become the focus of investigations for evaluation of possible damage. Geoscientists have to cope with different types of faults and breaks when looking at seismic sections. We showed the potential of the homogeneous function method for use in interpretation of refraction data of engineering seismic line running across the Dallackau Landslide located in Northern Caucasus (Russia). The resulting seismic section is much more detailed than that provided by the traditional method (previous models for these lines). New sections involve different faults and thrusts, even though the new section and the previous model are identical on the average. The purpose of this paper is to summarize how the faults can be identified from 2D seismic images by demonstrating some of the sections through the Dallackau Landslide.
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Shallow Shear Wave Reflection Seismic Applications in the Krueng Aceh River Delta
More LessAs part of the project "Management of Georisk" of the Federal Institute for Geosciences and Natural Resources (BGR), Hannover, high resolution shallow shear wave reflection seismic was applied in the Indonesian province Nanggroe Aceh Darussalam in cooperation with the Government of Indonesia and local counterparts. The investigations should support earthquake site effect classification for the reconstruction process and the groundwater exploration activities with the main focus for the city of Banda Aceh and the surrounding region of Aceh Besar. The shear wave seismic measurements were combined with standard geoengineering techniques like Cone Penetrometer Testings for a comprehensive site evaluation and have been supplemented partly by shallow P-wave seismic applications for the derivation of elastic subsurface parameters and the detection of groundwater spots.
Results show that high resolution shallow shear wave seismic is a useful tool to evaluate the subsurface stiffness in terms of international building codes for local site effect analysis. Furthermore, due to the resulting depth penetration of 100 m and more, this method lead to a better understanding of the sedimentation process for the Krueng Aceh river basin and can help to identify possible aquifer layers.
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Why High GPR Frequencies Don't Image the Water Table?
By M. BanoWe simulate two levels of the water table (at 72 and 48 cm depth) by injecting water in a sand box that contains also some buried objects. The GPR profiles acquired with a 1200 MHz antenna on the sand box do not show any clear reflections from the top of the phreatic surface. This is because of the existence of a transition zone in which the velocity is a continuous function of depth. Examples of real and synthetic radar reflection data will be shown in order to illustrate the methodology presented here.
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Modelling Short-Period Changes of Soil Thermal Parameters from Subsurface Temperature Data
Authors M. Behaegel, P. Sailhac and G. MarquisIn this study, we consider the heat flow modelling for the time variations of both ground temperature and surface temperature and use first a simple homogeneous semi-infinite half space, then a two-layer model. By data inversion, we recover the time variations of thermal diffusivity for the homogeneous case and the thickness of the first layer for the two-layer model. We have obtained reliable estimates of the near-surface thermal properties based on near surface temperature data and analytic solutions. The parameters show a dependance with soil water content during the year.
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Hydrates as an Energy Source – Risks and Opportunities
By S. DallimoreGas hydrates are solid crystalline substances consisting of natural gas (typically methane) and water molecules, that remain stable under conditions of relatively cold formation temperatures and high pressures. Significant natural gas hydrates deposits occur in the Arctic in association with areas of thick permafrost, and in many marine environments around the world. Their energy potential is significant as the in place estimates of gas hydrate are thought to significantly exceed conventional natural gas resource estimates. While gas hydrates could represent a vast unconventional, environmentally-friendly natural gas resource, the challenges to realise their energy potential remain significant. They occur in remote frontier settings, new exploration methods are required to locate concentrated deposits, and technologies to produce them have not proven. Success will likely require a combination of science, technology and favourable economics. Interest in gas hydrates as an energy resource has grown in recent years with many countries having established national research and development programs. Scientific and exploratory drilling has taken place in Japan, Canada and the USA, and field programs are also planned in the near future offshore of India and China. In 2002, a seven member research partnership conducted small-scale production testing at the Mallik site in Canada's Northwest Territories. Two 1188 m science observation wells and a 1166 m production research well were drilled and instrumented to examine gas production and the physical behaviour of reservoir sediments in response to depressurization and thermal stimulation. Other aspects of the program included the collection of gas hydrate core samples, downhole geophysical logging and extensive laboratory and modeling studies. The results of the production testing and scientific investigations have been released Geological Survey of Canada Bulletin that includes 62 scientific papers and an extensive data base.
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Heavy Oil – Challenges for Moving a Vast Oil Resource into Real Production
By X. PreelHeavy Oil is a quite abundant resource (estimated at roughly at 5000 Bbbls IOIP), of different characteristics. Most of these resources are located in Venezuela and Canada, 2 countries where Total is busy producing and developing these resources. Different technologies may be used to develop these resources. The presentation will try to describe benefits and disadvantages of each of these technologies addressing the main factors: oil recovery, cold or hot schemes (which, if hot schemes, has implications into gas requirements), mining or in situ production, overall CO2 emissions, environment aspects, … Oil production which can be expected from both Venezuela and Canada will be discussed.
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Non-Conventional Hydrocarbon Resources – Are They Capable of Meeting Forecast Demand?
By P. StarkAs concerns about the current capacity and future availability of oil and gas supply increase, many analysts see non-conventional resources as providing assured supply for decades to come. These “resource plays” of regional extent certainly contain enormous in-place resources but are they capable of meeting forecast demand increases? E&P companies (including all of the majors) are also attracted to such resources because they have low exploration risk, material production volumes and long-lasting production at stable production rates. In addition, with the exception of Canadian oil sand bitumen production, current recovery factors are low so these accumulations have the potential for a substantial “technology dividend”. At some 7.5 trillion barrels, estimates of the in-place resource of bitumen, extra-heavy oil and shale oil are over three times greater than the 2.25 trillion barrels of recoverable conventional oil estimated to have been discovered to date. Non-conventional liquids production from Canada and Venezuela currently comprises about 2% of world liquids production. Excluding gas hydrates, remaining recoverable resources of the three principal types of gas resource play are estimated at over 1,000 trillion cubic feet. While remaining recoverable resources of discovered conventional gas are six times as large, there is significant potential for growth in non-conventional gas resources outside North America, where no estimates are available to-date for shale gas and tight gas sands. Non-conventional gas production, which currently comes almost entirely from the USA, comprises almost 7% of world gas production. The paper will discuss the current status of resource play development, production and resources worldwide with emphasis on undeveloped future potential, and will provide commentary on the environmental impact of such developments and the steps being taken to mitigate adverse effects. Conversion technologies such as coal-to-gas, coal-to-liquids and gas-to-liquids will not be addressed in this paper.
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Electrokinetic Multiples - A Synthetic Example
Authors R. E. Plessix and J. SingerA modeling study is carried out to analyze the effects of a shallow water layer above a deep reservoir layer in an electrokinetic experiment. The presence of the water layer not only generates primary converted events, but also several other events, which can be seen as multiples. Theses multiple events mainly depend on the discontinuities in the elastic earth parameters. The strength of those multiple events can be much larger than the strength of the primary converted events at the reservoir interfaces, depending on the depth difference between the water layer and the reservoir layer.
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Investigation of Non-Linear Seismic Effects for Hydrocarbons Indication
Authors V. E. Shulakova, A. P. Zhukov, K. I. Loginov, M. B. Shneerson and V. A. EkimenkoLinear-elastic approach is commonly used in seismic methods theory. But in practice we’re often confronted with non-linear behavior of geological environment. The authors assert that oil and gas reservoirs show nonlinear properties. Thus it’s necessary to use a new model of subsurface considering the Earth’s non-linearity. The main goal of this paper is to define a level of non-linear effects and to investigate availability of non-linear properties in the problem of prognosis of hydrocarbon reservoir's properties. The special fieldwork had been realized using 2D vibroseis exploration. As a result of this investigation two main effects in hydrocarbon reservoirs were discovered:
- oscillations with multiple, combinative - summarized and differential - frequencies appear in the reservoir;
- non-linear behavior of registered signal amplitudes comparative to emitted signal amplitudes.
A new method for hydrocarbon indication was created on basis of these two phenomena and fieldworks.
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Some Nonlinear Effects Observed in Seismic Examples
Authors A. Glebov, G. Mitrofanov and S. GoldinSome examples of nonlinear effects that were found during various seismic experiments are observed. Peculiarities typical of nonlinear processes appeared in the form of seismic signals in these experiments. For example, pumping-over of energy from the zone of dominating carrying frequencies to the zone of low and high frequencies. For theoretical description of occurring effects the five-constant model of isotopic quadratic-nonlinear medium is used. In the context of this model a new way of evaluation of aq-parameter of elastic nonlinear medium is suggested.
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Micro Time-Lapse - Preliminary Results
More LessThis work presents preliminary theoretical and experimental results of a new seismic exploration method that can be used as Direct Hydrocarbon Indicator (DHI). It is based on inelastic attenuation and uses a dual field of seismic waves. By theoretically computing the composite deformation induced by a history loading of stress, it is observed that the second step stress comes across a different mechanical configuration than the first. This may imply that both pulses may propagate with different velocities in the dynamic case, a situation that will not occur in perfectly elastic media. This can be used to detect subsurface anomalies such as fractured or high porosity zones that may be associated to the presence of hydrocarbons. While the procedure to obtain the creep compliance in the case of multiple sequential loading may not be as accurate, it provides a good estimate of what may be happening within the reservoir rocks. The next step, which is currently underway, is to carry out similar studies in an acoustic laboratory using band-limited signals.
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Ocean Bottom Stations Data - Illumination Problems and Imaging Solutions
Authors S. Ronen, L. Comeaux, X. Miao and S. GrionOcean Bottom Stations provide wide-azimuth multi-component data with great advantages for exploration, reservoir characterization, and identification of drilling hazards. However, due to the high cost of deploying OBS nodes, large receiver intervals are used. In practice, poor illumination due to sparse receivers is a major problem. This problem is particularly, but not exclusively, associated with gaps in the coverage of shallow targets, and is greatly exasperated if some OBS nodes fail. The same problem affects both sparse OBS nodes and ocean bottom cables in the cross-line direction. Fortunately there is an effective solution. The first step in our method is the separation of seabed hydrophone and geophone data to upgoing and downgoing waves. Downgoing waves just above the seabed contain only multiples, or ghost reflections. Nevertheless, we image the ghosts, pretending that the data were acquired with a certain equivalent geometry recorded above the sea surface. This alternate surface is the top of a virtual water layer whose thickness is twice the sea depth. We applied this method to OBS data recorded in the North Sea and generated better images from the downgoing ghosts than the images produced conventionally from the primary upgoing waves.
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Filling the Gap - Integrating Nodes and Streamer Data for Geophysical Monitoring Purposes
Authors E. Ceragioli, A. Kabbej, A. Gonzalez Carballo and D. MarinIn the recent past, various tests and related publications have demonstrated that high quality data can be acquired with a relatively sparse distribution of seismic nodes on the ocean bottom.
One of the possible applications of this promising geophysical technology is to use it as a complement to streamer data, to fill in sensitive areas where conventional marine or OBC acquisitions are unfeasible or too risky from a HSE point of view.
In this paper, we assess the feasibility of such a joint streamer - nodes approach for the geophysical monitoring of an ultra deep water oil and gas field.
We develop a methodology for the planning of a joint survey, taking into account the different nature of the two sets of data, as well as other relevant operational constraints.
We validate both joint time and depth pre stack migration schemes, resolving the problem of the datum difference between ocean bottom and sea surface data.
We evaluate the impact of this merged approach on the interpretation of resulting seismic amplitudes, focussing on the time lapse characterization of turbidite fairways.
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Stereotomography for Nodes Data
By M. AleriniStereotomography, as a slope tomography method, requires the knowledge of the slopes in both common source and common receiver panels to constrain the velocity model. In case of nodes data, where individual receivers are set down to the sea floor, the acquisition is usually very sparse and does not allow to obtain the slope at receiver with enough accuracy. However, using the reciprocity of Green's functions, it is possible to bypass this difficulty. Indeed, after a redatuming of the data and considering sources as receivers, we can obtain a dense enough acquisition. The question which arises is whether or not this sparse acquisition is enough to estimate the velocity model. I show here good results on a synthetic example.
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3D Methodology for OBC Pre-Processing
Authors M. T. A. Soudani, J. L. Boelle, P. Hugonnet and A. GrandiIt is more and more observed that OBC PZ images show better quality than the streamer. This is due to better multiple attenuation, multi-azimuth and high fold coverage. This leads to a wider bandwidth and a better signal to noise ratio. However, while 3D OBC designs are considered as multi-2D acquisitions, the pre-processing will remain far from the ideals. In the following paper, a fully 3D OBC pre-processing methodology is presented. This methodology is based on the 3D(τ,p) transform. Due to the fact that a spatial transform is used, aliasing becomes a real issue. The interpolation solution to overcome such a problem is briefly described. Then, the generalization of the PZ summation to 3D is discussed and compared to the standard 1D approach. Finally, a method for linear noise attenuation is described and its application on a real dataset shown.
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Multiple Attenuation on OBS/OBC Data by Extended Wavefield Extrapolation
More LessSRME-based multiple attenuation methods are often ineffective when applied to OBS/OBC data due to the acute disparity in the shot and receiver distribution and the difference in source and receiver datum in ocean bottom acquisition geometries. Wavefield extrapolation based multiple attenuation schemes take advantage of the fine sampling of the source wavefield, and are insusceptible to poor receiver sampling or datum differences. The technique models the multiples in the common receiver domain by sending the recorded source wavefield into the subsurface and simulating the backscattered wavefield as first order multiples at the source locations. Synthetic examples demonstrate the effectiveness of the method. This technique, in combination with PZ summation to address receiver-side ghosts, provides an effective multiple attenuation flow for OBC/OBS data.
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Shear Wave Noise on OBS Vz Data - Part I Evidence from Field Data
Authors J. Paffenholz, R. Shurtleff, D. Hays and P. DochertyVertical geophone data on ocean bottom bottom recordings are often contaminated by varying amounts of noise. This noise has the moveout of converted waves, is coherent on common receiver records and random on common shot records. The noise also depends strongly on the condition of the ocean bottom, with muddy bottoms generating strong noise and sandy bottoms giving almost noise free data.
In the past it has been commonly assumed that the noise is essentially cross-talk of the shear component on the vertical component caused by design flaws in the recording unit.
In the course of the development of a new ocean bottom node system we have tested a number of different OBS configurations. Analysis of the Vz noise as function of configuration type allows us to separate effects into those which are dependent on configuration type and those that are not.
We conclude that the 'Vz noise' is not dependent of the recording station configuration and instead is a true measurement of the vertical movement of the ocean bottom. In part II we demonstrate a possible mechanism by which the vertical bottom movement is generated using finite difference modeling.
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Shear Wave Noise on OBS Vz Data - Part II Elastic Modeling of Scatterers in the Seabed
Authors J. Paffenholz, P. Docherty, R. Shurtleff and D. HaysShear wave energy contaminates the vertical component of ocean bottom seismic data worldwide, yet the mechanism that generates this Vz noise has not been adequately explained. By means of elastic finite-difference modeling we investigate scattering at the seabed as a possible cause of the phenomenon. Modeled as perturbations in shear speed, the scatterers are energized most strongly by converted waves and radiate Stoneley waves along the seabed. Resulting synthetics exhibit the characteristics of Vz noise observed on field data, in particular, converted wave moveout, coherence in the receiver domain, incoherence in the shot domain, and absence from the hydrophone.
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Seabed Properties Derived from Ambient Noise
By E. MuyzertAn extensive study of low-frequency ambient noise wavefields in the seabed has resulted in a new approach to determine the near-surface shear velocity. 33 minutes of continuous ambient noise recorded by an ocean-bottom cable (OBC) system without using an active source were analyzed for seafloor compliance and Scholte waves. Seafloor compliance was not observed and requires longer recording time. Scholte waves were observed in the frequency-wavenumber spectrum. The Scholte wave phase-velocity was modeled with a realistic one-dimensional near-surface model. The horizontal over vertical spectral ratio of the Scholte waves was also modeled and shown to be very sensitive to the near-surface shear velocity model. Applications of the method include shear-wave statics estimation and geohazard prediction.
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From Reflection to Transmission Data
Authors J. W. Thorbecke and C. P. A. WapenaarFrom the reciprocity theorem of the correlation type an implicit relation between seismic reflection and transmission data has previously been derived. In this paper this relation is used to estimate the transmission coda, at a certain depth, from reflection data measured at the surface. The transmission response is represented by a generalized propagator, consisting of a primary propagator and a coda operator. Using this representation, 1D approximations, and an eigenvalue decomposition on the correlation of the reflection response, it is possible, to solve the implicit relation for the coda operator. The calculated coda response may be used in seismic reflection imaging to obtain an image in which the internal multiple scattering effects are suppressed. A simple example for the estimation of the transmission coda illustrates the discussed procedure.
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The Tempa Rossa Passive Seismic Experiment
More LessPassive Seismic Tomography involving the continuous recording of natural microseismicity is increasingly being considered as a new exploration technique particularly in regions of complex geology such as fold and thrust belts. This technique also has the added advantage of being environmentally friendly. In this paper we present a feasibility modelling study on the Tempa Rossa oil and gas field in southern Italy.
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Seismic Interferometry with Underground Moving Source
Authors K. Shiraishi, K. Onishi, S. Ito, T. Aizawa and T. MatsuokaThe reflection response can be obtained by the cross-correlation of the transmission responses, which is called "seismic interferometry". We apply this technique to the field data observed by using several different seismic sources. In this paper, we introduce a result of the field examination done toward practical use of the seismic interferometry. Since this method requires a long record length, we developed a PC-based seismic recording system with 96 channels. This experimental survey was carried out in a hilly area where there exist two tunnels. We can acquire transmitted wavefield data generated by the sources moving in the tunnels. We obtained subsurface image of the hill by using the hitting type sources and also by truck running vibrations. Obtained subsurface images being properly data-processed are clear enough to estimate underground structures.
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Cross-Hole Tomography Using Seismic Interferometry
Authors K. Torii, K. Shiraishi, K. Onishi, T. Kimura, S. Ito, T. Aizawa, K. Tsukada and T. MatsuokaThe Virtual Source (VS) is a kind of Seismic Interferometry and synthesizes a new seismic record whose source comes from a receiver location by processing cross-correlation to plural records. We make experiments in the laboratory and simulations in order to synthesize a VS data from records between cross-holes, and confirm this data can be used for cross-hole tomography. By comparison with experiments, we make numerical simulation whose source is in the borehole1, and receivers are in boreholes2. In the cross-correlation results of experiments, we successfully synthesized the new records, which can be clearly picked up the positions of first motions of waves. This result indicates the validity of the VS method for applying the geotomography. In the next stage, we will try the experiment and simulation on the more complex model and measure the field data for improving the practicality of this method.
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Spectral Evaluation of Microseismic Signals
Authors V. Bardan, D. Zugravescu and L. AsimopolosSpectral evaluation is a very important operation in the processing of microseismic signals. In this poster we consider the microseismic signals that can be recorded at a point from the Earth’s surface as a random process (signal) with many realizations and we present a methodology for the evaluation and statistical stabilization of its frequency spectrum. This methodology requires the computation of a large number of discrete Fourier transforms (DFTs) for microseismic signal fragments represented by a very large number of samples. So, finally, we show that in this case it can be taken into consideration the use of a decomposition DFT algorithm. This algorithm optimizes the fact that fewer frequency samples than the original time samples are needed. The methodology for the evaluation of microseismic spectra is illustrated by real data examples.
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Integrated Anisotropic Velocity Modeling Using Perforation Shots, Passive Seismic and VSP Data
Authors S. C. Maxwell, J. Shemeta and N. House Inc.Economic development of tight gas reservoirs often rely on hydraulic fracturing to stimulate production. Passive microseismic mapping of these hydraulic fractures is a quickly growing technology to map fracture geometry and complexities created during these stimulations. Reliable microseismic locations depend on an accurate velocity model. In this study we examine velocities obtained from Vertical Seismic Profile (VSP) data, perforation shots from an adjacent well, and microseismic data to determine an anisotropic velocity model for improved microseismic hypocentral locations. The observed anisotropy is consistent with an effective media representation of the geological reservoir structure.
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Fracture-Induced Frequency-Dependent Anisotropy, Yibal Field, Oman
Authors A. Al-Anboori, M. Kendall and M. ChapmanFracture size is one of the main parameters that reservoir engineers are interested in due to its importance in hydrocarbon production. We estimate the fracture size using the Chapman (2003) theory of frequency-dependent shear-wave splitting on microseismic data recorded in the Yibal field. The Natih A reservoir demonstrates the largest fracture size and fracture density of 2 m and 0.07-0.23, respectively, as expected for a highly fracture reservoir. In contrast, the Fiqa exhibits moderate fracture density (3%) with fine-scale fractures (<0.1 micrometer in size) as expected for a seal rock. Collectively, the results of frequency-dependent S-wave splitting are mainly controlled by lithology.
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Spatial Variations in Microseismic Focal Mechanisms, Yibal Field, Oman
Authors A. Al-Anboori, M. Kendall, D. Raymer and R. JonesFault plane solutions (FPSs) are estimated for microseismic events in the Yibal field, west-central Oman. We analyse 22 days of data, containing over 600 located events recorded by a maximum of 5 monitoring wells (10 downhole 3-component stations in total). 43 reliable FPSs are determined using polarities and amplitudes of direct P-, SV- and SH-waves and based on assumption of a pure double-couple source. The analysis was guided by tests with synthetic data, which were generated by the reflectivity method. We observe a transition in faulting regime from strike-slip (with a thrusting component) in the shale Fiqa cap rock to pure thrusting in the gas-charged Natih A chalk reservoir. Deeper in the field we observe another transition from strike-slip in the Nahr Umr shale cap rock to normal faulting in the oil-bearing Shuaiba chalk reservoir. Collectively the results suggest that the fault regime is controlled by style of deformation and lithology.
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Lithofacies and Reservoir Features of Triassic Sediments in South Moesian Platform Central Margin
Authors N. D. Botoucharov and G. V. GeorgievThe analyses conducted in this paper are based mainly on the lithofacies characteristics of the well-penetrated Triassic series in the South Moesian Platform Central Margin. The purpose is to achieve better understanding of depositional environment and lithological composition of the sediments. Besides the detailed observation and study of the Triassic lithofacies, the spatial distribution of the different Formations is also clarified. The economic hydrocarbon fields and numerous shows in the study zone are accumulated in heterogeneous reservoirs. These rocks are situated in Lower and Upper Triassic coarse-grained clastics (Red colour sandstone unit and Moesian Group), Middle and Upper Triassic carbonates (Doyren Fm. with Dolni-Dubnik member and Russinovdel Fm.). The intensive diagenesisis and erosional events improve the filtration parameters of the Triassic succession. Hence, the Middle and Upper Triassic (Anisian and Carnian) limestones and dolomites, close beneath the Triassic-Jurassic unconformity, are the best reservoirs in the study zone. Their lithological and reservoir qualities are proven by numerous oil and gas discoveries. The litholofacies diversity as well as relationships with perspective reservoir intervals are an optimistic sign for future exploration in the South Moesian Platform Central Margin.
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Hydrocarbon Potential of the Carboniferous Strata on the Kołobrzeg and Gryfice Blocks (Northwestern Poland)
Authors P. Kosakowski, M. J. Kotarba, J. Pokorski and M. WróbelCarboniferous source rock (s.r.)was characterized in 22 profiles of wells on the Kołobrzeg Block and 10 on the Gryfice Block based on the results of geochemical analyses. The best source rocks occur within Tournaisian mudstones and claystones, where TOC values reach up to 10.7 wt. % (mean 1.0 wt.%). The terrestrial type III kerogen is located at the immature/early mature zone. The analysed Westphalian and Visean strata reveal lower petroleum potential. The history of hydrocarbon generation and expulsion was reconstructed by means of the 1-D BasinMod(tm) modelling, applied to 5 wells: Biesiekierz-2, Daszewo-17, Dobrzyca-2, Dygowo-4 and Dzwirzyno-1. Modelling revealed that Tournaisian source rocks generation of hydrocarbons commenced in the time span between Middle Triassic and Late Jurassic, locally perhaps in the Late Carboniferous. The generation potential was calculated from the hydrocarbon potential, its ranges change from 1.2 to 2.2 kg HC/m3 s.r.
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Molecular Geochemistry of The Palaeozoic Source Rocks and Oils from Ghadames Basin, North West, Libya
By M. HroudaA detailed molecular geochemical investigation of the source rocks and reservoired oils from Al-hamada field complex, (NC5, NC8), Al-Wafa field (NC169) and (NC3) throughout the Ghadames basin has revealed that all the oil samples display similar facies features to the Lower Silurian source rocks. There is a high probability that these oils were generated from the Lower Silurian 'hot shale' source rocks. Maturity evaluation of the oil samples based on the biomarker and aromatic hydrocarbon ratios indicates that the oil samples collected from the oil fields located in the South and southwestern parts of the basin are more mature than the oil samples collected from the northern parts of the basin. This is in consistent with the maturity trends of the source rocks of the Ghadames Basin.
Most of the Upper Devonian source rock samples have unusual proportions of the 20S isomers (relative to 20R isomers) of the C29 steranes, with values of more than 55% 20S. Such high values could be due to factors other than maturity.
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Radioactivity and Organic Matter in Mesocenozoic Rocks, The Eastern Azerbaijan - Correlation and Cyclicity
Authors C. S. Aliyev, A. A. Feyzullayev and S. A. BabayevThe paper presents results of radioactive and geochemical studies of rocks in different stratigraphic intervals in the sedimentary complex of the East Azerbaijan and their correlation. There have been studied regularities of distribution of integral radioactivity, amount of radioactive elements and geochemical characteristics of the organic matter of rocks in 40 natural exposures of Mesozoic and Paleogene-Neogene deposits. There has been determined correlation of radioactive and geochemical parameters, cyclicity in their distribution along the section.
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3D Modeling of Oil Generation and Secondary Migration in Western Siberia (Russia)
Authors N. V. Oblasov, I. V. Goncharov, V. V. Samoilenko, B. Erout and M. Saint-GermesFull 3D basin modeling is finding a practical application in oil and gas exploration. Temis 3D was used for study of oil generation and migration in the part of a prolific hydrocarbon province in Russia. Results of modeling provide new information, which allow to better understand influential factors for the formation and occurrence of oilfields.
Transformation ratio of main source rock in the studied area is from 0 to 44 % and firsts accumulations started to form nearly 60 million years ago. There were defined the factors guiding the formation and occurrence of oil fields. Depending on reservoir spreading and source rock maturity the coefficients of oil accumulation in two blocks of studied area differ in eight times. Comparison between proven reserves and reserved computed by Temis shows good accordance.
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Oil-Gas Bearing Complexes of Southeast Subsiding Zone of Greater Caucasus
More LessObject of investigations is being the Cenozoic deposits of the Anadyr basin located in the outermost north-eastern part of the Asian continent. At the moment four industrial fields have been discovered in the basin; semi-commercial HC inflows have been delivered practically from the whole sedimentary sequence - from Cretaceous to Neogene inclusive, that indicates on considerable HC potential of the Anadyr basin.
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Hydrocarbon Systems of the Anadyr Basin
Authors E. N. Poludetkina and N. P. FadeevaWide occurrence of Pre-Cambrian sedimentary formations, regional association of commercial oil-gas deposits and oil-shows let to consider Upper Proterozoic deposits of ancient platforms as promising object in respect of oil-gas content itself and as a source of oil in Paleozoic as well. Commercial oil-gas bearing established in South Oman, China and mainly Siberian Platform with main oilbering regions Nepsko-Botuobinsk and Bajkits anticlines. Small oil deposits were discovered in the East-European platform in Vendian and Riphean deposits.
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Upper Proterozoic Sedimentary Basins of Ancient Russian Platforms
Authors O. K. Bazhenova, T. K. Bazhenova and N. P. FadeevaSpectral decomposition is an important signal analysis tool for seismic data. The overall frequency content of a signal can be obtained from Fourier transform. However, for a non-stationary signal, such as seismic signal, whose frequency content varies with time, 1D transformation in frequency is not sufficient. Traditionally, 2D representation in time and frequency space for a 1D signal is achieved by taking the Fourier transform over a short-time window. This method is commonly known as short-time Fourier transform (STFT). The windowing problem in time-frequency analysis is absent in continuous wavelet transform (CWT) method. S transform is a phase corrected form of CWT that yield a good result in analysis of seismic signals. Newly developed time-frequency attributes and their drawbacks is studied in this paper.
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Petroleum System Analysis for a Back-Arc Basin Offshore South Korea - The Ulleung Basin
Authors S. Kargl, P. Y. Chenet, B. Yoo and H. G. ImThis petroleum system analysis of the Tertiary Ulleung Basin off-shore South Korea is part of the Korea National Oil Cooperation (KNOC) active exploration program. The basin displays only one producing gas condensate field and several gas/condensate shows. The basin is part of the Miocene East Sea back-arc basin formed at the margin of the Eurasian plate (Tamaki & Honza, 1985) with a Miocene shelf, slope and deep basin environment during the opening and subsidence stage and a following complex compressional and wrenching episode forming the present day back-arc basin.
The timing of the development of these compressional structures as traps in relation to the timing of hydrocarbon generation, migration and trap formation is a principal factor in the understanding of the behaviour petroleum system of the Ulleung Basin.
This petroleum system study allowed understanding and evaluation of the main features of the petroleum system, as the thermal regime reconstruction related to the tectonic phases, origin of the observed gas-condensate accumulation in relation to the hydrocarbon kitchen and migration pathways, the efficiency of source rocks, interest of the different play concepts in relation to overpressure barriers, migration pathways and prospect assessment.
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Sensitivity and Risk Analysis in 2D Petroleum System Study - A Case Study from the Jequitinhonha Basin, Offshore Brazil
Authors S. Kargl, I. Scotchman and F. SchneiderA 2D petroleum system analysis was undertaken to evaluate a consistent scenario for understanding the petroleum system behaviour in the Jequitinhonha Basin, offshore Brazil. The 2-D section is a seismic line from a 3-D seismic survey, where prospects were recognized, but no well was drilled along the section and well data are poor. But in this part of the Jequitinhonha Basin, the migration pattern, migration pathways and related drainage systems are complex and 3D phenomena, strongly controlled by the presence of salt and salt movements. The effect of different parameters and/or geological phenomena on the petroleum system behaviour could not be estimated quantitatively. Therefore a sensitivity and risk analysis was performed. The results of the sensitivity analysis allowed determining the sensitive parameters for the hydrocarbon saturation in the prospective areas and led additionally to new results for the petroleum system behaviour, their impact on migration and present day accumulations in this area. Based on these results different scenarios controlling the system for the petroleum system were tested and evaluated. The estimation of the risk on hydrocarbon charge and trap potential, according to the uncertainties on the petroleum system components could be established.
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An Atypical Early Mature Oil in Block 35/1, Norwegian North Sea; Hypersaline, Carbonate Jurassic Environment
Authors S. E. Ohm, H. Beeley, D. A. Karlsen, P. B. Hall and A. FossBlock 35/1 with the dry Sturlason structure, is located on the northernmost part of the Marflo Ridge in the Norwegian part of the Northern North Sea. It is separated by deep faults from the Sogn Graben to the east and the Marulk Basin to the west. The 35/1-1 well proved only minor shows of gas and oil in the well.
The Sturlason structure comprises a series of upthrown fault blocks in a structurally complex area. Structural backstripping suggests a part of the 35/1 Block to have been sub-aerially exposed during part of the Jurassic. A more oxic environment and greater influx of type III organic matter may have been the result in the area surrounding the island.
The geochemical analyses were hampered by contaminations from the use of oil based mud while drilling. Despite this, traces of true indigenous C4-10 and C25+ range hydrocarbon are demonstrated. The former carries the imprint of being an early mature evaporative condensate whereas the latter suggests origin from an early mature hypersaline carbonate related source rock.
A buoyancy driven fluid flow study without taking faults into account, shows the difficulty in charging the drilled structure and clearly suggests presence of sealing faults.
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Volumetric Calculation of Hydrocarbon Generated from Kazhdumi Formation in Dezful Embayment
Authors E. Mohsenian, M. R. Kamali and A. FathiF044 Volumetric Calculation of Hydrocar Generated from Kazhdumi Formation i Dezful Embayment E. Mohsenian* (National Iranian Oil Company - RIPI) M.R. Kamali (Na Oil Company - RIPI) & A. Fathi (National Iranian Oil Company - RIPI) SUMMARY Dezful Embayment is one of the most potential areas for exploration of hydrocarbon reservoirs in the world. The effective source rocks anoxic to suboxic conditions during Jurassic Cretaceous and Tertiar This study is focused on evaluation of petroleum generation potenti of the amounts of hydrocarbon generated from Kazhdumi Formation. Detailed geological and geochemical studies including volumetric ana that the source rock contains type
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The Atzbach-Schwanenstadt Gas Field - A Potential Site for Onshore CO2-Storage
Within the framework of the EU-funded CASTOR project the Atzbach-Schwanenstadt gas field in Upper Austria is being investigated as a potential underground CO2 storage site. Potential CO2 sources are a paper mill and a fertiliser plant.
The digital geological model ranges from the base of the Hall Series (Miocene) to the Top Eocene, with a special focus on the main reservoir zone ("A4") of the Upper Puchkirchen Series (Oligocene to Miocene). Reservoir properties were stochastically assigned, conditioned by their occurrence in the wells with petrophysical interpretation and by their statistical distribution in the various facies.
The reservoir model focuses on the A4 zone and includes only the central part of the field, where gas productivity is best and where a relatively uniform gas-water contact exists. Reservoir parameters were upscaled from the geological model to yield a model size that enables fast simulations. It is expected that injected CO2 will during the potential injection period replace produced gas in the reservoir. So far, approx. 3.2×109 sm3 gas have been produced from the field. Assuming that CO2 can replace all produced gas, this corresponds to a storage capacity of at least 3 million tonnes of CO2.
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Multicomponent Seismic Monitoring of a CO2 Sequestration Pilot, West Pearl Queen Field, U.S.A.
Authors R. D. Benson and T. L. DavisThis paper describes an experiment in West Pear Queen field, Lea County, New Mexico, to measure differences in the Queen Formation sandstone reservoir before and after an injection of 2100 tons of CO2 into the reservoir. Time-lapse (4-D), multicomponent (9-C) seismic data were used to monitor the thin sandstone and provides an improved understanding of the subtle structural and stratigraphic framework of the reservoir. Interpretation of the multicomponent seismic data volumes demonstrate that it is possible to detect and monitor injected CO2 in this reservoir interval and reveals that the CO2 migrates structurally up dip from the injection well.
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The Effect of CO2 Solubility on the Long Term Fate of CO2 Stored in a Water Saturated Subsurface Storage Location
More LessF047 The Effect of CO2 Solubility on the Long Term Fate of CO2 Stored in a Water Saturated Subsurface Storage Location L.G.H. van der Meer* (TNO) SUMMARY EAGE 68 th Conference & Exhibition — Vienna Austria 12 - 15 June 2006 Summary and Introduction CO2 storage in aquifers is an attractive solution to reduce CO2 emissions into the atmosphere. The successful example of CO2 storage in the Sleipner injection project proves that large volumes of CO2 can be stored in a subsurface water-bearing formation. In general we know that the most of the injected CO2 will displace water and will
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Elastic Full Waveform Inversion for CO2 Sequestration monitoring - 1D Synthetic Data Investigations
Authors A. Gosselet and S. C. SinghIn greenhouse gas geological sequestration frame, time-lapse seismic has been demonstrated to be a powerful tool for monitoring CO2 injection. So far, it has provided essentially qualitative insights, such as gas cloud extent or reservoir compartment identification. Getting quantitative information requires accessing subsurface elastic properties. This is commonly done through Amplitude Versus Offset analysis. Such methodology is limited in terms of angular aperture and only takes into account reflected data. Use of elastic full wave form inversion (FWFI) can overcome such limitations. In this study we investigate strategies to assess FWFI ability to retrieve some 1D models from synthetic noise free data. Models properties are based on the Sleipner injection site, including shale and gas sand thin beds. Low to high frequencies inversions of pre-injection data retrieves accurately the baseline model. Inversion of post-injection data is more difficult as gas introduces very large velocity decreases. Two approaches are then proposed: first one is based on weak "time-lapse" assumptions and include a rough data pre-conditioning; second one assumes overburden as fixed and invert only high frequency data in the injection layer. This gives encouraging results showing that FWFI is able to provide quantitative insights in such context.
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The Global Energy Crisis – Origins, Status, and Endgame
By J. LeggetFrom my perspective, and that of growing numbers like me, oil interests have hyped the product on which society has come to depend while stoking addiction and holding back alternatives. The oil industry's general contention is that peak oil lies far off in the 2030s or beyond. It doesn't. The peak is imminent, and will certainly happen this decade. When it arrives, it will send the oil price soaring beyond today's already dangerous level. This will trigger the worst-ever energy crisis, which itself stands to create economic chaos reminiscent of the depression in the 1930s. Meanwhile, global warming caused by oil, gas and coal burning is in danger of running out of control. Society will be forced, albeit in deplorable economic conditions, to solve oil depletion with a crash programme to accelerate alternative-energy sources. Whether it will do so with the technologies that can also solve global warming and save the planet is an open question. The biggest danger is that critical players like the US and China will use their enormous coal reserves to run power plants and provide gasoline substitutes without giving renewable alternatives enough of a chance. The extent to which we can accelerate renewable forms of power and fuel instead of coal, rather than alongside it, will be the final battleground in the effort to save Earth from the ravages of human-induced global warming. There is much that individuals, and organisations including businesses - oil companies among them - can do to influence the outcome of that struggle.
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Achieving Greener Fossil Fuels Faster
By B. WeilConcerns both about future supplies of energy and about the impact of energy on our climate are growing. The challenges should not be underestimated, but our ability to innovate and harness technology can offer solutions. The world will long depend on fossil fuels to meet expanding demand. So we need to find and recover more conventional oil and gas, develop the potential of unconventional hydrocarbons, and use coal more efficiently. At the same time, we must reduce the carbon dioxide emitted by fossil fuels, make alternative forms of energy economic, and increase energy efficiency. New technologies will have to be applied on an unprecedented scale and pace, in increasingly demanding projects. International energy companies – with their integrated capabilities, global experience and commercial drive – will have a key role in this.
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Alternative Energy, Growing Low Carbon Power
By L. EdwardsBP's Alternative Energy business was launched in November, 2005 to meet the worlds growing demand for secure, cleaner, low-carbon power. The portfolio of technologies BP Alternative Energy is actively pursuing includes Solar, Wind, Hydrogen for stationary, and high efficiency combined cycle gas turbine generation. The rationale and business strategy will be presented along with further details of specific programs now underway. The Alternative Energy story is based on business objectives to meet growing requirements for material alternative sources of power while providing returns to shareholders.
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Robust Wavelet Estimation and Quality Measures
By P. E. HarrisWe describe a stochastic method of wavelet estimation tying well logs to seismic data. It is insensitive to outliers in the reflection coefficients and in the seismic data. This is achieved by generating random perturbations to an initial wavelet and comparing the resulting synthetics to the seismic data by means of a robust norm. A set of best-matching wavelets is determined, providing uncertainty estimates for the wavelet and the synthetics. We use an iterative process to weight residuals by a function of the misfit determined in the previous iteration, thereby downweighting those parts of the data where the seismic and synthetic are in poor agreement.
Perhaps more important than the wavelets themselves are the resulting quality measures. Uncertainties in the wavelets’ amplitude and phase spectra are obtained. Wavelets from multiple wells within an area can then be compared quantitatively to ensure that the seismic phase is consistent. The weights also indicate where there is a mismatch between logs and seismic data. Such mismatches may be due to problems in the logs, such as poor log editing, or to seismic problems such as residual multiples. In either case the weights show where the data need further processing before reservoir characterisation work.
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Stochastic Fault Seal Analysis and Reservoir Simulation for Fields with Thin Layers and Many Faults
Authors B. Z. Shang, H. D. Yang and S. A. BourgeoisTraditional fault seal analysis requires deterministic structural and stratigraphic models and significant fluid flow data for transmissibility calibration. For multi-faulted reservoirs with large structural and stratigraphic uncertainties and little dynamic data, traditional method fails to capture the range of production scenarios. This paper proposes a new method to capture the range of possibilities via stochastic analysis in juxtaposition, shale gouge ratio, and fluid flow. First, we gather the stratigraphic and structural information and generate the parameter ranges, such as reservoir layer thicknesses, net-to-gross ratio, number of layers, etc. Then, many juxtaposition realizations are created from these parameters. When reservoir zone thickness is greater than the fault throw, the shale gouge ratio is reduced to a function of net-to-gross ratio alone. Afterward, we construct the probability distribution function of cross-fault transmissibility by combining juxtaposition, shale gouge ratio and dynamic data. Finally, the transmissibility probability is provided to the simulator for reservoir performance simulation. This procedure has been applied to the appraisal of an offshore oil field that has many faults and subseismic reservoir layers. The procedure is demonstrated in 1D but can be expanded into 3D by allowing the controlling parameters to vary with location.
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Matching to Geological Model Cuts Risk
Authors U. Strecker, M. Carr, S. Knapp, M. Smith, R. Uden, G. Taylor and M. T. TanerIn this case study from a fractured, locally karstified, and hydrothermally leached carbonate platform we show how proper selection of prognostic seismic attributes significantly rejuvenates a mature play by reducing drilling risk. To optimize rewards from applied subsurface geophysical interpretation, it proves beneficial to place seismic attributes into their proper regional geological context. The complex interplay between physical, geometric, and elastic formation parameters may assist exploration/exploitation efforts in advance by high-grading attribute selection during prospecting. The field-tested exploration strategy presented here encapsulates all pertinent play characteristics into a viable geological model within which each dominant reservoir property is expressed as a risk parameter that in turn can be resolved by a seismic attribute. Seismic attribute analysis permits illumination of discrete reservoir properties, specifically: 1.) fracturing, 2.) lithology (dolomitization), and, 3.) porosity.
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A New Approach to Quantifying Uncertainties, from Seismic Characterisation to Hydrocarbons in Place
Authors J. M. Guemene, B. PATERNOSTER, S. TOINET, P. BIVER, A. GORDON and H. DECLERCThe field presented is a gas accumulation situated in the UK. Three individual sands layers have been identified at the 4 wells. The total reservoir thickness is under seismic vertical resolution over most of the field’s extension.
An AVO seismic attribute obtained by combination of the near and far substacks exhibited a very good correlation with Net Sand Thickness at well locations.
An AVO versus net sand cross plot was generated from a massive modelling study. It was used to generate 200 possible Net Sand thickness maps by bivariate non linear collocated co-simulation.
200 top reservoir maps were simulated within the estimated uncertainty range. They were used to flex the geological 3D model.
For each of the 200 models, the porosity and permeabilities were produced by geostatistical simulation. The Gas Water Contact was randomly drawn within the uncertainty range, based on the interpretation of RFT data. The water saturation transition zone was defined by a J function and the associated uncertainty was modelled.
The resulting Gas in Place distribution was used to provide a set of realistic data as input for a range of reserves case scenarios and for key decision making.
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Comparison of Leadon and Gryphon Fields Sand Injectites - Occurrence and Performance
Authors G. Templeton, A. McInally, A. Melvin and T. BatchelorLeadon and Gryphon are early Eocene age Fields located 23 km apart but which could not be more different in terms of their production performance from sand injectites. Both Fields are located in the Beryl Embayment of the UKCS North Sea. Sub seismic Frigg sand injectites are the developed reservoir in the Leadon Field. First oil was achieved in November 2001. The main Gryphon reservoir is basin floor high density turbidite sandstones within the Balder Formation which were developed from October 1993. Since August 2004 production started from wells drilled into seismic scale sand injection wings in the Balder.
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Link between Elelctrical Resistivity and Seismic Velocity
Authors P. Hacikoylu, J. Dvorkin and G. MavkoThe main inputs for forward seismic modeling are the P- and S-wave velocity and density. A common problem is poor quality or absence of sonic, dipole, and density logs. It is important to reconstruct these curves from reliable measurements, such as resistivity. In an early attempt, Faust empirically relates the velocity and resistivity to the geologic age, depth, and lithology. This relation links the sonic velocity to the depth and formation factor (resistivity) and does not have any apparent physical basis because the velocity depends on the elasticity of a material while the resistivity describes its electrical charge transport capability. The observed link is most likely due to the dependence of both material properties on porosity. We analyze this link by using recent rock physics transforms between the velocity, porosity, and mineralogy, with existing empirical and theoretical resistivity-porosity models. We also use a number of high-quality data sets to verify the results. We find that Faust’s equation is applicable to consolidated cemented sandstones with low clay content and porosity between 5 and 20%. It should not be used in shale or unconsolidated and/or uncemented rock. We derive a family of new resistivity-velocity equations appropriate for various textures of clastic sediment.
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Seismic Reservoir Characterisation Using Vp-Vs Ratio in Tight Gas Sandstones
Authors E. Rojas, T. L. Davis, M. Batzle, M. Prasad and R. MichelenaBehavior of Vp/Vs depends on a variety of reservoir conditions such as lithology, pressure or fluids. However, common practice in Vp/Vs interpretation focuses on the effect of only one parameter at the time. Although it is common, for instance, to associate presence of sands to lower values of Vp/Vs, other parameters such as pressure or fluids may produce changes in Vp/Vs that diminish the lithology effect we are looking for.
In this paper we quantify the effect of different reservoir parameters on Vp/Vs to help the interpretation of Vp/Vs maps derived from seismic data. We find that in tight gas sandstones reservoirs, low Vp/Vs anomalies can be useful in prospect identification since they are related to good quality rocks (sandstones with low clay content), presence of gas, and overpressure conditions. These three conditions act in the same directions and all produce a decrease in Vp/Vs. In tight gas sandstones, gas saturation lowers Vp/Vs and the effect is larger if the reservoir is overpressured. Water saturation, however, increases Vp/Vs and this effect is enhanced with decreasing differential pressure. Tight gas sandstones typically have a Vp/Vs lower than that in shales.
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Mapping High Dis-Equilibrium Oil Saturations in the Chalk of the South Arne Field, Danish North Sea
Authors C. R. Schiøtt, O. V. Vejbaek, N. Bech and P. FrykmanFree water level (FWL) dips in excess of 200 m/km are encountered in the South Arne Field in spite of relatively normal mobility of the oil in main parts of this Upper Cretaceous - Paleocene chalk field. These dips are convincingly explained by filling simulation studies to be caused by variation in water phase mobility in combination with relatively late charging pulses. The low water mobility is controlled by the presence of a bottom seal Externally imposed pressure gradients in the water phase only plays a quite insignificant role. Pressure gradients in the oil phase due to oil migration into the structure are generally of minor importance. However, on the south-east flank natural imbibition is of some importance. In that part of the field, high FWL dips can also be sustained by reduced oil mobility. The dynamic nature of the field has imposed partial states of imbibition prior to production start. By accounting for the degree of imbibition, spatial variations in oil mobility and irreducible oil saturation can be predicted.
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Porosity Volume Attribute by Bayesian Estimation
Authors E. F. da Costa, A. P. Grell, F. S. Moraes and L. G. C. L. LouresWe propose a new volume attribute (residual porosity), consisting of a porosity perturbation generated from different saturation assumptions in a Bayesian porosity estimation framework. This idea explores the strong coupling existing between porosity and saturation. Using Bayesian inference and Gassmann model, porosity may be estimated using two different conditions for the reservoir water saturation: initial water saturation (e.g., Swi = 15 %) and fully water saturated (Sw = 100 %). The residual porosity volume attribute is further obtained by subtracting the two porosity volumes. This attribute should highlight the oil region of the reservoir, once the parameters for the Gassmann model are calibrated for oil reservoir condition from well-log data. We present an application to real data sets from Campos Basin, Brazil. A comparison of seismic volume inversion with well-log data inversion shows the usefulness of this approach for highlighting oil-saturated intervals.
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Example of Applied Stochastic Modeling in a Mature Field, A Case Study in Zamrud Field, Central Sumatra, Indonesia
Authors T. Norman, M. Willuweit, D. Hernadi and E. RukmonoThe Zamrud field is located in Badan Operasi Bersama PT. Bumi Siak Pusako – Pertamina Hulu (BOB CPP) block, Riau Province, 90 km east of Pekanbaru, Indonesia. Oil was discovered in September 1975 and the commercial production began in March 1982 and in December 1993 a combination of peripheral water injection and pattern water flood was initiated.
The sedimentological facies and the petrophysical properties of the field have previously been described through 2D average maps where the geological boundaries have been determined deterministically assuming homogeneous distribution in depth through each subzone. In order to capture the overall heterogeneity of the facies and petrophysical properties of the field, it was decided to model the field in 3D. The 3D modeling process for the Zamrud field consists of data preparation, import into a software package handling 3D modeling, quality control, definition and generation of a structural framework, stochastic facies and petrophysical modeling methods. The process of modeling also becomes repeatable and the updating process faster when new information is received through well data. Additionally, a better understanding of connectivities between the facies is gained.
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Studies of Reservoir Characteristics on the Basis of Proni Filtration Parameters
Authors G. Mitrofanov, A. Brekhuntsov and Y. IlyinIn the paper some approach to connection between surface seismic data and wells data, which characterize reservoir features, is presented. This connection is based introduces relationship between two combined parameters. One parameter is estimated from images of stacks in processing of the Proni filtration. Another parameter is a generalized characteristic of the logging data. As a result, we obtain equations which allow translation of the surface parameters into the interval values of the logging data. The estimating interval values provide basis for more accurate interpretation of the dynamic characteristics of the surface seismic data. We used this approach for determination of reservoir production features. The results were verified with the independent well data and provided good quality.
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P-Velocity - Porosity Relationship, an Approach to Characterize Carbonates Reservoir, Jurassic, Cavone Field, Italy
Authors M. Ibrahim and F. OglianiThe oil-bearing limestones of the Cavone field have been investigated to highlight the porosity types and their effectiveness, with the purpose of better characterize the reservoir and improve the production potentiality. The joint behavior of the wireline acoustic velocity and the neutron log has demonstrated to discriminate intergranular, fracture and vuggy porosities. Results are corroborated by core images at macro and micro scales. The obtained information enables the definition of new production intervals and hence sustains the field productivity.
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Comparisons of Model Independent Two-Parameter Moveout Formulas for the CMP Gather
More LessWe investigate different moveout equations used to describe reflection events in a CMP gather. For homogeneous models with flat and dipping reflectors the reflection event is hyperbolic and entirely defined by the well-known one-parametric normal moveout equation. To handle more complex reflection events several two-parametric moveout equations have been proposed. Although each traveltime equation has been derived for a specific class of models, our objective is to compare some of these moveout equations for a large range of different models. In addition to their ability to fit a reflection event from an arbitrary model we are interested in the accuracy of the parameter estimation.
For our tests we implemented a simultaneous parameter search to estimate the parameters from the data without using any a priori information of the model.
Our tests show that in cases where the standard hyperbola only accounts for near offset reflections, the investigated formulas are able to approximate a reflection event over a larger range of offsets.
However, the considered formulas are not similar, i.e. the equations show different behavior in order to treat deviations from the standard hyperbola.
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The Two-Parameter Approximation to Seismic Reflection Traveltimes
More LessThe seismic reflection traveltime curves are complicated, and depend on many parameters. There is a need for simplified equations involving a reduced number of parameters that can be estimated from data and used for moveout correction and velocity model building. Many authors have derived explicit equations for traveltime as a function of offset, involving several parameters depended on velocity. Some authors have also applied the approach in which velocity varies with offset. Here we present a new approach in which the velocity variation with depth or vertical travel time instead of offset. A simple linear variation of velocity is used to derive expressions for traveltime and offset as a function of ray parameter. Only two parameters are involved in defining the velocity depth profile, which leads to an implicit traveltime equation depending on only two parameters. However, the resulting traveltime-offset curves are very accurate for both short and long offsets. Alternatively, a two-parameter equation involving linear variations of slowness with depth or vertical travel time can also be obtained. Both the velocity and slowness expressions can be used for velocity analysis and moveout correction. Synthetic records are used to demonstrate their effectiveness.
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CRS-Stack-Based Seismic Imaging for Land Data - A Case Study from North Brazil
Authors Z. Heilmann, L. W. B. Leite and A. B. GomesAs recent case studies demonstrated, the Common-Reflection-Surface (CRS) stack produces reliable stack sections with high resolution and superior signal-to-noise ratio compared to conventional stacking methods. Particularly for land data, the
increased computational expense required by the generalized high-density velocity analysis preceding the CRS stacking process often proves to be worthwhile.
In order to define optimal spatial stacking operators, the CRS stack extracts for every sample of the zero-offset section an entire set of physically interpretable stacking parameters. These so-called kinematic wavefield attributes, can be applied to solve various dynamic and kinematic stacking, modeling, and inversion problems. By this means, a very flexible CRS-stack-based seismic reflection imaging workflow can be established. The main steps of this workflow are, besides the CRS stack itself, residual static correction,determination of a macrovelocity model via tomographic inversion, and limited aperture Kirchhoff migration. The presented extension of the CRS-stack-based imaging workflow supports arbitrary top-surface topography. Both CRS stack and also CRS-stack-based residual static correction are applied to the original prestack data without the need of any elevation statics. Finally, a redatuming procedure relates the CRS-stacked zero-offset section, the kinematic wavefield attribute sections, and the quality control sections to a chosen planar measurement level.
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Monitoring Reservoir Deformation on Land - Evidence for Fault Re-Activation from Microseismic, InSAR, and GPS Data
Authors S. J. Bourne, K. Maron, S. J. Oates and G. MuellerThree different types of areal reservoir monitoring data have been acquired over a compacting reservoir in Oman: (i) microseismic, (ii) GPS, and (iii) InSAR. The aim of this project is to demonstrate the value of these data for reservoir management.
More than 7,500 microseismic events were located during two years of continuous monitoring from five observation wells, 1 - 2 km apart. Microseismic events predominately occur on a specific subset of pre-existing faults. More than 2 years of near-continuous GPS monitoring are now available from a network of 50 sites. The pattern of horizontal displacements reveals a clear asymmetric pattern diagnostic of slip occurring on some buried portion of the main fault system. This is due to differential compaction on either side of the fault within the gas reservoir. Interferometric Synthetic Aperture Radar satellite images over the field show a sequence of increasing strain localisation above a specific fault segment that suddenly becomes a new centre for microseismic activity.
Together these data lead to the view that large-scale fault reactivation is occurring above, within, and below the depleting gas reservoir. To date, no well failures have been attributed to reservoir deformation. Microseismic and geodetic monitoring of the field is continuing.
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Monitoring Reservoir Fluids - Alternatives to 4D Seismic
More LessMany giant oil fields in the Middle East produce from prolific carbonate reservoirs. Collectively these reservoirs hold over 50% of world oil reserves. The high rigidity of rock matrix, a small contrast between the elastic properties of pore fluids, low gas-oil-ratio oil and mixed salinity water are responsible for the observed weak 4D seismic effect. An alternative reservoir monitoring technique is therefore considered. Permanent seismic sensors installed in a borehole and on the ground surface detect passive microseisms generated by reservoir pore pressure perturbations. Production and injection operations create these perturbations, induced by shear stress release, along zones of weakness in these rocks. Permanent pressure gauges will also be deployed for monitoring reservoir pressure changes. Microseisms emanating from the reservoir would be recorded simultaneously at multicomponent seismic sensors deployed permanently, at various levels in the borehole and over a surface area, surrounding the borehole. The triggered microseisms at the borehole sensors will be synchronized with microseismograms recorded in the surface sensors. The hypocenters are computed from such dense sensor network. Geophones with frequency response over 10-800Hz frequency would be installed. Reservoir heterogeneities affecting the fluid flow are mapped by the distribution of hypocenter locations of these microseisms.
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Added Value of a Long Term Subsurface Microseismic Surveillance - Case Study
Authors C. Maisons, E. Fortier and J. VernierThe paper presents results gained on a long-term permanent microseismic monitoring application case. It reviews the methodology applied to manage the data processing and it highlights the type of contribution to the dynamic characterization. From a case study dealing with solution mining it describes how the proof of microseismic surveillance concept can be evaluated using long-term experience gained outside the oil and gas business.
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Reservoir Compaction Quantification Using Geomechanical Inversion of Timelapse Timeshifts
Authors S. Tigrek and P. J. HatchellModelling and observation help us to quantify pressure-induced compaction in depleting reservoirs. Reservoir simulators and geomechanical modelling tools provide reservoir compaction maps based on forward modelling, while timelapse seismic data provide compaction maps based on observation in multi-dimensional space. Timeshift attribute of timelapse surveys is the key parameter to obtain reservoir compaction maps from seismic data.
The compaction timeshifts are small compared to seismic wave periods and various methods for measuring timeshifts will trade spatial and temporal resolution against noise suppression. For example, cross correlation techniques between the base and monitor surveys are robust to noise using long correlation gates but the resultant temporal smearing will mask the true timeshifts in the vicinity of the reservoir interval where the timeshift gradient changes sign. This can lead to inaccurate prediction of the reservoir compaction.
We propose to use geomechanical models to constrain our timeshift estimation and reduce the errors in the estimated reservoir compaction. This is done using an inversion algorithm that updates a geomechanical model to match the predicted time-lapse seismic response with the actual data. Tests on synthetic and real data examples show that the inversion procedure converges rapidly resulting in better resolution of the underlying reservoir compaction.
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Estimating Production Induced Stress Changes from 4D Finite Offset Timeshifts
Authors K. Hawkins, P. E. Harris and G. R. ConroySignificant stress changes are generated when producing reservoirs compact due to large reductions in the reservoir pore-pressure. These stress changes are not confined to the reservoir. They are redistributed to surrounding formations, modifying the formation velocity and thicknesses. These changes manifest themselves as timelapse time differences on 4D stacks.
Various authors (Hatchell et al, 2003; Barkved et al, 2005) have used geomechanical modelling to explain these 4D timeshifts, thereby gaining valuable insight into the behaviour of the subsurface around compacting reservoirs. This has been accomplished by assuming a simple relationship between thickness and velocity changes. The model is reiterated using updated relationships until a match is obtained with the observed 4D timeshifts.
We present an approach in which the 4D time differences are measured on prestack data. Without relying on assumed relationships between velocity and thickness changes, we use the additional finite offset information combined with raytracing and linear least squares techniques to derive the thickness and velocity changes. These resulting velocity and thickness changes combined with density and pore-pressure well data are then converted to stress and strain changes. Hence, the technique should close the loop between seismic 4D time differences and geomechanical stress and strain changes.
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Time Lapse Monitoring of Steam Injection Using High Resolution Seismic
Authors M. C. Schinelli, U. R. A. Lino, O. F. Keller and S. S. SacramentoIn order to monitor the efficiency of steam injection into thin reservoirs filled with paraffinic oil in Fazenda Alvorada field was decided to use uncommon acquisition parameters to obtain high resolution 4D. Other aspect of this project was the large time interval between successive acquisitions what became a challenge to that project where we achieved frequencies as high as 100 hz, superior to the 30 hz observed on the conventional seismic and which made possible to monitor the steam movement.
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Recovery Prediction for Cyclic-Steam Stimulation
Authors I. V. Kuvshinov, V. A. Kuvshinov and L. K. AltuninaThis paper describes the method for oil and water recovery prediction for Cyclic-Steam Stimulated (CSS) oil wells. The main feature of this prediction model is a choice of a cumulative injected steam quantity as "time" for a well activity. A validity of such a choice has been proved by experimental data. Basic predicted values are average water cut and total liquid production per cycle. Field data on water cut in chosen coordinate system has a simple fitted saturation function, and cumulative liquid production is linear. The special computer program, which allows entering field data and receiving all basic functional parameters for a future CSS cycle, has been developed for performing all necessary calculations.
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Time-Lapse Seismic Monitoring in the Gulf of Mexico - 10 Years of Experience
Authors M. M. Hartung and J. K. KosterShell has in the past 10 years acquired time-lapse data over 8 fields in the Gulf of Mexico (GoM). Direct cost for acquisition and processing for the total effort was $24 million. Total combined cost saving of the entire time-lapse effort is also $24 million. Most of the savings were realized in a single field. In addition, recoverable volumes were increased by 10 mmboe in one field and a contribution was made to mature another 3.5 mmboe in another field.
The observed time-lapse data was different from the expectation. The most important mismatch is the observed insensitivity of the reservoir impedance to depletion. For all surveys the expectation was that depleting reservoirs would show an easily detectable increase in impedance. It has now become clear that this increase is significantly smaller and hence harder to detect. The acquisition of future surveys has to better duplicate the base survey as a direct result of the need to detect subtle pressure depletion effects. Successful practices from the North Sea turned out to be inadequate in the GoM. On the positive side, saturation changes have invariably been larger than expected. Nearly all business impact from time-lapse seismic on the 8 fields has come from the interpretation of these saturation effects.
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Results of the Second Test Program in K12-B, a Site for CO2 Storage and Enhanced Gas Recovery
The project Offshore Re-injection of CO2 (ORC) aims to investigate the feasibility of CO2 injection and storage in depleted natural gas fields in the Netherlands. The objective is to realize a permanent CO2 injection facility in the near future. The mature gas field K12-B was selected as demonstration site for the ORC project. The project is subsidized by the CRUST subsidy arrangement of the Dutch Ministry of Economic Affairs.
K12-B is the first test site in the world where CO2 is injected into the same reservoir from which it originated. A unique measurement program is being executed including the use of tracers and the monitoring of pressure and temperature at various locations.
This paper presents the preliminary results of the second test in K12-B which commenced in February 2005 and, in case of sufficient CO2 supply, will continue at least until the second half of 2006. The measurements of this test are difficult to interpret as a result of unexpected features in the pressure data. The use of tracers has contributed to an improved understanding of how these data should be interpreted. The storage potential and potential for enhanced gas recovery are currently under investigation.
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Interpretation of Fluid-Induced Microseismicity at 4km Depth at the German Deep Drilling Site (KTB)
By J. KummerowWe analyzed micro seismic data observed during a recent hydraulic experiment at the KTB site, Southeastern Germany. Following a one-year fluid extraction phase in 2002-2003, fluid was injected directly into a continental crustal fault at 4 km depth over a period of one year in 2004-2005. Seismicity was monitored by a borehole sensor and a near-surface seismic network. Precise location of 150 micro earthquakes indicates that the seismicity remains guided by this fault. The seismicity is triggered by small positive pressure perturbations (<1 bar). Moreover, the onset of seismicity approximately coincides with the time of compensation of the extracted fluid volume by the following injection. This confirms that pressure diffusion is a dominant mechanism of seismicity triggering by fluid injections. We estimated the hydraulic diffusivity using the spatio-temporal characteristics of the induced events. The hydraulic diffusivity of the probed fault is about one order of magnitude larger than that of the surrounding rocks. The fault shows a significant anisotropy and non-linearity of its hydraulic behaviour.
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4D Reservoir Monitoring with Gravity Measurements and the Potential Application to Carbon Dioxide Sequestration
Authors D. Bate, P. Versnel and P. StylesPrecision measurements of Earths gravitational field with modern gravity meters can give useful information about subsurface reservoir fluid movement. A change in pore fluid density gives a change in the bulk rock density which is potentially detectable at the surface. Trial surveys over two depleted gas reservoirs now used as gas storage reservoirs have proved that reservoir fluid movement can be detected with gravity monitoring. Both continuous and time-lapse readings were taken. At the Hatfield Moors reservoir a high level of noise due to changes in the shallow water table was detected. However, at the Izaute reservoir a good correlation with the gas stock and pressure data was achieved. When the spatial pattern of maximum gravity change over the reservoir is compared with the forward modelled response, which assumes homogenous reservoir properties, a good first order correlation is observed. However, there are areas of the maximum gravity change pattern that do not fit with the modelled response. These anomalous areas could be showing areas of the reservoir that have different porosity and permeability. This technique has many applications in reservoir monitoring, particularly where 4D seismic is unsuccessful or expensive, and also as a monitoring tool for CO2 sequestration.
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Dynamic Non-Planar Crack Rupture by a Finite Volume Method
Authors J. M. Virieux, M. Ben Jemaa, N. Glinsky and S. PipernoUnderstanding the physics of the rupture process requires very sophisticated tools where the geometry of the ruptured surface has to be taken into account as well as realistic friction laws on this surface. New formulations have been recently proposed for modelling the dynamic shear crack rupture using various methods. We propose a complete new reformulation based on a finite volume approach and we apply it to canonical configurarions in order to assess the accuracy of the method we propose.
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Effective Elasticity of Rocks with Irregularly Shaped and Intersecting Cracks
Authors V. Grechka, I. Vasconcelos and M. KachanovA circle is the basic fracture shape adopted by conventional effective media theories to
describe the overall elasticity of cracked solids. As fractures in rocks do not resemble circles, it is important to find out to what extent the available theoretical results are applicable to realistic fracture shapes. To address this issue, we conduct 3D numerical experiments on the so-called digital rocks containing irregular cracks that might be
partially closed and might intersect each other.
Despite profound deviations of our fracture geometries from circles, we find that the theoretical results originally developed for penny-shaped cracks remain valid for a wide variety of irregular planar fractures. Based on a series of finite element computations, we show the following:
(1) As far as the effective elasticity is concerned, fractures with random in-plane irregularities are accurately represented by the circular ones.
(2) Approximate effective elliptical orthotropy established for multiple sets of dry,
non-intersecting, penny-shaped cracks embedded in otherwise isotropic host rock also
holds for irregular, possibly intersecting fractures.
In essence, our findings show that the theories developed for penny-shaped fractures can be applied with confidence to cracks in real rocks.
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Determining the Dilation Factor in 4D Monitoring of Compacting Reservoirs by Rock-Physics Models
More LessHydrocarbon depletion and fluid injection cause compaction and stretching of the reservoir and overburden layers. 4D pre-stack seismic data can be used to detect these changes because compaction/stretching causes changes in traveltimes and seismic velocities. We show that, by using two different petro-elastic models at varying effective pressures, a good approximation is to assume that the fractional changes in layer thickness and seismic velocity, are related by a linear function of the layer thickness. This function (dilation factor) is negative and its absolute value generally decreases (shale, low porosity) or increases (sandstone, high porosity) with increasing layer thickness and decreasing effective pressure. The dilation factor, which can be calculated from time-lapse seismic data, can be used to predict reservoir compaction/stretching as a function of depth and surface subsidence.
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Using RFT Data for Elastic Rock Properties' Dependency on Pore Pressure in 4D Quantitative Analysis
Authors H. J. Hansen, L. Gommesen and Y. El OuairFormation pressure data (RFT) for the Brent formation of the Gullfaks Field has been used together with quality checked well log data to estimate the dependency of elastic rock properties on in situ formation pressure. Acoustic impedance versus RFT pore pressure shows a decrease in acoustic impedance with increasing pore pressure. The observed trend in the acoustic impedance-RFT pore pressure domain shows a slight correlation with porosity, but no correlation with clay content and burial of depth. The analysis is focused on brine saturated points, as the estimation is very sensitive to fluid content. We suggest that the dependency of elastic rock properties on pore pressure estimated from well log and formation pressure data (RFT) may be used as an alternative to, or in combination with, core measurements, and in this way improve the understanding of the pressure component in 4D quantitative analysis.
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Scale in Rock Physics - Caveats and a Remedy
Authors L. Hubert, J. Dvorkin, R. Cooper and R. UdenInversion of the seismic amplitude into impedance is attractive because impedance is a layer property while amplitude is a property of the interface between layers. Impedance is directly measured during controlled experiments in the lab and in the well, together with porosity, mineralogy, pressure, and saturation. As a result, one can first establish rock physics transforms from the rock’s elastic properties into its bulk properties and conditions and then apply them to the seismic impedance to describe the subsurface. The scale of data acquisition is very important in this workflow. Remember that while a rock physics transform, such as that between velocity and porosity, is established at the lab or log scale of only inches and feet, we aspire to apply it to seismic data on the scale of tens and hundreds of feet. Direct and unconditional use of such rock physics transforms, applied to seismic impedance volumes without accounting for scale effects, will produce erroneous results. We show that a new type of seismic attributes - cumulative attributes - can help remedy this problem.
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Global Petro-Elastic Model (gPEM)
Authors I. Escobar, M. Recordon and P. WilliamsonA Petro-Elastic model is often tuned to a given dataset using a trial-and-error fitting approach. A new approach is presented, where this 'manual inversion' is re-formulated as a global and almost automatic optimization problem. The parameterization in terms of saturations, pressure, and temperature has been simplified and embedded as an objective function within a simulated annealing algorithm. The implementation is object-oriented, allowing for easy modification, and improvement, as well as an easy selection of inversion parameters. It has been successfully tested on well data from West Africa and the North Sea. In both cases, parameters controlling the pressure sensitivity (frame compressibility) of sand and shale were inverted. The global optimization also provides valuable information regarding uncertainties on the model predictions and eventually on the data itself.
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Dual Porosity Biot-Barenblatt Model
Authors G. M. Goloshubin and D. B. SilinDual porosity Biot-Barenblatt poroelastic model is analyzed. P-wave reflection at an impermeable interface between elastic and dual-porosity media is investigated. Asymptotic low-frequency analysis of the planar p-wave reflection coefficient from a hydrocarbon reservoir shows that the frequency-dependent component is proportional to the square root of the reservoir fluid mobility. Frequency-dependent seismic attribute analysis has been applied for mapping of high fluid mobility zones of oil-saturated reservoirs. As the obtained asymptotic scaling links reservoir rock and fluid properties with seismic attributes, it has a great potential for hydrocarbon exploration and production.
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Slow Compressional Wave in Porous Media - Finite Difference Simulations on Micro-Scale
Authors E. H. Saenger, R. Ciz, B. Gurevich and S. A. ShapiroWe perform wave propagation simulations in porous media on microscale in which
a slow compressional wave can be observed. Since the theory of dynamic
poroelasticity was developed by Biot (1956), the existence of the type II or
Biot's slow compressional wave (SCW) remains the most controversial of its
predictions. However, this prediction was confirmed experimentally in ultrasonic
experiments. The purpose of this paper is to observe the SCW by applying a recently
developed viscoelastic displacement-stress rotated staggered finite-difference (FD)
grid technique to solve the elastodynamic wave equation. To our knowledge this is
the first time that the slow compressional wave is simulated on first principles.
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Effective Diffusivity of Heterogeneous Porous Rocks
Authors T. M. Mueller and B. GurevichModern reservoir monitoring technologies often make use of diffusion waves
in order to estimate the hydraulic conductivity and diffusivity of reservoir rocks.
Analysis of diffusion wave fields in randomly inhomogeneous poroelastic structures
provides new insight how fluctuations of the compressible constituents of
the rock affect the effective diffusivity.
Based on the method of statistical smoothing an effective wave number of the
coherent diffusion wave field is computed.
From this wave number both an effective conductivity and diffusivity are
identified.
The correspondence between this conductivity and that estimated from unsteady
flow through porous media based on Darcy's law is elucidated.
It is shown that in the limits of low and high frequencies these effective
conductivities are identical.
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Attenuation and Dispersion in Fluid-Saturated Rocks Due to Circular Cracks
Authors R. J. Galvin and B. GurevichWe consider interaction of a normally incident time-harmonic longitudinal plane wave with a circular crack imbedded in a porous medium governed by Biot’s equations of dynamic poroelasticity. The problem is formulated in cylindrical coordinates as a system of dual integral equations for the Hankel transform of the wave field, which is then reduced to a single Fredholm integral equation of the second kind. The solution of this equation yields elastic wave dispersion and attenuation in a medium containing a random distribution of aligned cracks. These dissipation effects are caused by wave induced fluid flow between pores and cracks.
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