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58th EAGE Conference and Exhibition
- Conference date: 03 Jun 1996 - 07 Jun 1996
- Location: Amsterdam, Netherlands
- ISBN: 978-90-73781-07-8
- Published: 04 June 1996
61 - 80 of 604 results
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Stress-induced coupling between anisotropic permeability and shear wave splitting
Authors S. V. Zatsepin and S. CrampinThe stress-sensitivity (poro-reactivity) of fluid saturated porous rock leads to effective anisotropy in the permeability of many laboratory experiments and in large-scale field phenomena such as the natural directivity of water-flooding caused by horizontal differential components of the regional stress field (Heffer and Koutsabeloulis 1993). One of the most interesting features of stress-sensitivity of porous rock is the effect of the coupling between stress-induced variations in anisotropic permeability and elastic shear-waves (King et al. 1994) that in principle allows changes in reservoir rock permeability to be monitored with seismic shear waves (Crampin 1994). A previous theoretical consideration of the possible stress-induced coupling between the permeability and elastic waves (Gibson and Toksoz 1990) was restricted to uniaxial stress that seems inappropriate for in situ situations where the horizontal differential stress field and horizontal permeability anisotropy is of primary importance. We present a theoretical model for the coupling between permeability and elastic waves in a triaxial differential stress field and elevated pore-pressure based on the APE model of anisotropic poro-elasticity of Zatsepin and Crampin (1995).
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Acoustic monitoring of hydraulic fracture growth
Authors J. Groeneboom and R. RomynHydraulic fracturing is a technique to improve the production of oil and gas reservoirs by creating large fractures around the wellbore. The success of fracture treatments is critically dependent on our ability to predict and influence the fracture orientation and shape. Computer models based on simplified theoretical concepts are a useful tool to study the physics of fracture growth. However, theoretical models have to be calibrated by real physical experiments to prove their value. For this purpose an experimental set-up has been built in our laboratory in which we can carry out scaled hydraulic fracture treatments in a true tri-axial pressure cell [WIJERS 1995]. We have chosen to monitor the fracture growth process with ultrasonic waves. In this manner we obtain information on the growth process also away from the wellbore [SAVIC 1995]. The scaled experiment closely resembles seismic monitoring surveys of fracture treatments in the field [MEADOWS AND WINTERSTEIN 1994, WILLS ET AL. 1992]. Since the start of the project considerable experience has been gained in using ultrasonic measurements to interpret the scaled fracture experiments. We will present the major achievements of the ultrasonic experiments during the last few years.
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Numerical simulation of ultrasonic experiments on poroelastic samples
By B. GurevichSince the theory of dynamic poroelasticity was developed by M. Biot some 40 years ago, the existence of the type II or slow compressional wave (P2-wave or SCW) remains the most controversial of its predictions. This prediction was confirmed experimentally when SCW was observed in ultrasonic experiments by Plona (1980), and later by Rasolofosaon (1988) and others. Theoretical analysis shows that the observed vaveltimes of the SCW are consistent with Biot theory. And yet, the very existence of the SCW remains a mystery to many geophysicists and acousticians alike. The purpose of this paper is to further verify the predictions of Biot theory by accurate numerical simulations of the ultrasonic experiments in which SCW was observed.
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Effects of the conductivity / permittivity ratio on the dispersion and attenuation of radar signals
Authors J. W. Schoolmeesters and E. C. SlobIn modelling and processing of Ground Penetrating Radar (GPR) data, the distortion of the radar signal as it propagates through the ground is often neglected, see e.g. Davis and Annan, 1989. In the frequency range of interest for GPR applications, 10 MHz to 1 GHz, the loss mechanism in the ground is usually described by an exponential damping factor along the path of propagation.
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Dispersion of GPR waves
Authors S. Tillard, F. Hollender and F. JulienPerformed in boreholes drilled in galleries, Ground Penetrating Radar (or GPR) is a geophysical exploration technique expected to be used to characterize geological formations for deep radioactive waste disposal. In the case of an electrically resistive host rock such as granite, this technique must be able to localize in 3D, on a 0-100 m investigation range, the altered fissured zones. The aim is to know the ground water flow around the disposal.
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GPR Forward modelling applied to archaeological and engineering problems
More LessThe applications of ground penetrating radar (GPR) as an ecological, high resolution nondestructive technique are widely documented. A good review and state of the art can be found in the last special issue of the Journal of Applied Geophysics (Owen, 1995). In particular, forward modeling in heterogeneous media is essential to validate the geological interpretations.
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Recent advances in the multifold and 3D exploration of the Aquileia Archaeological Park
Authors M. Pipan, I. Finetti, A. Del Ben and F. FerigoA GPR exploration programme was completed in the area of the archaeological park of Aquileia. The research programme pursued the following primary objectives: 1. Implementation and test of integrated 2D and 3D multifold GPR techniques for the detection of buried masonries of archaeological interest 2. Implementation and test of radar soundings analysis techniques for optimum subsurface imaging and detection of the characteristic response of specific targets 3. Investigation of a unexplored sector of the Aquileia archaeological park for the identification of targets of potential archaeological interest
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Fragmentation processes in geodynamic systems - Clustering phenomena
Authors C. Suteanu, D. Zugravescu, C. Ioana and F. MunteaunuCracks' nucleation, growth and interaction, followed by solids fragmentation, are important processes affecting many geodynamic structures, with direct impact on man's environment.
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The effect of micro-properties on P- and S-wave attenuation in rocks
Authors M. Nabi-Bidhendi and M. S. KingThe spectral ratios technique is employed to measure the values of dissipation factor Q' , on four sandstone samples as functions of confining stress in both the dry and fully saturated states.
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Shock tube experiments on air-filled porous rocks
Authors C. J. Wisse, M. E. H. van Dongen and D. M. J. SmeuldersInterpreting seismic and petrophysical exploration data requires a thorough understanding of the effects of the medium's properties on wave propagation characteristics. It was already argued by Biot (1956) that acoustic waves in porous media may at low frequencies be described by diffusion-like equations. This means that inertia terms are negligible compared with viscosity terms, and that a strong dispersion both in damping and velocity occurs. Experiments, analytical and numerical calculations on an air-saturated porous rock sample have been carried out.
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Non destructive control of non metallic pipes using direct current and georadar
Authors P. Andrieux, O. Martire, L. Frobert and F. DubreucqGeoradar is now classical for non destructive control of large sewers and water pipes. There may be difficulties for the base of the pipes because of running water. A direct current technique, intermediate between logging and surface geophysics, is thus proposed for this purpose.
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A Practical accuracy of the surface NMR measurements
More LessA measurement of a Nuclear Magnetic Resonance (NMR) signal directly from subsurface water molecules is the most important distinction of the NMR in comparison with other methods of geophysics. The existence or absence of the NMR signal with a high degree of reliability also proves the existence or absence of subsurface water. The surface NMR system "Hydroscope" was developed by ICKC in the early eighties. It was tested in many countries in a variety of geological environments. The results affirm that parameters of the NMR signal depend on parameters of the aquifer. However the weakness of the signal, whose amplitude is not more than just a few micro volts, rises a question about the accuracy of the field measurements.
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The contact mode of polarisation curve - A Technique to evaluate conducting mineral deposits
Authors C. Serwanga, J. Roy, O. Putikov and M. HaleModem mineral exploration techniques are aimed at deep deposits under complex geological conditions, but the ultimate procedure for evaluating these deposits requires costly core drilling. Geophysical and geochemical methods of borehole investigation allow a significant decrease in the number of boreholes necessary to evaluate a deposit (Ryss, 1981). Some of these techniques are efficient but sometimes the lack of a good physical property contrast does not permit to decrease the number of boreholes necessary for a reliable evaluation due to the difficulties in the interpretation of the results. For a physicochemical investigation to be an adequate substitution for some of the boreholes, the chemical elements and minerals of which the ore body is made, should participate in processes which allow them to exhibit their own characteristic properties. The research work presented, sought in part, to verify the possibility of identifying known mineral potentials in a prototype contact polarisation curve (CPC) data set. After considering the problems experienced with the technique, an evaluation of the applicability of the technique in other environments was estimated.
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Change of a geoelectrical section under effect of elastic fields
Authors B. S. Svetov, E. L. Ozerkov, V. V. Tikshaev and O. A. AgeevaIn the last years Russian scientists from Low-Volga institute of geology and geophysics (Saratov) made some experiments to study an influence of vibrating effect on electromagnetic soundings results. These works were perfumed to investigate a possibility to raise on this basis the geological efficiency of oil and gas deposits prospecting. On fig .1 the results of one of such experiments perfumed on a broken by active faults seismic structure in Near Caspian depression are presented.
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Physical modelling electromagnetic field in dispersive media and criteria of similarity
More LessPractically the theory of all electromagnetic (EM) geophysical methods is based on the quasistationary approximation, which is valid for such a frequency range, in which usual displacement currents are neglected. However most of rocks display volume induced polarisation (IP), or low frequency dispersion of conductivity (LFDC) within of the same range.
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Electromagnetic sounding of frequency dispersive media
Authors B. S. Svetov and V. V. AgeevIn the last years Russian scientists experimentally established very high resolution of transient sounding (TS) inexplicable in frameworks of quasistationary electrodynamics of continuous media.
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Multipole arrays in direct current modelling and two case histories
Authors P. Brunel, P. Poussoumandji and P. AndrieuxResistivity and polarisability are two key parameters in environmental studies, civil engineering and archeology. Multipole arrays provide a large amount of data which lead to detailed images of the geology and ultimately to acceptable models via an inversion procedure.
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Magnetotelluric tracing of the Carpathian conductivity anomaly in the Vienna Basin
Authors L. Vero, A. Madarasi, W. Seiberl and G. VargaIn the framework of the scientific co-operation between the Geologische Bundesanstalt (Austria) and the Eotvos Lorand Geophysical Institute of Hungary (ELGI) the latter performed magnetotelluric soundings along a profile of about 80 km which traverses the Vienna Basin in NW-SE direction. The line starts from the Little Hungarian Plain, part of the Pannonian Basin, at the border zone of Austria, Slovakia and Hungary, while the NW end of the profile is located in the Cretaceous-Paleogene flysch zone.
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Distinguishing of faults and determination their tracing depth by electromagnetic sounding
Authors G. B. Agakuliyev, K. M. Kerimov, A. I. Manafli and A. A. AbbasovaAs is known, deep faults exert considerable influence on formation of the regional block structure of individual areas. They are one of important factors for formation and accumulation of useful minerals including oil and gas. Besides this accurate distinguishing of faults, determination of their orientation and tracing through the depth are very important to study and prognosticate earthquakes because of that site zones of earthquakes are mainly associated with the areas of intersection of faults. Definite criteria to single out deep faults both the ones traced at the surface and buried by young deposits are characteristic to geophysical methods and particularly to seismic and gravity prospecting.
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Strategies for reconciling seismic attributes with well data
Authors C. H. Skelt, M. D. Cann, D. A. Scott and C. P. WoodAreal prediction of formation petrophysical characteristics from seismic attributes related to well data has been transformed over the past few years from an esoteric technique practised by a small coterie of specialists to one used by most self-respecting petrophysicists and geophysicists. Much of the literature published to date has concentrated on demonstrating new detailed physics or mathematics in specialized case studies. Routine use of these techniques has necessitated developing various methodologies for applying them within the context of the broader hydrocarbon exploration and development decision malting process. With the benefit of several years practical experience several key recommendations may be made.
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