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- Conferences
54th EAEG Meeting
- Conference date: 01 Jun 1992 - 05 Jun 1992
- Location: Paris, France
- ISBN: 978-90-73781-04-7
- Published: 01 June 1992
1 - 50 of 405 results
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3D Seismic: A strategic tool in exploration and production
More LessSince the first 3D survey seventeen years ago, Companies of the Shell Group have operated nearly 250 such surveys outside North America and, as non-operating partners, have been involved in many others . Managing safety and paying proper attention to environmental impact is in increasing challenge.
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Comparison of seismic results after Dip and Strike acquisition
More LessModel studies have shown the advantage of acquiring seismic data parallel to the main tectonic directions or to lithological variations . For instance, for an imaging problem below a fault, if the acquisition is orthogonal to the fault plane, the seismic ray paths are crossing the fault and will be affected if the acquisition is parallel to the fault plane, all the-ray paths are in the same panel and wil] not be distorted . In the Jatter case, we therefore have better conditions for applying traditional processing tools and, more especially, for applying Normai (hyperbolic) Move Out .
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Seismic acquisition in the vicinity of a large compressor plant
Authors R. A. Brook, D. L. Bremner and R. P. DartThe use of 3-D seismic in the exploitation of mature fields is betoming increasingly common . However, in many cases noise generated by oil field equipment compromises data quality . This paper describes a prospect that was considered a no record area within a 3 km radius of a large compressor plant . A noise study shows that witti careful parameter design and new recording techniques useful data can be collected witpin 200 m of the plant .
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Design of 3D land acquisition in a structurally complex environment
Authors J. M. Mougenot, E. Robein, J. Ravat and A. MorashSince 1987, 3D seismics have been the main tool used by ELF AQUITAINE for exploration as well as for field development in the Pyrenees foothills (Aquitaine basin of South France) . The geological context made of very tectonized structures and the . rather poor signal/noise ratio at target depth (4500 m to 5500 m) have led to develop specific design tools for these 3D surveys .
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Efficient 3D surveys in a jungle environment
Authors M. F. Bee, H. Supiyanto, J. M. Bearden and E. F. HerkenhoffFor the last fourteen years , Caltex Pacific Indonesia (CPI) has been acquiring 3-D data over existing production fields in the jungle and/or swampy environment of Central Sumatra , Indonesia . The recent years have seen an increase in 3 -D activity in CPI which has forced an evolution towards cost reduction without jeopardizing data quality. CPI has successfully developed 3-D acquisition techniques which are operationally feasible and economically attractive . This achievement is the result of careful planning to optimize field parameters, the use of a gapped inline swath geometry, an increase in the number of channels available for recording , an increase in the rintis (Jungle cutting for acces) and drilling effort, surveying with GPS, and radio shooting . This paper wilt describe the above techniques and their advantages it will also demonstrate that the 3-D data acquired is of high quality with uniform fold , good offset and azimuth distributions, and economically reasonable for the difficult environment .
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Multidimensional seismic exploration and its first application results
Authors A. S. Kashik, V. KH. Kivelidi, D. P. Zemtsova and V. A. MilashinA further enhancement in the accuracy of the seismic explóration methods is associated witti the development of 4D and 5D technologies based on a rational integration of profile data witti borehole measurements for more detailed study of geologie features and for monitoring the wavefield parameters in the course of the reservoir development . Witti regard to onland operations, concurrent observat.ions in a number of Wells, with the shot point locations scattered over an area, will permit : a) depth of the subsurface survey to be enhanced by deeper placing both source and especially receiver locations, below the near-surface section which is narmally a severe filter for waves reflected from deeper interfaces ; b) velocity determination accuracy to be mach improved by processing data from individual Wells and by comparing the results in overlap zones ; c) time sections to be obtained from various depth levels ; d) reflection horizons to be correlated along profile lines and over an area
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Luna-Hera Lacinia 3D case history: solving complex structures in presence of heavy operative constraints by combining different acquisition techniques
Authors L. Bertelli, A. Nicora and L. SalvadorThe Luna - Hera Lacinia - 3D survey (Offhore Calabria, Southern Italy) covers an area of about 180 square Kms and represents an excellent example of the integration of deep, shallow marine and land 3D acquisition techniques . The survey has been acquired as a "full 3D" on an area characterised by a complex marine and land morfology with serious land operating constraints and complex subsurface structures at a commercially acceptable cost. The target of the survey was to define the structural setting of the miocene reservoirs of Luna and Hera Lacinia gas-fields in order to optimize their development stage. Considering the difficulties, the survey initially required an adequate planning of the various stages of operation and following this a numerical simulation to evaluate its effectiveness .
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Velocity errors in linearized elastic inversion
Authors A. de Nicolao and G. DrufucaErrors in velocity on the overburden produce depth errors in the target and also a distortion of behaviour of amplitude and phase versus offset . The paper presents a quantitative description of these effects for a simple Barth model using linearized roversion (De Nicolao et al ., 1991) . Even few percents of relative velocity error are very damaging to the results .
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Velocity discrimination by differential semblance
Authors W. M. Symes and M. KernThis paper presents an algorithmfor estimation of seismic p-wave velocity from multioffset reflection seismograms . The algorithm optimizes a cost function, part of which is the mean-square error between predicted and data seismograms . It also includes a, differential measure of event semblance or coherente, whence its name : differential semlance optimization . Unlike other implemations of the mean-square error criterion, the differential semblance version retains sensitivity over a wide range of velocity models . We present some numerical evidente of this sensitivity, using an example drawn from the Marmousi model [1] . A previous implementation of differential semblance optimization for acoustic p-tau data and layered models has been applied with success to both synthetic and field data sets and has a complete mathematical justification [4] . Therefore a, subsidiary purpose of this paper is to demonstrate an implementation of differential semblance in a non-layered ("complex structure") context . We employ the perturbational (generalized Born, primaries-only) approximation to the 2D constant density acoustic model . The velocity is split into a smooth background velocity v and a rough (oscillatory) reflectivity r = ðv/v, the latter regarded as a perturbation of the former . Denote the seismogram (i .e . suite of shot gathers corresponding to shot positions x,) by S(v)(x,t, x). Note that S depends linearly on R and nonlinearly on v . Let Sdata devote a, data set to be inverted.
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Linearized elastic inversion for multioffset marine seismic data
Authors D. Mace, A. Bourgeois, G. Etienne and V. RichardFor each shot s, the linearization consists in substituting the observed field Ps by the sum of the primary field Ps and of the scattered field ðPs where Ps corresponds to the non linear propagation in the reference medium m0 and ðPs is a linear function of the perturbation ðm which is computed from the Jacobian Js of the non linear operator at m0 . The process of linearization is associated with smalt perturbations.
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Paraxial wave equation inversion with geometric constraints
By C. BunksThe paraxial wave equation is one of the most accurate pre-stack imaging tools for seismic data . It has been shown that pre-stack paraxial wave equation migration correctly images seismic data even for very complex velocity models (such as those containing caustics). Furthermore, the fact that the paraxial approximation yields a one-way wave equation is ideal for migration and imaging since in principle it does not generate reflections as do the acoustic and elastic wave equations. Nevertheless, the formulation and implementation of the paraxial wave equation give rise to some undesirable numerical artifacts.
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Calculation of the differential semblance gradient
Authors M. Kern and W. M. SymesA major computational task in implementing the Differential Semblancce Optimization method (see the companion paper [2] for a presentation of the method) is an accurate computation of the gradient of the objective function. In this paper , we show how such a computation may be accomplished, and assess its accuracy on a representative example.
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Determination of fresnel zones by traveltime inversion
Authors P. Hurbal, J. Schleicher, M. Tygel and C. HanitzschSeismic wave propagation in the high-frequency range is usually described by (zero-order ) ray theory. Its validity conditions are extensively investigated, e.g., by Kravtsov and Orlov (1990) . For finite frequenties a ray can only be viewed as a mathematical concept . There is a ( frequency-dependent) region in its vicinity that influences the wavefield received at the end of the ray . This region is the so-called (first) Fresnel volume of the ray . Any cross-section through it is a Fresnel zone. (Gelchinsky, 1985; Cerveny and Soares, 1992; Knapp, 1991) . In other words, the Fresnel volume is the envelope of all Fresnel zones along the ray. For seismic stratigraphic modeling, usually the Fresnel zone at the reflector is of interest, so as to know which part of it contributes to the reflected field . Fresnel zones are computed very efficiently by forward dynamic ray tracing through a known velocity model (Cerveny and Soares, 1992) . However, exploration geophysicists involved in a stratigraphic analysis would prefer to know the Fresnel zone of a reflecting interface without knowing the details of the reflector overburden, i .e., they are interested in solving an inverse problém . For a plane layered Barth model, it is possible to solve this inverse problem (i e., to calculate the Fresnel zone directly from measured traveltimes, e.g., Erom the rms-velocity) .
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Nonlinear inversion of seismic reflection data: state-of-the-art
Authors A. Tarantola, M. Noble, C. Barnes, M. Charara, H. Igel, J. Lindgren, G. Röth and N. RoxisThere is little doubt that to extract a maximum of information from seismic data, one must try to fit the observed waveforms by synthetic waveforms, obtained through careful modeling of the propagation of seismic waves.
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Nonuniqueness in nonlinear traveltime tomography
Authors J. R. Matarese, W. L. Rodi and M. N. ToksozMethods of crosswell tomography have focused largely on the construction of images of seismic velocity and little on the uncertainty, or nonuniqueness, of such images . In this paper we address the Jatter problem using a Backus-Gilbert methodology adapted to nonlinear inverse problems.
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Borehole coupling effects on clamped geophone responses: experiments and theory
Authors M. H. Worthington, C. K. Jituboh, C. Chang and S. K. ChangSeismic waves detected by clamped geophones in a borehole can be affected by the borehole at high frequenties (Chang et al, 1989). A 20 cm diameter water filled borehole resonates in anti-syminetric mode at approximately 4 kHz and in symmetric mode at approximately 9 kHz. Below 2 kHz, the clamped geophone response is a combination of monopole, dipole and quadrapole vibirations in the borehole. To illustrate these effects, a, crosshole experiment was perfomed at the Imperial College borehole test site. Figure 1 Shows veldcity and gamma logs from the site and the source and receiver distribution in two, vertical holes. A three component clamped accelerometer was positianed at. 65m and 105m depth and detonators were fired at 5m intervals from 30m to 105m in the other Hole. The inter-hole spacing is 25m . The accelerometer was specifically designed to be free of resonances up to at least 2.5 kHz . Figure 2 (a.) and (b) show the recorded waveforms and the corresponding first arrival P wave hodograms from the radial and axial components of the accelerometer when positioned at 65m and 105m depth respectively. Depths in these figures refer to the positions of the source . The dominant frequency of these data. is at 1 kHz. Note that there is very little axial vibration when the source and the receiver are at approximately the same depth where as at, larger depth offsets, the hodograms are elliptical. It is conceivable that some hodogram ellipticity might result from interference between the direct and reflected or refracted waves within the multi layered medium. Full elastic wave finite difference modelling was perfomed with a model based on the borehole sonic and density logs. Hodograms calculated from these synthetic seismograms are shown in figure 2 (b) (labelled MODEL) and are seen to be essentially linear.
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Borehole effects on downhole seismic measurements
Authors C. Peng, C. H. Peng and M. N. ToksozThere are increasing interests in acquiring crosshole and VSP surveys at frequency up to 1 kHz or more, with the intention to resolve the fine details of structures and lithology between Wells (Bregman et al ., 1989; Harris, 1988; Tura, 1991) However, at frequencies on the order 1 kHz, the existence of the fluid-filled borehole has a strong influence on the downhole measurements. Depending on the frequency and angle of incidence, as well as the formation properties, the measured displacements on the borehole Wall or pressure at the center of borehole may be significantly different from those of the incident wave. Without taking proper care of this effect, any imaging or inversion algorithm which utilizes both the amplitude and phase information of recorded energy will produce erroneous results.
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Reservoir definition using triaxial walkaway VSPs
Authors K. J. Dodds, M. A. Jones, M. Idrees and W. S. LeaneyA gas discovery was made by British Gas with an exploration well in block 47/4b of the UK continental shelf. It was important to define the extern of the reservoir particularly to the North West . The structural history of this location is extremely complex, panicularly with respect to the near surface . Ray-path distortion through the complex overburden means conventional surface seismic data is of extremely poor quality, making interpretation difficult . British Gas embarked on an extensive walkaway and offset VSP program on well 47/4b- 5 The success of these surveys to image the Rotliegende azimuthally from the well was dependent on the ability of the processing to compensate for ray - path distortion together with a confident separation of shear and compressional components. The key step involved the extension of parametric inversion developed for VSP to walkaway geometry which resolved the raw triaxial data info its constituent wavefields (Fig 2). This allowed conventional migration with the 3D-lattice geometry to define the extent of the field (Fig 1 ).
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Practical aspects of processing crosshole seismic reflection data
Authors P. S. Rowbotham and N. R. GoultyA crosswell seismic dataset was acquired by SERES at Scheemderzwaag in the Groningen gas field in late 1990 (see news item in First Break, September 1991, p401) . Recordings were made in Triassic and Zechstein strata around 2200-2600m depth, where the Wells are just over 300m apart. Stanford University's acquisition system was used, which has cylindrical piezoelectric Bender transducers as sources and receivers.
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Reservoir monitoring using the VSP technique. A case study in the Oseberg field
Authors S. E. Johnstad and H. AhmedThe Oseberg Field is located in the Norwegian North Sea blocks 30/6 and 30/9, approximately 140 km northwest of Bergen with a maximum extension of 26 km north-south and a maximum width of 6 km east-west . The Field Game on stream in December 1988 . The Field comprises three major easterly rotated fault blocks Galled Alpha, Gamma and Alpha North . Hydrocarbons occur within the sandstones of the deltaic Middle Jurassic Brent Group . The reservoir sands exhibits excellent reservoir quality with porosities around 20-25% and permeabilities ranging up to several darcys . The structural dip is normally 6-10 ° east-northwest and the gross Brent thickness varies between 40 and 200 m .
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3D survey design and processing of a walkaway seismic line
Authors A. J. Calvert, J. Blanco and S. GarcanskiIn 1990, a walkaway borehole seismic survey was carried out over a producing field in Gabon with the objective of imaging a very specific section through the reservoir . In order to do this, and also to account fully for the three-dimensional nature of the target, three-dimensional raytracing was employed at the design stage to determine precisely the downhole tool position, the surface shot points and the location of the reflection points on the reservoir such that they all lay in a single, non-vertical plane. It was thus possible to treat the subsequent processing of the data as a conventional survey with the simple modification that the plane of propagation of the direct P-wave and the upgoing reflections was not vertical . A key element in the processing was the reorientation of the data from the borehole reference frame to that of the slanted processing plane. This increased the signal-to-noise ratio of the vertical component and oriented correctly the horizontal components, permitting, after velocity filtering and deconvolution, the use of both components in the final migration .
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Acoustics and very high resolution seismics in a highly deviated well
Authors J. L. Mari and P. GavinTo day horizontal Wells have been proven to be an efficient way of producing hydrocarbon reservoirs . Know-how on horizontal well drilling makes this technique very atractive considering the gain in productivity and recovery. In order to optimize production, one of the most important needs is to evaluate the reservoir in the horizontal welt area. Among possible reservoir characterization techniques, the available tools for horizontal wells are the vertical seismic profile and the full-waveform acoustic technique (J.L. Mari and J. Laurent, 1991). Full waveform acoustic data can be used to obtain acoustic sections, with a lateral investigation of several meters trom the borehole and vertical resolution of several lens of centimeters.
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SH-wave generator consisting of a vertical force and a pit in its vicinity
Authors C. Kitsunezaki, T. Yokio, K. Okuzumi and N. GotoContrary to conventional idea, predominant SH-waves are sometimes radiated from vertical impacts on the ground surface. Systematic field experiments were carried out to investigate the mechanism. The experiments revealed that the SH-waves are excited by waves incident on the boundary of a lower rigidity portion in the near-surface ground close to the impact positions. Accordingly inhomogeneities in the ground are considered to be the main cause of such SH-wave radiation that we encounter incidentally in usual seismic works using vertical forces as their sources.
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Anisotropy and crustal structure off Lofoten, Norway, from vertical incidence and wide-angle seismic data
Authors R. Mjelde, M. Sellevoll and E. W. BergA 15 sec TWT high-quality multichannel seismic reflection line was acquired in 1987 along a 175 km long NW-SE trending profile on the continental shelf across the Lofoten Islands, N. Norway. A seismic wide-angle experiment was performed in 1988 along the same profile as well as along a perpendicular profile, using 10 three-component Ocean Bottom Seismographs (OBS) with 20-25 km spacing .
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Design of acquisition systems for crustal studies using the reflectivity method
More LessWe have set up a code for the generation of synthetic seismograms which includes modeling of different acquisition systems and noise. It is based on the well-known reflectivity method because it allows a rigorous description of all the propagation phenomena that affect the spectrum of the signal. Some experiments on crustal models are presented. As a result, we can evaluate the offset range where the reflection acquisition systems conventionally used in hydrocarbon exploration improve the signal to noise ratio with respect to the methods traditionally applied to crustal studies (wide angle reflection seismics). We can also investigate the impact of different acquisition schemes on the success of single processing steps such as the velocity analysis of deep events. Moreover, during the survey, the noise generated by the program can be set at the level observed on the field records so that we can predict the expectable quality of deep reflections and we can perform a real time optimization of the acquisition parameters .
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The ecors 2.5D experiment: an attempt to image deep crustal structures with a sparse 3D recording geometry
Authors J. -M. Marthelot, M. Diagnieres, A. Hirn, A. Paul, D. Rapping, R. Silioi, B. Damotte, M. Layotte, M. Specht, J. Ravat, E. de Bazelaire and M. van ReesIn order to determine the 3D structure of crustal scale volumes by deep reflection profiling at a reasonable cost , the acquisition and processing parameters used in industrial exploration must be modified. A balance has to be found between the necessity to obtain data on a large su rfacé (for Jeep events migration distances can be quite large) and the necessity to use spatial sampling parameters appropriate for processing (taking into account the inherent loss of lateral resolution with depth) .
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Lower crustal reflectivity from waveform inversion
Authors M. Failly and S. C. SinghDeep seismic reflection profiles show that the lower part of the continental crust often contains many strong sub-horizontal reflections. These reflections are interpreted as a sequence of finely layered structuren. To confirm or invalidate this interpretation, we can use a seismic waveform inversion to estimate the reflectivity in the lower crust. However, it is very difficult to invert for the whole data set, partly because of large computation time in modelling and partly because the reflected energy in the upper crost dominates the misfit function.
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Two-dimensional modelling of resistivity and magnetotelluric data from the Belvedere Spinello salt mine, Italy
Authors G. Santarato and V. IlicetoMining the Earth's resources may often cause serious problems to the environment . In this study, mining of an evaporitic layer particularly rich in salt has caused the formation of underground cavities filled with brine . This brine has spread in all directions and probably upwards too, in largely unknown ways .
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Investigation for geothermal sources on Lesvos Island (Greece) by means of resistivity and P-wave seismic techniques
Authors J. Louis, T. Papadopoulos, N. Delibasis and N. BoulgarisCombined geophysical investigations including deep Schlumberger resistivity soundings, microearthquake monitoring and velocity inversion of local earthquake arrival time data have been performed on Lesvos island . Lesvos island, situated in the northeastern part of Aegean Sea, belongs to a Tertiary island arc system and is certainly affected by a regional anomaly of geothermal gradient, whose extent and importance are as yet unknown . The tectonics of the island, together with the occurence of some thermal springs, indicate that geothermal conditions could exist on it . The areas between villages Petra Árgenos, Kalloni - Stipsi and Polychnitos area can be considered of potential interest . The joint geophysical survey aimed to delineate areas through the tectonic structure of which there are indications of thermal fluid circulation .
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Seismic refraction and resistivity soundings as indicators of intricate properties of glacial deposits in North Germany
Authors M. G. El-Behiry, A. I. Bayoumi, R. Meissner, Y. E. Abdelhady and A. S. Aby El-EttaSeveral compressional and shear wave seismic refraction profiles together with, some full schlumberger array electrical resistivity soundings were conducted on glacial deposits in an area in the Northern part of Germany with the purpose of defining the petrophysical and mechanical properties and the structural setting of the subsurface layering.
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Structural mapping in 'basin and range-like' geology by electromagnetic methods - a powerful aid to seismics
Authors P. Y. Galibert and P. AndrieuxA large-scale magnetotelluric (MT) survey was designed to supply additional information to seismic studies for petroleum exploration in an area characterized by Cenozoïc normal faulting with graben-like structures filled up with clastic rocks . Seismic data is of high quality within the valleys and of very poor quality in between, due to outcropping hard limestones and/or igneous rocks. Initial drilling results show that even in high--quality seismic data areas , interpretation was erroneous because of unexpected thick interbedded igneous rocks .
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Concerning the digitization of high-resolution seismic signals
By T. M. McGeeSome commercially available marine seismic sources produce very broad-band signals. A high-resolution source signature can have a rise time of six-hundredths of a millisecond and a duration lens than two-tenths of a millisecond. Such sources, capable of penetrating tens of meters of sea-floor sediment with resolution on the order of a decimeter, are used extensively for engineering and environmental purposes. The digital recording and processing of data provided by them is increasingly common as faster and cheaper elcetronics become available . Thus two questions arise; how fast should they be sampled and to how many bits resolution? These questions have been addressed experimentally by field observation, but complete answers require a reconsideration of some traditional assumptions. That leads to conclusions that leem to fly in the face of conventional wisdom .
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Small vibrator development
More LessThe use of vibrators, as sources for seismic exploration of the Barth, have in the past been limited to large expensive surveys . To provide a broader range of exploration witti the advantages of a vibratory source, we have developed a small economical vibrator. Sources for use in shallow seismic surveys have in the past been impulsive . The acoustic energy was released in a short time at a high amplitude. The largest amounts of energy veere generated witti explosiees. Explosives are becoming more difficult to obtain and provide minimal control over the produced spectra. With a small vibrator acoustic energy can be released slowly, to sum to a large quantity, causing minimal environmental damage with maximum spectra control .
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The use of sigma-delta A/D convertors in modern engineering seismic data aquisition systems
Authors F. B. Michelsen, T. Kanemori, A. Peter and J. H. MimsSeismic surveys for engineering applications require relatively inexpensive seismic acquisition systems that are compact and rugged. As electronic technology has evolved, systems that meet these requirements have progressed from simple analog devices to computer controlled instruments that can record more channels and store the digital data.
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2-D FEM rock failure modeling in the vicinity of mining excavations
Authors Z. Mortimer and A. CichyThe process of rock failure due to mining exploitation is correlated with variations of geophysical fields. Some models of brittle failure of rocks in the Alain strain conditions have been tested on the base of stresses, seismic waves velocities and gravity anomaly distributions in the vicinity of the cicrular opening . It was assumed that in zones of rock failure the rock fracturing developes . Non-elastic behaviour of the rockmass in these zones is approximated by some changes of elastic parameters according to different failure models. Interaction between shear crack and working face was tested for their different configurations. Empirical Hoeck & Brown strenght criterion and the threshold of 50 % of this criterion for the begining of the dilatancy process have been used .
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A joint inversion algorithm to process geoelectric and subface wave seismic data
Authors M. Dobroka, L. Dresenz, A. Gyulai, A. Hering and R. MisiekIn the exploration of near surface structures geoelectric and seismic methods are commonly used. The independent inversion of the data is well-established. Surface wave data are usually considered as noise, however they contain valuable information about the geological structure which can be extracted by inverting the data. The independent inversion of both surface wave seismic and geoelectric data show internal ambiguity and nonuniqueness. Our aim in this paper is to show that these problems can sufficiently be reduced using the geoelectric and surface wave data together in a joint inversion algo rithm.
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Time domain electromagnetic, seismic refraction and potential field exploration of the Troodos ophiolite spreading structure
By N. J. CooperMineral exploration programs in complex geological environments require a clear understanding of both regional structure and local factors influencing mineralisation. Recent submarine images of active spreading environments have shown striking parallels between present ridge structuren and ancient ophiolitic terrasnes. Geological models now present a viable framework that requires evaluation in the structural and urineral environment by geophysical means .
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Recent geophysical surveys for massive sulphides in the Pyhasalmi area Central Finland
By T. RekolaThe search for economic Zn-Cu-S- deposits has been going on in the Pyhäsalmi area, central Finland for nearly 30 years . In 1958, when the Pyhäsalmi ore deposit was discovered the studies undertaken by Outokumpu Exploration in the area were given a big boost. immediately after discovery of the deposit, systematic magnetic, EM and gravimetric surveys were started over and in the vicinity of the orebody . The massive pyritic Pyhäsalmi Zn-Cu-S ore causes a distinct gravimetric and electrical slingram anomaly . The ore contains 2 - 4% pyrrhotite ; which greatly improves its electric conductivity . The results of the geophysical survey had a decisive impact on the instruments and methods used in the following search for a massive pyritic zinc ore of the Pyhäsalmi type .
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Soil investigation by radar techniques: first experiments by the Italian telecommunications operating company
Authors F. Esposto, F. Roscini and Gede PasqualeEvery year SIP, the Italian Telecommunications operating Company, performs thousands of kilometers of excavation, mainly open, for cable installation . Three kinds of excavation machinery are used : traditional, special and microtunnelling machines . In all cases preliminary investigations are needed before actual digging commences in order to détermine the position of any utilitys (pipes and cables) in the excavation cross section, not only in order to avoid damaging them, but also to plan the optimal excavation lay-out (for instante the road side less laden with pipes). Such investigations, useful in the case of traditional digging methods, become essential when using special or microtunelling machines, which characteristically breakthrough any utility in their path .
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Application of GPR to the construction of utilities
Authors J. M. Baltassat and G. PottecherThis paper presents how Ground Probing Radar can be used before laying shallow utility lines. The first reconnaissance problem is the selection of a path avoiding the other utilities present . The traditional methods have shortcomings which can be overcome by GPR : plans are inaccurate in location and depth, electromagnetic detection is inefficient for non-Metallic utilities . Another reconnaissance issue is geology, which governs the choice of laying technology, either open trench, impact moling or directional drilling . Trenchless technologies cannot work in some geological media and are sensitive to ground inhomogeneities. Geological raps are often meaningless at shallow depth in urban areas, while checking holes cannot provide continuity. GPR can detect boulders and underground masonry remains, as well as characterize the geologic media .
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Use of GPR to obtain layers thickness variation in a test track
Authors E. Lorenzo, I. Fernandez and V. CuellarA test track built by the official research center of the Spanish Ministry of Public Works (CEDER) came into operation in January 1988 . The track constituted by two 75 m long straight sections connected by two curves has an oval shape and a total length of 304 m . It stands on a concrete box 8 wide and 2 .60 m deep .
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Ground penetrating radar for roads and bridges: strengths and limitations
Authors N. S. Parry, J. les Davis and J. R. RossiterGround Penetrating Radar (GPR) has been used increasingly on roads and bridges over the last five years. GPR offers non-destructive evaluation of the subsurface along continuous profiles, providing unique information on the structural layers and material properties of roadways . Given that roads have a relatively simple geometry and are usually composed of homogeneous, engineered materials, this application would appear ideally suited to SPR . However, there are several pitfalls associated with this application . Some of these pitfalls are generated by equipment limitations, such as pulse length, sampling rates and fitter . Others are introduced when standard assumptions, commonly applied to GPR data from geotechnical environments, are used . In addition, the particular Weeds of the end client must be considered .
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Ground penetrating radar applications for nondestructive inspection of construction work
Authors M. Bashforth and S. KoppenjanThe nondestructive inspection of construction work has gained significant interest in the United States in the 1940's. The decire to verify building standards and codes has become an increasing problem. In many cases there - is no existing nondestructive method to accomplish this. Knowledge of the location and depth of building support mate rials is greatly needed .
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Groundradar applications for road constructions
Authors V. Hopman, A. J. M. Peters and J. W. de FeijterIn the Netherlands a large amount of infrastructural elements are concentrated on a relative small area . Highways, railways, waterways and all kinds of roads intersect each other at many locations . High investments are necessary to maintain these infrastuctures. Also cables, pipes and many cycle-paths cross main infrastructuren.
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Save Venice. A multidisciplinary investigation in the Rio Nuovo collapsing embankments
Authors M. Picollo, A. Fio, G. Niccolini and G. SpangheroBecause of erosion problems in the foundation wall of Rio Nuovo, probably caused by the ferry boat traffic, some collapse phenomena were observed on the surface of the embankment . A diagonal fracture in the asphalt surface interested a corner of the ferry boat station showing a collapse of about 15 cm. The interest was to understand the geometry of the collapsing structure, the depth limit of the event, the possible relationships with the morphology of the channel bottom and the identification of other hazard areas in west and east embankments .
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Radar techniques for the evaluation of masonry structures
More LessCivil engineers have a need to evaluate the condition of masonry structures such as bridges and tunnels in order to classify the condition of the structure . Impulse radar techniques have been used in the past, but interpretation of the data has been difficult as the radar data does not necessarily correspond with the geometrical structure . British Rail Research commissioned ERA Technology, over several years, to carry out a detailed investigation of the correlation between the radar image and the physical structure, in order to improve the clarity of the radar image .
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Subsurface imaging with EMAP - an aid to seismic processing and interpretation
By R. K. WarrenThe EMAP (Electromagnetic Array Profiling) exploration method has been combined with a direct inversion process for conversion to depth to produce a subsurface resistivity cross-section. This cross-section is interpreted in parallel with a seismic cross-section to enhance the prediction of rock type and structure. In complex thrust environments, areas of shallow volcanics and/or carbonates the EMAP method is used to provide additional data to either help the seismic processing and/or aid the seismic interpretation . In particular, the EM data are used to build an independent seismic velocity file for depth migration .
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Electromagnetic mapping of electrical conductivity beneath the Columbia basalt
Authors Y. Shoham, F. Morrison and C. Torres-VerdinThe Colombia basalts cover a petroliferous sedimentary section and they present a representative example of the challenging problems of trying to determine sedimentary thickness and structure in situations where seismic methods do not provide adequate depth of exploration . Between 1979 and 1986 Shell conducted a series of controlled source (CSEM) and natural field (MT) surveys at several sites in the Columbia basalts and the results for a profile near Boylston are described in this study .
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Advances in the integrated interpretation of seismics with magnetotellurics (illustrated by practical examples from the Pannonian basin in Hungary)
By Z. NagyIntegrated interpretation of seismic reflection and magnetotelluric (MT) surveys is a new approach to improve the results in prospecting for hydrocarbons. Recent, successful applications of MT method to the hydrocarbon exploration are discuseed by Christopherson (1991). However, there are few published case histories on the integration of seismic and MT data. The main purpose of this paper is to demonstrate that the interpretation of seismic sections can be improved by incorporating results from magnetotelluric surveys . In Hungary, the Hungarian Oil and Gas Co. is prospecting for hydrocarbons . Most of the work is in several subbasins of the Pannonian basin (Silverman and Barton, 1991) . Although the seismic reflection method is the primary tool employed, non-seismic methods are also applied, including magnetotelluric techniques (Ádám, Nagy and Varga, 1989) and other controlled source EM methods (Nagy et .al, 1991) . MT soundings are used for integrated interpretation purposes.
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Transient electromagnetic and seismic prospecting - an analysis of their similarities
More LessA fundamental introduction is presented to the similarities that exist between the transient electromagnetic and the seismic prospecting methods.
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