71st EAGE Conference and Exhibition - Workshops and Fieldtrips

Over the past years, Rocksource has studied and tested the application of Controlled Source Electromagnetic (CSEM) surveys for hydrocarbon detection in numerous shallow and deep water settings, mainly in the Norwegian continental shelf, the UK continental shelf, offshore West Africa, and offshore East India.

The efficiency, depth investigation and the spatial resolution of Controlled-Source Electromagnetic (CSEM) measurements in shallow and deep water environments are studied in both time- and frequency-domain.

The main objective of a well posed integrated approach should be to reduce the level of uncertainty and indetermination about the knowledge of the system under study. That is the desirable result when complementary geophysical disciplines, such as seismic and electromagnetic methods, are combined with each other through an integrated interpretation work flow.

Total with the assistance of WesternGecoEM acquired a rich 3D marine Controlled Source Electromagnetic (CSEM) dataset offshore West Africa toward the end of 2006 (Figure 1.). This dataset was intended to be a definitive validation of the technique or proof of concept over a well understood target for which definitive measures could be made of many different types of analysis and inversion. The dataset was also acquired at the beginning of the fields’ life so that the opportunity remained for monitoring the production development electrically.

To improve the interpretation of CSEM data, information from seismic data can be included in a CSEM inversion. The higher resolution of the seismic image makes it possible to accurately determine the location of potential resistivity contrasts.

The analysis of surface waves can be a powerful tool for characterising the near-surface down to penetration depth. In this framework, the surface wave analysis is part of the data processing workflow, and the surface waves are considered signal and not noise. After having extracted the information the surface waves carry, they become unwanted signal to be removed. The resulting near-surface model can be used for short- to long-wavelength statics and perturbation corrections, for velocity model building, and for better filter design which can take into account the complexity of near-surface phenomena.

Many reinforced concrete structures are suffering from deterioration occurring earlier than their expected service life. The first barrier against attacks of external environmental agents is the concrete cover. The damage mechanisms depend on the microstructure of the cover concrete. This microstructure can be assessed with various measurements. The paper presents the automated device designed for the non destructive control of the concrete using the ultrasonic surface waves. The measurements are carried out without any contact with tested sample. The increase of signal level, required for such solution, is obtained using the frequency swept signals, so called “chirps”. The recorded signals are processed using special software which permits to obtain the attenuation and the velocity dispersion of surface waves. These parameters can be next used in order to determine the parameters of concrete cover. Especially the inversion of velocity dispersion characteristics using the approaches developed for the multichannel analysis of surface waves (MASW) technique, enables to evaluate the variations of shear velocity as a function of the concrete cover depth. The potential possibilities of this approach are shown on an example of laboratory measurements carried on the cement slab especially manufactured, displaying the increasing porosity as a function of depth, and on the example of in-site measurements carried out in order to evaluate the depth of deterioration of a concrete platform in maritime port.

Three-dimensional (3D) seismic surveys are always more often used both in oil prospection and in near surface problems to handle complex geological structures. At the same time surface wave methods are often coupled to other seismic techniques (2D seismic reflection or refraction) where it is possible the use of seismic data to retrieve dispersion curve along the seismic line. In this work the possibilities and the limits of retrieving dispersion curves from 3D seismic acquisition scheme are analysed. Several tests based on synthetic and real data show that the estimated dispersion curves are in agreement with the dispersion curves estimated through the traditional methods. Furthermore, in case of “cross-spread” acquisition schemes, the proposed processing approach can be used to retrieve 3D subsoil models, also for inaccessible areas.

Surface wave methods are based on the inversion of observed Rayleigh wave phase-velocity dispersion curves. The goal is to estimate mainly the shear-wave velocity profile of the investigated site. The model used for the interpretation is 1D, hence results obtained wherever lateral variations are present cannot be considered reliable. In this paper, we consider synthetic models having a lateral heterogeneity. When we process the entire corresponding seismogram with a traditional f-k approach, the resulting 1D profile is representative only of the subsurface structure of the largest part of the considered model. This result shows that classical analysis disregards evidences of sharp lateral velocity changes even when they show up in the raw seismograms. In our research, we implemented a novel robust automated method to check the appropriateness of the 1D model assumption and locate the discontinuities. The method has been tested over synthetic models. This new approach is a development of the recent Multi- Offset Phase Analysis (MOPA) with the advantages that it does not need a-priori noise evaluation nor more than one shot. Only once the discontinuities are clearly identified, we confidently perform classical f-k dispersion curve extraction and inversion separately on either side of the discontinuity. Thus the final result, obtained by putting side by side the 1D profiles, is a correct 2D reconstruction of the discontinuous S-wave distribution, with no need for additional ad-hoc hypotheses.

Surface waves are widely used for determining properties of the subsurface on different scales. In most applications, the dispersion of surface waves is analyzed to yield depthdependent velocity profiles. However, the heterogeneity of the shallow subsurface complicates such an analysis because of the scattering it causes. Here, we use an inverse scattering method to determine the location and properties of the heterogeneity. First, we illustrate this method, using a regular receiver array. A synthetic example shows that the scatterer is imaged at the correct location with good resolution. In practice, we may want to take advantage of existing non-uniform arrays, such as those deployed for global seismic studies. In our next example, we generate scattered data at irregularly spaced locations. By simultaneously inverting the scattered wave field excited by different sources, we observe that the image is well focused on the scatterer. Further work is on the way to better understand the influence of non-uniform (and sparse) sampling on the image quality and what are the sampling requirements.

In the last decades, researchers focused their attention on using the Rayleigh waves dispersion characteristics to estimate the shear wave velocity profile of a site, since their dispersion characteristics can be extracted also from only one component recordings (namely the vertical ones) of active and passive seismic tests. In particular, inverse analysis of empirical surfacewaves dispersion curves from microtremor measurements (passive seismic test) is a very attractive tool since it allows to keep the cost of investigation relatively low and to avoid the use of active sources that might be prohibitive in urban areas. However, until now the full potential of seismic noise array methods was not fully exploited, and, in particular, the possibility of better constraining the subsoil structure by extracting also the Love wave part from microtremors recordings has not been fully investigated.

Observations of surface and near-surface waves show that shallow velocities change significantly in response to reservoir compaction that often takes place thousands of meters deeper. The compacting reservoir induces vertical and horizontal displacements and strains at the seafloor that lead to anisotropic changes in the shallow p- and s-wave velocities. Analyzing permanent OBC data from the Valhall field we observe large changes in the arrival times and phase velocities of Scholte and critically refracted compressional waves between several surveys acquired over a 5 year interval. The changes in the shallow velocities are compared with seafloor strains predicted by geomechanical models and a reasonable agreement is found. Shallow waves present us with an excellent laboratory for calibrating the stress and strain dependence of our rock physics models and are useful for constraining geomechanical models and monitoring the compaction of deep reservoirs.

Surface wave interferometry is the process of estimating inter-receiver surface waves by cross-correlation, cross-convolution or deconvolution of wavefields recorded at each receiver. We study seismic interferometry of scattered surface waves in attenuating media. One of the starting assumptions for interferometry by correlation is that the medium of interest is lossless, however the near surface of the Earth is often strongly attenuating. On the other hand interferometry by convolution makes no assumptions about medium losses. By investigating both correlation-type and convolution-type interferometry we identify how to successfully approach the problem of estimating inter-receiver scattered waves, and illustrate our findings using real and synthetic examples. Such estimates have applications in the attenuation of scattered ground roll and in near surface imaging and characterization.

Random vibrations monitoring and analysis represents a cheap and effective tool for the seismic characterization of the subsoil. A standard approach to the physical interpretation of ambient vibrations measurements is based on the hypothesis that surface waves dominates the relevant wave field. To evaluate the reliability of this hypothesis, a general physical model for ambient vibrations generated by anthropic activities has been. In this model, the complete wave field generated by a random distribution of independent point loads at the surface of a weakly dissipative layered Earth has been considered. Horizontal to Vertical Spectral Ratios computed from the complete wave field solution have been compared with those deduced in the surface waves hypothesis. This comparison suggests that this approximation supplies reliable only results in the frequency range above the resonance frequency of the local subsoil. At the resonance frequency, a reasonable agreement is obtained when a source-free area exists around the receiver with a radius of the order of few tens of meters.

A marine surface wave seismic investigation was performed in order to characterize the sediments and bedrock in Ystad harbor, southern Sweden. The dispersive nature of Sholte waves was analyzed and fundamental mode dispersion curves extracted. Using inverse modelling a few layer shear wave velocity, Vs, profile was successfully retrieved to a depth of 5-10 m below sea bottom. The seismic results were confirmed with result from geotechnical probing. The measurements were made with a 12-channel neutral buoyancy streamer with 2 m hydrophone separation. A small number of led plates were attached to the streamer in order to make it sink and for each measurement the ends of the streamer were fixed on the bottom using small concrete blocks. The streamer was pulled up on the vessel before moving to the next measurement position. As energy source a small amount of explosives was detonated on the sea bottom with the shot positioned at 15-30 m distance from the nearest hydrophone and inline with the streamer. The production rate of this approach was 30 measurements in one field day, which should be compared to the 1 or 2 geotechnical soundings that can be achieved at the same time.

Because of the cost, seismic data are seldom acquired with a sampling that is optimal for seismic processing. To produce data with optimal sampling, interpolating or regularizing the seismic data may be used, not only to improve the resolution of the results, but to reduce the cost of acquiring seismic surveys. Multi‐dimensional interpolation methods that allow seismic data to be de‐aliased can provide significant improvements in quality and ease‐of‐use over older interpolation methods.

When seismic data regularization is formulated as an inverse problem, it requires mathematical regularization, a method for imposing constraints on the reconstructed data. Mathematical regularization can take four different forms: a differential operator (such as a prediction-error filter or a plane-wave destructor), an integral operator (such as a recursive inverse of prediction-error filtering or a plane-wave constructor), a sparseness constraint in a special domain (such as Fourier or seislet), or a shaping operator. Similar results can be achieved with different methods but at a different computational cost. Using both onedimensional toy examples and seismic field data applications, we compare and illustrate properties of the four methods of data regularization.

In common-reflection-surface (CRS) imaging the reflection arrival time field is parameterized by a kinematic description of the recorded wavefield. Using the CRS approach locally in the unmigrated prestack data domain opens a potential for trace regularization and interpolation. The presented CRS interpolation operates in the original prestack data domain and accounts for irregular geometries. A distinction to existing methods is the use of local operators of the second order which are less sensitive to aliasing but imply a considerable increase of the computational expense.

Interferometry is used to reconstruct surface data from Walkaway VSP data. Together with a common receiver gather of a WVSP experiment we formulate a data-driven surface demultple scheme for WVSP data. The theory will be presented together with real data examples from the Nordkapp basin in the Barents Sea, an area well known for its complex geological structures.

The anti‐leakage Fourier transform (ALFT) is a robust and easy to implement regularisation method. In this talk first several aspects of the ALFT are illustrated using simple synthetic signals. The key observations are: 1) When the Fourier spectrum is sparse, very good results can be obtained using the ALFT with a limited number of iterations; 2) When the spectrum is not sparse, but data are well sampled, a very large number of iterations can be required for a similar quality reconstruction of the data as with Least Squares Fourier regularisation; 3) Sparsely sampled data with a sparse spectrum can be handled by the ALFT if the sampling is irregular, but results strongly degrade if the sampling is (close to) regular. To improve the handling of sparsely sampled data it is proposed to derive a weighting function in the spatial Fourier domain from the lower temporal frequencies. The weighting function is extrapolated to the higher frequencies where the data may be spatially aliased, and instead of selecting the strongest Fourier component in each iteration (as done in the standard ALFT), the component that would be strongest after weighting is selected. The advantages are shown on synthetic and field data.

The seismic data regularization, which maps the acquired irregularly sampled seismic traces to a regular grid, is an important processing for preparing the data for regular sampling based algorithm, such as wave equation migration, 3D SRME etc. The wide azimuth seismic data generally contains the shooting locations covering a patch over a 2D surface and the geophone locations as well. Combining with the recording time, the seismic data is fully represented in a five dimensional coordinate. Conventional data regularization scheme splits the five dimension problem in to two pass three dimensional procedures. The interpolation algorithm in higher dimension generally gives better chance to fill the acquisition holes. In this paper, we generalized the anti‐leakage Fourier Transform algorithm to five dimensions, which regularizes the seismic data in one pass. The initial tests on Gulf of Mexico data demonstrate promising results.

More than 100 geophysicists and engineers participated to the EAGE-sponsored Vibroseis Workshop (Prague, 13-15 October 2008). The conveners plan to share the highlights of this workshop with the participants to the annual EAGE meeting.

Surface seismic data are significantly affected by the properties of the near-surface strata. We propose to integrate information extracted from geomorphology into the seismic processing workflow. Topography classification of the elevation and lithology information of satellite imagery allows mapping formation tops, which in turn, provide the basis for 3D near-surface modelling. The lithology class map can be converted into a surface velocity map for the estimation of coherent noise velocities. The 3D geologic model can be converted into an elastic model using standardized velocities. The result is a model of the statics estimates, which can be generated prior to data acquisition. The comparison of the model with refraction statics from data processing reveals that the estimate matches the refraction statics in areas with homogeneous surface lithology. In terrain with heterogeneous surface lithology such as isolated limestone ridges and steep cliffs with rapidly changing lithology, differences are observed, which are yet to be explained.

Classical algorithms used for travel time tomography are not necessarily well-suited for handling very large seismic data sets, densely parameterized velocity models and for taking advantage of current supercomputers architecture. We revisit the classical approach of firstarrival travel time tomography by proposing to use a simple gradient-based approach without the need of estimating the inverse of the Hessian of the misfit function. The gradient-based approach is very attractive from a numerical point as it can handle large data sets and velocity models and is very robust with respect to the choice of the initial velocity model.

We shall review aspects of acquisition and processing of land seismic data, including spatial sampling requirements for reflected and refracted waves, surface waves and guided waves, use of surface waves to estimate the near-surface S-wave velocities, and processing methods to attenuate surface waves and guided waves, use of wide-angle reflections to image beneath basalt and carbonates, near-surface modeling, and image-based subsurface modeling.

In carbonate rocks, the rock frame and pore space are a function of the depositional environment and the diagenetic history. Cementation, recrystallisation and dissolution processes can change the mineralogy and texture of the original framework and hereby alter the original grain-to-grain contacts and/or occlude pore space. These diagenetic alterations and associated changes of the rock frame and pore structure result in a wide velocity range at a given porosity.

The construction of 3D reservoir models that are capable of confidently predicting flow behaviour in carbonate reservoirs requires that the porosity distribution in the reservoir is characterised appropriately and related to a robust conceptual geological model. Porosity is at the root of both reservoir characterisation and reservoir modelling, but its measurement and description remains an area of uncertainty since in many fields there is a discrepancy between core and log derived reservoir properties. In addition, robust conceptual models to predict reservoir properties in the interwell area of carbonate reservoirs are often weak. This largely reflects an immaturity in the tools available to predict the effects of diagenesis on porosity. The aim of this paper is to establish a picture as to where we currently stand with regard to the characterisation of carbonate pore systems and identify emerging technologies that will improve confidence in future models. The case is made here for a genuinely interdisciplinary approach to reservoir characterisation, but also for a return to truly geological models to increase confidence in the predictive capacity of 3D reservoir models. Central to this is a recommendation to more consistently consider the diagenetic process responsible for porosity development.

Fluid substitution and pore pressure changes are the main factors affecting time-lapse 4D seismic. Fluid changes are often predicted by Gassmann, which works generally well in clastic rocks. However, the applicability of Gassmann in carbonates is not well understood yet. Changes in pore pressure due to production might become important under certain conditions of reservoir production and injection. In addition, to be able to identify accurately these fluid and/or pressure changes in a time-lapse 4D seismic, uncertainty of the seismic signature should also be evaluated. Therefore, it is important to determine and quantify the effect of these factors to have a full understanding of the changes in the 4D seismic data. In this paper, we present a summary of preliminary results of different studies of pressure changes, fluid substitution, and seismic uncertainty analysis in a carbonate reservoir and surrounding facies from two different producing oil fields in the Middle East.

The need for rock physics information is exploding as we aspire to improve geo-steering; recovery; wellbore management; and reservoir simulation. The most reliable source of this information is experimentation. However, physical measurements on rock fragments are slow and cumbersome, and often impossible to conduct or conduct well. Even when available, such data are sparse -- required are properties not for tens but for thousands or tens of thousands of samples.

Carbonates are heterogeneous; their pore space is complex; and, as a result, their properties are challenging to predict. The new digital-rock technology helps quantify the pore space of these sediments, which eventually leads to a breakthrough in building relations between various rock properties and understanding their link to the pore-space geometry.

The fundamentals of Coalbed Methane are presented. Coalbed methane and conventional sand reservoirs are compared to illustrate their similarities and differences. Using numerous illustrations, fundamental concepts such as the structure of coal and the storage mechanisms, and how adsorption plays an important role are explained.

Coal is the most abundant hydrocarbon on the planet and locked within these reservoirs is almost 7500 Tcf of natural gas of which about 1000 Tcf is estimated to be currently technically recoverable. Current natural gas production from Coalbed Methane reservoirs, CBM, represents 10.0% of annual U.S. natural gas production with over 20,000 producing coalbed methane wells in 12 states. This is remarkable when one considers that, prior to about 1989, CBM contributed essentially nothing to US domestic gas production.

The North-eastern part of the Netherlands is a prolific hydrocarbon province, which contains the giant 100 Tcf (2850 Bcm) Groningen gas field within Permian Rotliegend desert sandstones and the 1 Bbbl (157 MMcm) Schoonebeek oil field within marine Lower Cretaceous clastic sediments. Next to these fields a large number of smaller gas fields have been found in strata ranging in age from Carboniferous to Paleogene. Currently this petroleum province is going through an important transition in its’ life cycle with underground gas storage and CO2 sequestration in depleted reservoirs becoming increasingly important. Furthermore enhanced oil recovery via the redevelopment of the Schoonebeek oil field is under way - more than 60 years after initial discovery and decades of production.

The coast of the Netherlands is dominated by barriers situated in front of a 50- to 100- km-wide, low-lying back-barrier area of heavily populated, reclaimed and cultivated tidal flats, estuaries and marshes. In the south, beyond Belgium, the barrier is connected to the mainland of Cap Blanc Nez of northwestern France. In the Netherlands, it follows the overall morphology of the Pleistocene subsurface as it connects the watersheds of the Late Weichselian drainage systems. Although the present morphology of the Dutch coast is strongly modified by tides and waves, first-order features, such as the change in strike from almost S-N in the west to almost W-E in the north, are completely defined by the Pleistocene morphology. Farther east, the barrier continues in German territory.

Summary not available

The IEEA, Altener funded GeoThermal Regulation – Heat (GTR-H (www.gtrh.eu)) project runs from 2006 to 2009 with the aim of identifying and reviewing the regulatory barriers and deficiencies for geothermal heat in unregulated EU countries.

In the recent years the uptake of geothermal energy through implementation of low enthalpy geothermal production systems for both electricity and heating have been growing rapidly in north-western Europe. Geothermal exploration and production takes largely place in sedimentary basins at depths from 2 to 5 km. Geothermal activities can take considerable advantage from a wealth of existing oil and gas data.

Geothermal energy is a major energy source for both electricity generation and for space heating in Iceland. In other countries it is emerging as alternative energy. A comprehensive geothermal research program in the Theistareykir high temperature area has been ongoing since 1972. Exploration drilling started in the year 2002 and at the end of 2008 six wells had been completed and tested. Our recent magnetotelluric (MT) survey in Theistareykir area has both characterized known geothermal reservoirs and identified new drilling opportunities.

After an introduction of Eneco and description of the role for (central) district heating in the Netherlands the presentation will be centered around the economic value of geothermal energy in district heating. The cost of geothermal energy will be compared with the cost of the alternative sources of thermal energy: a gas fired CHP in combination with peak boilers.

Geothermal energy is an increasing part of the worldwide energy supply. There are three geological provinces in Germany with hydrogeothermal potential: the North German Basin, the Upper Rhine Graben, and the Southern German Molasse Basin. Within the Southern German Molasse Basin the hydrogeothermal aquifer comprises carbonate rocks of the Upper Jurassic which were lowered to a depth of approximately 3500 m.

MeProRisk is a joint project of five university institutes at RWTH Aachen University, Free University Berlin, and Kiel University. Two partners, namely Geophysica Beratunggesellschaft mbH (Aachen) and RWE Dea AG (Hamburg) present the industrial side. It is funded by the German Ministry of Education and Science (BMBF).

Seismic imaging methods based on the concept of locally coherent event have known a strong expansion in the recent years. In addition to the fact that locally coherent events fit our intuitive understanding of seismic traces, this expansion must be put on the theoretical and numerical progresses of high frequency asymptotics in seismic imaging. Indeed geometrical optics offers a beautiful frame for the analysis of locally coherent events, which can be described by various kinematic and dynamic parameters. Among them, the travel time and the slopes of the event in the gather of traces have a direct connection with the classical ray parameters, and tomographic and migration methods can be based on. In the present paper I present the basis of these methods and review the recent progresses.

The Common-Reflection-Surface (CRS) stack is a well-established time imaging method that provides high quality stacks of three or two-dimensional seismic data and also important kinematic wavefield attributes as a byproduct. In the present work, we build from the CRS a common diffraction surface (CDS) and migrate multicoverage seismic data to zero-offset. The migration to zero offset CRS-MZO operator is defined by a second order (hyperbolic) travel time approximation that depends on two wavefield attributes (or CRS parameters): the emergence angle of the normal ray and the radius of curvature of the normal incidence point (NIP) wave. This parameter estimation is carried out by means of optimization procedures using as objective function the coherence (semblance) of the seismic traces along the CRSMZO operator. The CRS-MZO method is tested using the 2D Marmousi synthetic data and finally applied to 2D land seismic data of the Tacutu Basin (Brazil).

The Common Reflection Surface (CRS) stack is a multi-parameter processing approach based on locally coherent reflection events. Best coherency is obtained if the fitted reflection data are hyperbolic within the CRS apertures under consideration. The latter applies to the source receiver aperture and the CMP displacement. Based on the hyperbolic assumption the CRS attributes are determined during the optimisation procedure to best fit reflection events in the data. These attributes are the backbone of the CRS workflow. The CRS attributes are steering the stack, the velocity model building by Normal Incidence Point (NIP) tomography, the multiple suppression, and the enhancement and regularization of pre-stack data. Pre-stack data enhancement and data regularization is performed by so called partial stacks to form CRS supergathers. Partial stacks are essential to remove artefacts caused by adaptive filtering of multiples in pre-stack data. Pre-stack depth migration of CRS supergather leads to CIGs which have an improved S/N and are better suitable to residual move out analysis and quality control than conventional CIGs. Pre-stack depth migrated sections obtained from CRS supergathers display an S/N ratio almost comparable to the CRS stack section.

We describe a method of tomography that uses dip measurements taken from locally coherent events in surface data in time. The dip measurement needed for tomography is the offset dip, which is measured along the source-receiver azimuth. Following migration of an event, the error in offset dip can be computed, and this input to a tomography program to calculate the slowness field error. Adding this to the input subsurface model results in an updated model. Three iterations of dipscan tomography is needed at the present to generate a reasonably converged model.

Combining seismic data in a joint processing has several interests as complementary information and constrains on the sub-surface are available. For instance, surface and borehole seismic data integrated in joint tomography lead to intrinsic well-tie of reflection seismic, and allow anisotropy estimation. Joint tomography of reflected and refracted arrivals better determines near-surface models and consequently improves deep imaging. Accounting for reflections, diffractions plus transmissions in cross-hole tomography increases the resolution of velocity models.

Over the past decade, a number of beam depth migration methods have emerged. Papers by Sun et al. [2000] on slant-stack Kirchhoff migration and Hill [1990, 2001] on Gaussian beam migration showed the potential of migration methods that combine aspects of Kirchhoff migration with some novel preprocessing. Also during this period, a growing number of workers implemented beam migrations that combine efficiency and imaging fidelity. Unfortunately beam migration is complicated, so a simple interpretation of beam migration, analogous to that of Kirchhoff migration, has been hard to pin down. In this paper, I try to add some intuition to the discussion of beam migration methods. I describe Gaussian beam migration, which is possibly the most complicated of the slant-stack migrations; this makes my task challenging. However, an elementary interpretation of this method is possible, and allows an understanding of the entire family of newly-emerging beam migration techniques.

In the presentation we describe the mathematical basis of the Gaussian beam summation method and its applications in geophysics that concern the following topics: modelling, migration, inversion and velocity model reconstruction. For each topic we emphasize specific features of the method that lead to advantages in practical applications and demonstrate these for a number of numerical experiments with synthetic benchmark data. With regard to the migration problems, we pay special attention to the difference between the Gaussian beam migration method proposed by N.R. Hill and our Gaussian beam summation method. The numerical results presented here prove that the Gaussian beam summation method can be considered a powerful tool in a variety of geophysical applications.

During the last glaciation in northwestern Europe, major studies are consistent with the hypothesis of an ice-stream flowing southward in the Irish Sea Basin, in connection with tributary flows on the eastern part of the Irish Cap (Evans and Cofaigh, 2003; Eyles and McCabe, 1989). During the maximum extent, the ice front reached a position located off the coast of Wales at ca. 22ka BP (Lambeck, 1996; Thomas and Chiverrell, 2007). During deglaciation, sediment deposition processes are predominant, leaving a record of glacially influenced environments. Evidence of such deposits still remains on the coast of the UK and Ireland today. Although these deposits have been studied for many decades, their depositional environment is still under debate and interpretations are evolving, together with new concepts.