Summary This study emphasizes seismic acquisition and processing advances for strategic placement of geothermal doublets, in the pursuit of optimal geothermal and lithium exploration. The primary focus lies in identifying the most permeable zones associated with fractures and faults: enhancing seismic image bandwidth to lower frequencies proves crucial, improving vertical resolution and aiding fault interpretation. A 3D seismic survey in the French part of the Upper Rhine Graben is presented, showcasing the simultaneous use of Random Sweep and broadband multiscale data. The seismic acquisition involves a Dispersed Source Array (DSA) concept, emphasizing irregular, multi-grid, dual sweep, and dispersed source arrays for efficient data collection. Low-frequency acquisition is achieved through vibroseis. The study introduces a unique approach involving multiscale shooting grids to achieve spatial sampling intervals for low, mid, and high frequencies. The low-frequency sweeps, emitted by different vibrators during nighttime, are narrowband and strategically spaced. This approach overcomes limitations associated with broadband vibrators and enhances the clarity of basement images and deep structures. The study's processing sequence addresses the challenges of merging different datasets, providing a consistent kinematic and processing solution. The results demonstrate a considerable improvement of the images of the targets, for land geothermal surveys in complex environments.

Summary A novel approach to noise simulation for seismic survey design is presented. It allows generating realistic coherent and incoherent noise for a quantitative assessment of the signal to noise ratio for different geometries, to optimize the design

Although the requirement for accurate timing of both the sources and receivers used for land seismic data acquisition has long been known, the numerical requirement for, and impact of, timing accuracy on data quality is poorly defined. In this paper we derive a method for determining the theoretical timing requirement for data acquisition. We then demonstrate the impact of poorly timed data on data quality and examine our ability to remove timing errors in data processing. Source timing variations can be corrected through the application of surface-consistent static correction but only if multiple shots have not been stacked during acquisition. Receiver timing variations are more problematic and the ability to correct for them relies on a sufficiently dense acquisition geometry.

Disclaimer Text and Data Mining. Any automated analytical technique aimed at analysing text and data in digital form in order to generate information including - but not limited to - patterns, trends and correlations (so-called Text and Data Mining) may only be applied if it is done by a research organisation or cultural heritage institution solely for the purpose of (non-commercial) scientific research as mentioned in Clause 3 of Directive (EU) 2019/790 (the Digital Single Market Directive) and Clause 15n of the Dutch Copyright Act [Auteurswet]. Text and Data Mining for commercial purposes is not allowed; all rights in this respect are reserved pursuant to Clause 4 paragraph 3 of the Digital Single Market Directive and Clause 15o paragraph 1 of the Dutch Copyright Act.

In this paper we present the results of a seismic experiment using data produced by an active Vibroseis source and varying the drive force level, during a standard seismic reflection survey. We observed a clear non-linear response that can be linked to the presence of shallow soft sediment layers. The variation of the applied vibration force induces a change in both propagation velocity and attenuation of the Rayleigh waves, and this implies that such parameters are non-linear functions of the wave energy. We analyze the soil non-linear behavior with respect to the estimated induced strain, in order to compare the collected data against the observed reduction of shear modulus and damping values as usually measured in laboratory experiments and reported in the literature. The use of multi-component receivers allowed us also to identify the Rayleigh wave ellipticity and hence the resonance frequency of the studied site. Using active source data, rather than passive micro-tremors of unknown origin, for these applications is a novel approach. Thus, we propose an alternative and efficient method to characterize the non-linear key parameters of the soil seismic response, based on the use of controlled sources of widespread use in exploration seismics. This approach may pave the way to the development of utterly new site characterization techniques.

Summary Geothermal energy is expected to play an important role in the new zero-carbon emission era where renewable, sustainable and environmentally friendly energy sources should grow in the energy mix. The reduction of the subsurface risk for the geothermal energy development requires exploration technologies that can be borrowed, and adapted, from the O&G industry: the seismic method has a major role in the geothermal exploration. The challenges of "geothermal seismic" often come from the urban environment, with its obstructions and restrictions limiting the geometry options, the high incoherent noise level. The Oil&Gas industry has been pushing the limit of the seismic acquisition technology allowing denser surveys to be acquired. However, the price of these acquisition systems and their associated operation cost has been prohibitive, especially for non-Oil&Gas industries, limiting survey designs to 2D or sparse 3D. The emergence of new acquisition technologies, such as a new generation of much more nimble seismic nodes, allows agile and light operations, and opens new possibilities for urban exploration. Combined with the modern processing and imaging approaches, including model based coherent noise attenuation to precondition data not adequately sampled, allow deploying frugal and agile methods to deliver 3D seismic images at reduced cost.

Within the coal industry, there is a rich history of the use of the surface seismic method, principally for exploration and employing sparse 2D lines for broad resource delineation and structural modeling. However, the acquisition of 3D seismic surveys adjacent to open-cut mines (from which the majority of coal is extracted) for superior resource definition ahead of their expansion has been explored only recently. Although the reflection results are extremely useful and enable the mapping of faults with sub-5 m throws, there is still interest in determining if the seismic data can be used to image both structures and rock properties in the near surface. In addition to mapping near-surface structures that have geotechnical implications, the ability to map the overburden properties (which can be quite heterogeneous) is desired. Before mining activities can take place, the overburden needs to be removed. The cost of the removal method employed is directly affected by the depth of the weathered layer and rock properties. In particular, hardness can vary significantly. In this paper, we demonstrate how high-density seismic data originally acquired for reflection processing can be processed to generate high-resolution velocity (both VS and VP) depth volumes, which enable the successful identification of shallow structures and the creation of highly detailed near-surface rock-property volumes.

Surface wave tomography (SWT) is a powerful and well-established technique to retrieve 3D shear-wave (S-wave) velocity models at the regional scale from earthquakes and seismic noise measurements. We have applied SWT to 3D active-source data, in which higher modes and heterogeneous spatial sampling make phase extraction challenging. First, synthetic traveltimes calculated on a dense, regular-spaced station array are used to test the performance of three different tomography algorithms (linearized inversion, Markov chain Monte Carlo [MCMC], and eikonal tomography). The tests suggest that the lowest misfit to the input model is achieved with the MCMC algorithm, at the cost of a much longer computational time. Then, real phases were extracted from a 3D exploration data set at different frequencies. This operation included an automated procedure to isolate the fundamental mode from higher order modes, phase unwrapping in two dimensions, and the estimation of the zero-offset phase. These phases are used to compute traveltimes between each source-receiver couple, which are input into the previously tested tomography algorithms. The resulting phase-velocity maps show good correspondence, highlighting the same geologic structures for all three methods. Finally, individual dispersion curves obtained by the superposition of phase-velocity maps at different frequencies are depth inverted to retrieve a 3D S-wave velocity model.

Disclaimer Text and Data Mining. Any automated analytical technique aimed at analysing text and data in digital form in order to generate information including - but not limited to - patterns, trends and correlations (so-called Text and Data Mining) may only be applied if it is done by a research organisation or cultural heritage institution solely for the purpose of (non-commercial) scientific research as mentioned in Clause 3 of Directive (EU) 2019/790 (the Digital Single Market Directive) and Clause 15n of the Dutch Copyright Act [Auteurswet]. Text and Data Mining for commercial purposes is not allowed; all rights in this respect are reserved pursuant to Clause 4 paragraph 3 of the Digital Single Market Directive and Clause 15o paragraph 1 of the Dutch Copyright Act.

Noninvasive methods for the characterization of shallow subsurface have been used routinely for some 20–30 years. The growth in these methods has been driven by a variety of breakthroughs in the use of electrical, electromagnetic, and seismic methods, to mention only the most common techniques. Increasing field capabilities and computational power have yet to yield all their potential fruits. In this chapter, we introduce readers to the basic concepts of shallow subsurface methods. We guide them through some of the physical details and present a number of application examples all derived from our own experience, concerning both structural characterization and (fluid)-dynamic understanding of the shallow subsurface. Finally, we propose ideas concerning the future development of this wide and exciting discipline.

Multioffset phase analysis (MOPA) is a fairly recent technique for evaluating seismic surface wave dispersion and estimating the presence of lateral variations. The main limitation of MOPA is that it is based on the assumption of one predominant mode, usually the fundamental mode, in the wave propagation. However, MOPA can be extended (at least) to the two-mode case: this new technique will be called multimode MOPA (MMMOPA). The method employs both amplitude and phase spectral information. The analysis is performed for each frequency independently. The presence of two modes causes the amplitude to have an oscillating behaviour as a function of offset (beats): the spatial period of the oscillating amplitude is identified, amplitude maxima and minima are extracted, and the local wavenumber is computed via linear regression. The resulting multimodal dispersion curve is consequently derived. Model uncertainties can be estimated by propagating the experimental phase and amplitude error variances through the different steps of the analysis all the way to the final phase velocities. An algorithm running the process in an automatic way has been implemented and tested on both synthetic and real data, with success. This is the base for future developments that, in the MOPA framework, can take into account rapid lateral velocity variations within the same acquisition window and estimate the modal absorption, for the estimation of the damping ratio, even in the presence of multimode surface wave propagation.

ABSTRACTIn this paper, using synthetic and real data, we tested the capability of surface wave‐based methods for detecting subsoil lateral variations across an inclined slope. Simplified soil structures at different inclination angles were considered following an advanced 2D finite‐element modelling approach. Different values of inclination angle (10°–170° at 10° steps), spatial sampling rate and synthetic array length were used in different subsoil models to see the effects. It was found that, as low inclination angles (smaller than 40° with respect to the horizontal axis) are not detectable using the surface wave methods based on offset‐phase angle (X–ϕ), such methods are not able to correctly recognize the location of possible lateral variations at such inclination angles. On the other hand, for intermediate inclination angles (i.e. between 40° and 140°), the X–ϕ approach was successfully used to determine the exact location of the lateral variations for a wide range of frequencies, thereby opening new perspectives for the application of surface waves for detecting laterally inclined layers.

We applied a multi-offset surface wave analysis (MOPA) to detect subsoil lateral heterogeneities at a dismissed industrial site along the coast of the city of Trieste (Italy). The site is heavily contaminated and is undergoing characterization in view of possible remediation and re-use. Sea/land interactions and massive anthropic interventions make the site particularly complex. The main lateral heterogeneities consist of an extended buried quay, which also divides continental and marine sediments. We used seismic surface waves to define this contact, while also using supporting data from boreholes and geo-electrical surveys. A multi-offset phase and attenuation analysis was conducted on a few seismic lines, and produced clear evidence concerning the sought heterogeneities. Field data interpretation was corroborated also by ancillary information, and by synthetic modeling, that produced seismograms totally consistent with the recorded ones. In summary, the case study demonstrates how MOPA can be applied in a straightforward manner to define heterogeneities even at a very small spatial scale, and in complex environments such as derelict industrial sites.

Summary The successful exploration initiated in the 1940’s in the Aquitaine basin resulted in numerous seismic acquisitions, with often limited spread, to build a good overall understanding of this thrust and fold belt. Exploration wells sometimes encountered unexpected geological structures when drilling in the Pyrenean complex foothills. This occured for the Bellevue well drilled in 1991, covered by the long offset ECORS dataset. Since interpretation of the seismic section produced by conventional processing is difficult, we propose an interpretative procedure for constructing clearer structural images from land seismic data in foothills environment by picking events directly in the shot domain. This allows us to extract on the most relevant shots, for each structure, a noise free signal to feed the migration algorithm. The final image after migration enables us to revisit the geological concept of the Bellevue well area.

PreviousNext No AccessInternational Conference on Engineering Geophysics, Al Ain, United Arab Emirates, 9-12 October 2017Integrated seismic characterization for deep engineering targets: active and passive surface waves, reflection and refraction near-surface modelling from a single 2D acquisitionAuthors: Claudio StrobbiaJacopo BoagaGiorgio CassianiMehdi AshemijokarPaolo PrimieroClaudio StrobbiaRealtimeseismic, Pau, FranceSearch for more papers by this author, Jacopo BoagaUniversity of Padue, ItalySearch for more papers by this author, Giorgio CassianiUniversity of Padue, ItalySearch for more papers by this author, Mehdi AshemijokarUniversity of Padue, ItalySearch for more papers by this author, and Paolo PrimieroSeismometrix, ItalySearch for more papers by this authorhttps://doi.org/10.1190/iceg2017-039 SectionsAboutPDF/ePub ToolsAdd to favoritesDownload CitationsTrack CitationsPermissions ShareFacebookTwitterLinked InRedditEmail Abstract The use of surface wave methods for the near-surface characterization for land seismic data relies mainly on the analysis of the active surface waves, the ground roll. Passive data can be very valuable as they can extend the frequency bandwidth and the investigation depth, even when large seismic sources are used. With 2D geometries, however, most of the standard passive data analysis techniques cannot be applied. We developed a method to analyze the passive surface waves continuously along 2D and crooked lines and extract jointly the dispersion of active and passive surface wave data. Different noise distribution scenarios can be handled. The method can be applied to reflection 2D geometries. We demonstrate the method with a standard 2D crooked line: passive data were acquired for several hours on the whole spread, and analyzed to provide a continuous dispersion section together with the active vibroseis data. Despite the 2D receiver geometry and the use of receiver arrays, the dispersion has been extracted even well below the natural frequency of the geophones. The surface wave results are integrated with the refraction tomography, and with shallow reflection imaging. Keywords: surface wave, near surface, 2D, imagingPermalink: https://doi.org/10.1190/iceg2017-039FiguresReferencesRelatedDetails International Conference on Engineering Geophysics, Al Ain, United Arab Emirates, 9-12 October 2017ISSN (online):2159-6832Copyright: 2017 Pages: 382 publication data© 2017 Published in electronic format with permission by Society of Exploration Geophysicists (SEG)Publisher:Society of Exploration Geophysicists HistoryPublished Online: 12 Oct 2017 CITATION INFORMATION Claudio Strobbia, Jacopo Boaga, Giorgio Cassiani, Mehdi Ashemijokar, and Paolo Primiero, (2017), "Integrated seismic characterization for deep engineering targets: active and passive surface waves, reflection and refraction near-surface modelling from a single 2D acquisition," SEG Global Meeting Abstracts : 226-229. https://doi.org/10.1190/iceg2017-039 Plain-Language Summary Keywordssurface wavenear surface2DimagingPDF DownloadLoading ...

Summary Land surface seismic data are usually characterized by the presence of strong dispersive surface waves. It is very critical to attenuate the coherent and scattered surface-wave noise masking the subsurface reflection signal to produce high-resolution images for the reliable seismic attributes extraction of the reservoir characterization. Conventional noise attenuation methods can remove the coherent part but usually not be effective to attack the aliased components and difficult to address the apices of the scattered surface waves. Here we look at the application of a new model-based surface wave attenuation technique that is based on data-driven modeling of multiple modes of aliased direct and diffracted noise on the onshore tight sand gas reservoir. The surface consistent propagation properties of the surface waves are estimated first. The direct noise is modeled and then the scattering model is built by the integration of all possible diffractors. All of the noise models are finally subtracted from the raw data. In this paper, we demonstrate a successful case study on how this new technology can be used to help the improvement of the signal to noise ratio and the fidelity of seismic data with the finest resolution and amplitude preservation.