Papers by johannes singer
We review a general representation for retrieving seismic Green’s functions between two observati... more We review a general representation for retrieving seismic Green’s functions between two observation points in lossless arbitrary inhomogeneous media and evaluate its application for passive seismic exploration. The theory is validated with a field example, in which several coherent events are retrieved from seismic background-noise recordings in a desert area. Results match well with events in an active exploration data set at the same location. The retrieval of the Earth’s reflection response from crosscorrelations of seismic noise recordings can provide valuable information, which may otherwise not be available due to limited spatial distribution of seismic sources, difficult terrain conditions, economical reasons, etc.
Method and measuring device for investigation of a territory on presence / absence of a particular geophysical feature
Fugro is a worldwide oil and gas service operator with the core business of data acquisition offs... more Fugro is a worldwide oil and gas service operator with the core business of data acquisition offshore, onshore and in the air. In a world with increasingly complex and costly systems being installed, often in remote, harsh or difficult to access environments, large scale continuous monitoring of these valuable and critical assets is becoming an increasingly important challenge. These monitoring systems need to collect wide variety of data: strain, sound, vibrations, pressure, temperature etc. FAZ Technology as part of the Fugro group has developed an ultra-high performance data acquisition system based on fiber optics, perfectly suited for acquiring large amounts of system and structural health and status data. We will present the concept, its performance and capabilities, and we’ll present real field applications. A core example will be a system installed on the Fugro offshore survey vessel Pioneer, which monitors a large suite of performance and health data of this vessel allowing...
Spectroscopic Identification of Tremor Phenomena over Hydrocarbon Reservoirs
64th EAGE Conference & Exhibition
Hydrocarbon Reservoir Detection Using Acoustic / Seismic Spectroscopy Method
SPE Asia Pacific Oil and Gas Conference and Exhibition, 2002
The seismic signal of the earth in the frequency range 0.1–20 Hz is recorded continuously from th... more The seismic signal of the earth in the frequency range 0.1–20 Hz is recorded continuously from the surface using ultra-sensitive velocity sensors. Hydrocarbon reservoirs are characterised by a unique spectral signature present in the frequency range 1–6 Hz. This signature diminishes at the rim of the reservoir and is absent at non-reservoir locations. The results of our experiments are remarkably uniform for a great number of major oil producing areas worldwide, regardless if producing or virgin reservoirs are examined. Phenomenologically and structurally, the observed signals are similar to previously documented tremor signals ("continuous narrow band ground motion") originating, for example, from volcanoes and glaciers ("fluid-induced tremor"). Numerous continuous seismic signals exist which are usually rather weak and are often considered as useless background noise only. However, this "noise" also carries useful information, which is identified thro...
SEG Technical Program Expanded Abstracts 2009, 2009
Proceedings of the 8th SEGJ International Symposium, 2006
One of the applications of Seismic Interferometry (SI) is the reconstruction of the Earth's refle... more One of the applications of Seismic Interferometry (SI) is the reconstruction of the Earth's reflection response from the crosscorrelation of seismic background noise recorded at the surface. In recent years, several authors have derived the relations that govern this process. The quality of the reconstruction has been extensively examined with numerical modeling results. Several authors have applied the method to real data for the reconstruction of surface waves. We applied SI to background-noise field data recorded in a desert area. The reconstructed results show several coherent events-inclined and nearly horizontal. The inclined coherent events are interpreted as reconstructed surface waves. The nearly horizontal coherent events appear to align well with reflections from an active survey along the same line. Therefore, we interpret these events as reconstructed reflections.
Seg Technical Program Expanded Abstracts, 2006
Seismic Interferometry (SI) can construct reflection data from seismic background noise. In recen... more Seismic Interferometry (SI) can construct reflection data from seismic background noise. In recent years, several authors developed the theory and applied it to synthetic data. With field data, the only success until now was the reconstruction of surface waves from coda and microseisms. Here, we attempt to reconstruct reflection events from noise data recorded in a desert area. The SI result shows inclined and horizontal coherent events. Some of the reconstructed events appear to align with reflections from an active survey. We cannot, however, exclude alternative explanations.
Physica C: Superconductivity, 1997
We investigate with Quantum Monte Carlo (QMC) simulations supplemented by Hartree-Fock (HF) calcu... more We investigate with Quantum Monte Carlo (QMC) simulations supplemented by Hartree-Fock (HF) calculations the static spin susceptibilities in a 2D tight-binding Hubbard model with attractive pairing interaction as the simplest lattice superconductor. The susceptibility is experimentally accessible in the high-To cuprates via measurements of the spin part of the Knight shift Ks. Whereas K~ is quite understood and similar to conventional expectations at the normal state-superconductor transition in case of the overdoped and optimaUy doped cuprates, the behavior of Ks is highly unconventional in the underdoped materials. A maximum in the susceptibility is observed at Tc in the overdoped materials, and a strong decrease below To, usually associated with a spin singlet-i.e. pair-formation. The position of this maximum shifts to increasingly higher temperatures far above the superconducting transition temperature Tc in case of the underdoped materials. We investigate K~ in the frame of this simple lattice superconductor, and a short discussion on consequences for several other experimentally accessible quantities is given.
Physical Review B
Angular-dependent magnetic torque measurements performed near the critical temperature on single ... more Angular-dependent magnetic torque measurements performed near the critical temperature on single crystals of HgBa 2 CuO 4ϩy , La 2Ϫx Sr x CuO 4 , and YBa 2 Cu 3 O 6.93 are scaled, following the three-dimensional ͑3D͒ XY model, in order to determine the scaling function dG Ϯ (z)/dz which describes the universal critical properties of high-T c cuprates near T c. A systematic shift of the scaling function with increasing effective mass anisotropy ␥ϭͱm c */m a * is observed, which may be understood in terms of a 3D-2D crossover. Further evidence for a 3D-2D crossover is found from temperature-dependent torque measurements carried out in different magnetic fields at different field orientations ␦, which show a quasi-2D crossing region (M *,T*). The occurrence of this crossing phenomenon is explained in a phenomenological way from the weak z dependence of the scaling function around a value zϭz*. The crossing temperature T* is found to be angular dependent. Torque measurements above T c reveal that fluctuations are strongly enhanced in the underdoped regime where the anisotropy is large, whereas they are less important in the overdoped regime.
Physica C: Superconductivity
A quantum Monte Carlo approach is used to calculate the static spin susceptibility for the attrac... more A quantum Monte Carlo approach is used to calculate the static spin susceptibility for the attractive Hubbard model as a function of coupling strength. This method enables the investigation of strong correlation, precursor pair formation and fluctuation effects, thus, going far beyond a mean field approach. The resulting temperature dependence of the spin contribution to the NMR Knight shift explains the observed opening of a pseudogap at the transition from overdoped to underdoped cuprate superconductors. Marked differences between pair formation in the weak and the strong coupling regimes are predicted. We address this scenario in part, because there is experimental evidence for a pseudogap in NMR, ARPES and other data, and in part, because the cuprates are-at least when we approach the underdoped regime-quasi-2dimensional superconductors with short coherence length. Therefore, they are expected to exhibit important deviations from an abrupt, BCS-like transition.
Optimization of fiber Bragg grating parameters for sensing applications
Fiber Optic Sensors and Applications XIV
Interrogation and mitigation of polarization effects for standard and birefringent FBGs
Fiber Optic Sensors and Applications XIII, 2016
Apparatus, System and Method for Receiving a Vertical Component of a Signal and for Determining a Resistivity of a Region Below a Geologic Surface for Hydrocarbon Exploration
The retrieval of the earth's reflection response from cross-correlations of seismic noise recordi... more The retrieval of the earth's reflection response from cross-correlations of seismic noise recordings can provide valuable information, which may otherwise not be available due to limited spatial distribution of seismic sources. We cross-correlated ten hours of seismic background-noise data acquired in a desert area. The cross-correlation results show several coherent events, which align very well with reflections from an active survey at the same location. Therefore, we interpret these coherent events as reflections. Retrieving seismic reflections from background-noise measurements has a wide range of applications in regional seismology, frontier exploration and long-term monitoring of processes in the earth's subsurface.
Enabling technologies for fiber optic sensing
Optical Sensing and Detection IV, 2016
Multi-Mode Electromagnetic Surveying
Retrieving reflections from seismic background-noise recordings: theory and results
Symmetry and Pairing in Superconductors, 1999
Physical review. B, Condensed matter, 1996
We implement a Quantum Monte Carlo calculation for a repulsive Hubbard model with nearest and nex... more We implement a Quantum Monte Carlo calculation for a repulsive Hubbard model with nearest and next-nearest neighbor hopping interactions on clusters up to 12 × 12. A parameter region where the Fermi level lies close to the van Hove singularity at the Saddle Points in the bulk band structure is investigated. A pairing tendency in the d x 2 −y 2 symmetry channel, but no other channel, is found. Estimates of the effective pairing interaction show that it is close to the value required for a 40 K superconductor. Finite-size scaling compares with the attractive Hubbard model.
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Papers by johannes singer