Stefan Dangel

Phenomenology of tremor-like signals observed over hydrocarbon reservoirs

Abstract We have observed narrow-band, low-frequency (1.5–4 Hz, amplitude 0.01–10 μm/s) tremor signals on the surface over hydrocarbon reservoirs (oil, gas and water multiphase fluid systems in porous media) at currently 15 sites worldwide. These ‘hydrocarbon tremors’ possess remarkably similar spectral and signal structure characteristics, pointing to a common source mechanism, even though the depth (some hundreds to several thousands of meters), specific fluid content (oil, gas, gas condensate of different compositions and combinations) and reservoir rock type (such as sandstone, carbonates, etc.) for each of those sites are quite different. About half of the sites are fully explored or even developed and producing fields, and hard quantitative data on the reservoirs are available (well data, reservoir monitoring data, seismic surveys, etc.). The other areas are essentially either explored prospect areas where we did not have access to hard reservoir data or (in only one case) areas where no exploration wells have been drilled at all. The tremor signal itself was observed over ALL locations investigated so far. The signals weaken at the rim of the reservoirs and are not observed outside the reservoir area. There is a strong correlation of the tremor power with the thickness of the hydrocarbon-bearing layers (‘pay zone thickness’) determined by borehole log measurements. The overall correlation between surface tremor measurements and accessible subsurface well data is higher than 90%. The phenomenological comparison of hydrocarbon tremor signals with volcanic tremor signals from Stromboli and Arenal volcanoes using both conventional spectral analysis tools and non-linear dynamics methods reveals fundamental similarities between those two phenomena as well as their close relation to bandpass filtered noise. Nevertheless, the specific signal sources are expected to be different for volcanoes and hydrocarbon reservoirs. Using the currently available data we present possible concepts (active or passive mechanisms) on the nature of the hydrocarbon tremor source. Our data lead us to conclude that we are most likely observing a characteristic filtering/mixing effect, with the energy input supplied by the natural seismo-acoustic background. The reservoir, i.e. the hydrocarbon-water-multifluid system contained in a porous medium, is expected to be the oscillatory element able to act as a filter/mixer (resembling essentially a in-reservoir path effect) for the natural seismo-acoustic background. Most intriguing seems the application aspect, i.e. the practical usability of this spectroscopic approach as a direct from-the-surface, non-invasive hydrocarbon indicator.

The Improved Dual-view Field Goniometer System FIGOS

In spectrodirectional Remote Sensing (RS) the Earths surface reflectance characteristics are studied by means of their angular dimensions. Almost all natural surfaces exhibit an individual anisotropic reflectance behaviour due to the contrast between the optical properties of surface elements and background and the geometric surface properties of the observed scene. The underlying concept, which describes the reflectance characteristic of a specific surface area, is called the bidirectional reflectance distribution function (BRDF). BRDF knowledge is essential for both correction of directional effects in RS data and quantitative retrieval of surface parameters. Ground-based spectrodirectional measurements are usually performed with goniometer systems. An accurate retrieval of the bidirectional reflectance factors (BRF) from field goniometer measurements requires hyperspectral knowledge of the angular distribution of the reflected and the incident radiation. However, prior to the study at hand, no operational goniometer system was able to fulfill this requirement. This study presents the first dual-view field goniometer system, which is able to simultaneously collect both the reflected and the incident radiation at high angular and spectral resolution and, thus, providing the necessary spectrodirectional datasets to accurately retrieve the surface specific BRF. Furthermore, the angular distribution of the incoming diffuse radiation is characterized for various atmospheric conditions and the BRF retrieval is performed for an artificial target and compared to laboratory spectrodirectional measurement results obtained with the same goniometer system. Suggestions for further improving goniometer systems are given and the need for intercalibration of various goniometers as well as for standardizing spectrodirectional measurements is expressed.

Toward a direct comparison of field and laboratory goniometer measurements

Field and laboratory goniometers are widely used in the remote sensing community to assess spectrodirectional reflection properties of selected targets. Even when the same target and goniometer system are used, field and laboratory results cannot directly be compared due to inherent differences, mainly in the illumination conditions since actual goniometers measure a hemispherical-conical reflectance in the field and a biconical reflectance in the lab. Yet, the ability to compare and combine measurements from different instrumental designs is critical to ensure sensor cross-calibration and for all applications that rely on measurements obtained with both types of instruments. One approach to this problem consists in retrieving the bidirectional reflectance distribution function (BRDF) of the targets of interest for each experimental setup and to compare these, since theoretically they are independent of the particular conditions of illumination and observation. This involves a correction for diffuse incoming radiation in the case of field measurements, and a correction for conicity and inhomogeneity of illumination in the case of laboratory measurements. In this paper, we present a novel BRDF retrieval scheme for typical laboratory goniometers and compare it with the usual correction method assuming Lambertian behavior. We then discuss the first results of measurements and BRDF retrievals using the field and laboratory goniometer systems of the Remote Sensing Laboratories of the University of Zurich, which share the exact observation geometry, on the same inert, highly anisotropic target.

Combined field and laboratory goniometer system - FIGOS and LAGOS

Ground level measurements of surface directional reflectance properties can be performed either in the field or within a laboratory setup. The latter has the advantage of independence on weather conditions, constant illumination and neglectable atmospheric disturbances. On the other hand, the artificial laboratory light sources usually are less parallel and less homogeneous than the clear sky solar illumination. In order to compare these two types of measurements (or replace one by the other) a careful correction of the data (BRDF retrieval) with respect to the mentioned sources of error is necessary. For the field case, this can be done following the well known procedures proposed by Martonchick and others. The purpose of this paper is to present our laboratory goniometer system and a corresponding BRDF retrieval solution. The RSL laboratory goniometer system (LAGOS) is based on the field goniometer (FIGOS) with the addition of a 1000 W brightness-stabilized quartz tungsten halogen lamp and lens system, placed in a dark room for minimization of stray light. The inhomogeneity of the illuminated area has been directly measured and found to be within 10% mean deviation for the zenith position. A simulation of the complete geometry of LAGOS, including the angular distributions and inhomogeneity of the light source as well as the changing position of the radiometer footprint allows us to estimate the measurement error for any target with known BRDF. The same algorithm can be used as core for the BRDF retrieval.

THE IMPORTANCE OF REFLECTANCE TERMINOLOGY IN IMAGING SPECTROSCOPY

Abstract A technique is described which allowed about 23% of late yolk sac lemon sole larvae to be reared to metamorphosis. Early larvae were fed on mussel trochophores, followed by rotifers until newly hatched Artemia nauplii became acceptable for growth to metamorphosis. The marine flagellate, Dunaliella tertiolecta , an unidentified hypotrichid ciliate, and the ‘vinegar eelworm’, Turbatrix sp., had no food value for first-feeding larvae.

Spatial separation of circularly polarized laser beams in sodium vapor

We observed experimentally that a superposition of two co-propagating left and right hand circularly polarized laser beams is spatially unstable during propagation through a vapor of sodium atoms containing argon buffer gas. A small spatial asymmetry between the two input beams leads to their separation into two pure circularly polarized output beams. However a single linearly polarized input beam was found to be spatially stable. Our theoretical results from Maxwell-Bloch propagation calculations using both modal expansion and direct partial differential equation solution methods are in good agreement with the experiments. The splitting mechanism can be explained in simple terms as consisting of an absorption and dispersion dominated initial part and a diffraction dominated final part.

Dynamics of laser beam switching in sodium vapor

The interaction of left- and right-hand circularly polarized narrow-band cw laser beams that copropagate through sodium vapor and are tuned to the homogeneously broadened D1 transition can lead to the mutual extinction of both beams. Such beam switching is caused by an intensity- and polarization-dependent refractive index due to optical pumping even at low intensities. The dynamics of beam switching is investigated experimentally and explained qualitatively by the conventional J = 1/2 to J = 1/2 transition model. The accurate quantitative description, however, is only achieved by an extended model comprising hyperfine ground states in spite of homogeneous line broadening by argon buffer gas, which is larger than the hyperfine splitting.

Comparison of field and laboratory spectro-directional measurements using a standard artificial target

Spectro-directional surface measurements can either be performed in the field or within a laboratory setup. Laboratory measurements have the advantage of constant illumination and neglectable atmospheric disturbances. On the other hand, artificial light sources are usually less parallel and less homogeneous than the clear sky solar illumination. To account for these differences and for determining for which targets a replacement of field by laboratory experiments is indeed feasible, a quantitative comparison is a prerequisite. Currently, there exists no systematic comparison of field and laboratory measurements using the same targets. In this study we concentrate on the difference in spectro-directional field and laboratory data of the same target due to diffuse illumination. The field data were corrected for diffuse illumination following the proposed procedure by Martonchik . Spectro-directional data were obtained with a GER3700 spectroradiometer. In the field, a MFR sun photometer directly observed the total incoming diffuse irradiance. In the laboratory, a 1000W brightness-stabilized quartz tungsten halogen lamp was used. For the first direct comparison of field and laboratory measurements, we used an artificial and inert target with high angular anisotropy. Analysis shows that the diffuse illumination in the field is leading to a higher total reflectance and less pronounced angular anisotropy.

Optical-pumping-induced ring structures of polarized laser light propagating through sodium vapor

We describe a sensitive technique for observing small transverse modifications to intensity, phase, and polarization arising in nonlinear propagation of a laser beam through an atomic vapor. The technique, which in essence is an interferometric one, is based on the use of crossed polarizers that are nearly but not exactly pure circular. Illustrative results are presented for cw dye-laser radiation propagating through collisionally broadened atomic sodium that is near resonant to the D1 line. Well-defined ring patterns produced by nonlinear interactions are observed at both positive and negative laser detunings.

Comparison of Maximal Left Ventricular Intramyocardial Artery Lumen Diameter in 2 Aneurysmectomy Specimen after TMR and 44 Control Patients

Summary TMR (Transmyocardial Laser Revascularization) is of value in angina pectoris not accessible to medication or conventional heart surgery. Therapeutical benefit is thought to be due to patent channels conveying blood from the lumen right into the wall of the left ventricle. Interestingly, histopathological findings of some autopsy patients fail to prove patent laser channels after TMR. We examine histopathological findings of left ventricular aneurysmectomy specimen 7 and 11 months after TMR. We compare the estimated (aneurysmectomy patients) or calculated (44 control patients) Equivalent Value for Left Ventricular Wall Tension (ET) to the Maximal Intramyocardial Artery Lumen Diameter (MIALD). The 44 control patients are selected out of different clinicopathological groups. The ET value is calculated using a simplifying spherical model of the left ventricle, and, like the MIALD value, is based on standardized histological samples of the anterior left ventricular wall and additionally the heart weight. We find an inverse non-linear regressive relationship between ET and MIALD values. This provides a morphologically based model for intramyocardial perfusion, which fits into theoretical physical models, putting the value of the reptile heart theory into question. Additionally it provides first morphological clues that reducing ventricular wall tension actually improves intramyocardial perfusion. We discuss, how the data not fitting into this model represents exceptions, how TMR might provide its beneficial effects, and how its value might be limited by the left ventricular wall tension, and on what basis the mechanism of other procedures such as ventriculectomy (also known as the Batista procedure) and coronary bypass surgery could be compared to our proposed mechanism of the TMR procedure.