Borehole Electroseismic Measurements In Dolomite: Identifying Fractures And Permeable Zones

Measuring the electrical field induced by a borehole Stoneley wave is a new method for characterizing a rock formation around a borehole. Our field measurements demonstrate that the Stoneley-wave-induced electrical field can be detected in sedimentary rocks (dolomite in our experiment), and that the amplitude of this electroseismic phenomenon can be used to detect isolated fractures and permeable zones

Borehole electroseismic phenomena : field measurements and theory

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Earth, Atmospheric, and Planetary Sciences, 1998.Includes bibliographical references (leaves 163-173).A Stoneley wave propagating in a borehole generates a flow of pore fluid in permeable zones intersected by the borehole. In turn, this flow of pore fluid induces a streaming electrical field. This thesis is an experimental and theoretical investigation of the electrical fields induced by Stoneley waves. The main emphasis of this thesis is to understand the electroseismic phenomena that are observed in the field. In the first experiment described in this thesis, we measured Stoneley-wave-induced electrical fields in a borehole drilled through fractured igneous rocks. Analysis of field data confirms that the electrical fields that we measured were induced by fluid flow in fractures. The normalized amplitude of these electrical fields correlated with the fracture density log. In the second experiment, we measured Stoneley-wave-induced electrical fields in several boreholes in vuggy dolomite. In dolomite, the normalized amplitude of the Stoneley-wave-induced electrical field correlates with the porosity of the formation around the borehole. Further, the Stoneley-wave-induced electrical fields have anomalously high amplitudes at an isolated fracture that intersected two boreholes. To explain the experimental results, we developed a theoretical model for the Stoneley-wave-induced electrical fields. According to the model, the normalized amplitude of the Stoneley-wave-induced electrical field is proportional to the porosity and inversely proportional to the pore space tortuosity of a formation around a borehole. Moreover, the amplitude-versus-frequency behavior of this electrical field depends on the permeability of the formation. To further test the theory's prediction, we measured electrical potentials induced by the borehole Stoneley wave in the frequency range from 100Hz to 4kHz. The normalized amplitudes of the Stoneley-wave-induced electrical potentials measured in the field were consistent with the amplitudes predicted by the theory. Also, the amplitude- versus-frequency dependence of the electroseismic signals recorded at the depth of the large fracture roughly followed the trend predicted by the theory. However, the general amplitude-versus-frequency dependence of the electroseismic signals recorded in the field is more complicated than that predicted by the theory. The main contributions of this thesis are: 1. This thesis develops a borehole electroseismic measurement technique and demonstrates that it works in the field. This technique can be used to make electroseismic logging measurements. 2. This thesis investigates an electrical field induced by a borehole Stoneley wave. This electroseismic phenomenon is explained, measured in the field and modeled theoretically. 3. This thesis derives from field data a parameter that describes local electroseismic coupling in a formation around a borehole. This parameter, the normalized amplitude of the Stoneley-wave-induced electrical field, is defined as the ratio of an electrical field amplitude to a pressure amplitude in the Stoneley wave at a certain depth. This thesis demonstrates that the normalized amplitude of the Stoneley-wave- induced electrical field can be used to identify permeable fractures in situ. 4. This thesis uses field electroseismic measurements to quantitatively characterize rock formations around a borehole. Using the theoretical model developed in this thesis, a porosity log for fractured granite is derived from electroseismic field data.by Oleg Mikhailov.Ph.D

Electroseismic Investigation Of The Shallow Subsurface: Field Measurements And Numerical Modeling

Electroseismic phenomena in porous media, first observed almost 60 years ago (Ivanov, 1939), were recently "rediscovered" due to their potential to detect zones of high fluid mobility and fluid chemistry contrasts in the subsurface (Thompson and Gist, 1993; Haartsen et al., 1995). However, a limited number of field studies of these phenomena reported in the literature were not able to support the results with an explicit comparison to theoretical predictions. In this paper, we demonstrate that electroseismic phenomena in porous media can be observed in the field, explained, and modeled numerically, yielding a good agreement between the field and the synthetic data. We first outline the design of our field experiment and describe the procedure used to reduce noise in the electroseismic data. Then, we present and interpret the field data, demonstrating how and where different electroseismic signals originated in the subsurface. Finally, we model our field experiment numerically and demonstrate that the numerical results correctly simulate arrival times, polarity, and the amplitude-versus-offset behavior of the electroseismic signals measured in the field.United States. Dept. of Energy (Grant DE-FG02-93ER14322)Massachusetts Institute of Technology. Borehole Acoustics and Logging Consortiu

Using Borehole Electroseismic Measurements To Detect And Characterize Fractured (Permeable) Zones

We present a new type of field measurement capable of detecting and characterizing fractured (permeable) zones intersecting a borehole. The method is based on measuring electrical fields generated by a borehole Stoneley wave. In this paper, we describe the measurement technique, present field data, and propose a theoretical model, which correctly predicts amplitudes and phases of the electrical fields measured in the borehole experiment. The theoretical model and the field data demonstrate that the measurements of the Stoneley-wave-induced electrical fields can yield information about the interconnected porosity, and possibly about the permeability of the formation around the borehole. We derive an estimate of the interconnected porosity from the field data, and show that it correlates well with the density of fractures intersecting the borehole. Our results suggest that the borehole electroseismic method can be developed into a logging or a VSP tool, with possible applications in reservoir characterization.Massachusetts Institute of Technology. Borehole Acoustics and Logging Consortiu

Electroseismic Logging For The Detection And Characterization Of Permeable Zones: Field Measurements And Theory

A Stoneley wave propagating in a borehole generates pore fluid flow within the permeable zones intersected by the borehole. In turn, the fluid flow induces a streaming electrical potential. This electrical potential induced by the Stoneley wave can be -measured in the field at frequencies from 100Hz to 4000Hz. Measurements of this Stoneley-wave-induced electrical potential can be used to detect fractures and permeable zones. The amplitude-versus-frequency dependence of this electroseismic phenomenon provides a new way to test theories of the acoustics and the electrokinetics of porous media against field measurements in real :oeks.Massachusetts Institute of Technology. Borehole Acoustics and Logging ConsortiumMassachusetts Institute of Technology. Earth Resources Laboratory. Reservoir Delineation Consortiu

Logarithmic algorithms for fair division problems

We study the algorithmic complexity of fair division problems with a focus on minimizing the number of queries needed to find an approximate solution with desired accuracy. We show for several classes of fair division problems that under certain natural conditions on sets of preferences, a logarithmic number of queries with respect to accuracy is sufficient

Wireless power transfer in magnetic resonance imaging at a higher-order mode of a birdcage coil

Magnetic resonance imaging (MRI) is a crucial tool for medical visualization. In many cases, performing a scanning procedure requires the use of additional equipment, which can be powered by wires as well as via wireless power transfer (WPT) or wireless energy harvesting. In this Letter, we propose a novel scheme for WPT that uses a higher-order mode of the MRI scanner's birdcage coil for energy transmission. In contrast to the existing WPT solutions, our approach does not require additional transmitting coils. Compared to the energy harvesting, the proposed method allows supplying significantly more power. We perform numerical simulations demonstrating that one can use the fundamental mode of the birdcage coil to perform a scanning procedure while transmitting the energy to the receiver at a higher-order mode without any interference with the scanning signal or violation of safety constraints, as guaranteed by the mode structure of the birdcage. Also, we evaluate the specific absorption rate along with the energy transfer efficiency and verify our numerical model by a direct comparison with an experimental setup featuring a birdcage coil of a 1.5T MRI scanner.Comment: 6 pages, 5 figures + Supplementary Material 10 pages, 7 figure

Novel D-A-π-A1 Type Organic Sensitizers from 4,7-Dibromobenzo[d][1,2,3]thiadiazole and Indoline Donors for Dye-Sensitized Solar Cells

Two novel D-A-π-A1 metal-free organic dyes of the KEA series containing benzo[d][1,2,3]thiadiazole (isoBT) internal acceptor, indoline donors fused with cyclopentane or cyclohexane rings (D), a thiophene as a π-spacer, and a cyanoacrylate as an anchor part were synthesized. Monoarylation of 4,7-dibromobenzo[d][1,2,3]thiadiazole by Suzuki-Miyamura cross-coupling reaction showed that in the case of indoline and carbazole donors, the reaction was non-selective, i.e., two monosubstituted derivatives were isolated in each case, whereas only one mono-isomer was formed with phenyl- and 2-thienylboronic acids. This was explained by the fact that heterocyclic indoline and carbazole fragments are much stronger donor groups compared to thiophene and benzene, as confirmed by cyclic voltammetry measurements and calculation of HOMO energies of indoline, carbazole, thiophene and benzene molecules. The structure of monoaryl(hetaryl) derivatives was strictly proven by NMR spectroscopy and X-ray diffraction. The optical and photovoltaic properties observed for the KEA dyes showed that these compounds are promising for the creation of solar cells. A comparison with symmetrical benzo[c][1,2,3]thiadiazole dyes WS-2 and MAX114 showed that the asymmetric nature of benzo[d][1,2,3]thiadiazole KEA dyes leads to a hypsochromic shift of the ICT band in comparison with the corresponding benzo[c][1,2,5]thiadiazole isomers. KEA dyes have a narrow HOMO-LUMO gap of 1.5–1.6 eV. Amongst these dyes, KEA321 recorded the best power efficiency (PCE), i.e., 5.17%, which is superior to the corresponding symmetrical benzo[c][1,2,3]thiadiazole dyes WS-2 and MAX114 (5.07 and 4.90%)