Interpretation of deep directional resistivity measurements acquired in high-angle and horizontal wells using 3-D inversion

The interpretation of resistivity measurements acquired in high-angle and horizontal wells is a critical technical problem in formation evaluation. We develop an efficient parallel 3-D inversion method to estimate the spatial distribution of electrical resistivity in the neighbourhood of a well from deep directional electromagnetic induction measurements. The methodology places no restriction on the spatial distribution of the electrical resistivity around arbitrary well trajectories. The fast forward modelling of triaxial induction measurements performed with multiple transmitter-receiver configurations employs a parallel direct solver. The inversion uses a pre-conditioned gradient-based method whose accuracy is improved using the Wolfe conditions to estimate optimal step lengths at each iteration. The large transmitter-receiver offsets, used in the latest generation of commercial directional resistivity tools, improve the depth of investigation to over 30 m from the wellbore. Several challenging synthetic examples confirmthe feasibility of the full 3-D inversion-based interpretations for these distances, hence enabling the integration of resistivity measurements with seismic amplitude data to improve the forecast of the petrophysical and fluid properties. Employing parallel direct solvers for the triaxial induction problems allows for large reductions in computational effort, thereby opening the possibility to invert multiposition 3-D data in practical CPU times

Theoretical Developments in Electromagnetic Induction Geophysics with Selected Applications in the Near Surface

Near-surface applied electromagnetic geophysics is experiencing an explosive period of growth with many innovative techniques and applications presently emergent and others certain to be forthcoming. An attempt is made here to bring together and describe some of the most notable advances. This is a difficult task since papers describing electromagnetic induction methods are widely dispersed throughout the scientific literature. The traditional topics discussed herein include modeling, inversion, heterogeneity, anisotropy, target recognition, logging, and airborne electromagnetics (EM). Several new or emerging techniques are introduced including landmine detection, biogeophysics, interferometry, shallow-water electromagnetics, radiomagnetotellurics, and airborne unexploded ordnance (UXO) discrimination. Representative case histories that illustrate the range of exciting new geoscience that has been enabled by the developing techniques are presented from important application areas such as hydrogeology, contamination, UXO and landmines, soils and agriculture, archeology, and hazards and climat

Early Strength Of Shotcrete

This research studied the shotcrete strength development with time for worst and best conditions. The study included the minimum strength required of the shotcrete to support itself and how much time is required for that strength to develop after application including minimum strength required of the shotcrete to support an excavation. A field instrument was invented to indicate when re-entry conditions of the shotcrete have been met in situ

"Analysis of dynamic responses and instabilities in rotating machinery\u201d

The first task of the present research is to characterize both experimentally and numerically journal bearings with low radial clearances for rotors in small-scale applications (e.g., micro Gas Turbines); their diameter is in the order of ten millimetres, leading to very small dimensional clearances when the typical relative ones (order of 1/1000) are employed; investigating this particular class of journal bearings under static and dynamic loading conditions represents something unexplored. To this goal, a suitable test rig was designed, and the performance of its bearings were investigated under steady load. For the sake of comparison, numerical simulations of the lubrication were also performed by means of a simplified model. The original test rig adopted is a commercial Rotor Kit (RK), but substantial modifications were carried out in order to allow significant measurements. Indeed, the relative radial clearance of RK4 RK bearings is about 2/100, while it is around 1/1000 in industrial bearings. Therefore, the same original RK bearings are employed in this new test rig, but a new shaft was designed to reduce their original clearance. The new custom shaft allows to study bearing behaviour for different clearances, since it is equipped with interchangeable journals. Experimental data obtained by this test rig are then compared with further results of more sophisticated simulations. They were carried out by means of an in-house developed finite element (FEM) code, suitable for ThermoElasto-HydroDynamic (TEHD) analysis of journal bearings both in static and dynamic conditions. In this work, bearing static performances are studied to assess the reliability of the experimental journal location predictions by comparing them with the ones coming from already validated numerical codes. Such comparisons are presented both for large and small clearance bearings of original and modified RK, respectively. Good agreement is found only for the modified RK equipped with small clearance bearings (relative radial clearance 8/1000), as expected. In comparison with two-dimensional lubrication analysis, three-dimensional simulation improves prediction of journal location and correlation with experimental results. The second main task of the present work is the development and the implementation of a suitable analytical model to correctly capture rolling bearing radial stiffness, particularly nearby the critical speeds of the investigated rotor-bearings system. In this work, such bearing non-linear stiffness lumped parameter model is firstly validated on the commercial RK and then it is applied to both air bladeless turbines (or Tesla turbines) and to an innovative microturbine, in order to assess their global rotodynamic behavior when they are mounted on ball bearings. In order to properly investigate all the issues related to critical speeds and stiffness, an adequate number of experimental tests was performed by exploiting an experimental air Tesla turbine prototype located at TPG experimental facility of the University of Genoa. The correlation between measured flexural critical speeds and their numerical predictions is markedly conditioned by the correct identification of ball bearings dynamic characteristics; in particular, bearings stiffness effect may play a significant role in terms of rotor-bearings system natural frequencies and therefore it must be properly assessed. Indeed, Tesla turbine rotor FE model previously employed for numerical modal analysis relies on rigid bearings assumption and therefore it does not account for bearings stiffness overall contribution, which may become crucial in case of \u201chard mounting\u201d of rotor-bearings systems. Subsequently, high-speed air Tesla rotor is investigated by means of an enhanced FE model for numerical modal analysis within Ansys\uae environment, where ball bearings are modelled as non-linear springs whose stiffness is expressed according to the analytic model implemented in Matlab\uae. Two different numerical FE models are devised for microturbine rotor modelling which respectively rely on beam elements and on three-dimensional solid elements for mechanical system spatial discretization. The obtained results in terms of rotor-bearings system modal analysis exhibit an improvement in experimental-numerical results correlation by relying on such ball bearing stiffness model; moreover, beam-based FE model critical speeds predictions are coherent with experimental evidence and with respect to solid elements model it is characterized by lower computational time and it is more easily interpretable. Thus, such experimentally validated numerical model represents a reliable and easily adaptable tool for highspeed rotating machinery critical speeds prediction in practical industrial application cases. Finally In this work, several signal processing techniques performed on vibro-acoustic signals acquired from a T100 Turbec microturbine (which is furnished with a centrifugal compressor) are illustrated. Research activity goal focuses on the investigation different kinds of system response starting from non-intrusive probes signals like accelerometers and microphones; this is made by means of techniques such as HOSA and Wavelet Transform, developed in Matlab\uae environment, for early detection of the onset of unstable phenomena in centrifugal compressors. These new and different methods have been applied to the same set of data to get sufficiently independent information useful to synergistically improve knowledge in the diagnostic system. Data were acquired by means of an experimental facility based on a T100 turbine developed by the Thermochemical Power Group (TPG) at the University of Genoa. Sampling rate and sensor placement were carefully taken into account, basing both on the physical phenomena to be observed and on the sensor dynamic characteristics. In this context, it is meant to study microphones and accelerometers signals not from an isolated centrifugal turbomachine installed in a dedicated line, but from a whole compressor placed in a mGT system for energy generation. Indeed, the investigated machine is not operating in standalone mode, but its working point and angular velocity depend on the coupling with several elements. In particular, compressor working point and then its vibro-acoustic signals are expected to convey vibration and sound contributions coming from all the plant components; thus, they are more representative of machine realistic behavior in the energy system

Wideband directional complex electrical conductivity of geomaterials : a mechanistic description

textSubsurface electromagnetic (EM) measurements in shaly sands, sand-shale laminations, and organic-rich mudrocks, to name a few examples, exhibit directional and frequency dispersive characteristics primarily due to the effects of electrical conductivity anisotropy, dielectric permittivity anisotropy, and interfacial polarization phenomena. Conventional resistivity interpretation techniques for laboratory and subsurface EM measurements do not account for the effects of dielectric permittivity, dielectric loss factor, dielectric dispersion, and dielectric permittivity anisotropy arising from interfacial polarization phenomena. Furthermore, laboratory measurements on 1.5-inch-diameter, 2.5-inch-long core plugs acquired at discrete depths in wells are generally utilized to improve the estimation of petrophysical properties based on conventional resistivity interpretation of subsurface EM measurements. Electrical measurements performed on 4-inch-diameter, 2-feet-long whole core samples represent closer approximations to the electrical properties of subsurface formations compared to widely-used galvanic measurements of core plugs. The first objective of this dissertation is to develop a non-contact and non-invasive, laboratory-based EM induction apparatus, referred to as the WCEMIT, to measure the complex-valued electrical conductivity tensor of whole core samples at high resolution and at multiple frequencies for improved core-well log correlation. The tensor functionality of the WCEMIT is sensitive to the directional nature of electrical conductivity, dielectric permittivity, and dielectric loss factor, while its multi-frequency functionality is sensitive to the frequency-dispersive electrical properties of the samples. Finite-element and semi-analytic EM forward models of the WCEMIT are used to calibrate WCEMIT measurements and to estimate various effective electrical properties. WCEMIT measurements are successfully applied to the estimation of directional conductivity, dielectric permittivity, formation resistivity factor, Archie's porosity exponent, relative dip, azimuth, and anisotropy ratio. It is found that brine-saturated samples containing pyrite and graphite inclusions exhibit a negative X-signal response, large frequency dispersion in the R-signal response, large effective permittivity, and significant frequency dispersion of effective conductivity and permittivity in the frequency range of 10 kHz to 300 kHz. Further, graphite-bearing samples exhibit significantly different frequency dispersion properties compared to pyrite-bearing samples. Estimated values of effective relative permittivity of samples containing uniformly distributed 1.5-vol% of pyrite inclusions were in the range of 10³ to 10⁴, while those containing uniformly distributed 1.5-vol% of graphite inclusions were in the range of 10⁵ to 10⁶. At an operating frequency of 58.5 kHz, samples containing 1.5-vol% of graphite inclusions and those containing 1.5-vol% of pyrite inclusions exhibited effective conductivity values that were 200% and 95%, respectively, of the host conductivity. True conductivity and permittivity of hydrocarbon-bearing host media can be determined by processing the estimated effective conductivity and permittivity of conductive-mineral-bearing samples. Accordingly, the second objective of this dissertation is to develop a mechanistic electrochemical model, referred to as the PPIP-SCAIP model, that quantifies the directional complex electrical conductivity of geomaterials containing electrically conductive mineral inclusions, such as pyrite and magnetite, that are uniformly distributed in a fluid-filled, porous matrix made of non-conductive grains possessing surface conductance, such as silica, clay-sized particles, and clay minerals. PPIP-SCAIP model predictions successfully reproduce several laboratory measurements of multi-frequency complex electrical conductivity, relaxation time, and chargeability of mixtures containing electrically conductive inclusions in the frequency range of 100 Hz to 10 MHz. The mechanistic model predicts that the low-frequency effective electrical conductivity of geomaterials containing as low as 5% volume fraction of disseminated conductive inclusions will vary in the range of 70% to 200% of the host conductivity for operating frequencies between 100 Hz to 100 kHz, while its high-frequency effective relative permittivity will vary in the range of 190% to 90% of the host relative permittivity for operating frequencies between 100 kHz and 10 MHz. The model indicates high sensitivity of subsurface EM measurements to the electrical properties, shape, volumetric concentration, and size of the inclusion phase, and to the conductivity of pore-filling electrolyte.Petroleum and Geosystems Engineerin

Achievements and Prospects of Functional Pavement

In order to further promote the development of functional pavement technology, a Special Issue entitled “Achievements and Prospects of Functional Pavement” has been proposed by a group of guest editors. To achieve this objective, the articles included in this Special Issue are related to different aspects of functional pavements, including green roads to decrease carbon emissions, noise, and pollution, safety pavements to increase skid resistance through water drainage and snow removal, intelligent roads for monitoring, power generation, temperature control and management, and durable roads to increase service life with new theories, new design methods, and prediction models, as highlighted in this editorial