Compared to laboratory or clinical nuclear magnetic resonance (NMR), the dimensions of a typical borehole and the nature of continuous logging impose severe constraints on the physics, equipment, and operation of NMR logging tools. The NML tool--the first generation of NMR logging (1960–1994)--was an Earth's field device that measured the free-induction decay in the Earth's magnetic field. Proton polarization (alignment) was achieved using a magnetic field produced by a coil energized with a strong direct current. Each experiment required several seconds to allow complete polarization. The power was turned off, and the same coil was used to receive the free-induction signal.
Directional surveys obtain the measurements needed to calculate and plot the 3D well path. Instruments for conducting directional surveys can be set up in several different variations, depending on the intended use of the instrument and the methods used to store or transmit survey information. Depending on the method used to store the data, there are film and electronic systems. Survey systems can also be categorized by the methods used to transmit the data to the surface, such as wireline or measurement while drilling (MWD). Magnetic sensors must be run within a nonmagnetic environment [i.e., in uncased hole either in a nonmagnetic drill collar(s) or on a wireline].
Figure 1E.1 – NMR logging-tool response compared to conventional logging tools. NMR porosity is independent of matrix minerals, and the total response is very sensitive to fluid properties. Differences in relaxation times and/or fluid diffusivity allow NMR data to be used to differentiate clay-bound water, capillary-bound water, movable water, gas, light oil, and viscous oils. NMR-log data also provide information concerning pore size, permeability, hydrocarbon properties, vugs, fractures, and grain size. Within a few years after the first successful observations of NMR in 1946, and the demonstration of free-precession NMR in the earth's magnetic field in 1948, the petroleum industry recognized the potential of NMR measurements for evaluating reservoir rocks, pore fluids, and fluid displacement (flow). In the early 1950s, several companies--particularly California Research (Chevron), Magnolia (Mobil), Texaco, Schlumberger, and Shell--began extensive investigations to understand the ...
The synchronous motor is a type of alternating current motor. Like an induction motor, it has a stator and a rotor. Its stator winding closely resembles that of an induction motor, and it, too, receives AC power from the power source to drive the connected load. Synchronous motors are available with various rotor designs to fit different applications. In one type, for example, the rotor is constructed somewhat like a squirrel-cage rotor.
Nuclear magnetic resonance (NMR) has been, and continues to be, widely used in chemistry, physics, and biomedicine and, more recently, in clinical diagnosis for imaging the internal structure of the human body. The same physical principles involved in clinical imaging also apply to imaging any fluid-saturated porous media, including reservoir rocks. The petroleum industry quickly adapted this technology to petrophysical laboratory research and subsequently developed downhole logging tools for in-situ reservoir evaluation. NMR logging, a subcategory of electromagnetic logging, measures the induced magnet moment of hydrogen nuclei (protons) contained within the fluid-filled pore space of porous media (reservoir rocks). Unlike conventional logging measurements (e.g., acoustic, density, neutron, and resistivity), which respond to both the rock matrix and fluid properties and are strongly dependent on mineralogy, NMR-logging measurements respond to the presence of hydrogen protons.
Downhole magnetic surveys have been most commonly applied in highly magnetized igneous rocks, which have usually been studied within pure geoscience, especially beneath the ocean floor. These rocks preserve the direction of the Earth's field at the time of their formation (i.e., the prevailing magnetic field is "frozen" in the rocks as they solidify, giving them a strong natural remnant magnetization). A primary application has been to identify points in time at which the Earth's magnetic field has undergone a polarity reversal. These reversals have been dated globally (e.g., isotopically in the case of volcanic series or by correlation with biostratigraphy in the case of volcaniclastics) and have given rise to a geomagnetic polarity time scale (GPTS) that is based on laboratory measurements. This, in turn, has allowed dates to be assigned to a given magnetozone that is bounded by reversal phenomena.
Eltsov, T. (Ali I. Al-Naimi Petroleum Engineering Research Center, King Abdullah University of Science and Technology) | Patzek, T. W. (Ali I. Al-Naimi Petroleum Engineering Research Center, King Abdullah University of Science and Technology)
Electrically resistive composite casing materials are being introduced to the oil & gas industry. Resistive casing enables electromagnetic logging for exploration and reservoir monitoring, but it requires development of new logging methods. Here we present a technique for the detection of integrity of magnetic cement behind resistive casing. We demonstrate that an optimized induction logging tool can detect small changes in the magnetic permeability of cement through a non-conductive casing in a vertical (or horizontal) well. We can determine both integrity and solidification state of the cement filling annulus behind casing. Changes in magnetic permeability influence mostly the real part of the vertical component of magnetic field. The signal amplitude is more sensitive to a change of magnetic properties of the cement, rather than the signal phase. Our simulations show that optimum separation between the transmitter and receiver coils ranges from 0.25 to 0.6 meters, and the most suitable magnetic field frequencies vary from 0.1 to 10 kHz. A high-frequency induction probe operating at 200 MHz can measure the degree of solidification of cement. The proposed method can detect borehole cracks filled with cement, incomplete lift of cement, casing eccentricity and other borehole in homogeneities.
The objective of this work is to present the development of a numerical model for wave propagation in materials with time-varying, heterogeneous, and non-linear properties. Materials change with time as the result of complex linear and non-linear processes, which can occur due to natural causes or induced. Wave phenomena in this context brings about an interesting and complex problem, which involves the solution to coupled equations which describe interlinked multiphysics phenomena. Thus, understanding the dynamics of this interaction is beneficial to numerous applications across different industries and applied research; e.g. acoustic characterization of moving fluids, laser-fluid interaction, distributed optical fiber sensing, photonic integrated systems, among others. Numerical models, therefore, are indispensable to gain a deeper insight about the physical dynamics of the process and, ultimately, purvey a platform to design and test new applications and technologies.
Over time some numerical models have been proposed to simulate wave phenomena in these situations. The method and solution reviewed in this work provides a unique solution to develop and optimize multiple applications. For example, it can be used to model the interaction of electromagnetic waves with travelling Bragg mirrors produced by temperature or pressure changes in optical fibers, which is the basis of fiber-based distributed fiber sensing; the scattering of acoustic waves by transient disturbances in fluid flow that may arise from gas bubbles or variations in the density of fluids; and the propagation of an electromagnetic pulse in a rapidly moving and varying fluid.
The mathematical description of the process was derived originally for electromagnetics; yet, the numerical solver and mathematical treatment is generic and can be applied to other wave phenomena. The derivation departs from physical principles to write a generalized set of equations that describe wave propagation in time-varying, heterogeneous, and non-linear materials. The resulting set of hyperbolic partial differential equations (PDE) includes diffusive and convective terms that fully describe the wave interaction and process. Linear and nonlinear spatial and time heterogeneities in the material are assimilated into the convective terms of the hyperbolic wave equation. The solver was implemented using a semi-discrete and multidimensional scheme based in the finite-volume method which is highly scalable. Extension to other wave phenomena is discussed by analyzing the parameter correspondence for the acoustic and electromagnetic case.
Mitkus, Alexander (Helmerich & Payne Technologies) | Maus, Stefan (Helmerich & Payne Technologies) | Willerth, Marc (Helmerich & Payne Technologies) | Reetz, Andrew (Helmerich & Payne Technologies) | Oskarsen, Ray Tommy (Add Energy) | Emilsen, Morten Haug (Add Energy) | Gergerechi, Amir (Petroleumstilsynet)
As development of the Barents Sea continues with new plays such as the Castberg, accurate specification of the local magnetic field is important to reliably infer the orientation of the bottomhole assembly (BHA) in horizontal drilling. Since magnetic fields at high latitudes vary spatially and temporally, one requires both spatial models and a way to capture temporal changes. Large temporal changes in the magnetic field can severly distort measured azimuths and therefore must be corrected for. This study, based on a report written for Petroleumstilsynet (Maus et al., 2017), shows that in regions of the Barents Sea within 50 km of a magnetic observatory, either the nearest observatory, interpolated infield referencing (IIFR), or the disturbance function (DF) method may be used for corrections in wellbore surveying to meet accuracy requirements. IIFR and DF will give better error reduction but are slightly more complicated to implement. At distances between 50 km and 250 km, the disturbance field (DF) method best meets accuracy requirements. In remote regions beyond 250 km, a local observatory must be deployed to meet the highest accuracy specifications, but the DF will still far outperform the other interpolated methods at such large distances from an existing observatory. Despite having focused on the Barents Sea region, this comparison of the accuracy of different spatial and temporal magnetic field mitigation methods for wellbore surveying is applicable to high latitude northern and southern regions across the globe.