Abstract: An embodiment of the current invention provides a method for magnetic resonance (MR) imaging or spectroscopy, comprising: (a) selectively exciting exchangeable solute protons or protons of exchangeable solute-based water molecules within a frequency range in a subject using at least one frequency-selective radio frequency (RF) pulse, wherein the frequency range encompasses characteristic resonance frequencies of the exchangeable solute protons or protons of exchangeable solute-based water molecules, wherein the frequency range is substantially non-overlapping with a characteristic resonance frequency of bulk water protons in the subject, wherein the at least one frequency selective RF pulse performs a substantially minimal excitation on the bulk water protons, and wherein the at least one frequency-selective RF pulse, sometimes in combination with a time period that separates the at least one frequency-selective RF pulse, magnetically labels the exchangeable solute protons or the exchangeable solute-based wat

Abstract: A process using Nuclear Magnetic Resonance (NMR) with pre-determined oil specimens at the earth's surface by which to match the location and lateral boundaries of any and every producible oil reservoir responsive to NMR technology, to provide estimates to useable industry standards of porosity and permeability of said reservoirs for exploration purposes by NMR, to detect and identify depth and direction of faults in any given oil area by NMR, to provide mapping of surveyed areas prior to drilling either offset or wildcat ventures resulting from NMR testing, to evaluate reservoir and production potential in existing oil fields by NMR, to detect the existence of natural gas by NMR, and the ability to condemn any proposed drilling location in view of failure.

Abstract: An apparatus and method for determining a property of an earth formation using a radial basis function derived from a catalog of rock samples. Parameters of a Thomeer capillary pressure fitting curve are derived and used for analyzing rocks with unimodal or multimodal pore size distributions.

Abstract: An NMR apparatus disposed in a wellbore and having an array of two or more NMR sensors located at substantially the same axial position on the NMR apparatus and having different directional sensitivities is used to acquire an NMR signal from at least two of the two or more NMR sensors. The NMR signals are combined to obtain borehole information. The borehole information may include an azimuthal image of the formation surrounding the borehole. The azimuthal image may be a formation porosity image, a formation bound fluid image, a T2 distribution image, a T2 log mean image, a formation permeability image, or a formation fluid viscosity image. If two or more pre-amplifiers and receiver circuitry are also provided, the NMR signals may be combined prior to passing through the pre-amplifiers and receiver circuitry to improve the signal to noise ratio of the total signal from the desired sample space.

Abstract: During a drilling operation, measured data from the drilling operation may be received with a panistic inversion and risk estimate module. The panistic inversion and risk estimate module may generate a plurality of mathematical solutions from a panistic inversion that uses the measured data and one or more earth models. The one or more earth models having various parameters may be selected prior to drilling and/or while the drilling operation occurs. For each solution of the plurality of mathematical solutions generated from the panistic inversion, the panistic inversion and risk estimate module may determine if the measured data exceeds one or more probability risk thresholds associated with the drilling operation. If the measured data exceeds the probability risk threshold associated with the drilling operation, then the panistic inversion and risk estimate module may generate an alert.

Abstract: A nuclear magnetic resonance (NMR) logging method includes providing a hybrid pulse sequence having a saturation pulse, an inversion pulse, and a detection sequence. The method also includes measuring echo signals in response to the hybrid pulse sequence. The method also includes deriving a spin-lattice time constant (T1) distribution from the measured echo signals. A NMR system includes a hybrid pulse sequence module to provide a hybrid pulse sequence with a saturation pulse, an inversion pulse, and a detection sequence. The NMR system also includes a control module to select a time interval between the saturation pulse and the inversion pulse.

Abstract: Downhole nuclear magnetic resonance (NMR) methods that utilize oleophilic nanoparticle may allow for differentiation of light oil and oil-based filtrates. For example, a method may involve drilling a wellbore penetrating a subterranean formation using an oil-based drilling fluid that comprises an oil base fluid and a plurality of oleophilic nanoparticles; performing a plurality of NMR measurements at a plurality of depths of investigation (DOI) of a near-wellbore portion of the subterranean formation; and producing an invasion profile of an oil-based drilling fluid filtrate into the near-wellbore portion of the subterranean formation based on the plurality of NMR measurements.

Abstract: A method of calculating a 3-D geologic model in real time using, as input, 2-D geologic data. The 3-D is used for conducting further drilling operations. The model may be updated in real time using additional measurements obtained during drilling operations.

Abstract: The wettability of a formation may be estimated using a multi-frequency dielectric measurement tool. Multi-frequency dielectric dispersion measurements are made using the multi-frequency dielectric measurement tool on a sample. The bulk density and the total porosity of the sample are also otherwise acquired. The bulk density, matrix permittivity, total porosity, and multi-frequency dielectric dispersion measurements are input into a petrophysical dielectric model and the petrophysical dielectric model is applied to obtain inversion results. A wettability state of the sample is determined using the inversion results and one or more reservoir management decisions are made based on the determined wettability state of the sample. A non-transitory, computer-readable storage medium may be provided that has stored on it one or more programs that provide instructions.

Abstract: Method and apparatus for estimating a parameter of interest of an earth formation using a model based on NMR data, imaging data, and NMR tool response characteristics. The method may include constructing a model of the earth formation. The method may also include constructing a predictive model for estimating the parameter of interest. The apparatus may include an NMR tool and at least one processor configured to estimate the parameter of interest. The apparatus may also include an imaging tool configured to acquire the imaging data.

Abstract: A non-resonant transmitter for a magnetic resonance (MR) system, such as a nuclear magnetic resonance (NMR) system, is described herein. The transmitter includes a coil for applying NMR pulse sequences to a substance. The coil is coupled to a circuit that includes a capacitor, a number of switches, and a power source. The transmitter operates in two modes. In a charging mode, the switches decouple the coil from the capacitor and the capacitor is charged by the power source. In a discharging mode, a radio frequency pulse is generated and the switches couple and decouple the coil from the capacitor so that the capacitor provides power to the coil. The addition of the capacitor improves the power factor of the circuit and reduces power draw from the power source.

Abstract: A formation fluid sample is analyzed using NMR spectroscopy to obtain a NMR spectrum. The NMR spectrum is then analyzed to find evidence of the amount of olefins present in the sample. The amount of olefins present in the sample can then be correlated to the level of contamination of the sample. In one embodiment, a 1H chemical shift of between substantially 4.5 and 6 ppm is used to identify olefins present in the sample. In another embodiment, a 1H chemical shift of substantially 1.9 to 2.1 ppm is used to identify olefins present in the sample. The NMR spectral equipment can be located uphole or downhole.

Abstract: A method and system for applying nuclear quadrupole resonance (NQR) sequences to a substance and determining presence of a chemical species within the substance using the sequences are described herein. The method includes applying an NQR pulse sequence to the substance using a non-resonant transmitter circuit. The method further includes detecting a NQR signal within the substance and determining presence of a chemical species within the substance using the NQR signal.

Abstract: An apparatus and method to detect a fluid flow. The apparatus includes a nuclear magnetic resonance (NMR) tool to perform an NMR measurement on the fluid in a sensitive volume by establishing a magnetic field in the sensitive volume that exhibits a change in magnitude in a direction of the fluid flow when the fluid flow is radial with respect to the NMR tool and by transmitting refocus pulses, without any tipping pulse, to obtain the NMR measurement comprising spin echo signals. The system also includes a processor to receive the NMR measurement from the NMR tool and determine whether the fluid flow exists based on an amplitude of the NMR measurement.

Abstract: In some aspects, a downhole nuclear magnetic resonance (NMR) tool includes a magnet assembly and an antenna assembly. The NMR tool can operate in a wellbore in a subterranean region to obtain NMR data from the subterranean region. The magnet assembly produces a magnetic field in a volume about the wellbore. The antenna assembly produces excitation in the volume and acquires an azimuthally-selective response from the volume based on the excitation. The antenna assembly can include a transversal-dipole antenna and a monopole antenna.

Abstract: In some aspects, a downhole nuclear magnetic resonance (NMR) tool includes a magnet assembly and an antenna assembly. The NMR tool can operate in a wellbore in a subterranean region to obtain NMR data from the subterranean region. The magnet assembly produces a magnetic field in a volume about the wellbore. The magnet assembly includes a central magnet, a first end piece magnet spaced apart from a first axial end of the central magnet, and a second end piece magnet spaced apart from a second axial end of the central magnet. The antenna assembly includes a transversal-dipole antenna. In some cases, orthogonal transversal-dipole antennas produce circular-polarized excitation in the volume about the wellbore, and acquire a response from the volume by quadrature coil detection.

Abstract: A sensor device for sensing particles of a sample, the sensor device including a sensing unit adapted for sensing a detection signal indicative of the presence of the particles, a viscosity measurement unit adapted for measuring the viscosity of the sample, and a correction unit adapted for correcting the detection signal based on the measured viscosity.

Abstract: Various disclosed nuclear magnetic resonance (NMR) logging systems and methods employ a plurality of NMR sensors, including atomic magnetometers, mounted on pads. Certain method embodiments include: utilizing the Earth magnetic field to pre-polarize the protons in a formation; utilizing a plurality of atomic magnetometers to obtain NMR measurements; and determining at least one characteristic relaxation time of the formation. The NMR sensor may optionally include a permanent magnet assembly.

Abstract: Disclosed dielectric logging tools and methods employ three or more receive horn antennas positioned between at least two transmit antennas, which can also be horn antennas. The logging tools can operate in the range between 100 MHz and 10 GHz to provide logs of formation permittivity, formation conductivity, standoff distance, and electrical properties of material in the standoff gap. Logs of water-saturated porosity and/or oil movability can be readily derived. The presence of additional receive antennas offers a significantly extended operating range, additional depths of investigation, increased measurement accuracy, and further offers compensation for tool standoff and mudcake effects. In both wireline and logging while drilling embodiments, at least some disclosed dielectric logging tools employ a set of three axially-spaced receive antennas positioned between pairs of axially-spaced transmit antennas.

Abstract: A method for performing magnetic resonance measurements on a sample includes applying a first predetermined number of pulse trains for excitation, each pulse train having a constant amplitude and including a second predetermined number of pulses spaced by a predetermined time interval. The pulse trains are modulated by a bent function. After each pulse, data is sampled. Preferably a square number of pulses is generated being constant in power, and the Walsh transform of the sequence of their phases is constant in power, so that the power of the excitation in time and frequency domain is constant. The method can reduce power requirements and may permit undercutting specific absorption rate (SAR) limits due to the small excitation power necessary to create time signals with reasonable signal to noise ratio.

Abstract: Methods and systems are provided that enable logging while drilling NMR measurements to be made with magnets placed outside of the drill collar and magnetically permeable members to control the magnetic field gradient. A set of magnets can be disposed on and/or embedded on a drill collar, with an antenna disposed axially therebetween. Alternatively, a set of magnets and an antenna disposed therebetween can be disposed on a sleeve that is slid onto a recess in a drill collar. Additionally, a permeable member can be axially positioned between the set of magnets for affecting the depth of investigation.

Abstract: A well-logging method for a geological formation having a borehole therein may include collecting a plurality of nuclear magnetic resonance (NMR) snapshots from the borehole indicative of changes in the geological formation and defining NMR data. The method may further include identifying a plurality of fluids within the geological formation based upon the NMR data, determining respective NMR signatures for the identified fluids based upon the NMR data, determining apparent volumes for the identified fluids based upon the NMR signatures, and determining adjusted volumes for the identified fluids based upon the apparent volumes.

Abstract: A method for mineral analysis of a sample based on detection of NQR and/or Local Field Magnetic Resonance (LFMR) signals from a particular substance within a sample includes: setting a frequency of RF pulses to be approximately equal to one of the NQR or LFMR frequencies of the substance; setting a set of parameters of the RF pulses to be optimal for the substance; setting a set of receiving parameters to be optimal for the substance; tuning the probe to maximum sensitivity for the signals detected at predetermined frequency and/or to maximum power transfer efficiency for RF pulses transmitted with the probe; transmitting the RF pulses with the probe at said optimal level during a transmitting period to irradiate the sample and excite an NQR or LFMR signal in the substance, if present; detecting and processing NQR or LFMR signals emitted by the substance; and calculating the concentration of the substance in the sample.

Abstract: A method for determining at least one characteristic of a geological formation having a borehole therein may include collecting nuclear magnetic resonance (NMR) data of the geological formation adjacent the borehole, and collecting non-NMR data for the geological formation adjacent the wellbore. The method may further include performing a Monte Carlo analysis based upon a combination of the collected NMR and non-NMR data to determine the at least one characteristic of the geological formation having a bounded uncertainty therewith.

Abstract: A method of calculating a porosity of a geological formation includes determining a bulk pore volume and a movable fluid pore volume in the geological formation in which drilling mud including a mud filtrate is introduced, calculating a porosity of the formation based on a bulk pore volume, and correcting the porosity based on the movable fluid volume in the geological formation.

Abstract: Percolation theory is applied to establish a connection between magnetization decay of nuclear magnetic resonance (NMR) measurements and residual carbon dioxide saturation (Scr). As a result, estimations of Scr are obtained through use of an NMR tool in a formation and appropriate processing. Data may be displayed as a log.

Abstract: Methods and systems are provided that enable logging while drilling NMR measurements to be made with a tool having magnets with positions adjustable or movable relative to each other. Such movement can affect the depth of investigation of the NMR tool. A variety of moving assemblies can be used to effectuate the movement, which can be performed either at the surface or downhole. The tool also can include a magnetically permeable member to control the magnetic field gradient.

Abstract: Methods and systems for measuring nuclear magnetic resonance characteristics of formation fluid utilizing micro-NMR sensors are provided. The micro-NMR sensors can be used to analyze fluid flowing through the wellbore on a periodic, continuous, and/or batch-mode basis. More efficient sampling and analysis can be conducted using the micro-NMR sensors. In situ analysis and time-lapse logging are also enabled.

Abstract: A petrophysically regularized time domain nuclear magnetic resonance (NMR) inversion includes using an NMR tool to acquire NMR data and inverting the acquired NMR data in a time domain using petrophysical constraints. The inverted NMR data is analyzed. The petrophysical constraints may be identified by: determining a number of porobodons to seek, defining a plurality of zones in which only a subset of porobodon sets is present, and stacking all NMR echoes in each zone satisfying discriminators. The number of porobodons to seek may be based on knowledge of core samples, logs, and NMR sensitivity. The discriminator logs may be logs sensitive to porosity partitioning. A computing system having a processor, a memory, and a program stored in memory may be configured to perform the method. The system may be conveyed downhole on a wireline, a while-drilling drill string, a coiled tubing, a slickline, or a wired drill pipe.

Abstract: NMR measurements are made along with acoustic measurements using one tool. The antenna of the NMR sensor is used to create acoustic signals. Interference between the acoustic and NMR measurements is avoided due to the frequency difference, and by having the acoustic excitation during a wait time of the NMR pulse sequence.

Abstract: A nuclear magnetic resonance (NMR) measurement system for high pressure and temperature measurements on fluids is disclosed. The system has a sensor assembly that includes a sample holder having a body formed from a non-magnetic metal and defining an interior cavity for receiving a fluid sample, a frame member disposed in the interior cavity of the sample holder, an antenna coil disposed in the interior cavity about the frame member, an inlet that allows the fluid sample to enter the interior cavity, an outlet that allows for the fluid sample to be flushed from the interior cavity, and a magnet assembly having a central bore in which the sample holder is disposed. Adjacent to the sample holder are pulsed field gradient coils for performing diffusion measurements. The system further includes pulse sequencer circuitry that supplies signals to the antenna coil.

Abstract: Technologies applicable to noise canceling in-situ NMR detection and imaging are disclosed. An example noise canceling in-situ NMR detection apparatus may comprise one or more of a static magnetic field generator, an alternating magnetic field generator, an in-situ NMR detection device, an auxiliary noise detection device, and a computer.

Abstract: An NMR method and apparatus for analyzing a sample of interest applies a static magnetic field together with RF pulses of oscillating magnetic field across a sample volume that encompasses the sample of interest. The RF pulses are defined by a pulse sequence that includes a plurality of measurement segments configured to characterize a plurality of relaxation parameters related to relaxation of nuclear magnetization of the sample of interest. Signals induced by the RF pulses are detected in order to derive the relaxation parameters. The measurement segments of the pulse sequence include at least one first-type measurement segment configured to characterize relaxation of spin-lattice interaction between nuclei of the sample of interest in a rotating frame (T1?) at a predefined frequency. The T1? parameter can be measured in conjunction with the measurement of other relaxation and/or diffusion parameters as part of multidimensional NMR experiments.

Abstract: A method for estimating a property of subsurface material includes extracting a sample of the material using a downhole formation tester and performing a plurality of nuclear magnetic resonance (NMR) measurements on a sensitive volume in the sample where each measurement in the plurality is performed in a static homogeneous magnetic field with a pulsed magnetic field gradient that is different in magnitude from other NMR measurements to provide a waveform signal. The method further includes transforming each received waveform signal from a time domain into a frequency domain and comparing the frequency domain signal to a reference to provide proton chemical-shift information related to a chemical property of one or more molecules in the sample and transforming the frequency domain signals into a complex number domain that quantifies waveform signal amplitude changes to provide one or more diffusion rates with each diffusion rate being associated with a corresponding frequency.

Abstract: In one aspect, a method for insulating an antenna apparatus is provided, the method including coupling a transition piece to a bulkhead, wherein the bulkhead includes a first conductive path electrically coupled to a second conductive path in the transition piece and coupling an antenna cable to the transition piece, wherein the antenna cable includes a third conductive path electrically coupled to the second conductive path. The method further includes disposing an electrically insulating polymer on the bulkhead, transition piece, and antenna cable, wherein the insulating polymer is disposed by extrusion.

Abstract: An apparatus and method for performing nuclear magnetic resonance (NMR) or magnetic resonance imaging (MRI) on samples in metallic holders and vessels or in proximity to metallic objects is disclosed.

Abstract: A magnetic signal noise reduction and detection system has inputs configured to receive data from a first total field scalar magnetometer, data from a vector magnetometer, and data from a position, velocity and heading sensor, a signal processor configured with a pre-processor system, an adaptive noise cancellation system and a detection system, the pre-processor system configured to carry out initial processing of data received. The pre-processor is configured to convert data to the frequency domain and pass the converted data to the adaptive noise cancellation system. The adaptive noise cancellation system is configured to carry out multivariate regression on the converted data to reduce detected noise. The detection system is configured to detect magnetic anomalies and output information in real time about the magnetic anomalies to a user interface.

Abstract: Methods and related apparatuses of a downhole micro nuclear magnetic resonance (NMR) device having a resonant tuning (LC) circuit for use in a formation for collecting NMR signals from a fluid in the formation while under downhole pressures and temperatures. The downhole micro NMR device includes: a micro tube for the flowing fluid to flow therethrough; at least one magnet disposed about the micro tube; and at least one micro RF coil structured and arranged approximate to the micro tube and tuned to a Larmor frequency corresponding to a applied magnetic field from the at least one magnet.

Abstract: The Larmor frequency for an in situ nuclear magnetic resonance (NMR) tool is determined and used to acquire NMR data. An NMR tool is provided and placed in situ, for example, in a wellbore. An initial estimate of the Larmor frequency for the in situ NMR tool is made and NMR data are acquired using the in situ NMR tool. A spectral analysis is performed on the NMR data, or optionally, the NMR data are digitized and a discrete Fourier transform (DFT) is performed on the digitized NMR data. The modal frequency of the spectral analysis or DFT is determined, and the Larmor frequency for the in situ NMR tool is determined using the modal frequency. The NMR tool is modified to transmit at the determined Larmor frequency and then used to acquire further NMR data.

Abstract: Formation testing systems and methods may inject fluids into a formation to initiate fractures and facilitate measurements of various formation properties. In accordance with certain disclosed embodiments, the injection tools are further provided with nuclear magnetic resonance (NMR) sensors to monitor the injected fluids and provide measurements of near-borehole fracture orientations and volumes. Contrast agents and/or magnetic resonance imaging (MRI) techniques may be employed. The fluid injecion may occur via an extendible isolation pad, via a fracturing jet, or via an injection port in an isolated region of the borehole. The systems may employ pressure monitoring in conjunction with the NMR sensors to further enhance estimates of formation and fracture properties.

Abstract: Technologies including NMR logging apparatus and methods are disclosed. Example NMR logging apparatus may include surface instrumentation and one or more downhole probes configured to fit within an earth borehole. The surface instrumentation may comprise a power amplifier, which may be coupled to the downhole probes via one or more transmission lines, and a controller configured to cause the power amplifier to generate a NMR activating pulse or sequence of pulses. Impedance matching means may be configured to match an output impedance of the power amplifier through a transmission line to a load impedance of a downhole probe. Methods may include deploying the various elements of disclosed NMR logging apparatus and using the apparatus to perform NMR measurements.

Abstract: A technique utilizes the acquisition of data via nuclear magnetic resonance at multiple depths of investigation in a well region. The acquired data is processed to estimate variable fluid mixture densities at different radial depths. The variable fluid mixture densities and a radial response from a density tool, for example, can be used to calculate an effective fluid mixture density and used to interpret density logs. Other logs such as neutron log, induction resistivity log, and dielectric permittivity log can be combined with NMR. For these tools a corresponding effective formation property can be calculated and used to determine other formation characteristics, such as total porosity, total density, dielectric permittivity, electric resistivity, and formation characteristics derivable from these.

Abstract: A method and apparatus for estimating a flow rate of a phase of a multiphase fluid is disclosed. A first velocity distribution is obtained for a first set of nuclei in the fluid from a Nuclear Magnetic Resonance (NMR) signal received for the fluid in response to a first NMR excitation signal. A second velocity distribution is obtained for a second set of nuclei in the fluid from an NMR signal received for the fluid in response to a second NMR excitation signal. A velocity of the phase is estimated from the first velocity distribution and the second velocity distribution. The flow rate of the phase is estimated using the estimated velocity of the phase and an estimated volume fraction of the phase.

Abstract: A distributed drilling simulation system includes a choke manifold, a high pressure manifold, a blowout preventer console, a choke console, a remote console, a driller console, a teacher console and a graphic projecting unit, wherein the driller console, the remote console, the blowout preventer console, the choke console, the choke manifold, and the high pressure manifold are interconnected through a PPI (processor/peripheral interface) protocol. The teacher console is connected with the PPI protocol through a PPI interface. A communication program and a main control program run on a main control computer and a graphic processing program runs on a graphic computer. The invention has the advantages of realizing high-degree top driving drilling simulation, enhancing the field sense for teaching and training, shortening the training period and reducing the training cost.

Abstract: Asphaltene content and its spatial distribution in a reservoir containing crude oil is an important factor in determining the potential for formation damage and pipeline impairment, as well as planning for processing and refining of the oil. Exemplary uses include: reservoir modeling, development and depletion planning, pressure maintenance, and surface facilities management. A convenient method has been developed which uses two-dimensional NMR techniques during a temperature and/or pressure cycle to quantify the asphaltene content of the crude oil without the need for extracting the oil from the reservoir rock. The technique can be applied to core, down-hole logs, or, a combination of both.

Abstract: A method for determining particle size distribution of a subsurface rock formation having pore spaced filled with at least two different fluids using measurements of at least one nuclear magnetic resonance property thereof made from within a wellbore penetrating the rock formation includes determining a distribution of nuclear magnetic relaxation times from the measurements of the at least one nuclear magnetic resonance property. A fractional volume of the pore spaces occupied by each of the at least two fluids is determined. A surface relaxivity of the rock formation for portions of the rock pore spaces occupied by each of the at least two fluids is determined from a measurement of a formation parameter. The relaxation time distribution and the surface relaxivities are used to determine the particle size distribution.

Abstract: A nuclear magnetic resonance (NMR) logging tool assembly method that employs rotational indexing to optimize the sensing volume. At least some embodiments include establishing an initial arrangement of the permanent magnets and marking each magnet to indicate their relative rotational orientations in the initial arrangement. Thereafter a series of magnetic field measurements and individual magnet rotations are performed to improve uniformity of the magnetic field in the sensing volume. Once a satisfactory arrangement has been found, the magnets may be secured together and an antenna array installed along with the electronics for performing relaxation time measurements and providing logs of formation properties that can be derived therefrom, such as porosity, permeability, density, rock type, fluid type, etc. The tool may be packaged as a wireline sonde, a tubing-conveyed logging tool, or a logging while drilling (LWD) tool.

Abstract: NMR technology disclosed herein, such as an NMR apparatus or an NMR method, for example, may be useful for purposes described herein, such as determining presence or absence of magnetic resonance from a sample, for example. Methods pertaining to such NMR technology include methods of designing or constructing NMR apparatus, methods of using NMR apparatus, methods of employing data obtained from NMR apparatus, and/or the like. Various apparatus and methods for detection of magnetic resonance in sample material are disclosed herein. Additionally, various apparatus and methods for usefully employing magnetic resonance data are disclosed herein.

Abstract: Nano-particles that possess either selective fluid phase blocks or modify the relative permeability of an earth formation to different fluids are used to inhibit the invasion of borehole mud into the formation. This makes it possible to make formation evaluation measurements using sensors with a shallow depth of investigation.

Abstract: The Larmor frequency for an in situ nuclear magnetic resonance (NMR) tool is determined and used to acquire NMR data. An NMR tool is provided and placed in situ, for example, in a wellbore. An initial estimate of the Larmor frequency for the in situ NMR tool is made and NMR data are acquired using the in situ NMR tool. A spectral analysis is performed on the NMR data, or optionally, the NMR data are digitized and a discrete Fourier transform (DFT) is performed on the digitized NMR data. The modal frequency of the spectral analysis or DFT is determined, and the Larmor frequency for the in situ NMR tool is determined using the modal frequency. The NMR tool is modified to transmit at the determined Larmor frequency and then used to acquire further NMR data.