Abstract: A method for inversion of multiple echo trains with different wait times uses a cutoff times for each of the echo trains for full polarization. Simultaneous inversion is carried out for T2 bins where full polarization exists. It is emphasized that this abstract is provided to comply with the rules requiring an abstract which will allow a searcher or other reader to quickly ascertain the subject matter of the technical disclosure. It is submitted with the understanding that it will not be used to interpret or limit the scope or meaning of the claims.

Abstract: A method to correct for a systematic error of a sensor having a plurality of accelerometers configured to measure gravitational acceleration, the method including: rotating the plurality of accelerometers about a first axis; obtaining a first set of calibration measurements from the plurality of accelerometers from the rotation about the first axis; determining a first systematic error for each accelerometer in the plurality using the first set of calibration measurements; and removing the first systematic error from sensor measurements to correct for the systematic error.

Abstract: An instrument for measuring gravitational acceleration, the instrument including: a plurality of accelerometers disposed about a three-dimensional structure, the plurality of accelerometers providing output used for measuring the gravitational acceleration; wherein each accelerometer in the plurality is implemented by at least one of a micro-electromechanical system (MEMS) and a nano-electromechanical system (NEMS).

Abstract: A magnet assembly for measuring properties of a formation from a borehole, the magnet assembly including a first device and a second device, each device adapted for insertion into the borehole, the first device producing a first magnetic field, the second device producing a second magnetic field; wherein the second magnetic field is configurable for one of reinforcing and reducing the first magnetic field; and wherein the first device comprises a permanent magnet and the second device comprises at least one of one of a switchable magnet and switching windings.

Abstract: The quality factor of a NMR-antenna depends upon mud conductivity, formation resistivity and the borehole size. The Q of the antenna is measured. From measurement of one of formation conductivity or borehole size, the other can be determined.

Abstract: NMR measurements are made with a MWD tool having azimuthal sensitivity. The permanent magnet may be a U-shaped magnet or may have an opposed pair of magnets with axial orientation. The tool is designed for pulsing with short sequences for estimating BVI and CBW and minimizes the effect of tool motion.

Abstract: Wireline depths are estimated using cable depth measurements and accelerometer depth measurements made over a time interval encompassing the time for which the wireline depth is being estimated. A least squares smoothing filter or a weighted least squares smoothing filter may be used. Problems caused by washouts in the borehole are also addressed.

Abstract: A method of evaluating a characteristic of a fluid in a region, and a nuclear magnetic resonance (NMR) well logging apparatus for the implementation thereof, is disclosed. A magnetic field gradient is applied to the region, and first and second sequences of magnetic field gradient is applied to the region, with the second sequence differing in a pulse characteristic from the first sequence. A magnetization spectrum resulting from each of the sequences of pulse is captured, and a change in the magnetization spectrum resulting from the first and second sequences of pulses is analyzed to extract information about the fluid.

Abstract: Wireline NMR well logging measurements suffer from disadvantages of poor vertical resolution, logging speeds less than 20 ft/min, and power consumption in excess of 200 W. In spite of these disadvantages, NMR well logging is used because it is capable of providing estimates for a number of petrophysical parameters that are difficult to obtain from other wireline data. These include estimates of the bulk volume irreducible (BVI) of fluids in the formation. The present invention targets BVI and clay bound water (CBW) measurements. Logging speeds of up to 60 ft/min are attainable with little or no loss of resolution. In one preferred embodiment, the tool has four sensors circumferentially distributed around the logging tool and in contact with the borehole wall. A horseshoe like magnet is used to generate the static magnetic field.

Abstract: An objective oriented NMR logging method selects pulse sequences over a plurality of frequencies from a set of building blocks. The building blocks include trainlet sequences wherein each trainlet comprises an excitation pulse and a plurality of refocusing pulses, the total length of a trainlet being typically less than 10 ms. Another building block is a short CPMG or modified CPMG sequence and yet another building block is a regular CPMG or modified CPMG sequence. The modified CPMG sequences may have refocusing pulses with a tipping angle less than 180° to reduce the power consumption. Based on the logging objective (formation evaluation or FE, FE plus hydrocarbon typing, FE plus gas evaluation) the building blocks are combined at a plurality of frequencies with different wait times and TEs.

Abstract: A method and apparatus for performing NMR measurements suppressing contribution to NMR signals from within the borehole. Within the region of examination, the RF magnetic field has a spatially varying intensity. NMR signals (free induction decay or spin echo signals) are inverted to give spin density as a function of field intensity. This inversion is then mapped to spatial positions using the known RF field variation. The effect of signals arising from within the borehole can be suppressed. It is also possible to obtain an azimuthal image of the spin density.

Abstract: Wireline NMR well logging measurements suffer from disadvantages of poor vertical resolution, logging speeds less than 20 ft/min, and power consumption in excess of 200 W. In spite of these disadvantages, NMR well logging is used because it is capable of providing estimates for a number of petrophysical parameters that are difficult to obtain from other wireline data. These include estimates of the bulk volume irreducible (BVI) of fluids in the formation. The present invention targets BVI and clay bound water (CBW) measurements. Logging speeds of up to 60 ft/min are attainable with little or no loss of resolution. In one preferred embodiment, the tool has four sensors circumferentially distributed around the logging tool and in contact with the borehole wall. A horseshoe like magnet is used to generate the static magnetic field.

Abstract: A method and apparatus for performing NMR measurements suppressing contribution to NMR signals from within the borehole. Within the region of examination, the RF magnetic field has a spatially varying intensity. NMR signals (free induction decay or spin echo signals) are inverted to give spin density as a function of field intensity. This inversion is then mapped to spatial positions using the known RF field variation. The effect of signals arising from within the borehole can be suppressed. It is also possible to obtain an azimuthal image of the spin density.

Abstract: Wireline NMR well logging measurements suffer from disadvantages of poor vertical resolution, logging speeds less than 20 ft/min, and power consumption in excess of 200 W. In spite of these disadvantages, NMR well logging is used because it is capable of providing estimates for a number of petrophysical parameters that are difficult to obtain from other wireline data. These include estimates of the bulk volume irreducible (BVI) of fluids in the formation. The present invention targets BVI and clay bound water (CBW) measurements. Logging speeds of up to 60 ft/min are attainable with little or no loss of resolution. In one preferred embodiment, the tool has four sensors circumferentially distributed around the logging tool and in contact with the borehole wall. A horseshoe like magnet is used to generate the static magnetic field.

Abstract: A method for acquiring nuclear magnetic resonance measurements of a material uses a modified CPMG sequence with a refocusing pulse having a tipping angle less than 180 °. The results of using the shortened refocusing pulse with reduced power requirements are comparable to those obtained with a conventional CPMG sequence.

Abstract: Measurements from many logging instruments such as Gamma ray counts from a pulsed neutron instrument, and amplitudes of spin-echo signals from a NMR instrument, typically have a spectrum that contains a plurality of exponentially decaying components. The slowest decaying component is obtained by fitting a single exponential over the tail end of the data and selecting a beginning for the fitting window that minimizes the product of the chi-square and the standard error of the fit. The single determined component may be subtracted from the data and the process repeated to give additional components. The determined components are indicative of thermal neutron capture cross-sections (in the case of a pulsed neutron instrument) and of the distribution of relaxation times and fluids within the pores of a rock in the case of a NMR instrument.

Abstract: An objective oriented NMR logging method selects pulse sequences over a plurality of frequencies from a set of building blocks. The building blocks include trainlet sequences wherein each trainlet comprises an excitation pulse and a plurality of refocusing pulses, the total length of a trainlet being typically less than 10 ms. Another building block is a short CPMG or modified CPMG sequence and yet another building block is a regular CPMG or modified CPMG sequence. The modified CPMG sequences may have refocusing pulses with a tipping angle less than 180° to reduce the power consumption. Based on the logging objective (formation evaluation or FE, FE plus hydrocarbon typing, FE plus gas evaluation) the building blocks are combined at a plurality of frequencies with different wait times and TEs.

Abstract: A method for acquiring nuclear magnetic resonance measurements of a material uses a gradient tool. A modified CPMG sequence is used wherein the duration of the refocusing pulse is selected to maximize the SNR of the pulse echoes relative to a standard CPMG sequence in which the refocusing pulse has twice the duration of the tipping pulse. The results of using the shortened refocusing pulse with reduced power requirements are comparable to those obtained with a conventional CPMG sequence.

Abstract: Using phase-alternate pairs to eliminate the effects of ringing requires a large running average for multi-frequency NMR logging tools. At logging speeds greater than about five ft/min, the resolution may become unacceptable. An important realization is that field-shifting need only occur between two sensitive volumes to make sequential CPMG sequences a phase-alternate pair. Additional sensitive volumes can be obtained using the standard frequency-shifting approach. Thus, a substantial decrease in power is possible. The present invention uses a side-looking gradient NMR logging tool with 12 different sensitive volumes. An auxiliary electromagnet winding is placed so that the plane of the winding is substantially parallel to the symmetry axis of the permanent magnet configuration. The electromagnet is switched on and a CPMG sequence is performed. Immediately following this sequence the current in the electromagnet winding is reversed and a second CPMG sequence is acquired.

Abstract: A method for characterizing a fluid sample withdrawn from an earth formation. The method includes performing nuclear magnetic resonant spin echo measurements on the fluid sample at a nuclear magnetic resonant frequency of carbon-13. Amplitudes of the spin echo measurements are summed. The summed measurements are spectrally analyzed. The fluid is characterized by determining whether aromatic hydrocarbons are present by measuring an amplitude of the spectrally analyzed spin echo measurements at about 130 part per million shift from the carbon-13 frequency. The fluid is also characterized by determining whether aliphatic hydrocarbons are present by measuring an amplitude of the spectrally analyzed spin echo measurements at about 30 parts per million frequency shift.