Abstract: A method of estimating properties of a resource bearing formation includes receiving, by a processor, a measured echo train generated by a nuclear magnetic resonance (NMR) measurement device deployed in a region of interest, and a measured noise of the measured echo train, and calculating a T2 distribution subject to a nonlinear equality constraint, the nonlinear equality constraint dependent on the measured noise and a fitting error between the measured echo train and a modeled echo train. Calculating the T2 distribution includes estimating a solution for the T2 distribution that is closest to satisfying the nonlinear equality constraint.

Abstract: A method of estimating properties of a resource bearing formation includes receiving, by a processor, a measured echo train generated by a nuclear magnetic resonance (NMR) measurement device deployed in a region of interest, and a measured noise of the measured echo train, and calculating a T2 distribution subject to a nonlinear equality constraint, the nonlinear equality constraint dependent on the measured noise and a fitting error between the measured echo train and a modeled echo train. Calculating the T2 distribution includes estimating a solution for the T2 distribution that is closest to satisfying the nonlinear equality constraint.

Abstract: A partial least squares (PLS) regression relates spin echo signals with samples having a known parameter such as bound water (BW), clay bound water (CBW), bound volume irreducible (BVI), porosity (PHI) and effective porosity (PHE). The regression defines a predictive model that is validated and can then be applied to spin echo signals of unknown samples to directly give an estimate of the parameter of interest. The unknown samples may include earth formations in which a NMR sensor assembly is conveyed in a borehole.

Abstract: NMR spin echo signals are acquired downhole. A partial least squares method is used to determine parameters of a parametric model of the T2 distribution whose output matches the measurements. The model parameters are telemetered to the surface where the properties of the formation are reconstructed. 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. 37 CFR 1.72(b).

Abstract: NMR spin echo signals are corrected for axial motion of the borehole logging tool. An additional correction may be applied to correct for incomplete polarization of nuclear spins due to an insufficient wait time between pulse sequences.

Abstract: An expert system is included in a downhole processor designed to acquire and process NMR data downhole in real time. The downhole processor controls the acquisition of the NMR data based at least in part on instructions transmitted downhole from a surface location and at least in part on evaluation of downhole conditions by the expert system. The downhole conditions include drilling operation conditions (including motion sensors) as well as lithology and fluid content of the formation obtained from other MWD data. The wait time, number of echos, number of repetitions of an echo sequence, interecho time, bandwidth and shape of the tipping and refocusing pulses may be dynamically changed. Data processing is a combination of standard evaluation techniques. Selected data and diagnostics are transmitted uphole. The expert system may be implemented as a two stage neural net. The first stage does the formation evaluation and the second stage controls the NMR pulse sequence.

Abstract: NMR spin echo signals, acquired on a MWD logging tool, are susceptible to errors magnetic flux density has a gradient and the magnet on the logging tool is moving relative to the earth. The errors can be corrected by having the excitation pulse cover a smaller or a larger volume than the refocusing pulses. Correction may also be made by selective saturation, or by echo averaging.

Abstract: NMR spin echo signals are corrected for axial motion of the borehole logging tool. An additional correction may be applied to correct for incomplete polarization of nuclear spins due to an insufficient wait time between pulse sequences.

Abstract: NMR spin echo signals, acquired on a MWD logging tool, are susceptible to errors magnetic flux density has a gradient and the magnet on the logging tool is moving relative to the earth. The errors can be corrected by having the excitation pulse cover a smaller or a larger volume than the refocusing pulses. Correction may also be made by selective saturation, or by echo averaging.

Abstract: A partial least squares (PLS) regression relates spin echo signals with samples having a known parameter such as bound water (BW), clay bound water (CBW), bound volume irreducible (BVI), porosity (PHI) and effective porosity (PHE). The regression defines a predictive model that is validated and can then be applied to spin echo signals of unknown samples to directly give an estimate of the parameter of interest. The unknown samples may include earth formations in which a NMR sensor assembly is conveyed in a borehole.

Abstract: An expert system is included in a downhole processor designed to acquire and process NMR data downhole in real time. The downhole processor controls the acquisition of the NMR data based at least in part on instructions transmitted downhole from a surface location and at least in part on evaluation of downhole conditions by the expert system. The downhole conditions include drilling operation conditions (including motion sensors) as well as lithology and fluid content of the formation obtained from other MWD data. The wait time, number of echos, number of repetitions of an echo sequence, interecho time, bandwidth and shape of the tipping and refocusing pulses may be dynamically changed. Data processing is a combination of standard evaluation techniques. Selected data and diagnostics are transmitted uphole. The expert system may be implemented as a two stage neural net. The first stage does the formation evaluation and the second stage controls the NMR pulse sequence.

Abstract: An expert system is included in a downhole processor designed to acquire and process NMR data downhole in real time. The downhole processor controls the acquisition of the NMR data based at least in part on instructions transmitted downhole from a surface location and at least in part on evaluation of downhole conditions by the expert system. The downhole conditions include drilling operation conditions (including motion sensors) as well as lithology and fluid content of the formation obtained from other MWD data. The wait time, number of echos, number of repetitions of an echo sequence, interecho time, bandwidth and shape of the tipping and refocusing pulses may be dynamically changed. Data processing is a combination of standard evaluation techniques. Selected data and diagnostics are transmitted uphole. The expert system may be implemented as a two stage neural net. The first stage does the formation evaluation and the second stage controls the NMR pulse sequence.

Abstract: NMR measurements made in a borehole are susceptible to contamination by signals from the borehole fluid. Correction is made for this contamination by using a standoff measuring device to determine the fractional volume of the region of investigation of the NMR tool that lies within the borehole. Using known or determined characteristics of the borehole fluid, a correction is made either to the NMR signals prior to processing or to the processed results of the uncorrected signals.

Abstract: NMR data are acquired with variable spacing between refocusing pulses, giving data with a variable interecho time TE. Under certain conditions, diffusion effects can be neglected and data acquired with a multiple TE spacing may be used to obtain a T2 distribution with increased resolution and reduced power requirements. In gas reservoirs, the maximum TE may be determined from diffusion considerations using a dual wait time pulse sequence and this maximum TE is used to acquire data with dual TE.

Abstract: NMR measurements made in a borehole are susceptible to contamination by signals from the borehole fluid. Correction is made for this contamination by using a standoff measuring device to determine the fractional volume of the region of investigation of the NMR tool that lies within the borehole. Using known or determined characteristics of the borehole fluid, a correction is made either to the NMR signals prior to processing or to the processed results of the uncorrected signals.

Abstract: An expert system is included in a downhole processor designed to acquire and process NMR data downhole in real time. The downhole processor controls the acquisition of the NMR data based at least in part on instructions transmitted downhole from a surface location and at least in part on evaluation of downhole conditions by the expert system. The downhole conditions include drilling operation conditions (including motion sensors) as well as lithology and fluid content of the formation obtained from other MWD data. The wait time, number of echos, number of repetitions of an echo sequence, interecho time, bandwidth and shape of the tipping and refocusing pulses may be dynamically changed. Data processing is a combination of standard evaluation techniques. Selected data and diagnostics are transmitted uphole. The expert system may be implemented as a two stage neural net. The first stage does the formation evaluation and the second stage controls the NMR pulse sequence.