System and method for emulating nuclear magnetic resonance well logging tool diffusion editing measurements on a bench-top nuclear magnetic resonance spectrometer for laboratory-scale rock core analysis

A method for use in conjunction with a laboratory apparatus defining a sample volume, the method comprising:

• for a sample collected from a given subsurface formation, storing corresponding downhole tool data that includes parameters pertaining to nuclear magnetic resonance (NMR) measurements of the given subsurface formation performed by a downhole tool, wherein the downhole tool data includes at least one parameter that represents a time interval pertaining to a pulse sequence that is part of the NMR measurements performed by a downhole tool, the pulse sequence for generating at least one diffusion-encoding echo and comprising a stimulated echo (STE) sequence represented by a spatial encoding interval τSTE and a storage interval Δ stored as part of the downhole tool data, and wherein the pulsed-mode gradient field is based on the spatial encoding interval τSTE and the storage interval Δ, and wherein the NMR measurements performed by the downhole tool employ fixed field gradients that have constant amplitude at all times;
• positioning the sample in the sample volume;
• and
• performing at least one NMR measurement of the sample volume to thereby determine a property of the sample, the at least one NMR measurement applying to the sample volume a homogeneous static magnetic field in conjunction with a pulse sequence of oscillating magnetic field and a pulsed-mode gradient field, the pulsed-mode gradient field defined by the stored downhole tool data corresponding to the sample, wherein the pulsed-mode gradient field for a given NMR measurement is defined by a set of pulses that are equivalent to the fixed field gradient for a corresponding NMR measurement performed by the downhole tool.

A method for use in conjunction with a laboratory apparatus defining a sample volume, the method comprising:

• for a sample collected from a given subsurface formation, storing corresponding downhole tool data that includes parameters pertaining to nuclear magnetic resonance (NMR) measurements of the given subsurface formation performed by a downhole tool;
• positioning the sample in the sample volume;
• and
• performing at least one NMR measurement of the sample volume to thereby determine a property of the sample, the at least one NMR measurement applying to the sample volume a homogeneous static magnetic field in conjunction with a pulse sequence of oscillating magnetic field and a pulsed-mode gradient field, the pulsed-mode gradient field defined by the stored downhole tool data corresponding to the sample, wherein the property of the sample comprises one or more diffusion coefficients of the sample derived by an inversion methodology, and wherein the inversion methodology derives a multidimensional distribution function selected from the group including
• i) a two dimensional distribution function f(D,T2) relating diffusion coefficient D to the spin-spin (T2) relaxation times of the sample;
• ii) a two dimensional distribution function f(D,T1) relating diffusion coefficient D to the spin-lattice (T1) relaxation times of the sample;
• iii) a three dimensional distribution function f(D,T1,T2) relating diffusion coefficient D to the spin-lattice (T1) relaxation times of the sample and the spin-spin (T2) relaxation times of the sample.

A method for use in conjunction with a laboratory apparatus defining a sample volume, the method comprising:

• for a sample collected from a given subsurface formation, storing corresponding downhole tool data that includes parameters pertaining to nuclear magnetic resonance (NMR) measurements of the given subsurface formation performed by a downhole tool;
• positioning the sample in the sample volume;
• performing at least one NMR measurement of the sample volume to thereby determine a property of the sample, the at least one NMR measurement applying to the sample volume a homogeneous static magnetic field in conjunction with a pulse sequence of oscillating magnetic field and a pulsed-mode gradient field, the pulsed-mode gradient field defined by the stored downhole tool data corresponding to the sample;
• introducing synthetic noise into NMR measurement data derived by NMR analysis of the sample volume such that the signal-to-noise ratio (SNR) of the NMR measurement data corresponds to a predetermined SNR;
• processing said NMR measurement data derived from NMR analysis of the sample volume to generate tool-equivalent data;
• interpreting the tool-equivalent data to derive at least one petrophysical parameter expressed by the tool-equivalent data;
• comparing the at least one petrophysical parameter to a corresponding petrophysical parameter derived from a ground truth-type measurement;
• and
• using the results of the comparing to determine an accuracy estimate.

A method for use in conjunction with a laboratory apparatus defining a sample volume, the method comprising:

• i) positioning a sample in the sample volume;
• ii) performing a plurality of nuclear magnetic resonance (NMR) measurements of the sample volume, the plurality of NMR measurements applying to the sample volume a homogeneous static magnetic field in conjunction with a pulse sequence of oscillating magnetic field and a pulsed-mode gradient field, wherein the plurality of NMR measurements are defined by a plurality of parameters that vary across the measurements;
• iii) selecting parameters that define a desired NMR measurement;
• and
• iv) storing the parameters selected in iii) for output to a downhole tool for carrying out NMR measurements in accordance with the stored parameters;
• wherein the downhole tool employs a fixed gradient field in carrying out NMR measurement, the fixed gradient field having constant amplitude at all times, and the pulsed-mode gradient field is adapted to match the fixed gradient field of the downhole tool, and wherein the pulsed-mode gradient field for a given NMR measurement is defined by a set of pulses that are equivalent to the fixed field gradient for a corresponding NMR measurement performed by the downhole tool;
• and
• selecting at least one parameter that defines the set of pulses such that the integral of the time-varying amplitude of the pulses of the set over the time duration of the pulses of the set matches the product of the constant amplitude of the fixed field gradient and duration for the corresponding NMR measurement performed by the downhole tool.

A method for use in conjunction with a laboratory apparatus defining a sample volume, the method comprising:

• i) positioning a sample in the sample volume;
• ii) performing a plurality of nuclear magnetic resonance (NMR) measurements of the sample volume, the plurality of NMR measurements applying to the sample volume a homogeneous static magnetic field in conjunction with a pulse sequence of oscillating magnetic field and a pulsed-mode gradient field, wherein the plurality of NMR measurements are defined by a plurality of parameters that vary across the measurements;
• iii) selecting parameters that define a desired NMR measurement;
• and
• iv) storing the parameters selected in iii) for output to a downhole tool for carrying out NMR measurements in accordance with the stored parameters, wherein the stored parameters represent a time interval pertaining to a pulse sequence that is part of an NMR measurement to be performed by the downhole tool, the pulse sequence for generating at least one diffusion-encoding echo;
• wherein the downhole tool employs a fixed gradient field in carrying out NMR measurement, the fixed gradient field having constant amplitude at all times, and the pulsed-mode gradient field is adapted to match the fixed gradient field of the downhole tool;
• and
• wherein the pulse sequence for generating at least one diffusion-encoding echo comprises a stimulated echo (STE) sequence represented by a spatial encoding interval τSTE and a storage interval Δstored in iv).