Method of determining solid and liquid components in sedimentary rocks using NMR relaxation
A method for separating liquid-like (T 2e ) from solid-like (T 2G ) 1 H NMR transverse relaxation times in porous media uses novel pulse sequences together with a 1 H NMR spectrometer optimized for geological core samples. The method is applied to obtain 1D T 2 distributions and 2D T 1 -T 2 maps in organic-rich chalks for quantification of liquid-like signal (micropore fluids, meso-macropore fluids, fluids dissolved in organic matter, and clay-bound water) and solid-like signal (kerogen, bitumen, and clay hydroxyls). The novel pulse sequences comprise a solid-echo, which detects more solid-like signal than an FID. The method is used for fluid typing in micro/meso-macro pores, clay mineral identification, determination of kerogen content, and quantification of solvent-extracted bitumen versus bitumen expelled from kerogen due to swelling from dissolved hydrocarbons. The method is used to quantify the asphaltene, resin, aromatic, and/or saturate content of bitumen in the rock.
1. A method of nuclear magnetic resonance (NMR) measurement on a sample, the method comprising:
a) applying a 180° RF pulse to the sample, thereby yielding an inverted longitudinal magnetization M z =−M 0 away from equilibrium;
b) during a selected inversion recovery time τ 1 , allowing M z to recover towards an equilibrium value of M z =M 0 governed by a time constant T 1 ;
c) after the selected inversion recovery time τ 1 , applying a 90° RF pulse for rotating the instantaneous M z into a transverse plane M x,y ;
d) at a selected pulse-separation time τ S , applying a second 90° RF pulse for rotating M x,y within the transverse plane, creating observable magnetization by formation of a solid-echo;
e) sampling with discretized time steps the observable solid-echo magnetization during a time t following the applying of the second 90° RF pulse to acquire signal amplitude measurements as the observable transverse magnetization decays toward equilibrium with magnetization M x,y =0, wherein, during the time t, a decay time constant is T* 2G ;
f) repeating at least once, responsively to a recovery of the sample substantially to equilibrium, steps (a) to (e) with a different selected recovery time τ 1 in step (c); and
g) processing the solid-echo measurements to produce a T 1 -T* 2G map for use in characterizing the sample, wherein the characterizing includes at least one of determining a structure and determining a plurality of components.
2. The method of claim 1 , wherein the solid-like components comprise at least one of kerogen, bitumen, and a clay hydroxyl of a geologic sample.
3. The method of claim 1 , wherein the liquid-like components comprise at least one of a micropore fluid, a meso-macropore fluid, a fluid dissolved in organic matter, and a clay-bound water of a geologic sample.
4. The method of claim 1 , wherein the instrumental deadtime t d is not greater than 0.01 ms.
5. The method of claim 1 , wherein the longitudinal magnetization is saturated (M z =0) by a series of RF pulses, followed by a selected inversion recovery time τ 1 , followed by rotation into the transverse plane to form a solid-echo.
6. The method of claim 1 , additionally comprising: using the measurements before and after bitumen extraction of the sample to predict bitumen content and bitumen properties including at least one of asphaltene, resin, aromatic, and saturate fractions of the bitumen in the sample.
7. The method of claim 1 , additionally comprising: using the measurements before and after saturation of the sample with light hydrocarbons to predict expelled bitumen content and bitumen properties including at least one of asphaltene, resin, aromatic, and saturate fractions of the bitumen in the sample.
8. The method of claim 1 , wherein the sample comprises bulk crude-oil or bulk bitumen to predict the asphaltene, resin, aromatic, and/or saturate fractions of the bulk crude-oil or bulk bitumen.
9. The method of claim 1 , wherein the inversion is based on 2D inverse Laplace techniques for use in determining structure or components of the sample.
10. The method of claim 1 , wherein the transverse magnetization M x,y decay is inverted with one of an exponential function, a Gaussian function, and a sinc-Gaussian kernel function.
11. The method of claim 1 , wherein the longitudinal magnetization M z recovery is inverted with an exponential kernel.
12. The method of claim 1 , wherein one or more of the nominal 90° RF pulse comprises a different tip angle.
13. The method of claim 1 , wherein one or more of the nominal 180° RF pulse comprises a different tip angle.
14. The method of claim 1 , wherein one or more of the steps (a) to (g) is correlated with geochemistry data, such as RockEval or LECO, for determining structure or components of the sample.
15. The method of claim 1 , when applied to predict NMR-derived geochemical quantities including S1, S2, S1/S2, HI, OI, as well as elemental ratios H/C, H/S, H/O, H/N of elements for the crude-oil or bitumen.
16. The method of claim 1 , wherein a distinction between solid-like and liquid-like NMR signal is determined by a transverse relaxation time being respectively above or below a value of 0.1 ms.
17. The method of claim 1 , wherein a distinction between solid-like and liquid-like NMR signal is determined by a viscosity being respectively above or below a value of 10 7 cP.
18. A method of nuclear magnetic resonance (NMR) measurement on a sample, the method comprising:
a) measuring liquid-like components using an inversion-recovery CPMG sequence, without dephasing from the inhomogeneous magnetic field;
b) processing the measurements of the liquid-like components to produce a T 1 -T 2e map of the liquid-like components;
c) measuring solid-like components using an inversion-recovery solid-echo sequence, with minimal instrumental deadtime;
d) processing the measurements of the liquid-like components to produce a T 1 -T* 2G map of the solid-like components;
e) combining the T 1 -T 2e map with the T 1 -T* 2G map using a T 2 cutoff to create a spliced T 1 -{T* 2G ; T 2e } map; and
f) analyzing the T 1 -{T* 2G ; T 2e } map for use in characterizing the sample, wherein the characterizing includes at least one of determining a structure and determining a plurality of components.
19. The method of claim 18 , wherein the solid-like components comprise at least one of kerogen, bitumen, and a clay hydroxyl of a geologic sample.
20. The method of claim 18 , wherein the liquid-like components comprise at least one of a micropore fluid, a meso-macropore fluid, a fluid dissolved in organic matter, and a clay-bound water of a geologic sample.
21. The method of claim 18 , wherein the instrumental deadtime t d is not greater than 0.01 ms.
22. The method of claim 18 , wherein the longitudinal magnetization is saturated (M z =0) by a series of RF pulses, followed by a selected inversion recovery time τ 1 , followed by rotation into the transverse plane to form a solid-echo.
23. The method of claim 18 , additionally comprising: using the measurements before and after bitumen extraction of the sample to predict bitumen content and bitumen properties including at least one of asphaltene, resin, aromatic, and saturate fractions of the bitumen in the sample.
24. The method of claim 18 , additionally comprising: using the measurements before and after saturation of the sample with light hydrocarbons to predict expelled bitumen content and bitumen properties including at least one of asphaltene, resin, aromatic, and saturate fractions of the bitumen in the sample.
25. The method of claim 18 , wherein the sample comprises bulk crude-oil or bulk bitumen to predict the asphaltene, resin, aromatic, and/or saturate fractions of the bulk crude-oil or bulk bitumen.
26. The method of claim 18 , wherein the inversion is based on 2D inverse Laplace techniques for use in determining structure or components of the sample.
27. The method of claim 18 , wherein the transverse magnetization M x,y decay is inverted with one of an exponential function, a Gaussian function, and a sinc-Gaussian kernel function.
28. The method of claim 18 , wherein the longitudinal magnetization M z recovery is inverted with an exponential kernel.
29. The method of claim 18 , wherein one or more of the nominal 90° RF pulse comprises a different tip angle.
30. The method of claim 18 , wherein one or more of the nominal 180° RF pulse comprises a different tip angle.
31. The method of claim 18 , wherein one or more of the steps (a) to (g) is correlated with geochemistry data, such as RockEval or LECO, for determining structure or components of the sample.
32. The method of claim 18 , when applied to predict NMR-derived geochemical quantities including S1, S2, S1/S2, HI, OI, as well as elemental ratios H/C, H/S, H/O, H/N of elements for the crude-oil or bitumen.
33. The method of claim 18 , wherein a distinction between solid-like and liquid-like NMR signal is determined by a transverse relaxation time being respectively above or below a value of 0.1 ms.
34. The method of claim 18 , wherein a distinction between solid-like and liquid-like NMR signal is determined by a viscosity being respectively above or below a value of 10 7 cP.