Method for determining the composition of natural gas liquids, mean pore-size and tortuosity in a subsurface formation using NMR

Patent metadata

Field	Value
Publication number	US-11099292-B1
Application number	US-202016842928-A
Country	US
Kind code	B1
Filing date	Apr 8, 2020
Priority date	Apr 10, 2019
Publication date	Aug 24, 2021
Grant date	Aug 24, 2021

Abstract

New methods for determining the volumetric composition and saturation of methane and NGLs (natural gas liquids: ethane, propane, butane, and pentane) in a petroleum reservoir combining NMR (nuclear magnetic resonance) logging and NMR core analysis and for determining the mean pore-size and tortuosity of the light hydrocarbon-filled porosity in a petroleum reservoir using NMR core analysis.

First claim

The invention claimed is:

1. A method of measuring at least one of:
(i) respective downhole concentrations in a subsurface formation of one or more members of the C1-C5 alkane group consisting of methane, ethane, propane, butane and pentane;
(ii) a ratio between respective downhole concentrations of multiple members of the C1-C5 alkane group, and
(iii) a linear combination of ratios between respective downhole concentrations of multiple members of the C1-C5 alkane group:
the method comprising:
a. obtaining sample(s) of core from a target depth in a subsurface formation;
b. obtaining downhole NMR log data of the subsurface formation at the target depth;
c. when a given one of the core sample(s) is saturated with a first pressurized saturation fluid comprising a first member of the C1-C5 alkane group, obtaining first laboratory NMR data of the saturated core-sample(s); and
d. when the same given one or a different one of the core sample(s) is saturated with a second pressurized saturation fluid that is different from the first pressurized saturation fluid, the second saturation fluid comprising a second member of the C1-C5 alkane group that is different from the first member, obtaining second laboratory NMR data of the saturated core-sample(s), wherein the first and second laboratory NMR data collectively form a laboratory NMR data set, and wherein the method further comprises:
e. computing from the lab-NMR data set and the downhole NMR log data at least one downhole parameter selected from the group consisting of:
(i) respective downhole concentrations of one or more members of the C1-C5 alkane group consisting of methane, ethane, propane, butane and pentane; and
(ii) a ratio between respective downhole concentrations of multiple members of the C1-C5 alkane group.

2. The method of claim 1 wherein:
i. the method further comprises: when the same given one or a different one of the core sample(s) is saturated with a third pressurized saturation fluid comprising a third member of the C1-C5 alkane group that is different from the first and second members, obtaining third laboratory NMR data of the saturated core-sample(s); and
ii. the third pressurized saturation fluid is different from both of the first and second pressurized saturation fluids; and
iii. the first, second and third laboratory NMR data collectively form the laboratory NMR data set.

3. The method of claim 2 wherein:
i. the method further comprises: when the same given one or a different one of the core sample(s) is saturated with a fourth pressurized saturation fluid comprising a fourth member of the C1-C5 alkane group that is different from the first, second and third members, obtaining fourth laboratory NMR data of the saturated core-sample(s); and
ii. the 4th pressurized saturation fluid is different from all of the first, second, and 3rd pressurized saturation fluids; and
iii. the first, second, third and fourth laboratory NMR data collectively form the laboratory NMR data set.

4. The method of claim 3 wherein:
i. the method further comprises: when the same given one or a different one of the core sample(s) is saturated with a fifth pressurized saturation fluid comprising a fifth member of the C1-C5 alkane group that is different from the first, second, third and fourth members, obtaining fifth laboratory NMR data of the saturated core-sample(s); and
ii. the fifth pressurized saturation fluid is different from all of the first, second, 3rd and 4th pressurized saturation fluids; and
iii. the first, second, third, fourth and fifth laboratory NMR data collectively form the laboratory NMR data set.

5. The method of claim 1 wherein the downhole pressure and/or temperature are estimated for the subsurface formation at the target depth, and wherein the 1 st and/or 2 nd and/or 3 rd and/or 4 th and/or 5 th laboratory NMR data is obtained when the core sample(s) are saturated with the first and/or second and/or third and/or fourth and/or fifth pressurized saturation fluid at the estimated pressure and temperature.

6. The method of claim 1 wherein the laboratory NMR data and/or downhole NMR log data comprises one or more of (i.e. any combination of): T2 distribution data, T2apparent distribution data, T1 distribution data, T1/T2 data, T1/T2apparent, D (diffusion) vs. T2 data, D (diffusion) vs T2apparent data.

7. The method of claim 1 wherein the computing of the at least one downhole parameter comprises optimizing a fit of:
i. a mathematical combination of the 1St and/or 2 nd and/or 3 rd and/or 4th and/or 5th laboratory NMR data; to
ii. downhole NMR data.

8. The method of claim 7 wherein the computed downhole concentration and/or computed molar fraction of the 1 st and/or 2 nd and/or 3 rd and/or 4 th and/or 5 th member of the C1-C5 alkane group corresponds to a weighting coefficient for the 1 st and/or 2 nd and/or 3 rd and/or 4 th and/or 5 th laboratory NMR data.

9. The method of claim 1 performed to compute at least one of the following:
(i) a ratio between a downhole methane concentration and a downhole ethane concentration;
(ii) a ratio between a downhole methane concentration and a downhole propane concentration;
(iii) a ratio between a downhole methane concentration and a downhole butane concentration;
(iv) a ratio between a downhole methane concentration and a downhole pentane concentration; and/or
(v) any ratio involving any of C1-C5 alkane group.

10. The method claim 1 , performed to compute at least one of the following:
(i) a multi-alkane sum of downhole concentrations of ethane and/or propane and/or butane and/or pentane; and
(ii) a ratio between the multi-alkane sum and a downhole methane concentration.

11. The method of claim 1 performed for a plurality of target depths to characterize the subsurface reservoir at multiple target depths.

12. The method of claim 1 wherein the computing comprises converting T2 data into T2apparent data or vice versa using at least one of:
(i) an estimated restricted diffusion coefficient for one or more members of the C1-C5 alkane group; and/or
(ii) an estimated mean pore-size of the core sample(s).

13. The method of claim 12 wherein the restricted diffusion coefficient is computed by interpolating the following method:
a method using NMR to determine the mean pore-size and tortuosity of the light hydrocarbon-filled porosity in a reservoir formation by:
a) Obtaining core in selected zones from the reservoir formation,
b) Measuring NMR on the core in the laboratory including normalized diffusion coefficient D/Do as a function of diffusion time using one or more hydrogen-bearing fluids selected from the list (H2, HD, CH4, C2H6, C3H8, C4H10, C5H12) saturating the core,
c) Varying the pressure and/or temperature of the one or more hydrogen-bearing fluids to vary the diffusion length in the NMR measurement, and
d) Computing the mean pore-size and tortuosity of the light hydrocarbon-filled porosity of the reservoir formation from D/Do versus diffusion length of the hydrogen-bearing fluid using a numerical model for restricted diffusion in a porous medium.

14. The method of claim 1 wherein the NMR log is from a gradient-based NMR tool.

15. The method of claim 1 wherein
(i) a molar fraction of the first member of the C1-C5 alkane group within the first saturation fluids is at least 0.9, and
(ii) a molar fraction of the second member of the C1-C5 alkane group within the second saturation fluids is at least 0.9.

16. The method of claim 2 wherein
(i) a molar fraction of the first member of the C1-C5 alkane group within the fi

Assignees

• Vinegar Tech Llc
• Univ Rice William M

Inventors

• Vinegar Harold J
• Singer Philip M
• Hirasaki George J
• Chen Zeliang
• Wang Xinglin

Classifications

• G01N24/081 Primary

  Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity · CPC title

• G01V3/32 Primary

  operating with electron or nuclear magnetic resonance · CPC title

• G01R33/448

  Relaxometry, i.e. quantification of relaxation times or spin density (G01R33/50 takes precedence) · CPC title

• G01N33/241

  for hydrocarbon content · CPC title

• G01N33/0016

  by regulating a physical variable, e.g. pressure or temperature · CPC title