Determination of fluid saturation in shale reservoirs using NMR

Patent metadata

Field	Value
Publication number	US-10359537-B2
Application number	US-201514728703-A
Country	US
Kind code	B2
Filing date	Jun 2, 2015
Priority date	Jun 2, 2015
Publication date	Jul 23, 2019
Grant date	Jul 23, 2019

Abstract

A method of estimating fluid saturations includes obtaining amplitude values of nuclear magnetic resonance (NMR) data for a material, with each amplitude value being associated with a longitudinal magnetization recovery (T1 relaxation) time and a transverse magnetization decay (T2 relaxation) time. A mean is calculated as a function of the amplitude values and the T1 and T2 relaxation times for the amplitude values. Hydrocarbon saturation of pore space of the material is estimated as a function of the deviation of the mean from a threshold hydrocarbon saturation indicator and a threshold water saturation indicator, using the processor. Water saturation of the pore space of the material is estimated as a function of the deviation of the mean from the threshold hydrocarbon saturation indicator and the threshold water saturation indicator, using the processor.

First claim

The invention claimed is:

1. A method comprising:
obtaining amplitude values of nuclear magnetic resonance (NMR) data for a material via a downhole logging tool, each amplitude value being associated with a longitudinal magnetization recovery (T1 relaxation) time and a transverse magnetization decay (T2 relaxation) time;
calculating a mean as a function of the amplitude values and the T1 and T2 relaxation times for the amplitude values, using a processor;
estimating hydrocarbon saturation of pore space of the material as a function of the deviation of the mean from a threshold hydrocarbon saturation indicator and a threshold water saturation indicator, using the processor; and
estimating water saturation of the pore space of the material as a function of the deviation of the mean from the threshold hydrocarbon saturation indicator and the threshold water saturation indicator, using the processor.

2. The method of claim 1 , wherein the mean comprises a logarithmic mean.

3. The method of claim 1 , further comprising:
obtaining a porosity of the material; and
estimating an oil volume of the material as a function of the hydrocarbon saturation and the porosity, using the processor.

4. The method of claim 3 , further comprising estimating a water volume of the material as a function of the water saturation and the porosity, using the processor.

5. The method of claim 3 , wherein the porosity is obtained by summing the amplitude values of the NMR data for the material.

6. The method of claim 1 , wherein calculating the mean comprises:
calculating a one dimensional T1 distribution from the amplitude values;
calculating a one dimensional T2 distribution from the amplitude values;
calculating a mean of the one dimensional T1 distribution; and
calculating a mean of the one dimensional T2 distribution.

7. The method of claim 6 , further comprising calculating a ratio of the mean of the one dimensional T1 distribution to the mean of the one dimensional T2 distribution, using the processor; and wherein estimating the hydrocarbon saturation of the pore space comprises dividing a difference between the ratio and the threshold water saturation indicator by a difference between the threshold hydrocarbon saturation indicator and the threshold water saturation indicator.

8. The method of claim 7 , wherein estimating the water saturation of the pore space comprises subtracting the hydrocarbon saturation from a total fluid saturation of the material.

9. The method of claim 1 , wherein calculating the mean comprises for each T2 relaxation time, calculating a mean as a function of T1 relaxation time and the amplitude values that correspond therewith; and wherein estimating the hydrocarbon saturation of the pore space comprises for each T2 relaxation time, estimating hydrocarbon saturation of the pore space as a function of the deviation of the mean of the T1 relaxation times for that T2 relaxation time from the threshold hydrocarbon saturation indicator and the threshold water saturation indicator.

10. The method of claim 9 , wherein estimating the hydrocarbon saturation of the pore space for each T2 relaxation time comprises dividing a difference between the mean of the T1 relaxation times for that T2 relaxation time and a threshold water saturation indicator for that T2 relaxation time by a difference between a threshold hydrocarbon saturation indicator for that T2 relaxation time and the threshold water saturation indicator for that T2 relaxation time.

11. The method of claim 9 , wherein estimating the hydrocarbon saturation of the pore space comprises summing the estimated hydrocarbon saturation of the pore space for each T2 relaxation time.

12. The method of claim 1 , wherein calculating the mean comprises for each T2 relaxation time, calculating a mean as a function of T1 relaxation time and the amplitude values that correspond therewith; and wherein estimating the water saturation of the pore space comprises for each T2 relaxation time, estimating water saturation of the pore space as a function of the deviation of the mean of the T1 relaxation times for that T2 relaxation time from the threshold hydrocarbon saturation indicator and the threshold water saturation indicator.

13. The method of claim 12 , wherein estimating the water saturation for the pore space for each T2 relaxation time comprises dividing a difference between a threshold water saturation indicator for that T2 relaxation time and the mean of the T1 relaxation times for that T2 relaxation time by a difference between a threshold hydrocarbon saturation indicator for that T2 relaxation time and the threshold water saturation indicator for that T2 relaxation time.

14. The method of claim 12 , wherein estimating the water saturation of the pore space comprises summing the estimated water saturation of the pore space for each T2 relaxation time.

15. The method of claim 1 , wherein the material comprises a core sample; and wherein the amplitude values are obtained using a NMR machine.

16. The method of claim 1 , wherein the material comprises a subsurface formation; and wherein the amplitude values are obtained by placing a NMR tool in a wellbore penetrating the subsurface formation and logging the subsurface formation using the NMR tool.

17. A well-logging system comprising:
a well-logging tool configured to transmit energy into a subsurface formation, receive NMR resonance spin echoes from the subsurface formation resulting from the transmitted energy, and perform NMR analysis to determine amplitude values of NMR data for the subsurface formation, each amplitude value being associated with a longitudinal magnetization recovery (T1) time and a transverse magnetization decay (T2) time; and
a processor configured to:
calculate a mean as a function of the amplitude values and the T1 and T2 relaxation times for the amplitude values;
estimate hydrocarbon saturation of pore space of the subsurface formation as a function of the deviation of the mean from a threshold hydrocarbon saturation indicator and a threshold water saturation indicator;
estimate a total porosity of the subsurface formation by summing the amplitude values of the NMR data for the subsurface formation; and
calculate an oil volume of the subsurface formation as a function of the hydrocarbon saturation and the total porosity.

18. The well-logging system of claim 17 , wherein the processor calculates the mean by:
calculating a one dimensional T1 distribution from the amplitude values;
calculating a one dimensional T2 distribution from the amplitude values;
calculating a mean of the one dimensional T1 distribution; and
calculating a mean of the one dimensional T2 distribution.

19. The well-logging system of claim 18 , wherein the processor is further configured to calculate a ratio of the mean of the one dimensional T1 distribution to the mean of the one dimensional T2 distribution; and wherein the processor estimates the hydrocarbon saturation of the pore space by dividing a difference between the ratio and the threshold water saturation indicator by a difference between the threshold hydrocarbon saturation indicator and the threshold water saturation indicator.

20. The well-logging system of claim 18 , wherein the processor calculates the mean by, for each T2 relaxation time, calculating a mean as a function of T1 relaxation time and the amplitude value that corresponds therewith; and wherein the processor estimates the hydrocarbon saturation of the pore space by for each T2 relaxation time, e

Assignees

• Schlumberger Technology Corp

Inventors

• Ali Mansoor
• Anand Vivek

Classifications

• Y02A90/344

  Cross-Sectional Technologies · mapped topic

• G01V3/32 Primary

  operating with electron or nuclear magnetic resonance · CPC title

• G01V3/38

  Processing data, e.g. for analysis, for interpretation, for correction · CPC title

• Y02A90/30

  Assessment of water resources · CPC title