# US 11,029,250 B2 · Wellsite kerogen maturity determination utilizing raman spectroscopy

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- Number: US 11,029,250 B2
- Document ID: US11029250B2
- Status: Granted
- Kind: B2
- Application number: 16/489,188
- Filed: 2018-02-21
- Published: 2020-01-02
- Granted: 2021-06-08
- Earliest claimed: 2017-02-27
- Assignees: Schlumberger Technology Corporation
- Applicants: Schlumberger Technology Corporation
- Inventors: Bastian Sauerer; Wael Abdallah
- Web page: https://patentgrep.com/patent/US11029250B2

## CPC

- G01N 21/65: Raman scattering
- G01J 3/44: Raman spectrometry; Scattering spectrometry {; Fluorescence spectrometry}
- G01N 33/2823: {Raw oil, drilling fluid or polyphasic mixtures}
- G01N: INVESTIGATING OR ANALYSING MATERIALS BY DETERMINING THEIR CHEMICAL OR PHYSICAL PROPERTIES (measuring or testing apparatus or processes other than immunoassay, involving enzymes or microorganisms C12M, C12Q)
- G01J: MEASUREMENT OF INTENSITY, VELOCITY, SPECTRAL CONTENT, POLARISATION, PHASE OR PULSE CHARACTERISTICS OF INFRARED, VISIBLE OR ULTRAVIOLET LIGHT; COLORIMETRY; RADIATION PYROMETRY (light sources F21, H01J, H01K, H05B; investigating properties of materials by optical means G01N)

## Abstract

A method for determining thermal maturity of a formation sample. The method includes: cleaning the formation sample to remove residues of drilling fluid and reservoir fluid to obtain a cleaned sample; performing Raman spectroscopic measurements on the cleaned sample to obtain a Raman spectrum for the cleaned sample; fitting at least a G (graphite) peak and a D1 (defect) peak to the Raman spectrum to obtain Raman shift values for the G peak and the D1 peak and a Raman band separation (RBS) value; using the RBS to generate a vitrinite reflection equivalent (VRe) value using a relationship correlating RBS to VRe; and displaying the VRe as an indicator of formation sample maturity for a depth in the formation from which the cleaned sample was obtained.

## Claims

### Claim 1

A method for determining the maturity of a formation sample, comprising:
cleaning the formation sample to remove residues of drilling fluid and reservoir fluid to obtain a cleaned sample;
performing Raman spectroscopic measurements on the cleaned sample to obtain a Raman spectrum for the sample;
fitting at least a G (graphite) peak and a D1 (defect) peak to the Raman spectrum to obtain Raman shift values for the G peak and the D1 peak and a Raman band separation (RBS) value;
using the RBS to generate a vitrinite reflectance equivalent (VRe) value using a relationship correlating RBS to VRe; and
displaying the VRe as an indicator of formation sample maturity for a depth in the formation from which the sample was obtained.

### Claim 2 (depends on 1)

The method of claim 1, wherein said relationship is RBS=c1 ln(VRe)+c2, where c1 and c2 are constants.

### Claim 3 (depends on 1)

The method of claim 1, wherein the fitting of at least a G peak and a D1 peak comprises fitting said G peak, said D1 peak and three additional peaks.

### Claim 4 (depends on 3)

The method of claim 3, wherein said fitting comprises using peak shapes modeled using a Voigt, Lorentzian or Gaussian function or combination thereof.

### Claim 5 (depends on 1)

The method of claim 1, wherein the formation sample is selected from a group consisting of: cores, chunks, chips and cuttings from the formation.

### Claim 6 (depends on 1)

The method of claim 1, wherein said performing Raman spectroscopic measurements comprises utilizing a Raman laser having a wavelength of approximately 532 nm.

### Claim 7 (depends on 6)

The method of claim 6, wherein said performing Raman spectroscopic measurements comprises analyzing signals occurring in the Raman spectroscopic measurements between 200 cm−1 and 1877 cm−1.

### Claim 8 (depends on 1)

The method of claim 1, further comprising, after said cleaning and before said performing Raman spectroscopy, subjecting the cleaned sample to ultraviolet light and looking for a resulting fluorescence signal, and subjecting the cleaned sample to additional cleaning if a fluorescence signal is seen.

### Claim 9 (depends on 8)

The method of claim 8, wherein said additional cleaning comprises washing the sample with a base oil, then water, then water and soap, and then pure water.

### Claim 10 (depends on 1)

The method of claim 1, wherein said cleaning comprises washing the sample with a base oil, then water, then water and soap, and then pure water.

### Claim 11

A method for determining the maturity of a formation sample, comprising:
obtaining cuttings of the formation sample from drilling fluid at a wellbore;
at the wellbore, cleaning the cuttings to remove residues of drilling fluid and reservoir fluid to obtain a cleaned sample;
at the wellbore, performing Raman spectroscopic measurements on the cleaned sample to obtain a Raman spectrum for the sample;
fitting at least a G (graphite) peak and a D1 (defect) peak to the Raman spectrum to obtain Raman shift values for the G peak and the D1 peak and a Raman band separation (RBS) value;
using the RBS to generate a vitrinite reflectance equivalent (VRe) value using a relationship correlating RBS to VRe; and
displaying the VRe as an indicator of formation sample maturity for a depth in the formation from which the sample was obtained.

### Claim 12 (depends on 11)

The method of claim 11, further comprising, at the wellbore, after cleaning and before performing Raman spectroscopic measurements, drying the cleaned sample and subjecting the cleaned sample to ultraviolet light and looking for a resulting fluorescence signal, and subjecting the cleaned sample to additional cleaning if a fluorescence signal is seen.

### Claim 13 (depends on 12)

The method of claim 12, wherein said additional cleaning comprises washing the sample with a base oil, then water, then water and soap, and then pure water.

### Claim 14 (depends on 12)

The method of claim 12, wherein said relationship is RBS=c1 ln(VRe)+c2, where c1 and c2 are constants.

### Claim 15 (depends on 14)

The method of claim 14, wherein the fitting of at least a G peak and a D1 peak comprises fitting said G peak, said D1 peak and three additional peaks, and said fitting comprises using peak shapes modeled using a Voigt, Lorentzian or Gaussian function or combinations thereof.

### Claim 16 (depends on 15)

The method of claim 15, wherein said performing Raman spectroscopic measurements comprises utilizing a Raman laser having a wavelength of approximately 532 nm, and analyzing signals occurring in the Raman spectroscopic measurements between 200 cm−1 and 1877 cm−1.

### Claim 17

A method for providing indications of the maturity of a formation traversed by a wellbore as a function of formation depth, comprising:
at the wellbore, obtaining separate cutting samples of the formation from wellbore drilling fluid respectively representing the formation at multiple formation depths;
at the wellbore, cleaning the cutting samples to remove residues of drilling fluid and reservoir fluid to obtain cleaned samples respectively representing the multiple formation depths;
at the wellbore, for each of the cleaned samples, performing Raman spectroscopic measurements to obtain Raman spectra for the samples respectively representing the multiple formation depths;
for each formation depth, fitting at least a G (graphite) peak and a D1 (defect) peak to each Raman spectrum to obtain Raman shift values for the G peak and the D1 peak and a Raman band separation (RBS) value for that formation depth;
for each formation depth, using the RBS to generate a vitrinite reflectance equivalent (VRe) value for that formation depth using a relationship correlating RBS to VRe; and
for each formation depth, displaying in log format the VRe as an indicator of formation sample maturity for that depth in the formation.

### Claim 18 (depends on 17)

The method of claim 17, wherein said relationship is RBS=c1 ln(VRe)+c2, where c1 and c2 are constants.

### Claim 19 (depends on 17)

The method of claim 17, wherein the fitting at least a G peak and a D1 peak comprises fitting said G peak, said D1 peak and three additional peaks, and said fitting comprises using peak shapes modeled using a Voigt, Lorentzian or Gaussian function or a combination thereof.

### Claim 20 (depends on 17)

The method of claim 17, wherein said performing Raman spectroscopic measurements comprises utilizing a Raman laser having a wavelength of approximately 532 nm, and analyzing signals occurring in the Raman spectroscopic measurements between 200 cm−1 and 1877 cm−1.