# US 11,112,373 B1 · Systems and methods for slice selective nuclear magnetic resonance testing of fractured core plugs to determine in-situ pore volume

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- Number: US 11,112,373 B1
- Document ID: US11112373B1
- Status: Granted
- Kind: B1
- Application number: 16/801,492
- Filed: 2020-02-26
- Published: 2021-08-26
- Granted: 2021-09-07
- Earliest claimed: 2020-02-26
- Assignees: Saudi Arabian Oil Company
- Applicants: Saudi Arabian Oil Company
- Inventors: Marwah Mufid AlSinan; Hyung Tae Kwak
- Web page: https://patentgrep.com/patent/US11112373B1

## CPC

- G01N 24/081: {Making measurements of geologic samples, e.g. measurements of moisture, pH, porosity, permeability, tortuosity or viscosity}
- G01R 33/445: {MR involving a non-standard magnetic field B0, e.g. of low magnitude as in the earth's magnetic field or in nanoTesla spectroscopy, comprising a polarizing magnetic field for pre-polarisation, B0 with a temporal variation of its magnitude or direction such as field cycling of B0 or rotation of the direction of B0, or spatially inhomogeneous B0 like in fringe-field MR or in stray-field imaging}
- G01R 33/448: {Relaxometry, i.e. quantification of relaxation times or spin density (G01R33/50 takes precedence)}
- G01R 33/4835: {of multiple slices}
- G01V 3/14: operating with electron or nuclear magnetic resonance
- 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)
- G01R: MEASURING ELECTRIC VARIABLES; MEASURING MAGNETIC VARIABLES (indicating correct tuning of resonant circuits H03J3/12)
- G01V: GEOPHYSICS; GRAVITATIONAL MEASUREMENTS; DETECTING MASSES OR OBJECTS; TAGS (means for indicating the location of accidentally buried, e.g. snow-buried, persons A63B29/02)

## Abstract

Provided is a local slice selective T2 nuclear magnetic resonance (NMR) test procedure that includes: (1) identifying a location of a fracture within a core plug; (2) conducting an initial local slice selective T2 NMR test on a slice of the plug that corresponds to the location to generate initial T2 measurements; (3) determining an initial fracture pore volume of the fracture based on the initial T2 measurements; (4) conducting an in-situ local slice selective T2 NMR test on the slice of the plug to generate in-situ T2 measurements and corresponding measures of a volume of fluid expelled from the plug; (5) determining an in-situ fracture pore volume for the fracture based on the in-situ T2 measurements; and (6) comparing the volume of water to a difference between the initial and the in-situ fracture pore volumes to confirm the accuracy of the in-situ pore volume.

## Claims

### Claim 1

A method of slice selective nuclear magnetic resonance (NMR) testing of a fractured core plug, the method comprising:
obtaining a fractured core plug comprising a fracture;
saturating the fractured core plug with a saturating fluid to introduce the saturating fluid into the fracture;
sealing the fractured core plug to inhibit the saturating fluid from leaking out of the fracture;
identifying a location of the fracture within the core plug, the location including a position and orientation of the fracture;
identifying a slice of the core plug corresponding to the location of the fracture;
conducting initial local slice selective NMR testing of the core plug comprising:
subjecting the core plug to baseline conditions, the baseline conditions comprising a first stress level;
conducting an initial NMR scan of the core plug to acquire initial T2 NMR measurements, the initial NMR scan of the core plug comprising an NMR scan of the slice of the core plug corresponding to the fracture while the core plug is subjected to the baseline conditions; and
determining, based on the initial T2 NMR measurements, an initial fracture pore volume of the fracture;
conducting in-situ local slice selective NMR testing of the core plug comprising:
determining in-situ conditions of the core plug, the in-situ conditions comprising an in-situ stress level for the core plug;
subjecting the core plug to in-situ conditions comprising a second stress level that is greater than the first stress level and that corresponds to the in-situ stress level;
conducting an in-situ NMR scan of the core plug to acquire in-situ T2 NMR measurements, the in-situ NMR scan of the core plug comprising an NMR scan of the slice of the core plug corresponding to the fracture while the core plug is subjected to the in-situ conditions;
measuring a volume of water expelled from the core plug in response to subjecting the core plug to the in-situ condition;
determining, based on the in-situ T2 NMR measurements, an in-situ fracture pore volume of the fracture;
determining a difference between the initial fracture pore volume of the fracture and the in-situ fracture pore volume of the fracture;
comparing the difference between the initial fracture pore volume of the fracture and the in-situ fracture pore volume of the fracture to the volume of water expelled; and
verifying, based on the comparison of the difference between the initial fracture pore volume of the fracture and the in-situ fracture pore volume of the fracture to the volume of water expelled, the in-situ fracture pore volume of the fracture.

### Claim 2 (depends on 1)

The method of claim 1, wherein identifying the location of the fracture within the core plug comprises imaging the core plug to identify the location of the fracture within the core plug.

### Claim 3 (depends on 2)

The method of claim 2, wherein the imaging comprises x-ray imaging or magnetic resonance imaging (MRI) of the core plug.

### Claim 4 (depends on 1)

The method of claim 1, wherein sealing the fractured core plug comprises coating the fractured core plug with wax or paraffin.

### Claim 5 (depends on 1)

The method of claim 1, wherein the in-situ local slice selective NMR testing of the core plug is conducted using a tri-axial NMR test fixture comprising a first gradient coil oriented in an x direction, a second gradient coil oriented in a y direction, and a third gradient coil oriented in a z direction, wherein the orientation of the fracture is oriented at an angle relative to two or more of the x, y and z directions, and wherein the NMR scans of the slice of the core plug each comprise selectively energizing two or more of the first, second and third gradient coils to obtain corresponding ones of the in-situ T2 measurements for the slice.

### Claim 6 (depends on 1)

The method of claim 1, wherein the in-situ conditions comprise a confining stress or shear stress that is greater than a confining stress or shear stress of the first stress level.

### Claim 7 (depends on 1)

The method claim 1, wherein the in-situ conditions comprise an elevated in-situ stress level, and wherein the in-situ local slice selective NMR testing of the core plug comprises iteratively increasing a stress level applied to the core plug to reach the elevated in-situ stress level, and, for each iteration of an increase of the stress level applied to the core plug, conducting an in-situ NMR scan of the core plug and measuring a volume of water expelled from the core plug.

### Claim 8 (depends on 1)

The method of claim 1, wherein the core plug is extracted from a formation of a reservoir and the method further comprises developing the reservoir based on the in-situ fracture pore volume of the fracture.

### Claim 9 (depends on 8)

The method of claim 8, wherein developing the reservoir comprises:
determining, based on the in-situ fracture pore volume of the fracture, operating parameters for a well in the formation; and
operating the well in accordance with the operating parameters.

### Claim 10

A non-transitory computer readable storage medium comprising program instructions for slice selective nuclear magnetic resonance (NMR) testing of a fractured core plug, the program instructions executable by a computer processor to cause the following operations:
identifying a location of a fracture within a core plug, the location including a position and orientation of the fracture, the core plug being saturated with a saturating fluid to introduce the saturating fluid into the fracture and being sealed to inhibit the saturating fluid from leaking out of the fracture;
identifying a slice of the core plug corresponding to the location of the fracture;
conducting initial local slice selective NMR testing of the core plug comprising:
subjecting the core plug to baseline conditions, the baseline conditions comprising a first stress level;
conducting an initial NMR scan of the core plug to acquire initial T2 NMR measurements, the initial NMR scan of the core plug comprising an NMR scan of the slice of the core plug corresponding to the fracture while the core plug is subjected to the baseline conditions; and
determining, based on the initial T2 NMR measurements, an initial fracture pore volume of the fracture;
conducting in-situ local slice selective NMR testing of the core plug comprising:
determining in-situ conditions of the core plug, the in-situ conditions comprising an in-situ stress level for the core plug;
subjecting the core plug to in-situ conditions comprising a second stress level that is greater than the first stress level and that corresponds to the in-situ stress level;
conducting an in-situ NMR scan of the core plug to acquire in-situ T2 NMR measurements, the in-situ NMR scan of the core plug comprising an NMR scan of the slice of the core plug corresponding to the fracture while the core plug is subjected to the in-situ conditions;
measuring a volume of water expelled from the core plug in response to subjecting the core plug to the in-situ condition;
determining, based on the in-situ T2 NMR measurements, an in-situ fracture pore volume of the fracture;
determining a difference between the initial fracture pore volume of the fracture and the in-situ fracture pore volume of the fracture;
comparing the difference between the initial fracture pore volume of the fracture and the in-situ fracture pore volume of the fracture to the volume of water expelled; and
verifying, based on the comparison of the difference between the initial fracture pore volume of the fracture and the in-situ fracture pore volume of the fracture to the volume of water expelled, the in-situ fracture pore volume of the fracture.

### Claim 11 (depends on 10)

The medium of claim 10, wherein identifying the location of the fracture within the core plug comprises imaging the core plug to identify the location of the fracture within the core plug.

### Claim 12 (depends on 11)

The medium of claim 11, wherein the imaging comprises x-ray imaging or magnetic resonance imaging (MRI) of the core plug.

### Claim 13 (depends on 10)

The medium of claim 10, wherein the exterior of the fractured core plug is coated with wax or paraffin configured to provide for the core plug being sealed to inhibit the saturating fluid from leaking out of the fracture.

### Claim 14 (depends on 10)

The medium of claim 10, wherein the in-situ local slice selective NMR testing of the core plug is conducted using a tri-axial NMR test fixture comprising a first gradient coil oriented in an x direction, a second gradient coil oriented in a y direction, and a third gradient coil oriented in a z direction, wherein the orientation of the fracture is oriented at an angle relative to two or more of the x, y and z directions, and wherein the NMR scans of the slice of the core plug each comprise selectively energizing two or more of the first gradient coil, the second gradient coil and third gradient coils to obtain corresponding ones of the in-situ T2 measurements for the slice.

### Claim 15 (depends on 10)

The medium of claim 10, wherein the in-situ conditions comprise a confining stress or shear stress that is greater than a confining stress or shear stress of the first stress level.

### Claim 16 (depends on 10)

The medium of claim 10, wherein the in-situ conditions comprise an elevated in-situ stress level, and wherein the in-situ local slice selective NMR testing of the core plug comprises iteratively increasing a stress level applied to the core plug to reach the elevated in-situ stress level, and, for each iteration of an increase of the stress level applied to the core plug, conducting an in-situ NMR scan of the core plug and measuring a volume of water expelled from the core plug.

### Claim 17 (depends on 10)

The medium of claim 10, wherein the core plug is extracted from a formation of a reservoir and the reservoir is developed based on the in-situ fracture pore volume of the fracture.

### Claim 18 (depends on 17)

The medium of claim 17, wherein developing the reservoir comprises:
determining, based on the in-situ fracture pore volume of the fracture, operating parameters for a well in the formation; and
operating the well in accordance with the operating parameters.

### Claim 19

A system for slice selective nuclear magnetic resonance (NMR) testing of a fractured core plug, comprising:
a slice selective NMR test fixture configured to subject a fractured core plug to slice selective NMR scans; and
non-transitory computer readable storage medium comprising program instructions executable by a computer processor to cause the following operations:
identifying a location of a fracture within a core plug, the location including a position and orientation of the fracture, the core plug being saturated with a saturating fluid to introduce the saturating fluid into the fracture and being sealed to inhibit the saturating fluid from leaking out of the fracture;
identifying a slice of the core plug corresponding to the location of the fracture;
conducting initial local slice selective NMR testing of the core plug comprising:
subjecting the core plug to baseline conditions, the baseline conditions comprising a first stress level;
conducting an initial NMR scan of the core plug to acquire initial T2 NMR measurements, the initial NMR scan of the core plug comprising an NMR scan of the slice of the core plug corresponding to the fracture while the core plug is subjected to the baseline conditions; and
determining, based on the initial T2 NMR measurements, an initial fracture pore volume of the fracture;
conducting in-situ local slice selective NMR testing of the core plug comprising:
determining in-situ conditions of the core plug, the in-situ conditions comprising an in-situ stress level for the core plug;
subjecting the core plug to in-situ conditions comprising a second stress level that is greater than the first stress level and that corresponds to the in-situ stress level;
conducting an in-situ NMR scan of the core plug to acquire in-situ T2 NMR measurements, the in-situ NMR scan of the core plug comprising an NMR scan of the slice of the core plug corresponding to the fracture while the core plug is subjected to the in-situ conditions;
measuring a volume of water expelled from the core plug in response to subjecting the core plug to the in-situ condition;
determining, based on the in-situ T2 NMR measurements, an in-situ fracture pore volume of the fracture;
determining a difference between the initial fracture pore volume of the fracture and the in-situ fracture pore volume of the fracture;
comparing the difference between the initial fracture pore volume of the fracture and the in-situ fracture pore volume of the fracture to the volume of water expelled; and
verifying, based on the comparison of the difference between the initial fracture pore volume of the fracture and the in-situ fracture pore volume of the fracture to the volume of water expelled, the in-situ fracture pore volume of the fracture.

### Claim 20 (depends on 19)

The system of claim 19, wherein identifying the location of the fracture within the core plug comprises imaging the core plug to identify the location of the fracture within the core plug.

### Claim 21 (depends on 20)

The system of claim 20, wherein the imaging comprises x-ray imaging or magnetic resonance imaging (MRI) of the core plug.

### Claim 22 (depends on 19)

The system of claim 19, wherein the exterior of the fractured core plug is coated with wax or paraffin configured to provide for the core plug being sealed to inhibit the saturating fluid from leaking out of the fracture.

### Claim 23 (depends on 19)

The system of claim 19, wherein the slice selective NMR test fixture comprises a tri-axial NMR test fixture comprising a first gradient coil oriented in an x direction, a second gradient coil oriented in a y direction, and a third gradient coil oriented in a z direction, wherein the orientation of the fracture is oriented at an angle relative to two or more of the x, y and z directions, and wherein the NMR scans of the slice of the core plug each comprise selectively energizing two or more of the first gradient coil, the second gradient coil and the third gradient coils to obtain corresponding ones of the in-situ T2 measurements for the slice.

### Claim 24 (depends on 19)

The system of claim 19, wherein the in-situ conditions comprise a confining stress or shear stress that is greater than a confining stress or shear stress of the first stress level.

### Claim 25 (depends on 19)

The system of claim 19, wherein the in-situ conditions comprise an elevated in-situ stress level, and wherein the in-situ local slice selective NMR testing of the core plug comprises iteratively increasing a stress level applied to the core plug to reach the elevated in-situ stress level, and, for each iteration of an increase of the stress level applied to the core plug, conducting an in-situ NMR scan of the core plug and measuring a volume of water expelled from the core plug.

### Claim 26 (depends on 19)

The system of claim 19, wherein the core plug is extracted from a formation of a reservoir and the reservoir is developed based on the in-situ fracture pore volume of the fracture.

### Claim 27 (depends on 26)

The system of claim 26, wherein developing the reservoir comprises:
determining, based on the in-situ fracture pore volume of the fracture, operating parameters for a well in the formation; and
operating the well in accordance with the operating parameters.