# US 10,767,473 B2 · Systems and methods for detection of induced micro fractures

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- Number: US 10,767,473 B2
- Document ID: US10767473B2
- Status: Granted
- Kind: B2
- Application number: 16/426,189
- Filed: 2019-05-30
- Published: 2019-12-05
- Granted: 2020-09-08
- Earliest claimed: 2018-05-30
- Assignees: Saudi Arabian Oil Company
- Applicants: Saudi Arabian Oil Company
- Inventors: Hui-Hai Liu; Jilin Zhang; Gary Eppler
- Web page: https://patentgrep.com/patent/US10767473B2

## CPC

- E21B 49/02: by mechanically taking samples of the soil
- E21B 49/088: {combined with sampling}
- G01N 15/082: {Investigating permeability by forcing a fluid through a sample}
- E21B 43/26: by forming crevices or fractures
- E21B: EARTH OR ROCK DRILLING; OBTAINING OIL, GAS, WATER, SOLUBLE OR MELTABLE MATERIALS OR A SLURRY OF MINERALS FROM WELLS
- 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)

## Abstract

Methods and systems for detecting impact of induced micro-fractures in a subsurface formation are disclosed. The method includes determining an unloading effective stress (σul) in a formation sample taken from a wellbore drilled into the subsurface formation, determining a fracture closure stress (σcl) of the formation sample, determining that the unloading effective stress (σul) is greater than or equal to the fracture closure stress (σul), and in response to determining that unloading effective stress (σul) is greater than or equal to the fracture closure stress (σul), operating the well system to inhibit impact of micro-fractures in the wellbore.

## Claims

### Claim 1

A method of detecting impact of induced micro-fractures in a subsurface formation, the method comprising:
determining an unloading effective stress (σnl) in a formation sample taken from a wellbore drilled into the subsurface formation;
determining a fracture closure stress (σcl) of the formation sample;
determining that the unloading effective stress (σul) is greater than or equal to the fracture closure stress (σul); and
in response to determining that unloading effective stress (σul) is greater than or equal to the fracture closure stress (σul), operating the well system to inhibit impact of micro-fractures in the wellbore, wherein operating the well to inhibit impact of micro-fractures comprises circulating, into the wellbore, oil based drilling fluids.

### Claim 2 (depends on 1)

The method according to claim 1, wherein the unloading effective stress is equal to the effective stress in a reservoir or the difference between an overburden pressure and a pore pressure.

### Claim 3 (depends on 1)

The method according to claim 1, wherein the unloading effective stress is greater than the difference between an overburden pressure and a mud pressure at a coring depth.

### Claim 4 (depends on 1)

The method according to claim 1, further comprising:
performing permeability measurements for effective stress range between 500 psi and 9000 psi;
plotting the permeability measurements as a function of the effective stress for the core sample with micro-fractures; and
determining the fracture closure stress from the plot.

### Claim 5 (depends on 1)

The method according to claim 1, wherein the unloading effective stress and fracture closure stress are vertical stresses or normal stresses for the induced micro-fracture.

### Claim 6 (depends on 1)

The method according to claim 1, wherein determining the fracture closure stress further comprises determining the stress corresponding to transition from a more-stress-sensitive first stage to a less-stress-sensitive second stage.

### Claim 7 (depends on 1)

The method according to claim 1, wherein operating the well system to inhibit impact of micro-fractures in the wellbore further comprises correcting the effect of micro-fracture on the permeability measurements of the core sample, and determining a true permeability as a function of stress.

### Claim 8 (depends on 1)

The method according to claim 1, further comprising:
in response to determining that the subsurface formation is susceptible to micro-fractures, determining a threshold drilling fluid density, wherein operating the well to inhibit the occurrence of micro-fractures comprises circulating, into the wellbore, drilling fluids having a fluid density that is equal to or less than the threshold drilling fluid density.

### Claim 9

A non-transitory computer readable storage medium comprising program instructions stored thereon that are executable by a processor to perform the following operations:
determining an unloading effective stress (σul) in a formation sample taken from a wellbore drilled into a subsurface formation;
determining a fracture closure stress (σcl) of the formation sample;
determining that the unloading effective stress (σul) is greater than or equal to the fracture closure stress (σul);
in response to determining that unloading effective stress (σul) is greater than or equal to the fracture closure stress (σul), operating the well system to inhibit impact of micro-fractures in the wellbore;
performing permeability measurements for effective stress range between 500 psi and 9000 psi;
plotting the permeability measurements as a function of the effective stress for the core sample with micro-fractures; and
determining the fracture closure stress from the plot.

### Claim 10

A hydrocarbon production well system, comprising:
a well system; and
a well control system configured to perform the following operations:
determining an unloading effective stress (σul) in a formation sample taken from a wellbore drilled into a subsurface formation;
determining a fracture closure stress (σcl) of the formation sample;
determining that the unloading effective stress (σul) is greater than or equal to the fracture closure stress (σul);
in response to determining that unloading effective stress (σul) is greater than or equal to the fracture closure stress (σul), operating the well system to inhibit impact of micro-fractures in the wellbore, wherein operating the well to inhibit impact of micro-fractures comprises circulating, into the wellbore, oil based drilling fluids.

### Claim 11 (depends on 10)

The system according to claim 10, wherein the unloading effective stress is equal to the effective stress in a reservoir or the difference between an overburden pressure and a pore pressure.

### Claim 12 (depends on 10)

The system according to claim 10, wherein the unloading effective stress is greater than the difference between an overburden pressure and a mud pressure at a coring depth.

### Claim 13 (depends on 10)

The system according to claim 10, further comprising:
performing permeability measurements for effective stress range between 500 psi and 9000 psi;
plotting the permeability measurements as a function of the effective stress for the core sample with micro-fractures; and
determining the fracture closure stress from the plot.

### Claim 14 (depends on 10)

The system according to claim 10, wherein the unloading effective stress and fracture closure stress are vertical stresses or normal stresses for the induced micro-fracture.

### Claim 15 (depends on 10)

The system according to claim 10, wherein determining the fracture closure stress further comprises determining the stress corresponding to transition from a more-stress-sensitive first stage to a less-stress-sensitive second stage.

### Claim 16 (depends on 10)

The system according to claim 10, wherein operating the well system to inhibit impact of micro-fractures in the wellbore further comprises correcting the effect of micro-fracture on the permeability measurements of the core sample, and determining a true permeability as a function of stress.

### Claim 17 (depends on 10)

The system according to claim 10, further comprising:
in response to determining that the subsurface formation is susceptible to micro-fractures, determining a threshold drilling fluid density, wherein operating the well to inhibit the occurrence of micro-fractures comprises circulating, into the wellbore, drilling fluids having a fluid density that is equal to or less than the threshold drilling fluid density.