Determining rock properties

Patent metadata

Field	Value
Publication number	US-9983106-B2
Application number	US-201715463537-A
Country	US
Kind code	B2
Filing date	Mar 20, 2017
Priority date	Apr 13, 2016
Publication date	May 29, 2018
Grant date	May 29, 2018

Abstract

A compressive load is exerted with a test apparatus across a rock sample that has a specified length-to-diameter ratio. A strain on the rock sample is measured during the compressive loading with a strain gauge. A mechanical property of the rock sample is determined based at least in part on the compressive load. An elastic property of the rock sample is determined based at least in part on the measured strain and the compressive load.

First claim

What is claimed is:

1. A method for determining rock properties, comprising:
exerting a compressive load with a test apparatus across a rock sample that comprises a specified length-to-diameter ratio;
measuring, with a strain gauge coupled to a side face of the rock sample, a strain on the rock sample during the compressive loading, the measuring comprising:
measuring an incremental vertical strain on the rock sample during a compressive load increment with a first strain gauge, and
measuring an incremental horizontal strain on the rock sample during the compressive load increment with a second strain gauge;

determining, based at least in part on the compressive load, a mechanical property of the rock sample;
determining a first coefficient based at least in part on the diameter of the rock sample and the length of the rock sample;
determining a second coefficient based at least in part on the diameter of the rock sample and the length of the rock sample;
determining a third coefficient based at least in part on the diameter of the rock sample, the length of the rock sample, and the effective length of the first and second strain gauges;
determining a fourth coefficient based at least in part on the diameter of the rock sample, the length of the rock sample, and the effective length of the first and second strain gauges; and
determining, based at least in part on the measured incremental horizontal and vertical strains on the rock sample, the first and second coefficients, and the compressive load, an elastic property of the rock sample.

2. The method of claim 1 , wherein the specified length-to-diameter ratio is between 0.2 and 0.75.

3. The method of claim 1 , wherein the test apparatus comprises a Brazilian test apparatus.

4. The method of claim 1 , wherein determining, based at least in part on the measured strain and the compressive load, the elastic property of the rock sample comprises determining a Young's modulus of the rock sample based on:

E
=

P

π
⁢

⁢

ɛ
ly

⁢
Rt

⁡

[

C
3

+

C
4

⁢
v

]

,

where E is Young's modulus of the rock sample, P is a compressive pressure, R is a disc radius, t is a disc thickness, ε ly is a measured radial strain, v is a stress dependent Poisson's ratio, C 3 is the third coefficient, and C 4 is the fourth coefficient.

5. The method of claim 1 , wherein determining, based at least in part on the measured strain and the compressive load, the elastic property of the rock sample comprises determining Poisson's ratio of the rock sample based on:

v
=

-

C
3

⁢

ɛ
lx

+

C
1

⁢

ɛ
ly

C
2

⁢

ɛ
ly

+

C
4

⁢

ɛ
lx

,

where υ is Poisson's ratio of the rock sample, C 1 is the first coefficient, C 2 is the second coefficient, C 3 is the third coefficient, C 4 is the fourth coefficient, ε lx is a measured axial strain, and ε ly is a measured radial strain.

6. The method of claim 1 , further comprising determining the first, second, third, and fourth coefficients based on:

(
i
)

⁢

⁢

C
1

=

2

1
+

r
lx
2

-

2

r
lx

⁢

tan

-
1

⁢

r
lx

+
1

;

(
ii
)

⁢

⁢

C
2

=

2

1
+

r
lx
2

+

2

Assignees

• Saudi Arabian Oil Co

Inventors

• Han Yanhui
• Lai Bitao
• Liu Hui-Hai
• Li Hui

Classifications

• G01N33/24

  Earth materials (G01N33/42 takes precedence) · CPC title

• G01N3/08 Primary

  by applying steady tensile or compressive forces (G01N3/28 takes precedence) · CPC title

• E21B49/00

  Testing the nature of borehole walls; Formation testing; Methods or apparatus for obtaining samples of soil or well fluids, specially adapted to earth drilling or wells · CPC title

• G01N2203/0019

  Compressive · CPC title

• G01N2203/0252

  Monoaxial, i.e. the forces being applied along a single axis of the specimen · CPC title