Determining rock properties

Patent metadata

Field	Value
Publication number	US-10254207-B2
Application number	US-201715830853-A
Country	US
Kind code	B2
Filing date	Dec 4, 2017
Priority date	Apr 13, 2016
Publication date	Apr 9, 2019
Grant date	Apr 9, 2019

Abstract

Techniques for determining rock properties include exerting a compressive load with a test apparatus across a rock sample that includes a specified length-to-diameter ratio; measuring, with a strain gauge, a strain on the rock sample during the compressive loading; determining, based at least in part on the compressive load, a mechanical property of the rock sample; and determining, based at least in part on the measured strain and the compressive load, an elastic property of the rock sample.

First claim

What is claimed is:

1. A method for determining rock properties, comprising:
exerting a compressive load with a Brazilian test apparatus across a rock sample that comprises a specified length-to-diameter ratio;
measuring, with the Brazilian test apparatus, an indirect tensile strength of the rock sample based on the compressive load;
measuring, with a strain gauge, a strain on the rock sample during the compressive loading;
determining, based at least in part on the compressive load, a mechanical property of the rock sample; and
determining, based at least in part on the measured strain 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 strain gauge is coupled to an axial surface of the rock sample.

4. The method of claim 3 , wherein measuring a strain on the rock sample during the compressive loading comprises:
measuring an incremental axial strain on the rock sample during a compressive load increment with a first strain gauge; and
measuring an incremental radial strain on the rock sample during the compressive load increment with a second strain gauge.

5. The method of claim 4 , 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 at least one of:
(i)

E
=

Δ
⁢

⁢
P

Δɛ
x

⁢

(

-
F

+

v
⁢

⁢
G

)

,

where E is stress dependent Young's modulus of the rock sample, ΔP is a compressive loading increment, Δε x is an incremental radial strain, υ is Poisson's ratio of the rock sample, F is a first coefficient, and G is a second coefficient; or
(ii)

E
=

P

ɛ
x

⁢

(

-
F

+

v
⁢

⁢
G

)

,

where E is Young's modulus of the rock sample, P is a particular compressive load, ε x is a radial strain at the particular compressive load, υ is Poisson's ratio of the rock sample, F is the first coefficient, and G is the second coefficient.

6. The method of claim 4 , 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 at least one of:
(i)

υ
=

(

Δɛ
x

Δɛ
y

)

⁢
G

+
F

(

Δɛ
x

Δɛ
y

)

⁢
F

+
G

,

where υ is stress dependent Poisson's ratio of the rock sample, Δε x is an incremental radial strain, Δε y is an incremental axial strain, F is a first coefficient, and G is a second coefficient; or
(ii)

υ
=

(

ɛ
x

ɛ
y

)

⁢
G

+
F

(

ɛ
x

ɛ
y

)

⁢
F

+
G

,

where υ is Poisson's ratio of the rock sample, ε x is a radial strain at a particular compressive load on the rock sample, ε y is an axial strain at the particular compressive load on the rock sample, F is the first coefficient, and G is the second coefficient.

7. The method of claim 1 , wherein the mechanical property comprises at least one of a tensile strength or a brittleness of the rock sample.

8. The method of claim 1 , wherein the strain gauge comprises a linear variable differential transformer (LVDT).

9. A rock property test system, comprising:
a load cell configured

Assignees

• Saudi Arabian Oil Co

Inventors

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

Classifications

• G01N2203/0087

  Resistance to crushing · CPC title

• G01N2203/0075

  Strain-stress relations or elastic constants · CPC title

• 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