Indentation method to measure multiple rock properties

1. A method for performing an indentation test on a rock sample, comprising:

measuring load and displacement versus time on an indentation measurement unit, while:

indenting a saturated specimen to full load to generate a line segment 1;

releasing the load on the saturated specimen to generate a line segment 2;

indenting the saturated specimen to full load to generate a line segment 3;

holding the loading until the displacement curve levels off to generate a line segment 4; and

reducing the loading to zero to generate a line segment 5.

2. The method of claim 1 , comprising computing undrained stiffness based, at least in part, on the line segment 2.

3. The method of claim 2 , comprising computing the undrained stiffness (E u *) for a sample that does not show plastic deformation using the equations:

P

=

4

3

⁢

E

u

*

⁢

R

1

2

⁢

h

3

2

⁢

1

E

u

*

=

(

1

-

v

s

2

)

E

s

+

(

1

-

v

p

2

)

E

p

,

wherein E S is the Young's modulus of the indented material, ν S is the Poisson's ratio of the indented material, E P is the Young's modulus of the indenter, and ν P is the Poisson's ratio of the indenter.

4. The method of claim 2 , comprising computing the undrained stiffness (E u *) for a sample that shows plastic deformation using the equations:

E

u

*

=

1

β

⁢

π

2

⁢

S

A

c

,

1

E

u

*

=

(

1

-

v

s

2

)

E

s

+

(

1

-

v

p

2

)

E

p

,

wherein S is the slope of the unloading curve; β is the geometry correction factor of the indentation tip, and A c is the projected contact area calculated as A c =πR C 2 , wherein R C is contact radius at peak load.

5. The method of claim 1 , comprising draining a portion of the rock sample by holding the loading until the displacement versus time levels off.

6. The method of claim 1 , wherein comprising indenting the rock sample with a hemispherical tipped indenter.

7. The method of claim 1 , comprising indenting the rock sample with a flat-tipped indenter.

8. The method of claim 1 , comprising indenting the rock sample with a cone tipped indenter.

9. The method of claim 1 , comprising indenting the rock sample with a Berkovich, cubic corner, Vickers, or Knoop tipped indenter.

10. The method of claim 1 , comprising obtaining the rock sample from cuttings resulting from a wellbore drilling process.

11. The method of claim 1 , obtaining the rock sample from a core sample.

12. A method for performing an indentation test on a rock sample, comprising:

measuring load and displacement versus time on an indentation measurement unit, while:

indenting a saturated specimen to full load to generate a line segment 1;

releasing the load on the saturated specimen to generate a line segment 2;

indenting the saturated specimen to full load to generate a line segment 3;

holding the loading until the displacement curve levels off to generate a line segment 4;

reducing the loading to zero to generate a line segment 5;

computing drained stiffness (E d *) based, at least in part, on the line segment 5; and

computing the drained stiffness (E d *) for a sample that does not show plastic deformation using the equations:

P

=

4

3

⁢

E

d

*

⁢

R

1

2

⁢

h

3

2

⁢

1

E

d

*

=

(

1

-

v

s

2

)

E

s

+

(

1

-

v

p

2

)

E

p

,

wherein E S is the Young's modulus of the indented material, ν S is the Poisson's ratio of the indented material, E P is the Young's modulus of the indenter, and ν P is the Poisson's ratio of the indenter.

13. The method of claim 12 , comprising computing the drained stiffness (E d *) for a sample that shows plastic deformation using the equation:

E

d

*

=

1

β

⁢

π

2

⁢

S

A

c

,

1

E

d

*

=

(

1

-

v

s

2

)

E

s

+

(

1

-

v

p

2

)

E

p

,

wherein S is the slope of the unloading curve; β is the geometry correction factor of the indentation tip, and A c is the projected contact area calculated as A c =πR C 2 , wherein R C is the contact radius at peak load.

14. A method for performing an indentation test on a rock sample, comprising:

measuring load and displacement versus time on an indentation measurement unit, while:

indenting a saturated specimen to full load to generate a line segment 1;

releasing the load on the saturated specimen to generate a line segment 2;

indenting the saturated specimen to full load to generate a line segment 3;

holding the loading until the displacement curve levels off to generate a line segment 4;

reducing the loading to zero to generate a line segment 5;

measuring time from loading to level-off of the displacement versus time (t c ) from line segment 4; and

calculating the diffusivity (c) by the equation c=L c 2 /t c , where

L

c

=

min

⁢

{

H

2

,

L

2

}

,

and H is the total height of the rock sample, and L is the total length of the rock sample.