Methods and systems for determining gas permeability of a subsurface formation

Patent metadata

Field	Value
Publication number	US-10401274-B2
Application number	US-201615378305-A
Country	US
Kind code	B2
Filing date	Dec 14, 2016
Priority date	Dec 14, 2015
Publication date	Sep 3, 2019
Grant date	Sep 3, 2019

Abstract

Methods and systems for determining permeability, as a function of pore pressure, and porosity of a subsurface formation. The method includes positioning a sample in a sample assembly comprising of a gas and a pressure gauge, inside a pressure vessel comprising gas or liquid and a pressure gauge, measuring a first gas pressure, pi, of the sample inside the pressure vessel, applying a second gas pressure, po, to the pressure vessel, the second gas pressure being greater than the first gas pressure, measuring a third gas pressure, p, at time, t, at location, x, from the inlet of sample inside the pressure vessel, determining a total gas mass per unit volume of the subsurface formation, m, and determining the permeability, k, of the subsurface formation as a function of pore pressure based at least in part on the first gas pressure, the second pressure, the third gas pressure, and the gas density, with a single test run.

First claim

The invention claimed is:

1. A transient flow method for determining gas permeability of a subsurface formation, comprising:
acquiring a sample of the subsurface formation;
positioning the sample in a pressure vessel comprising a fluid and a pressure gauge;
equilibrating the sample at a predetermined first pore gas pressure, p i ;
applying a predetermined constant second pore gas pressure, p o , to an inlet of the sample, the second pore gas pressure being greater than the first pore gas pressure;
measuring a third pore gas pressure, p, as a function of time, t, at location, x, along the axis of the sample in the pressure vessel, wherein the location, x, is at a predetermined distance from the inlet of the sample;
in a computer, determining a gas density or total gas mass per unit volume of the subsurface formation, m; and
in the computer, determining the gas permeability of the subsurface formation as a function of pore pressure, k(p), based at least in part on the first pore gas pressure, the second pore gas pressure, the third pore gas pressure as a function of time, and the gas density as a function of pore pressure, with a single test run.

2. The method of claim 1 , wherein the subsurface formation comprises at least one of shale, limestone, and sandstone.

3. A transient flow method for determining gas permeability of a subsurface formation, comprising:
acquiring a sample of the subsurface formation;
positioning the sample in a pressure vessel comprising a fluid and a pressure gauge;
equilibrating the sample at a predetermined first pore gas pressure, p i ;
applying a predetermined constant second pore gas pressure, p o , to an inlet of the sample, the second pore gas pressure being greater than the first pore gas pressure;
measuring a third pore gas pressure, p, as a function of time, t, at location, x, along the axis of the sample in the pressure vessel, wherein the location, x, is at a predetermined distance from the inlet of the sample;
in a computer, determining a gas density or total gas mass per unit volume of the subsurface formation, m;
in the computer, determining the gas permeability of the subsurface formation as a function of pore pressure, k(p), based at least in part on the first pore gas pressure, the second pore gas pressure, the third pore gas pressure as a function of time, and the gas density as a function of pore pressure, with a single test run; and
determining a transport parameter of the subsurface formation, D(p), using a first formula:

D
⁡

(
p
)

=

-

∫

p
i

p

⁢

λ
2

⁢

dm
dp

⁢
dp

dp

d
⁢

⁢
λ

where λ is an independent variable calculated using the formula λ=xt −1/2 ; and
determining gas permeability k of the subsurface formation from D(p) using

D
⁡

(
p
)

=

k
⁢

⁢
ρ

μ

where μ stands for gas viscosity, and ρ for gas density.

4. The method of claim 3 , further comprising:
determining the total gas mass per unit volume of the subsurface formation, m, using a second formula:
m =ϕρ+(1−ϕ)ρ a

where Φ is porosity of the subsurface formation, ρ is gas density of the gas, and ρ a is adsorbed gas mass per unit volume of the subsurface formation.

5. The method of claim 4 , further comprising:
determining the porosity Φ of the subsurface formation using a third formula:

ϕ
=

B
-

A
⁢

∫

p
i

p
0

⁢

λ
⁢

d
⁢

⁢

ρ
a

dp

⁢
dp

A
⁢

∫

p
i

p
0

⁢

λ
⁢

d
⁡

(

ρ
-

ρ
a

)

dp

⁢
dp

where A is a cross-sectional area of the sample, and B is a slope of a curve of the cumulative gas flow into the sample at x=0 versus t 1/2 .

6. The method of claim 5 , further comprising:
determining the slope of the curve, B, using a fourth formula:

B
=

A
⁢

Assignees

• Saudi Arabian Oil Co

Inventors

• Liu Hui-Hai
• Lai Bitao
• Zhang Jilin Jay
• Georgi Daniel
• Huang Xinwo

Classifications

• G01N15/0826 Primary

  and measuring fluid flow rate, i.e. permeation rate or pressure change · CPC title

• G01N33/24

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