Method for determining content of lost gas in shale gas content test

Patent metadata

Field	Value
Publication number	US-11435336-B2
Application number	US-202016750076-A
Country	US
Kind code	B2
Filing date	Jan 23, 2020
Priority date	Jan 28, 2019
Publication date	Sep 6, 2022
Grant date	Sep 6, 2022

Abstract

The present invention discloses a method for determining a content of lost gas in a shale gas content test. The method includes: acquiring a shale core and recording the time required for acquiring the shale core; carrying out a desorption experiment on the shale core to obtain desorption data; acquiring a fitting objective function; fitting the desorption data by using the fitting objective function to obtain fitted desorption data; determining fitting parameters according to the desorption data and the fitted desorption data; correcting the time required for acquiring the shale core according to the fitting parameters; and obtaining the content of lost gas according to the fitting parameters and the corrected time required for acquiring the shale core. The present invention can improve the determining precision of the content of the lost gas.

First claim

What is claimed is:

1. A method for determining a content of lost gas in a shale gas content test, comprising:
acquiring a shale core and recording time required for acquiring the shale core;
carrying out a desorption experiment on the shale core to obtain desorption data;
acquiring a fitting objective function;
fitting the desorption data by using the fitting objective function to obtain fitted desorption data;
determining fitting parameters according to the desorption data and the fitted desorption data;
correcting the time required for acquiring the shale core according to the fitting parameters; and
obtaining the content of lost gas according to the fitting parameters and the corrected time required for acquiring the shale core,
wherein the time required for acquiring the shale core is corrected by using formula

t
0

¯

=

k
⁢

t
0

+

p
0

p
w

⁢

t
0

,

wherein t 0 is the corrected time required for acquiring the shale core, k is a depressurization rate in the process of acquiring the shale core, p 0 is a local atmospheric pressure, p w is a mud water column pressure, and t 0 is the time required for acquiring the shale core.

2. The method for determining a content of lost gas in a shale gas content test according to claim 1 , wherein the carrying out a desorption experiment on the shale core to obtain desorption data comprises:
putting the shale core into a desorption canister and discharging air in a dead volume of the desorption canister;
sealing the desorption canister;
heating the sealed desorption canister to a set temperature;
acquiring gas output of the desorption canister every set time and recording current acquisition time until the gas output of the desorption canister is stable; and
obtaining desorption data accord to the gas output of the desorption canister and the corresponding acquisition time.

3. The method for determining a content of lost gas in a shale gas content test according to claim 2 , wherein after the step of carrying out a desorption experiment on the shale core to obtain desorption data, before the step of acquiring a fitting objective function, the method further comprises:
preprocessing the acquisition time in the desorption data, so that a difference between adjacent acquisition time is the set time.

4. The method for determining a content of lost gas in a shale gas content test according to claim 1 , wherein, the fitting objective function is:

Q
=

4
⁢
π
⁢
k

D

⁢

∑

n
=
1

∞

⁢

exp
⁡

(

-
D

⁢

α
n
2

⁢
t

)

-

exp
⁡

(

-
D

⁢

α
n
2

⁢

t
0

)

α
n
4

-

2
⁢
π
⁢
k
⁢
R

D

⁢

∑

n
=
1

∞

⁢

exp
⁡

[

-
D

⁢

α
n
2

⁡

(

t
-

t
0

)

]

⁢

J
2

Assignees

• Univ Tsinghua
• Shanxi Research Institute For Clean Energy Tsinghua Univ

Inventors

• Xu Ruina
• Jiang Peixue
• Zeng Kecheng
• Zhang Fuzhen

Classifications

• E21B45/00

  Measuring the drilling time or rate of penetration · CPC title

• G01N33/241 Primary

  for hydrocarbon content · CPC title

• E21B49/02

  by mechanically taking samples of the soil · CPC title

• E21B47/00

  Survey of boreholes or wells (monitoring pressure or flow of drilling fluid E21B21/08) · CPC title

• E21B49/00 Primary

  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