Method and device for predicting ability of the temporary plugging agent to plug cracks and storage medium
The present disclosure relates to a method and a device for predicting ability of a temporary plugging agent to plug cracks and a storage medium, and includes the following steps: calculating a plane elastic modulus of a core through experiments, acquiring a maximum force load of a specimen, calculating rock fracture toughness through the maximum force load, manufacturing an artificial crack model and placing it in a core holder, preparing temporary plugging deflection fluid by selecting a temporary plugging agent, injecting the temporary plugging deflection fluid into the artificial crack so as to calculate apparent fracture toughness of the temporarily plugged crack, and finally calculating a fracture pressure of the temporarily plugged crack based on the calculated rock fracture toughness and the plane elastic modulus of the core. Through the above method, the present disclosure provides a standard fracture pressure calculation method.
1 . A method for predicting ability of a temporary plugging agent to plug cracks, comprising:
acquiring an elastic modulus E and a Poisson's ratio v of a core through experiments, and acquiring a plane elastic modulus E′ of the core through the elastic modulus E and the Poisson's ratio v;
prefabricating an initial crack with a certain length on a fracture toughness specimen to acquire a maximum force load P max of the fracture toughness specimen;
acquiring rock fracture toughness K IC through the length of the initial crack and the maximum force load P max ;
preparing an artificial crack model with a crack width of w and a crack height of H, and placing the artificial crack model in a core holder;
preparing temporary plugging deflection fluid by selecting any temporary plugging agent, applying a confining pressure Pc to the core holder, injecting the prepared temporary plugging deflection fluid into the crack with the width of w in the artificial crack model in the core holder at a certain rate, and temporarily plugging the crack;
acquiring the thickness w c of a filter cake forming a temporary plugging body in the crack with the width of w, and calculating apparent fracture toughness
k
p
c
of the temporarily plugged crack through the rock fracture toughness K IC , the plane elastic modulus E′ of the core, the thickness w c of the filter cake and the confining pressure Pc;
acquiring a fracture pressure
p
tip
c
of the temporarily plugged crack through the apparent fracture toughness
k
p
c
and the crack height H, and predicting the ability of the selected temporary plugging agent to plug cracks by the fracture pressure
p
tip
c
of the temporarily plugged crack.
2 . The method according to claim 1 , wherein
preparing an artificial crack model with a crack width of w and a crack height of H comprises:
selecting an initial rock mass of a cylinder or a cube with a height of H, preparing an artificial initial crack at the top or bottom of the initial rock mass, dividing the initial rock mass into two fractured rock masses through the artificial initial crack, arranging a filler strip with a thickness of w on both sides of the fractured plane of any fractured rock mass, respectively, and attaching the two fractured rock masses along the fractured plane to restore the initial rock mass, wherein due to the existence of the filler strip, there are cracks with a width of w and a height of H on the initial rock mass, so as to obtain the artificial crack model with the crack width of w and the crack height of H.
3 . A storage medium, wherein a computer program is stored in the storage medium, and the computer program, when being executed by a master controller, implements each step in the method for predicting ability of the temporary plugging agent to plug cracks according to claim 1 .
4 . The method according to claim 1 , wherein
the formula of calculating the plane elastic modulus E′ of the core is:
E
′
=
E
1
-
ν
2
where E denotes the elastic modulus of the core, and v denotes the Poisson's ratio.
5 . The method according to claim 4 , wherein
prefabricating an initial crack with a certain length on a fracture toughness specimen to acquire a maximum force load P max of the fracture toughness specimen comprises the following steps:
preparing a standard-shaped fracture toughness specimen, prefabricating an initial crack with a certain length at the bottom of the standard-shaped fracture toughness specimen, placing the bottom of the standard-shaped fracture toughness specimen on two support points at a certain distance for loading until the standard-shaped fracture toughness specimen fractures along the initial crack at the bottom, and acquiring the maximum force load P max of the standard-shaped fracture toughness specimen.
6 . The method according to claim 5 , wherein
the standard-shaped fracture toughness specimen comprises a semi-disk SCB fracture toughness specimen and a cube or cuboid fracture toughness specimen;
the formula of calculating the rock fracture toughness K IC of the semi-disk SCB fracture toughness specimen is:
K
IC
=
P
max
π
a
2
RB
Y
*
where K IC denotes rock fracture toughness; B denotes the thickness of the semi-disk SCB fracture toughness specimen; P max denotes the maximum force load of the semi-disk SCB fracture toughness specimen; a denotes the length of the initial crack prefabricated at the bottom of the semi-disk SCB fracture toughness specimen; R denotes the radius of the semi-disk SCB fracture toughness specimen; π denotes pi; and Y* is a dimensionless number;
the formula of calculating the dimensionless number Y* is:
Y
*
=
-
1
.
2
9
7
+
9
.
5
1
6
S
2
R
-
(
0
.
4
7
+
1
6
.
4
5
7
S
2
R
)
β
+
(
1
.
0
7
1
+
3
4
.
4
0
1
S
2
R
)
β
2
where β=a/R, S denotes the distance between two support points;
the formula of calculating the rock fracture toughness K IC of the cube or cuboid fracture toughness specimen is as follows:
K
IC
=
P
max
D
1.5
Y
*
where K IC denotes the rock fracture toughness; D denotes the height of the cube or cuboid fracture toughness specimen; P max denotes the maximum force load of the cube or cuboid fracture toughness specimen; and Y* is a dimensionless number;
the formula of calculating the dimensionless number Y* is as follows:
Y
*
=
[
1
.
8
3
5
+
7
.
1
5
a
0
D
+
9
.
8
5
(
a
0
D
)
2
]
S
D
where a 0 denotes the length of the prefabricated initial crack at the bottom of the cube or cuboid fracture toughness specimen, and S denotes the distance between two support points.
7 . The method according to claim 5 , wherein
preparing temporary plugging deflection fluid by selecting any temporary plugging agent comprises:
selecting a mass concentration of 0.3% guar gum +0.15% crosslinking regulator +0.02% citric acid +0.3% crosslinking agent +0.5% any temporary plugging agent +98.73% water, and uniformly stirring for a period of time to form temporary plugging deflection fluid.
8 . The method according to claim 7 , wherein
the formula of calculating the apparent fracture toughness
k
p
c
of the temporarily plugged crack is:
k
p
c
=
K
IC
2
+
(
K
IC
2
)
2
+
E
′
w
c
P
c
2
where
k
p
c
is the apparent fracture toughness of the temporarily plugged crack, K IC denotes the rock fracture toughness, E′ denotes the plane elastic modulus of the core, P c denotes the applied confining pressure, and w c denotes the thickness of filter cake.
9 . The method according to claim 8 , wherein
the formula of calculating the fracture pressure
p
tip
c
of the temporarily plugged crack is:
p
tip
c
=
coeff
×
k
p
c
2
×
π
0.5
H
-
σ
H
where H denotes the crack height of the artificial crack model,
k
p
c
denotes the apparent fracture toughness of the temporarily plugged crack, σ H denotes the magnitude of a horizontal principal stress, σ H =P c +P p , where P c denotes the applied confining pressure, P p denotes a pore pressure, the pore pressure P p of a stratum is a constant value, and coeff denotes a fitting coefficient.
10 . A device for predicting ability of a temporary plugging agent to plug cracks, comprising:
a plane elastic modulus acquiring module, which is configured to acquire an elastic modulus E and a Poisson's ratio v of a core through experiments, and acquire a plane elastic modulus E′ of the core through the elastic modulus E and the Poisson's ratio v;
a maximum force load acquiring module, which is configured to prefabricate an initial crack with a certain length on a fracture toughness specimen to acquire a maximum force load P max of the fracture toughness specimen;
a rock fracture toughness acquiring module, which is configured to acquire rock fracture toughness K IC through the length of the initial crack, geometric parameters of the fracture toughness specimen and the maximum force load P max ;
an artificial crack model preparing module, which is configured to prepare an artificial crack model with a crack width of w and a crack height of H, and place the artificial crack model in a core holder;
an artificial crack temporary plugging module, which is configured to prepare temporary plugging deflection fluid by selecting any temporary plugging agent, apply a confining pressure Pc to the core holder, inject the prepared temporary plugging deflection fluid into the crack with the width of w in the artificial crack model in the core holder at a certain rate, and temporarily plug the crack;
an apparent fracture toughness acquiring module, which is configured to acquire the thickness w c of a filter cake forming a temporary plugging body in the crack with the width of w, and calculate apparent fracture toughness
k
p
c
of the temporarily plugged crack through the rock fracture toughness K IC , the plane elastic modulus E′ of the core, the thickness w c of the filter cake and the confining pressure Pc;
a judging module, which is configured to acquire a fracture pressure
p
tip
c
of the temporarily plugged crack through the apparent fracture toughness
k
p
c
and the crack height H, and predict the ability of the selected temporary plugging agent to plug cracks by the fracture pressure
p
tip
c
of the temporarily plugged crack.