Method for proppant suspension and suspension parameter optimization based on bubble bridge effect
The present invention discloses a method for proppant suspension and suspension parameter optimization based on bubble bridge effect, comprising: select a proppant and hydrophobically modify its surface to obtain a hydrophobically surface-modified proppant; prepare a bubbly fracturing base fluid; make the first optimization of the base fluids according to the average radius of the proppant and the average radius of the bubbles of the base fluids; optimally select the base fluids selected for the second time according to the interaction energy between the proppant particle and the bubble after the hydrophobically surface-modified proppant mixed with the base fluid; the basic parameters of the bubbly fracturing base fluid selected at the third time were used for the perfect selection for proppant suspension. The present invention establishes a procedure on experimental evaluation and parameter calculation optimization by suspending fracturing proppant with the bubble bridge effect on the hydrophobic surface.
1. A method for proppant suspension parameter optimization based on bubble bridge effect, comprising the following steps:
Selecting a proppant and measuring its average particle size to obtain the average radius of the selected proppant;
Hydrophobically modifying the surface of the selected proppant to obtain a hydrophobically surface-modified proppant;
Preparing a water-based fracturing base fluid, injecting nitrogen into the base fluid, and stirring the base fluid to cause uniform bubbles to obtain a bubbly water-based fracturing base fluid;
Selecting a basic parameter of the bubbly water-based fracturing base fluid as a proppant suspension parameter for optimization, and preparing the bubbly water-based fracturing base fluid with different values of the basic parameter;
Measuring a Zeta potential of the bubbly water-based fracturing base fluid with different basic parameter values, and taking pictures of bubbles of each base fluid with a camera to obtain the average radius of the bubbles of each base fluid by image analysis;
Selecting a first optimization of the base fluids according to the average radius of the proppant and the average radii of the bubbles of the base fluids, wherein the first optimization includes calculating the ratio of the average radius of the proppant to the average radii of the bubbles of the base fluid; wherein the base fluids with a ratio in the range of 0.5-2 are the base fluids selected at the first optimization;
Preparing an electrolyte solution with the same pH as that of each base fluid selected at the first optimization, putting the hydrophobically surface-modified proppant into the electrolyte solution, and determining the Zeta potential of the hydrophobically surface-modified proppant in each electrolyte solution;
On the basis of the extended DLVO theory, calculating an interaction energy between the proppant particle and the bubble after the hydrophobically surface-modified proppant is mixed with the base fluids selected at the first optimization;
Optimally selecting the base fluids selected for a second optimization according to the interaction energy, wherein the second optimization comprises comparing the interaction energy of each base fluid, wherein the base fluids with relatively stronger hydrophobic attraction between the proppant particle and the bubble are the base fluids selected at the second optimization;
Putting the hydrophobically surface-modified proppant into each base fluid selected at the second optimization and strring them; wherein under the control of the interaction energy between the hydrophobic surface of the proppant and the bubble, the proppant particles are connected and aggregated through the bubble bridge effect into proppant-bubble aggregates; meanwhile, taking pictures of the proppant-bubble-proppant aggregation with the camera, determining a coefficient of bonding ratio between the proppant particle and the bubble through image observation and statistical analysis, and calculating an apparent density of the proppant-bubble aggregates; and
Optimally selecting the base fluids selected for the third optimization according to the apparent density of proppant-bubble aggregates, wherein the third optimization comprises sorting out proppant-bubble aggregates with an apparent density in the range of 0.91.1 g/cm3; wherein the base fluids corresponding to the sorted-out proppant-bubble aggregates are the base fluids selected at the third optimization;
wherein the basic parameters of the bubbly fracturing base fluid selected at the third optimization are the optimized proppant suspension parameters.
2. The method for proppant suspension parameter optimization based on bubble bridge effect according to claim 1 , wherein the proppant surface was hydrophobically modified by coating the proppant surface with an organic liquid suspending agent with hydrophobic effect.
3. The method for proppant suspension parameter optimization based on bubble bridge effect according to claim 1 , wherein the basic parameter of the bubbly fracturing base fluid includes pH value, salinity, Zeta potential, bubble size, amount of treating agent added, or volume of gas injected.
4. The method for proppant suspension parameter optimization based on bubble bridge effect according to claim 1 , wherein the interaction energy between the proppant particle and the bubble includes Van der Waals interaction energy, repulsive potential energy of the electric double layer, hydrophobic interaction force, and hydration repulsive force.
5. The method for proppant suspension parameter optimization based on bubble bridge effect according to claim 4 , wherein the interaction energy between the proppant particle and the bubble is calculated by the following equation:
Φ T =Φ LVD +Φ EDL +Φ HA +Φ HR (1)
Where, Φ T is the interaction energy between the proppant particle and the bubble, in J; Φ LVD is the Van der Waals interaction energy between the proppant particle and the bubble, in J; Φ EDL is the repulsive potential energy of the electric double layer between the proppant particle and the bubble, in J; Φ HA is the hydrophobic interaction force between the proppant particle and the bubble, in J; Φ HR is the hydration repulsive force between the proppant particle and the bubble, in J;
Where, the Van der Waals interaction energy is calculated by the following equation:
Φ
L
V
D
=
-
A
132
6
D
(
R
1
R
2
R
1
+
R
2
)
(
2
)
Where, A 132 is the Hamaker constant of the interaction between the proppant particle and the bubble in the base fluid, in J; D is the interaction distance between the proppant particle surface and the bubble surface, in m; R 1 and R 2 are the average values of proppant particles and bubbles, respectively, in m;
The repulsive potential energy of the electric double layer is calculated by the following equation:
Φ
E
D
L
=
π
ε
r
ε
0
R
1
R
2
R
1
+
R
2
{
2
ζ
1
ζ
2
ln
[
1
+
exp
(
-
κ
D
)
1
-
exp
(
-
κ
D
)
]
+
(
ζ
1
2
+
ζ
2
2
)
ln
[
1
-
exp
(
-
2
κ
D
)
]
}
(
3
)
Where: ε r is the relative permittivity, taken as 81.5 for aqueous solution; ε 0 is the permittivity in vacuum, taken as 8.854×10 −12 CV −1 m −1 ; ζ 1 and ζ 2 are the Zeta potentials of the proppant particle and the bubble, respectively, in V; κ is the reciprocal value of the Debye length, in m −1 ;
The hydrophobic interaction force is calculated by the following equation:
Φ
H
A
=
2
π
R
1
R
2
R
1
+
R
2
h
0
1
V
H
A
0
exp
(
-
D
h
0
1
)
(
4
)
Where, h 01 is the attenuation length of the hydrophobic interaction force, in m; V0 HA is the hydrophobic interaction energy constant between the proppant particle surface and the bubble, in J/m 2 ;
The hydration repulsive force is calculated by the following equation:
Φ
H
R
=
2
π
R
1
R
2
R
1
+
R
2
h
02
V
H
R
0
exp
(
-
D
h
02
)
(
5
)
Where, h 02 is the attenuation length of the hydration interaction force, in m; V0 HR is the hydration interaction energy constant between the proppant particle surface and the bubble, in J/m 2 .
6. The method for proppant suspension parameter optimization based on bubble bridge effect according to claim 1 , wherein the apparent density of the proppant-bubble aggregates was calculated by the following equation:
ρ
a
=
ρ
1
R
1
3
+
k
ρ
2
R
2
3
R
1
3
+
k
R
2
3
(
6
)
Where, ρ a is the apparent density of proppant-bubble aggregates, in g/cm 3 ; ρ 1 is the density of proppant particles, in g/cm 3 ; R 1 is the average radius of the proppant particles, in m; κ is the coefficient of bonding ratio between the proppant particle and the bubble in aggregates, causeless; ρ 2 is the density of the bubbles, in g/cm 3 ; R 2 is the average radius of the bubbles, in m.
7. A method for proppant suspension based on bubble bridge effect, comprising the following steps:
Selecting a proppant and hydrophobically modifying its surface to obtain a hydrophobically surface-modified proppant;
Optimally selecting the suspension parameters of the proppant according to the methods for proppant suspension parameter optimization based on bubble ridge effect in claim 1 ;
Preparing a bubbly water-based fracturing base fluid based on the results of the proppant suspension parameter optimization; and
Mixing the hydrophobically surface-modified proppant with the bubbly fracturing base fluid to obtain a proppant suspension fracturing fluid that forms a gas-liquid-solid mixed system.