Foam fracturing fluid with double interface layers of a phlogisticated air-liquid CO2 for shale gas production and preparation method thereof

Abstract

The disclosure discloses a foam fracturing fluid with double interface layers of a phlogisticated air-liquid CO.sub.2 for shale gas development, and a preparation method thereof. The foam fracturing fluid is prepared from a liquid CO.sub.2 phase, a gas phase and a nano-enhancer; the liquid CO.sub.2 phase is formed by dissolving a mixture of gas-soluble foaming agents in liquid CO.sub.2; the gas phase is a gas mixture of phlogisticated air and saturated vapor of the liquid CO.sub.2; the nano-enhancer is an aqueous solution of a mixture of hydrophobic silica nanoparticles, a cosolvent and a water-soluble surfactant. In the fracturing fluid prepared by the present disclosure, the phlogisticated air was encapsulated by the liquid CO.sub.2 to form an interface layer, the liquid CO.sub.2 was further encapsulated by the nano-enhancer to form the other interface layer, which enhanced the structural stability of the fracturing fluid while achieving high viscosity and thermal stability.

Claims

1. A foam fracturing fluid with double interface layers of a phlogisticated air-liquid CO.sub.2, wherein, the foam fracturing fluid is prepared from a liquid CO.sub.2 phase, a gas phase and a nano-enhancer; wherein, the phlogisticated air is air with a content of oxygen being 5% by volume; the double interface layers of the foam fracturing fluid refers to an interface layer formed by encapsulating the phlogisticated air with the liquid CO.sub.2 and the other interface layer formed by encapsulating the liquid CO.sub.2 with the nano-enhancer; the liquid CO.sub.2 phase is formed by dissolving a mixture of gas-soluble foaming agents in liquid CO.sub.2; the mixture of gas-soluble foaming agents is a mixture comprising at least two of 2-trifluoromethane-3-methoxydecafluoropentane, 3-ethoxytridecafluorohexane, fluorobutane ethyl ether, fluorobutane methyl ether and 1,1,2,2-tetrafluoroethyl-2,2,3,3-tetrafluoropropyl ether; an initial volume concentration of the mixture of gas-soluble foaming agents in the liquid CO.sub.2 phase is 0.2% to 2.0% by volume; the gas phase is a gas mixture of phlogisticated air and saturated vapor of the liquid CO.sub.2; the nano-enhancer is an aqueous solution of hydrophobic silica nanoparticles, a cosolvent and a mixture of water-soluble surfactants; wherein, the cosolvent is a solvent that solubilizes the hydrophobic silica nanoparticles; the hydrophobic silica nanoparticles are modified by silanol groups, and a density of the silanol groups is 0.3 to 0.5/nm.sup.2, a wetting angle of the hydrophobic silica nanoparticles to distilled water is 107 C.125 C., a particle size of the hydrophobic silica nanoparticles is 1040 nm; the cosolvent is ethanol, ethylene glycol or isopropanol; the mixture of water-soluble surfactants is a mixture of sodium bis(2-ethylhexyl) sulfosuccinate and sodium -sulfofatty acid methyl ester.

2. The foam fracturing fluid according to claim 1, wherein foam quality of the foam fracturing fluid is 40% to 90%; wherein, the foam quality refers to a percentage of a volume of the gas phase of the foam fracturing fluid to a total volume of the foam fracturing fluid.

3. The foam fracturing fluid according to claim 1, wherein in the gas phase, a gas partial pressure of the phlogisticated air is at least one time as that of the saturated vapor of liquid CO.sub.2.

4. The foam fracturing fluid according to claim 1, wherein the nano-enhancer is composed by the hydrophobic silica nanoparticles with a concentration of 0.4%2.0% by weight, the cosolvent with a concentration of 0.1%0.5% by weight, the mixture of water-soluble surfactants with a concentration of 0.1%0.6% by weight, and the balance of water.

5. The foam fracturing fluid according to claim 3, wherein the nano-enhancer is composed by the hydrophobic silica nanoparticles with a concentration of 0.4%2.0% by weight, the cosolvent with a concentration of 0.1%0.5% by weight, the mixture of water-soluble surfactants with a concentration of 0.1%0.6% by weight, and the balance of water.

6. The foam fracturing fluid according to claim 1, wherein in the foam fracturing fluid, the content of the nano-enhancer is 9% by volume.

7. The foam fracturing fluid according to claim 3, wherein in the foam fracturing fluid, the content of the nano-enhancer is 9% by volume.

8. The foam fracturing fluid according to claim 4, wherein in the foam fracturing fluid, the content of the nano-enhancer is 9% by volume.

9. The foam fracturing fluid according to claim 5, wherein in the foam fracturing fluid, the content of the nano-enhancer is 9% by volume.

10. A preparation method of the foam fracturing fluid according to claim 1, comprising the following steps: 1) preparing the aqueous solution of the hydrophobic silica nanoparticles, the cosolvent and the mixture of water-soluble surfactants so as to obtain the nano-enhancer; 2) injecting the nano-enhancer into a high-pressure agitated autoclave, and then injecting the phlogisticated air to a predetermined pressure; 3) while CO.sub.2 gas is injected into the high-pressure agitated autoclave by a booster pump, injecting the mixture of gas-soluble foaming agents, after stirring, the foam fracturing fluid is obtained.

11. The preparation method according to claim 10, wherein the predetermined pressure is 750 MPa; wherein a Waring Blender method is utilized for stirring, and the stirring is performed for 3 to 8 minutes at a speed of 3000 to 5000 rpm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic diagram of the microstructure and formation mechanism of the foam fracturing fluid with double interface layers of a phlogisticated air-liquid CO.sub.2.

(2) FIG. 2 is a photograph of the foam fracturing fluid with double interface layers of a phlogisticated air-liquid CO.sub.2 prepared in Embodiment 1.

(3) FIG. 3 is a viscosity-temperature curve of the foam fracturing fluid with double interface layers of a phlogisticated air-liquid CO.sub.2 prepared in Embodiment 1.

(4) FIG. 4 is a viscosity-temperature curve of the foam fracturing fluid with double interface layers of a phlogisticated air-liquid CO.sub.2 prepared in Embodiment 2.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(5) The experimental methods used in the following embodiments are conventional methods unless otherwise specified.

(6) The materials, reagents and the like used in the following embodiments are commercially available unless otherwise specified.

Embodiment 1 A Foam Fracturing Fluid with Double Interface Layers of a Phlogisticated Air-Liquid CO.SUB.2 .for Shale Gas Production

(7) The foam fracturing fluid is prepared from a liquid CO.sub.2 phase, a gas phase, a nano-enhancer, wherein:

(8) the liquid CO.sub.2 phase is formed by dissolving a mixture of gas-soluble foaming agents in liquid CO.sub.2, the initial volume concentration of the gas-soluble foaming agents in liquid CO.sub.2 is 0.5% by volume, and the mixture of gas-soluble foaming agents comprising 2-trifluoromethane-3-methoxydecafluoropentane and fluorobutane ethyl ether with a mass ratio of 1:3.3.

(9) The gas phase is composed of phlogisticated air and saturated vapor of the liquid CO.sub.2, the content of oxygen in the phlogisticated air is 4% by volume, and the gas partial pressure of the phlogisticated air is 1.3 times as that of the saturated vapor of the liquid CO.sub.2.

(10) The nano-enhancer is composed by the hydrophobic silica nanoparticles with the concentration of 1.0% by weight, the ethanol with the concentration of 0.2% by weight, the water-soluble surfactant with the concentration of 0.4% by weight, and the balance of water. The density of the silanol groups on the surface of the hydrophobic silica nanoparticles is 0.4/nm.sup.2. A wetting angle of the hydrophobic silica nanoparticles to distilled water is 122. A particle size of the hydrophobic silica nanoparticles is 18 nm. The water-soluble surfactant is a mixture of sodium bis(2-ethylhexyl) sulfosuccinate and sodium -sulfofatty acid methyl ester with a mass ratio of 5:1.

(11) The foam fracturing fluid with double interface layers of a phlogisticated air-liquid CO.sub.2 is prepared as follows:

(12) step 1. dissolving the water-soluble surfactant in water, after adequately stirring, a solution of the water-soluble surfactant was obtained;

(13) step 2. the hydrophobic silica nanoparticles and the cosolvent are uniformly mixed and added into the solution of the water-soluble surfactant, and after adequately stirring, a nano-enhancer was obtained;

(14) step 3. after injecting 60 mL of the nano-enhancer into a high-pressure agitated autoclave with a volume of 1000 mL, injecting the phlogisticated air into the autoclave until the pressure is reached to 8.6 MPa;

(15) step 4. injecting the CO.sub.2 gas into the high-pressure agitated autoclave through a booster pump (the CO.sub.2 gas was pressurized and liquefied below the critical temperature (31.26 C.) and the critical pressure (7.38 MPa) by the booster pump), and gradually increasing the CO.sub.2 injection amount until the total volume of liquid CO.sub.2 and the nano-enhancer in the high-pressure agitated autoclave is reached to about 460 mL, and then injecting 2 mL of the mixture of gas-soluble foaming agents into the high-pressure agitated autoclave;

(16) step 5. the Waring Blender method was utilized for stirring the liquid CO.sub.2 and the nano-enhancer in the high-pressure agitated autoclave, and the stirring was performed for 5 minutes at a stirring speed of 4000 rpm, and the foam fracturing fluid with double interface layers of a phlogisticated air-liquid CO.sub.2 was obtained.

(17) The schematic diagram of the microstructure and formation mechanism of the foam fracturing fluid with double interface layers of a phlogisticated air-liquid CO.sub.2 are shown in FIG. 1. It can be seen that the foam fracturing fluid with double interface layers of a phlogisticated air-liquid CO.sub.2 of the present disclosure has a structure that consisted of the following three parts: a liquid CO.sub.2 phase, a gas phase (gas mixture of phlogisticated air and saturated vapor of the liquid CO.sub.2) and a nano-enhancer. The double interface layers refers to an interface layer formed by encapsulating the phlogisticated air with the liquid CO.sub.2 and the other interface layer formed by encapsulating the liquid CO.sub.2 with the nano-enhancer. The gas-soluble foaming agents can be dissolved in the liquid CO.sub.2 and exhibit good interfacial activity, thereby the gas phase/liquid CO.sub.2 phase interface in the foam fracturing fluid can be stabilized. At the same time, the gas-soluble foaming agents in combination with the hydrophobic silica nanoparticles and the water-soluble surfactant can stabilize the interface of liquid CO.sub.2 phase/nano-enhancer.

(18) A photograph of the foam fracturing fluid with double interface layers of a phlogisticated air-liquid CO.sub.2 prepared in this embodiment is shown in FIG. 2. The foam quality of the foam fracturing fluid is about 56%. The content of the nano-enhancer in the foam fracturing fluid is 6% by volume, and the content of water is only 6% by volume, which means that the water consumption of the fracturing fluid system is low. The foam fracturing fluid is dense and uniform after being formed for 1 min. There is no obvious change of the foam fracturing fluid after standing for 120 min, indicating the stability of foam is high. The viscosity-temperature curve of the foam fracturing fluid was tested by a tube viscometer at a temperature of 5 C.90 C. The shear rate during the test was 170 s.sup.1. The experimental results shown in FIG. 3 indicated the fracturing fluid system has good viscosity-temperature stability, which is due to the viscosity-increasing effect provided by the structure of the double interface layers formed in the foam fracturing fluid of the present disclosure. The viscosity of the fracturing fluid system at a temperature of 5 C.90 C. is 3768 mPa.Math.s, which is much higher than that of the traditional fracturing fluid that using pure liquid CO.sub.2 (that is, using pure liquid CO.sub.2 as a fracturing fluid) (generally 0.020.16 mPa.Math.s).

Embodiment 2: A Foam Fracturing Fluid with Double Interface Layers of a Phlogisticated Air-Liquid CO.SUB.2 .for Shale Gas Production

(19) The foam fracturing fluid is prepared from a liquid CO.sub.2 phase, a gas phase, a nano-enhancer, wherein:

(20) the liquid CO.sub.2 phase is formed by dissolving a mixture of gas-soluble foaming agents in liquid CO.sub.2, the initial volume concentration of the gas-soluble foaming agents in liquid CO.sub.2 is 0.6% by volume, and the mixture of gas-soluble foaming agents comprising 3-ethoxytridecafluorohexane and fluorobutane ethyl ether with a mass ratio of 1:4.5.

(21) The gas phase is composed of phlogisticated air and saturated vapor of the liquid CO.sub.2, the content of oxygen in the phlogisticated air is 4% by volume, and the gas partial pressure of the phlogisticated air is 1.5 times as that of the saturated vapor of the liquid CO.sub.2.

(22) The nano-enhancer is composed by the hydrophobic silica nanoparticles with the concentration of 1.5% by weight, the ethanol with the concentration of 0.25% by weight, the water-soluble surfactant with the concentration of 0.5% by weight, and the balance of water. The density of the silanol groups on the surface of the hydrophobic silica nanoparticles is 0.4/nm.sup.2, a wetting angle of the hydrophobic silica nanoparticles to distilled water is 122, a particle size of the hydrophobic silica nanoparticles is 18 nm; and the water-soluble surfactant is a mixture of sodium bis(2-ethylhexyl) sulfosuccinate and sodium -sulfofatty acid methyl ester with a mass ratio of 5:1.

(23) The foam fracturing fluid with double interface layers of a phlogisticated air-liquid CO.sub.2 is prepared as follows:

(24) step 1. dissolving the water-soluble surfactant in water, after adequately stirring, a solution of the water-soluble surfactant was obtained;

(25) step 2. the hydrophobic silica nanoparticles and the cosolvent are uniformly mixed and added into the solution of the water-soluble surfactant, and after adequately stirring, a nano-enhancer was obtained;

(26) step 3. after injecting 50 mL of the nano-enhancer into a high-pressure agitated autoclave with a volume of 1000 mL at a temperature of 5 C., injecting the phlogisticated air into the autoclave until the pressure is reached to 9.7 MPa;

(27) step 4. injecting the CO.sub.2 gas into the high-pressure agitated autoclave through a booster pump, and gradually increasing the CO.sub.2 injection amount until the total volume of liquid CO.sub.2 and the nano-enhancer in the high-pressure agitated autoclave is reached to about 350 mL, and then injecting 2 mL of the mixture of gas-soluble foaming agents into the high-pressure agitated autoclave;

(28) step 5. the Waring Blender method was utilized for stirring the liquid CO.sub.2 and the nano-enhancer in the high-pressure agitated autoclave, and the stirring was performed for 4 minutes at a stirring speed of 5000 rpm, and the foam fracturing fluid with double interface layers of a phlogisticated air-liquid CO.sub.2 was obtained.

(29) In the foam fracturing fluid with double interface layers of a phlogisticated air-liquid CO.sub.2 prepared in this embodiment, the foam quality of the foam fracturing fluid is about 65%, the content of the nano-enhancer is 5% by volume. The foam fracturing fluid is dense and uniform, and there is no obvious change of the foam fracturing fluid after standing for 120 minutes, good stability can be maintained. The content of water in the foam fracturing fluid is only 5% by volume, which means that the water consumption of the fracturing fluid system is low. The viscosity-temperature curve of the foam fracturing fluid was tested by a tube viscometer at a temperature of 5 C.90 C., the shear rate during the test was 170 s.sup.1. The experimental results shown in FIG. 4 indicated the fracturing fluid system has good viscosity-temperature stability, which is due to good viscosity-increasing effect provided by the structure of the double interface layers formed in the foam fracturing fluid of the present disclosure. The viscosity of the fracturing fluid system at a temperature of 5 C.90 C. is 4272 mPas, which is much higher than that of the traditional fracturing fluid that using pure liquid CO.sub.2 (that is, using pure liquid CO.sub.2 as a fracturing fluid) (generally 0.020.16 mPa.Math.s).