Waterless foam generator for fracturing shale oil and gas reservoirs and use thereof

Abstract

The present disclosure discloses a waterless foam generator for fracturing shale oil and gas reservoirs and use thereof. The structure of the waterless foam generator includes: a top of the proppant storage tank is provided with a proppant inlet, a second feed port of liquid CO.sub.2 and a safety valve, and a bottom of the proppant storage tank is connected to the high-pressure gas-liquid-solid mixer, a side wall of the high-pressure gas-liquid-solid mixer is provided with a first feed port of liquid CO.sub.2, an feed port of N.sub.2 and an feed port of waterless foam foaming agent, and the high-pressure gas-liquid-solid mixer is connected to the first shaker of waterless foam fracturing fluid, the first shaker of waterless foam fracturing fluid, the second shaker of waterless foam fracturing fluid and the third shaker of waterless foam fracturing fluid are connected in sequence.

Claims

1. A waterless foam generator for fracturing shale oil and gas reservoirs, comprising: a proppant storage tank, a high-pressure gas-liquid-solid mixer, a first shaker of waterless foam fracturing fluid, a second shaker of waterless foam fracturing fluid, and a third shaker of waterless foam fracturing fluid; a top of the proppant storage tank is provided with a proppant inlet, a second feed port of liquid CO.sub.2 and a safety valve, and a bottom of the proppant storage tank is connected to the high-pressure gas-liquid-solid mixer through a proppant discharge pipe; the top of the proppant storage tank is connected to both the second shaker of waterless foam fracturing fluid and the third shaker of waterless foam fracturing fluid through a gas discharge pipe; a side wall of the high-pressure gas-liquid-solid mixer is provided with a first feed port of liquid CO.sub.2, a feed port of N.sub.2 and a feed port of waterless foam foaming agent; the high-pressure gas-liquid-solid mixer is connected to the first shaker of waterless foam fracturing fluid through a liquid discharge pipe, the first shaker of waterless foam fracturing fluid, the second shaker of waterless foam fracturing fluid and the third shaker of waterless foam fracturing fluid are connected in sequence; the first shaker of waterless foam fracturing fluid is a rectangular pipeline, wherein triangle protrusions are alternately formed on two opposite side walls of the rectangular pipeline; the second shaker of waterless foam fracturing fluid is a circular pipeline, wherein a plurality of arc-shaped Venturi tubes are formed along the inner wall of the circular pipeline; the third shaker of waterless foam fracturing fluid is a circular pipeline, wherein a plurality of arc-shaped Venturi tubes are formed along the inner wall of the circular pipeline, and a plurality of arc-shaped mini-Venturi tubes are arranged, in honeycomb briquet shape, at an end of a radially enlarged tube of each of the arc-shaped Venturi tubes; the third shaker of waterless foam fracturing fluid is connected to a discharge pipe of waterless foam.

2. The waterless foam generator according to claim 1, wherein a hydraulic sealing gate which is configured to control discharge amount of the proppant is arranged within the proppant storage tank.

3. The waterless foam generator according to claim 2, wherein the hydraulic sealing gate comprises a hydraulic cylinder arranged in the proppant storage tank, a hydraulic shaft connected to the hydraulic cylinder, an oil inlet fixed on a top of the hydraulic shaft and a hydraulic gate fixed at a bottom of the hydraulic shaft, and the discharge amount of the proppant is controlled by upward or downward movement of the hydraulic gate.

4. The waterless foam generator according to claim 3, wherein the bottom of the proppant storage tank has a shape of a conical funnel, a cone apex of which is connected to the proppant discharge pipe.

5. The waterless foam generator according to claim 1, wherein both the circular pipeline of the second shaker and the third shaker, and the rectangular pipeline are each steel pipe, an outer surface of the each steel pipe is provided with a thermal insulation layer, and an inner surface of the steel pipe is inlaid with a wear-resistant ceramic layer.

6. The waterless foam generator according to claim 1, wherein an apex angle of the triangle protrusion is 110-130; a maximum diameter of the arc-shaped Venturi tube is 6.90 cm-7.60 cm, and a minimum diameter of the arc-shaped Venturi tube is 2.75 cm-3.25 cm; a maximum diameter of the arc-shaped mini-Venturi tube is 1.50 cm-2.15 cm, and a minimum diameter of the arc-shaped mini-Venturi tube is 0.75 cm-1.25 cm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIG. 1 is a schematic structural diagram of a waterless foam generator for fracturing shale oil and gas reservoirs according to the present disclosure;

(2) FIG. 2 is a sectional view of 1-1 in FIG. 1 (the first shaker of waterless foam fracturing fluid);

(3) FIG. 3 is a sectional view of 1-2 in FIG. 1 (the second shaker of waterless foam fracturing fluid);

(4) FIG. 4 is a sectional view of 1-3 in FIG. 1 (the third shaker of waterless foam fracturing fluid);

(5) FIG. 5 is a partial enlarged drawing of 1-3 in FIG. 1 (the third shaker of waterless foam fracturing fluid).

(6) The reference numbers in the figures are shown as follows:

(7) 1. body of the proppant storage tank; 2. cavity of the proppant storage tank; 3. proppant; 4. cavity of the hydraulic cylinder; 5. sealing ring; 6. oil inlet; 7. hydraulic shaft; 8. hydraulic gate; 9. conical funnel; 10. proppant inlet; 11. upper cover of the proppant storage tank; 12. second feed port of liquid CO.sub.2; 13. safety valve, 14. feed port of N.sub.2; 15. first feed port of liquid CO.sub.2; 16. feed port of waterless foam foaming agent; 17. high-pressure gas-liquid-solid mixer; 18. liquid discharge pipe; 19. valve of the liquid discharge pipe; 20. wear-resistant ceramic layer; 21. triangle protrusion; 22. 24. 28. steel body; 23. thermal insulation layer; 25. 30. arc-shaped Venturi tube; 26. gas discharge pipe; 27. valve of the gas discharge pipe; 29. arc-shaped mini-Venturi tube, 31. discharge pipe of waterless foam; 32. proppant discharge pipe.

DETAILED DESCRIPTION OF THE EMBODIMENTS

(8) Embodiments of the present disclosure will be further illustrated below with reference to the drawings, but the present disclosure will not be limited by the following embodiments.

(9) As shown in FIG. 1, it is a schematic structural diagram of a waterless foam generator for fracturing shale oil and gas reservoirs according to the present disclosure, the waterless foam generator includes a proppant storage tank (including a body of the proppant storage tank 1 and a cavity of the proppant storage tank 2), a high-pressure gas-liquid-solid mixer 17, a first shaker of waterless foam fracturing fluid, a second shaker of waterless foam fracturing fluid and the third shaker of waterless foam fracturing fluid. Atop of the body of proppant storage tank 1 (an upper cover 11 of the proppant storage tank) is provided with a proppant inlet 10, a second feed port 12 of liquid CO.sub.2 and a safety valve 13, and a bottom of the proppant storage tank is connected to the high-pressure gas-liquid-solid mixer 17 through a proppant discharge pipe 32; the upper cover 11 of the proppant storage tank is also equipped with a gas discharge pipe 26, and the other side of the gas discharge pipe 26 is connected to the second shaker of waterless foam fracturing fluid and the third shaker of waterless foam fracturing fluid. A side wall of the high-pressure gas-liquid-solid mixer 17 is provided with a first feed port 15 of liquid CO.sub.2, a feed port 14 of N.sub.2 and a feed port 16 of waterless foam foaming agent. The high-pressure gas-liquid-solid mixer 17 is connected to the first shaker of waterless foam fracturing fluid through a liquid discharge pipe 18, the first shaker of waterless foam fracturing fluid, the second shaker of waterless foam fracturing fluid and the third shaker of waterless foam fracturing fluid are connected in sequence, the third shaker of waterless foam fracturing fluid is connected to a discharge pipe 31 of waterless foam.

(10) Specifically, as shown in FIG. 2, the first shaker of waterless foam fracturing fluid is a rectangular pipeline, where triangle protrusions 21 are alternately formed on two opposite side walls of the rectangular pipeline, and the apex angle of the triangle protrusion is 120; the total length of the pipeline in the first shaker is 80.00 cm, the external width and height of the cuboid are 10.00 cm, and the thickness is 2.25 cm.

(11) Specifically, as shown in FIG. 3, the second shaker of waterless foam fracturing fluid is a circular pipeline, a plurality of arc-shaped Venturi tubes 25 (formed by a steel body 24) are formed on the inner wall of the circular pipeline, the minimum diameter of the arc-shaped Venturi tube 25 is 3.00 cm, the maximum diameter of the same is 7.00 cm, the total length of the pipeline is 80.00 cm, and the outside diameter of alloy steel is 10.00 cm.

(12) Specifically, as shown in FIG. 4, the third shaker of waterless foam fracturing fluid is a circular pipeline, a plurality of arc-shaped Venturi tubes 30 (formed by a steel body 28) are formed on the inner wall of the circular pipeline, and a plurality of arc-shaped mini-Venturi tubes 29 are arranged, in honeycomb briquet shape, at an end of a radially enlarged tube of each of the arc-shaped Venturi tubes 30. The minimum diameter of the arc-shaped Venturi tube 30 is 3.00 cm, the maximum diameter of the same is 7.00 cm, the total length of the pipeline is 80.00 cm; the minimum diameter of five arc-shaped mini-Venturi tubes is 1.00 cm, and the maximum diameter of the same is 1.75 cm, and the outside diameter of alloy steel is 10.00 cm.

(13) The pipe wall of the first shaker of waterless foam fracturing fluid, the second shaker of waterless foam fracturing fluid and the third shaker of waterless foam fracturing fluid is composed of a wear-resistant ceramic layer 20, a steel body 22 (24, 28) and a thermal insulation layer 23 from the inside to the outside.

(14) In order to control the discharge amount of the proppant, a hydraulic sealing gate is arranged within the proppant storage tank, where the hydraulic sealing gate includes a hydraulic cylinder arranged in the proppant storage tank (the cavity of the hydraulic cylinder 4), a hydraulic shaft 7 which is connected to the hydraulic cylinder, an oil inlet 6 which is fixed on a top of the hydraulic shaft 7 and a hydraulic gate 8 fixed at a bottom of the hydraulic shaft, the discharge amount of the proppant is controlled by upward or downward movement of the hydraulic gate 8. A sealing ring 5, such as a graphite sealing ring, is arranged between the hydraulic cylinder and the hydraulic shaft 7, in order to achieve beneficial effects of resistance to the corrosion of liquid CO.sub.2 and high pressure. The bottom of the proppant storage tank has a shape of a conical funnel 9, a cone apex of which is connected to the proppant discharge pipe 32.

(15) In order to prepare waterless foam fracturing fluid, the waterless foam generator for fracturing shale oil and gas reservoirs in the present disclosure is used according to the following steps:

(16) (1) Adding proppant and testing pressure: connecting the discharge pipe 31 of waterless foam of the waterless foam generator for fracturing shale oil and gas reservoirs to a high-pressure pipeline for fracturing which is in equipped valves, and adding the proppant 3 through the proppant inlet; after adding proppant, sealing the proppant inlet with a flange, and closing the proppant inlet, the safety valve 13, the gas discharge pipe 26, the first feed port 15 of liquid CO.sub.2, the feed port 16 of waterless foam foaming agent and the feed port 14 of N.sub.2, feeding liquid CO.sub.2 through the first feed port 15 of liquid CO.sub.2, keeping a pressure of 90 MPa for 30-40 minutes, and holding the pressure, and it is qualified if there is no piercing-caused leakage.

(17) (2) Cooling: after testing pressure, injecting liquid CO.sub.2 through the first feed port 15 of liquid CO.sub.2, and controlling the opening degree of the valves on the gas discharge pipe 27 and the hydraulic gate 8, so as to make part of CO.sub.2 be divided into the proppant storage tank and be discharged through the gas discharge pipe 26, the third shaker of waterless foam fracturing fluid and the discharge pipe 31 of waterless foam in sequence; and so as to make the other part of CO.sub.2 be divided into the first shaker of waterless foam fracturing fluid, the second shaker of waterless foam fracturing fluid and the third shaker of waterless foam fracturing fluid in sequence, and be discharged through the discharge pipe 31 of waterless foam; when temperature of each part of the waterless foam generator is lowered to a temperature required for the fracturing operation, stop the waterless foam generator.

(18) (3) Generating foam: after cooling, closing the gas discharge pipe 26 and fully opening the hydraulic gate 8 of the proppant storage tank; injecting liquid CO.sub.2 through the first feed port 15 and the second feed port 12 of liquid CO.sub.2, injecting N.sub.2 through the feed port 14 of N.sub.2, injecting a foaming agent through the feed port 16 of waterless foam foaming agent, and then fracturing; during a process of fracturing, controlling a flow rate of the first feed port 15 of liquid CO.sub.2, the second feed port 12 of liquid CO.sub.2 and the feed port 14 of N.sub.2, and controlling proppant concentration, so as to complete fracturing operation.

(19) (4) Slagging: after the fracturing operation, releasing pressure in the waterless foam generator, orienting the discharge pipe 31 of waterless foam in a safe direction, feeding high-pressure CO.sub.2 through the first feed port 15 of liquid CO.sub.2, and discharging the proppant 3 and residual foaming agent in the first shaker of waterless foam fracturing fluid, the second shaker of waterless foam fracturing fluid and the third shaker of waterless foam fracturing fluid.

(20) In step (2), the relationship between the proppant concentration and the amount of usage of liquid CO.sub.2 at the first feed port 15 and the second feed port 12, the amount of usage of N.sub.2 at the feed port 14, and the amount of usage of proppant at the proppant inlet 10 is shown in the following equation:

(21) $\mathrm{Proppant}\mathrm{Concentration}=\frac{Q_{\mathrm{Proppant}}}{Q_{N_2}+Q_1+Q_2+Q_{\mathrm{Foaming}\mathrm{Agent}}}=\frac{K_1{K}_2{K}_3{Q}_2}{Q_{N_2}+Q_1+Q_2+Q_{\mathrm{Foaming}\mathrm{Agent}}}$

(22) In the equation, Q.sub.Proppant represents volumetric discharge amount of the proppant, Q.sub.N2 represents volumetric discharge amount of N.sub.2, Q.sub.1 represents volumetric discharge amount of liquid CO.sub.2 at the first feed port of liquid CO.sub.2, Q.sub.2 represents volumetric discharge amount of liquid CO.sub.2 at the second feed port of liquid CO.sub.2, Q.sub.Foaming Agent represents volumetric discharge amount of the foaming agent at the feed port of waterless foam foaming agent, K.sub.1 represents a flow coefficient of CO.sub.2 (K.sub.1=8.0), K.sub.2 represents an opening coefficient of the hydraulic gate of the proppant storage tank (determined before the fracturing operation, K.sub.2=S.sub.Gap/S.sub.Proppant Storage Tank=0.12, S.sub.Proppant Storage Tank represents cross sectional area of the proppant storage tank, and S.sub.Gap represents cross sectional area of a gap between the hydraulic gate and the proppant storage tank when the hydraulic gate is open), and K.sub.3 represents a volumetric coefficient of the proppant (related to the shape of the particle, if spherical ceramic particles are used, K.sub.3=V.sub.Ball/V.sub.Cube=0.52);

(23) In the process of fracturing operation, the total designed discharge amount in the fracturing operation is 8 m.sup.3/min, Q.sub.N2=3.98 m.sup.3/min, Q.sub.Foaming Agent=0.02 m.sup.3/min, proppant concentration is 8%, and finally the discharge amount of CO.sub.2 during the fracturing operation can be determined, Q.sub.1=2.18 m.sup.3/min, Q.sub.2=1.18 m.sup.3/min.