APPARATUS AND METHOD FOR CO2 MICROBUBBLE FLOODING

Abstract

A device for CO.sub.2 microbubble flooding comprises a microbubble generating device, a stirring and liquid storage device, an injection pump, a gas compressor, a gas-liquid mixer and a pressure stabilizing system, wherein the microbubble generating device adopts an integrally formed multi-layer cylindrical metal powder-sintered porous plate, and the diameters of microchannels on the porous plate are sequentially reduced from inside to outside. A solution containing additives in the storage device is stirred uniformly and then enters into a downhole gas injection base pipe through the gas-liquid mixer to be injected into a stratum, then a carbon dioxide gas compressed by the gas compressor is pumped into the downhole gas injection base pipe through the gas injection pump, and the gas generates microbubbles in situ when passing through the multi-layer porous device under the action of pressure difference.

Claims

1. An apparatus for CO.sub.2 microbubble flooding, comprising a liquid flow path, a gas flow path and a microbubble generating device (5), wherein the liquid flow path is connected to a first passage of a gas-liquid mixer (3) through an injection pump (2) by adopting a stirring and liquid storage device (1), the gas flow path is connected to a second passage of the gas-liquid mixer (3) by adopting a gas compressor (4) and a pressure stabilizing system (6), and a third passage of the gas-liquid mixer (3) is connected to a threaded connection port (5d) of the microbubble generating device (5); the microbubble generating device (5) adopts a metal powder-sintered integrated multilayer cylindrical arc-shaped porous plate, wherein an inner layer porous plate (5a), a middle layer porous plate (5b) and an outer layer porous plate (5c) are sequentially arranged from inside to outside, a diameter of a microchannel on the outer layer porous plate (5c) are smaller than 0.5 m, a diameter of a microchannel on the middle layer porous plate (5b) are smaller than 2 m, and a diameter of a microchannel on the inner layer porous plate (5a) are smaller than 3 m.

2. A working method of the apparatus for CO.sub.2 microbubble flooding according to claim 1, comprising the steps of: S1, injecting an aqueous solution containing xanthan gum and sodium dodecyl sulfate into a liquid storage tank, and then stirring at a speed of 500 r/min-1000 r/min for at least two hours, wherein the foregoing uniformly stirred solution is used as a base solution comprising 3% of xanthan gum and 0.05% of sodium dodecyl sulfate; S2, injecting stirred base solution into a gas-liquid mixer (3) at a certain flow rate through an injection pump and pumping the base solution into a stratum to allow the base solution to saturate a bubble generating structure and the stratum around a wellhead in advance so as to provide a proper environment for subsequently injecting a CO.sub.2 gas and generating stable microbubbles; S3, pumping the carbon dioxide gas compressed by a gas compressor (4) into the gas-liquid mixer (3) through a gas injection pump at a pressure of 4 MPa; and S4, enabling the gas to pass through a three-layer metal-sintered porous plate under the action of pressure difference to generate microbubbles in situ; and after the microbubbles enter into the stratum, a Jamin effect is generated, and larger bubbles block a macroporous throat such that a flow direction of follow-up flow changes, the base solution for flooding is capable of entering into small pores, thereby storing carbon dioxide in the stratum while completing the flooding.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0021] FIG. 1 is a schematic diagram of an experimental system.

[0022] FIG. 2 is a structural diagram of a microbubble generating device.

[0023] FIG. 3 is a diameter comparison diagram of microbubbles generated by microbubble generating device.

[0024] In the figure: 1, stirring and liquid storage device; 2, injection pump; 3, gas-liquid mixer; 4, gas compressor; 5, microbubble generating device; 5a, inner layer porous plate; 5b, middle layer porous plate; 5c, outer layer porous plate; 5d, threaded connection port; 6, pressure stabilizing system.

DESCRIPTION OF THE EMBODIMENTS

[0025] An experimental apparatus for generating CO.sub.2 microbubbles and promoting the flooding includes a microbubble generating device, a stirring and liquid storage device, a gas injection pump, a gas compressor, a gas-liquid mixer and an oil recovery system. A multi-layer porous plate in the microbubble generating device is formed by sintering metal powders, a diameter of a microchannel on an outer layer porous plate is smaller than 0.5 m, a diameter of a microchannel on a middle layer porous plate is smaller than 2 m, a diameter of a microchannel on an inner layer porous plate is smaller than 3 m, and a wall thickness of each layer porous plate is 3 mm. The multi-layer porous plate is fixed through a stainless-steel structure and connected with a gas injection end through a thread structure.

[0026] The experimental method for generating CO.sub.2 microbubbles and promoting the flooding includes the following steps that a solution containing additives in a stirring and liquid storage device was uniformly stirred and then entered into a downhole gas injection base pipe through a gas-liquid mixer and injected into the stratum, and subsequently a carbon dioxide gas compressed by a gas compressor was pumped into the downhole gas injection base pipe through a gas injection pump such that the gas generated microbubbles in situ when passing through the multi-layer porous plate under the action of pressure difference, thereby storing carbon dioxide in the stratum while promoting the flooding.

[0027] Specifically, as shown in FIG. 1, a process system in this example includes a microbubble generating device, a stirring and liquid storage device, a gas injection pump, a gas compressor and a gas-liquid mixer. The apparatus includes a liquid flow path, a gas flow path and the microbubble generating device 5, where the liquid flow path is connected to a first passage of the gas-liquid mixer 3 via the injection pump 2 by adopting the stirring and liquid storage device 1, the gas flow path is connected to a second passage of the gas-liquid mixer 3 by adopting the gas compressor 4 and the pressure stabilizing system 6, and a third passage of the gas-liquid mixer 3 is connected to a threaded connection port 5d of the microbubble generating device 5; and the microbubble generating device 5 is provided with an inner layer porous plate 5a, a middle layer porous plate 5b and an outer layer porous plate 5c from inside to outside, the diameter of the microchannel on the outer layer porous plate 5c is smaller than 0.5 m, the diameter of the microchannel on the middle layer porous plate 5b is smaller than 2 m, and the diameter of the microchannel on the inner layer porous plate 5a is smaller than 3 m.

[0028] In this example, a method for in situ generating microbubbles in the downhole and promoting the flooding was as follows: [0029] a solution containing additives (3% of xanthan gum and 0.05% of sodium dodecyl sulfate) was injected into a liquid storage tank, and stirred at a speed of 500 r/min for at least two hours until the solution was uniformly stirred to obtain a base solution; [0030] subsequently, the stirred base solution was injected into a gas-liquid mixer at a certain flow rate through a pump and pumped into the stratum to saturate a bubble generating structure and the stratum around a wellhead in advance; a carbon dioxide gas compressed by a gas compressor was pumped into a gas-liquid mixer by a gas injection pump at a pressure of 4 MPa, and the gas passed through a three-layer metal-sintered porous plate under the action of pressure difference to generate microbubbles in situ, where a pore diameter of the outermost layer porous plate was 0.5 m, a pore diameter of the second layer porous plate was 2 am, and a pore diameter of the innermost layer porous plate was 3 m; after the microbubbles entered into the stratum, a Jamin effect was generated, and larger bubbles blocked a macroporous throat, such that a flow direction of follow-up flow changed, and the base solution for flooding was capable of entering into small pores, with an improved flooding sweep rate, thereby storing carbon dioxide in the stratum while flooding. The simulation result showed that through CO.sub.2 microbubble flooding, the dissolution rate of CO.sub.2 was improved by 18.7%, the injection speed and injection amount of CO.sub.2 were improved, the recovery efficiency of crude oil was finally improved by 16.7%, and the displacement advantage of microbubbles CO.sub.2 in a rock core was superior to that of the conventional CO.sub.2. Therefore, the injection of microbubbles CO.sub.2 is a promising technology for enhancing oil recovery efficiency and geological carbon fixation.