Carbon dioxide working fluid and preparation method thereof, and drainage gas recovery method for hypotonic gas reservoir

Abstract

The invention relates to the technical field of gas field development, and discloses a carbon dioxide working solution, a preparation method thereof and a drainage gas recovery method for a low-permeability gas reservoir. The carbon dioxide working solution comprises liquid carbon dioxide, an entrainer, a foaming agent and a foam stabilizer, wherein the weight ratio of the liquid carbon dioxide to the entrainer to the foaming agent to the foam stabilizer is 100: (1-3): (0.1-2): (0.1-1.5); the entrainer comprises an alcohol auxiliary agent and a solvent. The carbon dioxide working solution provided by the invention has excellent water carrying, foaming and foam stabilizing properties, high foaming efficiency, foaming rate of more than 75%, stable foam and foam drainage half-life period of more than 9 minutes, and can realize the reduction degree of rock core water saturation by 53% or more in a rock core throughput simulation experiment. The water saturation of the rock core is reduced by 80.1% at most, the water saturation of a near-well area of a low-permeability gas reservoir can be remarkably reduced, and water control and yield increase of an old well of a gas field are effectively achieved.

Description

Technical Field

[0001] The invention relates to the technical field of gas field development, and in particular to a carbon dioxide working fluid and a preparation method thereof, and a method for draining water and recovering gas from a low-permeability gas reservoir. Background Art

[0002] As a future alternative energy source for oil and gas exploration and development with great potential, low-permeability gas reservoirs play an important role in the global energy structure. However, most gas reservoirs will have the characteristics of low production and associated water production during the development process. For example, in the Jingbian gas field with a long history of exploration and development, due to the sudden intrusion of edge and bottom water and pressure attenuation in the middle and late stages of development, the water saturation in the near-well area was high, and the wellbore was seriously filled with liquid, resulting in a decline in production or even shutdown. In addition, in recent years, the measures to tap the potential of old wells in gas fields mainly include layer inspection and perforation repair, repeated fracturing, bridge plugging, reservoir unblocking in the near-well area, and well repair, which have achieved certain results, but there is a pressure deficit in the old layer, a large amount of filtration loss during well pressure, a low return rate after pressure, and serious residual liquid retention in the formation, which is prone to water sensitivity and water lock damage.

[0003] For low-yield and low-efficiency water-expelling gas reservoirs, the water-expelling and gas-recovery technology is currently usually used to control water and increase gas. This technology is to inject a certain proportion of foaming agent into the wellbore to reduce the density of the accumulated liquid under the stirring of the natural gas flow, reduce the surface tension of the formation water, and transform the accumulated liquid at the bottom of the well into a foamy and easy-to-lift fluid, which is then carried from the bottom of the well to the ground by the gas. However, during the development of gas reservoirs, the residual liquid is seriously retained in the formation, the gas wells produce a large amount of water, and the water saturation in the near-well area increases. The water-expelling and gas-recovery technology can only carry out the accumulated liquid in the wellbore, but cannot be used to reduce the water saturation in the near-well area.

[0004] Therefore, providing a material for reducing the water saturation in the near-well area for old wells in low-permeability gas reservoirs is of great significance for controlling water and increasing production in old wells in low-permeability gas fields, and facilitating further high-quality and high-efficiency development of low-permeability gas reservoirs. Summary of the invention

[0005] In order to overcome the problem of reduced gas production due to high water saturation in the near-wellbore area in the middle and late stages of development of low-permeability gas reservoirs, the present invention provides a carbon dioxide working fluid and a preparation method thereof, and a method for draining water and recovering gas from low-permeability gas reservoirs, which can significantly reduce the water saturation in the near-wellbore area of ​​the low-permeability gas reservoir and achieve water control and increased production in old wells in the gas field.

[0006] In order to achieve the above-mentioned object, the present invention provides a carbon dioxide working fluid in a first aspect, comprising: liquid carbon dioxide, an entrainer, a foaming agent and a foam stabilizer;

[0007] Wherein, the weight ratio of the liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100: (1-3): (0.1-2): (0.1-1.5);

[0008] The entrainer includes an alcohol auxiliary agent and a solvent.

[0009] A second aspect of the present invention provides a method for preparing a carbon dioxide working fluid, comprising:

[0010] (1) performing a first mixing of an entrainer, a foaming agent, and a foam stabilizer to obtain a mixed solution;

[0011] (2) performing a second mixing of the mixed liquid and liquid carbon dioxide to obtain a carbon dioxide working liquid;

[0012] The weight ratio of the liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100: (1-3): (0.1-2): (0.1-1.5); the entrainer includes an alcohol auxiliary agent and a solvent.

[0013] The third aspect of the present invention provides a carbon dioxide working fluid prepared by the method described in the second aspect.

[0014] A fourth aspect of the present invention provides a method for water drainage and gas production in a low permeability gas reservoir, comprising: injecting the carbon dioxide working fluid described in the first aspect or the third aspect into a gas production well of a low permeability gas reservoir, and foaming the carbon dioxide foam produced by the foaming into a high water content gas production formation from the gas production well, and then returning the carbon dioxide foam to the ground, and using the carbon dioxide foam to carry out water in the near-well area of ​​the high water content gas production formation;

[0015] Wherein, the water content of the high-water-content gas-producing formation is greater than 80% by volume;

[0016] The permeability of the high water-content gas-producing formation is less than 1 md, preferably 0.1-0.5 md.

[0017] The carbon dioxide working fluid provided by the present invention uses liquid carbon dioxide as the main functional component. Under the joint action of the entrainer, foaming agent and foam stabilizer contained therein, the carbon dioxide can be changed The phase behavior of carbon dioxide can increase the solubility of carbon dioxide in water, and the water carrying capacity of carbon dioxide can be improved. The working fluid has excellent foaming performance, can generate foam at a low shear rate, has high foaming efficiency, a foaming rate of more than 75%, stable foam, and a foam liquid separation half-life of more than 9 minutes, which brings further improved water carrying capacity to the working fluid. Using the working fluid to carry out a core throughput simulation experiment, the core water saturation can be reduced by more than 53%, and the highest core water saturation reduction can be 80.1%. It can significantly reduce the water saturation in the near-well area of ​​the low-permeability gas reservoir, and effectively achieve water control and production increase in old wells in the gas field. DETAILED DESCRIPTION

[0018] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0019] The specific embodiments of the present invention are described in detail below. It should be understood that the specific embodiments described herein are only used to illustrate and explain the present invention, and are not used to limit the present invention.

[0020] The first aspect of the present invention provides a carbon dioxide working fluid, comprising: liquid carbon dioxide, an entrainer, a foaming agent and a foam stabilizer;

[0021] Wherein, the weight ratio of the liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100: (1-3): (0.1-2): (0.1-1.5);

[0022] The entrainer includes an alcohol auxiliary agent and a solvent.

[0023] According to the present invention, in the carbon dioxide working fluid, the liquid carbon dioxide as the main functional component has good mutual solubility with fluids, especially water, and can play a role in dissolving a large amount of water; the entrainer can increase the solubility of carbon dioxide in water by changing the phase behavior of carbon dioxide; the foaming agent and the foam stabilizer can promote the foaming of the working fluid to form a large amount of stable foam, the foaming rate is greater than 75%, and the foam liquid separation half-life is greater than 9min, which can further improve the water solubility, and at the same time reduce the overall density of the working fluid, which is conducive to lifting and carrying water. Under the synergistic effect of the above-mentioned components, the working fluid is given excellent water solubility and efficient and stable foaming performance, and can efficiently carry water under the conditions of 80-120℃ and 10-15MPa. The core huff-and-puff simulation experiment using the working fluid can achieve a core water saturation reduction of more than 53%, and the highest core water saturation reduction can achieve 80.1%. When the components and proportions contained in the carbon dioxide working fluid do not meet the limiting conditions of the present invention, the working fluid with the above-mentioned effect cannot be obtained.

[0024] According to the present invention, in the carbon dioxide working fluid, on the basis of satisfying the above-mentioned quantitative relationship, preferably, the weight ratio of the liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100: (1.5-2): (1-1.5): (0.8-1), so that the carbon dioxide working fluid has better water solubility and foaming and stabilizing properties.

[0025] According to the present invention, the liquid carbon dioxide refers to carbon dioxide in liquid form under low temperature and high pressure. The present invention has a wide definition of the liquid carbon dioxide, which can be carbon dioxide in liquid form obtained by any means, preferably liquid carbon dioxide with a purity of ≥99%.

[0026] Normally, due to the strong polarity of water molecules, the interaction between water molecules and carbon dioxide is weak. In the present invention, under the joint action of the alcohol auxiliary agent and the solvent, the entrainer can change the phase behavior of carbon dioxide at a certain temperature and pressure by forming interactions such as van der Waals forces and hydrogen bonds between the entrainer and water, thereby increasing the solubility of carbon dioxide in water.

[0027] According to the present invention, preferably, the content of the alcohol auxiliary agent in the entrainer is not higher than 50wt%. Further preferably, in the entrainer, the weight ratio of the alcohol auxiliary agent to the solvent is 1:(1-1.5), which can make the carbon dioxide working fluid have better water solubility.

[0028] According to the present invention, the alcohol auxiliary agent may be a monohydric alcohol or a polyhydric alcohol, for example, at least one selected from methanol, ethanol, propanol, ethylene glycol, triethylene glycol, propylene glycol, glycerol, and dipropylene glycol. Preferably, the alcohol auxiliary agent is a polyhydric alcohol.

[0029] According to a preferred embodiment of the present invention, the alcohol auxiliary agent is at least one selected from ethylene glycol, glycerol and dipropylene glycol. Further preferably, the alcohol auxiliary agent is a mixture of ethylene glycol, glycerol and dipropylene glycol in a weight ratio of 1: (0.8-1.8): (0.5-1.5).

[0030] According to the present invention, the solvent can be selected from alcoholamine compounds, carboxylic acid compounds and aldehyde compounds, preferably at least one of monoethanolamine, diethanolamine, triethanolamine, formic acid, acetic acid, propionic acid, formaldehyde and acetaldehyde.

[0031] According to a preferred embodiment of the present invention, the solvent is selected from triethanolamine, acetic acid and acetaldehyde. Further preferably, the solvent is a mixture of triethanolamine, acetic acid and acetaldehyde in a weight ratio of 1: (0.8-1.8): (1-2).

[0032] According to the present invention, the foaming agent can make the working fluid at a low shear rate (e.g., 20-60s -1 ) to generate carbon dioxide foam, which can then enter the reservoir to dissolve water better, while reducing the density of the working fluid, which is conducive to lifting and carrying water. Preferably, the foaming agent is a non-ionic surfactant.

[0033] According to the present invention, the nonionic surfactant can be selected from at least one of 1-polyoxyethylene phenol-3-octyl, 1-polyoxyethylene phenol-3-nonyl, 1-polyoxyethylene phenol-3-dodecyl, 1-polyoxypropylene phenol-3-octyl, 1-polyoxypropylene phenol-3-nonyl, 1-polyoxypropylene phenol-3-dodecyl, 1-polyoxybutylene phenol-3-octyl, 1-polyoxybutylene phenol-3-nonyl and 1-polyoxybutylene phenol-3-dodecyl, preferably at least one of 1-polyoxyethylene phenol-3-dodecyl, 1-polyoxypropylene phenol-3-dodecyl and 1-polyoxybutylene phenol-3-dodecyl.

[0034] According to a preferred embodiment of the present invention, the foaming agent is further preferably a mixture of 1-polyoxyethylenephenol-3-dodecyl, 1-polyoxypropylenephenol-3-dodecyl and 1-polyoxybutylenephenol-3-dodecyl in a weight ratio of 1:(0.8-1.5):(0.8-1.5).

[0035] According to the present invention, the foam stabilizer can stabilize the liquid film, has high interfacial desorption energy, and can be adsorbed on the surface of the foam liquid film to form a stable adsorption layer under the synergistic effect of the surfactant, and delays the thinning of the liquid film by hindering the flow of the liquid phase in the liquid film, thereby inhibiting the coalescence effect of bubbles and achieving the purpose of stabilizing the foam. Preferably, the foam stabilizer is selected from nano metal oxide particles and / or cellulose nanofibers.

[0036] According to the present invention, preferably, the average particle size of the nano metal oxide particles is 10-40 nm, which is conducive to better adsorption of the foam liquid film, plays a barrier protection role for the foam, increases the surface elasticity of the foam, weakens the drainage effect of the liquid film, and reduces the bubble aggregation speed, thereby making the carbon dioxide foam more stable and having a longer life.

[0037] In the present invention, the average particle size refers to D50, which can be measured by a laser particle size analyzer.

[0038] According to the present invention, preferably, the diameter of the cellulose nanofibers is 3-8 nm and the length is 5-10 μm, which is conducive to better adsorption of the foam liquid film, plays a barrier protection role for the foam, increases the surface elasticity of the foam, weakens the drainage effect of the liquid film, and reduces the aggregation rate of bubbles, thereby making the carbon dioxide foam more stable and having a longer life.

[0039] In the present invention, the diameter and length of the cellulose nanofibers can be measured by a transmission electron microscope.

[0040] According to the present invention, preferably, the nano metal oxide particles can be selected from at least one of nano titanium dioxide particles, nano aluminum oxide particles, nano zirconium dioxide particles, nano silicon dioxide particles, nano zinc oxide particles, nano chromium trioxide particles and nano manganese trioxide particles.

[0041] According to the present invention, preferably, the cellulose nanofibers may be selected from at least one of carboxymethylated cellulose nanofibers, ethyl cellulose nanofibers, hydroxyethyl cellulose nanofibers, hydroxypropyl methyl cellulose nanofibers and cellulose acetate butyrate nanofibers.

[0042] According to a preferred embodiment of the present invention, the foam stabilizer is a mixture of nano metal oxide particles and cellulose nanofibers, and more preferably a mixture of nano titanium dioxide particles, nano aluminum oxide particles and hydroxyethyl cellulose nanofibers in a weight ratio of 1: (0.5-1.5): (1-2).

[0043] In the present invention, the foaming rate is calculated by the following formula:

[0044] Foaming rate % = (AB) / A × 100%

[0045] Wherein, A represents the foaming volume (mL), and B represents the initial volume of the foaming liquid (mL); wherein, the “initial volume of the foaming liquid” refers to the volume of the liquid before foaming; and the “foaming volume” is determined according to the method specified in the Petroleum and Natural Gas Industry Standard SY / T 7494-2020 of the People’s Republic of China.

[0046] In the present invention, the foam liquid separation half-life is determined by the method specified in the petroleum and natural gas industry standard SY / T7494-2020 of the People's Republic of China.

[0047] In the present invention, a core huff and puff simulation experiment is performed on the carbon dioxide working fluid to evaluate its effect of reducing the water saturation of the core (or formation). The process of the core huff and puff simulation experiment is as follows:

[0048] (1) Determination of core dimensions: Use a vernier caliper to measure the diameter and length of a cylindrical core plunger (about 25 mm in diameter) that has been cleaned (oil and salt removed) and dried for three times. After each measurement, rotate the core 120° around the line connecting the centers of the two bottom surfaces of the plunger before measuring again. The average of the three diameter and length measurements is taken as the final diameter and length measurement value of the core, and the total volume of the core is calculated, which is recorded as V1.

[0049] (2) Calibration of core analysis instrument: Set the helium test pressure to 1.38 MPa and use a stainless steel standard volume block to calibrate the Boyle's law core analysis instrument;

[0050] (3) Determination of core pore volume: The core obtained in step (1) is placed in the sample cell of a calibrated Boyle's law core analysis instrument, the helium pressure is set to 1.38 MPa, and the volume of dry core particles is measured, which is recorded as V2. The pore volume of the core (recorded as V3) = V1-V2;

[0051] (4) Core saturation: The core whose pore volume was measured in step (3) was saturated with formation water or standard brine for 48-72 hours under vacuum, and the water adhering to the surface of the core was absorbed with filter paper, and then the core was tightly wrapped with plastic wrap for standby use;

[0052] (5) Determination of water saturation of saturated core: remove the plastic wrap from the core treated in step (4), and measure the particle volume of the saturated core (denoted as V4) according to the method in step (3), then the water saturation of the saturated core (denoted as μ1) = (V4-V2) / V3×100%;

[0053] (6) Core huff-and-puff simulation: The core whose water saturation has been determined in step (5) is placed in a high-pressure (not higher than 30 MPa) sealed container, and the core is soaked in a carbon dioxide working fluid for 2-3 h (temperature is 80-120° C., pressure is 10-15 MPa), and then the pressure is slowly released at a rate of less than 0.5 MPa / min. After the pressure release is completed, the core is taken out, and the adhesion on the surface of the core is absorbed with filter paper, and then tightly wrapped with plastic wrap for standby use;

[0054] (7) Determination of water saturation of the core after huff and puff: remove the plastic wrap from the core treated by immersion in the carbon dioxide working solution in step (6), and measure the particle volume of the core after huff and puff (denoted as V5) according to the method in step (3), then the water saturation of the core after huff and puff (denoted as μ2) = (V5-V2) / V3×100%;

[0055] (8) Calculation of the degree of reduction in core water saturation (denoted as μ2): μ3 = μ1-μ2.

[0056] According to a most preferred embodiment of the present invention, in the carbon dioxide working fluid, the alcohol auxiliary agent in the entrainer is a mixture of ethylene glycol, glycerol and dipropylene glycol in a weight ratio of 1: (0.8-1): 1, the solvent is a mixture of triethanolamine, acetic acid and acetaldehyde in a weight ratio of 1: (1-1.5): (1.2-1.5), and the weight ratio of the alcohol auxiliary agent: the solvent is 1: (1.2-1.5); the foaming agent is -polyoxyethylene phenol-3-dodecyl, 1 - a mixture of polyoxypropylene phenol-3-dodecyl and 1-polyoxybutylene phenol-3-dodecyl in a weight ratio of 1: (0.8-1): 1; the foam stabilizer is a mixture of nano titanium dioxide particles, nano aluminum oxide particles and hydroxyethyl cellulose nanofibers in a weight ratio of 1: (0.8-1.5): 1.5; the weight ratio of the liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100: (1.6-1.8): (1-1.2): (0.8-1). The carbon dioxide working fluid of the most preferred embodiment has further improved water solubility and efficient and stable foaming performance, a foaming rate of more than 82wt%, a foam liquid separation half-life of more than 12min, and can efficiently carry water under the conditions of 80-120℃ and 10-15MPa. In the core huff-and-puff simulation experiment, the core water saturation can be reduced by more than 70%, thereby showing a more excellent effect of reducing the water saturation in the near-wellbore area of ​​the low-permeability gas reservoir.

[0057] The carbon dioxide working liquid provided by the present invention can be stored under any conditions that can make the carbon dioxide liquid, preferably stored under the conditions of -20 to -15°C and 1.8-2.5MPa for use.

[0058] A second aspect of the present invention provides a method for preparing a carbon dioxide working fluid, comprising:

[0059] (1) performing a first mixing of an entrainer, a foaming agent, and a foam stabilizer to obtain a mixed solution;

[0060] (2) performing a second mixing of the mixed liquid and liquid carbon dioxide to obtain a carbon dioxide working liquid;

[0061] The weight ratio of the liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100:100:(1-3):(0.1-2):(0.1-1.5); the entrainer includes an alcohol auxiliary agent and a solvent.

[0062] The preparation method of the carbon dioxide working fluid provided by the present invention comprises the following steps: firstly preparing a mixed liquid from an entrainer, a foaming agent and a foam stabilizer, and then mixing the obtained mixed liquid with liquid carbon dioxide to form a working fluid with liquid carbon dioxide as a main functional component, and combining the control of the feeding amount of each raw material to meet the above-mentioned quantitative relationship, so as to achieve that the prepared carbon dioxide working fluid has excellent water solubility and efficient and stable foaming performance, a foaming rate of more than 75%, a foam liquid separation half-life of more than 9 minutes, and can efficiently carry water under the conditions of 80-120° C. and 10-15 MPa. In a core throughput simulation experiment, the core water saturation can be reduced by more than 53%, and the maximum core water saturation reduction can be 80.1%, so that the working fluid can be used to effectively reduce the water saturation in the near-wellbore area of ​​a low-permeability gas reservoir, and has an excellent water control and production increase effect on old wells in gas fields.

[0063] According to the present invention, in the method for preparing the carbon dioxide working fluid, the feeding amount of each raw material is based on satisfying the above-mentioned quantitative relationship. Preferably, the feeding weight ratio of the liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100: (1.5-2): (1-1.5): (0.8-1), so that the prepared carbon dioxide working fluid has better water solubility and foaming and stabilizing properties.

[0064] According to the present invention, in the method for preparing the carbon dioxide working fluid, the liquid carbon dioxide refers to carbon dioxide in liquid form under low temperature and high pressure. The present invention has a relatively broad definition of the liquid carbon dioxide, which can be carbon dioxide in liquid form obtained by any means, preferably liquid carbon dioxide with a purity of ≥99%.

[0065] According to the present invention, in the method for preparing the carbon dioxide working fluid, the entrainer comprises an alcohol auxiliary agent and a solvent. Under the combined action of the alcohol auxiliary agent and the solvent, the entrainer can change the phase behavior of carbon dioxide at a certain temperature and pressure by forming interactions such as van der Waals forces and hydrogen bonds between the entrainer and water, thereby increasing the solubility of carbon dioxide in water.

[0066] According to the present invention, in the method for preparing the carbon dioxide working fluid, preferably, the content of the alcohol auxiliary agent in the entrainer is not higher than 50wt%. Further preferably, in the entrainer, the weight ratio of the alcohol auxiliary agent to the solvent is 1:(1-1.5), so that the prepared carbon dioxide working fluid has better water solubility.

[0067] According to the present invention, in the method for preparing the carbon dioxide working fluid, the alcohol auxiliary agent may be a monohydric alcohol or a polyhydric alcohol, for example, at least one selected from methanol, ethanol, propanol, ethylene glycol, triethylene glycol, propylene glycol, glycerol, and dipropylene glycol. Preferably, the alcohol auxiliary agent is a polyhydric alcohol.

[0068] According to a preferred embodiment of the present invention, the alcohol auxiliary agent is at least one selected from ethylene glycol, glycerol and dipropylene glycol. Further preferably, the alcohol auxiliary agent is a mixture of ethylene glycol, glycerol and dipropylene glycol in a weight ratio of 1: (0.8-1.8): (0.5-1.5).

[0069] According to the present invention, in the method for preparing the carbon dioxide working fluid, the solvent can be selected from alcoholamine compounds, carboxylic acid compounds and aldehyde compounds, preferably at least one of monoethanolamine, diethanolamine, triethanolamine, formic acid, acetic acid, propionic acid, formaldehyde and acetaldehyde.

[0070] According to a preferred embodiment of the present invention, the solvent is selected from at least one of triethanolamine, acetic acid and acetaldehyde. Further preferably, the solvent is a mixture of triethanolamine, acetic acid and acetaldehyde in a weight ratio of 1: (0.8-1.8): (1-2).

[0071] According to the present invention, in the method for preparing the carbon dioxide working fluid, the foaming agent can make the working fluid flow at a low shear rate (e.g., 20-60s -1 ) to generate carbon dioxide foam, which can then enter the reservoir to dissolve water better, while reducing the density of the working fluid, which is conducive to lifting and carrying water. Preferably, the foaming agent is a non-ionic surfactant.

[0072] According to the present invention, the nonionic surfactant can be selected from at least one of 1-polyoxyethylene phenol-3-octyl, 1-polyoxyethylene phenol-3-nonyl, 1-polyoxyethylene phenol-3-dodecyl, 1-polyoxypropylene phenol-3-octyl, 1-polyoxypropylene phenol-3-nonyl, 1-polyoxypropylene phenol-3-dodecyl, 1-polyoxybutylene phenol-3-octyl, 1-polyoxybutylene phenol-3-nonyl and 1-polyoxybutylene phenol-3-dodecyl, and is further preferably at least one of 1-polyoxyethylene phenol-3-dodecyl, 1-polyoxypropylene phenol-3-dodecyl and 1-polyoxybutylene phenol-3-dodecyl.

[0073] According to a preferred embodiment of the present invention, the foaming agent is further preferably a mixture of 1-polyoxyethylenephenol-3-dodecyl, 1-polyoxypropylenephenol-3-dodecyl and 1-polyoxybutylenephenol-3-dodecyl in a weight ratio of 1:(0.8-1.5):(0.8-1.5).

[0074] According to the present invention, in the method for preparing the carbon dioxide working fluid, the foam stabilizer can stabilize the liquid film and play a role in stabilizing the foam. Preferably, the foam stabilizer is selected from nano metal oxide particles and / or cellulose nanofibers.

[0075] According to the present invention, preferably, the average particle size of the nano metal oxide particles is 10-40 nm, which is conducive to better adsorption on the foam liquid film, plays a barrier protection role on the foam, increases the surface elasticity of the foam, weakens the drainage effect of the liquid film, and reduces the bubble aggregation speed, thereby making the carbon dioxide foam more stable and having a longer life.

[0076] According to the present invention, preferably, the cellulose nanofibers have a diameter of 3-8 nm and a length of 5-10 μm, which is conducive to better adsorption of the foam liquid film, plays a barrier protection role for the foam, increases the surface elasticity of the foam, weakens the drainage effect of the liquid film, and reduces the bubble aggregation rate, thereby making the carbon dioxide foam more stable and having a longer life.

[0077] According to the present invention, preferably, the nano metal oxide particles can be selected from at least one of nano titanium dioxide particles, nano aluminum oxide particles, nano zirconium dioxide particles, nano silicon dioxide particles, nano zinc oxide particles, nano chromium trioxide and nano manganese trioxide.

[0078] According to the present invention, preferably, the cellulose nanofibers may be selected from at least one of carboxymethylated cellulose nanofibers, ethyl cellulose nanofibers, hydroxyethyl cellulose nanofibers, hydroxypropyl methyl cellulose nanofibers and cellulose acetate butyrate nanofibers.

[0079] According to a preferred embodiment of the present invention, the foam stabilizer is a mixture of nano metal oxide particles and cellulose nanofibers, and more preferably a mixture of nano titanium dioxide particles, nano aluminum oxide particles and hydroxyethyl cellulose nanofibers in a weight ratio of 1: (0.5-1.5): (1-2).

[0080] According to the present invention, in the method for preparing the carbon dioxide working fluid, there is no particular limitation on the first mixing method, as long as the entrainer, the foaming agent and the foam stabilizer can be fully mixed to obtain a uniform mixed liquid. Preferably, the first mixing is performed at a stirring rate of 500-3000 rpm, and the mixing time is 1-5 min.

[0081] According to a preferred embodiment of the present invention, for the first mixing, preferably, the entrainer and the foam stabilizer are first mixed, and then the foaming agent is added and mixed to obtain a uniform mixed solution. This mixing method can make the foam stabilizer disperse more evenly, and thus the prepared carbon dioxide working fluid has better water solubility and foaming and stabilizing properties.

[0082] According to the present invention, in the method for preparing the carbon dioxide working fluid, there is no particular limitation on the second mixing method, as long as the mixed liquid and liquid carbon dioxide can be fully mixed to obtain a uniform carbon dioxide working fluid. During the second mixing process, the carbon dioxide can be kept in a liquid state by controlling the temperature and pressure. Preferably, the conditions for the second mixing include: a temperature of -20 to -15°C and a pressure of 1.8-2.5MPa.

[0083] Preferably, the second mixing is performed at a stirring rate of 500-3000 rpm, and the mixing time is 1-5 min.

[0084] The third aspect of the present invention provides a carbon dioxide working fluid prepared by the method described in the second aspect.

[0085] According to the present invention, the carbon dioxide working fluid prepared by the method described in the second aspect has the same composition and properties as the carbon dioxide working fluid described in the first aspect of the present invention, and will not be described in detail herein.

[0086] A fourth aspect of the present invention provides a method for water drainage and gas production in a low permeability gas reservoir, comprising: injecting the carbon dioxide working fluid described in the first aspect or the third aspect into a gas production well of a low permeability gas reservoir, and foaming the carbon dioxide foam produced by the foaming into a high water content gas production formation from the gas production well, and then returning the carbon dioxide foam to the ground, and using the carbon dioxide foam to carry out water in the near-well area of ​​the high water content gas production formation;

[0087] Wherein, the water content of the high-water-content gas-producing formation is greater than 80% by volume;

[0088] The permeability of the high water-content gas-producing formation is less than 1 md, preferably 0.1-0.5 md.

[0089] In the present invention, the near-wellbore area refers to the area within 5m from the wellbore where the pressure drops sharply in the pressure drop funnel curve from the bottom hole pressure to the formation pressure of the production well of the low-permeability gas reservoir. Since low-permeability gas reservoirs generally have the characteristics of low porosity, low permeability, and high water content, liquid accumulation is very easy to form in the near-wellbore area, resulting in reduced production or even shutdown of the gas well.

[0090] The low-permeability gas reservoir drainage gas production method provided by the present invention utilizes the carbon dioxide working fluid of the present invention and adopts a huff-and-puff process to carry the formation water in the near-wellbore area of ​​the low-permeability gas reservoir to the ground, wherein the phase behavior of carbon dioxide is changed by an entrainer to increase the solubility of the carbon dioxide working fluid in water, so that the carbon dioxide working fluid can carry more formation water in the near-wellbore area during the return process of the injection of the reservoir; carbon dioxide foam is generated by a foaming agent during the low-flow / low-shear-rate return flow process of the reservoir, and the carbon dioxide working fluid is brought into the reservoir and easily returned; the foam is stabilized by a foam stabilizer, so that the carbon dioxide foam is more stable and has a longer life. The water saturation reduction degree of the near-wellbore area of ​​the low-permeability gas reservoir can be reduced by more than 53%, and the maximum reduction degree of the water saturation in the near-wellbore area of ​​the low-permeability gas reservoir can be 80.1%, effectively realizing water control and production increase of old wells in the gas field.

[0091] The present invention will be described in detail below by way of examples. In the following examples and comparative examples, unless otherwise specified, all are conventional methods; the reagents and materials, unless otherwise specified, can be obtained from commercial sources.

[0092] Nano-titanium dioxide particles: average particle size 30 nm, purchased from Jiangsu Xianfeng Nanomaterial Technology Co., Ltd.;

[0093] Nano-alumina particles: average particle size 25 nm, purchased from Jiangsu Xianfeng Nanomaterial Technology Co., Ltd.;

[0094] Nano zirconium dioxide particles: average particle size 30 nm, purchased from Jiangsu Xianfeng Nanomaterial Technology Co., Ltd.;

[0095] Carboxymethylated cellulose nanofibers: 6 nm in diameter and 8 μm in length, purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.;

[0096] Hydroxyethyl cellulose nanofibers: 8 nm in diameter and 10 μm in length, purchased from Jiangsu Xianfeng Nanomaterials Technology Co., Ltd.

[0097] Example 1

[0098] (1) An entrainer (mixed with an alcohol auxiliary agent and a solvent in a weight ratio of 1:1.2; wherein the alcohol auxiliary agent is ethylene glycol, glycerol and dipropylene glycol mixed in a weight ratio of 1:0.8:1; and the solvent is triethanolamine, acetic acid and acetaldehyde mixed in a weight ratio of 1:1:1.2) and a foam stabilizer (mixed with nano-titanium dioxide particles, nano-alumina particles and hydroxyethyl cellulose nanofibers in a weight ratio of 1:0.8:1.5) are stirred and mixed at a stirring rate of 2000 rpm for 3 minutes, and then a foaming agent (mixed with 1-polyoxyethylene phenol-3-dodecyl, 1-polyoxypropylene phenol-3-dodecyl and 1-polyoxybutylene phenol-3-dodecyl in a weight ratio of 1:0.8:1) is added and stirred and mixed for 2 minutes to obtain a uniform mixed solution;

[0099] (2) injecting liquid carbon dioxide (purity of 99%, -18°C, 2.1MPa) into the high-pressure visualization container, turning on the agitator and adjusting the stirring rate to 1000 rpm, and injecting the above mixed solution into the liquid carbon dioxide using a high-pressure pump (during the injection process, the temperature was controlled to be -18°C and the pressure was 2.1MPa), stirring and mixing for 5 minutes after the injection, and obtaining a carbon dioxide working solution (referred to as S1);

[0100] In S1, the weight ratio of liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100:1.8:1.2:1.

[0101] Example 2

[0102] (1) An entrainer (mixed with an alcohol auxiliary agent and a solvent in a weight ratio of 1:1.5; wherein the alcohol auxiliary agent is ethylene glycol, glycerol and dipropylene glycol mixed in a weight ratio of 1:1:1; and the solvent is triethanolamine, acetic acid and acetaldehyde mixed in a weight ratio of 1:1.5:1.5) and a foam stabilizer (mixed with nano-titanium dioxide particles, nano-alumina particles and hydroxyethyl cellulose nanofibers in a weight ratio of 1:1.5:1.5) are stirred and mixed at a stirring rate of 2000 rpm for 5 minutes, and then a foaming agent (mixed with 1-polyoxyethylene phenol-3-dodecyl, 1-polyoxypropylene phenol-3-dodecyl and 1-polyoxybutylene phenol-3-dodecyl in a weight ratio of 1:1:1) is added and stirred and mixed for 2 minutes to obtain a uniform mixed solution;

[0103] (2) injecting liquid carbon dioxide (purity of 99%, -18°C, 2.1MPa) into the high-pressure visualization container, turning on the agitator and adjusting the stirring rate to 1000 rpm, and injecting the above mixed solution into the liquid carbon dioxide using a high-pressure pump (during the injection process, the temperature was controlled to be -18°C and the pressure was 2.1MPa), stirring and mixing for 5 minutes after the injection, and obtaining a carbon dioxide working solution (referred to as S2);

[0104] In S2, the weight ratio of liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100:1.8:1.2:1.

[0105] Example 3

[0106] (1) an entrainer (mixed with a solvent in a weight ratio of 1:1; wherein the alcohol auxiliary agent is ethylene glycol, glycerol and dipropylene glycol mixed in a weight ratio of 1:0.8:0.5; and the solvent is triethanolamine, acetic acid and acetaldehyde mixed in a weight ratio of 1:0.8:1) and a foam stabilizer (mixed with nano-titanium dioxide particles, nano-alumina particles and hydroxyethyl cellulose nanofibers in a weight ratio of 1:0.5:1) are stirred and mixed at a stirring rate of 2000 rpm for 2 minutes, and then a foaming agent (mixed with 1-polyoxyethylene phenol-3-dodecyl, 1-polyoxypropylene phenol-3-dodecyl and 1-polyoxybutylene phenol-3-dodecyl in a weight ratio of 1:0.8:0.8) is added and stirred and mixed for 2 minutes to obtain a uniform mixed solution;

[0107] (2) injecting liquid carbon dioxide (purity of 99%, -18°C, 2.1MPa) into the high-pressure visualization container, turning on the agitator and adjusting the stirring rate to 1000 rpm, and injecting the above mixed solution into the liquid carbon dioxide using a high-pressure pump (during the injection process, the temperature was controlled to be -18°C and the pressure was 2.1MPa), stirring and mixing for 5 minutes after the injection, and obtaining a carbon dioxide working solution (referred to as S3);

[0108] In S3, the weight ratio of liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100:1.5:1:0.8.

[0109] Example 4

[0110] (1) An entrainer (mixed with an alcohol auxiliary agent and a solvent in a weight ratio of 1:1.5; wherein the alcohol auxiliary agent is ethylene glycol, glycerol and dipropylene glycol mixed in a weight ratio of 1:1.8:1.5; and the solvent is triethanolamine, acetic acid and acetaldehyde mixed in a weight ratio of 1:1.8:2) and a foam stabilizer (mixed with nano-titanium dioxide particles, nano-alumina particles and hydroxyethyl cellulose nanofibers in a weight ratio of 1:1.5:2) are stirred and mixed at a stirring rate of 2000 rpm for 3 minutes, and then a foaming agent (mixed with 1-polyoxyethylene phenol-3-dodecyl, 1-polyoxypropylene phenol-3-dodecyl and 1-polyoxybutylene phenol-3-dodecyl in a weight ratio of 1:1.5:1.5) is added and stirred and mixed for 2 minutes to obtain a uniform mixed solution;

[0111] (2) injecting liquid carbon dioxide (purity of 99%, -18°C, 2.1MPa) into the high-pressure visualization container, turning on the agitator and adjusting the stirring rate to 1000 rpm, and injecting the above mixed solution into the liquid carbon dioxide using a high-pressure pump (during the injection process, the temperature was controlled to be -18°C and the pressure was 2.1MPa), stirring and mixing for 5 minutes after the injection, and obtaining a carbon dioxide working solution (referred to as S4);

[0112] In S4, the weight ratio of liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100:2:1.5:1.

[0113] Example 5

[0114] (1) an entrainer (mixed with an alcohol auxiliary agent and a solvent in a weight ratio of 1:1; wherein the alcohol auxiliary agent is ethanol; and the solvent is diethanolamine) and a foam stabilizer (nano zirconium dioxide particles) are stirred and mixed at a stirring rate of 2000 rpm for 2 min, and then a foaming agent (1-polyoxyethylene phenol-3-octyl) is added and stirred and mixed for another 2 min to obtain a uniform mixed solution;

[0115] (2) Inject liquid carbon dioxide (purity of 99%, -18°C, 2.1 MPa) into the high-pressure visualization container, turn on the agitator and adjust the stirring rate to 1000 rpm, and use a high-pressure pump to inject the mixed solution into the liquid carbon dioxide (during the injection process, the temperature is controlled to be -18°C and the pressure is 2.1 MPa). After the injection is completed, stir and mix for 5 minutes to obtain a carbon dioxide working solution (referred to as S5);

[0116] In S5, the weight ratio of liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100:1:0.1:0.1.

[0117] Example 6

[0118] (1) An entrainer (mixed with a solvent in a weight ratio of 1:1.5; wherein the alcohol auxiliary agent is methanol, propylene glycol and dipropylene glycol mixed in a weight ratio of 1:1.5:1.5; and the solvent is monoethanolamine, formic acid and formaldehyde mixed in a weight ratio of 1:1.5:1.8) and a foam stabilizer (mixed with nano zinc oxide particles, nano zirconium dioxide particles and hydroxypropyl methylcellulose nanofibers in a weight ratio of 1:1.3:1.8) are stirred and mixed at a stirring rate of 2000 rpm for 3 min, and then a foaming agent (mixed with 1-polyoxyethylene phenol-3-octyl, 1-polyoxypropylene phenol-3-nonyl and 1-polyoxybutylene phenol-3-dodecyl in a weight ratio of 1:1.5:1.8) is added and stirred and mixed for 2 min to obtain a uniform mixed solution;

[0119] (2) injecting liquid carbon dioxide (purity of 99%, -18°C, 2.1MPa) into the high-pressure visualization container, turning on the agitator and adjusting the stirring rate to 1000 rpm, and injecting the above mixed solution into the liquid carbon dioxide using a high-pressure pump (during the injection process, the temperature was controlled to be -18°C and the pressure was 2.1MPa), stirring and mixing for 5 minutes after the injection, and obtaining a carbon dioxide working solution (referred to as S6);

[0120] In S6, the weight ratio of liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100:3:2:1.5.

[0121] Example 7

[0122] (1) An entrainer (mixed with a solvent in a weight ratio of 1:1.5; wherein the alcohol auxiliary agent is ethanol, ethylene glycol and propylene glycol mixed in a weight ratio of 1:1.5:1.5; and the solvent is diethanolamine, propionic acid and acetaldehyde mixed in a weight ratio of 1:1.5:1.8) and a foam stabilizer (mixed with nano zinc oxide particles, nano zirconium dioxide particles and hydroxypropyl methylcellulose nanofibers in a weight ratio of 1:1.3:1.8) are stirred and mixed at a stirring rate of 2000 rpm for 3 min, and then a foaming agent (mixed with 1-polyoxyethylene phenol-3-octyl, 1-polyoxypropylene phenol-3-nonyl and 1-polyoxybutylene phenol-3-dodecyl in a weight ratio of 1:1.5:1.8) is added and stirred and mixed for 2 min to obtain a uniform mixed solution;

[0123] (2) injecting liquid carbon dioxide (purity of 99%, -18°C, 2.1MPa) into the high-pressure visualization container, turning on the agitator and adjusting the stirring rate to 1000 rpm, and injecting the above mixed solution into the liquid carbon dioxide using a high-pressure pump (during the injection process, the temperature was controlled to be -18°C and the pressure was 2.1MPa), stirring and mixing for 5 minutes after the injection, and obtaining a carbon dioxide working solution (referred to as S7);

[0124] In S7, the weight ratio of liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100:3:2:1.5.

[0125] Example 8

[0126] (1) An entrainer (mixed with an alcohol auxiliary agent and a solvent in a weight ratio of 1:1.5; wherein the alcohol auxiliary agent is obtained by mixing methanol, propylene glycol and dipropylene glycol in a weight ratio of 1:1.5:1.5; and the solvent is obtained by mixing monoethanolamine, formic acid and formaldehyde in a weight ratio of 1:1.5:1.8) and a foam stabilizer (mixed with nano zinc oxide particles, nano zirconium dioxide particles and hydroxypropyl methylcellulose nanofibers in a weight ratio of 1:1.3:1.8) are stirred and mixed at a stirring rate of 2000 rpm for 3 minutes, and then a foaming agent (mixed with 1-polyoxyethylene phenol-3-octyl, 1-polyoxypropylene phenol-3-nonyl and 1-polyoxybutylene phenol-3-dodecyl in a weight ratio of 1:1.5:1.8) is added and stirred and mixed for 2 minutes to obtain a uniform mixed solution;

[0127] (2) injecting liquid carbon dioxide (purity of 99%, -18°C, 2.1MPa) into the high-pressure visualization container, turning on the agitator and adjusting the stirring rate to 1000 rpm, and injecting the above mixed solution into the liquid carbon dioxide using a high-pressure pump (during the injection process, the temperature was controlled to be -18°C and the pressure was 2.1MPa), stirring and mixing for 5 minutes after the injection, and obtaining a carbon dioxide working solution (referred to as S8);

[0128] In S8, the weight ratio of liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100:1:2:1.5.

[0129] Example 9

[0130] (1) An entrainer (mixed with a solvent in a weight ratio of 1:0.8; wherein the alcohol auxiliary agent is methanol, propylene glycol and dipropylene glycol mixed in a weight ratio of 1:1.5:1.5; and the solvent is monoethanolamine, formic acid and formaldehyde mixed in a weight ratio of 1:1.5:1.8) and a foam stabilizer (mixed with nano zinc oxide particles, nano zirconium dioxide particles and hydroxypropyl methylcellulose nanofibers in a weight ratio of 1:1.3:1.8) are stirred and mixed at a stirring rate of 2000 rpm for 3 min, and then a foaming agent (mixed with 1-polyoxyethylene phenol-3-octyl, 1-polyoxypropylene phenol-3-nonyl and 1-polyoxybutylene phenol-3-dodecyl in a weight ratio of 1:1.5:1.8) is added and stirred and mixed for 2 min to obtain a uniform mixed solution;

[0131] (2) injecting liquid carbon dioxide (purity of 99%, -18°C, 2.1MPa) into the high-pressure visualization container, turning on the stirrer and adjusting the stirring rate to 1000 rpm, and injecting the above mixed solution into the liquid carbon dioxide using a high-pressure pump (during the injection process, the temperature was controlled to be -18°C and the pressure was 2.1MPa), stirring and mixing for 5 minutes after the injection, and obtaining a carbon dioxide working solution (referred to as S9);

[0132] In S9, the weight ratio of liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100:3:2:1.5.

[0133] Example 10

[0134] (1) An entrainer (mixed with an alcohol auxiliary agent and a solvent in a weight ratio of 1:1.5; wherein the alcohol auxiliary agent is methanol, propylene glycol and dipropylene glycol mixed in a weight ratio of 1:1.5:1.5; and the solvent is monoethanolamine, formic acid and formaldehyde mixed in a weight ratio of 1:1.5:1.8), a foam stabilizer (mixed with nano zinc oxide particles, nano zirconium dioxide particles and hydroxypropyl methylcellulose nanofibers in a weight ratio of 1:1.3:1.8) and a foaming agent (mixed with 1-polyoxyethylene phenol-3-octyl, 1-polyoxypropylene phenol-3-nonyl and 1-polyoxybutylene phenol-3-dodecyl in a weight ratio of 1:1.5:1.8) are stirred together at a stirring rate of 2000 rpm for 5 minutes to obtain a uniform mixed solution;

[0135] (2) injecting liquid carbon dioxide (purity of 99%, -18°C, 2.1MPa) into the high-pressure visualization container, turning on the agitator and adjusting the stirring rate to 1000 rpm, and injecting the above mixed solution into the liquid carbon dioxide using a high-pressure pump (during the injection process, the temperature was controlled to be -18°C and the pressure was 2.1MPa), stirring and mixing for 5 minutes after the injection is completed, and obtaining a carbon dioxide working solution (recorded as S10);

[0136] In S10, the weight ratio of liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100:3:2:1.5.

[0137] Comparative Example 1

[0138] The method of Example 6 is followed, except that no entrainer is added in step (1), and a uniform mixed solution is obtained by mixing the foam stabilizer and the foaming agent at a stirring rate of 2000 rpm for 5 min. The other steps, conditions and parameters are the same as those of Example 6, to obtain a carbon dioxide working solution (denoted as D1);

[0139] In D1, the weight ratio of liquid carbon dioxide: foaming agent: foam stabilizer is 100:2:1.5.

[0140] Comparative Example 2

[0141] According to the method of Example 6, the difference is that the feeding ratio of liquid carbon dioxide, entrainer, foaming agent and foam stabilizer is changed. The other steps, conditions and parameters are the same as those of Example 6 to obtain a carbon dioxide working liquid (denoted as D2);

[0142] In D2, the weight ratio of liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100:3.5:2.5:2.

[0143] Comparative Example 3

[0144] According to the method of Example 6, the difference is that the entrainer is obtained by mixing methanol, propylene glycol and dipropylene glycol at a weight ratio of 1:1.5:1.5. The other steps, conditions and parameters are the same as those of Example 6 to obtain a carbon dioxide working fluid (denoted as D3);

[0145] In D3, the weight ratio of liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100:3.5:2.5:2.

[0146] Comparative Example 4

[0147] The method of Example 6 is followed, except that the entrainer is obtained by mixing monoethanolamine, formic acid and formaldehyde at a weight ratio of 1:1.5:1.8. The other steps, conditions and parameters are the same as those of Example 6, and a carbon dioxide working fluid (denoted as D4) is obtained;

[0148] In D4, the weight ratio of liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100:3.5:2.5:2.

[0149] Test Case

[0150] 1. Foaming rate and foam separation half-life test

[0151] The high-pressure visual container filled with the carbon dioxide working liquids S1-S10 and D1-D4 prepared in Examples 1-10 and Comparative Examples 1-4 was heated to 90°C, and the pressure in the container was controlled to be 15 MPa. The working liquid was stirred at a stirring rate of 500 rpm for 5 minutes for foaming, and the foaming rate and foam liquid separation half-life of each working liquid were measured.

[0152] The results are shown in Table 1.

[0153] Table 1

[0154]

[0155]

[0156] As can be seen from Table 1, the carbon dioxide working fluid provided by the present invention has excellent foaming and foam stabilizing properties, with a foaming rate greater than 75% and a foam liquid half-life greater than 9 minutes. Among them, the foaming rate and half-life of working fluids S1-S4 are better than those of working fluids S5 and S6, and working fluids S1 and S2 have higher foaming rates and longer foam liquid half-lives, indicating that the composition of the carbon dioxide working fluid under the preferred conditions can bring about better foaming and foam stabilizing effects; the foaming rate and half-life of working fluids S7 and S8 are similar to those of working fluid S6, indicating that within the range of entrainer type and dosage specified by the present invention, only changing the material type or dosage of the entrainer has limited effect on the foam performance; compared with working fluid S6, working fluid S9 has a higher proportion of alcohol additives in S9, which makes the foaming rate and half-life of working fluid S9 inferior to those of S6; working fluid S10 is improved compared to working fluid S6. By changing the order of adding materials and mixing the entrainer, foam stabilizer and frother together, the foam expansion rate and half-life of S10 were both lower than those of S6. This may be because the dispersion effect of the foam stabilizer in the working liquid S10 was not as good as that produced by the working liquid S6. No entrainer was added to the working liquid D1, but since the foaming agent and foam stabilizer were the same as those of the working liquid S6, the foaming performance of the working liquid D1 was still equivalent to that of S6. The dosage of the foaming agent and foam stabilizer in the working liquid D2 was higher than that of S6, which made the foaming rate and half-life of the working liquid D2 larger. Compared with S6, the working liquids D3 and D4 used different entrainers, but since the foaming agent and foam stabilizer were the same as those of the working liquid S6, the foaming performance of D3 and D4 was still equivalent to that of S6.

[0157] 2. Core throughput simulation experiment

[0158] A core throughput simulation experiment was conducted on the carbon dioxide working fluids S1-S10 and D1-D4 prepared in Examples 1-10 and Comparative Examples 1-4 to evaluate their effect of reducing the water saturation of the core, so as to simulate and evaluate the effect of the working fluid on reducing the water saturation in the near-wellbore area of ​​a low-permeability gas reservoir.

[0159] The core huff-and-puff simulation experiment process is as follows:

[0160] (1) Determination of core dimensions: Use a vernier caliper to measure the diameter and length of a cylindrical core plunger (about 25 mm in diameter) that has been cleaned (oil and salt removed) and dried for three times. After each measurement, rotate the core 120° around the line connecting the centers of the two bottom surfaces of the plunger before measuring again. The average of the three diameter and length measurements is taken as the final diameter and length measurement value of the core, and the total volume of the core is calculated, which is recorded as V1.

[0161] (2) Calibration of core analysis instrument: Set the helium test pressure to 1.38 MPa and use a stainless steel standard volume block to calibrate the Boyle's law core analysis instrument;

[0162] (3) Determination of core pore volume: The core obtained in step (1) is placed in the sample cell of a calibrated Boyle's law core analysis instrument, the helium pressure is set to 1.38 MPa, and the volume of dry core particles is measured, which is recorded as V2. The pore volume of the core (recorded as V3) = V1-V2;

[0163] (4) Core saturation: The core whose pore volume was measured in step (3) was saturated with formation water (the salt content and mineralization of the formation water are shown in Table 2) under vacuum for 48 h, and the adhering water on the surface of the core was absorbed with filter paper, and then tightly wrapped with plastic wrap for standby use;

[0164] (5) Determination of water saturation of saturated core: remove the plastic wrap from the core treated in step (4), and measure the particle volume of the saturated core (denoted as V4) according to the method in step (3), then the water saturation of the saturated core (denoted as μ1) = (V4-V2) / V3×100%;

[0165] (6) Core throughput simulation: The core whose water saturation has been determined in step (5) is placed in a high-pressure (10 MPa) sealed container, and the core is soaked in a carbon dioxide working fluid for 2 h (temperature is 80-120°C, pressure is 10-15 MPa), and then the pressure is slowly released at a rate of less than 0.5 MPa / min. After the pressure is released, the core is taken out, and the adhesion on the surface of the core is absorbed with filter paper, and then tightly wrapped with plastic wrap for standby use;

[0166] (7) Determination of water saturation of the core after huff and puff: remove the plastic wrap from the core treated by immersion in the carbon dioxide working solution in step (6), and measure the particle volume of the core after huff and puff (denoted as V5) according to the method in step (3), then the water saturation of the core after huff and puff (denoted as μ2) = (V5-V2) / V3×100%;

[0167] (8) Calculation of the reduction degree of core water saturation (denoted as μ2): μ3 = μ1-μ2. The evaluation results are shown in Table 3.

[0168] Table 2

[0169]

[0170] Table 3

[0171]

[0172]

[0173]

[0174] Note: The permeabilities of SU15-5, SM58-61, M46-37 and L102-25 cores are 0.23md, 0.41md, 0.36md and 0.17md, respectively.

[0175] As can be seen from Table 3, the working fluids S1-S10 provided by the present invention can achieve a core water saturation reduction of more than 53% in the core throughput simulation experiment, and the highest core water saturation reduction can reach 80.1%, which indicates that the working fluid provided by the present invention can significantly reduce the water saturation in the near-well area of ​​the low-permeability gas reservoir, thereby achieving water control and increased production in the old wells of the gas field. Among them, the effect of working fluids S1-S4 in reducing the core water saturation is better than that of working fluids S5 and S6, indicating that the carbon dioxide working fluid composition under the preferred conditions can bring better effects of reducing the core water saturation; compared with S6, the proportion of alcohol additives in working fluid S9 is higher, so that the foaming rate and half-life of working fluid S9 are not as good as S6, and thus the effect of S9 in reducing the core water saturation is lower than that of S6. In particular, although the foaming and foam stabilizing properties of the working fluid D1 are comparable to those of S6, D1 does not contain an entrainer, which significantly reduces the water solubility of D1, resulting in D1 having a significantly worse effect on reducing the water saturation of the core than S1-S10; the ratio of the entrainer, foaming agent and foam stabilizer in the working fluid D2 does not meet the working fluid composition of the present invention, and its effect on reducing the water saturation of the core is also significantly worse than S1-S10; the working fluids D3 and D4 do not use the composite entrainer of the present invention, and their effect on reducing the water saturation of the core is also significantly worse than S1-S10.

[0176] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A carbon dioxide working fluid, characterized in that: include: Liquid carbon dioxide, entrainers, foaming agents and foam stabilizers; Wherein, the weight ratio of the liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100: (1-3): (0.1-2): (0.1-1.5); The entrainer includes an alcohol auxiliary agent and a solvent.

2. The carbon dioxide working fluid according to claim 1, wherein: The weight ratio of the liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100: (1.5-2): (1-1.5): (0.8-1).

3. The carbon dioxide working fluid according to claim 1 or 2, wherein: The weight ratio of the alcohol auxiliary agent to the solvent is 1:(1-1.5).

4. The carbon dioxide working fluid according to claim 3, wherein: The alcohol auxiliary agent is selected from at least one of methanol, ethanol, propanol, ethylene glycol, triethylene glycol, propylene glycol, glycerol, and dipropylene glycol, preferably at least one of ethylene glycol, glycerol, and dipropylene glycol; And / or, the solvent is selected from at least one of alcoholamine compounds, carboxylic acid compounds and aldehyde compounds, preferably at least one of monoethanolamine, diethanolamine, triethanolamine, formic acid, acetic acid, propionic acid, formaldehyde and acetaldehyde, and more preferably triethanolamine, acetic acid and acetaldehyde.

5. The carbon dioxide working fluid according to any one of claims 1 to 4, wherein: The foaming agent is a nonionic surfactant.

6. The carbon dioxide working fluid according to claim 5, wherein: The nonionic surfactant is selected from at least one of 1-polyoxyethylene phenol-3-octyl, 1-polyoxyethylene phenol-3-nonyl, 1-polyoxyethylene phenol-3-dodecyl, 1-polyoxypropylene phenol-3-octyl, 1-polyoxypropylene phenol-3-nonyl, 1-polyoxypropylene phenol-3-dodecyl, 1-polyoxybutylene phenol-3-octyl, 1-polyoxybutylene phenol-3-nonyl and 1-polyoxybutylene phenol-3-dodecyl, and is further preferably at least one of 1-polyoxyethylene phenol-3-dodecyl, 1-polyoxypropylene phenol-3-dodecyl and 1-polyoxybutylene phenol-3-dodecyl.

7. The carbon dioxide working fluid according to any one of claims 1 to 4, wherein: The foam stabilizer is selected from nano metal oxide particles and / or cellulose nanofibers.

8. The carbon dioxide working fluid according to claim 7, wherein: The average particle size of the nano metal oxide particles is 10-40 nm; And / or, the cellulose nanofibers have a diameter of 3-8 nm and a length of 5-10 μm.

9. The carbon dioxide working fluid according to claim 8, wherein: The nano-metal oxide particles are selected from at least one of nano-titanium dioxide particles, nano-aluminum oxide particles, nano-zirconium dioxide particles, nano-silicon dioxide particles, nano-zinc oxide particles, nano-chromium trioxide particles and nano-manganese trioxide particles; And / or, the cellulose nanofibers are selected from at least one of carboxymethylated cellulose nanofibers, ethyl cellulose nanofibers, hydroxyethyl cellulose nanofibers, hydroxypropyl methyl cellulose nanofibers and cellulose acetate butyrate nanofibers.

10. A method for preparing a carbon dioxide working fluid, comprising: (1) performing a first mixing of an entrainer, a foaming agent, and a foam stabilizer to obtain a mixed solution; (2) performing a second mixing of the mixed liquid and liquid carbon dioxide to obtain a carbon dioxide working liquid; Wherein, the weight ratio of the liquid carbon dioxide: entrainer: foaming agent: foam stabilizer is 100: (1-3): (0.1-2): (0.1-1.5); The entrainer includes an alcohol auxiliary agent and a solvent.

11. The preparation method according to claim 10, wherein: The first mixing includes: firstly mixing the entrainer and the foam stabilizer, and then adding the foaming agent to mix.

12. The preparation method according to claim 10 or 11, wherein: The second mixing conditions include: a temperature of -20 to -15°C and a pressure of 1.8 to 2.5 MPa.

13. The preparation method according to claim 10 or 11, wherein: The weight ratio of the alcohol auxiliary agent to the solvent is 1:(1-1.5); And / or, the foaming agent is a nonionic surfactant; And / or, the foam stabilizer includes nano metal oxide particles and / or cellulose nanofibers.

14. A carbon dioxide working fluid obtained by the method according to any one of claims 10 to 13.

15. A method for recovering gas from a low-permeability gas reservoir by draining water, comprising: Injecting the carbon dioxide working fluid described in any one of claims 1 to 9 and 14 into a gas production well of a low-permeability gas reservoir, and then foaming the carbon dioxide foam generated by the foaming into the ground, and using the carbon dioxide foam to carry out water in the near-well area of ​​the high-water-content gas-producing formation; Wherein, the water content of the high-water-content gas-producing formation is greater than 80% by volume; The permeability of the high water-content gas-producing formation is less than 1 md, preferably 0.1-0.5 md.

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