Water-gas alternating flooding gas solubilizing and crude oil viscosity reducing method and construction method thereof

Abstract

The invention relates to a water-gas alternate flooding gas solubilization and crude oil viscosity reduction method and a construction method thereof in the field of oil and gas development. The method comprises gas flooding and water flooding processes which are alternately carried out; before gas drive, a solubilizer is added into supercritical CO2 in advance to obtain a supercritical fluid I, and the solubilizer is formed by compounding tetrachloroethylene and a synergist; before water flooding, a water-soluble surfactant is added into matrix water in advance to obtain a second water flooding fluid, and the water-soluble surfactant is polyoxyethylene ether and / or polyoxyethylene ester. The gas solubilization and crude oil viscosity reduction method for water-gas alternating flooding has the following advantages that the compounded solubilizing agent and viscosity reducer are added in the CO2 flooding stage and the matrix water flooding stage respectively, and the solubilizing agent capable of being fully mixed with CO2 is prepared by taking the organic solvent tetrafluoroethylene as a main component and cooperating with the synergist; a surfactant with excellent emulsifying performance is compounded with matrix water to form the emulsifying viscosity reducer with relatively strong oil washing capacity. The expansion, viscosity reduction and extraction effects of CO2 are fully exerted in the water-gas alternating flooding process, the viscosity reduction and oil displacement effects of a water phase are improved, and water-gas alternating synergistic interaction is achieved.

Description

Technical Field

[0001] The present invention relates to the field of oil and gas development, and in particular to a water-gas alternating flooding gas solubilization and crude oil viscosity reduction method and a construction method thereof. Background Art

[0002] my country has extensive continental low-permeability oil and gas reservoirs, but under current economic and technical conditions, they cannot be effectively developed using conventional methods. Low-permeability reservoirs, despite their low porosity and permeability, present injection difficulties with conventional water flooding. Fracturing can lead to ineffective crossflow of the injected medium, making it difficult to achieve high recovery rates. Carbon dioxide flooding is a technique that can effectively increase the recovery rate of low-permeability reservoirs. Alternating water-gas flooding, using carbon dioxide as the primary recovery medium, can also effectively avoid problems such as gas crossflow after injection.

[0003] When CO2 is used to develop such reservoirs, it can effectively increase oil (gas) recovery and improve the reservoir environment by dissolving and expanding crude oil, reducing viscosity, lowering interfacial tension, and evaporating and extracting it. For heavy oil, CO2 dissolved in crude oil can significantly reduce its viscosity and enhance its fluidity by expanding it. However, the limited ability of heavy oil to dissolve CO2 limits its improvement. Furthermore, the significant difference in viscosity between the two can lead to rapid gas cross-flow. Therefore, CO2 alone is not very effective in developing heavy oil.

[0004] Although the water phase in conventional water-gas alternating flooding can effectively seal channeling and expand the swept volume of CO2 in the reservoir, the water phase has a low oil displacement efficiency and also produces a water shield in the reservoir, which has a significant negative impact on CO2 oil displacement. In addition, conventional CO2 and water alternating flooding also has problems such as limited crude oil viscosity reduction effect and ineffective reduction of interfacial tension.

[0005] Using CO2 solubilizing viscosity reducer as a CO2 additive can, on the one hand, enhance the solubility of CO2 in crude oil, thereby achieving the purpose of reducing viscosity over a large range and lowering interfacial tension. On the other hand, the agent itself has the function of reducing the viscosity of heavy oil, and can be carried by CO2 to deep formations to fully and effectively contact with crude oil, dissolving in crude oil, thereby achieving the purpose of dual viscosity reduction of viscosity reducer and CO2.

[0006] At present, in the research on CO2 enhanced oil recovery, the main focus is on the analysis of influencing factors of the minimum miscible pressure of CO2 flooding, which has a certain effect on reducing the miscible pressure. In the related research on CO2 solubilizing and viscosity reducing agents for heavy oil, viscosity reducing agents generally only have the function of reducing viscosity and cannot achieve the purpose of enhancing the ability of crude oil to dissolve CO2. Therefore, it is necessary to conduct in-depth development and research on CO2 solubilizing and viscosity reducing agents, and combine them with water-gas alternating flooding to give full play to their advantages in order to maximize the oil recovery rate. Summary of the Invention

[0007] The present invention addresses the shortcomings of CO2 alternating water-gas flooding in the prior art and provides a method for solubilizing gas and reducing crude oil viscosity during alternating water-gas flooding. This method allows CO2 to fully mix with crude oil, achieving multiple viscosity reductions and effectively controlling gas channeling, significantly enhancing the enhanced oil recovery (ERR) effect of alternating water-gas flooding. By adding a surfactant to the injected water during the water flooding phase to enhance the oil-washing capacity, and adding a solubilizing agent to the supercritical CO2 during the gas flooding phase, the solubility of CO2 in crude oil is significantly increased at the same pressure, promoting full mixing of the crude oil and CO2, and causing greater expansion of the crude oil, reducing viscosity, and lowering interfacial tension.

[0008] The object of the present invention is achieved by providing a method for gas solubilization and crude oil viscosity reduction by alternating water-gas flooding, characterized in that it includes alternating gas flooding and water flooding processes; before gas flooding, a solubilizer is added to supercritical CO2 to obtain supercritical fluid one, wherein the solubilizer is a compound of tetrachloroethylene and a synergist; before water flooding, a water-soluble surfactant is added to matrix water to obtain water flooding fluid two, wherein the water-soluble surfactant is polyoxyethylene ether and / or polyoxyethylene ester.

[0009] Compared with the prior art water-gas alternating flooding, the present invention has the following advantages: based on the development of water-gas alternating flooding in low-permeability oil reservoirs, a compounded solubilizer and viscosity reducer are added in the CO2 flooding and matrix water flooding stages, respectively. The organic solvent tetrafluoroethylene is mainly used in combination with a synergist to prepare a solubilizer that can fully mix with CO2. A water-soluble nonionic surfactant with good emulsification effect is compounded with matrix water to form an emulsified viscosity reducer with strong oil washing ability. While fully utilizing the expansion, viscosity reduction and extraction effects of CO2 during the water-gas alternating flooding process, the oil displacement effect of the water phase is enhanced, thereby further improving the oil displacement effect of the water-gas alternating flooding.

[0010] Furthermore, the synergist comprises at least two of alkanes and their derivatives, alcohols, and aromatic hydrocarbons and their derivatives, with at least one of each type. This combination of two synergists can significantly increase the solubility of CO2 in crude oil, thereby fully utilizing the dissolution and expansion properties of CO2 in oil recovery, reducing crude oil viscosity and lowering the interfacial tension between the two, thereby improving oil recovery efficiency. Furthermore, the alkane and its derivatives include benzene, toluene, or chloroform.

[0011] Furthermore, the alcohol is ethanol, propanol or butanol.

[0012] Furthermore, the aromatic hydrocarbons and their derivatives are benzene, toluene and chloroform.

[0013] As a preferred embodiment of the present invention, the solubilizer accounts for 2% to 5% by weight of the supercritical fluid.

[0014] As a preferred embodiment of the present invention, the mass composition of the solubilizer is: 70% to 90% tetrachloroethylene and 10% to 30% synergist.

[0015] As a preferred embodiment of the present invention, the supercritical CO2 is a fluid obtained by pressurizing and heating CO2 with a purity of 99.99% (pressure greater than 7.3 MPa and temperature greater than 31.1°C).

[0016] As a preference of the present invention, the mass ratio of the water-soluble surfactant in the second water flooding fluid is 2% to 5% by weight.

[0017] As a preference of the present invention, the matrix water is formation water.

[0018] In order to facilitate the application of the water-gas alternating flooding of the present invention in mine stratum construction, the present invention also provides a water-gas alternating flooding construction method, the specific process of which is: configuring supercritical fluid one and water flooding fluid two, alternately setting the cycle of water-gas alternating flooding, and performing the gas flooding and water flooding processes alternately according to the cycle.

[0019] Furthermore, the cycle period is 3-6 months, with the first half of each cycle being gas drive and the second half being water drive.

[0020] The construction method of the present invention improves the comprehensive effect of crude oil recovery rate and CO2 storage efficiency in the current CO2 capture and storage technology by setting the water-gas alternating flooding construction method at a certain period. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] Figure 1 This is a comparison chart of the water-gas alternating flooding results of 0.2PV water-0.2PV carbon dioxide. DETAILED DESCRIPTION

[0022] The application method and effects of the present invention are further described below through examples.

[0023] First, the viscosity, solubility and other physical property parameters of the mixed system are measured in a high-temperature and high-pressure formation fluid phase measurement instrument (hereinafter referred to as PVT) under simulated formation temperature and pressure conditions to illustrate the application effect of the present invention.

[0024] The instruments, reagents, and materials used in the following examples were prepared in accordance with SY / T 5154-2014, "Sampling Methods for Oil and Gas Reservoir Fluids," and GB / T 26981-2020, "Analysis Methods for Physical Properties of Oil and Gas Reservoir Fluids." Unless otherwise specified, these instruments, reagents, and materials are conventional instruments, reagents, and materials available in the prior art and can be obtained through reputable commercial channels. The experimental methods and testing methods used in the following examples are also conventional experimental methods and testing methods available in the prior art, unless otherwise specified.

[0025] Comparative Example 1: Gas flooding simulation experiment with only CO2 single-phase medium and no water added under laboratory conditions (1) Live oil (what is live oil? Please explain in detail) is prepared above the saturation pressure according to the formation gas-oil ratio. Under laboratory simulated formation conditions, 100 ml of live oil is introduced into the crude oil PVT device at a pressure above the saturation pressure. The original live oil viscosity is tested by the falling ball method and is 147 mPa·s. Live oil is a live crude oil prepared in the laboratory by mixing gas samples and degassed oil samples taken from the wellhead of the oil field according to the formation temperature, pressure and original gas-oil ratio. (2) The supercritical fluid is a supercritical fluid obtained by pressurizing 99.99% pure CO2 to a pressure greater than 7.3 MPa and a temperature greater than 31.1°C; (3) The volume of the PVT device reactor was kept constant, and supercritical fluid was injected into the PVT device until the formation pressure was reached. After sufficient stirring, the viscosity of the mixed system was measured by the falling ball method to be 134.7 mPa·s, the viscosity reduction rate was 8.35%, and the CO2 solubility was 2.62%wt.

[0026] Comparative Example 2: Water-gas alternating flooding simulation experiment without adding solubilizer and viscosity reducing formula (1) Prepare the formation water for the experiment, heat it up and stir it to make it fully mixed, pour it into the intermediate container after it reaches the formation temperature, and pressurize it to the formation pressure for use; (2) Live oil above the saturation pressure was prepared according to the formation oil-gas-oil ratio. Under laboratory simulated formation conditions, 100 ml of live oil was introduced into the crude oil PVT device at a pressure above the saturation pressure. The viscosity of the original live oil was tested by the falling ball method and found to be 147 mPa·s. (3) Continue to inject 10 ml of formation water into the PVT device at a constant pressure; (4) The volume of the reactor of the PVT device was kept unchanged, and the supercritical fluid in Comparative Example 1 was injected into the reactor until the formation pressure was reached. After sufficient stirring, the viscosity of the mixed system was measured by the falling ball method to be 136.0 mPa·s, the viscosity reduction rate was 7.50%, and the CO2 solubility was 1.78%wt.

[0027] Comparative Example 3: Simulation Experiment 1 of Water-Gas Alternating Flooding Using Water Flooding Fluid 2 (1) Add 5%wt of alkylphenol polyoxyethylene ether to the prepared formation matrix water, heat and stir to mix thoroughly, and obtain the water flooding fluid 2 of this comparative example. After reaching the formation temperature, pour it into an intermediate container and pressurize it to the formation pressure for standby use; (2) Live oil above the saturation pressure was prepared according to the formation oil-gas-oil ratio. Under laboratory simulated formation conditions, 100 ml of live oil was introduced into the crude oil PVT device at a pressure above the saturation pressure. The viscosity of the original live oil was tested by the falling ball method and found to be 147 mPa·s. (3) Continue to inject 10 ml of water flooding fluid 2 into the PVT device at constant pressure; (4) The volume of the reactor of the PVT device was kept unchanged, and the supercritical fluid in Comparative Example 1 was injected into the reactor until the formation pressure was reached. After sufficient stirring, the viscosity of the mixed system was measured by the falling ball method to be 98.97 mPa·s, the viscosity reduction rate was 32.66%, and the CO2 solubility was 2.52%wt.

[0028] Comparative Example 4: Simulation Experiment 2 using Water Flooding Fluid 2 for Water-Gas Alternating Flooding (1) Add 5%wt fatty acid polyoxyethylene ester to the prepared matrix water (formation water), heat and stir to mix thoroughly, and obtain the water flooding fluid 2 of this comparative example. After reaching the formation temperature, pour it into an intermediate container and pressurize it to the formation pressure for standby use; (2) Live oil above the saturation pressure was prepared according to the formation oil-gas-oil ratio. Under laboratory simulated formation conditions, 100 ml of live oil was introduced into the crude oil PVT device at a pressure above the saturation pressure. The viscosity of the original live oil was tested by the falling ball method and found to be 147 mPa·s. (3) Continue to inject 10 ml of the water flooding liquid 2 of this comparative example into the PVT device at a constant pressure; (4) The volume of the reactor of the PVT device was kept unchanged. The supercritical fluid of Comparative Example 1 was injected into the PVT device until the formation pressure was reached. After sufficient stirring, the viscosity of the mixed system was measured by the falling ball method to be 83.54 mPa·s, the viscosity reduction rate was 43.17%, and the CO2 solubility was 2.83%wt.

[0029] Example 1: A simulation experiment for gas solubilization and crude oil viscosity reduction in water-gas alternating flooding (1) Add 3%wt fatty acid polyoxyethylene ester to the prepared matrix water (formation water), heat and stir to mix thoroughly, to obtain the water flooding fluid 2 of this embodiment, pour it into an intermediate container after reaching the formation temperature, and pressurize it to the formation pressure for standby use; (2) The supercritical fluid is a supercritical fluid 1 of this embodiment obtained by pressurizing 99.99% pure CO2 with a mass fraction of 3% wt of a solubilizer (70% tetrachloroethylene, 20% dichloromethane, and 10% butanol); (3) Live oil above the saturation pressure was prepared according to the formation oil-gas-oil ratio. Under laboratory simulated formation conditions, 100 ml of live oil was introduced into the crude oil PVT device at a pressure above the saturation pressure. The viscosity of the original live oil was tested by the falling ball method and found to be 147 mPa·s. (4) Continue to inject 10 ml of the water flooding fluid from step (1) into the PVT device at constant pressure; (5) Keeping the volume of the PVT device reactor unchanged, the supercritical fluid from step (2) was injected into the reactor until it reached the formation pressure. After sufficient stirring, the compounding of the composite formula 3 and its miscibility with the original formation oil sample were achieved. The viscosity of the mixed system was measured by the falling ball method to be 59.93 mPa·s, the viscosity reduction rate was 59.23%, and the CO2 solubility was 8.06%wt; Example 2 to Example 4: The steps are the same as Example 1, and the added viscosity reducer and solubilizing agent and their contents are also the same. The difference is that the component composition of the synergist of supercritical fluid one and the water-soluble surfactant component of water flooding fluid two are different, and different implementation plans are formed by combining them in pairs. The synergist content is also the same in each group of examples and a parallel comparison has been carried out. The formula details, viscosity reduction and solubilization effects of the four groups of examples are compared in Table 1. As can be seen from the table, the extent of crude oil viscosity reduction in each group of examples compared with the control example is greatly improved from 43.17% to more than 55%, with a maximum of 64.23%. At the same time, the CO2 solubility is greatly increased from 2.83% to more than 5.8%, with a maximum of 8.06%. This shows that the combined formula system achieves a significant improvement in crude oil viscosity reduction and CO2 solubilization effects, achieving a synergistic additive effect.

[0030] Example 5

[0031] To clarify the practical application of the water-gas alternating flooding method for gas solubilization and crude oil viscosity reduction, this study conducted core fluid linear nuclear magnetic resonance (NMR) monitoring following water-gas alternating flooding experiments under reservoir temperature conditions. The experimental procedures were conducted in accordance with GB / T 28912-2012, "Method for Determination of Relative Permeability of Two-Phase Fluids in Rocks," and the NMR measurements during the process were conducted in accordance with SY / T 6490-202, "Laboratory Measurement Range of Nuclear Magnetic Resonance Parameters for Rock Samples." The oil displacement effects of the basic comparative example (Comparative Example 2) and the example (Example 1) of water-gas alternating flooding were then compared.

[0032] The experimental core is an artificial core with a length of 8 cm, a diameter of 2.5 cm, a porosity of 13.01%, and a permeability of 30 mD.

[0033] The crude oil used in the experiment is the active formation oil configured by the L Block Oil and Gas Reservoir Fluid Analysis Experiment.

[0034] The experimental gas used was high-purity CO2 gas with a purity of 99.99%.

[0035] The tetrachloroethylene, kerosene, n-butane and inorganic salts used in the experiment to prepare the formation water were all purchased from the market.

[0036] In order to shield the interference of hydrogen signals, heavy water (D2O) was used as the experimental water, which has no signal detected by nuclear magnetic resonance. Therefore, the hydrogen signal obtained during the displacement experiment only reflects the changes in oil.

[0037] The online nuclear magnetic resonance monitoring instrument is the HCFX-5 nuclear magnetic resonance core analysis system jointly developed by Suzhou Newmai Analytical Instrument Co., Ltd. and Jiangsu Tuochuang Technology.

[0038] After connecting the core to monitor the gas tightness, it was saturated with bound water, saturated with oil and then subjected to an aging process.

[0039] The water-gas alternating flooding was carried out with 0.2PV water-0.2PV carbon dioxide. The experimental results are as follows: Figure 1 .

[0040] pass Figure 1 It can be seen intuitively that the embodiment in which a formula for gas solubilization and crude oil viscosity reduction for water-gas alternating flooding is added has significantly better effects than the comparative example in large, medium and small pores of the core.

[0041] In order to guide the popularization and application of this invention in the mine and improve the comprehensive effect of the current CO2 capture flooding and storage technology in improving the oil recovery rate and CO2 storage efficiency, the following alternating flooding and storage construction method is adopted in the on-site implementation: (1) Optimize the injection layer and well pattern based on the geological and reservoir conditions of the target reservoir for technology implementation; (2) The injection method is designed according to the water-gas alternation method, with water injection first and gas injection later. The injection cycle is 3-6 months, with water injection in the first half of the cycle and gas injection in the second half of the cycle. (3) Before water injection, add 3% fatty acid polyoxyethylene ester (or alkylphenol polyoxyethylene ether) to water to prepare the aqueous injection solution, namely water flooding fluid 2; before gas injection, add 1.05% tetrachloroethylene, 0.3% dichloromethane and 0.15% butanol to supercritical CO2 to prepare ultra-supercritical fluid 1; (4) The designed total injection volume is 0.3 PV (a multiple of the reservoir pore volume, a dimensionless quantity that represents the injection volume), and the gas injection volume and injection volume are 0.15 PV respectively; (5) The water injection rate is 0.05PV / year and the gas injection rate is 0.06PV / year; (6) Considering the complex composition of the formula system and the characteristics of CO2, a process technology plan for corrosion and scale prevention needs to be formulated.

[0042] By calculating the saturated oil nuclear magnetic resonance T2 value and the nuclear magnetic resonance signal T2 value of the comparative example (and the present embodiment), the recovery rate changes and the degree of utilization of different pores of the water-gas alternating flooding gas solubilization and crude oil viscosity reduction construction method of the present embodiment and the blank comparative example were obtained, as shown in Table 2. The water flooding fluid 2 and the ultra-supercritical fluid 1 in the water-gas alternating flooding construction method of the blank comparative example were configured according to Comparative Example 3.

[0043]

[0044] By comparison, it was found that the water-gas alternating flooding construction method with the addition of the synergist compound component and the matrix water viscosity reducing component in this example had a significantly higher recovery rate than the water-gas alternating flooding in the comparative example, with the recovery rate increased by 16.67%, which has a relatively considerable benefit.

[0045] Further comparison shows that the water-gas alternating flooding construction method in which a synergist compound component and a matrix water viscosity-reducing component are added in this embodiment has a surfactant added to the water phase. During the process of crude oil emulsification and viscosity reduction, the water phase in the small pores reduces the length of the water column in the pore throat, reduces the capillary force, and makes it easier for CO2 to penetrate the water column and contact the crude oil, thereby increasing the crude oil utilization rate in the medium pores.

Claims

1. A method for gas solubilization and crude oil viscosity reduction by alternating water and gas flooding, characterized in that: The method comprises alternating gas drive and water drive processes; before gas drive, a solubilizer is added to supercritical CO2 to obtain supercritical fluid 1, wherein the solubilizer is a compound of tetrachloroethylene and a synergist; before water drive, a water-soluble surfactant is added to matrix water to obtain water drive fluid 2, wherein the water-soluble surfactant is polyoxyethylene ether and / or polyoxyethylene ester.

2. The method for gas solubilization and crude oil viscosity reduction by water-gas alternating flooding according to claim 1, characterized in that: The synergist is at least two types of alkanes and their derivatives, alcohols, aromatic hydrocarbons and their derivatives, and at least one of each type.

3. The method for gas solubilization and crude oil viscosity reduction by water-gas alternating flooding according to claim 2, characterized in that: The alkanes and their derivatives include benzene, toluene or chloroform; the alcohols are ethanol, propanol or butanol; and the aromatic hydrocarbons and their derivatives are benzene, toluene and chloroform.

4. The method for gas solubilization and crude oil viscosity reduction by water-gas alternating flooding according to claim 2, characterized in that: The solubilizer accounts for 2% to 5% by weight of the supercritical fluid.

5. The method for gas solubilization and crude oil viscosity reduction by water-gas alternating flooding according to claim 2, characterized in that: The mass components of the solubilizer are: 70% to 90% of tetrachloroethylene and 10% to 30% of a synergist.

6. The method for gas solubilization and crude oil viscosity reduction by water-gas alternating flooding according to claim 1, characterized in that: The supercritical CO2 is a fluid obtained by pressurizing CO2 with a purity of 99.99%.

7. The method for gas solubilization and crude oil viscosity reduction by water-gas alternating flooding according to claim 1, characterized in that: The mass ratio of the water-soluble surfactant in the second water flooding fluid is 2% to 5% by weight.

8. The method for gas solubilization and crude oil viscosity reduction by water-gas alternating flooding according to claim 1, characterized in that: The matrix water is formation water.

9. A water-gas alternating flooding construction method, characterized in that: The supercritical fluid 1 and the water flooding fluid 2 are configured according to the method described in any one of claims 1 to 7, and the cycle of water-gas alternating flooding is alternately set, and the gas flooding and water flooding processes are alternately performed in each cycle.

10. The construction method according to claim 9, characterized in that: The cycle period is 3-6 months, with the first half of each cycle being gas drive and the second half being water drive.

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