Viscosity reduction and cold production method for thickened oil

Abstract

The invention belongs to the technical field of oil and gas exploitation, and discloses a viscosity reduction and cold production method for thickened oil. Comprising the steps of oil field crude oil HLB value determination, viscosity reducer preparation, viscosity reducer formula screening, test well potential evaluation and thick oil viscosity reduction cold production method selection. When the developed viscosity reducer is mixed with overseas river crude oil, the viscosity reduction rate of the crude oil is 96-99%, the average oil-water interfacial tension is 3.1 * 10 <-3 > mN / m, the emulsification stability is good, the critical micelle concentration (CMC) is 0.82-3.55 g / L, the interfacial tension gamma cmc under the critical micelle concentration is 34.81-40.76 mN / m, and the temperature resistance is 30-80 DEG C.

Description

Technical Field

[0001] The invention belongs to the technical field of oil and gas production, and in particular relates to a method for cold production of heavy oil with reduced viscosity. Background Art

[0002] At present, steam injection for heavy oil production faces the problems of high energy consumption, high carbon emissions, and low economic benefits. It is increasingly not adapted to the development of the times. In addition, steam injection development is also subject to the limitations of the ground steam injection pipeline network, safety hazards of non-prestressed completion steam injection, and the hazards of high temperature and high pressure on the ground. In addition, some heavy oil reservoirs cannot guarantee the dryness of steam injection or the thermal recovery effect is poor due to problems such as low reservoir permeability, deep burial, sand production, and the presence of edge and bottom water. Similarly, electric heating lifting technology also has problems such as high energy consumption, high investment cost, and the effective area is limited to the wellbore. Therefore, it is necessary to develop new viscosity reduction cold recovery technology. First, to find energy-saving, consumption-reducing, and emission-reducing development methods for heavy oil development; second, to provide effective viscosity reduction and production-increasing technologies for heavy oil blocks that are not suitable for thermal recovery, which can effectively promote oil and gas companies to reduce costs, increase efficiency, and save energy and reduce emissions.

[0003] At present, relevant technical tests have been carried out in various oil production plants of oil field companies, mainly using commercial sulfonate viscosity reducers, and the injection process adopts one-time injection. The main problems of this technology are low viscosity reduction performance of the viscosity reducer, the viscosity reduction rate is below 95%, and the miscibility of the viscosity reducer in the well is poor. For crude oil with a colloid + asphaltene content of more than 30%, the viscosity reduction effect is poor, and the maximum applicable crude oil viscosity is 20000mPa·s; the formed O / W emulsion has poor stability, cannot take into account both viscosity reduction and oil washing functions, and cannot achieve ultra-low interfacial tension (≤10 -3 mN / m) has limited effect on improving oil recovery; the injection process is single and the effective period is short. Summary of the invention

[0004] In order to overcome the shortcomings of the prior art, the present invention provides a method for heavy oil viscosity reduction and cold production, including molecular design and preparation of a high-efficiency viscosity reducer, a method for screening wells, and design and selection of an injection process, to form a complete set of viscosity reduction and cold production methods, so as to achieve the purpose of efficient production of heavy oil under non-thermal production conditions.

[0005] The above object of the present invention is achieved through the following technical solution: A method for cold production of heavy oil with reduced viscosity, comprising the following steps:

[0006] 1. Determination of HLB value of oil field crude oil: Use Span-60 and TW-80 to prepare a series of compound emulsifiers with different HLB values ​​for calibration in different proportions. Take the compound emulsifier for calibration with a concentration of 1%. According to the oil-water mass ratio of 7:3, put 200ml of dehydrated crude oil and compound emulsifier solution for calibration in a beaker, keep the temperature at 70℃, let it stand for 1h, stir to form a uniformly mixed oil-water emulsion, take 20ml and put it in a centrifuge tube, keep it at a constant temperature for 6h, and compare the volume of precipitated water to obtain the HLB value of the crude oil. The sample with the least precipitated water is the most stable;

[0007] 2. Preparation of viscosity reducer: In a high temperature and high pressure reactor, introduce N 2 As a protective gas, then add THF as a solvent, raise the temperature to 30°C, stir polystyrene maleic anhydride (SMA) and side-link grafting agents 2-phenylethanol, stearyl alcohol (octadecyl alcohol) and stigmasterol until fully dissolved, raise the temperature to 60°C, and add a small amount of PTSA as a catalyst. Keep the temperature at not less than 60°C for 8 hours, and stir thoroughly during the reaction. Then stop heating and stirring, and use a vacuum pump to recover the solvent under negative pressure until it is basically recovered. Add to acetone not higher than 20°C, and obtain a white powder after precipitation. Wash repeatedly with acetone to obtain the final product; prepare a viscosity reducer solution at a concentration of 1%, and then use the critical micelle concentration method to determine the HLB value of the synthesized viscosity reducer;

[0008] 3. Viscosity reducer formula screening: According to standard Q / SY LH0552-2021, viscosity reduction test was carried out, samples close to the HLB value range of crude oil were respectively prepared into 0.5% aqueous solution, and then viscosity reduction experiments were carried out with crude oil respectively. The samples with the highest viscosity reduction rate and the stable emulsion at 70°C (simulated formation temperature) for 72 hours were statistically selected, and no stratification problem occurred, which was the best formula system for preparing viscosity reducer;

[0009] 4. Potential evaluation of test wells: Summarize the reservoir characteristics and dynamic parameters of the test wells, and give the main influencing factors of the viscosity reduction cold production measures, namely crude oil viscosity, reservoir depth, oil layer thickness, permeability, oil saturation, and formation pressure coefficient, based on the technical indicators of the viscosity reducer and related indoor experimental parameters. The well selection criteria are crude oil viscosity (degassing at 50°C on the ground) ≤ 50000mPa·s, reservoir depth ≤ 3000m, oil layer thickness 3-30m, and permeability ≥ 10×10 -3 μm 2 , oil saturation ≥ 0.35, formation pressure coefficient ≥ 0.2;

[0010] 5. Selection of cold production methods for heavy oil viscosity reduction: You can choose between one-time injection by pump truck and periodic injection. The one-time injection by pump truck is suitable for any of the following production conditions:

[0011] a. High production in the early stage and low liquid production in the late stage, with the liquid volume decreasing by more than 30%, which is suspected to be a problem well with low liquid volume due to thick oil;

[0012] b. Wells that were previously in huff-and-puff production but are currently producing low amounts of liquid and are suspected to be nearing the end of production in this cycle;

[0013] c. Wells that are not suitable for steam injection production due to restrictions on the surface, well completion, formation sand production or active bottom water;

[0014] The specific method of periodic injection is the ground automatic dosing device + injection and production column pump, which is aimed at any of the following production conditions:

[0015] A. Moisture content is less than 70%;

[0016] B. Soft sticking due to thick oil, high load on the pumping unit, and the power diagram showing the influence of thick oil, resulting in difficulty in lifting or low pump efficiency;

[0017] C. The oil is poorly dispersed in the produced fluid and is in the form of clumps;

[0018] The one-time injection method of the pump truck is: casing annulus injection, sweep radius ≥ 4m, viscosity reducer injection concentration 0.5%, permeation agent injection concentration 0.03%, displacement water ≥ 30 cubic meters, the wellbore must be filled, and the viscosity reducer must be displaced into the formation, and the displacement volume ≤ 20m 3 / h, injection pressure ≤18MPa, well shut-in for 7-10d;

[0019] The periodic injection method is: using the ground automatic dosing device, injecting the agent into the pump-effective casing through the injection-production integrated pipe string, once every 1-3 days, each time takes 0.5-1h, and the injection volume is 0.5-1.0m 3 The viscosity reducer injection concentration is 0.5%, the penetrant injection concentration is 0.03%, and the pump is stopped during the injection.

[0020] Furthermore, the relationship between the dewatering volume and the HLB value of the crude oil in step 1 is: dewatering volume 10.5 ml, HLB value 12.86; dewatering volume 7.2 ml, HLB value 11.33; dewatering volume 1.0 ml, HLB value 10.12; dewatering volume 0.7 ml, HLB value 9.28; dewatering volume 3.7 ml, HLB value 8.66; dewatering volume 8.1 ml, HLB value 7.31.

[0021] Furthermore, the relationship between the viscosity reducer formula and the HLB value in the step 2 is: SMA: 2-phenylethanol = 10:3, HLB value 12.7; SMA: 2-phenylethanol: stearyl alcohol: stigmasterol = 10:3:1:1, HLB value 11.5; SMA: 2-phenylethanol: stearyl alcohol: stigmasterol = 10:2:2:1, HLB value 10.7; SMA: 2-phenylethanol: stearyl alcohol: stigmasterol = 10:1:3:1, HLB value 10.1; SMA: 2-phenylethanol: stearyl alcohol: stigmasterol = 20:1:8:1, HLB value 9.6; SMA: 2-phenylethanol: stearyl alcohol: stigmasterol = 20:1:10:1, HLB value 9.2; SMA: stearyl alcohol: stigmasterol = 20:12:1, HLB value 8.5.

[0022] Compared with the prior art, the beneficial effects of the present invention are as follows: when the developed viscosity reducer is mixed with overseas river crude oil, the crude oil viscosity reduction rate is 96%-99%, the average oil-water interfacial tension is 3.1×10-3mN / m, the emulsification stability is good, the critical micelle concentration (CMC) is 0.82-3.55g / L, the interfacial tension γcmc at the critical micelle concentration is 34.81-40.76mN / m, and the temperature resistance is 30-80°C.

[0023] The test was carried out in 6 wells in Haiwaihe Oilfield, with an investment of 589,000 yuan. The measures achieved 100% efficiency, and the viscosity of crude oil produced at the wellhead was reduced from 10964.3mPa·s to 159.2mPa·s, with an average effective period of 146.4d, an average water content reduction of 8.6%, a cumulative increase of 1,137 tons of oil, and an increase in oil production of 1.968 million yuan. After the measures, the average current of the pumping unit decreased by 17.0A, with a current reduction rate of 16.9%, saving 93,000 yuan in electricity costs, 5,100 tons of steam, and 734,000 yuan in steam costs, with a total cumulative benefit of 2.795 million yuan, which has a positive role in promoting the company's low-carbon green development. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments.

[0025] Figure 1 It is the technical roadmap for designing and screening viscosity reducers of the present invention;

[0026] Figure 2 It is a flow chart of parameter design and construction scheme of the measure well of the present invention;

[0027] Figure 3 This is a structural diagram of the ground automatic dosing device of the present invention;

[0028] Figure 4 This is a structural diagram of the injection-production integrated pump of the present invention;

[0029] Figure 5This is a production curve diagram of the Hai 141-19 well before and after the measures in Example 1 of the present invention;

[0030] Figure 6 This is the performance diagram before and after the implementation of measures in Example 2 of the present invention (left 222-4-2 before the measures, right 2022-5-12 after the measures);

[0031] Figure 7 This is a production curve diagram of the C13-25C well before and after measures in Example 2 of the present invention.

[0032] In the figure, 1. medicine tank; 2. liquid level meter; 3. medicine adding port; 4. thermal insulation cover; 5. electric heater; 6. control cabinet; 7. metering pump; 8. pressure gauge; 9. high-pressure rubber tube; 10. anti-blowout tee; 11. injection hole; 12. long plunger; 13. pump barrel. DETAILED DESCRIPTION

[0033] The present invention is described in detail below by specific examples, but the protection scope of the present invention is not limited. Unless otherwise specified, the experimental methods used in the present invention are all conventional methods, and the experimental equipment, materials, reagents, etc. used can be obtained from commercial channels.

[0034] 1. Technical ideas

[0035] The HLB values ​​of crude oil from different reservoirs vary due to differences in components (such as the percentage of colloids and asphaltene).

[0036] According to the HLB approximation principle, the closer the HLB value of the emulsifier is to that of the crude oil, the better the stability of the emulsion generated by the emulsifier and the crude oil, and the better the viscosity reduction effect. Currently, commonly used commercial viscosity reducers such as sodium dodecylbenzene sulfonate and alkylphenol polyoxyethylene ether cannot adjust the HLB value due to differences in crude oil. Therefore, their viscosity reduction and emulsification stability cannot meet the needs of all oil reservoir development, especially for extra-heavy oil with a viscosity higher than 10000mPa·s. The present invention uses styrene maleic anhydride copolymer as the main chain and hard alcohol, 2-phenylethanol, etc. as side chains. By adjusting the molar mass ratio of the main chain and side chain reactants, a "comb-type" polymer viscosity reducer with controllable HLB value can be prepared, which can improve the specificity of emulsification and viscosity reduction of specific crude oils. The technical route is as follows. See attached. Figure 1 .

[0037] 2. Determination of HLB value of crude oil from Haiwaihe Oilfield

[0038] Referring to the method of He Jie et al. for screening heavy oil emulsification viscosity reduction system by HLB value method, the HLB value of crude oil from Haiwaihe Oilfield was determined, and a series of emulsified viscosity reducers with different HLB values ​​were prepared by using Span-60 and TW-80 in different proportions. The viscosity reducer was prepared at a concentration of 1%. According to the oil-water mass ratio of 7:3, 200 ml of dehydrated crude oil and viscosity reducer solution were placed in a beaker at a constant temperature of 70°C. After standing for 1 hour, the mixture was stirred to form a uniformly mixed oil-water emulsion. 20 ml was placed in a centrifuge tube and kept at a constant temperature for 6 hours. The volume of precipitated water was compared. The sample with the least precipitated water was considered to be the most stable. The results are shown in Table 1, indicating that the HLB value of Haiwaihe crude oil is between 9.2 and 10.1.

[0039] Table 1 Stability test of mixing Haiwaihe crude oil with emulsifiers of different HLB values

[0040] Serial number HLB value Water volume / ml 1 12.86 10.5 2 11.33 7.2 3 10.12 1.0 4 9.28 0.7 5 8.66 3.7 6 7.31 8.1

[0041] 3. Preparation of comb-type viscosity reducer

[0042] (1) Principle of reaction synthesis technology

[0043] The first part is based on the principle of the optimal HLB value, using organic synthesis technology to synthesize a series of comb-shaped viscosity reducers. The main agent of this type of viscosity reducer is a non-ionic viscosity reducer with a molecular structure similar to a comb. The main chain uses styrene maleic anhydride copolymer (SMA) and three chemical agents, stearyl alcohol (octadecyl alcohol), 2-phenylethanol, and stigmasterol. Under the catalysis of p-toluenesulfonic acid (PTSA), tetrahydrofuran (THF) is used as a solvent, and a grafting reaction occurs at 60°C to produce a comb-shaped high molecular polymer. The polymer has a molecular structure like a comb. By adjusting the ratio of the reactants, the side chain long chain ratio, aromatic ring ratio and polarity can be controlled, so components with different HLB values ​​can be synthesized.

[0044] (2) Preparation process of viscosity reducer

[0045] In the high temperature and high pressure reactor, N 2 As a protective gas, then add THF as a solvent, heat to 30 ° C, stir polystyrene maleic anhydride (SMA) and side chain grafting agent 2-phenylethanol, stearyl alcohol (octadecyl alcohol) and stigmasterol until fully dissolved, heat to 60 ° C, add a small amount of PTSA as a catalyst. Keep at not less than 60 ° C, react at a constant temperature for 8 hours, and stir well during the period. Then stop heating and stirring, and use a vacuum pump to recover the solvent under negative pressure until it is basically recovered. Add to acetone not higher than 20 ° C, obtain a white powder after precipitation, and repeatedly wash with acetone to obtain the final product.

[0046] A viscosity reducer solution was prepared at a concentration of 1%, and the HLB value of the synthesized viscosity reducer was determined using the critical micelle concentration method. This method first used a spectrophotometer to determine the critical micelle concentration, and based on the quantitative relationship between the HLB value of the non-ionic surfactant and the critical micelle concentration, the HLB value of the sample was calculated, as shown in Table 2.

[0047] Table 2 Statistics of HLB values ​​of viscosity reducers prepared with different formulations

[0048]

[0049] (3) Optimal formula screening

[0050] According to standard Q / SY LH0552-2021, viscosity reduction tests were carried out. Samples 4, 5, 6 and 7, which are close to the HLB value range of Overseas River crude oil, were respectively prepared into 0.5% aqueous solutions, and then viscosity reduction experiments were carried out with Overseas River crude oil. The results showed that Sample 5 had the highest viscosity reduction rate for Overseas River crude oil, reaching 99.3%. The emulsion remained stable at a constant temperature of 70°C (simulated formation temperature) for 72 hours, and no stratification problems occurred. It is the best formula system for preparing viscosity reducers. Therefore, the HLB range of viscosity reducers suitable for Overseas River crude oil is 9.2-9.6.

[0051] Table 3 Statistics of viscosity reduction rate of viscosity reducers prepared with different formulas and mixed with overseas river crude oil

[0052]

[0053]

[0054] 4. Potential evaluation and scheme design of measure wells

[0055] Summarize the reservoir characteristics and dynamic parameters of the measure wells, and based on the technical indicators of the viscosity reducer and related indoor experimental parameters, give the main influencing factors on the effect of the viscosity reduction cold production measures, such as crude oil viscosity, oil layer thickness, permeability, oil saturation, etc., to form the standard for selecting measure wells. See Table 4. This standard is used to select the test wells.

[0056] Table 4 Well selection criteria for viscosity reduction cold production technology

[0057] Serial number Reservoir parameters unit Recommended range 1 Crude oil viscosity (degassed at 50°C on the ground) mPa·s ≤50000 2 Reservoir Depth m ≤3000 3 Oil layer thickness m 3～30 4 Permeability <![CDATA[×10 -3 μm 2 ]]> ≥10 5 Oil saturation - ≥0.35 6 Formation pressure coefficient - ≥0.2

[0058] Different injection methods are designed for different problems of oil wells. For wells with high production in the early stage and low liquid production in the later stage, and suspected low liquid due to oil viscosity, a one-time injection method (casing injection) is adopted, with a designed treatment radius of ≥4m, a well shut-in time of 7-10d, and liquid control production; for problems such as soft sticking due to oil viscosity, high load of the pumping unit, and low pump efficiency shown on the power diagram, a ground automatic dosing device and a one-time injection and production string pump string are used. By regularly injecting viscosity reducers under the pump, the wellbore is lifted to the ground, the oil and water are emulsified, the pump efficiency is improved, and the production effect is improved.

[0059] Table 5 Selection of cold production technology for oil well viscosity reduction under different production conditions

[0060]

[0061]

[0062] The ground automatic dosing device includes a medicine tank 1, a liquid level meter 2, a dosing port 3, an insulating outer cover 4, an electric heater 5, a control cabinet 6, a metering pump 7, a pressure gauge 8, a high-pressure rubber tube 9 (electrically heated and insulated), and a blowout-proof tee 10. The integrated injection-production pump includes an injection hole 11, a long plunger 12, and a pump barrel 13. The medicine tank 1 is provided with a liquid level meter 2 and an electric heater 5. The medicine tank 1 is provided with a dosing port 3. The medicine tank 1, the control cabinet 6, and the metering pump 7 are provided with an insulating outer cover 4. A pressure gauge 8 is provided on the high-pressure rubber tube 9 on the injection hole 11 of the integrated injection-production pump 7, and a blowout-proof tee 10 is provided at the connection between the high-pressure rubber tube 9 and the injection hole 11.

[0063] Example 1

[0064] Hai 141-19 is located in the Hai 1 block Hai 14-18 well area, the production strata are d 3 , thickness 23m / 15 layers, average porosity 15.8%, average permeability 466×10-3μm 2 , crude oil viscosity 6612mPa·s. It was put into production in November 2014, with a total oil production of 6563t and a total water production of 16,000m3. Three rounds of steam injection were completed, with a total steam injection of 2,760 tons. The average daily liquid production in August 2022 decreased from 19.5m 3 ↘17.3m 3 , daily oil production of 3.6 tons ↘ 1.8 tons, water content 81.5% ↗ 89.4%, the overall performance is liquid drop, water content increase, production decreased significantly. Analysis shows that the crude oil viscosity is high, more than 420 days have passed since the last cycle of steam injection, steam injection viscosity reduction has failed, the formation crude oil viscosity is high, the oil-water mobility ratio is large, and the single well production has decreased. Therefore, it is planned to use viscosity reduction cold production to increase production.

[0065] In September 2022, a viscosity reduction cold production test was carried out. Using a one-time injection method, a total of 15 cubic meters of pre-fluid and 204.7 cubic meters of viscosity reducer plug were injected through the casing. The injection pressure was increased from 0 MPa to 4 MPa, 30 cubic meters of sewage was replaced, the treatment radius was 4.5 m, the well was shut down for 10 days, and then the well was opened and resumed production.

[0066] Well Hai 141-19, before the measures, produced 17.3 cubic meters of liquid per day, 1.8 tons of oil per day, and 89.8% water content. After the measures, the effective period was 131 days, with a cumulative increase of 360 tons of oil, a peak daily increase of 5.2 tons, and an average water content of 89% to 9.7% (Comparison chart is Figure 5 ).

[0067] Example 2

[0068] Hai C13-25C well, Hai 26 block d1, 6.8m / 2 layer, adjusted layer in August 2015, 5 rounds of huff and puff, cumulative steam injection 2218 tons, cumulative oil production 2144 tons, cumulative water production 4895 cubic meters. The well has been in a low liquid and low production state for a long time due to heavy oil sanding, with a daily liquid production of 2.1 cubic meters, daily oil production of 1.4 tons, water content of 30%, average pump efficiency of 15.8%, and the indicator diagram shows the influence of heavy oil.

[0069] Before measures, daily liquid production was 2.1m 3 , daily oil production is 1.4t, average liquid level is 1340m, from April 11 to September 30, 2022, a wellhead drip pump was used to inject viscosity reducer, with an average daily dosing of 0.5t, a concentration of 1%, and a cumulative injection of 85.5t of viscosity reducer. The flushing frequency increased from 0.7 to 1 times / min. After the measures, the upward current increased from 71 to 59A, and the downward current increased from 68 to 50A. After the measures, the daily liquid production was 5.6m 3 , 2.7t oil, 51.7% water content, average pump efficiency 29.5%, average liquid level 1190m, cumulative oil increase 222.8t during the test period, valid period 185d, the test ended in the later period due to the design of the scheme (before and after the measures as shown Figure 6 , the comparison chart is as follows Figure 7 ).

[0070] The above-described embodiments are only preferred embodiments of the present invention, but not all feasible embodiments of the present invention. For those skilled in the art, any obvious changes made thereto without departing from the principles and spirit of the present invention should be considered to be included in the scope of protection of the claims of the present invention.

Claims

1. A method for reducing viscosity of heavy oil by cold production, characterized in that: Here are the steps: S1. Determination of HLB value of crude oil in oilfield; S2. Preparation of viscosity reducing agent; S3. Viscosity reducer formulation screening; S4. Evaluation of the potential of the test well; S5. Selection of cold production methods for heavy oil viscosity reduction.

2. The method for cold production of heavy oil by reducing viscosity according to claim 1, characterized in that: The step S1 specifically comprises: using Span-60 and TW-80 to prepare a series of compound emulsifiers for calibration with different HLB values ​​in different proportions, taking the compound emulsifier for calibration with a concentration of 1%, placing 200 ml of dehydrated crude oil and the compound emulsifier solution for calibration in a beaker according to an oil-water mass ratio of 7:3, keeping a constant temperature of 70° C., standing for 1 hour, stirring to form a uniformly mixed oil-water emulsion, taking 20 ml and placing it in a centrifuge tube, keeping the constant temperature for 6 hours, and comparing the volume of precipitated water to obtain the HLB value of the crude oil.

3. The method for cold production of heavy oil by reducing viscosity according to claim 1, characterized in that: The step S2 is specifically as follows: in a high-temperature and high-pressure reactor, N2 is introduced as a protective gas, and then THF is added as a solvent, the temperature is raised to 30°C, polystyrene maleic anhydride and side-link grafting agents 2-phenylethanol, stearyl alcohol and stigmasterol are stirred until fully dissolved, the temperature is raised to 60°C, and a small amount of PTSA is added as a catalyst. The temperature is maintained at not less than 60°C, and the reaction is carried out at a constant temperature for 8 hours, during which sufficient stirring is performed. Then the heating and stirring are stopped, and the solvent is recovered by negative pressure with a vacuum pump until it is basically recovered. Add acetone not higher than 20°C, obtain a white powder after precipitation, and repeatedly wash with acetone to obtain the final product; prepare a viscosity reducer solution at a concentration of 1%, and then use the critical micelle concentration method to determine the HLB value of the synthesized viscosity reducer.

4. The method for cold production of heavy oil by reducing viscosity according to claim 1, characterized in that: Specifically, step S3 includes: carrying out a viscosity reduction test according to standard Q / SYLH0552-2021, preparing samples close to the HLB value range of crude oil into 0.5% aqueous solutions, and then conducting viscosity reduction experiments with crude oil respectively. The samples with the highest viscosity reduction rate and the stable emulsion at 70°C for 72 hours are statistically analyzed without stratification problems, which is the best formula system for preparing viscosity reducers.

5. The method for cold production of heavy oil by reducing viscosity according to claim 1, characterized in that: The step S4 specifically includes: summarizing the reservoir characteristics and dynamic parameters of the measure wells, and according to the technical indicators of the viscosity reducer and the relevant indoor experimental parameters, giving the main influencing factors on the effect of the viscosity reduction cold production measures, namely, crude oil viscosity, reservoir depth, oil layer thickness, permeability, oil saturation, and formation pressure coefficient. The well selection criteria are crude oil viscosity ≤50000mPa·s under the degassing condition of 50°C on the ground, reservoir depth ≤3000m, oil layer thickness 3-30m, and permeability ≥10×10 -3 μm 2 , oil saturation ≥ 0.35, formation pressure coefficient ≥ 0.

2.

6. The method for cold production of heavy oil by reducing viscosity according to claim 1, characterized in that: In step S5, the heavy oil viscosity reduction cold production method can be selected by a one-time injection method using a pump truck or a periodic injection method.

7. The method for cold production of heavy oil by reducing viscosity according to claim 6, characterized in that: The one-time injection method of the pump truck is aimed at any of the following production situations: a. High production in the early stage and low liquid production in the late stage, with the liquid volume decreasing by more than 30%, which is suspected to be a problem well with low liquid volume due to thick oil; b. Wells that were previously in huff-and-puff production but are currently producing low amounts of liquid and are suspected to be nearing the end of production in this cycle; c. Wells that are not suitable for steam injection production due to restrictions on the surface, well completion, sand production in the formation or active bottom water.

8. The method for cold production of heavy oil by reducing viscosity according to claim 7, characterized in that: The one-time injection method of the pump truck is: casing annulus injection, sweep radius ≥ 4m, viscosity reducer injection concentration 0.5%, permeation agent injection concentration 0.03%, displacement water ≥ 30 cubic meters, the wellbore must be filled, and the viscosity reducer must be displaced into the formation, and the displacement volume ≤ 20m 3 / h, injection pressure ≤18MPa, well shut-in for 7-10d.

9. The method for cold production of heavy oil by reducing viscosity according to claim 6, characterized in that: The periodic injection method is targeted at any of the following production situations: A. Moisture content is less than 70%; B. Soft sticking due to thick oil, high load on the pumping unit, and the power diagram showing the influence of thick oil, resulting in difficulty in lifting or low pump efficiency; C. The oil is poorly dispersed in the produced fluid and is in clumpy form.

10. The method for cold production of heavy oil by reducing viscosity according to claim 9, characterized in that: The periodic injection method is: using the ground automatic dosing device, injecting the agent into the pump-effective casing through the injection-production integrated pipe string, once every 1-3 days, each time takes 0.5-1h, and the injection volume is 0.5-1.0m 3 The viscosity reducer injection concentration is 0.5%, the penetrant injection concentration is 0.03%, and the pump is stopped during the injection.

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