A method for improving water flooding heavy oil recovery by biological oxidation

Abstract

The application discloses a method for improving water flooding heavy oil recovery rate by biological oxidation, which comprises the following steps: (1) selection of test block; (2) selection of oxidizing microorganism; (3) selection of activator system; (4) optimization of injection process parameters, the injection process parameters being soak period and water flooding speed; and (5) field construction and acceptance. The application has the following beneficial effects: 1. The oxygen content in water is reduced for the first time by biological oxidation, the purpose of reducing the viscosity of heavy oil is achieved, and the water flooding heavy oil reservoir recovery rate is finally improved by 3-5%; 2. The injection process and soak time are mainly adjusted according to the microorganism system and the field situation at any time, and the effect efficiency of the system on the reservoir is improved; and 3. The application has the advantages of green environmental protection, good oil increasing effect and high input-output ratio, the water flooding efficiency is improved by 30%, the average daily oil increasing amount of a single well is greater than 2t, and the input-output ratio is greater than 1:3.

Description

Technical Field

[0001] This invention relates to a method for improving the recovery rate of water-driven heavy oil using biological oxidation, belonging to the field of microbial enhanced oil recovery technology. Background Technology

[0002] The Role of Petroleum in the National Economy: Petroleum is an important energy source. Compared with coal, it has advantages such as higher energy density (the calorific value of petroleum is 50% higher than that of standard coal for the same weight), easier transportation and storage, and lower atmospheric pollution after combustion. Fuel oil refined from petroleum is the main fuel for transportation vehicles, power plant boilers, and various kilns in the metallurgical and building materials industries. Liquefied petroleum gas (LPG) and piped gas, made from petroleum, are high-quality fuels for urban residents. Aircraft, tanks, ships, rockets, and other spacecraft also consume large quantities of petroleum fuel. Therefore, many countries classify petroleum as a strategic resource.

[0003] The extraction of oil from reservoirs using their energy is generally called primary oil recovery; secondary oil recovery involves injecting water or gas into the reservoir to replenish its energy; and tertiary oil recovery uses chemical substances to improve the properties of oil, gas, water, and rock to extract more oil.

[0004] Tertiary oil recovery primarily employs waterflooding. After decades of extraction, the viscosity of the produced oil shows a gradual upward trend, further complicating the enhancement of recovery rates in later stages of reservoir development. Based on the characteristics of the produced fluids and changes in the crude oil structure, the presence of oxygen or oxidizing substances in the water exacerbates changes in the crude oil's properties, leading to a further increase in viscosity, increased water cut, and a further decrease in production. Therefore, improving the recovery rate of waterflooded heavy oil has become an urgent problem to solve. Summary of the Invention

[0005] Purpose of the invention: In view of the shortcomings of the prior art, the present invention discloses a method for improving the recovery rate of water-driven heavy oil by utilizing biological oxidation.

[0006] Technical solution: A method for improving the recovery rate of water-driven heavy oil using biological oxidation, comprising the following steps:

[0007] (1) Screening of test blocks;

[0008] (2) Screening of oxidizing microorganisms;

[0009] (3) Screening of activator systems;

[0010] (4) Optimization of injection process parameters, namely well shut-in period and water drive rate;

[0011] (5) On-site construction and acceptance.

[0012] Furthermore, the selection criteria for the test oil blocks in step (1) are as follows: select water-driven heavy oil reservoirs with a complete water-driven well network, reservoir temperature less than 100℃, underground crude oil viscosity less than 500mPa·s, produced fluid salinity less than 100000mg / L, and reservoir permeability greater than 50mD.

[0013] Further, the oxidizing microorganisms mentioned in step (2) are one or more of Pseudomonas, Bacillus terrestris, Vibrio halophilus, Bacillus licheniformis, oleobacterium, and thermoaerobic bacteria. Oxidizing microorganisms are mainly reservoir microorganisms that can grow and metabolize under suitable reservoir temperature and salinity conditions, and are aerobic or facultative microorganisms that also have a certain emulsifying and viscosity-reducing function for crude oil.

[0014] Further, the screening indicators for the oxidizing microorganisms mentioned in step (2) are: BOD5 and the emulsification and viscosity reduction rate of crude oil by the microorganisms, wherein:

[0015] BOD5 should be between 0 and 1 mg / L;

[0016] The required emulsification and viscosity reduction rate of crude oil by microorganisms is 35% to 75%.

[0017] Furthermore, the BOD5 testing method is as follows: Water samples, or diluted water samples, are statically incubated for 5 days at the reservoir temperature of the test block. The dissolved oxygen content of the water samples before and after incubation is tested, and the test values ​​are D1 and D2, respectively.

[0018] BOD5 = (D1 - D2) / P

[0019] Where: D1: Initial dissolved oxygen in the diluted water sample, in mg / L;

[0020] D2: Dissolved oxygen in diluted water samples after 5 days of incubation in a reservoir temperature-controlled incubator, in mg / L;

[0021] P = Original volume of water sample / Final volume of water sample after dilution.

[0022] Furthermore, to determine the viscosity reduction rate of crude oil through microbial emulsification, it is necessary to test the viscosity of heavy oil. The test method for heavy oil viscosity is as follows:

[0023] The initial viscosity μ0 of the dehydrated crude oil was measured using a rotational viscometer at 50°C.

[0024] Dehydrated crude oil and thermophilic anaerobic emulsified Bacillus subtilis bacterial solution were heated at a ratio of 7:3 in a 50°C water bath for 30 minutes, and the viscosity μ1 at 50°C was measured by rapid stirring. The viscosity reduction rate was calculated using the following formula:

[0025] f = (μ0 - μ1) / μ0 × 100%

[0026] Where: μ0: initial viscosity of crude oil, in mPa·s;

[0027] μ1: Crude oil viscosity after treatment with thermophilic anaerobic Bacillus emulsification solution, in mPa·s.

[0028] Furthermore, the specific steps for screening the activator system described in step (3) are as follows:

[0029] Take 100 mL of the produced fluid from the test reservoir and add 2 wt% of the activator formulation to each. Screen the activation system according to the activation direction. Then place it at the test reservoir temperature and incubate for 2-5 days. Measure the number of oxidizing microorganisms in the culture medium and select the activator system with the highest specific oxygen consumption rate.

[0030] Furthermore, the activator system comprises a carbon source, a nitrogen source, and a phosphorus source, wherein the carbon source is one of glucose and sucrose, the nitrogen source is one or more of NH4Cl, urea, and corn steep liquor powder, and the phosphorus source is one of K2HPO4 and KH2PO4, and the mass concentrations of the carbon source, nitrogen source, and phosphorus source are 1.0–2.0 wt%, 0.1–0.3 wt%, and 0.03–0.05 wt%, respectively.

[0031] Furthermore, the specific oxygen consumption rate refers to the mass of oxygen consumed per unit mass of biomass per unit time. This is achieved by first testing the dissolved oxygen content of the culture medium before treatment, which is DO1; then, after adding microorganisms and the activator, culturing under reservoir conditions for 2–5 days, and then testing the dissolved oxygen content of the system again, which is DO2; simultaneously, taking 1 ml of the culture medium after the test to test the total bacterial count, which is M, and finally obtaining the specific oxygen consumption rate S, calculated as follows:

[0032] S=(DO1-DO2) / M

[0033] Wherein: DO1: Dissolved oxygen content in the culture medium before biological action, in mg / L;

[0034] DO2: Dissolved oxygen content in the culture medium after biological action, in mg / L;

[0035] M: The amount of reservoir microorganisms in 1 ml of culture medium, in mg.

[0036] Furthermore, step (4) includes the following steps:

[0037] (41) Fill a 3-meter-long sand-filled core, vacuum-saturate the formation water of the oil reservoir, and calculate the pore volume (PV).

[0038] (42) Crude oil from saturated test wells, core aged for 7 days;

[0039] (43) Water flooding continues until the water content of the produced liquid is consistent with the water content of the test block;

[0040] (44) The selected oxidizing microorganisms and activator system were injected into the core tube at an injection rate of 0.02–0.2 ml / min using a slug or continuous injection method. After the injection volume was 0.1 PV, the core tube was placed at reservoir temperature and cultured for 2–5 days. The injection process parameters were then optimized by analyzing the BOD5 value, heavy oil viscosity, and enhanced oil recovery rate of the produced liquid after water flooding. Among them:

[0041] The well-steaming cycle is determined based on the dissolved oxygen content in the produced fluid and the specific oxygen consumption rate of oxidizing microorganisms, namely:

[0042]

[0043] Furthermore, the injection rate of the reservoir microbial system is determined by the dissolved oxygen content of the produced fluid from the one-dimensional model, including the following steps:

[0044] ① Core filling, with core permeability equal to the target reservoir permeability;

[0045] ② Vacuum the core, saturate it with formation water, and measure the core PV (pore volume);

[0046] ③ Saturated crude oil, core aged for 7 days, calculate the original oil saturation;

[0047] ④ For the first water flood, water flood until the produced fluid has a water content of 95%, and calculate the recovery rate of the first water flood;

[0048] ⑤ Injection into a biological oxidation system, in which the control core was continuously water-driven, and the experimental group determined the injection process parameters, with the same injection volume for the control core and the experimental core;

[0049] ⑥ Secondary waterflooding: waterflooding continues until the produced fluid contains 100% water. The enhanced oil recovery value of the secondary waterflooding is calculated for the control group core and the experimental group core, and the dissolved oxygen content in the produced fluid is analyzed.

[0050] Furthermore, step (5) evaluates the viscosity and oxygen content of the crude oil in the produced fluid. The absence of an increase in crude oil viscosity indicates that the injection system effectively reduced the oxygen content of the water and maintained the crude oil viscosity.

[0051] Beneficial effects: The beneficial effects of the method for improving waterflood heavy oil recovery using biological oxidation disclosed in this invention are as follows:

[0052] 1. For the first time, the oxygen content in the water is reduced through biological oxidation, thereby reducing the viscosity of heavy oil and ultimately increasing the recovery rate of water-driven heavy oil reservoirs by 3-5%.

[0053] 2. The injection process and well-clogging time are adjusted at any time based on the microbial system and site conditions to improve the system's efficiency in acting on the reservoir;

[0054] 3. This invention has the advantages of being green and environmentally friendly, having a good oil-increasing effect, and a high input-output ratio. The water drive efficiency is increased by 30%, the average daily oil increase per well is greater than 2t, and the input-output ratio is greater than 1:3. Attached Figure Description

[0055] Figure 1 This is a schematic diagram comparing the oxygen consumption in the effluent by different oxidizing microorganisms in Example 1.

[0056] Figure 2 This is a schematic diagram comparing the effects of different oxidizing microorganisms on the viscosity reduction rate of heavy oil in Example 1.

[0057] Figure 3 This is a schematic diagram comparing the oxygen consumption in the effluent by different oxidizing microorganisms in Example 2.

[0058] Figure 4 This is a schematic diagram comparing the effects of different oxidizing microorganisms on the viscosity reduction rate of heavy oil in Example 2.

[0059] Figure 5 This is a schematic diagram comparing the oxygen consumption in the effluent by different oxidizing microorganisms in Example 3.

[0060] Figure 6 This is a schematic diagram comparing the effects of different oxidizing microorganisms on the viscosity reduction rate of heavy oil in Example 3. Detailed Implementation

[0061] The specific embodiments of the present invention are described in detail below.

[0062] Example 1

[0063] A method for enhancing waterflood heavy oil recovery using bio-oxidation includes the following steps:

[0064] (1) Screening of test blocks

[0065] In Block A of Shengli Oilfield, the reservoir temperature is 45℃, the viscosity of the underground crude oil is 498 mN / m, the reservoir pressure is 8 MPa, the porosity is 32.0%, and the pore volume is 2.8 × 10⁻⁶. 4 m 3 The reservoir has a permeability of 60 mD and geological reserves of 1.65 × 10⁻⁶ mD. 5 The formation water salinity was 16000 mg / L, meeting the screening criteria for the test block. Before the test, the average water content of Block A was 93.5%.

[0066] (2) Screening of oxidizing microorganisms

[0067] The product effluent from block A was treated with *Pseudomonas aeruginosa*, *Bacillus cereus*, *Vibrio halophilus*, *Bacillus licheniformis*, *Oleobacterium*, and *Thermoaerobic Bacillus*, respectively. The difference in BOD5 in the product effluent before and after treatment showed that... Figure 1 As shown, the aerobic bacterium *Bacillus subtilis* and the facultative bacterium *Vibrio halosa* exhibit the highest oxygen content metabolism. Meanwhile, as... Figure 2 As shown, the above-mentioned reservoir microorganisms have little difference in their ability to emulsify and reduce viscosity of crude oil. By comparison, the oxidizing microorganisms in this block are Bacillus terrestris and Vibrio halophilus.

[0068] (3) Screening of activator systems

[0069] Based on the optimized combination of carbon, nitrogen, and phosphorus sources in the activator, six different activator formulations were obtained, as follows:

[0070]

[0071] The activator components were added to 100 ml of the product liquid, and 2 wt% of oxidizing microbial culture was added. After incubation at the reservoir temperature for 3 days, the bacterial concentration and specific oxygen consumption rate were tested. The specific results are shown in Table 1. The preferred oxidizing microbial activator system is activator 2, namely: 1.0 wt% glucose, 0.1 wt% NH4Cl, 0.1 wt% corn steep liquor powder and 0.01 wt% K2HPO4.

[0072] Table 1 Comparison of oxygen consumption of different microorganisms by activator systems

[0073]

[0074] (4) Optimization of injection process parameters

[0075] (41) Fill a 3-meter-long sand-filled core, vacuum-saturate the formation water of the oil reservoir, and calculate the pore volume (PV).

[0076] (42) Crude oil from the saturated test block, core aged for 7 days;

[0077] (43) Water flooding continues until the water content of the produced liquid is consistent with the water content of the test block;

[0078] (44) Using slug injection and continuous injection methods, the screened oxidizing microorganisms and activator system were injected into the core tube at an injection rate of 0.02 ml / min. In the slug injection method, injection was paused for 1 day after every 0.02 PV of oxidizing microorganism solution injected, and this process was repeated until the injected volume of the oxidizing microorganism solution reached 0.1 PV, followed by 1 day of water flooding. In the continuous injection method, after injecting 0.1 PV, the core tube was placed at reservoir temperature and incubated for 5 days. The injection process parameters were then optimized by analyzing the BOD5 value, heavy oil viscosity, and the extent of enhanced oil recovery in the produced liquid after water flooding.

[0079] The oxygen content in the produced fluid was 36.2 mg / L, as determined by testing the BOD5 content. Based on the well shut-in cycle calculation formula, the average oxygen consumption rate of oxidizing microorganisms was 0.385 mg O2·L. -1 ·h -1 The oxidation biological system was found to have a simmering cycle of 95 hours for Block A.

[0080] Furthermore, the injection rate of the reservoir microbial system is determined by the dissolved oxygen content of the produced fluid from the one-dimensional model, including the following steps:

[0081] ① Core filling, with core permeability equal to the target reservoir permeability;

[0082] ② Vacuum the core, saturate it with formation water, and measure the core PV (pore volume);

[0083] ③ Saturated crude oil, core aged for 7 days, calculate the original oil saturation;

[0084] ④ For the first water flood, water flood until the produced fluid has a water content of 95%, and calculate the recovery rate of the first water flood;

[0085] ⑤ Injection into a biological oxidation system, in which the control core was continuously water-driven, and the experimental group determined the injection process parameters, with the same injection volume for the control core and the experimental core;

[0086] ⑥ Secondary waterflooding: waterflooding continues until the produced fluid contains 100% water. The enhanced oil recovery value of the secondary waterflooding is calculated for the control group core and the experimental group core, and the dissolved oxygen content in the produced fluid is analyzed.

[0087] According to the physical model evaluation test, when the injection rate is 0.1 ml / min, the dissolved oxygen content of the produced fluid is 0.1 mg / L, the viscosity of the produced crude oil decreases by 23.1%, and the recovery rate increases by up to 7.8%.

[0088] (5) On-site construction and acceptance

[0089] After implementing microbial flooding using bio-oxidation in this block, the efficiency of water flooding increased by 30% compared to the previous method, with an average daily oil increase of 2.2 tons per well and an input-output ratio greater than 1:3.1.

[0090] Example 2

[0091] A method for enhancing waterflood heavy oil recovery using bio-oxidation includes the following steps:

[0092] (1) Screening of test blocks

[0093] In Block B of Shengli Oilfield, the reservoir temperature is 65℃, the viscosity of the underground crude oil is 378 mN / m, the reservoir pressure is 10 MPa, the porosity is 32.0%, and the pore volume is 5.2 × 10⁻⁶.4 m 3 The reservoir permeability is 75 mD, and the recoverable reserves are 5.3 × 10⁻⁶ mD. 5 The formation water salinity was 7600 mg / L, meeting the screening criteria for the test block. Before the test, Block B had a water content of 95.8%.

[0094] (2) Screening of oxidizing microorganisms

[0095] The effluent from block B was treated with Pseudomonas, Bacillus terrestris, Vibrio halophilus, Bacillus licheniformis, Lactobacillus oleiferus, and thermoaerobic bacteria, respectively. The difference in BOD5 levels before and after treatment indicated that, as... Figure 3 As shown, the aerobic bacteria *Pseudomonas aeruginosa* and the facultative bacteria *Bacillus licheniformis* exhibit the highest metabolic activity in water bodies with high oxygen content. Meanwhile, as... Figure 4 As shown, the above-mentioned reservoir microorganisms have little difference in their ability to emulsify and reduce viscosity of crude oil. The comparison shows that the oxidizing microorganisms in this block are Pseudomonas and Bacillus licheniformis.

[0096] (3) Screening of activator systems

[0097] Based on the optimized combination of carbon, nitrogen, and phosphorus sources in the activator, six different activator formulations were obtained, as follows:

[0098]

[0099] The activator components were added to 100 ml of the product liquid, and 2 wt% of oxidizing microbial culture was added. After incubation at the reservoir temperature for 3 days, the bacterial concentration and specific oxygen consumption rate were tested according to the patented method, as shown in Table 2. The preferred oxidizing microbial activator system is activator 3, namely: 1.5 wt% sucrose, 0.2 wt% urea, 0.1 wt% corn steep liquor powder and 0.02 wt% KH2PO4.

[0100] Table 2 Comparison of oxygen consumption of different microorganisms by activator systems

[0101]

[0102] (4) Optimization of injection process parameters

[0103] (41) Fill a 3-meter-long sand-filled core, vacuum-saturate the formation water of the oil reservoir, and calculate the pore volume (PV).

[0104] (42) Crude oil from the saturated test block, core aged for 7 days;

[0105] (43) Water flooding continues until the water content of the produced liquid is consistent with the water content of the test block;

[0106] (44) The selected oxidizing microorganisms and activator system were injected into the core tube at an injection rate of 0.2 ml / min using both slug injection and continuous injection methods. In the slug injection method, after each injection of 0.05 PV, injection was paused for 1 day, followed by another injection of 0.05 PV of oxidizing microbial solution and 1 day of cultivation before water flooding. In the continuous injection method, after an injection volume of 0.1 PV, the core tube was placed at reservoir temperature and incubated for 2 days. The injection process parameters were then optimized by analyzing the BOD5 value, heavy oil viscosity, and enhanced oil recovery rate after water flooding.

[0107] The oxygen content in the produced fluid was 26.2 mg / L, as determined by testing the BOD5 content. Based on the well shut-in cycle calculation formula, the average oxygen consumption rate of oxidizing microorganisms was 0.395 mg O2·L. -1 ·h -1 The oxidation biological system was found to have a simmering cycle of 67 hours for Block A.

[0108] Furthermore, the injection rate of the reservoir microbial system is determined by the dissolved oxygen content of the produced fluid from the one-dimensional model, including the following steps:

[0109] ① Core filling, with core permeability equal to the target reservoir permeability;

[0110] ② Vacuum the core, saturate it with formation water, and measure the core PV (pore volume);

[0111] ③ Saturated crude oil, core aged for 7 days, calculate the original oil saturation;

[0112] ④ For the first water flood, water flood until the produced fluid has a water content of 95%, and calculate the recovery rate of the first water flood;

[0113] ⑤ Injection into a biological oxidation system, in which the control core was continuously water-driven, and the experimental group determined the injection process parameters, with the same injection volume for the control core and the experimental core;

[0114] ⑥ Secondary waterflooding: waterflooding continues until the produced fluid contains 100% water. The enhanced oil recovery value of the secondary waterflooding is calculated for the control group core and the experimental group core, and the dissolved oxygen content in the produced fluid is analyzed.

[0115] According to the physical model evaluation test, when the injection rate is 0.1 ml / min, the dissolved oxygen content of the produced fluid is 0.11 mg / L, the viscosity of the produced crude oil decreases by 20.7%, and the recovery rate is increased by 8.1%.

[0116] (5) On-site construction and acceptance

[0117] After implementing microbial flooding using bio-oxidation in this block, the efficiency of water flooding increased by 31% compared to the previous method, with an average daily oil increase of 2.1 tons per well and an input-output ratio greater than 1:3.0.

[0118] Example 3

[0119] A method for enhancing waterflood heavy oil recovery using bio-oxidation includes the following steps:

[0120] (1) Screening of test blocks

[0121] In Block C of Shengli Oilfield: reservoir temperature 70℃, underground crude oil viscosity 226 mN / m, reservoir pressure 12 MPa. Porosity 29.0%, pore volume 3.4 × 10⁻⁶. 4 m 3 The reservoir permeability is 80 mD, and the recoverable reserves are 5.2 × 10⁻⁶ mD. 4 The formation water salinity was 17000 mg / L, meeting the screening criteria for the test block. Before the test, the water content of block C was 97.2%.

[0122] (2) Screening of oxidizing microorganisms

[0123] The differences in BOD5 in the water before and after the treatment of the effluent by *Pseudomonas*, *Bacillus cereus*, *Vibrio halophilus*, *Bacillus licheniformis*, *Oleobacterium*, and thermophytic bacteria indicated that, for example... Figure 5 As shown, aerobic thermoaerobic bacteria have the highest metabolic rate for oxygen content in water, and at the same time, as Figure 6 As shown, the above-mentioned thermo-aerobic bacteria have the highest efficiency in emulsifying and reducing viscosity of crude oil. Therefore, the oxidizing microorganisms in this block are thermo-aerobic bacteria.

[0124] (3) Screening of activator systems

[0125] Based on the optimized combination of carbon, nitrogen, and phosphorus sources in the activator, six different activator formulations were obtained, as follows:

[0126]

[0127]

[0128] After adding the activator components to 100 ml of the product and adding 2 wt% of oxidizing microorganisms, the mixture was incubated at the reservoir temperature for 3 days. Based on the test bacterial concentration and specific oxygen consumption rate (see Table 3), the preferred oxidizing microorganism activator system was activator 5, namely: 2.0 wt% sucrose, 0.3 wt% corn steep liquor powder and 0.05 wt% K2HPO4.

[0129] Table 3 Comparison of oxygen consumption of different microorganisms by activator systems

[0130]

[0131] (4) Optimization of injection process parameters

[0132] (41) Fill a 3-meter-long sand-filled core, vacuum-saturate the formation water of the oil reservoir, and calculate the pore volume (PV).

[0133] (42) Crude oil from the saturated test block, core aged for 7 days;

[0134] (43) Water flooding continues until the water content of the produced liquid is consistent with the water content of the test block;

[0135] (44) The selected oxidizing microorganisms and activator system were injected into the core tube at an injection rate of 0.1 ml / min using both slug injection and continuous injection methods. In the slug injection method, injection was paused for 1 day after every 0.03 PV injection, and this process was repeated until the oxidizing microorganism solution was injected to 0.4 PV, followed by 1 day of waterflooding. In the continuous injection method, after injecting 0.1 PV, the core tube was placed at reservoir temperature and incubated for 3 days. The injection process parameters were then optimized by analyzing the BOD5 value, heavy oil viscosity, and enhanced oil recovery rate after waterflooding.

[0136] The oxygen content in the produced fluid was found to be 15.8 mg / L based on the BOD5 test. According to the well shut-in cycle calculation formula, the average oxygen consumption rate of oxidizing microorganisms was 0.36 mg O2·L. -1 ·h -1 The oxidation biological system was found to have a simmering cycle of 44 hours for Block A.

[0137] Furthermore, the injection rate of the reservoir microbial system is determined by the dissolved oxygen content of the produced fluid from the one-dimensional model, including the following steps:

[0138] ① Core filling, with core permeability equal to the target reservoir permeability;

[0139] ② Vacuum the core, saturate it with formation water, and measure the core PV (pore volume);

[0140] ③ Saturated crude oil, core aged for 7 days, calculate the original oil saturation;

[0141] ④ For the first water flood, water flood until the produced fluid has a water content of 95%, and calculate the recovery rate of the first water flood;

[0142] ⑤ Injection into a biological oxidation system, in which the control core was continuously water-driven, and the experimental group determined the injection process parameters, with the same injection volume for the control core and the experimental core;

[0143] ⑥ Secondary waterflooding: waterflooding continues until the produced fluid contains 100% water. The enhanced oil recovery value of the secondary waterflooding is calculated for the control group core and the experimental group core, and the dissolved oxygen content in the produced fluid is analyzed.

[0144] According to the physical model evaluation test, when the injection rate is 0.15 ml / min, the dissolved oxygen content of the produced fluid is 0.09 mg / L, the viscosity of the produced crude oil decreases by 21.1%, and the recovery rate increases by 8.3%.

[0145] (5) On-site construction and acceptance

[0146] After implementing microbial flooding using bio-oxidation in this block, the efficiency of water flooding increased by 33% compared to the previous method, with an average daily oil increase of 2.4 tons per well and an input-output ratio greater than 1:3.3.1

[0147] The embodiments of the present invention have been described in detail above. However, the present invention is not limited to the above embodiments, and various changes can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention.

Claims

1. A method for improving the recovery rate of water-driven heavy oil using biological oxidation, characterized in that, Includes the following steps: (1) Screening of test blocks; (2) Screening of oxidizing microorganisms; (3) Screening of activator systems; (4) Optimization of injection process parameters, namely well shut-in period and water drive rate; (5) On-site construction and acceptance, including: The screening criteria for oxidizing microorganisms mentioned in step (2) are: BOD5 and the emulsification and viscosity reduction rate of crude oil by the microorganisms; The specific steps for screening the activator system described in step (3) are as follows: Take 100 mL of the produced fluid from the test reservoir and add 2 wt% of the activator formulation to each. Screen the activation system according to the activation direction. Then place it at the temperature of the test reservoir and incubate for 2 to 5 days. Measure the number of oxidizing microorganisms in the culture medium and select the activator system with the highest specific oxygen consumption rate. The activator system consists of a carbon source, a nitrogen source, and a phosphorus source. The carbon source is one of glucose and sucrose, the nitrogen source is one or more of NH4Cl, urea, and corn steep liquor powder, and the phosphorus source is one of K2HPO4 and KH2PO4. The mass concentrations of the carbon source, nitrogen source, and phosphorus source are 1.0–2.0 wt%, 0.1–0.3 wt%, and 0.03–0.05 wt%, respectively. The specific oxygen consumption rate refers to the mass of oxygen consumed per unit mass of biomass per unit time. First, the dissolved oxygen content of the culture medium before treatment is tested, and its value is DO1. After adding microorganisms and activators, the culture is incubated under reservoir conditions for 2–5 days, and the dissolved oxygen content of the system is tested again, and its value is DO2. Simultaneously, 1 ml of the culture medium after the test is taken to test the total bacterial count, which is M. Finally, the specific oxygen consumption rate S is obtained, calculated as follows: S=(DO1-DO2) / M Wherein: DO1: Dissolved oxygen content in the culture medium before biological action, in mg / L; DO2: Dissolved oxygen content in the culture medium after biological action, in mg / L; M: The amount of reservoir microorganisms in 1 ml of culture medium, in mg; Step (4) includes the following steps: (41) Fill a 3-meter-long sand-filled core, vacuum-saturate the formation water of the oil reservoir, and calculate the pore volume PV. (42) Crude oil from saturated test wells, core aged for 7 days; (43) Water flooding continues until the water content of the produced liquid is consistent with the water content of the test block; (44) The selected oxidizing microorganisms and activator system were injected into the core tube at an injection rate of 0.02–0.2 ml / min using a slug or continuous injection method. After the injection volume was 0.1 PV, the core tube was placed at reservoir temperature and cultured for 2–5 days. The injection process parameters were then optimized by analyzing the BOD5 value, heavy oil viscosity, and enhanced oil recovery rate of the produced liquid after water flooding. Among them: The well-steaming cycle is determined based on the dissolved oxygen content in the produced fluid and the specific oxygen consumption rate of oxidizing microorganisms, namely:

2. The method for improving waterflood heavy oil recovery using biological oxidation as described in claim 1, characterized in that, The selection criteria for the test oil blocks in step (1) are as follows: select water-driven heavy oil reservoirs with a complete water-driven well network, reservoir temperature less than 100℃, underground crude oil viscosity less than 500mPa·s, produced fluid salinity less than 100000mg / L, and reservoir permeability greater than 50mD.

3. The method for improving waterflood heavy oil recovery using biological oxidation as described in claim 1, characterized in that, The oxidizing microorganisms mentioned in step (2) are one or more of the following: Pseudomonas, Bacillus terrestris, Vibrio halophilus, Bacillus licheniformis, Leptobacillus, and thermo-aerobic bacteria.

4. The method for improving waterflood heavy oil recovery using biological oxidation as described in claim 1, characterized in that, In step (2), the BOD5 is required to be between 0 and 1 mg / L; in step (2), the emulsification and viscosity reduction rate of crude oil by microorganisms is required to be between 35% and 75%.

5. The method for improving waterflood heavy oil recovery using biological oxidation as described in claim 4, characterized in that, The BOD5 test method is as follows: Water samples, or diluted water samples, are statically incubated for 5 days at the reservoir temperature in the test block. The dissolved oxygen content of the water samples before and after incubation is tested, and the test values ​​are D1 and D2, respectively. BOD5 = (D1 - D2) / P Where: D1: Initial dissolved oxygen in the diluted water sample, in mg / L; D2: Dissolved oxygen in diluted water samples after 5 days of incubation in a reservoir temperature-controlled incubator, in mg / L; P = Original volume of water sample / Final volume of water sample after dilution.

6. The method for improving waterflood heavy oil recovery using biological oxidation as described in claim 4, characterized in that, The viscosity reduction rate of crude oil emulsification by microorganisms requires testing the viscosity of heavy oil. The test method for heavy oil viscosity is as follows: The initial viscosity μ0 of the dehydrated crude oil was measured using a rotational viscometer at 50°C. Dehydrated crude oil and thermophilic anaerobic emulsified Bacillus subtilis bacterial solution were heated at a ratio of 7:3 in a 50°C water bath for 30 minutes, and the viscosity μ1 at 50°C was measured by rapid stirring. The viscosity reduction rate was calculated using the following formula: f = (μ0 - μ1) / μ0 × 100% Where: μ0: initial viscosity of crude oil, in mPa·s; μ1: Crude oil viscosity after treatment with thermophilic anaerobic Bacillus emulsification solution, in mPa·s.

7. The method for improving waterflood heavy oil recovery using biological oxidation as described in claim 1, characterized in that, The injection rate of the reservoir microbial system is determined by the dissolved oxygen content of the produced fluid from a one-dimensional model, including the following steps: ① Core filling, with core permeability equal to the target reservoir permeability; ② Vacuum the core, saturate it with formation water, and measure the core pore volume PV; ③ Saturated crude oil, core aged for 7 days, calculate the original oil saturation; ④ For the first water flood, water flood until the produced fluid has a water content of 95%, and calculate the recovery rate of the first water flood; ⑤ Injection into a biological oxidation system, in which the control core was continuously water-driven, and the experimental group determined the injection process parameters, with the same injection volume for the control core and the experimental core; ⑥ Secondary waterflooding: waterflooding continues until the produced fluid contains 100% water. The enhanced oil recovery value of the secondary waterflooding is calculated for the control group core and the experimental group core, and the dissolved oxygen content in the produced fluid is analyzed.

8. The method for improving waterflood heavy oil recovery using biological oxidation as described in claim 1, characterized in that, In step (5), the viscosity and oxygen content of crude oil in the produced fluid are evaluated.

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