Screening method for viscosity reducer for carbon dioxide flooding

Abstract

The present application relates to the technical field of heavy oil reservoir development, in particular to a screening method of viscosity reducer for carbon dioxide flooding, which comprises calculating the viscosity reduction rates of a plurality of viscosity reducers for heavy oil at different test temperatures, and then obtaining a plurality of viscosity reduction rate arrays of the viscosity reducers at different temperatures; based on the viscosity reduction rate arrays, based on the normalized values of the average viscosity reduction rate and oil displacement efficiency corresponding to each viscosity reducer, average normalization, standard deviation, coefficient of variation, weighted factor, the comprehensive evaluation index corresponding to each viscosity reducer is calculated, and the optimal viscosity reducer is screened based on the comprehensive evaluation index; the present application comprehensively evaluates the static viscosity reduction performance and dynamic oil displacement performance of the heavy oil viscosity reducer through the heavy oil viscosity reduction effect evaluation experiment and the physical simulation oil displacement experiment, thereby guiding the optimization of the viscosity reducer for carbon dioxide flooding, and realizing the maximum amplitude improvement of heavy oil reservoir recovery efficiency and the best economic benefit obtained by the carbon dioxide and viscosity reducer compound flooding.

Description

TECHNICAL FIELD

[0001] The application relates to the technical field of heavy oil reservoir development, in particular to a screening method of a viscosity reducer for carbon dioxide flooding. BACKGROUND

[0002] The biggest problem in the development process of heavy oil reservoirs is that the high-viscosity heavy oil has poor flowability in the reservoir pore medium, the oil well shaft and the ground gathering and transportation pipe network system, resulting in low oil well production, great difficulty in lifting and gathering and transportation, and poor development benefits. At present, the main technologies for heavy oil development at home and abroad include steam huff and puff, steam flooding, steam assisted gravity drainage, hot water flooding, fire flooding, carbon dioxide flooding and viscosity reducer flooding. Among them, carbon dioxide flooding, as a heavy oil cold production technology that can realize efficient development of heavy oil and effective storage of greenhouse gas carbon dioxide, and viscosity reducer flooding, as a low-cost heavy oil development technology, have attracted widespread attention at home and abroad, and a technology for improving the recovery efficiency of heavy oil reservoirs by combining carbon dioxide flooding and viscosity reducer flooding has been proposed. Therefore, in the process of implementing carbon dioxide and viscosity reducer composite flooding in the field, the evaluation and optimization of the viscosity reducer system are of great significance to the realization of the maximum increase of the recovery efficiency of heavy oil reservoirs and the best economic benefits. SUMMARY

[0003] The application aims to provide a screening method of a viscosity reducer for carbon dioxide flooding to improve the above technical problems.

[0004] In order to achieve the above-mentioned purpose, the embodiments of the present application provide the following technical solutions:

[0005] The embodiments of the present application provide a screening method of a viscosity reducer for carbon dioxide flooding, which comprises the following steps: calculating the viscosity reduction rates of a plurality of viscosity reducers for heavy oil at different test temperatures, and then obtaining a plurality of viscosity reduction rate arrays of the viscosity reducers at different temperatures; sequentially calculating the average viscosity reduction rates of each viscosity reducer for heavy oil based on the viscosity reduction rate arrays; sequentially calculating the oil displacement efficiencies of each viscosity reducer and CO2, and calculating the comprehensive evaluation indexes of each viscosity reducer based on the normalized values of the average viscosity reduction rate and the oil displacement efficiency of each viscosity reducer, the average normalized value, the standard deviation of the normalized value, the coefficient of variation of the normalized value and the weighting factor, and screening the optimal viscosity reducer based on the comprehensive evaluation indexes.

[0006] Optionally, the calculation of the viscosity reduction rates of a plurality of viscosity reducers for heavy oil at different test temperatures comprises the following steps:

[0007] The heavy oil is placed in a constant-temperature oil bath with a temperature set to a first temperature for 1 h, then free water and air bubbles in the heavy oil are removed by stirring, and the viscosity u0 of the heavy oil at the temperature is measured by a rotary viscometer;

[0008] The formation water is used to configure a preset concentration of viscosity reducer solution, 280 g of thick oil sample is weighed in a beaker, 120 g of viscosity reducer solution is added, the stirring paddle is placed at the center of the beaker at a distance of 2-3 mm from the bottom of the beaker, the rotating speed is adjusted to 250 r / min, and the mixture is stirred for 2 min under constant temperature, and the viscosity μ of the mixture at the temperature is measured by a rotary viscometer;

[0009] The viscosity reduction rate of the viscosity reducer at the first temperature is calculated by a viscosity reduction rate calculation formula, wherein the viscosity reduction rate calculation formula is:

[0010]

[0011] In the formula, x is the viscosity reduction rate of the viscosity reducer to the thick oil, %; μ o is the viscosity of the thick oil sample at the first temperature, mPa·s; μ is the viscosity of the mixture of the thick oil and the viscosity reducer at the same temperature, mPa·s.

[0012] Optionally, based on the viscosity reduction rate array, the average viscosity reduction rate of each viscosity reducer to the thick oil is sequentially calculated, including:

[0013] The average viscosity of the first viscosity reducer at different experimental temperatures is calculated based on an average viscosity calculation formula, wherein the average viscosity calculation formula is:

[0014]

[0015] In the formula, μ is the average viscosity, mPa·s; T is the temperature, ℃; T i is the initial experimental temperature, ℃; T s is the highest experimental temperature, ℃; μ(T) is the viscosity of the thick oil sample at the temperature T, mPa·s.

[0016] The average viscosity is used to calculate the average viscosity reduction rate, wherein the calculation formula of the average viscosity reduction rate is:

[0017]

[0018] In the formula, X is the average viscosity reduction rate, dimensionless.

[0019] Optionally, the oil displacement efficiency of each viscosity reducer and CO2 is sequentially calculated, including:

[0020] The dried quartz sand is used to fill the sand filling pipe, and the weight of the sand filling pipe is m1;

[0021] After the filled sand filling pipe is vacuumed for 3 hours, the saturated water is weighed, and the weight of the sand filling pipe after the saturated water is m2, the pore volume Vp of the sand filling pipe model is calculated as (m2-m1) / ρw, and the water phase permeability of the sand filling pipe is measured; wherein, ρw is the saturated water density;

[0022] After the sandpack is kept at the target heavy oil reservoir temperature for 4 hours, saturate the sandpack with oil at a speed of 0.2 mL / min, measure the volume of the saturated oil, and calculate the initial oil saturation of the sandpack model;

[0023] Under the target heavy oil reservoir temperature and pressure, carry out CO2 flooding at a speed of 2 mL / min, stop the experiment when no oil is produced at the outlet end of the sandpack, and record the pressure changes at the front and rear ends of the sandpack and the oil, gas and water production data at different times during the experiment;

[0024] Based on the oil displacement efficiency and residual oil saturation calculation formula, the oil displacement efficiency of the viscosity reducer corresponding to CO2 is calculated, and the oil displacement efficiency and residual oil saturation calculation formula is:

[0025]

[0026] S or =(1-R o )×S oi ;

[0027] Wherein, R is the oil displacement efficiency; S oi is the initial oil saturation; S or is the residual oil saturation; R o is the final oil displacement efficiency.

[0028] Optionally, the average viscosity reduction rate and the normalized value of the oil displacement efficiency corresponding to each viscosity reducer, the average normalized value, the standard deviation of the normalized value, the coefficient of variation of the normalized value, and the weighted factor are used to calculate the comprehensive evaluation index corresponding to each viscosity reducer, including:

[0029] Based on the comprehensive evaluation index calculation formula, the comprehensive evaluation index corresponding to the viscosity reducer is calculated, and the comprehensive evaluation index calculation formula is:

[0030]

[0031] In the formula, C EI is the comprehensive evaluation index of the viscosity reducer for CO2 flooding; ω is the weighted factor; X i is the average viscosity reduction rate of the i-th viscosity reducer; X max is the maximum viscosity reduction percentage among all viscosity reducers; R i is the oil displacement efficiency of the i-th viscosity reducer; R max is the maximum oil displacement efficiency among all viscosity reducers.

[0032] Optionally, the calculation method of the weighted factor ω is:

[0033] The normalized value of the average viscosity reduction rate (X) and the oil displacement efficiency (R) is calculated, and the formula is as follows:

[0034]

[0035] wherein y is a normalized value of the average viscosity reduction rate (X) or the oil displacement efficiency (R), dimensionless; x is the average viscosity reduction rate (X) or the oil displacement efficiency (R) ; x max is the maximum value of the average viscosity reduction rate (X) or the oil displacement efficiency (R) ; x min is the minimum value of the average viscosity reduction rate (X) or the oil displacement efficiency (R).

[0036] The average normalized value of the average viscosity reduction rate (X) and the oil displacement efficiency (R) is calculated according to the following formula:

[0037]

[0038] wherein is the average normalized value of the average viscosity reduction rate (X) or the oil displacement efficiency (R), dimensionless; n is the number of the evaluated viscosity reducer system.

[0039] The standard deviation of the normalized value of the average viscosity reduction rate (X) and the oil displacement efficiency (R) is calculated according to the following formula:

[0040]

[0041] wherein σ is the standard deviation of the normalized value of the average viscosity reduction rate (X) or the oil displacement efficiency (R).

[0042] The coefficient of variation of the normalized value of the average viscosity reduction rate (X) and the oil displacement efficiency (R) is calculated according to the following formula:

[0043]

[0044] wherein C V is the coefficient of variation of the normalized value of the average viscosity reduction rate (X) or the oil displacement efficiency (R).

[0045] The weighting factor ω is calculated according to the following formula:

[0046]

[0047] wherein C VX is the coefficient of variation of the normalized value of the average viscosity reduction rate; C VR is the coefficient of variation of the normalized value of the oil displacement efficiency.

[0048] In a third aspect, the embodiments of the present application provide a screening device for a viscosity reducer for carbon dioxide flooding, which comprises a memory and a processor.

[0049] The memory is used for storing a computer program; and the processor is used for executing the computer program to implement the steps of the above-mentioned screening method for a viscosity reducer for carbon dioxide flooding.

[0050] In a fourth aspect, the embodiments of the present application provide a medium, which stores a computer program, and the computer program is executed by a processor to implement the steps of the screening method of the viscosity reducer for carbon dioxide flooding.

[0051] The present application has the following advantages:

[0052] The present application provides a screening method of a viscosity reducer for carbon dioxide flooding, which mainly focuses on the viscosity reduction of the viscosity reducer for thick oil and the improvement of the flowability of the thick oil in the performance evaluation and optimization of the viscosity reducer in the prior art, and does not consider the problem of the influence of the mixture of the thick oil and the viscosity reducer on the oil displacement efficiency of the thick oil.

[0053] Other features and advantages of the present application will be described in the following description, and some will become apparent from the description, or will be learned through practice of the embodiments of the present application. The purposes and other advantages of the present application can be achieved and obtained by the structures specifically pointed out in the written description, claims, and drawings. BRIEF DESCRIPTION OF DRAWINGS

[0054] In order to more clearly illustrate the technical solutions of the embodiments of the present application, the following will briefly introduce the drawings needed to be used in the embodiments, and it should be understood that the following drawings only show some embodiments of the present application, and therefore should not be regarded as a limitation to the scope, and for those skilled in the art, other related drawings can also be obtained without creative labor on the basis of these drawings.

[0055] Figure 1 is a flowchart of the screening method of the viscosity reducer for carbon dioxide flooding in the embodiments of the present application;

[0056] Figure 2 is a structural schematic diagram of the screening device of the viscosity reducer for carbon dioxide flooding in the embodiments of the present application;

[0057] Figure 3 is an experimental test data-temperature influence diagram in the embodiments of the present application;

[0058] Figure 4 is an experimental test data-viscosity reduction rate curve diagram in the embodiments of the present application;

[0059] Figure 5 is an experimental test data-average viscosity reduction rate histogram in the embodiments of the present application;

[0060] Figure 6 is the experimental test data-oil displacement efficiency curve in the embodiment of the present application;

[0061] Figure 7 is the experimental test data-final oil displacement efficiency and residual oil saturation column chart in the embodiment of the present application;

[0062] Figure 8 is the experimental test data-oil displacement efficiency curve a in the embodiment of the present application. DETAILED DESCRIPTION

[0063] In order to make the objects, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. The components of the embodiments of the present application described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present application provided in the drawings is not intended to limit the scope of the claimed present application, but only represents selected embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art without creative work based on the embodiments in the present application are within the scope of protection of the present application.

[0064] It should be noted that: similar reference numerals or letters represent similar items in the following drawings, therefore, once an item is defined in one drawing, it does not need to be further defined and explained in subsequent drawings. Meanwhile, in the description of the present application, the terms "first", "second", etc. are only used to distinguish the description, and cannot be understood as indicating or implying relative importance.

[0065] Embodiment 1

[0066] As shown in Figure 1 , the embodiment provides a screening method of a viscosity reducer for carbon dioxide flooding, and the method comprises steps S100, S200, S300 and S400.

[0067] Step S100, calculating the viscosity reduction rates of a plurality of viscosity reducers on thick oil at different test temperatures, and then obtaining a plurality of viscosity reduction rate arrays of the viscosity reducers at different temperatures;

[0068] Step S200, based on the viscosity reduction rate array, sequentially calculating the average viscosity reduction rate of each viscosity reducer on thick oil;

[0069] Step S300, the oil displacement efficiency of each viscosity reducer and CO2 is calculated in turn, and the comprehensive evaluation index corresponding to each viscosity reducer is calculated based on the normalized value, average normalized value, standard deviation of normalized value, coefficient of variation of normalized value, and weighting factor of the average viscosity reduction rate corresponding to each viscosity reducer and the oil displacement efficiency, and the optimal viscosity reducer is screened out based on the comprehensive evaluation index.

[0070] Secondly, in step S100, the viscosity reduction rates of the plurality of viscosity reducers for thick oil at different test temperatures are calculated, including:

[0071] Step S110, the thick oil is placed in a constant temperature oil bath with the temperature set to the first temperature for 1 h, then the free water and bubbles in the thick oil are removed by stirring, and the viscosity μ0 of the thick oil at the temperature is measured by a rotary viscometer;

[0072] Step S120, a viscosity reducer solution with a preset concentration is prepared using formation water, and 280 g of a thick oil sample is weighed in a beaker, 120 g of the viscosity reducer solution is added, and the beaker is placed in a constant temperature oil bath for 1 h. The stirring paddle is placed at the center 2-3 mm away from the bottom of the beaker, and the rotation speed is adjusted to 250 r / min. The mixture is stirred for 2 min under constant temperature conditions, and the viscosity μ of the mixture at the temperature is measured by a rotary viscometer;

[0073] Step S130, the viscosity reduction rate of the viscosity reducer at the first temperature is calculated by the viscosity reduction rate calculation formula, wherein the viscosity reduction rate calculation formula is:

[0074]

[0075] In the formula, x is the viscosity reduction rate of the viscosity reducer for thick oil, %; μ o is the viscosity of the thick oil sample at the first temperature, mPa·s; μ is the viscosity of the mixture of thick oil and viscosity reducer at the same temperature, mPa·s.

[0076] Secondly, in step S200, based on the viscosity reduction rate array, the average viscosity reduction rate of each viscosity reducer for thick oil is calculated in turn, including:

[0077] Step S210, the average viscosity of the first viscosity reducer at different experimental temperatures is calculated based on the average viscosity calculation formula, wherein the average viscosity calculation formula is:

[0078]

[0079] In the formula, x is the viscosity reduction rate of the viscosity reducer for thick oil, %; μ is the average viscosity, mPa·s; T is the temperature, ℃; T i is the initial experimental temperature, ℃; T s is the highest experimental temperature, ℃; μ(T) is the viscosity of the mixture of thick oil and viscosity reducer at temperature T, mPa·s;

[0080] Step S220, calculating the average viscosity reduction rate based on the average viscosity, wherein the formula for calculating the average viscosity reduction rate is:

[0081]

[0082] wherein, X is the average viscosity reduction rate, dimensionless.

[0083] Secondly, in step S300, the oil displacement efficiency of each viscosity reducer and CO2 is calculated in turn, including:

[0084] Step S310, filling the sand pipe with dried quartz sand, and weighing the sand pipe as m1;

[0085] Step S320, saturating the filled sand pipe with water after vacuumizing for 3 hours, and weighing the sand pipe after saturation as m2, calculating the sand pipe model pore volume Vp=(m2-m1) / pW, and measuring the water phase permeability of the sand pipe; wherein, pW is the saturated water density;

[0086] Step S330, saturating the sand pipe with oil at a speed of 0.2 mL / min after constant temperature for 4 hours under the target heavy oil reservoir temperature condition, measuring the volume of saturated oil, and calculating the initial oil saturation of the sand pipe model;

[0087] Step S340, conducting CO2 oil displacement at a speed of 2 mL / min under the target heavy oil reservoir temperature and pressure condition, stopping the experiment when no oil is produced at the outlet end of the sand pipe, and recording the pressure change data at the front and rear ends of the sand pipe, the oil and gas production, and the water volume change data at different times during the experiment;

[0088] Step S350, calculating the oil displacement efficiency of the viscosity reducer corresponding to CO2 based on the oil displacement efficiency and residual oil saturation calculation formula, wherein the oil displacement efficiency and residual oil saturation calculation formula is:

[0089]

[0090] S or =(1-R o )×S oi ;

[0091] wherein, R is the oil displacement efficiency; S oi is the initial oil saturation; S or is the residual oil saturation; R o is the final oil displacement efficiency.

[0092] Secondly in step S300, the average viscosity reduction rate and oil displacement efficiency of each viscosity reducer are normalized, and the normalized values, average normalized values, standard deviation of normalized values, coefficient of variation of normalized values, and weighting factor are used to calculate the comprehensive evaluation index of each viscosity reducer, including:

[0093] Step S360, based on the comprehensive evaluation index calculation formula, the comprehensive evaluation index of the viscosity reducer is calculated, and the comprehensive evaluation index calculation formula is:

[0094]

[0095] In the formula, C EI is the comprehensive evaluation index of CO2 oil displacement viscosity reducer; ω is the weighting factor; X i is the average viscosity reduction rate of the i-th viscosity reducer; X max is the maximum viscosity reduction percentage of all viscosity reducers; R i is the oil displacement efficiency of the i-th viscosity reducer; R max is the maximum oil displacement efficiency of all viscosity reducers.

[0096] Secondly in step S360, the calculation method of the weighting factor ω is:

[0097] Step S361, the normalized values of the average viscosity reduction rate (X) and the oil displacement efficiency (R) are calculated, and the formula is as follows:

[0098]

[0099] In the formula, y is the normalized value of the average viscosity reduction rate (X) or the oil displacement efficiency (R), which is dimensionless; x is the average viscosity reduction rate (X) or the oil displacement efficiency (R); x max is the maximum value of the average viscosity reduction rate (X) or the oil displacement efficiency (R); x min is the minimum value of the average viscosity reduction rate (X) or the oil displacement efficiency (R).

[0100] Step S362, the average normalized value of the average viscosity reduction rate (X) and the oil displacement efficiency (R) is calculated, and the formula is as follows:

[0101]

[0102] In the formula, is the average normalized value of the average viscosity reduction rate (X) or the oil displacement efficiency (R), which is dimensionless; n is the number of evaluated viscosity reducer systems.

[0103] Step S363, the standard deviation of the normalized values of the average viscosity reduction rate (X) and the oil displacement efficiency (R) is calculated, and the formula is as follows:

[0104]

[0105] wherein σ is the standard deviation of the average viscosity reduction rate (X) or the normalized value of oil displacement efficiency (R).

[0106] Step S364, the coefficient of variation of the average viscosity reduction rate (X) and the normalized value of oil displacement efficiency (R) is calculated, and the formula is as follows:

[0107]

[0108] wherein C V is the coefficient of variation of the average viscosity reduction rate (X) or the normalized value of oil displacement efficiency (R).

[0109] Step S365, the weighting factor ω is calculated, and the formula is as follows:

[0110]

[0111] wherein C VX is the coefficient of variation of the average viscosity reduction rate (X) or the normalized value of oil displacement efficiency (R). VR is the coefficient of variation of the average viscosity reduction rate (X) or the normalized value of oil displacement efficiency (R).

[0112] Example 2

[0113] As Figures 3-8 shown, in order to more clearly illustrate the screening method of the viscosity reducer for carbon dioxide flooding provided by the present application, the specific implementation steps of the present application are exemplified as follows:

[0114] (1) Evaluation of the viscosity reduction performance of the viscosity reducer on heavy oil

[0115] Four viscosity reducers (viscosity reducer A, viscosity reducer B, viscosity reducer C and viscosity reducer D) are selected to evaluate their viscosity reduction effects on heavy oil at 50℃, 80℃, 100℃, 120℃ and 150℃, and the viscosity reduction rates (x) of the four viscosity reducers on heavy oil at different temperature conditions are calculated according to formula (2), and the experimental results are shown in Table 1. Figure 3 As shown in Table 1, the results show that the viscosity of heavy oil can be reduced by adding the four viscosity reducers, and the viscosity reduction rate at lower temperature is greater than that at higher temperature, indicating that the viscosity reduction effect is mainly reflected in the low temperature zone. Except for viscosity reducer D, the viscosity reduction rates of the remaining three viscosity reducers from low temperature to high temperature are all greater than 75%. In order to comprehensively evaluate the dual effects of temperature and viscosity reducer on the viscosity reduction of heavy oil, the average viscosity reduction rates (X) of the four viscosity reducers on heavy oil are calculated according to formula (3) and formula (4), and the experimental results are shown in Table 2. Figure 4 As shown in Table 2, the results show that the viscosity reduction ability of the four viscosity reducers is ranked as follows: viscosity reducer C > viscosity reducer A > viscosity reducer B > viscosity reducer D. Therefore, viscosity reducer A, viscosity reducer B and viscosity reducer C are preferred to continue the oil displacement experiment.

[0116] (2) Evaluation of the oil displacement performance of the CO2 and viscosity reducer system

[0117] The physical simulation displacement experimental device is used for evaluating the oil displacement effects of pure CO2 flooding and CO2 + viscosity reducer A compound flooding, CO2 + viscosity reducer B compound flooding and CO2 + viscosity reducer C compound flooding respectively, and the experimental parameters and experimental results are shown in Table 1 and Figure 5 The final oil displacement efficiency of pure CO2 flooding is 47.99%, the final oil displacement efficiency of CO2 + viscosity reducer C compound flooding is 70.3%, which is 22.4% higher than that of pure CO2 flooding; the final oil displacement efficiency of CO2 + viscosity reducer A compound flooding is 68.4%, which is slightly lower than that of CO2 + viscosity reducer C compound flooding; and the final oil displacement efficiency of CO2 + viscosity reducer B compound flooding is 64.9%. It can be seen that the addition of viscosity reducer in CO2 can significantly improve the oil displacement efficiency of heavy oil. The ability of CO2 + viscosity reducer C compound flooding to mobilize residual oil is the strongest, and the residual oil saturation can be reduced to below 30%.

[0118] Table 1 Physical simulation displacement experimental parameter table of sand filling pipe

[0119]

[0120] (3) Comprehensive performance evaluation of viscosity reducer for CO2 flooding of heavy oil reservoir

[0121] The average viscosity reduction rate and the normalized value (y) of oil displacement efficiency of the four viscosity reduction systems of CO2, viscosity reducer A, viscosity reducer B and viscosity reducer C are calculated respectively, and the average normalized value The standard deviation (σ) of the normalized value, the coefficient of variation (C V ) of the normalized value, the weighted factor (ω) and the comprehensive evaluation index (C EI ) of the viscosity reducer for CO2 flooding are calculated, and the calculation results are shown in Table 2. The results show that the comprehensive evaluation indexes of viscosity reducer A and viscosity reducer C are equal, and are higher than those of pure CO2 and viscosity reducer B. Therefore, viscosity reducer A and viscosity reducer C are determined as the best viscosity reducers for CO2 flooding of heavy oil reservoir.

[0122] Table 2 Comprehensive evaluation results of different viscosity reducers

[0123]

[0124] Example 3

[0125] Corresponding to the above method embodiment, the disclosure embodiment also provides a screening device for viscosity reducer for carbon dioxide flooding. The screening device for viscosity reducer for carbon dioxide flooding described below can be mutually corresponding to the screening method for viscosity reducer for carbon dioxide flooding described above.

[0126] Figure 2 is a block diagram of a screening device 800 for viscosity reducer for carbon dioxide flooding according to an exemplary embodiment. As Figure 3As shown, the electronic device 800 can include a processor 801, a memory 802. The electronic device 800 can further include one or more of a multimedia component 803, an I / O interface 804, and a communication component 805.

[0127] The processor 801 is configured to control overall operations of the electronic device 800 to complete all or part of the steps in the method for screening a viscosity reducer for carbon dioxide flooding described above. The memory 802 is configured to store various types of data to support operations of the electronic device 800, which can include, for example, instructions for operating any application or method on the electronic device 800, and application-related data, such as contact data, sent and received messages, pictures, audio, video, and the like. The memory 802 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as a static random access memory (SRAM), an electrically erasable programmable read-only memory (EEPROM), an erasable programmable read-only memory (EPROM), a programmable read-only memory (PROM), a read-only memory (ROM), a magnetic memory, a flash memory, a magnetic disk, or an optical disk. The multimedia component 803 can include a screen and an audio component. The screen can be, for example, a touch screen, and the audio component is configured to output and / or input audio signals. For example, the audio component can include a microphone configured to receive external audio signals. The received audio signals can be further stored in the memory 802 or transmitted through the communication component 805. The audio component further includes at least one speaker configured to output audio signals. The I / O interface 804 provides an interface between the processor 801 and other interface modules, which can be a keyboard, a mouse, a button, and the like. The buttons can be virtual buttons or physical buttons. The communication component 805 is configured to perform wired or wireless communication between the electronic device 800 and other devices. The wireless communication, such as Wi-Fi, Bluetooth, near field communication (NFC), 2G, 3G, or 4G, or a combination of one or more of them, so the corresponding communication component 805 can include a Wi-Fi module, a Bluetooth module, and an NFC module.

[0128] In an example embodiment, the electronic device 800 can be implemented by one or more Application Specific Integrated Circuit (ASIC), Digital Signal Processor (DSP), Digital Signal Processing Device (DSPD), Programmable Logic Device (PLD), Field Programmable Gate Array (FPGA), controller, microcontroller, microprocessor or other electronic elements for executing the above-mentioned method for screening a viscosity reducer for carbon dioxide flooding.

[0129] In another example embodiment, a computer-readable storage medium including program instructions is also provided, which when executed by a processor, implement the steps of the above-mentioned method for screening a viscosity reducer for carbon dioxide flooding. For example, the computer-readable storage medium can be the above-mentioned memory 802 including program instructions, which can be executed by the processor 801 of the electronic device 800 to complete the above-mentioned method for screening a viscosity reducer for carbon dioxide flooding.

[0130] Embodiment 4

[0131] Corresponding to the above method embodiments, the embodiments of the present disclosure also provide a readable storage medium, which can be mutually corresponding to the above-mentioned method for screening a viscosity reducer for carbon dioxide flooding.

[0132] A readable storage medium, on which a computer program is stored, the computer program being executed by a processor to implement the steps of the above-mentioned method for screening a viscosity reducer for carbon dioxide flooding.

[0133] The readable storage medium can specifically be a U disk, a mobile hard disk, a Read-Only Memory (ROM), a Random Access Memory (RAM), a magnetic disk or an optical disk and various readable storage media that can store program codes.

[0134] The above only describes the preferred embodiments of the present disclosure and is not used to limit the present disclosure. For those skilled in the art, the present disclosure can have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present disclosure shall be included in the protection scope of the present disclosure.

Claims

1. A method for screening viscosity reducers for carbon dioxide flooding, characterized in that, The method includes: The viscosity reduction rate of various viscosity reducers on heavy oil at different test temperatures was calculated, and then multiple sets of viscosity reduction rate arrays of viscosity reducers at different temperatures were obtained; Based on the viscosity reduction rate array, the average viscosity reduction rate of each viscosity reducer on heavy oil is calculated sequentially; The oil displacement efficiency of each viscosity reducer with CO2 was calculated sequentially. Based on the normalized values ​​of the average viscosity reduction rate and oil displacement efficiency, the average normalized value, the standard deviation of the normalized value, the coefficient of variation of the normalized value, and the weighting factor, a comprehensive evaluation index was calculated for each viscosity reducer. The optimal viscosity reducer was then selected based on this comprehensive evaluation index. The comprehensive evaluation index for each viscosity reducer is calculated based on the normalized value, average normalized value, standard deviation of the normalized value, coefficient of variation of the normalized value, and weighting factor of the normalized value, including: Based on the comprehensive evaluation index calculation formula, the comprehensive evaluation index corresponding to the viscosity reducer is calculated. The comprehensive evaluation index calculation formula is as follows: In the formula, C EI X is the comprehensive evaluation index for viscosity reducers used in CO2 flooding; ω is the weighting factor; X i X represents the average viscosity reduction rate of the i-th viscosity reducer; max R represents the maximum viscosity reduction percentage among all viscosity reducers. i R represents the oil displacement efficiency of the i-th viscosity reducer. max It has the highest oil displacement efficiency among all viscosity reducers.

2. The screening method for viscosity reducers for carbon dioxide flooding according to claim 1, characterized in that, Calculate the viscosity reduction rate of various viscosity reducers on heavy oil at different test temperatures, including: The heavy oil was placed in a constant temperature oil bath with the temperature set to the first temperature and kept at the temperature for 1 hour. Then, the free water and air bubbles in the heavy oil were removed by stirring. The viscosity μ0 of the heavy oil at this temperature was measured by a rotational viscometer. A viscosity reducer solution of a predetermined concentration was prepared using formation water. 280g of heavy oil sample was weighed into a beaker, 120g of viscosity reducer solution was added, and the beaker was placed in a constant temperature oil bath for 1 hour. The stirring paddle was placed 2-3mm from the bottom of the beaker, the rotation speed was adjusted to 250r / min, and the mixture was stirred for 2 minutes under constant temperature conditions. The viscosity μ of the mixture at this temperature was measured using a rotational viscometer. The viscosity reduction rate of the viscosity reducer at the first temperature is calculated using the viscosity reduction rate calculation formula, wherein the viscosity reduction rate calculation formula is: In the formula, x is the viscosity reduction rate of the viscosity reducer on heavy oil, %; μ o ρ is the viscosity of the heavy oil sample at the first temperature, in mPa·s; μ is the viscosity of the mixture of heavy oil and viscosity reducer at the same temperature, in mPa·s.

3. The screening method for viscosity reducers for carbon dioxide flooding according to claim 2, characterized in that, Based on the aforementioned viscosity reduction rate array, the average viscosity reduction rate of each viscosity reducer on heavy oil is calculated sequentially, including: The average viscosity of the first viscosity reducer at different experimental temperatures was calculated based on the average viscosity calculation formula, wherein the average viscosity calculation formula is: in, The average viscosity is given in mPa·s; T is the temperature in °C. i T represents the initial experimental temperature in °C. s The highest experimental temperature is ℃; μ(T) is the viscosity of the mixture of heavy oil and viscosity reducer at temperature T, mPa·s; The average viscosity reduction rate is calculated based on the average viscosity, wherein the formula for calculating the average viscosity reduction rate is: Where X is the average viscosity reduction rate, which is dimensionless.

4. The screening method for viscosity reducers for carbon dioxide flooding according to claim 1, characterized in that, The calculation of the oil displacement efficiency of each viscosity reducer with CO2 includes: Dry quartz sand is used to fill the sand-filling pipe, and the weight of the sand-filling pipe is m1. After vacuuming the sand-filled pipe for 3 hours, saturate it with water and weigh the saturated sand-filled pipe as m2. Calculate the pore volume of the sand-filled pipe model Vp=(m2-m1) / ρw, and determine the water phase permeability of the sand-filled pipe; where ρw is the density of saturated water. After the sand-filled tube was kept at a constant temperature for 4 hours under the target heavy oil reservoir temperature, it was saturated with oil at a rate of 0.2 mL / min. The volume of saturated oil was measured, and the initial oil saturation of the sand-filled tube model was calculated. Under the target heavy oil reservoir temperature and pressure conditions, CO2 flooding was carried out at a rate of 2 mL / min. The experiment was stopped when no oil was produced at the outlet end of the sand-filled pipe. During the experiment, the changes in pressure and oil, gas and water production at the front and rear ends of the sand-filled pipe at different times were recorded. Based on the formulas for calculating oil displacement efficiency and residual oil saturation, the oil displacement efficiency of the viscosity reducer corresponding to CO2 is calculated. The formulas for calculating oil displacement efficiency and residual oil saturation are as follows: S or =(1-R o )×S oi ; Where R is the oil displacement efficiency; S oi S represents the initial oil saturation. or R represents the remaining oil saturation. o For the final oil displacement efficiency.

5. The method for screening viscosity reducers for carbon dioxide flooding according to claim 1, characterized in that, The weighting factor ω is calculated as follows: The normalized values ​​of the average viscosity reduction rate (X) and oil displacement efficiency (R) are calculated using the following formulas: In the formula, y is the normalized value of the average viscosity reduction rate (X) or oil displacement efficiency (R), which is dimensionless; x is the average viscosity reduction rate (X) or oil displacement efficiency (R); x max The maximum value of the average viscosity reduction rate (X) or oil displacement efficiency (R); x min This represents the minimum average viscosity reduction rate (X) or oil displacement efficiency (R). The average normalized values ​​of the average viscosity reduction rate (X) and oil displacement efficiency (R) are calculated using the following formula: In the formula, , which is the average normalized value of the average viscosity reduction rate (X) or oil displacement efficiency (R), is dimensionless; n is the number of viscosity reducer systems being evaluated; The standard deviations of the normalized values ​​of the average viscosity reduction rate (X) and oil displacement efficiency (R) are calculated using the following formulas: In the formula, σ is the standard deviation of the normalized value of the average viscosity reduction rate (X) or oil displacement efficiency (R); The coefficients of variation for the normalized values ​​of the average viscosity reduction rate (X) and oil displacement efficiency (R) are calculated using the following formulas: In the formula, C V The coefficient of variation is the normalized value of the average viscosity reduction rate (X) or oil displacement efficiency (R). The weighting factor ω is calculated using the following formula: In the formula, C VX C is the coefficient of variation of the normalized average viscosity reduction rate; VR The coefficient of variation is the normalized value of the oil displacement efficiency.

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