Screening method of viscosity reducer for carbon dioxide oil displacement

Abstract

The invention relates to the technical field of heavy oil reservoir development, in particular to a screening method of a viscosity reducer for carbon dioxide oil displacement, and the method comprises the following steps: calculating the viscosity reduction rates of various viscosity reducers to heavy oil at different test temperatures so as to obtain viscosity reduction rate arrays of multiple groups of viscosity reducers at different temperatures; calculating a comprehensive evaluation index corresponding to each viscosity reducer on the basis of the viscosity reduction rate array, the average viscosity reduction rate corresponding to each viscosity reducer and the normalized value of the oil displacement efficiency, the average normalization, the standard deviation, the variable coefficient and the weighting factor, and screening out an optimal viscosity reducer on the basis of the comprehensive evaluation index; the static viscosity reduction performance and the dynamic oil displacement performance of the thick oil viscosity reducer are comprehensively evaluated through a thick oil viscosity reduction effect evaluation experiment and a physical simulation oil displacement experiment, so that optimization of the viscosity reducer for carbon dioxide oil displacement is guided; and the recovery efficiency of the heavy oil reservoir is improved to the maximum extent and the optimal economic benefit is obtained by carbon dioxide and viscosity reducer combination flooding.

Description

Technical Field

[0001] The invention relates to the technical field of heavy oil reservoir development, and in particular to a method for screening a viscosity reducer for carbon dioxide oil recovery. Background Art

[0002] The biggest problem faced in the development of heavy oil reservoirs is the poor fluidity of high-viscosity heavy oil in the porous media of the reservoir, the wellbore of the oil well and the ground gathering and transportation pipeline system, which leads to low oil well production, great difficulty in lifting and gathering, and poor development benefits. At present, the main technologies for heavy oil development at home and abroad include steam stimulation, steam drive, steam-assisted gravity drainage, hot water drive, fire oil layer burning, carbon dioxide drive, viscosity reducer drive, etc. Among them, carbon dioxide drive as a heavy oil cold recovery technology that can simultaneously achieve efficient development of heavy oil and effective storage of greenhouse gas carbon dioxide, and viscosity reducer drive as a low-cost heavy oil development technology, have received widespread attention at home and abroad, and a technology combining carbon dioxide drive with viscosity reducer drive to improve the recovery rate of heavy oil reservoirs has been proposed. Therefore, in the process of implementing the composite drive of carbon dioxide and viscosity reducer on site, the evaluation and optimization of the viscosity reducer system is of great significance for achieving the maximum increase in the recovery rate of heavy oil reservoirs and obtaining the best economic benefits. Summary of the invention

[0003] The object of the present invention is to provide a method for screening a viscosity reducer for carbon dioxide flooding to improve the above technical problems.

[0004] In order to achieve the above objectives, the present application provides the following technical solutions:

[0005] The embodiment of the present application provides a method for screening viscosity reducers for carbon dioxide oil recovery, the method comprising: calculating the viscosity reduction rates of multiple viscosity reducers for heavy oil at different test temperatures, thereby obtaining a viscosity reduction rate array of multiple groups of viscosity reducers at different temperatures; based on the viscosity reduction rate array, calculating the average viscosity reduction rate of each viscosity reducer for heavy oil in turn; calculating the oil recovery efficiency of each viscosity reducer with CO2 in turn, and calculating a comprehensive evaluation index corresponding to each viscosity reducer based on the normalized value, average normalization, standard deviation, coefficient of variation, and weighting factor of the average viscosity reduction rate and oil recovery efficiency corresponding to each viscosity reducer, and screening out the best viscosity reducer based on the comprehensive evaluation index.

[0006] Optionally, the viscosity reduction rates of various viscosity reducers for heavy oil at different test temperatures are calculated, including:

[0007] The heavy oil is placed in a constant temperature oil bath set at a first temperature for 1 hour, free water and bubbles in the heavy oil are removed by stirring, and its viscosity μo at the temperature is measured by a rotational viscometer;

[0008] Prepare a viscosity reducer solution of preset concentration using formation water and weigh 280g of heavy oil sample into a beaker, add 120g of viscosity reducer solution, put into a constant temperature oil bath for 1h, place the stirring paddle at the center 2-3mm away from the bottom of the beaker, adjust the speed to 250r / min, stir at constant temperature for 2min, and measure the viscosity μ of the mixture at this temperature using a rotational viscometer;

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

[0010]

[0011] Where x is the viscosity reduction rate of the viscosity reducer on the heavy oil, %; μ o is the viscosity of the heavy oil sample at a certain temperature, mPa·s; μ is the viscosity of the mixture of heavy oil and 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 heavy oil is calculated in sequence, including:

[0013] 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:

[0014]

[0015] in, is the average viscosity, mPa·s; T is the temperature, ℃; Ti is the initial experimental temperature, ℃; Ts is the maximum experimental temperature, ℃; μ o is the viscosity of the heavy oil sample at temperature T, mPa·s;

[0016] The average viscosity reduction rate is calculated based on the average viscosity, wherein the calculation formula of the average viscosity reduction rate is:

[0017]

[0018] Wherein, X is the average viscosity reduction rate, dimensionless; μo is the viscosity of the heavy oil under the initial experimental temperature conditions, mPa·s.

[0019] Optionally, the oil recovery efficiency of each viscosity reducer and CO2 is calculated in sequence, including:

[0020] Use dried quartz sand to fill the sand filling tube, and weigh the weight of the sand filling tube as m1;

[0021] The sand-filled tube was saturated with water after vacuuming for 3 hours, and the weight of the sand-filled tube saturated with water was weighed as m2, and the pore volume of the sand-filled tube model Vp = (m2-m1) / ρw was calculated, and the water phase permeability of the sand-filled tube was measured;

[0022] After the sand-filled tube is kept at a constant temperature for 4 hours under the target heavy oil reservoir temperature, it is saturated with oil at a rate of 0.2 mL / min, the volume of saturated oil is measured, and the initial oil saturation of the sand-filled tube model is calculated;

[0023] 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 of the sand-filled pipe. During the experiment, the pressure at the front and rear ends of the sand-filled pipe and the change data of the produced oil, gas and water volume were recorded at different times.

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

[0025]

[0026] S or =(1-R o )×S oi ;

[0027] Among them, R is the oil recovery efficiency; Soi is the initial oil saturation; Sor is the remaining oil saturation; Ro is the final oil recovery efficiency.

[0028] Optionally, the comprehensive evaluation index corresponding to each viscosity reducer is calculated based on the normalized value of the average viscosity reduction rate and oil displacement efficiency corresponding to each viscosity reducer, the average normalization, the standard deviation, the coefficient of variation, and the weighting factor, including:

[0029] 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:

[0030]

[0031] Wherein, CEI is the comprehensive evaluation index of viscosity reducers for CO2 flooding; ω is the weighting factor; Xi is the average viscosity reduction rate of the i-th viscosity reducer; Xmax is the maximum viscosity reduction percentage among all viscosity reducers; Ri is the oil recovery efficiency of the i-th viscosity reducer; and Rmax is the maximum oil recovery efficiency among all viscosity reducers.

[0032] Optionally, the weighting factor ω is calculated as follows:

[0033] The normalized values ​​of the average viscosity reduction rate (X) and oil displacement efficiency (R) are calculated as follows:

[0034]

[0035] Wherein, y is the normalized value of the average viscosity reduction rate (X) or oil recovery efficiency (R), dimensionless; x is the average viscosity reduction rate (X) or oil recovery efficiency (R); xmax is the maximum value of the average viscosity reduction rate (X) or oil recovery efficiency (R); xmin is the minimum value of the average viscosity reduction rate (X) or oil recovery efficiency (R).

[0036] The average normalized values ​​of the average viscosity reduction rate (X) and the oil displacement efficiency (R) are calculated as follows:

[0037]

[0038] In the formula, is the average normalized value of the average viscosity reduction ratio (X) and oil displacement efficiency (R), dimensionless; n is the number of viscosity reducer systems evaluated.

[0039] The standard deviation of the normalized values ​​of the average viscosity reduction rate (X) and oil displacement efficiency (R) is calculated as follows:

[0040]

[0041] Where σ is the standard deviation of the normalized values ​​of the average viscosity reduction rate (X) and oil recovery efficiency (R).

[0042] The coefficient of variation of the normalized values ​​of the average viscosity reduction rate (X) and the oil displacement efficiency (R) is calculated as follows:

[0043]

[0044] Where CV is the coefficient of variation of the normalized values ​​of the average viscosity reduction rate (X) and oil displacement efficiency (R).

[0045] Calculate the weighting factor ω, the formula is as follows:

[0046]

[0047] Where CVX is the coefficient of variation of the normalized value of the average viscosity reduction rate; CVR is the coefficient of variation of the normalized value of the displacement efficiency.

[0048] In a third aspect, an embodiment of the present application provides a device for screening viscosity reducers for carbon dioxide oil recovery, the device comprising a memory and a processor.

[0049] The memory is used to store computer programs; the processor is used to implement the steps of the above-mentioned method for screening viscosity reducers for carbon dioxide oil recovery when executing the computer program.

[0050] In a fourth aspect, an embodiment of the present application provides a medium having a computer program stored thereon, and when the computer program is executed by a processor, the steps of the above-mentioned method for screening a viscosity reducer for carbon dioxide oil recovery are implemented.

[0051] The beneficial effects of the present invention are:

[0052] The invention provides a method for screening a viscosity reducer for carbon dioxide oil recovery. The method is aimed at the prior art that the evaluation and optimization of the performance of the viscosity reducer mainly focus on the two aspects of reducing the viscosity of the heavy oil and improving the fluidity of the heavy oil by the viscosity reducer, but does not consider the problem of the influence of the mixture of the heavy oil and the viscosity reducer on the oil recovery efficiency of the heavy oil. Through a heavy oil viscosity reduction effect evaluation experiment and a physical simulation oil recovery experiment, the static viscosity reduction performance and the dynamic oil recovery performance of the heavy oil viscosity reducer are comprehensively evaluated, thereby guiding the optimization of the viscosity reducer for carbon dioxide oil recovery, and realizing the maximum improvement of the recovery rate of the heavy oil reservoir and obtaining the best economic benefit by the composite flooding of carbon dioxide and the viscosity reducer.

[0053] Other features and advantages of the present invention will be described in the following description, and partly become apparent from the description, or be understood by implementing the embodiments of the present invention. The purpose and other advantages of the present invention can be realized and obtained by the structures particularly pointed out in the written description, claims, and drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings required for use in the embodiments are briefly introduced below. It should be understood that the following drawings only show certain embodiments of the present invention and therefore should not be regarded as limiting the scope. For ordinary technicians in this field, other related drawings can be obtained based on these drawings without creative work.

[0055] Figure 1 It is a schematic flow chart of a method for screening a viscosity reducer for carbon dioxide oil recovery described in an embodiment of the present invention;

[0056] Figure 2 It is a schematic structural diagram of a device for screening a viscosity reducer for carbon dioxide oil recovery according to an embodiment of the present invention;

[0057] Figure 3 Schematic diagram of experimental test data-temperature influence in an embodiment of the present invention;

[0058] Figure 4 It is the experimental test data-viscosity reduction curve diagram in the embodiment of the present invention;

[0059] Figure 5 It is a bar graph of experimental test data-average viscosity reduction rate in the embodiment of the present invention;

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

[0061] Figure 7It is the experimental test data of the embodiment of the present invention - the bar graph of the final oil displacement efficiency and the residual oil saturation;

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

[0063] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, rather than all of the embodiments. The components of the embodiments of the present invention generally described and shown in the drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

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

[0065] Example 1

[0066] like Figure 1 As shown, this embodiment provides a method for screening a viscosity reducer for carbon dioxide oil recovery, and the method includes step S100, step S200, step S300 and step S400.

[0067] Step S100, calculating the viscosity reduction rates of the heavy oil by the various viscosity reducers 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 to the heavy oil;

[0069] Step S300, calculating the oil recovery efficiency of each viscosity reducer and CO2 in turn, and calculating the comprehensive evaluation index corresponding to each viscosity reducer based on the average viscosity reduction rate and normalized value of the oil recovery efficiency, average normalization, standard deviation, coefficient of variation, and weighting factor corresponding to each viscosity reducer, and screening out the best viscosity reducer based on the comprehensive evaluation index.

[0070] Secondly, in step S100, the viscosity reduction rates of various viscosity reducers on heavy oil at different test temperatures are calculated, including:

[0071] Step S110, placing the heavy oil in a constant temperature oil bath set at a first temperature for 1 hour, then removing free water and bubbles in the heavy oil by stirring, and measuring its viscosity μo at the temperature by a rotational viscometer;

[0072] Step S120, using formation water to prepare a viscosity reducer solution of preset concentration and weighing 280g of heavy oil sample into a beaker, adding 120g of viscosity reducer solution, placing in a constant temperature oil bath for 1h, placing a stirring paddle at a distance of 2-3mm from the bottom of the beaker, adjusting the speed to 250r / min, stirring at a constant temperature for 2min, and measuring the viscosity μ of the mixture at the temperature with a rotational viscometer;

[0073] Step S130, calculating the viscosity reduction rate of the viscosity reducing agent at the first temperature by using a viscosity reduction rate calculation formula, wherein the viscosity reduction rate calculation formula is:

[0074]

[0075] Where x is the viscosity reduction rate of the viscosity reducer on the heavy oil, %; μ o is the viscosity of the heavy oil sample at a certain temperature, mPa·s; μ is the viscosity of the mixture of heavy 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 to the heavy oil is calculated in turn, including:

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

[0078]

[0079] in, is the average viscosity, mPa·s; T is the temperature, ℃; Ti is the initial experimental temperature, ℃; Ts is the maximum experimental temperature, ℃; μ o is the viscosity of the heavy oil sample at temperature T, mPa·s;

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

[0081]

[0082] Wherein, X is the average viscosity reduction rate, dimensionless; μo is the viscosity of the heavy oil under the initial experimental temperature conditions, mPa·s.

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

[0084] Step S310, using dried quartz sand to fill a sand filling tube, and weighing the sand filling tube as m1;

[0085] Step S320, evacuate the sand-filled pipe for 3 hours and then saturate it with water, weigh the saturated sand-filled pipe as m2, calculate the pore volume Vp=(m2-m1) / ρw of the sand-filled pipe model, and measure the water permeability of the sand-filled pipe;

[0086] Step S330, after the sand-filled pipe is kept at a constant temperature for 4 hours under the target heavy oil reservoir temperature condition, the sand-filled pipe is saturated with oil at a rate of 0.2 mL / min, the volume of the saturated oil is measured, and the initial oil saturation of the sand-filled pipe model is calculated;

[0087] Step S340, under the target heavy oil reservoir temperature and pressure conditions, CO2 flooding is performed at a rate of 2 mL / min, and the experiment is stopped when no oil is produced at the outlet of the sand filling pipe. During the experiment, the pressure at the front and rear ends of the sand filling pipe and the change data of the produced oil, gas and water volume at different times are recorded;

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

[0089]

[0090] S or =(1-R o )×S oi ;

[0091] Among them, R is the oil recovery efficiency; Soi is the initial oil saturation; Sor is the remaining oil saturation; Ro is the final oil recovery efficiency.

[0092] Secondly, in step S300, the comprehensive evaluation index corresponding to each viscosity reducer is calculated based on the normalized value of the average viscosity reduction rate and oil displacement efficiency corresponding to each viscosity reducer, the average normalization, the standard deviation, the coefficient of variation, and the weighting factor, including:

[0093] Step S360: Calculate the comprehensive evaluation index corresponding to the viscosity reducer based on the comprehensive evaluation index calculation formula, wherein the comprehensive evaluation index calculation formula is:

[0094]

[0095] Wherein, CEI is the comprehensive evaluation index of viscosity reducers for CO2 flooding; ω is the weighting factor; Xi is the average viscosity reduction rate of the i-th viscosity reducer; Xmax is the maximum viscosity reduction percentage among all viscosity reducers; Ri is the oil recovery efficiency of the i-th viscosity reducer; and Rmax is the maximum oil recovery efficiency among all viscosity reducers.

[0096] Next, in step S360, the weighting factor ω is calculated as follows:

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

[0098]

[0099] Wherein, y is the normalized value of the average viscosity reduction rate (X) or oil recovery efficiency (R), dimensionless; x is the average viscosity reduction rate (X) or oil recovery efficiency (R); xmax is the maximum value of the average viscosity reduction rate (X) or oil recovery efficiency (R); xmin is the minimum value of the average viscosity reduction rate (X) or oil recovery efficiency (R).

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

[0101]

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

[0103] Step S363: Calculate the standard deviation of the normalized values ​​of the average viscosity reduction rate (X) and the oil displacement efficiency (R), using the following formula:

[0104]

[0105] Where σ is the standard deviation of the normalized values ​​of the average viscosity reduction rate (X) and oil recovery efficiency (R).

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

[0107]

[0108] Where CV is the coefficient of variation of the normalized values ​​of the average viscosity reduction rate (X) and oil displacement efficiency (R).

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

[0110]

[0111] Where CVX is the coefficient of variation of the normalized value of the average viscosity reduction rate; CVR is the coefficient of variation of the normalized value of the displacement efficiency.

[0112] Example 2

[0113] like Figure 3-8 As shown, in order to more clearly illustrate the screening method of a viscosity reducer for carbon dioxide oil recovery provided by the present invention, the specific implementation steps of the present invention are described by example:

[0114] (1) Evaluation of viscosity reducing agent on heavy oil viscosity reducing performance

[0115] Four viscosity reducers (viscosity reducer A, viscosity reducer B, viscosity reducer C and viscosity reducer D) were selected to evaluate their viscosity reduction effects on heavy oil at 50°C, 80°C, 100°C, 120°C and 150°C. The viscosity reduction rates (x) of the four viscosity reducers on heavy oil at different temperatures were calculated according to formula (2). The experimental results are shown in Figure 2. Figure 3 As shown in the figure, the results show that adding four viscosity reducers to heavy oil can reduce the viscosity of heavy oil, 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 other 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 rate (X) of the four viscosity reducers on heavy oil is calculated according to formula (3) and formula (4). The experimental results are shown in Figure 4 As shown in the figure, the results show that the viscosity reducing ability of the four viscosity reducers is ranked as follows: viscosity reducer C> viscosity reducer A> viscosity reducer B> viscosity reducer D. Therefore, viscosity reducers A, B and C are preferred to continue the oil displacement experiment.

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

[0117] The physical simulation displacement experimental device was used to evaluate the oil displacement effects of simple CO2 flooding and CO2+viscosity reducer A composite flooding, CO2+viscosity reducer B composite flooding, and CO2+viscosity reducer C composite flooding. The experimental parameters and experimental results are shown in Tables 1 and Figure 5 As shown. The final oil recovery efficiency of pure CO2 flooding is 47.99%, and the final oil recovery efficiency of CO2+viscosity reducer C composite flooding is 70.3%, which is 22.4% higher than that of pure CO2 flooding; the final oil recovery efficiency of CO2+viscosity reducer A composite flooding is 68.4%, slightly lower than that of CO2+viscosity reducer C composite flooding; and the final oil recovery efficiency of CO2+viscosity reducer B composite flooding is 64.9%. It can be seen that adding viscosity reducers to CO2 can significantly improve the efficiency of heavy oil recovery. The ability of using CO2+viscosity reducer C composite flooding is the strongest, and the residual oil saturation can be reduced to below 30%.

[0118] Table 1 Parameters of physical simulation displacement experiment of sand filling pipe

[0119]

[0120]

[0121] (3) Comprehensive performance evaluation of viscosity reducers for CO2 flooding in heavy oil reservoirs

[0122] The average viscosity reduction rate and normalized value (y) of oil displacement efficiency and the average normalized value (y) of the four viscosity reduction systems of CO2, viscosity reducer A, viscosity reducer B and viscosity reducer C were calculated respectively. The standard deviation (σ), coefficient of variation (CV), weighting factor (ω) and comprehensive evaluation index (CEI) of viscosity reducers for CO2 flooding are calculated and shown in Table 2. The results show that the comprehensive evaluation indexes of viscosity reducers A and C are equal, both higher than pure CO2 and viscosity reducer B. Therefore, viscosity reducers A and C are determined to be the best viscosity reducers for CO2 flooding to develop heavy oil reservoirs.

[0123] Table 2 Comprehensive evaluation results of different viscosity reducers

[0124]

[0125] Example 3

[0126] Corresponding to the above method embodiment, the embodiment of the present disclosure also provides a screening device for a viscosity reducer for carbon dioxide oil recovery. The screening device for a viscosity reducer for carbon dioxide oil recovery described below and the screening method for a viscosity reducer for carbon dioxide oil recovery described above can be referenced to each other.

[0127] Figure 2 FIG. 8 is a block diagram of a device 800 for screening a viscosity reducer for carbon dioxide flooding according to an exemplary embodiment. Figure 3 As shown, the electronic device 800 may include: a processor 801 and a memory 802. The electronic device 800 may also include one or more of a multimedia component 803, an I / O interface 804, and a communication component 805.

[0128] Among them, the processor 801 is used to control the overall operation of the electronic device 800 to complete all or part of the steps in the above-mentioned method for screening viscosity reducers for carbon dioxide flooding. The memory 802 is used to store various types of data to support the operation of the electronic device 800, and these data may include instructions for any application or method used to operate on the electronic device 800, and application-related data, such as contact data, messages sent and received, pictures, audio, video, etc. The memory 802 can be implemented by any type of volatile or non-volatile storage device or a combination thereof, such as static random access memory (Static Random Access Memory, referred to as SRAM), electrically erasable programmable read-only memory (Electrically Erasable Programmable Read-Only Memory, referred to as EEPROM), erasable programmable read-only memory (Erasable Programmable Read-Only Memory, referred to as EPROM), programmable read-only memory (Programmable Read-Only Memory, referred to as PROM), read-only memory (Read-Only Memory, referred to as ROM), magnetic memory, flash memory, disk or optical disk. The multimedia component 803 may include a screen and an audio component. The screen may be, for example, a touch screen, and the audio component is used to output and / or input audio signals. For example, the audio component may include a microphone, which is used to receive external audio signals. The received audio signal may be further stored in the memory 802 or sent through the communication component 805. The audio component also includes at least one speaker for outputting audio signals. The I / O interface 804 provides an interface between the processor 801 and other interface modules, and the above-mentioned other interface modules may be keyboards, mice, buttons, etc. These buttons may be virtual buttons or physical buttons. The communication component 805 is used for wired or wireless communication between the electronic device 800 and other devices. 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 may include: Wi-Fi module, Bluetooth module, NFC module.

[0129] In an exemplary embodiment, the electronic device 800 can be implemented by one or more application specific integrated circuits (ASIC), digital signal processors (DSP), digital signal processing devices (DSPD), programmable logic devices (PLD), field programmable gate arrays (FPGA), controllers, microcontrollers, microprocessors or other electronic components to perform the above-mentioned method for screening viscosity reducers for carbon dioxide oil recovery.

[0130] In another exemplary embodiment, a computer-readable storage medium including program instructions is also provided, and when the program instructions are executed by a processor, the steps of the above-mentioned method for screening a viscosity reducer for carbon dioxide oil recovery are implemented. For example, the computer-readable storage medium can be the above-mentioned memory 802 including program instructions, and the above-mentioned program instructions 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 oil recovery.

[0131] Example 4

[0132] Corresponding to the above method embodiment, the embodiment of the present disclosure further provides a readable storage medium. The readable storage medium described below and the method for screening a viscosity reducer for carbon dioxide oil recovery described above can refer to each other.

[0133] A readable storage medium stores a computer program, which, when executed by a processor, implements the steps of the method for screening a viscosity reducer for carbon dioxide oil recovery in the above method embodiment.

[0134] The readable storage medium may 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, or other readable storage medium that can store program codes.

[0135] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the protection scope of the present invention.

Claims

1. A method for screening a viscosity reducer for carbon dioxide flooding, characterized in that: The method comprises: Calculate the viscosity reduction rates of heavy oil by various viscosity reducers at different test temperatures, and then obtain the viscosity reduction rate arrays of multiple groups of viscosity reducers at different temperatures; Based on the viscosity reduction rate array, the average viscosity reduction rate of each viscosity reducer to the heavy oil is calculated in turn; The oil recovery efficiency of each viscosity reducer and CO2 is calculated in turn, and a comprehensive evaluation index corresponding to each viscosity reducer is calculated based on the normalized value of the average viscosity reduction rate and oil recovery efficiency corresponding to each viscosity reducer, the average normalization, the standard deviation, the coefficient of variation, and the weighting factor, and the optimal viscosity reducer is screened out based on the comprehensive evaluation index.

2. The method for screening a viscosity reducer for carbon dioxide flooding according to claim 1, characterized in that: The calculated viscosity reduction rates of various viscosity reducers for heavy oil at different test temperatures include: The heavy oil is placed in a constant temperature oil bath set at a first temperature for 1 hour, free water and bubbles in the heavy oil are removed by stirring, and its viscosity μo at the temperature is measured by a rotational viscometer; Prepare a viscosity reducer solution of preset concentration using formation water and weigh 280g of heavy oil sample into a beaker, add 120g of viscosity reducer solution, put into a constant temperature oil bath for 1h, place the stirring paddle at the center 2-3mm away from the bottom of the beaker, adjust the speed to 250r / min, stir at constant temperature for 2min, and measure the viscosity μ of the mixture at this temperature using a rotational viscometer; The viscosity reduction rate of the viscosity reducing agent at the first temperature is calculated by the viscosity reduction rate calculation formula, wherein the viscosity reduction rate calculation formula is: Where x is the viscosity reduction rate of the viscosity reducer on the heavy oil, %; μ o is the viscosity of the heavy oil sample at a certain temperature, mPa·s; μ is the viscosity of the mixture of heavy oil and viscosity reducer at the same temperature, mPa·s.

3. The method for screening a viscosity reducer for carbon dioxide flooding according to claim 2, characterized in that: Based on the viscosity reduction rate array, the average viscosity reduction rate of each viscosity reducer to the heavy oil is calculated in turn, including: 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: in, is the average viscosity, mPa·s; T is the temperature, ℃; Ti is the initial experimental temperature, ℃; Ts is the maximum experimental temperature, ℃; μ o is the viscosity of the heavy oil sample at temperature T, mPa·s; The average viscosity reduction rate is calculated based on the average viscosity, wherein the calculation formula of the average viscosity reduction rate is: Wherein, X is the average viscosity reduction rate, dimensionless; μo is the viscosity of the heavy oil under the initial experimental temperature conditions, mPa·s.

4. The method for screening a viscosity reducer for carbon dioxide flooding according to claim 1, characterized in that: The oil recovery efficiency of each viscosity reducer and CO2 is calculated in sequence, including: Use dried quartz sand to fill the sand filling tube, and weigh the weight of the sand filling tube as m1; The sand-filled tube was saturated with water after vacuuming for 3 hours, and the weight of the sand-filled tube saturated with water was weighed as m2, and the pore volume of the sand-filled tube model Vp = (m2-m1) / ρw was calculated, and the water phase permeability of the sand-filled tube was measured; After the sand-filled tube is kept at a constant temperature for 4 hours under the target heavy oil reservoir temperature, it is saturated with oil at a rate of 0.2 mL / min, the volume of saturated oil is measured, and the initial oil saturation of the sand-filled tube model is 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 of the sand-filled pipe. During the experiment, the pressure at the front and rear ends of the sand-filled pipe and the change data of the produced oil, gas and water volume were recorded at different times. Based on the calculation formula of oil displacement efficiency and residual oil saturation, the oil displacement efficiency of the viscosity reducer corresponding to CO2 is calculated. The calculation formula of oil displacement efficiency and residual oil saturation is: S or =(1-R o )×S oi ; Among them, R is the oil recovery efficiency; Soi is the initial oil saturation; Sor is the remaining oil saturation; Ro is the final oil recovery efficiency.

5. The method for screening a viscosity reducer for carbon dioxide flooding according to claim 1, characterized in that: The comprehensive evaluation index corresponding to each viscosity reducer is calculated based on the normalized value of the average viscosity reduction rate and oil displacement efficiency corresponding to each viscosity reducer, the average normalization, the standard deviation, the coefficient of variation, and the weighting factor, 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: Wherein, CEI is the comprehensive evaluation index of viscosity reducers for CO2 flooding; ω is the weighting factor; Xi is the average viscosity reduction rate of the i-th viscosity reducer; Xmax is the maximum viscosity reduction percentage among all viscosity reducers; Ri is the oil recovery efficiency of the i-th viscosity reducer; and Rmax is the maximum oil recovery efficiency among all viscosity reducers.

6. The method for screening a viscosity reducer for carbon dioxide flooding according to claim 5, characterized in that: The calculation method of the weighting factor ω is: The normalized values ​​of the average viscosity reduction rate (X) and oil displacement efficiency (R) are calculated as follows: Wherein, y is the normalized value of the average viscosity reduction rate (X) or oil recovery efficiency (R), dimensionless; x is the average viscosity reduction rate (X) or oil recovery efficiency (R); xmax is the maximum value of the average viscosity reduction rate (X) or oil recovery efficiency (R); xmin is the minimum value of the average viscosity reduction rate (X) or oil recovery efficiency (R); The average normalized values ​​of the average viscosity reduction rate (X) and the oil displacement efficiency (R) are calculated as follows: In the formula, is the average normalized value of the average viscosity reduction ratio (X) and oil displacement efficiency (R), dimensionless; n is the number of viscosity reducer systems evaluated; The standard deviation of the normalized values ​​of the average viscosity reduction rate (X) and oil displacement efficiency (R) is calculated as follows: Where, σ is the standard deviation of the normalized values ​​of the average viscosity reduction rate (X) and oil displacement efficiency (R); The coefficient of variation of the normalized values ​​of the average viscosity reduction rate (X) and the oil displacement efficiency (R) is calculated as follows: Where, CV is the coefficient of variation of the normalized values ​​of the average viscosity reduction rate (X) and oil displacement efficiency (R); Calculate the weighting factor ω, the formula is as follows: Where CVX is the coefficient of variation of the normalized value of the average viscosity reduction rate; CVR is the coefficient of variation of the normalized value of the oil displacement efficiency.

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