Device and method for continuously evaluating the expansion / extraction rate of crude oil by CO2 at different pressures

Abstract

The present invention discloses a device for continuously evaluating the expansion / extraction rate of crude oil by CO2 at different pressures, comprising a volume variable visual container, a transparent graduated tube, a piston, a CO2 high pressure container, a balance, a pressure sensor, and a high pressure pump; a piston is arranged inside the volume variable visual container, and the piston divides the interior of the volume variable visual container into a first cavity and a second cavity; the first cavity of the volume variable visual container is connected to the atmosphere; the first cavity of the volume variable visual container is also connected to the high pressure pump; a transparent graduated tube is arranged in the second cavity of the volume variable visual container; the second cavity of the volume variable visual container is also connected to the CO2 high pressure container; the balance is arranged below the CO2 high pressure container; the second cavity of the volume variable visual container is also connected to the pressure sensor and the atmosphere in sequence. The device and method of the present invention can continuously measure the expansion rate and extraction rate of crude oil by CO2 at different pressures for the same sample, reduce the number of times of weighing the sample, and reduce the error of the experimental data.

Description

Technical Field

[0001] The invention relates to the technical field of oil and gas field development and gas injection to improve recovery, and in particular to a device and method for continuously evaluating the expansion / extraction rate of crude oil by CO2 at different pressures. Background Art

[0002] Gas injection is one of the important methods to improve oil recovery during oilfield development. Gas injection methods include nitrogen injection, air injection, methane and other alkane gas injection, and CO2 injection. Among them, CO2 injection has attracted much attention because during oilfield development, CO2 can be injected underground, which can not only increase crude oil production, but also store CO2 underground. Therefore, how to efficiently use CO2 to improve oil recovery and achieve stable storage of CO2 has become an important way to reduce carbon emissions and increase oil production.

[0003] Studying the interaction between CO2 and crude oil is the key to achieving CO2 enhanced oil recovery and effective storage. CO2 can dissolve in crude oil, causing it to expand, and can also extract part of the crude oil into CO2. Therefore, how to give full play to the expansion and extraction effects of CO2 on crude oil to greatly improve the oil recovery rate, and at the same time, how to achieve efficient CO2 storage by changing pressure and other conditions during the geological storage stage is of great significance for improving oil recovery, especially for the continued stable production increase of tight oil reservoirs and shale reservoirs in the later stages of fracturing and elastic development.

[0004] After CO2 contacts with crude oil, expansion and extraction will occur simultaneously. The two will affect each other at the same time. However, the study of expansion or extraction alone cannot truly reflect the real effect between CO2 and crude oil. Some literature has reported the expansion and extraction experiment of liquid CO2 on crude oil, but this method can only measure the volume of heavy and light phase components. Before CO2 is mixed with crude oil, it will form two phases, heavy phase and light phase. Both phases are mixtures of crude oil and CO2, but the heavy phase is mainly crude oil and the light phase is mainly CO2. The specific content of crude oil and CO2 in the heavy phase and light phase cannot be obtained by this method. At the same time, it is inaccurate to distinguish expansion and extraction by the volume change of heavy phase and light phase, because with the increase of pressure, the extraction effect is enhanced, the volume of light phase increases and the volume of heavy phase decreases, and the decrease in the volume of heavy phase is not caused by the weakening of expansion effect, but by more oil being extracted into the light phase. Therefore, it is impossible to accurately evaluate the size of expansion and extraction only by the volume change of heavy phase and light phase. The numerical simulation method can calculate the phase state of crude oil and CO2, but the selection of the interaction parameters between crude oil and CO2 is very critical and often needs to be obtained through experiments. Improper parameter selection often leads to large deviations in the guidance of the actual production process. Summary of the invention

[0005] In view of this, the present invention provides a device and method for continuously evaluating the expansion / extraction rate of crude oil by CO2 at different pressures, which can evaluate and measure the expansion rate and extraction rate of crude oil by CO2 by experimental methods. The device is easy and quick to assemble, and can continuously and accurately measure the expansion rate and extraction rate of crude oil by CO2 at different ratios and pressures. It can avoid the need to refill CO2 and crude oil samples at each pressure during a single measurement, which makes it difficult to ensure that the amount of sample filled each time is completely consistent, resulting in large experimental errors. The device and method provided by the present invention have accurate measurement data and low testing costs.

[0006] Specifically, the following technical solutions are included:

[0007] In a first aspect, the present invention discloses a device for continuously evaluating the expansion / extraction rate of crude oil by CO2 at different pressures, comprising a volume-variable visual container, a transparent graduated tube, a stirring system, a piston, a CO2 high-pressure container, a balance, a pressure sensor, a high-pressure pump, a first cavity, a second cavity, a first pipeline, a second pipeline, a third pipeline, a fourth pipeline, a fifth pipeline, a first valve, a second valve, a third valve, and a fourth valve;

[0008] A piston is provided in the variable volume visual container, and the piston divides the interior of the variable volume visual container into a first cavity and a second cavity;

[0009] The first cavity of the variable-volume visual container is connected to the atmosphere through the first pipeline, and the first pipeline is provided with a first valve;

[0010] The first cavity of the variable-volume visual container is also connected to the high-pressure pump through the second pipeline, and a second valve is provided on the second pipeline;

[0011] A transparent graduated tube is provided in the second cavity of the variable volume visual container, and a stirring device is provided in the transparent graduated tube;

[0012] The second cavity of the variable volume visual container is also connected to the CO2 high pressure container through the fourth pipeline, and the fourth pipeline is provided with a fourth valve; the balance is arranged below the CO2 high pressure container;

[0013] The second cavity of the variable-volume visual container is also connected to the pressure sensor and the atmosphere in sequence through the third pipeline, and a third valve is provided on the third pipeline between the pressure sensor and the atmosphere.

[0014] In one possible design, the variable volume visual container, transparent graduated tube, stirring system, piston, CO2 high pressure container, balance, high pressure pump, first valve, second valve, third valve, fourth valve, first pipeline, second pipeline, third pipeline, fourth pipeline, and fifth pipeline are all arranged in a constant temperature control system.

[0015] In a possible design, one end of the transparent graduated tube is open, a plug is provided at the opening of the transparent graduated tube, and a vent hole is provided on the plug.

[0016] In a possible design, the variable-volume visual container includes a barrel and an end cap threadably connected to the barrel.

[0017] In a possible design, an observation window is provided on the side wall of the cylinder of the variable-volume visual container.

[0018] In a possible design, the first cavity of the variable-volume viewable container is located above the second cavity.

[0019] In a first aspect, the present invention also discloses a method for continuously evaluating the expansion / extraction rate of crude oil by CO2 at different pressures, comprising the following steps:

[0020] S1. Add a set volume V0 of oil phase into the transparent graduated tube under normal pressure. The mass of the oil phase is recorded as m1.

[0021] S2, placing the transparent graduated tube into the second cavity of the variable volume visual container 1, ensuring that the liquid level is visible, connecting the pipelines, closing all valves, turning on the constant temperature control system, setting the temperature, and turning on the stirring system;

[0022] S3, closing all valves, opening the first valve and the fourth valve, passing the CO2 in the CO2 high pressure container into the second cavity in the variable volume visual container, so that the piston in the variable volume visual container is pushed to the end away from the transparent graduated tube;

[0023] S4. Record the mass of CO2 introduced into the second cavity of the variable volume visual container and the corresponding pipeline by a balance as m g ;

[0024] S5. Close all valves, open the high-pressure pump and the second valve, push the piston in the variable volume visual container toward the end close to the transparent graduated tube, dissolve CO2 in the oil phase, and when the pressure sensor reaches the set pressure P0, record the liquid level in the transparent graduated tube at this time and calculate the volume V of the oil phase at this time. P0 ;

[0025] S6, close all valves, open the first valve, quickly discharge the CO2 in the second cavity of the variable volume visual container, and when the pressure in the second cavity becomes normal pressure, record the liquid level in the transparent graduated tube at this time and calculate the volume V'0 of the oil phase at this time;

[0026] S7, calculate the mass ratio of CO2 to oil phase under the condition of pressure P0, m g : The expansion rate of CO2 per unit mass in a system composed of m1 is α P0 and extraction rate β P0 :

[0027] The extraction amount of CO2 on the oil phase (V e,P0 ) and expansion (V s,P0 ):

[0028] V e，P0 =V0-V'0 (1)

[0029] V s，P0 =V P0 -V'0 (2)

[0030] Where V e,P0 is the extraction amount of CO2 on the oil phase under P0 pressure, ml; V s,P0 is the expansion amount of CO2 on the oil phase under P0 pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube under normal pressure, ml; V P0 is the volume of the oil phase in the transparent graduated tube (2) at the pressure of P0, ml; V'0 is the volume of the oil phase in the transparent graduated tube after the pressure in the second cavity of the variable volume visual container changes from P0 to normal pressure, ml;

[0031] The expansion rate α per unit mass of CO2 is obtained by equations (3) and (4): P0 and extraction rate β P0 They are:

[0032]

[0033]

[0034] In the formula, α P0 is the expansion rate of unit mass CO2 at P0 pressure, g -1 ; V s,P0 is the expansion amount of CO2 on the oil phase under P0 pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube under normal pressure, ml; m gis the mass of CO2 introduced from the CO2 high pressure container (6) into the second cavity of the variable volume visual container and its corresponding pipeline, g; V'0 is the volume of the oil phase in the transparent graduated tube after the pressure in the second cavity of the variable volume visual container changes from P0 to normal pressure, ml; β P0 is the extraction rate of unit mass CO2 at P0 pressure, g -1 ; V e,P0 is the extraction amount of CO2 on the oil phase under P0 pressure, ml; V P0 is the volume of the oil phase in the transparent graduated tube at P0 pressure, ml;

[0035] S8, at room temperature, replacing the oil phase in the transparent graduated tube in S6 with a new oil phase having a volume of V0, and repeating steps S2-S4;

[0036] S9, close all valves, open the high-pressure pump and the second valve, push the piston in the variable volume visual container toward the end close to the transparent graduated tube, dissolve CO2 in the oil phase, and when the pressure sensor reaches the set pressure P1 (P1>P0), record the liquid level of the oil phase in the transparent graduated tube at this time and calculate the volume V of the oil phase at this time P1 ;

[0037] S10, close all valves, open the high-pressure pump and the second valve, move the piston in the variable-volume visual container toward the end away from the transparent graduated tube, and when the pressure sensor reaches the set pressure P0, change the high-pressure pump to the constant pressure mode, record the change in the pumping volume of the high-pressure pump with the pressure, and when the pumping volume remains basically unchanged within 2 hours, it is considered that the first cavity and the second cavity in the variable-volume visual container have reached pressure equilibrium, record the liquid level in the transparent graduated tube and calculate the volume V' of the oil phase at this time P0 ;

[0038] S11, calculate the mass ratio of CO2 to oil phase under the condition of pressure P1, m g : The expansion rate of CO2 per unit mass in a system composed of m1 is α P1 and extraction rate β P1 ;

[0039] The extraction amount of crude oil by CO2 (V e,P1 ) and expansion (V s,P1 ):

[0040] V e,P1 =V e,P0 +V P0 -V' P0 (5)

[0041] V s,P1 =V P1-(V0-V e,P1 ) (6)

[0042] Where V e,P1 is the extraction amount of CO2 on the oil phase under P1 pressure, ml; V e,P0 is the extraction amount of CO2 on the oil phase under P0 pressure, ml; V P0 is the volume of the oil phase in the transparent graduated tube at P0 pressure, ml; V' P0 V is the volume of the oil phase in the transparent graduated tube after the pressure in the second cavity of the variable volume visual container changes from P1 to P0, ml; s,P1 V is the expansion amount of CO2 on the oil phase at P1 pressure, ml; P1 is the volume of the oil phase in the transparent graduated tube at P1 pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube at normal pressure, ml;

[0043] According to equations (7) and (8), the expansion rate α of unit mass CO2 is P1 and extraction rate β P1 They are:

[0044]

[0045]

[0046] In the formula, α P1 is the expansion rate of unit mass CO2 at P1 pressure, g -1 ; V s,P1 is the expansion of the oil phase by CO2 under P1 pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube under normal pressure, ml; m g The mass of CO2 introduced into the second cavity of the variable volume visual container and the corresponding pipeline of the CO2 high pressure container, g; β P1 is the extraction rate of unit mass CO2 at P1 pressure, g -1 ; V e,P1 is the extraction amount of CO2 on the oil phase under P1 pressure, ml;

[0047] S12, close all valves, open the high-pressure pump and the second valve, push the piston in the variable volume visual container toward the end close to the transparent graduated tube, dissolve CO2 in the oil phase, and when the pressure sensor reaches the set pressure P i (i=2, 3, 4, ... n, n is a positive integer greater than or equal to 2, and P i >P i-1), the high-pressure pump is changed into a constant pressure mode, and the change value of the pumping volume of the high-pressure pump with the pressure is recorded. When the pumping volume remains substantially unchanged within 2 hours, it is considered that the first cavity and the second cavity in the variable-volume visual container have reached pressure equilibrium, and the liquid level in the transparent graduated tube is recorded and the volume V of the oil phase at this time is calculated. Pi ;

[0048] S13, close all valves, open the high-pressure pump and the second valve, move the piston in the variable volume visual container toward the end away from the transparent graduated tube, and when the pressure sensor reaches the set pressure P i-1 When the oil volume V' in the transparent graduated tube is recorded P(i-1) ;

[0049] S14, calculate the pressure as P i Under the conditions, the mass ratio of CO2 to oil phase is m g : The expansion rate of CO2 per unit mass in a system composed of m1 is α Pi and extraction rate β Pi ;

[0050] The extraction amount of crude oil by CO2 (V e,Pi ) and expansion (V s,Pi ):

[0051] V e,Pi =V e,P(i-1) +V P(i-1) -V' P(i-1) (9)

[0052] V s,Pi =V Pi -(V0-V e,Pi ) (10)

[0053] Where V e,Pi P i Extraction amount of oil phase by CO2 under pressure, ml; V e,P(i-1) P i-1 Extraction amount of oil phase by CO2 under pressure, ml; V P(i-1) P i-1 The volume of the oil phase in the transparent graduated tube under pressure, ml; V' P(i-1) The pressure in the second cavity of the variable volume visual container is P i Change to P i-1 The volume of the oil phase in the transparent graduated tube, ml; V s,Pi P i Expansion of CO2 on the oil phase under pressure, ml; V Pi P iV0 is the volume of the oil phase added to the transparent graduated tube under pressure, ml;

[0054] According to equations (11) and (12), the expansion rate α of unit mass CO2 is Pi and extraction rate β Pi They are:

[0055]

[0056]

[0057] In the formula, α Pi P i Expansion rate per unit mass of CO2 under pressure, g -1 ; V s,Pi P i The expansion amount of CO2 on the oil phase under pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube under normal pressure, ml; m g The mass of CO2 introduced into the second cavity of the variable volume visual container and the corresponding pipeline of the CO2 high pressure container, g; β Pi P i Extraction rate per unit mass of CO2 under pressure, g -1 ; V e,Pi P i The amount of oil phase extracted by CO2 under pressure, ml.

[0058] In one possible design, the set pressures P0, P1, P i (i=2, 3, 4, ... n, n is a positive integer greater than or equal to 2) are all greater than the bubble point pressure of CO2 at this temperature to ensure that CO2 is in a supercritical or liquid state.

[0059] In one possible design, in steps S5 and S9, opening the high-pressure pump 9 and the second valve 302 to push the piston in the variable-volume visual container toward one end close to the transparent graduated tube includes opening the high-pressure pump and the second valve to push the piston in the variable-volume visual container toward one end close to the transparent graduated tube at a constant speed.

[0060] In a third aspect, the present invention also discloses a method for continuously evaluating the expansion / extraction rate of crude oil using CO2 at different pressures and its application in improving crude oil recovery.

[0061] The beneficial effects of the technical solution provided by the present invention include at least:

[0062] The device provided by the present invention can continuously measure the expansion rate and extraction rate of crude oil by CO2 under different pressures for the same sample through ingenious design, has a simple structure, is easy to build, reduces the number of sample weighing times, and reduces the error of experimental data.

[0063] The measuring method provided by the present invention can continuously measure the expansion rate and extraction rate of CO2 to crude oil under different pressures. With the aid of the above device, a process of continuous change of field pressure can be simulated through a simple calculation process. In addition, during the test, there is no need to refill the sample at each pressure. The expansion rate and extraction rate under multiple pressures of continuous change under the composition can be obtained by only two samplings, which can greatly save time and sample costs, reduce errors caused by multiple samplings, and obtain more accurate data. It is more instructive for the actual oil recovery process than the results obtained from a single expansion experiment and extraction experiment, and is more conducive to guiding the selection and control of pressure during field development. BRIEF DESCRIPTION OF THE DRAWINGS

[0064] Figure 1 2 is a schematic diagram of the structure of a device for continuously evaluating the expansion / extraction rate of crude oil by CO2 at different pressures provided in an embodiment of the present invention;

[0065] Figure 2 is a top view of a plug provided by an embodiment of the present invention;

[0066] Figure 3 is a schematic structural diagram of a volume-variable visual container provided by an embodiment of the present invention;

[0067] Among them, 1. a visible volume variable container, 2. a transparent graduated tube, 3. an electromagnetic stirrer, 4. a magnet, 5. a piston, 6. a CO2 high-pressure container, 7. a balance, 8. a pressure sensor, 9. a high-pressure pump, 10. a stopper, 11. a vent, 12. a cylinder, 13. an end cover, 14. a temperature control system, 15. an observation window, 101. a first cavity, 102. a second cavity, 201. a first pipeline, 202. a second pipeline, 203. a third pipeline, 204. a fourth pipeline, 205. a fifth pipeline, 301. a first valve, 302. a second valve, 303. a third valve, 304. a fourth valve. DETAILED DESCRIPTION

[0068] The present invention is further described below in conjunction with the accompanying drawings and embodiments.

[0069] CO2 has good solubility and strong extraction ability in crude oil, which can significantly reduce the viscosity of crude oil, expand and increase the volume, and reduce the interfacial tension through multiple phase contacts with crude oil, thereby significantly improving the recovery rate of oil reservoirs. Therefore, giving full play to the expansion and extraction effect of CO2 on crude oil will become an important method for subsequent production increase.

[0070] However, in the actual process, expansion and extraction are phase behaviors that occur simultaneously between CO2 and crude oil. The two occur simultaneously and affect each other. The study of expansion and extraction alone cannot truly reflect the true interaction between CO2 and crude oil. The phase state of crude oil and CO2 can be calculated by numerical simulation, but the selection of interaction parameters between crude oil and CO2 is very critical and often needs to be obtained through experiments. Therefore, it is very important and necessary to establish an experimental method to evaluate and measure the expansion rate and extraction rate of crude oil under the action of CO2.

[0071] In the first aspect, the present invention discloses a device for continuously evaluating the expansion / extraction rate of crude oil by CO2 at different pressures, such as Figure 1 As shown, it includes a volume variable visual container 1, a transparent graduated tube 2, a stirring system, a piston 5, a CO2 high pressure container 6, a balance 7, a pressure sensor 8, a high pressure pump 9, a first cavity 101, a second cavity 102, a first pipeline 201, a second pipeline 202, a third pipeline 203, a fourth pipeline 204, a fifth pipeline 205, a first valve 301, a second valve 302, a third valve 303, and a fourth valve 304;

[0072] A piston 5 is provided in the variable volume visual container 1, and the piston 5 divides the interior of the variable volume visual container 1 into a first cavity 101 and a second cavity 102;

[0073] The first cavity 101 of the variable volume visual container 1 is connected to the atmosphere through a first pipeline 201, and a first valve 301 is provided on the first pipeline 201;

[0074] The first cavity 101 of the variable volume visual container 1 is also connected to the high pressure pump 9 via a second pipeline 202, and a second valve 302 is provided on the second pipeline 202;

[0075] A transparent graduated tube 2 is provided in the second cavity 102 of the variable volume visual container 1, and a stirring device is provided in the transparent graduated tube 2;

[0076] The second cavity 102 of the variable volume visual container 1 is also connected to the CO2 high pressure container 6 through a fourth pipeline 204, and a fourth valve 304 is provided on the fourth pipeline 204; the balance 7 is arranged below the CO2 high pressure container 6;

[0077] The second cavity 102 of the variable-volume visual container 1 is also connected to the pressure sensor 8 and the atmosphere in sequence through the third pipeline 203 . A third valve 303 is provided on the third pipeline 203 between the pressure sensor 8 and the atmosphere.

[0078] The device provided by the embodiment of the present invention can obtain the expansion rate and extraction rate of unit mass of CO2 when studying the expansion and extraction effects in the same experiment, which is more instructive for the actual oil recovery process than the results obtained from a single expansion experiment and extraction experiment; and can continuously control the pressure in the transparent graduated tube 2 through the variable volume visual container 1 to simulate the process of continuous change of field pressure, so as to design a reasonable pressure during the development process of CO2 throughput or displacement in the oil field, better exert the expansion and extraction effects, and achieve the purpose of improving the recovery rate.

[0079] In one possible design, the volume-variable visual container 1, the transparent graduated tube 2, the stirring system, the piston 5, the CO2 high-pressure container 6, the balance 7, the high-pressure pump 9, the first valve 101, the second valve 102, the third valve 103, the fourth valve 104, the first pipeline 201, the second pipeline 202, the third pipeline 203, the fourth pipeline 204, and the fifth pipeline 205 are all arranged in a constant temperature control system 14.

[0080] In one possible design, Figure 2 As shown, one end of the transparent graduated tube 2 is open, a plug 10 is provided at the opening of the transparent graduated tube 2, and a vent hole 11 is provided on the plug 10.

[0081] Optionally, several vent holes may be provided.

[0082] In a possible design, the volume variable visual container 1 includes a barrel 12 and an end cap 13 threadedly connected to the barrel 12. Figure 3 shown.

[0083] It can be understood that the variable-volume visual container 1 can be opened through the end cover 13 and the transparent graduated tube 2 can be placed therein.

[0084] In a possible design, an observation window 15 is provided on the side wall of the cylinder 12 of the variable-volume visual container 1 .

[0085] Optionally, an observation window 15 is provided on the side wall of the cylinder 12 of the variable-volume visual container 1 at a position corresponding to the transparent graduated tube 2 .

[0086] It is understandable that the change in the volume of oil in the transparent graduated tube 2 can be monitored by observing the viewing window 15 .

[0087] In a possible design, the first cavity 101 of the variable-volume viewable container 1 is located above the second cavity 102 .

[0088] Optionally, the stirring device includes an electromagnetic stirrer 3 and a magnet 4 , the electromagnetic stirrer 3 is arranged below the variable-volume visual container 1 , and the magnet 4 is arranged in the transparent graduated tube 2 .

[0089] In a second aspect, the present invention also discloses a method for continuously evaluating the expansion / extraction rate of crude oil by CO2 at different pressures, comprising the following steps:

[0090] S1, under normal pressure, add the oil phase of set volume V0 into the transparent graduated tube 2, and the mass of the oil phase is recorded as m1;

[0091] S2, put the transparent graduated tube 2 into the second cavity 102 of the variable volume visual container 1, ensure that the liquid level is visible, connect the pipelines, close all valves, turn on the constant temperature control system 14, set the temperature, and turn on the stirring system;

[0092] S3, close all valves, open the first valve 301 and the fourth valve 304, and pass the CO2 in the CO2 high pressure container 6 into the second cavity 102 in the variable volume visual container 1, so that the piston 5 in the variable volume visual container 1 is pushed to the end away from the transparent graduated tube 2;

[0093] S4. The mass of CO2 introduced into the second cavity 102 of the variable volume visual container 1 and the corresponding pipeline is recorded by the balance 7 as m g ;

[0094] S5. Close all valves, open the high-pressure pump 9 and the second valve 302, push the piston 5 in the variable volume visual container 1 toward the end close to the transparent graduated tube 2, dissolve CO2 in the oil phase, and when the pressure sensor 8 reaches the set pressure P0, record the liquid level in the transparent graduated tube 2 at this time and calculate the volume V of the oil phase at this time. P0 ;

[0095] S6, close all valves, open the first valve 301, quickly discharge the CO2 in the second cavity 102 of the variable volume visual container 1, and when the pressure in the second cavity 102 becomes normal pressure, record the liquid level in the transparent graduated tube 2 at this time and calculate the volume V'0 of the oil phase at this time;

[0096] S7, calculate the mass ratio of CO2 to oil phase under the condition of pressure P0, m g : The expansion rate of CO2 per unit mass in a system composed of m1 is α P0 and extraction rate β P0 :

[0097] The extraction amount of CO2 on the oil phase (V e,P0 ) and expansion (V s,P0 ):

[0098] V e，P0 =V0-V'0 (1)

[0099] V s，P0 =V P0 -V'0 (2)

[0100] Where V e,P0 is the extraction amount of CO2 on the oil phase under P0 pressure, ml; V s,P0 is the expansion amount of CO2 on the oil phase under P0 pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube 2 under normal pressure, ml; V P0 is the volume of the oil phase in the transparent graduated tube 2 at the pressure of P0, ml; V'0 is the volume of the oil phase in the transparent graduated tube 2 after the pressure in the second cavity 102 of the variable volume visual container 1 changes from P0 to normal pressure, ml;

[0101] The expansion rate α per unit mass of CO2 is obtained by equations (3) and (4): P0 and extraction rate β P0 They are:

[0102]

[0103]

[0104] In the formula, α P0 is the expansion rate of unit mass CO2 at P0 pressure, g -1 ; V s,P0 is the expansion amount of CO2 on the oil phase under P0 pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube 2 under normal pressure, ml; m g is the mass of CO2 introduced from the CO2 high pressure container 6 into the second cavity 102 of the variable volume visual container 1 and its corresponding pipeline, g; V'0 is the volume of the oil phase in the transparent graduated tube 2 after the pressure in the second cavity 102 of the variable volume visual container 1 changes from P0 to normal pressure, ml; β P0 is the extraction rate of unit mass CO2 at P0 pressure, g -1 ; V e,P0 is the extraction amount of CO2 on the oil phase under P0 pressure, ml; V P0 is the volume of the oil phase in the transparent graduated tube 2 at the pressure of P0, ml;

[0105] S8, at room temperature, replace the oil phase in the transparent graduated tube 2 in S6 with a new oil phase with a volume of V0, and repeat steps S2-S4;

[0106] S9, close all valves, open the high-pressure pump 9 and the second valve 302, push the piston 5 in the variable volume visual container 1 toward the end close to the transparent graduated tube 2, dissolve CO2 in the oil phase, and when the pressure sensor 8 reaches the set pressure P1 (P1>P0), record the liquid level of the oil phase in the transparent graduated tube 2 at this time and calculate the volume V of the oil phase at this time P1 ;

[0107] S10, close all valves, open the high-pressure pump 9 and the second valve 302, move the piston 5 in the variable-volume visual container 1 toward the end away from the transparent graduated tube 2, and when the pressure sensor 8 reaches the set pressure P0, change the high-pressure pump 9 to the constant pressure mode, record the change value of the pumping amount of the high-pressure pump 9 with the pressure, and when the pumping amount remains basically unchanged within 2 hours, it is considered that the first cavity 101 and the second cavity 102 in the variable-volume visual container 1 have reached pressure balance, record the liquid level in the transparent graduated tube 2 and calculate the volume V' of the oil phase at this time P0 ;

[0108] S11, calculate the mass ratio of CO2 to oil phase under the condition of pressure P1, m g : The expansion rate of CO2 per unit mass in a system composed of m1 is α P1 and extraction rate β P1 ;

[0109] The extraction amount of crude oil by CO2 (V e,P1 ) and expansion (V s,P1 ):

[0110] V e,P1 =V e,P0 +V P0 -V' P0 (5)

[0111] V s,P1 =V P1 -(V0-V e,P1 ) (6)

[0112] Where V e,P1 is the extraction amount of CO2 on the oil phase under P1 pressure, ml; V e,P0 is the extraction amount of CO2 on the oil phase under P0 pressure, ml; V P0 is the volume of the oil phase in the transparent graduated tube (2) at P0 pressure, ml; V' P0 is the volume of the oil phase in the transparent graduated tube (2) after the pressure in the second cavity (102) of the variable volume visual container (1) changes from P1 to P0, in ml; V s,P1 V is the expansion amount of CO2 on the oil phase at P1 pressure, ml; P1 is the volume of the oil phase in the transparent graduated tube (2) at the pressure of P1, ml; V0 is the volume of the oil phase added to the transparent graduated tube (2) at normal pressure, ml;

[0113] According to equations (7) and (8), the expansion rate α of unit mass CO2 is P1 and extraction rate β P1 They are:

[0114]

[0115]

[0116] In the formula, α P1 is the expansion rate of unit mass CO2 at P1 pressure, g -1 ; V s,P1 is the expansion amount of CO2 on the oil phase under P1 pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube 2 under normal pressure, ml; m g The mass of CO2 introduced into the second cavity 102 of the variable volume visual container 1 and the corresponding pipeline by the CO2 high pressure container 6, g; β P1 is the extraction rate of unit mass CO2 at P1 pressure, g -1 ; V e,P1 is the extraction amount of CO2 on the oil phase under P1 pressure, ml;

[0117] S12, close all valves, open the high pressure pump 9 and the second valve 302, push the piston 5 in the variable volume visual container 1 toward the end close to the transparent graduated tube 2, dissolve CO2 in the oil phase, and when the pressure sensor 8 reaches the set pressure P i (i=2, 3, 4, ... n, n is a positive integer greater than or equal to 2, and P i >P i-1 ), the high pressure pump 9 is changed into the constant pressure mode, and the change value of the pumping amount of the high pressure pump 9 with the pressure is recorded. When the pumping amount remains basically unchanged within 2 hours, it is considered that the first cavity 101 and the second cavity 102 in the variable volume visual container 1 have reached pressure equilibrium, and the liquid level in the transparent graduated tube 2 is recorded and the volume V of the oil phase at this time is calculated. Pi ;

[0118] S13, close all valves, open the high pressure pump 9 and the second valve 302, move the piston 5 in the variable volume visual container 1 to the end away from the transparent graduated tube 2, and when the pressure sensor 8 reaches the set pressure P i-1 When the oil volume V' in the transparent graduated tube 2 is P(i-1) ;

[0119] S14, calculate the pressure as P i Under the conditions, the mass ratio of CO2 to oil phase is m g : The expansion rate of CO2 per unit mass in a system composed of m1 is α Pi and extraction rate β Pi ;

[0120] The extraction amount of crude oil by CO2 (V e,Pi ) and expansion (V s,Pi ):

[0121] V e,Pi =Ve,P(i-1) +V P(i-1) -V' P(i-1) (9)

[0122] V s,Pi =V Pi -(V0-V e,Pi ) (10)

[0123] Where V e,Pi P i Extraction amount of oil phase by CO2 under pressure, ml; V e,P(i-1) P i-1 Extraction amount of oil phase by CO2 under pressure, ml; V P(i-1) P i-1 Volume of the oil phase in the transparent graduated tube 2 under pressure, ml; V' P(i-1) The pressure in the second cavity 102 of the variable volume visual container 1 is P i Change to P i-1 The volume of the oil phase in the transparent graduated tube 2, ml; V s,Pi P i Expansion of CO2 on the oil phase under pressure, ml; V Pi P i V0 is the volume of the oil phase added to the transparent graduated tube 2 under pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube 2 under normal pressure, ml;

[0124] According to equations (11) and (12), the expansion rate α of unit mass CO2 is Pi and extraction rate β Pi They are:

[0125]

[0126]

[0127] In the formula, α Pi P i Expansion rate per unit mass of CO2 under pressure, g -1 ; V s,Pi P i The expansion amount of CO2 on the oil phase under pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube 2 under normal pressure, ml; m g The mass of CO2 introduced into the second cavity 102 of the variable volume visual container 1 and the corresponding pipeline by the CO2 high pressure container 6, g; β Pi P i Extraction rate per unit mass of CO2 under pressure, g -1 ; V e,Pi P i The amount of oil phase extracted by CO2 under pressure, ml.

[0128] It should be noted that under the pressure of P0, CO2 is in liquid state. On the one hand, CO2 in the second cavity 102 of the variable volume visual container 1 dissolves into the oil phase in the transparent graduated tube 2. Under the action of the stirring system, the oil phase is stirred to accelerate the equilibrium process between the oil phase and CO2, so that the oil phase and CO2 are mixed, the oil phase will expand, and the volume will increase. On the other hand, part of the oil phase in the transparent graduated tube 2 will diffuse and be extracted into CO2, resulting in a decrease in the volume of the oil phase. Under the combined action of the two aspects, when the pressure in the second cavity 102 of the variable volume visual container 1 reaches P0 and maintains pressure balance, the oil phase also reaches a balance between expansion and extraction. At this time, the volume of the oil phase in the transparent graduated tube 2 is the volume of the remaining oil phase after the oil phase extracted into the CO2 phase is removed and the CO2 is dissolved and expanded.

[0129] When the pressure in the second cavity 102 of the variable visual container 1 becomes normal pressure, CO2 becomes gaseous and is released from the oil phase. At this time, the oil phase extracted into the CO2 phase falls back into the second cavity 102 of the variable volume visual container 1. Considering that the volume of the transparent graduated tube 2 is much smaller than the volume of the second cavity 102 of the variable volume visual container 1, and the transparent graduated tube 2 is provided with a plug 10 with a vent hole 11, as shown in FIG. Figure 3 As shown, it plays a role in blocking the oil phase from falling back into the second cavity 102 of the variable volume visual container 1, so the volume of the oil phase falling back into the transparent graduated tube 2 can be ignored. At this time, the oil phase in the transparent graduated tube 2 is the oil phase that has not been extracted under the pressure of P1, that is, the oil phase that only expands under the pressure of P1. Therefore, the volume of the oil phase at this time is the volume of the oil phase before the expansion occurs under the pressure of P1.

[0130] Optionally, the temperature setting range of the constant control system 14 is 20-100°C.

[0131] In one possible design, in steps S5 and S9, starting the high-pressure pump 9 and the second valve 302 to push the piston in the variable visual container 1 toward one end close to the transparent graduated tube 2 includes starting the high-pressure pump 9 and the second valve 302 to push the piston in the variable visual container 1 toward one end close to the transparent graduated tube 2 at a constant speed.

[0132] It can be understood that by pushing the piston in the variable visual container 1 toward one end close to the transparent graduated tube 2, the volume of CO2 in the intermediate container 6 and the visual container 1 can be compressed, so that the pressure increases, and the pressure is increased to a set value, so that the expansion and extraction effect of CO2 on oil under a certain pressure can be obtained, which is more conducive to guiding the selection of pressure during field development.

[0133] In a third aspect, an embodiment of the present invention further discloses an application of a method for continuously evaluating the expansion / extraction rate of crude oil using CO2 at different pressures in improving crude oil recovery.

[0134] Expansion and extraction are important mechanisms for CO2 to enhance crude oil recovery. The quantitative evaluation method of the present invention can screen out the pressure values ​​at which CO2 has a high extraction rate and expansion rate for crude oil and the mass ratio of oil to CO2. That is, under this condition, CO2 interacts with crude oil and can give full play to the expansion and extraction effects, so that more crude oil can be produced. The basic data of expansion rate and extraction rate under different compositions and pressures can be used to guide the injection amount and injection pressure of CO2 during the development process, as well as the selection of pressure changes during the subsequent depressurization development process.

[0135] All the above optional technical solutions can be arbitrarily combined to form optional embodiments disclosed in the present invention, and will not be described one by one here.

[0136] The present invention will be further described below through specific examples.

[0137] Unless otherwise specified, the experimental methods used in the following specific examples are all conventional methods.

[0138] In the following specific examples, the operations involved in the operation without specifying the conditions were all carried out under conventional conditions or the conditions recommended by the manufacturer. The raw materials used without specifying the manufacturer and specifications were all conventional products that can be obtained through commercial purchase.

[0139] In the following specific examples: the oil phase is hexadecane, chemically pure, from Sinopharm Chemical Reagent Co., Ltd.; CO2 gas, 99.9%, from Qingdao Tianyuan Gas Manufacturing Co., Ltd.

[0140] This embodiment adopts Figure 1 The device for continuously evaluating the expansion / extraction rate of crude oil by CO2 at different pressures includes the device for continuously evaluating the expansion / extraction rate of crude oil by CO2 at different pressures, including a volume-variable visual container 1, a transparent graduated tube 2, a stirring system, a piston 5, a CO2 high-pressure container 6, a balance 7, a pressure sensor 8, a high-pressure pump 9, a first cavity 101, a second cavity 102, a first pipeline 201, a second pipeline 202, a third pipeline 203, a fourth pipeline 204, a fifth pipeline 205, a first valve 301, a second valve 302, a third valve 303, and a fourth valve 304;

[0141] The volume-variable visual container 1 comprises a cylinder 12 and an end cap 13 threadedly connected to the cylinder 12. An observation window 15 is provided on the side wall of the cylinder 12 of the volume-variable visual container 1 at a position corresponding to the transparent graduated tube 2.

[0142] A piston 5 is provided in the volume-variable visual container 1, and the piston 5 divides the interior of the volume-variable visual container 1 into a first cavity 101 and a second cavity 102, wherein the first cavity 101 is located above the second cavity 102;

[0143] The first cavity 101 of the variable volume visual container 1 is connected to the atmosphere through a first pipeline 201, and a first valve 301 is provided on the first pipeline 201;

[0144] The first cavity 101 of the variable volume visual container 1 is also connected to the high pressure pump 9 via a second pipeline 202, and a second valve 302 is provided on the second pipeline 202;

[0145] A transparent graduated tube 2 is provided in the second cavity 102 of the variable volume visual container 1. One end of the transparent graduated tube 2 is open. A plug 10 is provided at the opening of the transparent graduated tube 2. A vent hole 11 is provided on the plug 10. An electromagnetic stirrer 3 is provided below the second cavity 102 of the variable volume visual container 1. A magnet 4 is provided in the transparent graduated tube 2.

[0146] The second cavity 102 of the variable volume visual container 1 is also connected to the CO2 high pressure container 6 through a fourth pipeline 204, and a fourth valve 304 is provided on the fourth pipeline 204; the balance 7 is arranged below the CO2 high pressure container 6;

[0147] The second cavity 102 of the variable-volume visual container 1 is also connected to the pressure sensor 8 and the atmosphere in sequence through the third pipeline 203 . A third valve 303 is provided on the third pipeline 203 between the pressure sensor 8 and the atmosphere.

[0148] The volume variable visual container 1, the transparent graduated tube 2, the stirring system, the piston 5, the CO2 high pressure container 6, the balance 7, the high pressure pump 9, the first valve 101, the second valve 102, the third valve 103, the fourth valve 104, the first pipeline 201, the second pipeline 202, the third pipeline 203, the fourth pipeline 204, and the fifth pipeline 205 are all arranged in a constant temperature box.

[0149] A method for continuously evaluating the expansion / extraction rate of crude oil by CO2 at different pressures comprises the following steps:

[0150] S1. Under normal pressure, put the oil phase with a set volume V0 and the magnet 4 into the transparent graduated tube 2, and the mass of the oil phase is recorded as m1;

[0151] S2, put the transparent graduated tube 2 into the second cavity 102 of the variable volume visual container 1, ensure that the liquid level is visible, connect the pipelines, close all valves, open the thermostat, set the temperature to 50°C, and turn on the electromagnetic stirrer;

[0152] S3, close all valves, open the first valve 301 and the fourth valve 304, and pass the CO2 in the CO2 high pressure container 6 into the second cavity 102 in the variable volume visual container 1, so that the piston 5 in the variable volume visual container 1 is pushed to the end away from the transparent graduated tube 2;

[0153] S4. The mass of CO2 introduced into the second cavity 102 of the variable volume visual container 1 and the corresponding pipeline is recorded by the balance 7 as m g ;

[0154] S5. Close all valves, open the high-pressure pump 9 and the second valve 302, and push the piston 5 in the variable volume visual container 1 toward the end close to the transparent graduated tube 2 at a constant speed to dissolve CO2 in the oil phase. When the pressure sensor 8 reaches the set pressure P0, record the liquid level in the transparent graduated tube 2 at this time and calculate the volume V of the oil phase at this time. P0 ;

[0155] S6, close all valves, open the first valve 301, quickly discharge the CO2 in the second cavity 102 of the variable volume visual container 1, and when the pressure in the second cavity 102 becomes normal pressure, record the liquid level in the transparent graduated tube 2 at this time and calculate the volume V'0 of the oil phase at this time;

[0156] S7, calculate the mass ratio of CO2 to oil phase under the condition of pressure P0, m g : The expansion rate of CO2 per unit mass in a system composed of m1 is α P0 and extraction rate β P0 :

[0157] The extraction amount of CO2 on the oil phase (V e,P0 ) and expansion (V s,P0 ):

[0158] V e，P0 =V0-V'0 (1)

[0159] V s，P0 =V P0 -V'0 (2)

[0160] Where V e,P0 is the extraction amount of CO2 on the oil phase under P0 pressure, ml; V s,P0 is the expansion amount of CO2 on the oil phase under P0 pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube 2 under normal pressure, ml; V P0 is the volume of the oil phase in the transparent graduated tube 2 at the pressure of P0, ml; V'0 is the volume of the oil phase in the transparent graduated tube 2 after the pressure in the second cavity 102 of the variable volume visual container 1 changes from P0 to normal pressure, ml;

[0161] The expansion rate α per unit mass of CO2 is obtained by equations (3) and (4): P0 and extraction rate β P0 They are:

[0162]

[0163]

[0164] In the formula, α P0 is the expansion rate of unit mass CO2 at P0 pressure, g -1 ; V s,P0 is the expansion amount of CO2 on the oil phase under P0 pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube 2 under normal pressure, ml; m g is the mass of CO2 introduced from the CO2 high pressure container 6 into the second cavity 102 of the variable volume visual container 1 and its corresponding pipeline, g; V'0 is the volume of the oil phase in the transparent graduated tube 2 after the pressure in the second cavity 102 of the variable volume visual container 1 changes from P1 to normal pressure, ml; β P0 is the extraction rate of unit mass CO2 at P0 pressure, g -1 ; V e,P0 is the extraction amount of CO2 on the oil phase under P0 pressure, ml; V P0 is the volume of the oil phase in the transparent graduated tube 2 at the pressure of P0, ml;

[0165] S8, at room temperature, replace the oil phase in the transparent graduated tube in S6 with a new oil phase with a volume of V0, and repeat steps S2-S4;

[0166] S9, close all valves, open the high-pressure pump 9 and the second valve 302, and push the piston 5 in the variable volume visual container 1 toward the end close to the transparent graduated tube 2 at a constant speed mode to dissolve CO2 in the oil phase. When the pressure sensor 8 reaches the set pressure P1 (P1>P0), record the liquid level of the oil phase in the transparent graduated tube 2 at this time and calculate the volume V of the oil phase at this time. P1 ;

[0167] S10, close all valves, open the high-pressure pump 9 and the second valve 302, move the piston 5 in the variable-volume visual container 1 toward the end away from the transparent graduated tube 2, and when the pressure sensor 8 reaches the set pressure P0, change the high-pressure pump 9 to the constant pressure mode, record the change value of the pumping amount of the high-pressure pump 9 with the pressure, and when the pumping amount remains basically unchanged within 2 hours, it is considered that the first cavity 101 and the second cavity 102 in the variable-volume visual container 1 have reached pressure balance, record the liquid level in the transparent graduated tube 2 and calculate the volume V' of the oil phase at this time P0 ;

[0168] S11, calculate the mass ratio of CO2 to oil phase under the condition of pressure P1, m g : The expansion rate of CO2 per unit mass in a system composed of m1 is α P1 and extraction rate β P1 ;

[0169] The extraction amount of crude oil by CO2 (V e,P1 ) and expansion (V s,P1 ):

[0170] V e,P1 =V e,P0 +V P0 -V' P0 (5)

[0171] V s,P1 =V P1 -(V0-V e,P1 ) (6)

[0172] Where V e,P1 is the extraction amount of CO2 on the oil phase under P1 pressure, ml; V e,P0 is the extraction amount of CO2 on the oil phase under P0 pressure, ml; V P0 is the volume of the oil phase in the transparent graduated tube 2 at P0 pressure, ml; V' P0 is the volume of the oil phase in the transparent graduated tube 2 after the pressure in the second cavity 102 of the variable volume visual container 1 changes from P1 to P0, ml; V s,P1 V is the expansion amount of CO2 on the oil phase at P1 pressure, ml; P1 is the volume of the oil phase in the transparent graduated tube 2 at P1 pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube 2 at normal pressure, ml;

[0173] According to equations (7) and (8), the expansion rate α of unit mass CO2 is P1 and extraction rate β P1 They are:

[0174]

[0175]

[0176] In the formula, α P1 is the expansion rate of unit mass CO2 at P1 pressure, g -1 ; V s,P1 is the expansion amount of CO2 on the oil phase under P1 pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube 2 under normal pressure, ml; m g The mass of CO2 introduced into the second cavity 102 of the variable volume visual container 1 and the corresponding pipeline by the CO2 high pressure container 6, g; β P1 is the extraction rate of unit mass CO2 at P1 pressure, g -1 ; V e,P1 is the extraction amount of CO2 on the oil phase under P1 pressure, ml;

[0177] S12, close all valves, open the high pressure pump 9 and the second valve 302, push the piston 5 in the variable volume visual container 1 toward the end close to the transparent graduated tube 2, dissolve CO2 in the oil phase, and when the pressure sensor 8 reaches the set pressure P i (i=2, 3, 4, ... n, n is a positive integer greater than or equal to 2, and P i >P i-1 ), the high pressure pump 9 is changed into the constant pressure mode, and the change value of the pumping amount of the high pressure pump 9 with the pressure is recorded. When the pumping amount remains basically unchanged within 2 hours, it is considered that the first cavity 101 and the second cavity 102 in the variable volume visual container 1 have reached pressure equilibrium, and the liquid level in the transparent graduated tube 2 is recorded and the volume V of the oil phase at this time is calculated. Pi ;

[0178] S13, close all valves, open the high pressure pump 9 and the second valve 302, move the piston 5 in the variable volume visual container 1 to the end away from the transparent graduated tube 2, and when the pressure sensor 8 reaches the set pressure P i-1 When the oil volume V' in the transparent graduated tube 2 is P(i-1) ;

[0179] S14, calculate the pressure as P i Under the conditions, the mass ratio of CO2 to oil phase is m g : The expansion rate of CO2 per unit mass in a system composed of m1 is α Pi and extraction rate β Pi ;

[0180] The extraction amount of crude oil by CO2 (V e,Pi ) and expansion (V s,Pi ):

[0181] V e,Pi =V e,P(i-1) +V P(i-1) -V' P(i-1) (9)

[0182] V s,Pi =V Pi -(V0-V e,Pi ) (10)

[0183] Where V e,Pi P i Extraction amount of oil phase by CO2 under pressure, ml; V e,P(i-1) P i-1 Extraction amount of oil phase by CO2 under pressure, ml; V P(i-1) P i-1 Volume of the oil phase in the transparent graduated tube 2 under pressure, ml; V' P(i-1)The pressure in the second cavity 102 of the variable volume visual container 1 is P i Change to P i-1 The volume of the oil phase in the transparent graduated tube 2, ml; V s,Pi P i Expansion of CO2 on the oil phase under pressure, ml; V Pi P i V0 is the volume of the oil phase added to the transparent graduated tube 2 under pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube 2 under normal pressure, ml;

[0184] According to equations (11) and (12), the expansion rate α of unit mass CO2 is Pi and extraction rate β Pi They are:

[0185]

[0186]

[0187] In the formula, α Pi P i Expansion rate per unit mass of CO2 under pressure, g -1 ; V s,Pi P i The expansion amount of CO2 on the oil phase under pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube 2 under normal pressure, ml; m g The mass of CO2 introduced into the second cavity 102 of the variable volume visual container 1 and the corresponding pipeline by the CO2 high pressure container 6, g; β Pi P i Extraction rate per unit mass of CO2 under pressure, g -1 ; V e,Pi P i The amount of oil phase extracted by CO2 under pressure, ml.

[0188] Example 1

[0189] The temperature of the thermostat is set at 50°C, the volume V0 of hexadecane added to the transparent graduated tube 2 under normal pressure is 5.570 mL, the mass m1 is 3.73 g, the mass of CO2 in the second cavity 102 of the variable volume visual container 1 and the corresponding pipeline is 347.16 g, and the above device and method are used to obtain the expansion rate α of unit mass of CO2 in a system with a mass ratio of CO2 to hexadecane of 93.0:1 under the set pressure P0 of 12 MPa. P0 and extraction rate β P0 , see Table 1.

[0190] Table 1 Expansion rate α per unit mass of CO2 when the mass ratio of CO2 to hexadecane is 93.0:1 at 12 MPaP0 and extraction rate β P0 value

[0191] <![CDATA[V P0 / mL]]> <![CDATA[V’0 / mL]]> <![CDATA[V e,P0 / mL]]> <![CDATA[V s,P0 / mL]]> <![CDATA[α P0 / % / g]]> <![CDATA[β P0 / % / g]]> 6.167 4.778 0.792 1.389 0.083 0.041

[0192] The pressure P of the CO2 and crude oil system is changed by a high-pressure pump i They are 13MPa, 14MPa, 15MPa and 16MPa respectively. The above device and method are used to continuously measure the expansion rate and extraction rate of crude oil by CO2 under different pressures. The experimental data are shown in Tables 2 and 3.

[0193] Table 2 Set pressure P when the mass ratio of CO2 to hexadecane is 93.0:1 i Change in oil phase volume from 12MPa to 16MPa

[0194] <![CDATA[V 12 / mL]]> <![CDATA[V 13 / mL]]> <![CDATA[V’ 12 / mL]]> <![CDATA[V 14 / mL]]> <![CDATA[V’ 13 / mL]]> <![CDATA[V 15 / mL]]> <![CDATA[V’ 14 / mL]]> <![CDATA[V 16 / mL]]> <![CDATA[V’ 15 / mL]]> 6.167 6.209 5.791 5.901 5.047 4.746 4.459 3.365 3.226

[0195] Table 3 When the mass ratio of CO2 to hexadecane is 93.0:1, the set pressure P i The expansion rate of CO2 to the oil phase from 12MPa to 16MPa α Pi and extraction rate β Pi value

[0196]

[0197]

[0198] Table 2 shows the set pressure P when the mass ratio of CO2 to hexadecane is 93.0:1. i Changes in the volume of the oil phase from 12MPa to 16MPa. It can be seen that when the pressure increases from 12MPa to 16MPa, the volume of the hexadecane phase increases first and then decreases. At the same time, when the pressure drops to the previous equilibrium pressure, the volume of the oil phase decreases significantly, indicating that the oil in the transparent graduated tube 2 is indeed extracted into CO2, and the amount of extraction also increases with the increase in pressure.

[0199] Table 3 shows the set pressure P when the mass ratio of CO2 to hexadecane is 93.0:1 i The expansion rate of CO2 to the oil phase from 12MPa to 16MPa α Pi and extraction rate β PiIt can be seen that the extraction volume and expansion volume gradually increase with the increase of pressure, and the expansion rate and extraction rate per unit mass also increase with the increase of CO2 pressure, indicating that the expansion and extraction effects are enhanced with the increase of pressure. However, it can also be found that when the pressure is lower than 15MPa, the expansion volume is significantly higher than the extraction volume, indicating that the expansion effect is more obvious at this time, and when the pressure is higher than 15MPa, the extraction volume begins to be higher than the expansion volume, indicating that the extraction effect is more significantly improved when the pressure is higher than 15MPa.

[0200] Example 2

[0201] The temperature of the thermostat is set at 50°C, the volume V0 of hexadecane added to the transparent graduated tube 2 under normal pressure is 5.570 mL, the mass m1 is 3.73 g, the mass of CO2 in the second cavity 102 of the variable volume visual container 1 and the corresponding pipeline 6 is 184.2 g, and the above device and method are used to obtain the expansion rate α of the unit mass of CO2 in the system with a mass ratio of CO2 to hexadecane of 49.4:1 under the set pressure P0 of 10 MPa. P0 and extraction rate β P0 , see Table 4.

[0202] Table 4 Expansion extraction experimental data at 10 MPa pressure when the mass ratio of CO2 to hexadecane is 49.4:1

[0203] <![CDATA[V P0 / mL]]> <![CDATA[V’0 / mL]]> <![CDATA[VV e,P0 / mL]]> <![CDATA[VV s,P0 / mL]]> <![CDATA[α P0 / % / g]]> <![CDATA[β P0 / % / g]]> 6.586 5.176 0.394 1.411 0.148 0.0384

[0204] The pressure P of the CO2 and crude oil system is changed by a high-pressure pump i They are 11MPa, 12MPa, 13MPa, 14MPa and 15MPa respectively. The above device and method are used to carry out continuous measurement experiment of CO2 expansion / extraction rate of crude oil under different pressures. The experimental data are shown in Tables 5 and 6.

[0205] Table 5 Changes in oil phase volume when pressure increases from 10 MPa to 15 MPa when the mass ratio of CO2 to hexadecane is 49.4:1

[0206]

[0207] Table 6 Expansion rate α of CO2 at different pressures when the mass ratio of CO2 to hexadecane is 49.4:1 Pi and extraction rate β Pi value

[0208] P / MPa <![CDATA[VV e,Pi / mL]]> <![CDATA[VV s,Pi / mL]]> <![CDATA[αα Pi / % / g]]> <![CDATA[ββ Pi / % / g]]> 10 0.394 1.411 0.148 0.038 11 1.026 1.858 0.222 0.100 12 1.458 2.320 0.306 0.142 13 2.432 2.900 0.502 0.237 14 3.161 3.359 0.757 0.308 15 4.542 4.108 2.169 0.443

[0209] Table 5 shows the set pressure P when the mass ratio of CO2 to hexadecane is 49.4:1. iChanges in the volume of the oil phase from 11MPa to 15MPa. It can be seen that when the pressure increases from 11MPa to 15MPa, the volume of the hexadecane phase increases first and then decreases. At the same time, when the pressure drops to the previous equilibrium pressure, the volume of the oil phase decreases significantly, indicating that the oil in the transparent graduated tube 2 is indeed extracted into CO2, and the amount of extraction also increases with the increase in pressure. Table 6 shows the CO2 to hexadecane mass ratio of 49.4:1, set pressure P i The expansion rate of CO2 to the oil phase from 11MPa to 15MPa α Pi and extraction rate β Pi It can be seen that the extraction volume and expansion volume gradually increase with the increase of pressure. At the same time, the expansion rate and extraction rate per unit mass also increase with the increase of CO2 pressure, indicating that the expansion and extraction effects will increase with the increase of pressure. In addition, under different pressures, the value of the expansion rate is significantly higher than the extraction rate, indicating that the expansion effect is more obvious.

[0210] Compared with the expansion rate and extraction rate at the same pressure in Example 1, it can be found that when the mass ratio of CO2 to hexadecane is reduced from 93:1 to 49.4:1, that is, the hexadecane content is increased, it is more conducive to the expansion and extraction effect of CO2 on crude oil, and the expansion and extraction efficiency is higher.

[0211] Example 3

[0212] The temperature of the thermostat is set at 50°C, the volume V0 of hexadecane added to the transparent graduated tube at normal pressure is 5.570mL, the mass m1 is 3.73g, the mass of CO2 in the second cavity of the variable visual container 1 and the corresponding pipeline is 71.0g, and the above device and method are used to obtain the expansion rate α of unit mass of CO2 in a system with a mass ratio of CO2 to hexadecane of 19.0:1 under the set pressure P0 of 8MPa. P0 and extraction rate β P0 , see Table 7.

[0213] Table 7 Expansion extraction experimental data at 8 MPa pressure when the mass ratio of CO2 to hexadecane is 19.0:1

[0214] <![CDATA[V P0 / mL]]> <![CDATA[V’0 / mL]]> <![CDATA[VV e,P0 / mL]]> <![CDATA[VV s,P0 / mL]]> <![CDATA[α P0 / % / g]]> <![CDATA[β P0 / % / g]]> 6.586 5.176 0.394 1.411 0.148 0.0384

[0215] The pressure P of the CO2 and crude oil system is changed by a high-pressure pump i They are 9MPa, 10MPa, 11MPa, 12MPa, 13MPa, 14MPa, 15MPa and 16MPa respectively. The above device and method are used to carry out continuous measurement experiment on the expansion / extraction rate of crude oil by CO2 under different pressures. The experimental data are shown in Tables 8 and 9.

[0216] Table 8 Changes in oil phase volume when pressure increases from 8 MPa to 16 MPa when the mass ratio of CO2 to hexadecane is 19.0:1

[0217]

[0218] Table 9 Expansion rate α of CO2 at different pressures when the mass ratio of CO2 to hexadecane is 19.0:1 Pi and extraction rate β Pi value

[0219] P / MPa <![CDATA[VV e,Pi / mL]]> <![CDATA[VV s,Pi / mL]]> <![CDATA[αα Pi / % / g]]> <![CDATA[ββ Pi / % / g]]> 8 0.006 0.365 0.092 0.001 9 0.085 0.701 0.180 0.021 10 0.259 0.901 0.238 0.065 11 0.357 1.134 0.306 0.090 12 0.577 1.455 0.410 0.146 13 1.183 1.960 0.628 0.299 14 2.220 2.606 1.092 0.560 15 3.621 3.079 2.213 0.914 16 4.497 3.591 4.668 1.135

[0220] Table 8 shows the set pressure P when the mass ratio of CO2 to hexadecane is 19.0:1 i Changes in the volume of the oil phase from 9MPa to 16MPa. It can be seen that when the pressure increases from 9MPa to 16MPa, the volume of the hexadecane phase increases first and then decreases. At the same time, when the pressure drops to the previous equilibrium pressure, the volume of the oil phase decreases significantly, indicating that the oil in the transparent tube is indeed extracted into CO2, and the amount of extraction also increases with the increase in pressure.

[0221] Table 9 shows the set pressure P when the mass ratio of CO2 to hexadecane is 19.0:1 i The expansion rate of CO2 to the oil phase from 9MPa to 16MPa is α Pi and extraction rate β Pi It can be seen that the extraction volume and expansion volume gradually increase with the increase of pressure. At the same time, the expansion rate and extraction rate per unit mass also increase with the increase of CO2 pressure. The value of the expansion rate is significantly higher than the extraction rate, indicating that the expansion effect is more obvious.

[0222] In addition, compared with Example 1 and Example 2, it can be found that as the mass ratio of CO2 to hexadecane increases, the expansion rate and extraction rate of CO2 per unit mass decrease, that is, as the amount of CO2 increases, the expansion rate and extraction rate of CO2 per unit mass decrease, that is, the efficiency of expansion and extraction decreases. Therefore, in the process of CO2 development, in order to give full play to the expansion and extraction effect of CO2 on crude oil, it is necessary to maintain a high pressure and minimize the decay rate of CO2 pressure, so that it is more conducive to CO2 to bring out more oil.

[0223] The method for quantitatively evaluating the expansion / extraction rate of crude oil under the action of CO2 provided in the embodiment of the present invention has a simple structure and is easy to build. Through the ingenious design of the experimental device and the simple experimental process, the expansion rate and extraction rate of crude oil under different pressures of CO2 can be continuously measured for the same sample. The method has a simple structure and is easy to build, which reduces the number of times the sample is weighed and reduces the error of the experimental data.

[0224] The method for quantitatively evaluating the expansion / extraction rate of crude oil under the action of CO2 provided in the embodiment of the present invention can obtain the expansion rate and extraction rate of unit mass of CO2. The evaluation result is more comparative and can more clearly compare and analyze the expansion effect and extraction effect at different pressures. It is more instructive for the actual oil recovery process than the results obtained from a single expansion experiment and extraction experiment. At the same time, it has a targeted guiding role in the pressure control for improving the recovery rate during oil field development.

[0225] The measuring method provided by the present invention can continuously measure the expansion rate and extraction rate of CO2 to crude oil under different pressures. With the aid of the above device, a process of continuous change of field pressure can be simulated through a simple calculation process. In addition, during the test, there is no need to refill the sample at each pressure. The expansion rate and extraction rate under multiple pressures of continuous change under the composition can be obtained by only two samplings, which can greatly save time and sample costs, reduce errors caused by multiple samplings, and obtain more accurate data. It is more instructive for the actual oil recovery process than the results obtained from a single expansion experiment and extraction experiment, and is more conducive to guiding the selection and control of pressure during field development.

[0226] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the aforementioned embodiments, a person skilled in the art should understand that the technical solutions described in the aforementioned embodiments may still be modified, or some of the technical features may be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A device for continuously evaluating the expansion and extraction rate of crude oil by CO2 at different pressures, characterized in that: The device comprises a volume-variable visual container (1), a transparent graduated tube (2), a stirring system, a piston (5), a CO2 high-pressure container (6), a balance (7), a pressure sensor (8), a high-pressure pump (9), a first cavity (101), a second cavity (102), a first pipeline (201), a second pipeline (202), a third pipeline (203), a fourth pipeline (204), a fifth pipeline (205), a first valve (301), a second valve (302), a third valve (303), and a fourth valve (304); The volume-variable visual container (1) is provided with a piston (5), and the piston (5) divides the interior of the volume-variable visual container (1) into a first cavity (101) and a second cavity (102); The first cavity (101) of the variable-volume visual container (1) is connected to the atmosphere via the first pipeline (201), and the first pipeline (201) is provided with a first valve (301); The first cavity (101) of the variable-volume visual container (1) is also connected to the high-pressure pump (9) via the second pipeline (202), and the second pipeline (202) is provided with a second valve (302); A transparent graduated tube (2) is provided in the second cavity (102) of the variable-volume visual container (1), and a stirring device is provided in the transparent graduated tube (2); The second cavity (102) of the variable-volume visual container (1) is also connected to the CO2 high-pressure container (6) via the fourth pipeline (204), and a fourth valve (304) is provided on the fourth pipeline (204); the balance (7) is arranged below the CO2 high-pressure container (6); The second cavity (102) of the variable-volume visual container (1) is also connected to the pressure sensor (8) and the atmosphere in sequence through the third pipeline (203), and a third valve (303) is provided on the third pipeline (203) between the pressure sensor (8) and the atmosphere.

2. The device for continuously evaluating the expansion and extraction rate of crude oil by CO2 at different pressures as claimed in claim 1, characterized in that: The variable volume visual container (1), the transparent graduated tube (2), the stirring system, the piston (5), the CO2 high pressure container (6), the balance (7), the high pressure pump (9), the first valve (101), the second valve (102), the third valve (103), the fourth valve (104), the first pipeline (201), the second pipeline (202), the third pipeline (203), the fourth pipeline (204), and the fifth pipeline (205) are all arranged in a constant temperature control system (14).

3. The device for continuously evaluating the expansion and extraction rate of crude oil by CO2 at different pressures as claimed in claim 1, characterized in that: One end of the transparent graduated tube (2) is open, a plug (10) is provided at the opening of the transparent graduated tube (2), and a vent hole (11) is provided on the plug (10).

4. The device for continuously evaluating the expansion and extraction rate of crude oil by CO2 at different pressures as claimed in claim 1, characterized in that: The variable-volume visual container (1) comprises a barrel (12) and an end cover (13) threadedly connected to the barrel (12).

5. The device for continuously evaluating the expansion and extraction rate of crude oil by CO2 at different pressures as claimed in claim 4, characterized in that: An observation window (15) is provided on the side wall of the cylinder (12) of the variable-volume visual container 1.

6. The device for continuously evaluating the expansion and extraction rate of crude oil by CO2 at different pressures as claimed in claim 1, characterized in that: The first cavity (101) of the variable-volume viewable container 1 is located above the second cavity (102).

7. A method for continuously evaluating the expansion and extraction rate of crude oil by CO2 at different pressures, using the device for continuously evaluating the expansion and extraction rate of crude oil by CO2 at different pressures as claimed in claim 2, characterized in that: The steps include: S1, under normal pressure, add a set volume V0 of oil phase into the transparent graduated tube (2), the mass of the oil phase is recorded as m1; S2, placing the transparent graduated tube (2) into the second cavity (102) of the variable volume visual container 1, ensuring that the liquid level is visible, connecting the pipelines, closing all valves, turning on the constant temperature control system (14), setting the temperature, and turning on the stirring system; S3, closing all valves, opening the first valve (301) and the fourth valve (304), and passing the CO2 in the CO2 high pressure container (6) into the second cavity (102) in the variable volume visual container (1), so that the piston (5) in the variable volume visual container (1) is pushed to the end away from the transparent graduated tube (2); S4. Record the mass of CO2 introduced into the second cavity (102) of the variable volume visual container (1) and the corresponding pipeline as m by using a balance (7). g ; S5, close all valves, open the high-pressure pump (9) and the second valve (302), push the piston (5) in the variable-volume visual container 1 toward one end close to the transparent graduated tube (2), dissolve CO2 in the oil phase, and when the pressure sensor (8) reaches the set pressure P0, record the height of the liquid level in the transparent graduated tube (2) at this time and calculate the volume V of the oil phase at this time P0 ; S6, close all valves, open the first valve (301), quickly discharge the CO2 in the second cavity (102) of the variable volume visual container (1), and when the pressure in the second cavity (102) becomes normal pressure, record the height of the liquid level in the transparent graduated tube (2) at this time and calculate the volume V0' of the oil phase at this time; S7, calculate the mass ratio of CO2 to oil phase under the condition of pressure P0, m g : The expansion rate of CO2 per unit mass in a system composed of m1 is α P0 and extraction rate β P0 : The extraction amount of CO2 on the oil phase (V e,P0 ) and expansion (V s,P0 ): V e，P0 =V0-V0' (1) V s，P0 =V P0 -V0' (2) Where V e,P0 is the extraction amount of CO2 on the oil phase at P0 pressure, ml; V s,P0 is the expansion amount of CO2 on the oil phase at P0 pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube (2) at normal pressure, ml; V P0 is the volume of the oil phase in the transparent graduated tube (2) at the pressure of P0, ml; V0' is the volume of the oil phase in the transparent graduated tube (2) after the pressure in the second cavity (102) of the variable volume visual container (1) changes from P0 to normal pressure, ml; The expansion rate α per unit mass of CO2 is obtained by equations (3) and (4): P0 and extraction rate β P0 They are: In the formula, α P0 is the expansion rate of unit mass CO2 at P0 pressure, g -1 ; V s,P0 is the expansion amount of CO2 on the oil phase at P0 pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube (2) at normal pressure, ml; m g is the mass of CO2 introduced from the CO2 high pressure container (6) into the second cavity (102) of the variable volume visual container (1) and its corresponding pipeline, g; V0' is the volume of the oil phase in the transparent graduated tube (2) after the pressure in the second cavity (102) of the variable volume visual container (1) changes from P0 to normal pressure, ml; β P0 is the extraction rate of unit mass CO2 at P0 pressure, g -1 ; V e,P0 is the extraction amount of CO2 on the oil phase at P0 pressure, ml; V P0 is the volume of the oil phase in the transparent graduated tube (2) at the pressure of P0, ml; S8, at room temperature, replacing the oil phase in the transparent graduated tube (2) in S6 with a new oil phase having a volume of V0, and repeating steps S2-S4; S9, close all valves, open the high-pressure pump (9) and the second valve (302), push the piston (5) in the variable-volume visual container (1) toward one end close to the transparent graduated tube (2), dissolve CO2 in the oil phase, and when the pressure sensor (8) reaches the set pressure P1, P1>P0, record the liquid level of the oil phase in the transparent graduated tube (2) at this time and calculate the volume V of the oil phase at this time P1 ; S10, close all valves, open the high-pressure pump (9) and the second valve (302), move the piston (5) in the variable-volume visual container (1) toward the end away from the transparent graduated tube (2), and when the pressure sensor (8) reaches the set pressure P0, change the high-pressure pump (9) to a constant pressure mode, record the change in the pumping volume of the high-pressure pump (9) as the pressure changes, and when the pumping volume remains substantially unchanged within 2 hours, it is considered that the first cavity (101) and the second cavity (102) in the variable-volume visual container (1) have reached pressure equilibrium, record the liquid level in the transparent graduated tube (2), and calculate the volume V′ of the oil phase at this time. P0 ; S11, calculate the mass ratio of CO2 to oil phase under the condition of pressure P1, m g : The expansion rate of CO2 per unit mass in a system composed of m1 is α P1 and extraction rate β P1 ; The extraction amount of crude oil by CO2 (V e,P1 ) and expansion (V s,P1 ): V e,P1 =V e,P0 +V P0 -V′ P0 (5) V s,P1 =V P1 -(V0-V e,P1 ) (6) Where V e,P1 is the extraction amount of CO2 on the oil phase under P1 pressure, ml; V e,P0 is the extraction amount of CO2 on the oil phase at P0 pressure, ml; V P0 is the volume of the oil phase in the transparent graduated tube (2) at the pressure of P0, ml; V' P0 is the volume of the oil phase in the transparent graduated tube (2) after the pressure in the second cavity (102) of the variable volume visual container (1) changes from P1 to P0, in ml; V s,P1 V is the expansion amount of CO2 on the oil phase at P1 pressure, ml; P1 is the volume of the oil phase in the transparent graduated tube (2) at the pressure of P1, ml; V0 is the volume of the oil phase added to the transparent graduated tube (2) at normal pressure, ml; According to equations (7) and (8), the expansion rate α of unit mass CO2 is P1 and extraction rate β P1 They are: In the formula, α P1 is the expansion rate of unit mass CO2 at P1 pressure, g -1 ; V s,P1 is the expansion amount of CO2 on the oil phase at P1 pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube (2) at normal pressure, ml; m g is the mass of CO2 introduced from the CO2 high pressure container (6) into the second cavity (102) of the variable volume visual container (1) and the corresponding pipeline, g; β P1 is the extraction rate of unit mass CO2 at P1 pressure, g -1 ; V e,P1 is the extraction amount of CO2 on the oil phase under P1 pressure, ml; S12, close all valves, open the high-pressure pump (9) and the second valve (302), push the piston (5) in the variable-volume visual container (1) toward the end close to the transparent graduated tube (2), dissolve CO2 in the oil phase, and when the pressure sensor (8) reaches the set pressure P i (i=2, 3, 4, ... n, n is a positive integer greater than or equal to (2), and P i >P i-1 ), the high-pressure pump (9) is changed to a constant pressure mode, and the change value of the pumping volume of the high-pressure pump (9) as the pressure changes. When the pumping volume remains substantially unchanged within 2 hours, it is considered that the first cavity (101) and the second cavity (102) in the variable-volume visual container 1 have reached pressure equilibrium, and the liquid level in the transparent graduated tube (2) is recorded and the volume V of the oil phase at this time is calculated. Pi ; S13, close all valves, open the high-pressure pump (9) and the second valve (302), move the piston (5) in the variable-volume visual container (1) toward the end away from the transparent graduated tube (2), and when the pressure sensor (8) reaches the set pressure P i-1 When the oil volume V' in the transparent graduated tube (2) is recorded, P(i-1) ; S14, calculate the mass ratio of CO2 to oil phase under the condition of pressure Pi, m g : The expansion rate of CO2 per unit mass in a system composed of m1 is α Pi and extraction rate β Pi ; The extraction amount of crude oil by CO2 (V e,Pi ) and expansion (V s,Pi ): V e,Pi =V e,P(i-1) +V P(i-1) -V′ P(i-1) (9) V s,Pi =V Pi -(V0-V e,Pi ) (10) Where V e,Pi V is the extraction amount of CO2 on the oil phase under Pi pressure, ml; e,P(i-1) For Pi -1 Extraction amount of oil phase by CO2 under pressure, ml; V P(i-1) P i-1 Volume of the oil phase in the transparent graduated tube (2) under pressure, ml; V' P(i-1) The pressure in the second cavity (102) of the variable volume visual container (1) is P i Change to P i-1 The volume of the oil phase in the transparent graduated tube (2), ml; V s,Pi P i Expansion of the oil phase by CO2 under pressure, ml; V Pi P i V0 is the volume of the oil phase added to the transparent graduated tube (2) under pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube (2) under normal pressure, ml; According to equations (11) and (12), the expansion rate α of unit mass CO2 is Pi and extraction rate β Pi They are: In the formula, α Pi P i Expansion rate per unit mass of CO2 under pressure, g -1 ; V s,Pi P i Expansion of the oil phase by CO2 under pressure, ml; V0 is the volume of the oil phase added to the transparent graduated tube (2) at normal pressure, ml; m g The mass of CO2 introduced from the CO2 high pressure container (6) into the second cavity (102) of the variable volume visual container (1) and the corresponding pipeline, g; β Pi P i Extraction rate per unit mass of CO2 under pressure, g -1 ; V e,Pi P i The amount of oil phase extracted by CO2 under pressure, ml.

8. The method for continuously evaluating the expansion and extraction rate of crude oil by CO2 at different pressures as claimed in claim 7, characterized in that: The set pressures P0, P1, P i (i=2, 3, 4, ... n, n is a positive integer greater than or equal to 2) are all greater than the bubble point pressure of CO2 at this temperature to ensure that CO2 is in a supercritical or liquid state.

9. The method for continuously evaluating the expansion and extraction rate of crude oil by CO2 at different pressures as claimed in claim 7, characterized in that: In the steps S5 and S9, the step of opening the high-pressure pump (9) and the second valve (302) to push the piston in the variable-volume visual container (1) toward one end close to the transparent graduated tube (2) comprises opening the high-pressure pump (9) and the second valve (302) to push the piston (5) in the variable-volume visual container (1) toward one end close to the transparent graduated tube (2) at a constant speed.

10. Use of the method according to any one of claims 7 to 9 in improving crude oil recovery.

Images