In-pump negative pressure de-mixing experiment method applied to carbon dioxide oil displacement

Abstract

The invention discloses an in-pump negative pressure de-mixing experiment method applied to carbon dioxide oil displacement, an experiment device is applied to experiment, the experiment device comprises a petroleum CO2 supersaturation container, a reciprocating pump and a piston pump, and the piston pump is placed in a constant temperature box to simulate formation temperature; petroleum and carbon dioxide are injected into the petroleum CO2 supersaturation container and mixed, a reciprocating pump is used for pumping an oil-gas mixture into a piston pump, and pressure and temperature changes in the piston pump in the pumping process are detected in real time through a pressure sensor and a temperature sensor; the layering condition of internal gas and liquid can be visually observed through the visual piston pump, and the accumulated negative pressure de-mixing rate of crude oil under the carbon dioxide flooding condition is calculated by analyzing experimental data through a computer. The problem of negative pressure de-mixing in the pump under the carbon dioxide oil displacement condition is solved, the stability and efficiency of the carbon dioxide injection and oil extraction process are remarkably improved, the equipment loss is reduced, and the oil and gas recovery efficiency is improved.

Description

Technical Field

[0001] The invention belongs to the technical field of oil production, and in particular relates to a negative pressure demixing experimental method in a pump applied to carbon dioxide oil recovery. Background Art

[0002] In oil production, CO2 flooding technology is increasingly used because it can significantly improve the recovery rate. During the application process, CO2 is injected into the oil layer. After CO2 is injected into the oil reservoir, it will form a miscible or immiscible system with crude oil to increase the fluidity of crude oil and drive it to the production well. However, when the oil and CO2 mixture flows into the pump, due to pressure changes, negative pressure will occur, and CO2 will be demixed from the mixed system. This demixing phenomenon will cause the fluid properties in the pump to change, such as destroying the continuity of the oil phase and forming a gas-liquid two-phase flow. It interacts with crude oil and can reduce crude oil viscosity and many other favorable properties to improve production efficiency.

[0003] In the case of carbon dioxide flooding, gas and oil exist at the same time. Under certain temperature and pressure conditions, the fluid is in a reverberation state. When it enters the pump, demixing will occur because the pump is pumping liquid upward under negative pressure. From the perspective of pump efficiency, since the compressibility of gas is much greater than that of liquid, during the suction stroke of the pump, gas overflow occupies part of the space in the pump barrel, resulting in a decrease in the amount of liquid entering the pump, which will reduce the filling degree of the pump. Moreover, the existence of gas-liquid two-phase flow will complicate the working conditions of the pump, cause energy loss, increase the hydraulic loss, volume loss and mechanical loss of the pump, and ultimately reduce the pump efficiency. This not only affects the efficiency of crude oil recovery, but also increases the cost of recovery. Traditional oil well pump design and working theory are insufficient in dealing with this special gas-liquid change in carbon dioxide flooding, and lack special research and effective countermeasures for the demixing phenomenon of carbon dioxide in the pump.

[0004] From the perspective of the characteristics of the reservoir exploitation stage, the geological conditions and crude oil properties of different reservoirs vary greatly. In complex reservoir environments, the uniformity and stability of the mixing of carbon dioxide and crude oil vary, which makes the occurrence of negative pressure demixing in the pump more complicated and increases the difficulty of studying and solving the problem. Moreover, as the reservoir exploitation deepens, parameters such as reservoir pressure and temperature will also change, further affecting the state of carbon dioxide in the pump and the pump efficiency. On the technical level, traditional pump design and operation theories are mostly based on single-phase fluids or simple gas-liquid two-phase flows. For the special gas demixing problem caused by negative pressure in carbon dioxide flooding, the existing theories and technologies are obviously insufficient and cannot effectively guide the practice of improving pump efficiency. New research is urgently needed to fill this gap.

[0005] In view of this, it is of great significance to study a device and method that can solve the problem of negative pressure demixing in the pump under carbon dioxide flooding conditions. Summary of the invention

[0006] In order to solve the above problems, the present invention provides a negative pressure demixing experimental method in a pump applied to carbon dioxide flooding.

[0007] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A method for negative pressure demixing experiment in a pump for carbon dioxide flooding is disclosed. The method uses a negative pressure demixing experiment device in a pump to conduct the experiment. The negative pressure demixing experiment device in the pump comprises a petroleum CO2 supersaturated container, a reciprocating pump and a visualized piston pump. The petroleum CO2 supersaturated container can contain petroleum and carbon dioxide and mix them into an oil-gas mixture. The outlet of the petroleum CO2 supersaturated container is connected to the inlet of the piston pump. The reciprocating rod of the reciprocating pump is connected to the piston rod in the piston pump. The piston pump is arranged in a thermostatic box capable of simulating formation temperature. A pressure sensor and a temperature sensor are arranged on the side wall of the piston pump. The reciprocating pump, the pressure sensor and the temperature sensor are all connected to a computer. The method comprises the following steps: (1) Heating the piston pump: Place the piston pump in a thermostatic box in advance and set the temperature of the thermostatic box to the formation temperature; (2) Mixing oil and carbon dioxide: inject oil and carbon dioxide into the oil CO2 supersaturated container in sequence, pressurize and rotate the oil CO2 supersaturated container to fully mix the oil and carbon dioxide; (3) Extracting the oil-gas mixture: Connect the outlet of the petroleum CO2 supersaturated container to the inlet of the piston pump, start the reciprocating pump to extract the oil-gas mixture in the petroleum CO2 supersaturated container, and fill the piston pump with the oil-gas mixture; During the extraction of the oil-gas mixture, the temperature and pressure at different positions in the piston pump are detected in real time through the pressure sensor and the temperature sensor; the extraction is stopped, and the oil CO2 supersaturated container continues to rotate; During the extraction of the oil-gas mixture, observe the oil-gas mixture in the piston pump, and read the volumes of oil and gas through the scale on the outer wall of the piston pump, which are recorded as V1 and V2 respectively. The oil-gas ratio α is expressed as follows: The negative pressure demixing rate Di of crude oil under CO2 flooding conditions is expressed as follows

[0008] Among them, V1 is the volume of gas in the piston pump; V0 is the total volume of the piston pump.

[0009] Furthermore, the petroleum CO2 supersaturated container includes a drive box and a supersaturated cavity, the two sides of the supersaturated cavity are respectively connected to a driving rotating shaft and a driven rotating shaft, the driving rotating shaft is connected to the output shaft of the drive box, the driven rotating shaft is arranged on a support seat, and the drive box is used to drive the supersaturated cavity to rotate; the inlet of the supersaturated cavity is used to inject petroleum and carbon dioxide gas, and the inlet is provided with a valve, and the outlet of the supersaturated cavity can be connected to the inlet of a piston pump through a high-pressure resistant pipeline, and the inlet and outlet of the high-pressure resistant pipeline are both provided with valves.

[0010] Furthermore, the inlet of the supersaturated cavity can be connected to the oil pipeline and the carbon dioxide cylinder respectively, and the pressure in the supersaturated cavity is greater than 15 MPa.

[0011] Furthermore, the piston pump is placed upright and a scale is provided in the height direction of its side wall. A plurality of pressure sensors and temperature sensors are arranged on the side wall of the piston pump from top to bottom, and the pressure sensors and temperature sensors are arranged at intervals; the inlet of the piston pump is arranged at the bottom, and the top of the piston head in the piston pump is connected to the piston rod.

[0012] Furthermore, the reciprocating pump is a DC motor reciprocating pump.

[0013] Furthermore, repeat steps (1)-(3) N times, observe the temperature and pressure change curves, and calculate the final cumulative demixing rate, that is, After the calculation is completed, a set of control experiments are carried out using crude oil that is not saturated with CO2. The reduction in the piston pump efficiency η under positive and negative pressures is calculated as follows:

[0014] Among them, Q 实际 is the actual displacement of the piston pump, Q 理论 is the theoretical displacement of the piston pump.

[0015] Furthermore, in step (2), the petroleum CO2 supersaturated container is pressurized to greater than 15 MPa and rotated for 30 minutes.

[0016] Furthermore, in step (3), when the supersaturated cavity of the petroleum CO2 supersaturated container turns to a vertical state with the outlet facing downward, the supersaturated cavity stops rotating; a high-pressure pipeline is installed between the outlet of the supersaturated cavity and the inlet of the piston pump, and the valves at both ends of the high-pressure pipeline are opened to extract the oil-gas mixture.

[0017] Compared with the prior art, the present invention has the following technical advances: The present invention can simulate the formation temperature by setting the piston pump in the thermostat; then the oil and carbon dioxide are fully mixed into an oil-gas mixture through the oil CO2 supersaturated container, and the oil-gas mixture in the oil CO2 supersaturated container is pumped into the piston pump by a reciprocating pump to simulate the on-site pumping operation process; the pressure and temperature changes in the piston pump during the extraction process are detected in real time by the pressure sensor and the temperature sensor, and the visual piston pump can intuitively observe the stratification of the internal gas and liquid, and the cumulative negative pressure demixing rate of crude oil under the carbon dioxide flooding condition can be calculated using these experimental data. The present invention can solve the problem of negative pressure demixing in the pump under the carbon dioxide flooding condition, and can significantly improve the stability and efficiency of the carbon dioxide injection and oil production process, reduce equipment loss and improve the oil and gas recovery rate. Compared with the existing technology, the optimized pump design, intelligent monitoring system, pressurized injection technology and other solutions provide a more efficient, energy-saving and environmentally friendly solution path, which can greatly improve the limitations of traditional carbon dioxide flooding technology and promote the sustainable development of the oil and gas industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The accompanying drawings are used to provide further understanding of the present invention and constitute a part of the specification. They are used to explain the present invention together with the embodiments of the present invention and do not constitute a limitation of the present invention.

[0019] In the attached picture: Figure 1 Schematic diagram of the structure of the negative pressure demixing experimental device in the pump used in the embodiment of the present invention; In the figure: 1-petroleum CO2 supersaturated container, 11-drive box, 12-supersaturated chamber, 13-active shaft, 14-driven shaft, 15-support seat; 2-reciprocating pump, 20-reciprocating rod; 3-piston pump, 30-piston rod, 31-piston head; 4-constant temperature box; 5-pressure sensor; 6-temperature sensor; 7-computer; 8-valve; 9-high pressure pipeline; 10-scale; 16-display. DETAILED DESCRIPTION

[0020] The following specific embodiments may be combined with each other, and the same or similar concepts or processes may not be described in detail in some embodiments. The embodiments of the present invention will be described below in conjunction with the accompanying drawings.

[0021] like Figure 1As shown, the negative pressure demixing experimental device in the pump includes a petroleum CO2 supersaturated container 1, a reciprocating pump 2 and a visualized piston pump 3. The petroleum CO2 supersaturated container 1 can contain petroleum and carbon dioxide and mix them into an oil-gas mixture. The outlet of the petroleum CO2 supersaturated container 1 is connected to the inlet of the piston pump 3, and the reciprocating rod 20 of the reciprocating pump 2 is connected to the piston rod 30 in the piston pump 3; the piston pump 3 is arranged in a constant temperature box 4 that can simulate the formation temperature, and a pressure sensor 5 and a temperature sensor 6 are arranged on the side wall of the piston pump 3. The reciprocating pump 2, the pressure sensor 5 and the temperature sensor 6 are all connected to a computer 7, and the experimental data can be displayed through a display 16. The piston pump is set in a constant temperature box to simulate the formation temperature; the oil and carbon dioxide are then fully mixed into an oil-gas mixture through a petroleum CO2 supersaturated container, and the computer controls the reciprocating pump to pump the oil-gas mixture in the petroleum CO2 supersaturated container into the piston pump, simulating the on-site pumping operation process; the pressure and temperature changes in the piston pump during the extraction process are detected in real time through pressure sensors and temperature sensors, and the visualized piston pump can intuitively observe the stratification of internal gas and liquid.

[0022] As a preferred structure, Figure 1 As shown, the oil CO2 supersaturated container 1 includes a drive box 11 and a supersaturated cavity 12. The two sides of the supersaturated cavity 12 are respectively connected to the driving shaft 13 and the driven shaft 14. The driving shaft 13 is connected to the output shaft of the drive box 11, and the driven shaft 14 is arranged on the support seat 15. The drive box 11 is used to drive the supersaturated cavity 12 to rotate; the inlet of the supersaturated cavity 12 is used to inject oil and carbon dioxide gas, and the inlet is provided with a valve 8. The outlet of the supersaturated cavity 12 can be connected to the inlet of the piston pump 3 through a high-pressure pipeline 9, and the inlet and outlet of the high-pressure pipeline 9 are both provided with valves 8. Among them, a pressure pump is provided in the drive box, and the pressure pump can pressurize the supersaturated cavity through the through hole in the middle of the driving shaft. After the oil and CO2 are injected into the supersaturated cavity in proportion, the drive box is started to continuously pressurize the supersaturated cavity during the rotation process, ensuring that the pressure in the supersaturated cavity is in a suitable pressure state before entering the piston pump, avoiding premature demixing due to negative pressure.

[0023] In specific operation, the inlet of the supersaturated cavity 12 is connected to the oil pipeline and the carbon dioxide cylinder respectively, and crude oil and carbon dioxide can be injected into the supersaturated cavity in sequence to mix the oil and CO2 in proportion, and at the same time, the pressure in the supersaturated cavity 12 is controlled to be greater than 15MPa to ensure that CO2 and oil are fully mixed in the supersaturated cavity to reach a supersaturated state. During the experiment, the pressure change in the supersaturated cavity is detected, and the pressure is adjusted in real time to ensure that the pressure at the outlet of the supersaturated cavity makes the fluid in a suitable pressure state before entering the piston pump to avoid premature demixing due to negative pressure.

[0024] In a specific embodiment of the present invention, Figure 1 As shown, the piston pump 3 is placed upright, and a scale 10 is provided in the height direction of its side wall. Multiple pressure sensors 5 and temperature sensors 6 are arranged from top to bottom on the side wall of the piston pump 3, and the pressure sensors 5 and temperature sensors 6 are arranged at intervals, which is helpful to understand the state changes of the fluid in the piston pump cavity; the inlet of the piston pump 3 is set at the bottom, and the top of the piston head 31 in the piston pump 3 is connected to the piston rod 30. In the experiment, the gas ratio is read according to the scale, and the proportion of gas in the cavity of the piston pump is analyzed, and then the cumulative negative pressure demixing rate of crude oil under carbon dioxide flooding conditions is studied.

[0025] In addition, the reciprocating pump adopts a DC motor reciprocating pump, which is similar to a plunger pump structure. The stroke frequency of the linear motor reciprocating pump is controlled by a computer to make it consistent with the actual pumping unit stroke, simulating the on-site pumping unit operation process.

[0026] The present invention provides a method for conducting a negative pressure demixing experiment in a pump for carbon dioxide flooding, and uses the negative pressure demixing experiment device in a pump to conduct an experiment, comprising the following steps: (1) Heating the piston pump: the piston pump 3 is placed in a thermostatic box 4 in advance, and the temperature of the thermostatic box 4 is set to the formation temperature; (2) Mixing oil and carbon dioxide: inject oil into the oil CO2 supersaturated container 1, and then inject carbon dioxide into the oil CO2 supersaturated container 1 with a gas cylinder. After the injection is completed, close the inlet valve of the oil CO2 supersaturated container; pressurize the oil CO2 supersaturated container 1 to more than 15MPa, and rotate it for 30 minutes to allow the oil and carbon dioxide to fully contact and fuse; (3) Extracting the oil-gas mixture: When the supersaturated cavity 12 of the petroleum CO2 supersaturated container 1 turns to a vertical state and the outlet is downward, the supersaturated cavity 12 stops rotating; a high-pressure pipeline 9 is installed between the outlet of the supersaturated cavity 12 and the inlet of the piston pump 3, and the valves 8 at both ends of the high-pressure pipeline 9 are opened to extract the oil-gas mixture. When the outlet of the supersaturated cavity 12 is vertically downward, the valves at both ends of the high-pressure pipeline are opened, and the DC motor reciprocating pump is started to drive the piston rod to start extracting the oil-gas mixture in the petroleum CO2 supersaturated container 1. The extraction is paused for a period of time, and the volume occupied by the gas and liquid in the piston pump cavity is read; the extraction action is repeated until the pump cavity of the piston pump 3 is filled with the oil-gas mixture.

[0027] Note: Each extraction needs to be performed when the outlet of the supersaturated chamber 12 is turned downward. Because, if the outlet of the supersaturated chamber 12 is turned upward, CO2 in the upper part of the supersaturated chamber 12 may be extracted instead of the oil-gas mixture.

[0028] During the extraction of the oil-gas mixture, the temperature and pressure at different positions in the piston pump 3 are detected in real time by the pressure sensor 5 and the temperature sensor 6; the extraction is stopped, and the valve is closed to allow the oil CO2 supersaturated container 1 to continue rotating; During the extraction of the oil-gas mixture, the oil-gas mixture is in a state of oil-gas separation in the pump chamber. By observing the oil-gas mixture in the transparent piston pump 3, the volumes of oil and gas are read through the scale 10 on the outer wall of the piston pump 3, which are recorded as V1 and V2 respectively. The oil-gas ratio α is expressed as follows: The negative pressure demixing rate Di of crude oil under CO2 flooding conditions is expressed as follows

[0029] Wherein, V1 is the volume of the gas in the piston pump 3 ; V0 is the total volume of the piston pump 3 .

[0030] Furthermore, repeat steps (1)-(3) N times, observe the temperature and pressure change curves, and calculate the final cumulative demixing rate, that is, After the calculation is completed, a set of control experiments are carried out using crude oil that is not saturated with CO2. The reduction in the efficiency η of the piston pump 3 under positive and negative pressures is calculated as follows:

[0031] Among them, Q 实际 is the actual displacement of the piston pump 3, Q 理论 is the theoretical displacement of the piston pump 3.

[0032] In summary, the present invention has the advantages of simple structure and convenient and fast operation. The piston pump is set in a constant temperature box to simulate the formation temperature; the oil and carbon dioxide are fully mixed into an oil-gas mixture through the oil CO2 supersaturated container, and the oil-gas mixture in the oil CO2 supersaturated container is pumped into the piston pump by a reciprocating pump to simulate the on-site pumping unit operation process; the pressure and temperature changes in the piston pump during the extraction process are detected in real time by the pressure sensor and the temperature sensor, and the visual piston pump can intuitively observe the stratification of the internal gas and liquid, and the cumulative negative pressure demixing rate of crude oil under the condition of carbon dioxide flooding can be calculated using these experimental data. The present invention can solve the problem of negative pressure demixing in the pump under the condition of carbon dioxide flooding, and can significantly improve the stability and efficiency of carbon dioxide injection and oil production process, reduce equipment loss and improve oil and gas recovery rate. Compared with the prior art, the optimized pump design, intelligent monitoring system, boost injection technology and other solutions provide a more efficient, energy-saving and environmentally friendly solution path, which can greatly improve the limitations of traditional carbon dioxide flooding technology and promote the sustainable development of the oil and gas industry.

[0033] Finally, it should be noted that the above is only a preferred embodiment of the present invention and is not intended to limit the present invention. Although the present invention has been described in detail with reference to the aforementioned embodiments, those skilled in the art can still modify the technical solutions described in the aforementioned embodiments or replace some of the technical features therein with equivalents. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention shall be included in the scope of protection of the claims of the present invention.

Claims

1. A negative pressure demixing experimental method for carbon dioxide flooding in a pump, characterized in that: The experiment is conducted by using a negative pressure demixing experimental device in a pump, which includes a petroleum CO2 supersaturated container, a reciprocating pump and a visualized piston pump. The petroleum CO2 supersaturated container can contain petroleum and carbon dioxide and mix them into an oil-gas mixture. The outlet of the petroleum CO2 supersaturated container is connected to the inlet of the piston pump, and the reciprocating rod of the reciprocating pump is connected to the piston rod in the piston pump; the piston pump is arranged in a thermostatic box that can simulate the formation temperature, and a pressure sensor and a temperature sensor are arranged on the side wall of the piston pump, and the reciprocating pump, the pressure sensor and the temperature sensor are all connected to a computer; the following steps are included: (1) Heating the piston pump: Place the piston pump in a thermostatic box in advance and set the temperature of the thermostatic box to the formation temperature; (2) Mixing oil and carbon dioxide: inject oil and carbon dioxide into the oil CO2 supersaturated container in sequence, pressurize and rotate the oil CO2 supersaturated container to fully mix the oil and carbon dioxide; (3) Extracting the oil-gas mixture: Connect the outlet of the petroleum CO2 supersaturated container to the inlet of the piston pump, start the reciprocating pump to extract the oil-gas mixture in the petroleum CO2 supersaturated container, and fill the piston pump with the oil-gas mixture; During the extraction of the oil-gas mixture, the temperature and pressure at different positions in the piston pump are detected in real time through the pressure sensor and the temperature sensor; the extraction is stopped, and the oil CO2 supersaturated container continues to rotate; During the extraction of the oil-gas mixture, observe the oil-gas mixture in the piston pump, and read the volumes of oil and gas through the scale on the outer wall of the piston pump, which are recorded as V1 and V2 respectively. The oil-gas ratio α is expressed as follows: ； The negative pressure demixing rate Di of crude oil under carbon dioxide flooding conditions is expressed as follows: ； Among them, V1 is the volume of gas in the piston pump; V0 is the total volume of the piston pump.

2. A negative pressure demixing experimental method in a pump for carbon dioxide flooding according to claim 1, characterized in that: The petroleum CO2 supersaturated container includes a drive box and a supersaturated cavity. The two sides of the supersaturated cavity are respectively connected to a driving shaft and a driven shaft. The driving shaft is connected to the output shaft of the drive box, and the driven shaft is arranged on a support seat. The drive box is used to drive the supersaturated cavity to rotate. The inlet of the supersaturated cavity is used to inject petroleum and carbon dioxide gas, and a valve is provided at the inlet. The outlet of the supersaturated cavity can be connected to the inlet of a piston pump through a high-pressure resistant pipeline, and the inlet and outlet of the high-pressure resistant pipeline are both provided with valves.

3. A negative pressure demixing experimental method in a pump for carbon dioxide flooding according to claim 2, characterized in that: The inlet of the supersaturated cavity can be connected to the oil pipeline and the carbon dioxide cylinder respectively, and the pressure in the supersaturated cavity is greater than 15MPa.

4. The negative pressure demixing experimental method in a pump for carbon dioxide flooding according to claim 1, characterized in that: The piston pump is placed upright, and a scale is provided in the height direction of its side wall. A plurality of pressure sensors and temperature sensors are arranged on the side wall of the piston pump from top to bottom, and the pressure sensors and temperature sensors are arranged at intervals; the inlet of the piston pump is arranged at the bottom, and the top of the piston head in the piston pump is connected to the piston rod.

5. The method for negative pressure demixing in a pump for carbon dioxide flooding according to claim 1, characterized in that: The reciprocating pump is a DC motor reciprocating pump.

6. A negative pressure demixing experimental method in a pump for carbon dioxide flooding according to any one of claims 1 to 5, characterized in that: Repeat steps (1)-(3) N times, observe the temperature and pressure change curves, and calculate the final cumulative demixing rate, that is, ； After the calculation is completed, a set of control experiments are carried out using crude oil that is not saturated with CO2. The reduction in the piston pump efficiency η under positive and negative pressures is calculated as follows: ； In, Q 实际 is the actual displacement of the piston pump, Q 理论 is the theoretical displacement of the piston pump.

7. The method for negative pressure demixing in a pump for carbon dioxide flooding according to claim 1, characterized in that: In step (2), the petroleum CO2 supersaturated container is pressurized to greater than 15 MPa and rotated for 30 minutes.

8. The method for negative pressure demixing in a pump for carbon dioxide flooding according to claim 1, characterized in that: In step (3), when the supersaturated chamber of the petroleum CO2 supersaturated container turns to a vertical state with the outlet facing downward, the supersaturated chamber stops rotating; a high-pressure pipeline is installed between the outlet of the supersaturated chamber and the inlet of the piston pump, and the valves at both ends of the high-pressure pipeline are opened to extract the oil-gas mixture.

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