An apparatus and method for determining the solubility of carbon dioxide in formation water

Abstract

The present application relates to a kind of device and method for determining the solubility of carbon dioxide in formation water.The device for determining the solubility of carbon dioxide in formation water includes: CO2 supply device, reaction device, sampler and nuclear magnetic resonance instrument;CO2 supply device is connected with reaction device, CO2 supply device is used to add CO2 to reaction device, and reaction device is used to prepare CO2-formation water solution of dissolved to reach equilibrium;Sampler is connected with reaction device, and nuclear magnetic resonance instrument is used to detect diffusion coefficient of CO2-formation water solution in sampler.The above-mentioned device can be used to determine the solubility of CO2 in geological storage under high temperature and high pressure conditions, with the advantages of high measurement accuracy, good accuracy, fast detection speed, continuous measurement of CO2 solubility in formation water under different temperature and pressure conditions, etc.

Description

Technical Field

[0001] This invention belongs to the field of detection technology, and in particular relates to an apparatus and method for determining the solubility of carbon dioxide in formation water. Background Technology

[0002] Currently, commonly used methods for determining the solubility of carbon dioxide in high-temperature, high-pressure water, both domestically and internationally, can be categorized into direct and indirect methods based on their characteristics. Based on differences in apparatus and principles, they can be classified into static methods, circulating methods, bubble point / dew point methods, flow methods, kinetic methods, in-situ spectroscopic methods, and laser Raman methods. Static method: Degassed liquid is added to a vacuum-sealed reactor. Gas is introduced into the reactor and stirred, maintaining a constant temperature (equilibrium temperature) for a period of time to allow the gas and liquid phases to reach equilibrium and obtain the equilibrium pressure. The basic principle of this method is to calculate the gas solubility by the difference in the number of moles of gas under different conditions. Circulating method: Solute gas is introduced into an equilibrium reactor containing the sample. A circulating pump circulates the gas and liquid phases at a constant temperature, obtaining the temperature and pressure at gas-liquid equilibrium. Chromatographic analysis of the gas phase at this equilibrium is then performed to calculate the gas solubility. Bubble point / dew point method: By increasing (decreasing) pressure, a certain amount of liquid and gas in the reactor are mixed and balanced. While maintaining a constant temperature, the pressure is gradually decreased (increased). The temperature and pressure at which the first bubble (droplet) forms are observed through a viewing window, thus obtaining the bubble point (dew point) of the liquid (gas) mixture in the reactor. Connecting the bubble points (dew points) of liquid (gas) mixtures with different proportions yields the liquidus (gasus) line. This allows for indirect determination of gas solubility. Flow method: Gas and liquid materials are simultaneously injected into a preheated mixer. At a determined outlet temperature, they enter the reactor to form balanced gas and liquid phases. The balanced gas and liquid phases are extracted from the upper and lower parts of the reactor, respectively, and condensed for sampling and analysis. Kinetic method: Based on the premise of complete physical absorption without any chemical reaction, and grounded in a kinetic model, the solubility of the gas is solved by regression analysis of instantaneous rate and instantaneous concentration. In-situ spectroscopy: After adjusting the temperature of the reaction vessel containing an appropriate amount of solute to the test temperature, CO2 is introduced, and a magnetic stirrer is used to ensure full contact between the solute and CO2. The solute will gradually dissolve under increasing pressure, forming a mixture with CO2. Under a defined pressure, the absorbance of the mixture is measured periodically until the absorbance remains constant, indicating that the solute and CO2 have reached dissolution equilibrium. Laser Raman spectroscopy: The peak height ratio of CO2 and pure water in the system is detected and calculated over a certain period. By comparing the measured values, it is determined whether the system has reached thermodynamic equilibrium.

[0003] However, these methods all have their own shortcomings in measuring solubility: the static method requires a lot of time to reach equilibrium; the cyclic method must ensure that the gas phase is not affected by condensation or overheating inside the equipment before chromatographic analysis in order to reduce errors; the bubble point and dew point method is difficult to operate and it is hard to determine whether the mixture in the reaction vessel has reached the bubble point (dew point); the flow method is difficult to measure continuously and accurately, and requires a compressor for transporting gas and a pump for transporting liquid, resulting in high experimental costs; the in-situ spectroscopic method has the advantages of high accuracy, simple sampling and maintaining system equilibrium, but it is not yet clear whether the density change of supercritical carbon dioxide will affect the absorption of the spectrum.

[0004] Therefore, establishing a testing method with high data accuracy, fast detection speed, and the ability to continuously measure the solubility of carbon dioxide in formation water under high temperature and high pressure is of great significance to the development of carbon dioxide sequestration technology. Summary of the Invention

[0005] In view of the problems existing in the prior art, the present invention provides an apparatus and method for determining the solubility of carbon dioxide in formation water. Using the above apparatus and method, the solubility characteristics of CO2 in geological sequestration can be determined under high temperature and high pressure conditions, and it has advantages such as high measurement accuracy, good precision, fast detection speed, and the ability to continuously measure the solubility of CO2 in formation water under different temperature and pressure conditions.

[0006] The technical solution of the present invention to solve the above-mentioned technical problems is as follows:

[0007] The present invention provides an apparatus for determining the solubility of carbon dioxide in formation water, comprising: a CO2 supply device, a reaction device, a sampler, and a nuclear magnetic resonance spectrometer;

[0008] The CO2 supply device is connected to the reaction device, which is used to add CO2 to the reaction device. The reaction device is used to prepare a CO2-formation aqueous solution that has reached equilibrium. The sampler is connected to the reaction device and is used to sample the CO2-formation aqueous solution of the reaction device. The nuclear magnetic resonance spectrometer is used to detect the diffusion coefficient of the CO2-formation aqueous solution in the sampler.

[0009] The beneficial effects of adopting the above technical solution include: the above-mentioned device provided by the present invention can be used to determine the solubility characteristics of CO2 in geological storage under high temperature and high pressure conditions, and has the advantages of high measurement accuracy, good accuracy, fast detection speed, and continuous measurement of the solubility of CO2 in formation water under different temperature and pressure conditions.

[0010] Furthermore, the CO2 supply device includes a CO2 cylinder and a high-pressure pump. The CO2 cylinder is connected to the high-pressure pump, and a valve is installed on the pipeline connecting the CO2 cylinder and the high-pressure pump. The high-pressure pump is connected to the reaction device, and a pressure sensor and a valve are installed on the pipeline connecting the high-pressure pump and the reaction device. The CO2 in the CO2 cylinder is delivered to the reaction device through the high-pressure pump.

[0011] The beneficial effects of adopting the above technical solution include: the CO2 supply device provides CO2 to the reaction device, facilitating the preparation of CO2-formation aqueous solution for subsequent diffusion coefficient detection; and the valve configuration facilitates the control of pipeline opening and closing to meet detection requirements.

[0012] Furthermore, the reaction apparatus includes a PVT reaction chamber, which is equipped with a vacuum pump, a circulation pump, a stirrer, and a constant temperature chamber. The vacuum pump is connected to the PVT reaction chamber and the circulation pump, and a valve is installed on the connecting pipeline. The circulation pump is also connected to a sampler, and a valve is installed on the connecting pipeline between the circulation pump and the sampler. The circulation pump circulates the liquid inside the PVT reaction chamber and the sampler. The stirrer is used to stir the liquid inside the PVT reaction chamber. The constant temperature chamber is located outside the PVT reaction chamber and is used to maintain a constant temperature for the PVT reaction chamber.

[0013] The beneficial effects of adopting the above technical solution include: the PVT reaction chamber is used to prepare CO2-formation aqueous solution, the vacuum pump facilitates evacuating the entire device before the detection begins, the circulation pump is used to circulate the sampler and the liquid in the PVT reaction chamber, and the constant temperature chamber is used to control the temperature.

[0014] Furthermore, the sampler is also equipped with a circulating heating device, which circulates and heats the liquid inside the sampler.

[0015] The beneficial effects of adopting the above technical solution include: by setting up a circulating pump and a circulating heating device, it is possible to continuously measure the solubility of CO2 in formation water under different temperature and pressure conditions.

[0016] Furthermore, valves are installed on the connecting pipelines of the CO2 supply device and the reaction device, and on the connecting pipelines of the reaction device and the sampler.

[0017] This invention provides a method for determining the solubility of carbon dioxide in formation water, comprising the following steps:

[0018] (1) Prepare a standard curve of solubility with respect to diffusion coefficient: Prepare a CO2-formation aqueous solution that has reached equilibrium at T℃ and P MPa. Use a nuclear magnetic resonance spectrometer to detect the diffusion coefficient of the CO2-formation aqueous solution and record a constant diffusion coefficient value. Based on the detected diffusion coefficient values ​​of CO2-formation aqueous solution with known solubility, plot a standard curve of solubility with respect to diffusion coefficient.

[0019] (2) Using formation water containing dissolved carbon dioxide as the sample to be tested, prepare a CO2-formation water solution that has reached equilibrium at T℃ and P MPa. Use a nuclear magnetic resonance spectrometer to detect its diffusion coefficient at different times. Calculate the solubility of CO2 in formation water based on the diffusion coefficient and the standard curve prepared in step (1).

[0020] The beneficial effects of adopting the above technical solution include: the method provided by the present invention innovatively applies nuclear magnetic resonance testing technology to the system, which significantly improves the measurement accuracy and detection speed, and provides a new approach for studying the solubility characteristics of CO2 in geological storage under high temperature and high pressure conditions.

[0021] Furthermore, the temperature range of T is 30-80℃; the range of P MPa is 3-30MPa.

[0022] The beneficial effects of adopting the above technical solutions include: covering the main temperature and pressure ranges for CO2 dissolution and sequestration in current formations.

[0023] Furthermore, it also includes steps for checking the airtightness of the device and evacuating the vacuum.

[0024] The benefits of adopting the above technical solution include: avoiding the impact of poor airtightness on the accuracy of test results.

[0025] Furthermore, the solubility of carbon dioxide in formation water was determined using the aforementioned apparatus.

[0026] The beneficial effects of adopting the above technical solution include: the device provided by the present invention for detecting the solubility of carbon dioxide in formation water has the advantages of high measurement accuracy, good precision, fast detection speed, and the ability to continuously measure the solubility of CO2 in formation water under different temperature and pressure conditions.

[0027] Furthermore, the determination of carbon dioxide solubility in formation water using the above-mentioned apparatus includes the following steps:

[0028] (1) To prepare a standard curve of solubility with respect to diffusion coefficient: Inject formation water into the reaction device, adjust the temperature to T℃, inject CO2 while maintaining the pressure P MPa, stir, circulate, and let stand until the dissolution in the solution reaches equilibrium, and obtain CO2-formation water solution; circulate the CO2-formation water solution in the reaction device to the sampler, use nuclear magnetic resonance to detect the diffusion coefficient of CO2-formation water solution, and record the constant diffusion coefficient value; by injecting CO2, detect and record the diffusion coefficient under known solubility, and draw a standard curve of solubility with respect to diffusion coefficient;

[0029] (2) Measurement of CO2 solubility in formation: Simulated formation water is injected into the reaction device, the temperature is adjusted to T℃, excess CO2 gas is injected, and the pressure is maintained at P MPa. Stirring, circulation, and standing are carried out until the dissolution in the solution reaches equilibrium, and CO2-formation water solution is obtained. The CO2-formation water solution in the reaction device is circulated to the sampler. The diffusion coefficient of CO2-formation water solution at different times is detected by nuclear magnetic resonance spectrometer. Based on the diffusion coefficient and the standard curve drawn in step (1), the solubility data of CO2 in formation water under T℃ and P MPa conditions are calculated.

[0030] The beneficial effects of adopting the above technical solution include: the method provided by the present invention has the advantages of high measurement accuracy, good precision, fast detection speed, and the ability to continuously measure the solubility of CO2 in formation water under different temperature and pressure conditions. Attached Figure Description

[0031] Figure 1 The schematic diagram of the device for measuring the solubility of CO2 in formation water under high temperature and high pressure provided by the present invention is shown below, with each component represented by a number as follows:

[0032] 1. CO2 cylinder; 2. High-pressure pump; 3. Constant temperature chamber; 4. PVT reaction chamber; 5. Stirrer; 6. Vacuum pump; 7. Circulation pump; 8. Sampler; 9. Nuclear magnetic resonance spectrometer; 10. Circulation heating device; 11. Main unit of the instrument; V1 to V6 are valves one through six respectively; P is a pressure sensor.

[0033] Figure 2 The flowchart of the method for determining the solubility of carbon dioxide in formation water provided by the present invention is shown.

[0034] Figure 3 A standard curve plotted for the example.

[0035] Figure 4 This is a comparison chart of solubility calculated using a standard curve and known solubility. Detailed Implementation

[0036] The principles and features of the present invention are described below with reference to the accompanying drawings. The examples given are only for explaining the present invention and are not intended to limit the scope of the present invention.

[0037] like Figure 1As shown, this invention provides an apparatus for determining the solubility of carbon dioxide in formation water, comprising: a CO2 supply device, a reaction device, a sampler 8, and a nuclear magnetic resonance (NMR) spectrometer 9. The CO2 supply device is connected to the reaction device and is used to add CO2 to the reaction device, which is used to prepare a CO2-formation water solution at dissolution equilibrium. The sampler 8 is connected to the reaction device, and the NMR spectrometer 9 is used to detect the diffusion coefficient of the CO2-formation water solution in the sampler 8. The NMR spectrometer 9 may include a main unit 11, an electronic control cabinet, and a high-temperature, high-pressure clamp power distribution box. The NMR spectrometer 9 can provide commonly used pulse sequences and data processing functions. The NMR spectrometer 9 used in this embodiment is manufactured by Bruker and is a Minispec MQ20 ​​model.

[0038] The CO2 supply device includes a CO2 cylinder 1 and a high-pressure pump 2. The CO2 cylinder 1 is connected to the high-pressure pump 2. The CO2 cylinder 1 can be a high-pressure CO2 cylinder. A valve is installed on the pipeline connecting the CO2 cylinder 1 and the high-pressure pump 2. The high-pressure pump 2 is connected to the reaction device. A pressure sensor P is installed on the pipeline connecting the high-pressure pump 2 and the reaction device to detect pressure. CO2 in the CO2 cylinder 1 is delivered to the reaction device through the high-pressure pump 2. The CO2 supply device also includes valves: a first valve V1 is installed on the pipeline between the CO2 cylinder 1 and the high-pressure pump 2; a second valve V2 is installed on the pipeline between the high-pressure pump 2 and the pressure sensor P; and a third valve V3 is installed on the pipeline between the pressure sensor P and the reaction device.

[0039] The reaction apparatus includes a PVT reaction chamber 4, which is equipped with a vacuum pump 6, a circulation pump 7, a stirrer 5, and a constant temperature chamber 3. The circulation pump 7 can be a liquid-phase circulation pump. The PVT reaction chamber 4 is connected to a high-pressure pump 2, and the vacuum pump 6 is connected to both the PVT reaction chamber 4 and the circulation pump 7. A third valve V3 is installed on the pipeline between the pressure sensor P and the PVT reaction chamber 4, and a fourth valve V4 is installed on the pipeline between the PVT reaction chamber 4 and the vacuum pump 6. Both the PVT reaction chamber 4 and the circulation pump 7 are connected to a sampler 8. A fifth valve V5 is installed on the pipeline between the PVT reaction chamber 4 and the sampler 8, and a sixth valve V6 is installed on the pipeline between the circulation pump 7 and the sampler 8. The circulation pump 7 circulates the liquid inside the PVT reaction chamber 4 and the sampler 8. The stirrer 5 is used to stir the liquid inside the PVT reaction chamber 4. The constant temperature chamber 3 is located outside the PVT reaction chamber 4 and is used to maintain a constant temperature for the PVT reaction chamber 4.

[0040] The sampler 8 is made of zirconium dioxide and is placed inside the nuclear magnetic resonance spectrometer 9. One end of the sampler 8 is connected to the PVT reaction chamber 4, and the other end is connected to the circulation pump 7. The sampler 8 is also equipped with a circulating heating device 10, which circulates and heats the liquid inside the sampler 8. The circulating heating device 10 can consist of a hose and a controller, with silicone oil inside the hose.

[0041] This invention provides a method for determining the solubility of carbon dioxide in formation water, comprising the following steps:

[0042] (1) Prepare a standard curve of solubility with respect to diffusion coefficient: Prepare a CO2-formation aqueous solution that has reached equilibrium at T℃ and P MPa. Detect the diffusion coefficient of the CO2-formation aqueous solution using a nuclear magnetic resonance spectrometer and record a constant diffusion coefficient value. Based on the detected diffusion coefficient values ​​of CO2-formation aqueous solutions with different solubilities, plot a standard curve of solubility with respect to diffusion coefficient.

[0043] (2) Using formation water containing dissolved carbon dioxide as the sample to be tested, prepare a CO2-formation water solution that has reached equilibrium at T℃ and P MPa. Use a nuclear magnetic resonance spectrometer 9 to detect its diffusion coefficient at different times. Calculate the solubility of CO2 in formation water based on the diffusion coefficient and the standard curve prepared in step (1).

[0044] by Figure 1 Taking the apparatus shown as an example, the method for determining the solubility of carbon dioxide in formation water using the above apparatus may include the following steps:

[0045] (1) Pretreatment of the device: Nitrogen gas is injected into the pipeline of the reaction device to check the airtightness of the device, and then the pipeline connected to the reaction device is evacuated.

[0046] (2) Plotting the standard diffusion coefficient curve: Inject formation water into the PVT reaction vessel 4, turn on the constant temperature chamber 3 to adjust the temperature to T℃, use the high-pressure pump 2 to inject high-pressure CO2 while maintaining the pressure P MPa, turn on the stirrer 5 and the circulation pump 7 (which can be a liquid phase circulation pump) until the pressure fluctuation is small, let it stand for a period of time, at which point the dissolution in the solution reaches equilibrium, use the circulation pump 7 to circulate the CO2-formation water solution in the PVT reaction vessel 4 to the sampler 8, use the nuclear magnetic resonance spectrometer 9 to detect the diffusion coefficient of the CO2-formation water solution, and record the constant diffusion coefficient value; by injecting CO2, detect and record the diffusion coefficient value under known solubility, and plot the standard diffusion coefficient curve. The range of T℃ is 30-80℃; the range of P MPa is 3-30MPa; the range of CO2 solubility is 10-35m³ / m³;

[0047] (3) Measurement of CO2 solubility data in formation: Inject simulated formation water into PVT reaction chamber 4, turn on constant temperature chamber 3 to adjust temperature to T℃, use high pressure pump 2 to inject excess CO2 gas, and maintain pressure P MPa at the same time, turn on stirrer 5 and circulation pump 7 (can be liquid phase circulation pump) until the pressure fluctuation is small, let stand for a period of time, at which time the dissolution in the solution reaches equilibrium, use circulation pump 7 to circulate CO2-formation water solution in PVT reaction chamber 4 to sampler 8, use nuclear magnetic resonance spectrometer 9 to detect the diffusion coefficient of CO2-formation water solution at different times, substitute the obtained diffusion coefficient into the standard curve drawn in step (2), and calculate the solubility data of CO2 in formation water under T℃ and P MPa conditions; the T℃ in step (3) needs to be the same as the T℃ in step (2); the range of P MPa is 3-30 MPa.

[0048] Specifically, in step (1) of the present invention, injecting nitrogen into the pipeline of the reaction device to check the airtightness of the device may include the following steps: replacing CO2 cylinder 1 with N2 cylinder, opening the first valve V1 to connect N2 cylinder and high pressure pump 2, allowing nitrogen to enter the high pressure pump 2 and then closing the first valve V1, then opening the second valve V2 and the third valve V3 to connect the high pressure pump 2 and the pipeline of the reaction device, using the high pressure pump 2 to pressurize nitrogen into the pipeline of the reaction device, and judging the airtightness of the device by the pressure change of pressure sensor P;

[0049] The subsequent vacuuming of the pipeline may include the following steps: closing the first valve V1 and the second valve V2 to isolate CO2 cylinder 1 and high-pressure pump 2; opening the third valve V3, the fourth valve V4, the fifth valve V5, and the sixth valve V6 to connect the pipeline between vacuum pump 6 and PVT reaction cylinder 4, sampler 8, and circulation pump 7; using vacuum pump 6 to create a vacuum; when the pressure on pressure sensor P shows zero, adjusting the fourth valve V4 to isolate the pipeline between vacuum pump 6 and PVT reaction cylinder 4, and the pipeline between vacuum pump 6 and circulation pump 7; and finally turning off vacuum pump 6.

[0050] Specifically, in step (3) of the present invention, the detection of the diffusion coefficient of CO2-formation aqueous solution using nuclear magnetic resonance spectrometer 9 may include the following steps: after the pressure sensor P reading stabilizes, open the fourth valve V4, the fifth valve V5, and the sixth valve V6 to connect the pipeline between the PVT reaction cylinder 4 and the sampler 8, start the circulation pump 7, and after the pressure sensor P reading stabilizes, close the fifth valve V5 and the sixth valve V6 to isolate the pipeline between the PVT reaction cylinder 4 and the sampler 8, and use nuclear magnetic resonance spectrometer 9 to detect the diffusion coefficient of the solution.

[0051] The present invention will be further described below with reference to specific embodiments, but the scope of protection of the present invention is not limited thereto. Example

[0052] The experimental apparatus used in this embodiment for measuring the solubility of CO2 in formation water under high temperature and high pressure is as follows: Figure 1 As shown, the device includes: a nuclear magnetic resonance spectrometer 9, a CO2 supply device, a PVT reaction chamber 4, a constant temperature chamber 3, a vacuum pump 6, a circulating pump 7, a sampler 8, a circulating heating device 10, and a pressure sensor P.

[0053] The nuclear magnetic resonance spectrometer 9 includes a main unit 11, an electronic control cabinet, and a high-temperature, high-pressure clamp power distribution box. The nuclear magnetic resonance spectrometer 9 can provide commonly used pulse sequences and data processing functions. The CO2 supply device includes a CO2 cylinder 1 and a high-pressure pump 2, which is connected to the CO2 cylinder 1. The PVT reaction chamber 4 is placed in a constant temperature chamber 3 and connected to the high-pressure pump 2. It is equipped with a stirrer 5, and a liquid-phase circulation pump 7 is connected below the device. The vacuum pump 6 is connected to the PVT reaction vessel 4. The sampler 8 is made of zirconium dioxide and is connected to the PVT reaction chamber 4 and the circulation pump 7. The sampler 8 is placed inside the nuclear magnetic resonance spectrometer 9. A circulating heating device 10 is used to circulate heat the sampler 8. The circulating heating device 10 consists of a hose and a controller, with silicone oil inside the hose. The pressure sensor P is connected to the high-pressure pump 2, which is connected to the PVT reaction chamber 4. CO2 cylinder 1 is connected to high-pressure pump 2 via first valve V1. High-pressure pump 2 is connected to pressure sensor P via second valve V2. Pressure sensor P is connected to PVT reaction cylinder 4 via third valve V3. A fourth valve V4 is provided between PVT reaction cylinder 4 and vacuum pump 6. A fifth valve V5 is provided between PVT reaction cylinder 4 and sampler 8. A sixth valve V6 is provided between circulation pump 7 and sampler 8.

[0054] like Figure 2 As shown, the method for determining the solubility of carbon dioxide in formation water using the above-mentioned apparatus includes the following steps:

[0055] (1) Check the airtightness of the device: Replace CO2 cylinder 1 with high-pressure N2 cylinder, open the high-pressure valve (first valve V1), add a certain amount of N2 through the high-pressure N2 cylinder, close the first valve V1, and open the second valve V2 and the third valve V3 to connect the pipeline between the high-pressure pump 2 and the PVT reaction cylinder 4. Then pressurize to about 30MPa through the high-pressure pump 2, let it stand for 3-4 hours, and check the airtightness of the device according to the pressure change.

[0056] (2) Vacuuming: Open the fourth valve V4, turn on the vacuum pump 6, evacuate all pipelines in the device, and turn off the vacuum pump 6 when the pressure on the pressure sensor P is zero.

[0057] (3) Inject formation water into the PVT reaction chamber 4, turn on the constant temperature chamber 3 to adjust the temperature to 40℃, turn on the high-pressure CO2 cylinder, use the high-pressure pump 2 to inject high-pressure CO2 while maintaining the pressure at 3 MPa, then turn off the high-pressure CO2 cylinder, turn on the stirrer 5 until the pressure fluctuation is small, let it stand for 2 hours, use the liquid phase circulation pump to circulate the CO2-formation water solution in the PVT reaction chamber to the sampler 8 for 15 minutes, turn on the circulation heating device 10, and after the temperature and pressure stabilize, let it stand for 1 hour, use the nuclear magnetic resonance spectrometer 9 to detect the diffusion coefficient of the CO2-formation water solution, and record the constant diffusion coefficient value; by injecting CO2, detect and record the diffusion coefficient values ​​at 3 MPa, 7 MPa, and 20 MPa under known solubility conditions, and plot the standard diffusion coefficient curve (e.g. Figure 3 (As shown).

[0058] (4) Simulated formation water was injected into the PVT reaction chamber 4. The temperature was adjusted to 40℃ by turning on the constant temperature chamber 3. Excess CO2 gas was injected using the high-pressure pump 2, while maintaining a pressure of 5 MPa. The stirrer 5 and the liquid phase circulation pump were turned on until the pressure fluctuation was small. After standing for a period of time, the dissolution in the solution reached equilibrium. The CO2-formation water solution in the PVT reaction chamber 4 was circulated to the sampler using the circulation pump 7. The diffusion coefficient of the CO2-formation water solution was detected using the nuclear magnetic resonance spectrometer 9. The diffusion coefficient at 5 MPa was measured to be 2.88 x 10⁻⁶. -9 m² / s. Substituting the obtained diffusion coefficient into the standard curve plotted in step (3), the solubility data of CO2 in formation water at 5 MPa under 40℃ conditions were calculated. The experimental pressure was adjusted to 10 MPa and 15 MPa, and the above steps were repeated. The diffusion coefficients at 10 MPa and 15 MPa were measured to be 2.82 x 10⁻⁶ m² / s. -9 m² / s and 2.81x10 -9 The solubility data of CO2 in formation water were calculated using m² / s at temperatures of 40℃ and pressures of 10MPa and 15MPa (e.g., m² / s). Figure 4 (As shown).

[0059] Figure 4 It can be seen that the calculated solubility is close to the known solubility value, indicating that the detection method provided by this invention is accurate.

Claims

1. A method of determining the solubility of carbon dioxide in formation water, characterized by, The application discloses a device for measuring the solubility of carbon dioxide in formation water, and belongs to the technical field of carbon dioxide storage. The CO2 supply device is connected with the reaction device, and is used for adding CO2 into the reaction device; the reaction device is used for preparing a CO2-formation water solution in which CO2 is dissolved to reach equilibrium; the sampler (8) is connected with the reaction device, and is used for sampling the CO2-formation water solution in the reaction device; and the nuclear magnetic resonance instrument (9) is used for detecting the diffusion coefficient of the CO2-formation water solution in the sampler (8). The device comprises the following steps: (1) preparing a standard curve of the solubility with respect to the diffusion coefficient: preparing a CO2-formation water solution in which CO2 is dissolved to reach equilibrium at T ℃ and P MPa, detecting the diffusion coefficient of the CO2-formation water solution by using the nuclear magnetic resonance instrument (9), and recording the constant diffusion coefficient value; and drawing the standard curve of the solubility with respect to the diffusion coefficient according to the detected diffusion coefficients of the CO2-formation water solutions with different solubilities; (2) taking the formation water in which CO2 is dissolved as a sample to be detected, preparing a CO2-formation water solution in which CO2 is dissolved to reach equilibrium at T ℃ and P MPa, detecting the diffusion coefficient of the CO2-formation water solution at different times by using the nuclear magnetic resonance instrument (9), and calculating the solubility of CO2 in the formation water according to the diffusion coefficient and the standard curve prepared in the step (1).

2. The method of claim 1, wherein, The CO2 supply device comprises a CO2 cylinder (1) and a high-pressure pump (2), the CO2 cylinder (1) is connected with the high-pressure pump (2), and a valve is arranged on a pipeline connected between the CO2 cylinder (1) and the high-pressure pump (2); the high-pressure pump (2) is connected with the reaction device, and a pressure sensor and a valve are arranged on a pipeline connected between the high-pressure pump (2) and the reaction device, and CO2 in the CO2 cylinder (1) is delivered to the reaction device through the high-pressure pump (2).

3. The method of claim 1, wherein, The reaction device comprises a PVT reaction cylinder (4), and the PVT reaction cylinder (4) is provided with a vacuum pump (6), a circulating pump (7), a stirrer (5) and a constant-temperature box (3); the vacuum pump (6) is connected with the PVT reaction cylinder (4) and the circulating pump (7), and a valve is arranged on a pipeline connected therebetween; the circulating pump (7) is further connected with the sampler (8), and a valve is arranged on a pipeline connected between the circulating pump (7) and the sampler (8); the internal liquid of the PVT reaction cylinder (4) and the sampler (8) is circulated through the circulating pump (7); the stirrer (5) is used for stirring the liquid in the PVT reaction cylinder (4); and the constant-temperature box (3) is located outside the PVT reaction cylinder (4) and is used for keeping the PVT reaction cylinder (4) at a constant temperature.

4. The method of claim 1, wherein, The sampler (8) is placed in the nuclear magnetic resonance instrument (9), and the sampler (8) is further provided with a circulating heating device for cyclically heating the liquid in the sampler (8).

5. The method of claim 1, wherein, Valves are arranged on the pipelines connected between the CO2 supply device and the reaction device and between the reaction device and the sampler (8).

6. The method of claim 1, wherein, The range of T ℃ is 30-80 ℃, and the range of P MPa is 3-30 MPa.

7. The method of claim 1, wherein, The device further comprises steps of checking the air tightness and vacuumizing.

8. The method of claim 1, wherein, The device comprises the following steps: (1) Standard curve of solubility vs. diffusion coefficient is made: inject formation water into the reaction device, adjust the temperature to T ℃, inject CO2 while maintaining the pressure P MPa, stir, circulate, and stand until the dissolution in the solution reaches equilibrium, to obtain a CO2-formation water solution; circulate the CO2-formation water solution in the reaction device to the sampler (8), use the nuclear magnetic resonance instrument (9) to detect the diffusion coefficient of the CO2-formation water solution, and record the constant diffusion coefficient value; through several times of adding CO2, the diffusion coefficient under the known solubility is detected and recorded, and the standard curve of solubility vs. diffusion coefficient is drawn; (2) Measure the solubility of CO2 in the formation: inject simulated formation water into the reaction device, adjust the temperature to T ℃, inject excess CO2 gas while maintaining the pressure P MPa, stir, circulate, and stand until the dissolution in the solution reaches equilibrium, to obtain a CO2-formation water solution; circulate the CO2-formation water solution in the reaction device to the sampler (8), use the nuclear magnetic resonance instrument (9) to detect the diffusion coefficient of the CO2-formation water solution at different times, and calculate the solubility data of CO2 in the formation water under the conditions of T ℃ and P MPa according to the diffusion coefficient and the standard curve drawn in step (1).

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