Method and device for determining thermal stability of crude oil under pressure constraint

Abstract

The application discloses a method and device for determining thermal stability of crude oil under pressure constraint, which comprises the following steps: loading equal amounts of the same kind of crude oil samples into several capillary quartz tubes; then, applying different preset pressures to the capillary quartz tubes; synchronously heating the capillary quartz tubes with different pressures to a target temperature, and then continuing constant temperature heating for a period of time; monitoring the change of the crude oil in the capillary quartz tubes during the constant temperature heating; and finally determining the thermal stability of the crude oil under pressure constraint by comparing the change of the crude oil in the capillary quartz tubes. Through the above method, the changes of the form and fluorescence characteristics of the cracking products of the crude oil under different pressure constraints can be compared in real time, and then the real influence of the pressure on the cracking gas generation of the crude oil during the temperature rising process can be accurately revealed according to the information, and the thermal stability of the crude oil under the pressure constraint can be accurately determined. The method can bear a large pressure test range, and is simple and easy to operate, time-saving and labor-saving, and low in cost.

Description

Technical Field

[0001] This invention relates to the field of oil and gas geochemistry, and in particular to a method and apparatus for determining the thermal stability of crude oil under pressure constraints. Background Technology

[0002] Determining the lower limit of oil retention depth under geological conditions is a crucial scientific issue that urgently needs to be addressed in deep exploration and development, and it is of great significance for the exploration and deployment of deep oil and gas. The thermal stability of crude oil, to some extent, determines this lower limit. Therefore, revealing the cracking mechanism of crude oil and exploring its thermal stability and influencing factors are currently a research hotspot and challenge in deep oil and gas exploration.

[0003] The classic Tissot hydrocarbon generation model posits that hydrocarbon generation begins when organic matter has a vitrinite reflectance (Ro) of 0.5–0.6%, peaking at Ro of 1.0%. 15+ Cracks begin to occur when Ro is greater than 1.3% and all C 15+ The hydrocarbons have disappeared; at Ro 2.0%, only CH4 remains, and at Ro 4.0%, CH4 is completely broken down, initiating metamorphism. However, recent advances in related research and exploration practices, particularly the discovery of deep liquid hydrocarbons, have questioned the applicability of the classic Tissot model under deep geological conditions. Researchers have conducted detailed geochemical studies on wells at depths of 7544m and 9600m, finding that liquid hydrocarbons still exist at temperatures exceeding 300℃ and Ro of 3.0%. At Ro 2.0–5.0%, C… 15+ Hydrocarbons can still maintain a moderate to high concentration; trace amounts of C can still be detected when Ro is 7.0–8.0%. 15+ Hydrocarbons. Meanwhile, increasing exploration practices also show that oil and gas reservoirs can still be discovered in deep strata beyond the traditional optimal temperature range.

[0004] Traditional hydrocarbon generation theory posits that the thermal evolution of organic matter is primarily influenced by the synergistic effects of temperature and time. In recent years, numerous studies have shown that environmental factors, particularly pressure conditions, have a greater-than-expected impact on the stability of liquid hydrocarbons. However, petroleum geologists have long disagreed on whether pressure affects the thermal stability of crude oil and the direction of this effect. Some studies suggest that pressure has no significant role in hydrocarbon formation. Nevertheless, with further research, more and more scholars have come to recognize that pressure can influence the thermal stability of crude oil. Some researchers have found in experiments that increased pressure promotes hydrocarbon pyrolysis. However, others point out that hydrocarbon generation is a process of increasing volume, and increased pressure should hinder the process. To verify this hypothesis, researchers conducted high-pressure autoclave thermal simulation experiments on lignite samples, finding that the hydrocarbon formation process does indeed slow down with increasing pressure. Furthermore, in comparative simulation experiments of the effect of pressure on crude oil cracking, researchers also found that pressure has an inhibitory or delaying effect on crude oil cracking; under 20 MPa pressure, the initial cracking time of crude oil is delayed, resulting in a higher cracking temperature threshold. Moreover, pressure may inhibit the growth of heavy hydrocarbon C6O6. 2-5 Secondary cracking occurs. Other researchers believe that increased pressure reduces the concentration of free radicals in the cracking reaction system, thereby slowing down the rate of free radical chain reactions. Simulation experiments have confirmed that high pressure can delay the oil generation period, and abnormally high pressure can extend the lower limit of petroleum generation to 9000m. Conversely, some scholars have proposed that the effect of pressure on hydrocarbon formation is not constant but related to external geological conditions. Researchers have studied the cracking rate of alkanes and cycloalkanes with pressure. The results showed that when the pressure is less than 40 MPa, the cracking rate of alkanes increases with increasing pressure, while when the pressure is greater than 40 MPa, increasing pressure inhibits the cracking of alkanes. Other researchers have indicated that the effect of pressure is related to the heating rate and the stage of maturation. Under slow heating conditions, pressure has an inhibitory effect on oil cracking and gas generation; while under rapid heating conditions, the effect of pressure on oil cracking and gas generation is not significant.

[0005] In summary, current research by scholars both domestically and internationally on the cracking mechanism and thermal stability of crude oil under pressure constraints lacks systematic analysis, and opinions are not unified. One major reason is that current mainstream experimental methods for crude oil thermal simulation, including gold tube thermal simulation technology, have limited pressure tolerance and cannot be coupled with techniques such as fluorescence spectroscopy, laser Raman spectroscopy, and micro-infrared spectroscopy. Furthermore, this simulation technology suffers from drawbacks such as complex operating procedures, long processing times, and high experimental costs.

[0006] In view of this, there is an urgent need to provide a crude oil cracking heat simulation experimental method that can withstand a wide pressure range, is simple and easy to operate, saves time and effort, is low in cost, and can be combined with technologies such as fluorescence spectroscopy, laser Raman, and micro-infrared to achieve a systematic study of the essential laws of crude oil thermal evolution under pressure constraints. Summary of the Invention

[0007] The purpose of this invention is to provide a method for analyzing the thermal stability of crude oil based on high-pressure quartz tube artificial inclusion technology. This method combines high-pressure quartz tube artificial inclusions with fluorescence spectroscopy to compare in real-time changes in the morphology and fluorescence characteristics of crude oil cracking products under different pressure constraints, thereby enabling in-depth exploration of the thermal stability of crude oil under pressure constraints. Compared with gold tube thermal simulation technology, quartz tube artificial inclusion technology has the following advantages: 1. Strong pressure resistance, capable of withstanding pressures up to 200 MPa; 2. Convenient experimental operation and lower cost; 3. Can be combined with fluorescence spectroscopy, laser Raman spectroscopy, and micro-infrared spectroscopy for real-time in-situ observation, helping to reveal the reaction mechanism of pressure on the cracking and generation of crude oil during heating.

[0008] To achieve the above-mentioned objectives, the present invention provides the following technical solution:

[0009] A method for determining the thermal stability of crude oil under pressure constraint, the method comprising:

[0010] Equal amounts of the same type of crude oil sample were loaded into several capillary quartz tubes.

[0011] Different preset pressures are applied to several capillary quartz tubes;

[0012] After simultaneously heating several capillary quartz tubes under different pressures to the target temperature, they are then kept at a constant temperature for a period of time.

[0013] Monitor the changes in crude oil in several capillary quartz tubes during constant temperature heating;

[0014] By comparing the changes in crude oil in each capillary quartz tube, the thermal stability of crude oil under pressure constraint is determined.

[0015] As a further improvement of the present invention, when a preset pressure is applied to each capillary quartz tube, the pressure difference between each capillary quartz tube is controlled to be ≥20MPa.

[0016] As a further improvement of the present invention, applying different preset pressures to the plurality of capillary quartz tubes specifically involves: applying high pressure to one of the capillary quartz tubes and applying low pressure to another capillary quartz tube.

[0017] The pressure difference between the high pressure and the low pressure is ≥20MPa, and 10MPa≤low pressure<high pressure≤200MPa.

[0018] As a further improvement of the present invention, the monitoring of changes in crude oil in several capillary quartz tubes during the isothermal heating process, and the comparison of changes in crude oil in each capillary quartz tube to determine the thermal stability of crude oil under pressure constraint, includes:

[0019] In situ observation of the morphological changes of crude oil in each capillary quartz tube during the isothermal heating process;

[0020] By comparing the morphological changes of crude oil in each capillary quartz tube, the thermal stability of crude oil under pressure constraint is determined.

[0021] As a further improvement of the present invention, the monitoring of changes in crude oil in several capillary quartz tubes during the isothermal heating process, and the comparison of changes in crude oil in each capillary quartz tube to determine the thermal stability of crude oil under pressure constraint, includes:

[0022] Real-time monitoring of the changes in fluorescence color, main peak wavelength λmax, and / or fluorescence intensity of the cracking products of crude oil in each capillary quartz tube during isothermal heating;

[0023] The thermal stability of crude oil under pressure constraint is determined by comparing the changes in fluorescence color, main peak wavelength λmax, and / or fluorescence intensity of crude oil cracking products in each capillary quartz tube.

[0024] As a further improvement of the present invention, the monitoring of changes in crude oil in several capillary quartz tubes during the isothermal heating process, and the comparison of changes in crude oil in each capillary quartz tube to determine the thermal stability of crude oil under pressure constraint, includes:

[0025] Real-time monitoring of the changes in the red-green quotient of cracking products of crude oil in each capillary quartz tube during constant temperature heating;

[0026] The thermal stability of crude oil under pressure constraint is determined by comparing the changes in the red-green quotient of crude oil cracking products in each capillary quartz tube.

[0027] The present invention also provides a device for determining the thermal stability of crude oil under pressure constraint, the device comprising:

[0028] Several capillary quartz tubes are used to hold equal amounts of the same type of crude oil samples.

[0029] The pressurization device is used to apply different preset pressures to several capillary quartz tubes containing crude oil samples.

[0030] The heating device is used to simultaneously heat several capillary quartz tubes with different pressures to the target temperature and then continue to heat them at a constant temperature for a period of time.

[0031] The monitoring device is used to monitor the changes in crude oil in several capillary quartz tubes under different preset pressures during the constant temperature heating process.

[0032] The determination device is used to compare the changes in crude oil in each capillary quartz tube and determine the thermal stability of crude oil under pressure constraints.

[0033] As a further improvement of the present invention, when the pressurizing device is used to apply different preset pressures to several capillary quartz tubes containing crude oil samples, the pressure difference between each capillary quartz tube is controlled to be ≥20MPa.

[0034] As a further improvement of the present invention, the plurality of capillary quartz tubes specifically comprises: two capillary quartz tubes;

[0035] The pressurizing device is used to apply high pressure to one of the capillary quartz tubes and low pressure to the other capillary quartz tube.

[0036] The pressure difference between the high pressure and the low pressure is ≥20MPa, and 10MPa≤low pressure<high pressure≤200MPa.

[0037] As a further improvement of the present invention, the monitoring device is used to monitor the changes in crude oil in several capillary quartz tubes under different preset pressures during constant temperature heating, and the determination device is used to compare the changes in crude oil in each capillary quartz tube to determine the thermal stability of crude oil under pressure constraints, including:

[0038] The monitoring device is used to observe in situ the morphological changes of crude oil in each capillary quartz tube during the isothermal heating process.

[0039] The determination device is used to compare the morphological changes of crude oil in each capillary quartz tube and determine the thermal stability of crude oil under pressure constraints.

[0040] As a further improvement of the present invention, the monitoring device is used to monitor the changes in crude oil in several capillary quartz tubes under different preset pressures during constant temperature heating, and the determination device is used to compare the changes in crude oil in each capillary quartz tube to determine the thermal stability of crude oil under pressure constraints, including:

[0041] The monitoring device is used to monitor in real time the changes in fluorescence color, main peak wavelength λmax, fluorescence intensity and / or red-green quotient of the cracking products of crude oil in each capillary quartz tube during isothermal heating.

[0042] The determination device is used to compare the changes in fluorescence color, main peak wavelength λmax, fluorescence intensity and / or red-green quotient of crude oil cracking products in each capillary quartz tube to determine the thermal stability of crude oil under pressure constraint.

[0043] The beneficial effects of this invention are:

[0044] The present invention provides a method and apparatus for determining the thermal stability of crude oil under pressure constraint. This involves loading equal amounts of the same type of crude oil sample into several capillary quartz tubes; applying different preset pressures to the capillary quartz tubes; simultaneously heating the capillary quartz tubes with different pressures to a target temperature and then continuing to heat at a constant temperature for a period of time; monitoring the changes in the crude oil in the capillary quartz tubes under different preset pressures during the constant temperature heating process; comparing the changes in the crude oil in each capillary quartz tube, and finally determining the thermal stability of the crude oil under pressure constraint. Through this method, the morphology and fluorescence characteristics of crude oil cracking products can be compared in real time under different pressure constraints. Based on this information, the true impact of pressure on the cracking and gas generation process of crude oil during heating can be accurately revealed, thus achieving an accurate determination of the thermal stability of crude oil under pressure constraint.

[0045] The method and apparatus for determining the thermal stability of crude oil under pressure constraints provided by this invention can withstand a wide pressure range, are simple and easy to operate, save time and effort, and are low in cost. They can provide reliable conclusions on the essential laws of the thermal evolution of crude oil under pressure constraints.

[0046] Other features and advantages of the invention will be set forth in the description which follows, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures pointed out in the description, claims and drawings. Attached Figure Description

[0047] Figure 1 This is a flowchart illustrating the method for determining the thermal stability of crude oil under pressure constraints according to the present invention.

[0048] Figure 2 This is a schematic diagram of the overall structure of the device for determining the thermal stability of crude oil under pressure constraint according to the present invention.

[0049] Figures 3a-3f The images show the morphological comparison of crude oil after being heated at 430℃ for 30 min, 3 h, 5 h, 7 h, 10 h and 12 h under pressures of 30 MPa and 100 MPa, respectively, in the embodiments of the present invention.

[0050] Figures 4a-4f The image shows a comparison of the fluorescence colors of the cracking products after crude oil was heated at 430℃ for 30 min, 3 h, 5 h, 7 h, 10 h and 12 h under pressures of 30 MPa and 100 MPa, respectively, in an embodiment of the present invention.

[0051] Figure 5 This is a comparison of the fluorescence main peak wavelength λmax of the cracking products of crude oil under pressures of 30MPa and 100MPa during isothermal heating at 430℃ in an embodiment of the present invention.

[0052] Figure 6 This is a graph showing the relationship between the red-green quotient of the cracking products and the heating time during the isothermal heating of crude oil at 430℃ under pressures of 30MPa and 100MPa in an embodiment of the present invention. Detailed Implementation

[0053] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0054] The method for determining the thermal stability of crude oil under pressure constraint provided by this invention, such as... Figure 1 As shown, the main steps include:

[0055] Equal amounts of the same type of crude oil sample were loaded into several capillary quartz tubes.

[0056] Different preset pressures were applied to several capillary quartz tubes that contained crude oil samples.

[0057] After simultaneously heating several capillary quartz tubes with different pressures to the target temperature, continue heating at a constant temperature for a period of time.

[0058] Monitor the changes in crude oil in several capillary quartz tubes under different preset pressures during constant temperature heating;

[0059] By comparing the changes in crude oil in each capillary quartz tube, the thermal stability of crude oil under pressure constraint is determined based on the comparison results.

[0060] Specifically, the experiment first involved selecting a crude oil sample, dividing it into at least two equal portions, and then placing each portion into a separate capillary quartz tube. This was for subsequent observation and comparative analysis of the crude oil cracking process within the capillary quartz tubes under different pressure conditions. The two quartz tubes used were fused silica capillary tubes manufactured by Polymicro Technologies, model TSP300665, with an inner diameter of 300 μm and a length of 15 cm. These tubes possess strong pressure resistance, capable of withstanding pressures exceeding 200 MPa, and are also heat-resistant (773 K ≈ 500℃ or higher). Due to the small size of the capillary quartz tube cavity, pressure and temperature control are very easy. The sample loading process included the following steps: first, the capillary quartz tube was fixedly connected to a pressure pump used to adjust the internal pressure of the capillary tube. (Refer to...) Figure 2After understanding the process, crude oil samples were placed into two quartz tubes, and mercury was sealed at both ends of the tubes. Then, the internal pressure of the two sealed quartz tubes was adjusted using a pressure pump, and they were simultaneously heated to the target temperature. The specific steps included: opening the first and second valves, applying pressure to the first quartz tube using the pressure pump, maintaining a stable pressure reading for a period of time, closing the first and second valves, removing the pressure pump, and replacing it with another capillary quartz tube to continue pressurizing (the third valve controls the on / off state of this capillary quartz tube). It is worth noting that during this process, the internal pressure difference between the two capillary quartz tubes should be at least 20 MPa, and it should be ensured that 10 MPa ≤ low pressure < high pressure ≤ 200 MPa. Then, two capillary quartz tubes with different preset pressures are placed simultaneously on the same hot and cold stage (heating device). The two capillary quartz tubes are heated to the target temperature at a certain heating rate (the target temperature is determined by the type of crude oil selected). Then, the temperature is kept constant for a period of time (the temperature is also determined by the type of crude oil selected). During this process, the changes in the crude oil in the two capillary quartz tubes are compared and observed.

[0061] Specifically, the changes in the morphology of crude oil within two capillary quartz tubes during the cracking process can be observed in situ during isothermal heating. Photos and videos can be taken and recorded for comparative analysis. Based on the different morphological changes exhibited by the crude oil in the two quartz tubes during heating, the influence of different pressure constraints on the thermal stability of the crude oil can be determined. Furthermore, while observing the changes in crude oil morphology, the fluorescence color of the crude oil cracking products can be monitored in real time under a 10x objective lens, or the fluorescence spectrum of the products can be obtained using a fluorescence spectrometer, recording the main peak wavelength λmax and changes in fluorescence intensity. This is because fluorescence characteristics can reflect the compositional characteristics of crude oil and its degree of thermal evolution. The generation of fluorescence mainly depends on the aromatic conjugated π-bond system and C=O functional groups in the crude oil. Traditional experimental observations suggest that the fluorescence color of liquid hydrocarbons can reflect the degree of organic matter evolution; that is, as organic matter evolves from low maturity to high maturity, its fluorescence color changes in the order of fiery red → yellow → orange → blue → bluish-white. Furthermore, by observing and comparing the fluorescence color of the crude oil cracking products in the two quartz tubes, the degree of thermal evolution of the cracking products, i.e., the thermal maturity, can be determined, thereby identifying the impact of different pressure constraints on the thermal stability of crude oil.

[0062] Correspondingly, the fluorescence peak wavelength λmax and fluorescence intensity of the crude oil cracking products in the two capillaries will also show different changes with further extension of heating time. Among them, the fluorescence peak wavelength λmax can reflect the thermal maturity of the cracking products. The higher the thermal maturity of the cracking products, the smaller λmax. The fluorescence intensity can reflect the concentration of the cracking products. The higher the concentration of the cracking products, the higher the fluorescence intensity. Therefore, the influence of different pressure constraint conditions on the thermal stability of crude oil can also be determined based on the fluorescence peak wavelength λmax or fluorescence intensity of the crude oil cracking products in the two capillaries.

[0063] Furthermore, this invention also utilizes the red-green quotient (Q = I650 / I550) of fluorescence spectra in fluid inclusions to evaluate the thermal maturity and thermal stability of crude oil. A higher I650 value (fluorescence intensity at 650 nm) indicates a greater content of macromolecular components in the crude oil, signifying lower maturity; conversely, a higher I500 value (fluorescence intensity at 500 nm) indicates a greater content of small molecule components, signifying higher maturity. Therefore, a larger red-green quotient indicates lower crude oil maturity, and vice versa. The red-green quotient can eliminate biases in fluorescence intensity caused by human error, making it a more accurate and effective parameter for analyzing differences in oil and gas composition and maturity. Correspondingly, based on the results of determining the thermal maturity of crude oil in two capillary quartz tubes, the influence of pressure on the thermal stability of crude oil can also be determined.

[0064] The experimental results of the method for determining the thermal stability of crude oil under pressure constraints provided by the present invention will be described in detail below with reference to a specific embodiment.

[0065] 1. Select an L5 crude oil sample, divide it into two equal parts, and put them into two quartz tubes respectively.

[0066] The two quartz tubes selected were model TSP300665, with an inner diameter of 300 μm and a length of 15 cm. The sample loading process included the following steps: First, the quartz tubes were fixedly connected to the steel tube (1 / 16 inch inner diameter, 9 cm length) on the pressure pump used to adjust the internal pressure of the capillary. Then, the L5 crude oil sample was loaded into the two quartz tubes respectively, and mercury was sealed at both ends of the quartz tubes after loading.

[0067] 2. Adjust the internal pressure of the two quartz tubes after sealing them with mercury, and heat them simultaneously to the target temperature.

[0068] The specific steps include: using a pressure pump to adjust the pressure inside the two quartz tubes, setting one tube to 30 MPa and the other to 100 MPa. After maintaining the pressure gauge readings stable for a period of time, remove the pressure pump and place the two quartz tubes containing the same sample on the same heating / cooling stage. Simultaneously heat them to the target temperature of 430°C at a heating rate of 10°C / h, and then continue heating at a constant temperature for 12 hours.

[0069] 3. Observe in situ the changes in the crude oil morphology in the two quartz tubes during the cracking process under constant temperature heating at 430℃, take photos and videos to record the changes, and conduct comparative analysis.

[0070] Specifically, during the heating process, the morphological changes of crude oil samples under different pressure conditions during the cracking process are observed in real time, and photographs and videos are taken for comparison. For example... Figures 3a-3f The figure shows a comparison of the morphology of crude oil in two quartz tubes under different pressure conditions during isothermal heating. As can be seen from the figure, under isothermal conditions of 430℃, the morphology of crude oil cracking products differentiated between 30MPa and 100MPa as heating time increased. Particularly after 5 hours of heating, the crude oil in the 30MPa capillary quartz tube clearly produced bubbles, and the bubble volume gradually increased, indicating that the crude oil underwent a cracking reaction, generating gaseous products. This phenomenon was not observed in the crude oil in the 100MPa capillary quartz tube. It is evident that different pressure conditions have different effects on crude oil cracking, and pressure does indeed influence the thermal cracking process of crude oil.

[0071] IV. Real-time monitoring of changes in the fluorescence color, main peak wavelength λmax, and fluorescence intensity of crude oil cracking products.

[0072] While observing the changes in the morphology of crude oil, the fluorescence color of the crude oil cracking products was monitored in real time under a 10x objective lens, and the fluorescence spectrum of the products was obtained using a fluorescence spectrometer. The main peak wavelength λmax and the changes in fluorescence intensity in the spectrum were recorded.

[0073] Specifically, Figures 4a-4fThe fluorescence color changes of crude oil cracking products under different pressure conditions were recorded and compared. It can be seen that, corresponding to the changes in crude oil morphology, the fluorescence color of the crude oil cracking products under 30 MPa and 100 MPa also differentiated after 5 hours of heating. Under the 30 MPa heating condition, bluish-green clumps appeared in the crude oil cracking products in the capillary (quartz tube), corresponding to the production of light hydrocarbons or gaseous substances after cracking. Under the 100 MPa heating condition, the fluorescence color of the crude oil cracking products was more uniform, indicating that no light hydrocarbons or gaseous substances were produced. With further increase in heating time, the fluorescence of the crude oil cracking products in the 30 MPa capillary gradually became uniform, and the fluorescence color changed from yellow to a final blue, the so-called blue shift. However, the fluorescence of the crude oil cracking products in the 100 MPa capillary remained yellow and did not change with increasing heating time.

[0074] Correspondingly, the fluorescence main peak wavelength λmax of crude oil cracking products in a capillary at 30 MPa gradually shortens with further increase in heating time, such as... Figure 5 As shown, the fluorescence peak wavelength λmax of crude oil cracking products in a capillary at 100 MPa remained essentially unchanged after 8 hours of heating. This demonstrates that high pressure does indeed inhibit the high-temperature cracking process of crude oil, meaning that crude oil has higher thermal stability under high pressure conditions.

[0075] 5. Calculate the red-green quotient of crude oil cracking products, and evaluate the thermal maturity and thermal stability of crude oil based on the red-green quotient.

[0076] Specifically, based on the measured fluorescence spectra, a cross-plot of the red-green quotient and heating time was calculated (e.g., Figure 6 It is evident that the red-green quotient of crude oil cracking products under high pressure of 100 MPa is significantly higher than that under 30 MPa after heating for 3 hours. Therefore, the thermal maturity of crude oil cracking products under high pressure of 100 MPa is significantly lower than that under 30 MPa, indicating that the cracking process of crude oil is inhibited under high pressure, that is, the thermal stability of crude oil is higher under high pressure.

[0077] In summary, the method and apparatus for determining the thermal stability of crude oil under pressure constraint provided by this invention involve: loading equal amounts of the same type of crude oil sample into several capillary quartz tubes; applying different preset pressures to the capillary quartz tubes containing the crude oil samples; simultaneously heating the capillary quartz tubes with different pressures to a target temperature and then continuing to heat at a constant temperature for a period of time; monitoring the changes in crude oil in the capillary quartz tubes under different preset pressures during the constant temperature heating process; comparing the changes in crude oil in each capillary quartz tube, and finally determining the thermal stability of crude oil under pressure constraint. Through this method, the morphology and fluorescence characteristics of crude oil cracking products under different pressure constraints can be compared in real time, thereby accurately revealing the true impact of pressure on the cracking and gas generation process of crude oil during the heating process, and achieving an accurate determination of the thermal stability of crude oil under pressure constraint. Furthermore, the method and apparatus for determining the thermal stability of crude oil under pressure constraint provided by this invention can withstand a wide pressure range, are simple and easy to operate, save time and effort, and are low in cost, providing reliable conclusions about the essential laws of the thermal evolution of crude oil under pressure constraint.

[0078] Finally, it should be noted that the above description 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 foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for determining the thermal stability of crude oil under pressure constraint, characterized in that, The method includes: Equal amounts of the same type of crude oil sample were placed in several capillary quartz tubes, and after the crude oil sample was added to the capillary quartz tubes, mercury was sealed at both ends of the quartz tubes. Different preset pressures are applied to several capillary quartz tubes; After simultaneously heating several capillary quartz tubes under different pressures to the target temperature, they are then kept at a constant temperature for a period of time. Monitor the changes in crude oil in several capillary quartz tubes during constant temperature heating; By comparing the changes in crude oil in each capillary quartz tube, the thermal stability of crude oil under pressure constraint is determined. The monitoring of changes in crude oil in several capillary quartz tubes during the isothermal heating process, and the comparison of changes in crude oil in each capillary quartz tube, determines the thermal stability of crude oil under pressure constraint, including: Real-time monitoring of the changes in fluorescence color, main peak wavelength λmax, and / or fluorescence intensity of the cracking products of crude oil in each capillary quartz tube during isothermal heating; The thermal stability of crude oil under pressure constraint is determined by comparing the changes in fluorescence color, main peak wavelength λmax, and / or fluorescence intensity of crude oil cracking products in each capillary quartz tube.

2. The method for determining the thermal stability of crude oil under pressure constraint according to claim 1, wherein, When a preset pressure is applied to each capillary quartz tube, the pressure difference between each capillary quartz tube is controlled to be ≥20MPa.

3. The method for determining the thermal stability of crude oil under pressure constraint according to claim 1 or 2, wherein, Applying different preset pressures to several capillary quartz tubes specifically involves applying high pressure to one capillary quartz tube and low pressure to another capillary quartz tube. The pressure difference between the high pressure and the low pressure is ≥20MPa, and 10MPa≤low pressure<high pressure≤200MPa.

4. A device for determining the thermal stability of crude oil under pressure constraint, the device comprising: Several capillary quartz tubes are used to hold equal amounts of the same type of crude oil sample, and after the crude oil sample is added to the capillary quartz tube, mercury is sealed at both ends of the quartz tube. A pressurizing device is used to apply different preset pressures to several capillary quartz tubes containing crude oil samples. The heating device is used to simultaneously heat several capillary quartz tubes with different pressures to the target temperature and then continue to heat them at a constant temperature for a period of time. The monitoring device is used to monitor the changes in crude oil in several capillary quartz tubes under different preset pressures during the constant temperature heating process. The determination device is used to compare the changes in crude oil in each capillary quartz tube and determine the thermal stability of crude oil under pressure constraint. The monitoring device is used to monitor the changes in crude oil in several capillary quartz tubes under different preset pressures during constant temperature heating. The determination device is used to compare the changes in crude oil in each capillary quartz tube and determine the thermal stability of the crude oil under pressure constraints, including: The monitoring device is used to monitor in real time the changes in fluorescence color, main peak wavelength λmax, fluorescence intensity and / or red-green quotient of the cracking products of crude oil in each capillary quartz tube during isothermal heating. The determination device is used to compare the changes in fluorescence color, main peak wavelength λmax, fluorescence intensity and / or red-green quotient of crude oil cracking products in each capillary quartz tube to determine the thermal stability of crude oil under pressure constraint.

5. The device for determining the thermal stability of crude oil under pressure constraint according to claim 4, wherein, The pressurizing device is used to apply different preset pressures to several capillary quartz tubes containing crude oil samples, and to control the pressure difference between each capillary quartz tube to be ≥20MPa.

6. The apparatus for determining the thermal stability of crude oil under pressure constraint according to claim 4 or 5, wherein, Specifically, the plurality of capillary quartz tubes are: two capillary quartz tubes. The pressurizing device is used to apply high pressure to one of the capillary quartz tubes and low pressure to the other capillary quartz tube. The pressure difference between the high pressure and the low pressure is ≥20MPa, and 10MPa≤low pressure<high pressure≤200MPa.

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