Method and apparatus for measuring the dew point pressure of rock condensate gas.

Abstract

This invention provides a method and apparatus for measuring the dew point pressure of shale condensate gas, belonging to the field of natural gas extraction technology. The method includes: raising the temperature of a core holder to a preset temperature; injecting condensate gas into the core holder to a first preset pressure; after a preset time, reducing the pressure of the core holder to a second preset pressure according to a first preset change amount, while simultaneously acquiring the acoustic transit time of the core under different pressures; determining the dew point pressure range of shale condensate gas based on the acquired acoustic transit time; injecting condensate gas into the core holder to the maximum pressure value within the dew point pressure range; after a preset time, reducing the pressure of the core holder to the minimum pressure value within the dew point pressure range according to a second preset change amount, while simultaneously acquiring the acoustic transit time of the core under different pressures; and determining the dew point pressure of the shale condensate gas based on the newly acquired acoustic transit time. This invention is simple to operate, provides accurate measurement results, and can provide a technical basis for the efficient development of shale condensate gas reservoirs.

Description

Technical Field

[0001] This invention relates to the field of natural gas extraction technology, specifically to a method for measuring the dew point pressure of condensate gas, a device for measuring the dew point pressure of condensate gas, an electronic device, and a readable storage medium. Background Technology

[0002] Given the continuous decline in conventional oil and gas production and the continuous increase in extraction costs, unconventional oil and gas resources have become an important part of global oil and gas production. Unconventional oil and gas mainly include heavy / medium oil, oil sands, shale oil, shale condensate gas, natural gas hydrates, shale gas, and coalbed methane. Among these, shale condensate gas refers to the oil and gas mixture hosted in unconventional shale reservoirs. Under the high temperature and pressure conditions of shale reservoirs, condensate gas is in a gaseous state, and upon extraction to the surface, it undergoes reverse condensation into light oil under the required temperature and pressure. During actual extraction, as the formation pressure drops below the dew point pressure, the heavier components in the shale condensate gas undergo reverse condensation and liquefaction, accumulating in large quantities near the wellbore, clogging the pore throats of the shale matrix and severely weakening the production capacity of shale gas wells. To avoid reservoir damage and condensate oil loss caused by reverse condensation of shale condensate gas, the formation pressure must be maintained above the dew point pressure during its development. Therefore, accurately measuring the dew point pressure of shale condensate gas is of great significance for guiding its efficient development.

[0003] Currently, the industry typically uses constant-mass expansion experiments and constant-volume depletion experiments to determine the dew point pressure of condensate gas. Both methods require injecting condensate gas into an empty PVT cylinder to the formation pressure, then gradually reducing the pressure, and determining the condensate gas dew point pressure based on the pressure-volume relationship within the PVT cylinder. However, these methods fail to consider the influence of the shale matrix's nano-confinement effect on the condensate gas dew point pressure. Shale condensate gas exists in nanopores in both free and adsorbed states (the adsorbed state can account for up to 85%), and its phase transition behavior differs from that of conventional reservoir condensate gas.

[0004] Among the existing patents, Chinese patent CN117074242A discloses a method and device for testing the dew point pressure of condensate gas in porous media. It determines the actual dew point pressure of condensate gas in porous media based on the gas permeability response, but still suffers from the problem that gas permeability is insensitive to phase change behavior in the nano-confined space of the shale matrix. Chinese patent CN116127715A discloses a method for calculating the dew point pressure of condensate gas reservoirs based on pressure recovery well testing. It uses pressure recovery well testing to determine the dew point pressure of the condensate gas reservoir, but this dew point pressure is controlled by the macroscopic performance of the gas well and cannot determine the dew point pressure at the shale core scale. Chinese patent CN115569679A discloses a microfluidic chip for rapidly determining dew point and bubble point, which uses microfluidic experiments... While this method can determine the dew point pressure of condensate gas reservoirs, it simulates micron-level capillaries and is not applicable to shale matrices where nanoscale capillaries are widely developed. Chinese patent CN117094107A discloses a method, apparatus, equipment, and medium for predicting condensate gas dew point pressure, which calculates the condensate gas dew point pressure based on an improved equation of state (MPR). However, this calculation method does not consider the gas adsorption effect and phase transition confinement effect in the nanopores of the shale matrix. Chinese patent CN117706062A discloses a long core experimental apparatus and method for monitoring saturation and pressure distribution along the path, which determines condensate oil saturation based on radial acoustic transit time. However, conventional acoustic wavelengths are relatively long, resulting in limited measurement accuracy, and are not suitable for determining phase transitions in the nanopores of the shale matrix. Summary of the Invention

[0005] The purpose of this invention is to provide a method and apparatus for measuring the dew point pressure of rock condensate gas, in order to solve the above-mentioned problems.

[0006] To achieve the above objectives, embodiments of the present invention provide a method for measuring the dew point pressure of rock condensate, the method comprising: Once the measurement command is received, the temperature of the core holder is raised to the preset temperature, and condensate gas is injected into the core holder until the pressure value of the core holder reaches the first preset pressure, at which point the injection is stopped. After a preset time, the pressure of the core holder is reduced to the second preset pressure according to the first preset change amount, and the pressure reduction is stopped. During the pressure reduction process, the acoustic transit time of the core under different pressures is acquired in real time. Based on the acoustic transit time of the core samples under different pressures, the dew point pressure range of shale condensate gas was determined. Inject condensate gas into the core holder again until the pressure reaches the maximum pressure value of the dew point pressure range, then stop injecting. After a preset time, the pressure of the core holder is reduced to the minimum pressure value of the dew point pressure range according to the second preset change amount, and the pressure reduction is stopped. During the pressure reduction process, the acoustic transit time of the core under different pressures is acquired in real time. Based on the acoustic transit time of the core samples obtained again under different pressures, the dew point pressure of shale condensate gas was determined. Among them, the first preset pressure is greater than the second preset pressure; the first preset change is greater than the second preset change.

[0007] Optionally, based on the acoustic transit time of the core sample under different pressures, the dew point pressure range of shale condensate gas is determined, including: Based on the acoustic transit time and length of the rock core under different pressures, the sound velocity under different pressures is obtained; Determine the rate of change of sound velocity, and determine the dew point pressure range based on the rate of change of sound velocity.

[0008] Optionally, based on the acoustic transit time of the core sample under different pressures and the length of the core sample, the sound velocity under different pressures can be obtained, including: The speed of sound under different pressures can be calculated using the following formula: ; in, Speed ​​of sound; The length of the rock core to be measured; This refers to the time difference of sound waves.

[0009] Optionally, the dew point pressure range can be determined based on the rate of change of sound velocity, including: The pressure point at which the rate of change of the speed of sound changes from positive to negative is determined as the reference point; The dew point pressure range is obtained based on two pressure points adjacent to the reference point.

[0010] Optionally, based on the acoustic transit time of the core sample under different pressures obtained again, the dew point pressure of the shale condensate gas is determined, including: Based on the acoustic transit time and length of the core sample obtained under different pressures, new acoustic velocities under different pressures are obtained. The pressure point at which the rate of change of the new sound velocity changes from positive to negative is defined as the dew point pressure of shale condensate gas.

[0011] Secondly, embodiments of the present invention also provide a shale condensate gas dew point pressure measuring device, which can be used to implement the above-described shale condensate gas dew point pressure measuring method, the device comprising: A constant temperature chamber is provided, and a core holder is provided inside the constant temperature chamber. The core holder is used to hold shale cores, and the constant temperature chamber is used to adjust the temperature value of the core holder. An ultrasonic device, connected to the core holder, is used to obtain the acoustic time difference of the core under different pressures during the pressure reduction process inside the core holder. An air supply mechanism, connected to the core holder, is used to inject air into the core holder and to regulate the pressure inside the core holder. A back pressure pump, connected to the core holder, is used to regulate the pressure inside the core holder; A confining pressure pump, connected to the core holder, is used to adjust the pressure inside the core holder; The controller, connected to the constant temperature chamber, ultrasonic device, gas supply mechanism, back pressure pump and confining pressure pump, is used to control the operation of the constant temperature chamber, ultrasonic device, gas supply mechanism, back pressure pump and confining pressure pump, and to determine the dew point pressure of shale condensate gas based on the acoustic transit time of the rock core under different pressures.

[0012] Optionally, the device further includes: A separator, the air inlet of which is connected to the air outlet of the core holder, and the air outlet of the separator is equipped with a flow sensor.

[0013] Optionally, the device further includes: Multiple pressure sensors are provided, one inside the core holder, one between the core holder and the gas supply mechanism, one between the back pressure pump and the confining pressure pump, and one for collecting the pressure inside the core holder, between the core holder and the gas supply mechanism, and between the back pressure pump and the confining pressure pump.

[0014] Thirdly, embodiments of the present invention also provide an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor, wherein the processor executes the computer program to implement the above-described shale condensate gas dew point pressure measurement method.

[0015] Fourthly, embodiments of the present invention also provide a readable storage medium storing instructions for causing a machine to perform the above-described shale condensate gas dew point pressure measurement method.

[0016] This technical solution utilizes high-frequency ultrasound to detect the phase change behavior of condensate gas in shale samples, detects the acoustic transit time of shale cores, and determines the dew point pressure based on the relationship between pore pressure and acoustic velocity. High-frequency ultrasound has high sensitivity, does not damage the rock sample, allows for repeated testing of the same rock sample, avoids interference from shale heterogeneity with measurement results, reduces sample consumption, and offers high measurement accuracy and simple operation. It can be widely applied to the exploration and development of shale condensate gas.

[0017] Other features and advantages of the embodiments of the present invention will be described in detail in the following detailed description section. Attached Figure Description

[0018] The accompanying drawings are provided to further illustrate embodiments of the present invention and form part of the specification. They are used together with the following detailed description to explain the embodiments of the present invention, but do not constitute a limitation thereof. In the drawings: Figure 1 This is a flowchart of the shale condensate gas dew point pressure measurement method provided by the present invention; Figure 2 This is a schematic diagram of the shale condensate gas dew point pressure measuring device provided by the present invention; Figure 3 This is a schematic diagram illustrating the relationship between sound wave time difference and pressure in Embodiment 1 provided by the present invention; Figure 4 This is a schematic diagram illustrating the relationship between sound velocity and pressure in Embodiment 1 provided by the present invention; Figure 5 This is a schematic diagram illustrating the relationship between local sound velocity and pressure in Embodiment 1 provided by the present invention; Figure 6 This is a schematic diagram illustrating the relationship between sound wave time difference and pressure in Embodiment 2 provided by the present invention; Figure 7 This is a schematic diagram illustrating the relationship between sound velocity and pressure in Embodiment 2 provided by the present invention; Figure 8 This is a schematic diagram illustrating the relationship between local sound velocity and pressure in Embodiment 2 provided by the present invention; Figure 9 This is a schematic diagram illustrating the relationship between sound wave time difference and pressure in Embodiment 3 provided by the present invention; Figure 10 This is a schematic diagram illustrating the relationship between sound velocity and pressure in Embodiment 3 provided by the present invention; Figure 11 This is a schematic diagram illustrating the relationship between local sound velocity and pressure in Embodiment 3 provided by the present invention; Figure 12 This is a schematic diagram illustrating the relationship between sound wave time difference and pressure in Comparative Example 1 provided by the present invention; Figure 13 This is a schematic diagram illustrating the relationship between sound velocity and pressure in Comparative Example 1 provided by the present invention; Figure 14 This is a schematic diagram illustrating the relationship between local sound velocity and pressure in Comparative Example 1 provided by the present invention; Figure 15 This is a schematic diagram illustrating the relationship between sound wave time difference and pressure in Comparative Example 2 provided by the present invention; Figure 16 This is a schematic diagram illustrating the relationship between sound velocity and pressure in Comparative Example 2 provided by the present invention; Figure 17 This is a schematic diagram illustrating the relationship between local sound velocity and pressure in Comparative Example 2 provided by the present invention; Figure 18This is a schematic diagram illustrating the relationship between sound wave time difference and pressure in Comparative Example 3 provided by the present invention; Figure 19 This is a schematic diagram illustrating the relationship between sound velocity and pressure in Comparative Example 3 provided by the present invention; Figure 20 This is a schematic diagram showing the relationship between local sound velocity and pressure in Comparative Example 3 provided by the present invention.

[0019] Explanation of reference numerals in the attached figures 1-Constant temperature chamber; 2-Core holder; 3-Ultrasonic device; 4-Gas supply mechanism; 5-Back pressure pump; 6-Containing pressure pump; 7-Controller; 8-Separator; 9-Pressure sensor; 41-Air storage tank; 42-Booster pump; 43-Air compressor; 81 - Flow sensor. Detailed Implementation

[0020] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the scope of the present invention.

[0021] In the embodiments of the present invention, unless otherwise stated, directional terms such as "up," "down," "left," and "right" generally refer to the orientation or positional relationship shown in the accompanying drawings, or the orientation or positional relationship in which the product of the invention is usually placed when in use.

[0022] The terms “first,” “second,” “third,” etc., are used only to distinguish descriptions and should not be interpreted as indicating or implying relative importance.

[0023] The terms "parallel" and "perpendicular" do not mean that the components must be absolutely parallel or perpendicular, but rather that they can be slightly tilted. For example, "parallel" simply means that its direction is more parallel than "perpendicular," not that the structure must be completely parallel, but that it can be slightly tilted.

[0024] The terms "horizontal," "vertical," and "sag" do not imply that a component must be absolutely horizontal, vertical, or sagging, but rather that it can be slightly tilted. For example, "horizontal" simply means that its direction is more horizontal than "vertical," not that the structure must be completely horizontal, but can be slightly tilted.

[0025] Furthermore, terms like "roughly" and "basically" are used to indicate that the content does not require absolute precision, but rather allows for a certain degree of deviation. For example, "roughly equal" does not simply mean absolute equality; in actual production and operation, achieving absolute "equality" is difficult, and a certain degree of deviation is generally present. Therefore, besides absolute equality, "roughly equal to" also includes the aforementioned situation where a certain degree of deviation exists. Using this as an example, in other cases, unless otherwise specified, terms like "roughly" and "basically" have similar meanings.

[0026] In the description of this invention, it should also be noted that, unless otherwise explicitly specified and limited, the terms "set," "install," "connect," and "link" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0027] like Figure 1 As shown, this embodiment provides a method for measuring the dew point pressure of shale condensate gas, the method comprising: Once the measurement command is received, the temperature of the core holder is raised to the preset temperature, and condensate gas is injected into the core holder until the pressure value of the core holder reaches the first preset pressure, at which point the injection is stopped. After a preset time, the pressure of the core holder is reduced to the second preset pressure according to the first preset change amount, and the pressure reduction is stopped. During the pressure reduction process, the acoustic transit time of the core under different pressures is acquired in real time. Based on the acoustic transit time of the core samples under different pressures, the dew point pressure range of shale condensate gas was determined. Inject condensate gas into the core holder again until the pressure reaches the maximum pressure value of the dew point pressure range, then stop injecting. After a preset time, the pressure of the core holder is reduced to the minimum pressure value of the dew point pressure range according to the second preset change amount, and the pressure reduction is stopped. During the pressure reduction process, the acoustic transit time of the core under different pressures is acquired in real time. Based on the acoustic transit time of the core samples obtained again under different pressures, the dew point pressure of shale condensate gas was determined. Among them, the first preset pressure is greater than the second preset pressure; the first preset change is greater than the second preset change.

[0028] Furthermore, based on the acoustic transit time of the core samples under different pressures, the dew point pressure range of shale condensate gas is determined, including: Based on the acoustic transit time and length of the rock core under different pressures, the sound velocity under different pressures is obtained; Determine the rate of change of sound velocity, and determine the dew point pressure range based on the rate of change of sound velocity.

[0029] Furthermore, based on the acoustic transit time and length of the core sample under different pressures, the sound velocity under different pressures is obtained, including: The speed of sound under different pressures can be calculated using the following formula: ; in, Speed ​​of sound; The length of the rock core to be measured; This refers to the time difference of sound waves.

[0030] Specifically, the above calculation formula can accurately calculate the speed of sound under different pressures, thus improving the accuracy of subsequent calculation results.

[0031] Furthermore, based on the rate of change of sound speed, the dew point pressure range is determined, including: The pressure point at which the rate of change of the speed of sound changes from positive to negative is determined as the reference point; The dew point pressure range is obtained based on two pressure points adjacent to the reference point.

[0032] Specifically, in this embodiment, the rate of change of sound velocity is calculated using two adjacent pressure points and their corresponding sound velocities. This includes a point where the rate of change of sound velocity suddenly increases and then immediately becomes negative. Therefore, the pressure point where the rate of change changes from positive to negative is determined as the reference point. The adjacent pressure points smaller than the reference point are taken as the minimum value of the dew point pressure range, and the adjacent pressure points larger than the reference point are taken as the maximum value of the dew point pressure range, thus forming the dew point pressure range.

[0033] In another implementation, after collecting different pressure points and obtaining the corresponding sound velocities, a relationship chart between pressure points and sound velocities can be constructed using pressure points as the horizontal axis and sound velocities as the vertical axis. The dew point pressure range can be determined by using the pressure points in the relationship chart where the rate of change changes from positive to negative.

[0034] Furthermore, based on the acoustic transit time of the core samples obtained again under different pressures, the dew point pressure of the shale condensate gas is determined, including: Based on the acoustic transit time and length of the core sample obtained under different pressures, new acoustic velocities under different pressures are obtained. The pressure point at which the rate of change of the new sound velocity changes from positive to negative is defined as the dew point pressure of shale condensate gas.

[0035] Specifically, in this embodiment, firstly, the new speed of sound under different pressures is calculated using a formula: ;in, For a new speed of sound; The length of the rock core to be measured; The new sound wave transit time is determined; then, using two adjacent pressure points and their corresponding sound velocities, the rate of change of sound velocity is calculated. This includes a point where the rate of change of sound velocity suddenly increases and then immediately becomes negative. Therefore, the pressure point where this rate of change changes from positive to negative is used to determine the dew point pressure of shale condensate gas. Using the above method, the dew point pressure of shale condensate gas can be accurately determined.

[0036] In another implementation, after collecting different pressure points and obtaining the corresponding new sound velocities, a relationship chart between pressure points and sound velocities can be constructed using pressure points as the horizontal axis and the new sound velocities as the vertical axis. The dew point pressure of shale condensate gas can be determined by using the pressure points in the relationship chart where the rate of change changes from positive to negative.

[0037] This embodiment also provides a shale condensate gas dew point pressure measuring device, which can be used to implement the above-described shale condensate gas dew point pressure measuring method, such as... Figure 2 As shown, the device includes: The constant temperature chamber 1 is equipped with a core holder 2, which is used to hold shale cores, and the constant temperature chamber 1 is used to adjust the temperature value of the core holder 2. The ultrasonic device 3 is connected to the core holder 2 and is used to obtain the acoustic time difference of the core under different pressures during the pressure reduction process in the core holder 2. The gas supply mechanism 4 is connected to the core holder 2 and is used to inject gas into the core holder 2 and to adjust the pressure inside the core holder 2. Back pressure pump 5, connected to the core holder 2, is used to adjust the pressure inside the core holder 2; The confining pressure pump 6 is connected to the core holder 2 and is used to adjust the pressure inside the core holder 2; The controller 7 is connected to the constant temperature chamber 1, the ultrasonic device 3, the gas supply mechanism 4, the back pressure pump 5, and the confining pressure pump 6. It is used to control the operation of the constant temperature chamber 1, the ultrasonic device 3, the gas supply mechanism 4, the back pressure pump 5, and the confining pressure pump 6, and to determine the dew point pressure of shale condensate gas based on the acoustic transit time of the rock core under different pressures.

[0038] Specifically, the gas supply mechanism 4 includes a gas storage tank 41, a booster pump 42, and an air compressor 43. The gas storage tank 41 is used to store condensate gas. The booster pump 42, under the action of the air compressor 43, compresses the condensate gas and increases its pressure value. The booster pump 42 is connected to the air inlet of the core holder 2. The confining pressure pump 6 is connected to the confining pressure port of the core holder 2. The back pressure pump 5 is connected to the air outlet of the core holder 2. The ultrasonic device 3 emits ultrasonic waves at a frequency of 1 MHz.

[0039] Furthermore, the device also includes: Separator 8, the air inlet of which is connected to the air outlet of the core holder 2, and the air outlet of separator 8 is equipped with a flow sensor 81.

[0040] Specifically, the separator 8 includes a reaction bottle containing a separation liquid. The outlet of the core holder 2 is connected to a pipe, the end of which is below the separation liquid level. This pipe delivers gas into the separation liquid, enabling the absorption of combustible gases in the emitted gas and reducing safety risks. Additionally, a discharge pipe is installed on the reaction bottle, the end of which is above the separation liquid level. A flow sensor 81 is installed on the discharge pipe to measure the amount of emitted gas.

[0041] Furthermore, the device also includes: Multiple pressure sensors 9 are provided, one inside the core holder 2, one between the core holder 2 and the gas supply mechanism 4, the back pressure pump 5, and the confining pressure pump 6, respectively, for collecting the pressure inside the core holder 2 and between the core holder 2 and the gas supply mechanism 4, the back pressure pump 5, and the confining pressure pump 6.

[0042] Specifically, the core holder 2 is connected to the gas supply mechanism 4, the back pressure pump 5 and the confining pressure pump 6 through pipes. A pressure sensor 9 is installed on each of the corresponding pipes to collect the pressure value inside the pipe. A pressure sensor 9 is also installed inside the core holder 2 to collect the pressure value inside the core holder 2.

[0043] This embodiment also provides an electronic device, including a memory, a processor, and a computer program stored in the memory and executable on the processor. When the processor executes the computer program, it implements the above-described method for measuring the dew point pressure of shale condensate gas.

[0044] This embodiment also provides a readable storage medium storing instructions for causing a machine to perform the above-described shale condensate gas dew point pressure measurement method.

[0045] Example 1: This embodiment provides a method for measuring the dew point pressure of shale condensate gas, including: (1) Preparation of shale core columns Obtain the shale sample to be tested and cut it to the standard core column size (25 mm in diameter and 50 mm in length). Dry the core column at 80°C until its mass is constant. (2) Preparation of shale condensate gas samples Shale condensate gas samples were taken from a gas well site in a condensate gas reservoir. The composition of the condensate gas samples was measured using gas chromatography-mass spectrometry. The measurement results showed that the mass fraction of methane was 70%, the mass fraction of ethane was 20%, and the mass fraction of propane was 10%. Condensate gas samples were prepared in the above proportions. (3) Simulate the original stratigraphic conditions of the core The core column was placed in the core holder, the temperature was raised to the formation temperature of 65°C, the condensate gas sample was pressurized to 50MPa by a booster pump and slowly injected into the core holder, and the temperature and pressure were kept constant at 65°C and 50MPa for 5 minutes. (4) Simulate the exhaustion-style development process To reduce the back pressure at the core outlet, the core pore pressure is gradually decayed from the original formation pressure to the abandonment pressure at 1 MPa / step. During the decay process, the acoustic transit time of the core is measured using a high-frequency ultrasonic device. Based on the acoustic transit time of the core under different pressures, the dew point pressure range of shale condensate gas is determined. Figure 3 As shown, the acoustic transit time of shale condensate gas under different pressures during the depletion process is obtained; (5) Data processing and analysis The sound velocity was calculated based on the acoustic transit time and the core sample length, and a sound velocity vs. pressure cross-plot was plotted. Pressure points where the sound velocity increases with decreasing formation pressure were selected, such as... Figure 4 As shown, the dew point pressure range of shale condensate gas is preliminarily determined to be 45-47 MPa; (6) Based on the shale condensate gas dew point pressure range, inject condensate gas into the core holder until the pressure reaches the maximum pressure value of the dew point pressure range. After 5 minutes, reduce the pressure of the core holder at 0.25 MPa / step until it reaches the minimum pressure value of the dew point pressure range. During the attenuation process, use a high-frequency ultrasonic device to test the acoustic transit time of the core. Based on the newly obtained acoustic transit time of the core under different pressures, determine the dew point pressure of the shale condensate gas. Figure 5 As shown, the dew point pressure of shale condensate gas is determined to be 46.25 MPa based on the intersection diagram of sound velocity and pressure.

[0046] Example 2: This embodiment provides a method for measuring the dew point pressure of shale condensate gas, including: (1) Preparation of shale core columns Obtain the shale sample to be tested and cut it to the standard core column size (25 mm in diameter and 50 mm in length). Dry the core column at 80°C until its mass is constant. (2) Preparation of shale condensate gas samples Shale condensate gas samples were taken from a gas well site in a condensate gas reservoir. The composition of the condensate gas samples was measured using gas chromatography-mass spectrometry. The measurement results showed that the mass fraction of methane was 80%, the mass fraction of ethane was 15%, and the mass fraction of propane was 5%. Condensate gas samples were prepared in the above proportions. (3) Simulate the original stratigraphic conditions of the core The core column was placed in the core holder, the temperature was raised to the formation temperature of 65°C, the condensate gas sample was pressurized to 50MPa by a booster pump and slowly injected into the core holder, and the temperature and pressure were kept constant at 65°C and 50MPa for 5 minutes. (4) Simulate the exhaustion-style development process To reduce the back pressure at the core outlet, the core pore pressure is gradually decayed from the original formation pressure to the abandonment pressure at 1 MPa / step. During the decay process, the acoustic transit time of the core is measured using a high-frequency ultrasonic device. Based on the acoustic transit time of the core under different pressures, the dew point pressure range of shale condensate gas is determined. Figure 6 As shown, the acoustic transit time of shale condensate gas under different pressures during the depletion process is obtained; (5) Data processing and analysis The sound velocity was calculated based on the acoustic transit time and the core sample length, and a sound velocity vs. pressure cross-plot was plotted. Pressure points where the sound velocity increases with decreasing formation pressure were selected, such as... Figure 7 As shown, the dew point pressure range of shale condensate gas is preliminarily determined to be 44-46 MPa; (6) Based on the shale condensate gas dew point pressure range, inject condensate gas into the core holder until the pressure reaches the maximum pressure value of the dew point pressure range. After 5 minutes, reduce the pressure of the core holder at 0.25 MPa / step until it reaches the minimum pressure value of the dew point pressure range. During the attenuation process, use a high-frequency ultrasonic device to test the acoustic transit time of the core. Based on the newly obtained acoustic transit time of the core under different pressures, determine the dew point pressure of the shale condensate gas. Figure 8 As shown, the dew point pressure of shale condensate gas is determined to be 44.75 MPa based on the intersection diagram of sound velocity and pressure.

[0047] Example 3: This embodiment provides a method for measuring the dew point pressure of shale condensate gas, including: (1) Preparation of shale core columns Obtain the shale sample to be tested and cut it to the standard core column size (25 mm in diameter and 50 mm in length). Dry the core column at 80°C until its mass is constant. (2) Preparation of shale condensate gas samples Shale condensate gas samples were taken from a gas well site in a condensate gas reservoir. The composition of the condensate gas samples was measured using gas chromatography-mass spectrometry. The measurement results showed that the mass fraction of methane was 90% and the mass fraction of ethane was 10%. Condensate gas samples were prepared in the above proportions. (3) Simulate the original stratigraphic conditions of the core The core column was placed in the core holder, the temperature was raised to the formation temperature of 65°C, the condensate gas sample was pressurized to 50MPa by a booster pump and slowly injected into the core holder, and the temperature and pressure were kept constant at 65°C and 50MPa for 5 minutes. (4) Simulate the exhaustion-style development process To reduce the back pressure at the core outlet, the core pore pressure is gradually decayed from the original formation pressure to the abandonment pressure at 1 MPa / step. During the decay process, the acoustic transit time of the core is measured using a high-frequency ultrasonic device. Based on the acoustic transit time of the core under different pressures, the dew point pressure range of shale condensate gas is determined. Figure 9 As shown, the acoustic transit time of shale condensate gas under different pressures during the depletion process is obtained; (5) Data processing and analysis The sound velocity was calculated based on the acoustic transit time and the core sample length, and a sound velocity vs. pressure cross-plot was plotted. Pressure points where the sound velocity increases with decreasing formation pressure were selected, such as... Figure 10 As shown, the dew point pressure range of shale condensate gas is preliminarily determined to be 42-44 MPa; (6) Based on the shale condensate gas dew point pressure range, inject condensate gas into the core holder until the pressure reaches the maximum pressure value of the dew point pressure range. After 5 minutes, reduce the pressure of the core holder at 0.25 MPa / step until it reaches the minimum pressure value of the dew point pressure range. During the attenuation process, use a high-frequency ultrasonic device to test the acoustic transit time of the core. Based on the newly obtained acoustic transit time of the core under different pressures, determine the dew point pressure of the shale condensate gas. Figure 11 As shown, the dew point pressure of shale condensate gas is determined to be 43.25 MPa based on the intersection diagram of sound velocity and pressure.

[0048] Comparative Example 1: (1) Preparation of sandstone core columns Obtain the sandstone sample to be tested and cut it to the standard core column size (25 mm in diameter and 50 mm in length). Dry the core column at 80°C until its mass is constant. (2) Preparation of condensate gas sample The condensate gas sample composition is 70% methane, 20% ethane, and 10% propane. The condensate gas sample is prepared in the above proportions. (3) Simulate the original stratigraphic conditions of the core The core column was placed in the core holder, the temperature was raised to the formation temperature of 65°C, the condensate gas sample was pressurized to 50MPa by a booster pump and slowly injected into the core holder, and the temperature and pressure were kept constant at 65°C and 50MPa for 5 minutes. (4) Simulate the exhaustion-style development process To reduce the back pressure at the core outlet, the core pore pressure was gradually decayed from the original formation pressure to the abandonment pressure at 1 MPa / step. During the decay process, the acoustic transit time of the core was measured using a high-frequency ultrasonic device. Based on the acoustic transit time of the core under different pressures, the dew point pressure range of sandstone condensate gas was determined. Figure 12 As shown, the acoustic transit time of sandstone condensate gas under different pressures during the depletion process is obtained; (5) Data processing and analysis The sound velocity was calculated based on the acoustic transit time and the core sample length, and a sound velocity vs. pressure cross-plot was plotted. Pressure points where the sound velocity increases with decreasing formation pressure were selected, such as... Figure 13 As shown, the dew point pressure range of sandstone condensate gas is preliminarily determined to be 41-43 MPa; (6) Based on the dew point pressure range of sandstone condensate gas, inject condensate gas into the core holder until the pressure reaches the maximum pressure value of the dew point pressure range. After 5 minutes, reduce the pressure of the core holder at 0.25 MPa / step until it reaches the minimum pressure value of the dew point pressure range. During the attenuation process, use a high-frequency ultrasonic device to test the acoustic transit time of the core. Based on the newly obtained acoustic transit time of the core under different pressures, determine the dew point pressure of the sandstone condensate gas. Figure 14 As shown, the dew point pressure of sandstone condensate gas is determined to be 42.25 MPa based on the intersection diagram of sound velocity and pressure.

[0049] Comparative Example 2: (1) Preparation of sandstone core columns Obtain the sandstone sample to be tested and cut it to the standard core column size (25 mm in diameter and 50 mm in length). Dry the core column at 80°C until its mass is constant. (2) Preparation of condensate gas sample The condensate gas sample composition is 80% methane, 15% ethane, and 5% propane. The condensate gas sample is prepared in the above proportions. (3) Simulate the original stratigraphic conditions of the core The core column was placed in the core holder, the temperature was raised to the formation temperature of 65°C, the condensate gas sample was pressurized to 50MPa by a booster pump and slowly injected into the core holder, and the temperature and pressure were kept constant at 65°C and 50MPa for 5 minutes. (4) Simulate the exhaustion-style development process To reduce the back pressure at the core outlet, the core pore pressure was gradually decayed from the original formation pressure to the abandonment pressure at 1 MPa / step. During the decay process, the acoustic transit time of the core was measured using a high-frequency ultrasonic device. Based on the acoustic transit time of the core under different pressures, the dew point pressure range of sandstone condensate gas was determined. Figure 15 As shown, the acoustic transit time of sandstone condensate gas under different pressures during the depletion process is obtained; (5) Data processing and analysis The sound velocity was calculated based on the acoustic transit time and the core sample length, and a sound velocity vs. pressure cross-plot was plotted. Pressure points where the sound velocity increases with decreasing formation pressure were selected, such as... Figure 16 As shown, the dew point pressure range of sandstone condensate gas is preliminarily determined to be 41-43 MPa; (6) Based on the dew point pressure range of sandstone condensate gas, inject condensate gas into the core holder until the pressure reaches the maximum pressure value of the dew point pressure range. After 5 minutes, reduce the pressure of the core holder at 0.25 MPa / step until it reaches the minimum pressure value of the dew point pressure range. During the attenuation process, use a high-frequency ultrasonic device to test the acoustic transit time of the core. Based on the newly obtained acoustic transit time of the core under different pressures, determine the dew point pressure of the sandstone condensate gas. Figure 17 As shown, the dew point pressure of sandstone condensate gas is determined to be 41.75 MPa based on the intersection diagram of sound velocity and pressure.

[0050] Comparative Example 3: (1) Preparation of sandstone core columns Obtain the sandstone sample to be tested and cut it to the standard core column size (25 mm in diameter and 50 mm in length). Dry the core column at 80°C until its mass is constant. (2) Preparation of condensate gas sample The condensate gas sample composition is 90% methane and 10% ethane. The condensate gas sample is prepared in the above proportion. (3) Simulate the original stratigraphic conditions of the core The core column was placed in the core holder, the temperature was raised to the formation temperature of 65°C, the condensate gas sample was pressurized to 50MPa by a booster pump and slowly injected into the core holder, and the temperature and pressure were kept constant at 65°C and 50MPa for 5 minutes. (4) Simulate the exhaustion-style development process To reduce the back pressure at the core outlet, the core pore pressure was gradually decayed from the original formation pressure to the abandonment pressure at 1 MPa / step. During the decay process, the acoustic transit time of the core was measured using a high-frequency ultrasonic device. Based on the acoustic transit time of the core under different pressures, the dew point pressure range of sandstone condensate gas was determined. Figure 18 As shown, the acoustic transit time of sandstone condensate gas under different pressures during the depletion process is obtained; (5) Data processing and analysis The sound velocity was calculated based on the acoustic transit time and the core sample length, and a sound velocity vs. pressure cross-plot was plotted. Pressure points where the sound velocity increases with decreasing formation pressure were selected, such as... Figure 19 As shown, the dew point pressure range of sandstone condensate gas is preliminarily determined to be 40-42 MPa; (6) Based on the dew point pressure range of sandstone condensate gas, inject condensate gas into the core holder until the pressure reaches the maximum pressure value of the dew point pressure range. After 5 minutes, reduce the pressure of the core holder at 0.25 MPa / step until it reaches the minimum pressure value of the dew point pressure range. During the attenuation process, use a high-frequency ultrasonic device to test the acoustic transit time of the core. Based on the newly obtained acoustic transit time of the core under different pressures, determine the dew point pressure of the sandstone condensate gas. Figure 20 As shown, the dew point pressure of sandstone condensate gas is determined to be 41.50 MPa based on the intersection diagram of sound velocity and pressure.

[0051] In summary, the condensate gas composition, rock sample lithology, and temperature of Examples (1, 2, and 3) and Comparative Examples (1, 2, and 3) were recorded. The relationship between sound velocity and formation pressure was analyzed to determine the condensate gas dew point pressure. The specific results are shown in Table 1 below. Comparative Examples 1, 2, and 3 correspond to Examples 1, 2, and 3, respectively. The experimental temperature for Examples 1, 2, and 3, and Comparative Examples 1, 2, and 3 was 65°C. Example 1 is shale condensate gas, with a composition of 70% methane, 20% ethane, and 10% propane by mass. Example 2 is shale condensate gas, with a composition of 80% methane, 15% ethane, and 5% propane by mass. Example 3 is shale condensate gas, with a composition of 90% methane and 10% ethane by mass. Comparative Example 1 is sandstone condensate gas, with a composition of 70% methane, 20% ethane, and 10% propane by mass. Comparative Example 2 is sandstone condensate gas, with a composition of 80% methane, 15% ethane, and 5% propane by mass. Comparative Example 3 is sandstone condensate gas, with a composition of 90% methane and 10% ethane by mass. According to the data in Table 1, the dew point pressure of Example 1 is significantly higher than that of Comparative Example 1, the dew point pressure of Example 2 is significantly higher than that of Comparative Example 2, and the dew point pressure of Example 3 is significantly higher than that of Comparative Example 3. This demonstrates that the shale condensate gas dew point pressure testing method based on high-frequency ultrasound proposed in this invention can measure the difference in dew point pressure between shale condensate gas and sandstone condensate gas under the same conditions, proving the effectiveness of the testing method provided by this invention.

[0052] Table 1 Comparison of Condensate Dew Point Pressure Test Results between Rock and Sandstone

[0053] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details in the above embodiments. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention.

[0054] Those skilled in the art will understand that all or part of the steps in the methods of the above embodiments can be implemented by a program instructing related hardware. This program is stored in a storage medium and includes several instructions to cause a microcontroller, chip, or processor to execute all or part of the steps of the methods described in the various embodiments of the present invention. The aforementioned storage medium includes various media capable of storing program code, such as a USB flash drive, a portable hard drive, a read-only memory (ROM), a random access memory (RAM), a magnetic disk, or an optical disk.

[0055] The optional embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the embodiments of the present invention are not limited to the specific details described above. Within the scope of the technical concept of the embodiments of the present invention, various simple modifications can be made to the technical solutions of the embodiments of the present invention, and these simple modifications all fall within the protection scope of the embodiments of the present invention. It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the embodiments of the present invention will not describe the various possible combinations separately. Furthermore, various different implementations of the present invention can be combined arbitrarily, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed in the present invention.

Claims

1. A method for measuring the dew point pressure of shale condensate gas, characterized in that, The method includes: Once the measurement command is received, the temperature of the core holder is raised to the preset temperature, and condensate gas is injected into the core holder until the pressure value of the core holder reaches the first preset pressure, at which point the injection is stopped. After a preset time, the pressure of the core holder is reduced to the second preset pressure according to the first preset change amount, and the pressure reduction is stopped. During the pressure reduction process, the acoustic transit time of the core under different pressures is acquired in real time. Based on the acoustic transit time of the core samples under different pressures, the dew point pressure range of shale condensate gas was determined. Inject condensate gas into the core holder again until the pressure reaches the maximum pressure value of the dew point pressure range, then stop injecting. After a preset time, the pressure of the core holder is reduced to the minimum pressure value of the dew point pressure range according to the second preset change amount, and the pressure reduction is stopped. During the pressure reduction process, the acoustic transit time of the core under different pressures is acquired in real time. Based on the acoustic transit time of the core samples obtained again under different pressures, the dew point pressure of shale condensate gas was determined. Among them, the first preset pressure is greater than the second preset pressure; the first preset change is greater than the second preset change.

2. The method for measuring the dew point pressure of shale condensate gas according to claim 1, characterized in that, Based on the acoustic transit time of the core samples under different pressures, the dew point pressure range of shale condensate gas was determined, including: Based on the acoustic transit time and length of the rock core under different pressures, the sound velocity under different pressures is obtained; Determine the rate of change of sound velocity, and determine the dew point pressure range based on the rate of change of sound velocity.

3. The method for measuring the dew point pressure of shale condensate gas according to claim 2, characterized in that, Based on the acoustic transit time and length of the rock core under different pressures, the sound velocity under different pressures is obtained, including: The speed of sound under different pressures can be calculated using the following formula: ； in, Speed ​​of sound; The length of the rock core to be measured; This refers to the time difference of sound waves.

4. The method for measuring the dew point pressure of shale condensate gas according to claim 3, characterized in that, Based on the rate of change of sound speed, the dew point pressure range is determined, including: The pressure point at which the rate of change of the speed of sound changes from positive to negative is determined as the reference point; The dew point pressure range is obtained based on two pressure points adjacent to the reference point.

5. The method for measuring the dew point pressure of shale condensate gas according to claim 1, characterized in that, Based on the acoustic transit time of the core sample obtained again under different pressures, the dew point pressure of shale condensate gas is determined, including: Based on the acoustic transit time and length of the core sample obtained under different pressures, new acoustic velocities under different pressures are obtained. The pressure point at which the rate of change of the new sound velocity changes from positive to negative is defined as the dew point pressure of shale condensate gas.

6. A shale condensate gas dew point pressure measuring device, characterized in that, For implementing the shale condensate gas dew point pressure measurement method according to any one of claims 1-5, the apparatus comprises: A constant temperature chamber (1) is provided with a core holder (2) inside the constant temperature chamber (1). The core holder (2) is used to hold shale cores. The constant temperature chamber (1) is used to adjust the temperature value of the core holder (2). An ultrasonic device (3) is connected to the core holder (2) and is used to obtain the acoustic time difference of the core under different pressures during the pressure reduction process in the core holder (2). The gas supply mechanism (4) is connected to the core holder (2) and is used to inject gas into the core holder (2) and to adjust the pressure inside the core holder (2); A back pressure pump (5) is connected to the core holder (2) and is used to adjust the pressure inside the core holder (2); A confining pressure pump (6) is connected to the core holder (2) and is used to adjust the pressure inside the core holder (2); The controller (7) is connected to the constant temperature chamber (1), ultrasonic device (3), gas supply mechanism (4), back pressure pump (5) and confining pressure pump (6) to control the operation of the constant temperature chamber (1), ultrasonic device (3), gas supply mechanism (4), back pressure pump (5) and confining pressure pump (6), and to determine the dew point pressure of shale condensate gas based on the acoustic transit time of the rock core under different pressures.

7. The shale condensate gas dew point pressure measuring device according to claim 6, characterized in that, The device further includes: The separator (8) has an air inlet connected to the air outlet of the core holder (2), and the air outlet of the separator (8) is equipped with a flow sensor (81).

8. The shale condensate gas dew point pressure measuring device according to claim 6, characterized in that, The device further includes: Multiple pressure sensors (9) are provided, one inside the core holder (2), one between the core holder (2) and the gas supply mechanism (4), one between the back pressure pump (5) and the confining pressure pump (6), for collecting the pressure inside the core holder (2), between the core holder (2) and the gas supply mechanism (4), and between the back pressure pump (5) and the confining pressure pump (6).

9. An electronic device comprising a memory, a processor, and a computer program stored in the memory and executable on the processor, characterized in that, When the processor executes the computer program, it implements the shale condensate gas dew point pressure measurement method according to any one of claims 1-5.

10. A readable storage medium, characterized in that, The readable storage medium stores instructions for causing a machine to perform the shale condensate gas dew point pressure measurement method according to any one of claims 1-5.

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