Test method and system for rapidly determining phase equilibrium condition of gas hydrate in sediment

Abstract

The invention relates to a test method and system for rapidly determining phase equilibrium conditions of gas hydrate in sediment, and the method comprises the following steps: S1, obtaining a relation curve of the gas pressure of the gas hydrate along with time change, and constructing a mathematical model; s2, selecting a gas pressure curve in a preset time period in the relation curve, fitting a change relation of gas pressure in the gas pressure curve by utilizing a mathematical model, and obtaining a unit temperature pressure release rate and characteristic time under the action of the corresponding reservoir temperature; s3, calculating the gas pressure intensity of the gas hydrate in an equilibrium state under the action of the reservoir temperature by utilizing the unit temperature pressure release rate and the characteristic time; and S4, repeating the steps S2-S3 until the gas pressure intensity when the gas hydrate is in a balanced state is equal to the initial gas pressure intensity. According to the invention, determination can be carried out without waiting for the sample to reach a balanced state, so that the test time is greatly shortened, and the problem of inaccurate gas pressure caused by the fact that methane gas in a high-pressure state is dissolved in unfrozen water is effectively avoided.

Description

Technical Field

[0001] The invention relates to the technical field of gas hydrate phase equilibrium testing, and in particular to a testing method for rapidly determining the gas hydrate phase equilibrium conditions in sediments. Background Art

[0002] Gas hydrate is an ice-like encapsulated compound formed by gas and water under high pressure and low temperature conditions. In nature, methane hydrate is commonly found in deep sea, submarine continental shelves and permafrost areas. At present, as a potential clean energy, it is expected to replace traditional energy and become a new strategic energy, which has attracted widespread attention from all walks of life in the world. The current methods of hydrate extraction mainly include pressure reduction method, heat injection method and inhibitor injection method. These methods all require forcing hydrates to decompose and then extracting methane gas to achieve the purpose of extraction. In this process, the stability conditions of hydrates in sediments are important parameters that control the entire decomposition behavior.

[0003] Hydrate stability conditions refer to the temperature conditions at which hydrates decompose or form in sediments. They can play an important role in determining hydrate reserves, evaluating the distribution of hydrate deposits, and predicting the potential for hydrate development. They also help to more accurately evaluate the physical and mechanical properties and parameters of hydrate reservoirs in numerical simulations of hydrate resource exploitation, and achieve safe and efficient hydrate exploitation. Therefore, determining the phase equilibrium conditions of gas hydrates in sediments plays an important role in solving problems related to hydrate phase equilibrium.

[0004] At present, there are four main experimental methods for determining the phase equilibrium conditions of gas hydrates in sediments:

[0005] The first type is the direct observation method. This method is one of the most common methods for testing the phase equilibrium of pure hydrates in the early days without considering the presence of porous media. The formation and decomposition of hydrates can be observed directly by human eyes and cameras. Generally, high-pressure gas and water are injected into a transparent reactor body, and hydrates are synthesized under a set temperature environment. Then, the hydrates are forced to decompose by reducing pressure or increasing temperature. The generation of bubbles can be observed in the reactor, and the temperature-pressure data are recorded after the temperature and pressure are stabilized.

[0006] The second type is the constant temperature method. This method is to gradually change the pressure of the system at a constant temperature and record the phase equilibrium state under different pressures. However, this method requires precise control of temperature conditions, the experimental conditions are relatively harsh, and it is not applicable to multi-component systems.

[0007] The third type is the constant pressure method. This method is to gradually change the temperature of the system under constant pressure and record the phase equilibrium state at different temperatures. However, this method requires precise control of pressure conditions and requires high precision of laboratory equipment.

[0008] The fourth type is the constant volume method, which is to keep the volume of the reactor constant and induce the synthesis and decomposition of hydrates by increasing or decreasing the temperature and pressure. The heating and decomposition methods are divided into two types: gradual heating and continuous heating. Gradual heating is to carry out the next level of heating after the pressure at each level is stable. This process requires sufficient time for the hydrate to reach equilibrium; while the continuous heating method has a large heating gradient and a fast heating rate, and the data points deviate greatly from the actual situation, which directly leads to low accuracy of phase equilibrium data.

[0009] The principle of the traditional test method for determining the phase equilibrium conditions of gas hydrates in sediments is to test the relationship between the gas pressure of hydrate-containing sediments and the reservoir temperature when the sample is in equilibrium. However, it takes a process for the sample to reach equilibrium. This means that it takes a long time to obtain the phase equilibrium conditions of gas hydrates in sediments, which is mainly determined by the basic physical properties of the sample and the number of temperature gradients to be measured. In addition, since the traditional test method for determining the phase equilibrium conditions of gas hydrates in sediments takes a long time, it will cause another inevitable problem: although methane gas under high pressure is still difficult to dissolve in water, the water dissolution time is relatively sufficient, and methane gas will still fully dissolve in uncombined water, which directly affects the test accuracy.

[0010] Although these traditional test methods have their own characteristics, they all have the common defect that they have to wait until the sample reaches a state of equilibrium before they can be measured, which leads to a long test cycle. Therefore, how to shorten the test time and achieve the purpose of quickly determining the equilibrium conditions of gas hydrate phases in sediments has become a key issue that needs to be solved. Summary of the invention

[0011] The purpose of the present invention is to overcome the above-mentioned shortcomings and deficiencies of the prior art, optimize the test method and shorten the test time, and provide a test method and system for quickly determining the phase equilibrium conditions of gas hydrates in sediments.

[0012] To achieve the above object, the present invention provides the following solutions:

[0013] A test method for rapidly determining the phase equilibrium conditions of gas hydrates in sediments comprises:

[0014] S1. Based on the phase equilibrium test, obtain the relationship curve of the gas pressure and reservoir temperature of the gas hydrate over time, and construct a mathematical model corresponding to the relationship curve;

[0015] S2. Selecting the gas pressure curve of a preset time period in the relationship curve, fitting the change relationship of the gas pressure in the gas pressure curve using the mathematical model, and obtaining the unit temperature pressure release rate and characteristic time under the action of the reservoir temperature corresponding to the preset time period;

[0016] S3. Calculate the gas pressure of the gas hydrate in equilibrium under the reservoir temperature using the unit temperature release rate and characteristic time;

[0017] S4. Repeat S2 and S3 until the gas pressure of the gas hydrate in equilibrium is equal to the initial gas pressure.

[0018] Optionally, obtaining a relationship curve of the gas pressure and reservoir temperature of the gas hydrate changing with time includes:

[0019] applying periodic reservoir temperature changes, wherein each cycle begins with the reservoir temperature suddenly increasing by a predetermined increment to a new level and remaining constant at that level for a period of time;

[0020] In each cycle, the change of gas pressure with time is monitored and recorded, and a relationship curve between the gas pressure of gas hydrate and the reservoir temperature with time is obtained.

[0021] Optionally, the mathematical model is:

[0022]

[0023] Among them, P(t ij ) indicates that in [t i , t i+1 ) represents the gas pressure corresponding to the jth moment in time, P(t1) represents the initial gas pressure of gas hydrate, k represents the completed reservoir heating stage, i.e., stage i-1, i represents the ongoing reservoir heating stage, ΔT k Indicates the change of reservoir temperature at each stage, A k Indicates the unit temperature pressure release rate of the reservoir at each stage, t ij Indicates that in [t i , t i+1 ) at any time within the time period, t k represents the last moment of the i-1th stage, τ i Indicates characteristic time.

[0024] Optionally, fitting the changing relationship of the gas pressure in the gas pressure curve using the mathematical model includes:

[0025]

[0026] Among them, P(t i1 ) and P(t i2 ) represents the relationship curve in which any two moments t are taken within a preset time period i1 ,t i2 The corresponding gas pressure.

[0027] Optionally, the gas pressure P of the gas hydrate in equilibrium eq，i for:

[0028]

[0029] Among them, P eq，i Indicates the gas pressure when the gas hydrate is in equilibrium.

[0030] A test system for quickly determining the phase equilibrium conditions of gas hydrates in sediments, the system comprising: a phase equilibrium test device, a data acquisition module, a data fitting module, a pressure calculation module and a circulation module;

[0031] The phase equilibrium test device is used to perform a phase equilibrium test on gas hydrates;

[0032] The data acquisition module is used to obtain a relationship curve of the gas pressure and reservoir temperature of the gas hydrate changing with time based on a phase equilibrium test, and to construct a mathematical model corresponding to the relationship curve;

[0033] The data fitting module is used to select the gas pressure curve of a preset time period in the relationship curve, fit the change relationship of the gas pressure in the gas pressure curve using the mathematical model, and obtain the unit temperature pressure release rate and characteristic time under the action of the reservoir temperature corresponding to the preset time period;

[0034] The pressure calculation module is used to calculate the gas pressure of the gas hydrate in an equilibrium state under the action of the reservoir temperature by using the unit temperature pressure release rate and the characteristic time;

[0035] The circulation module is used to repeat the processing of the data fitting module and the pressure calculation module until the gas pressure of the gas hydrate in the equilibrium state is equal to the initial gas pressure.

[0036] Optionally, the phase equilibrium test device comprises: a reactor, a gas supply subsystem, a vacuum subsystem, and a temperature-pressure control subsystem;

[0037] The reactor has a built-in hydrate reservoir, a cavity is provided between the hydrate reservoir and the top cover of the reactor body, a methane gas inlet is provided at the top cover to connect with the gas supply subsystem and the vacuum subsystem, the gas supply subsystem and the vacuum subsystem are independent of each other by a horizontal valve, and when in use, only the horizontal valve needs to be opened to realize the connection between the gas supply subsystem and the vacuum subsystem and the reactor;

[0038] The temperature-pressure control subsystem includes: a constant temperature water tank, a water tank, a pressure sensor and a temperature sensor; wherein the pressure sensor is arranged at the air inlet of the reactor, a temperature sensor is arranged in the reservoir and the cavity in the reactor and connected to the reactor by a quick connector, and the temperature of the reactor is controlled by circulating an ethylene glycol aqueous solution.

[0039] Optionally, the relationship curve between the gas pressure and reservoir temperature of the gas hydrate obtained in the data acquisition module and the time variation includes:

[0040] applying periodic reservoir temperature changes, wherein each cycle begins with the reservoir temperature suddenly increasing by a predetermined increment to a new level and remaining constant at that level for a period of time;

[0041] In each cycle, the change of gas pressure with time is monitored and recorded, and a relationship curve between the gas pressure of gas hydrate and the reservoir temperature with time is obtained.

[0042] The beneficial effects of the present invention are:

[0043] The present invention first obtains a relationship curve of the gas pressure of gas hydrates and the reservoir temperature changing with time based on a phase equilibrium test, and constructs a mathematical model corresponding to the relationship curve; then, the gas pressure curve of a preset time period in the relationship curve is selected, and the mathematical model is used to fit the change relationship of the gas pressure in the gas pressure curve to obtain the unit temperature pressure release rate and characteristic time under the action of the reservoir temperature corresponding to the preset time period; secondly, the unit temperature pressure release rate and characteristic time are used to calculate the gas pressure of the gas hydrate in an equilibrium state under the action of the reservoir temperature.

[0044] The present invention is a method for determining the phase equilibrium conditions of gas hydrates in sediments using the results of phase equilibrium tests under certain conditions. The method does not need to wait for the sample to reach an equilibrium state before conducting the test, thereby greatly shortening the test time and effectively avoiding the problem of inaccurate gas pressure caused by methane gas under high pressure dissolving in unfrozen water.

[0045] The present invention is an efficient and simple method that can determine the gas hydrate phase equilibrium conditions in sediments in a relatively short time, thus overcoming the time-consuming and labor-intensive defects of traditional methods for determining the gas hydrate phase equilibrium conditions in sediments, and improving the efficiency and accuracy of determining the gas hydrate phase equilibrium conditions in sediments.

[0046] The present invention is suitable for determining the reserves of hydrates, evaluating the distribution of hydrate deposits and predicting the development potential of hydrates. It also helps to more accurately evaluate the physical and mechanical properties and parameters of hydrate reservoirs in numerical simulations of hydrate resource exploitation, thereby achieving safe and efficient exploitation of hydrates. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0048] Figure 1 Schematic diagram of a hydrate-containing sediment phase equilibrium test device according to an embodiment of the present invention

[0049] Figure 2 Schematic diagram of the relationship between reservoir temperature and gas pressure over time in an embodiment of the present invention

[0050] Figure 3 A of the embodiment of the present invention i ~T i Schematic diagram of the relationship curve;

[0051] Figure 4 A comparison diagram of the model fitting curve and the sample measured result curve of the embodiment of the present invention;

[0052] Among them, 1. Reactor; 2. Gas supply system; 3. Vacuum system; 4. Temperature-pressure control system; 5. Data acquisition system. DETAILED DESCRIPTION

[0053] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0054] In order to make the above-mentioned objects, features and advantages of the present invention more obvious and easy to understand, the present invention is further described in detail below with reference to the accompanying drawings and specific embodiments.

[0055] A test method for rapidly determining the phase equilibrium conditions of gas hydrates in sediments comprises:

[0056] S1. Based on the phase equilibrium test, obtain the relationship curve of the gas pressure and reservoir temperature of the gas hydrate over time, and construct a mathematical model corresponding to the relationship curve;

[0057] S2. Selecting the gas pressure curve of a preset time period in the relationship curve, fitting the change relationship of the gas pressure in the gas pressure curve using a mathematical model, and obtaining the unit temperature pressure release rate and characteristic time under the action of the reservoir temperature corresponding to the preset time period;

[0058] S3. Calculate the gas pressure of gas hydrate in equilibrium state under the effect of reservoir temperature by using the unit temperature release rate and characteristic time;

[0059] S4. Repeat S2 and S3 until the gas pressure of the gas hydrate in equilibrium is equal to the initial gas pressure. That is, this process is divided into multiple heating stages. The result of the test method is to fit the unit temperature pressure release rate and characteristic time of each temperature point, and cumulatively calculate the gas pressure of the gas hydrate equilibrium state at each stage temperature until the methane hydrate in the reservoir is completely decomposed.

[0060] Specifically, the working principle of this embodiment is: carry out a phase equilibrium test under certain conditions, and obtain a curve of the relationship between the pressure of the sample gas and time. From the [t i , t i+1 ) Take any two moments t i1 ,t i2 and its corresponding gas pressure P(t i1 )、P(t i2 ), the reservoir temperature T is calculated by the established mathematical model i Unit temperature pressure release rate A under action i and characteristic time τ i ; Then, using the unit temperature pressure release rate A i , characteristic time τ i The gas pressure P in equilibrium eq，i The relationship between the reservoir temperature T i Under the action, the gas pressure P when the sample is in equilibrium eq，i .

[0061] Furthermore, the relationship curve between the gas pressure and reservoir temperature of the gas hydrate and the time change includes:

[0062] applying periodic reservoir temperature changes, wherein each cycle begins with the reservoir temperature suddenly increasing by a predetermined increment to a new level and remaining constant at that level for a period of time;

[0063] In each cycle, the change of gas pressure with time is monitored and recorded, and a relationship curve between the gas pressure of gas hydrate and the reservoir temperature with time is obtained.

[0064] Specifically, in this embodiment, carrying out a phase equilibrium test under certain conditions includes:

[0065] Use Figure 1 The phase equilibrium test device shown in the figure mainly includes five parts: a reactor 1, a gas supply system 2, a vacuum system 3, a temperature-pressure control system 4 and a data acquisition system 5. Figure 2The relationship between the reservoir temperature and time is shown in FIG. 1 (at time t1, the reservoir temperature T0 is suddenly increased by a small increment △T1 to the reservoir temperature T1, and it is kept unchanged until time t2; then, at time t2, the reservoir temperature T1 is suddenly increased by a small increment △T2 to the reservoir temperature T2, and it is kept unchanged until time t3; and so on, at time tn, the reservoir temperature T(n-1) is suddenly increased by a small increment △Tn to the reservoir temperature Tn, and it is kept unchanged until time tn+1), and the relationship curve between the test gas pressure and time is obtained, as shown in FIG. Figure 2 shown.

[0066] Figure 2 The meanings of the characters in are explained as follows: i —The time corresponding to the application of the i-th level reservoir temperature increment; t ij —In [t i , t i+1 ) any time in the time range; T i —In t i The reservoir temperature at the time [t i , t i+1 ) time remains unchanged; △T i —In t i The reservoir temperature increment at time t1; P(t1)—gas pressure of the sample at time t1; P(t i1 )—in [t i , t i+1 ) The gas pressure corresponding to the moment t1 within the time period; P(t i2 )—in [t i , t i+1 ) is the gas pressure corresponding to the moment t2 within the time period.

[0067] Constructing mathematical models under certain conditions includes:

[0068] When the hydrate sediment reservoir in equilibrium is subjected to temperature disturbance, the gas pressure will change with time. At any time tij within the time [ti, ti+1), the gas pressure of the hydrate reservoir is:

[0069]

[0070] Specifically, in this embodiment, fitting the changing relationship of the gas pressure in the gas pressure curve using a mathematical model includes:

[0071] From the measured relationship between gas pressure and time [t i , t i+1 ) Take any two moments t in the time period i1 ,t i2 and its corresponding gas pressure P(t i1 ) and P(ti2 ). According to formula (1), P(t i1 ) and P(t i2 ) and τ i and A i The following correspondence exists between the values:

[0072]

[0073]

[0074] Starting from time t1, using equations (2) and (3), we can obtain the reservoir temperature T i τ under the action i and A i .

[0075] Specifically, in this embodiment, the reservoir temperature in the equilibrium state is calculated as T i The corresponding gas pressure P eq，i .

[0076] According to the calculated reservoir temperature T i Unit temperature pressure release rate A i , establish A i ~T i Relationship curve, such as Figure 3 As shown. According to the temperature pressure release rate A i By defining and applying a small reservoir temperature increment, we can obtain that the reservoir temperature of the sample in equilibrium is T i The corresponding gas pressure P eq，i , it can be used Figure 3 It is represented by the area of ​​the rectangle with a slash plus the gas pressure at the initial moment. That is:

[0077]

[0078] Since P(t1), A i , △T i are known, so the reservoir temperature in the equilibrium state is T i The corresponding gas pressure P eq，i It can be obtained by formula (4).

[0079] This embodiment also proposes a test system for quickly determining the phase equilibrium conditions of gas hydrates in sediments, the system comprising: a phase equilibrium test device, a data acquisition module, a data fitting module, a pressure calculation module and a circulation module;

[0080] Phase equilibrium test device, used to conduct phase equilibrium test on gas hydrate;

[0081] A data acquisition module is used to obtain the relationship curve between the gas pressure and reservoir temperature of gas hydrate and time based on the phase equilibrium test, and to construct a mathematical model corresponding to the relationship curve;

[0082] The data fitting module is used to select the gas pressure curve of the preset time period in the relationship curve, fit the change relationship of the gas pressure in the gas pressure curve using a mathematical model, and obtain the unit temperature pressure release rate and characteristic time under the action of the reservoir temperature corresponding to the preset time period;

[0083] The pressure calculation module is used to calculate the gas pressure of gas hydrates in equilibrium under the influence of reservoir temperature by using the unit temperature release rate and characteristic time;

[0084] The loop module is used to repeat the processing of the data fitting module and the pressure calculation module until the gas pressure of the gas hydrate in the equilibrium state is equal to the initial gas pressure.

[0085] Specifically, Figure 1 As shown, the phase equilibrium test device includes: a reactor, a gas supply subsystem, a vacuum subsystem, and a temperature-pressure control subsystem. The reactor has a built-in hydrate reservoir, and there is a cavity between the hydrate reservoir and the top cover of the reactor body. A methane gas inlet is set on the top cover to connect with the gas supply subsystem and the vacuum subsystem. The two subsystems are independent of each other by a horizontal valve. When in use, only the horizontal valve needs to be opened to achieve the connection between each system and the reactor body; the temperature-pressure control subsystem consists of a constant temperature water tank, a water tank, a pressure sensor and a temperature sensor, wherein the pressure sensor is set at the reactor air inlet, a temperature sensor is set in the reservoir and the cavity in the reactor and connected to the reactor with a quick connector, and the reactor temperature is controlled by circulating ethylene glycol aqueous solution.

[0086] Furthermore, the relationship curve between the gas pressure and reservoir temperature of the gas hydrate obtained in the data acquisition module and the time variation includes:

[0087] applying periodic reservoir temperature changes, wherein each cycle begins with the reservoir temperature suddenly increasing by a predetermined increment to a new level and remaining constant at that level for a period of time;

[0088] In each cycle, the change of gas pressure with time is monitored and recorded, and a relationship curve between the gas pressure of gas hydrate and the reservoir temperature with time is obtained.

[0089] Specifically, the mathematical model in the data acquisition module is:

[0090]

[0091] Among them, P(t ij ) indicates that in [t i , ti+1 ) represents the gas pressure corresponding to the jth moment in time, P(t1) represents the initial gas pressure of gas hydrate, k represents the completed reservoir heating stage, i.e., stage i-1, i represents the ongoing reservoir heating stage, ΔT k Indicates the change of reservoir temperature at each stage, A k Indicates the unit temperature pressure release rate of the reservoir at each stage, t ij Indicates that in [t i , t i+1 ) at any time within the time period, t k represents the last moment of the i-1th stage, τ i Indicates characteristic time.

[0092] Specifically, the data fitting module uses a mathematical model to fit the changing relationship of the gas pressure in the gas pressure curve, including:

[0093]

[0094] Among them, P(t i1 ) and P(t i2 ) represents the relationship curve in which any two moments t are taken within a preset time period i1 ,t i2 The corresponding gas pressure.

[0095] Specifically, the gas pressure P of the gas hydrate in the equilibrium state in the pressure calculation module is eq，i for:

[0096]

[0097] Among them, P eq，i Indicates the gas pressure when the gas hydrate is in equilibrium.

[0098] In order to better fit the natural gas hydrate storage conditions in nature, this example refers to the particle size distribution information of the GMGS3 reservoir in the Shenhu area of ​​the South China Sea, and prepares fine-grained soil with similar particle grading as the test soil. Figure 1 The hydrate-containing sediment phase equilibrium test device shown carries out a phase equilibrium test to obtain a curve of transient gas pressure changing with time.

[0099] Under the conditions of initial reservoir temperature of 18°C ​​and initial gas pressure of 8MPa, methane hydrate was synthesized by cooling in the reactor. After the methane hydrate was synthesized in the reservoir, the reservoir temperature was 0°C. The initial setting was to apply 20 levels of temperature, and the temperature path was 0°C-0.5°C-1°C-1.5°C-2°C-3°C-4°C-5°C-6°C-7°C-8°C-9°C-10°C-11°C-12°C-13°C-14°C-15°C-16°C-17°C-18°C. Since the hydrate saturation generated by reservoirs with different water contents is different, the temperature path will be adjusted according to the actual situation during the test. It is worth noting that the sample can adjust the next level of temperature when the gas pressure has not reached equilibrium.

[0100] According to the change of gas pressure over time, the mathematical model of the present invention can be used to fit the unit temperature pressure release rate A under various reservoir temperature states. i and characteristic time τ i , and then calculate the unit temperature pressure release rate A under the step-by-step temperature state i and characteristic time τ i Accumulate and get the fitted value of gas pressure. The fitting parameters of the sample model are shown in Table 1 below, and the fitting results are shown in Figure 4 In the figure, the simulated curve of reservoir gas pressure obtained by the multi-step heating method for the hydrate sample and the curve of the measured value changing with time basically coincide, and the fitting effect is good.

[0101] Table 1 Summary of sample model fitting parameters

[0102]

[0103] This embodiment is a method for determining the phase equilibrium conditions of gas hydrates in sediments using the results of a phase equilibrium test under certain conditions. This method does not need to wait for the sample to reach an equilibrium state before conducting the test, thereby greatly shortening the test time and effectively avoiding the problem of inaccurate gas pressure caused by methane gas under high pressure dissolving in unfrozen water.

[0104] This embodiment is an efficient and simple method that can determine the phase equilibrium conditions of gas hydrates in sediments in a relatively short time, thus overcoming the time-consuming and labor-intensive defects of traditional methods for determining the phase equilibrium conditions of gas hydrates in sediments, and improving the efficiency and accuracy of determining the phase equilibrium conditions of gas hydrates in sediments.

[0105] This embodiment is used to determine the reserves of hydrates, evaluate the distribution of hydrate deposits, and predict the development potential of hydrates. It also helps to more accurately evaluate the physical and mechanical properties and parameters of hydrate reservoirs in numerical simulations of hydrate resource exploitation, thereby achieving safe and efficient exploitation of hydrates.

[0106] The embodiments described above are only descriptions of the preferred embodiments of the present invention and are not intended to limit the scope of the present invention. Without departing from the design spirit of the present invention, various modifications and improvements made to the technical solutions of the present invention by ordinary technicians in this field should all fall within the protection scope determined by the claims of the present invention.

Claims

1. A test method for rapidly determining the phase equilibrium conditions of gas hydrates in sediments, characterized in that: include: S1. Based on the phase equilibrium test, obtain the relationship curve of the gas pressure and reservoir temperature of the gas hydrate over time, and construct a mathematical model corresponding to the relationship curve; S2. Selecting the gas pressure curve of a preset time period in the relationship curve, fitting the change relationship of the gas pressure in the gas pressure curve using the mathematical model, and obtaining the unit temperature pressure release rate and characteristic time under the action of the reservoir temperature corresponding to the preset time period; S3. Calculate the gas pressure of the gas hydrate in equilibrium under the reservoir temperature using the unit temperature release rate and characteristic time; S4. Repeat S2-S3 until the gas pressure of the gas hydrate in equilibrium is equal to the initial gas pressure.

2. The test method for rapidly determining the phase equilibrium conditions of gas hydrates in sediments according to claim 1, characterized in that: The relationship curves of gas pressure and reservoir temperature over time for obtaining gas hydrates include: applying periodic reservoir temperature changes, wherein each period begins with the reservoir temperature suddenly increasing by a predetermined increment to a new level and remaining constant at the new level for a period of time; In each cycle, the change of gas pressure with time is monitored and recorded, and a relationship curve between the gas pressure of gas hydrate and the reservoir temperature with time is obtained.

3. The test method for rapidly determining the phase equilibrium conditions of gas hydrates in sediments according to claim 1, characterized in that: The mathematical model is: Among them, P(t ij ) indicates that in [t i , t i+1 ) represents the gas pressure corresponding to the jth moment in time, P(t1) represents the initial gas pressure of gas hydrate, k represents the number of completed reservoir heating stages, i represents the number of ongoing reservoir heating stages, ΔT k Indicates the change of reservoir temperature at each stage, A k Indicates the unit temperature pressure release rate of the reservoir at each stage, t ij Indicates that in [t i , t i+1 ) at any time within the time period, t k represents the last moment of the i-1th stage, τ i Indicates characteristic time.

4. The test method for rapidly determining the phase equilibrium conditions of gas hydrates in sediments according to claim 3, characterized in that: Using the mathematical model to fit the changing relationship of the gas pressure in the gas pressure curve includes: Among them, P(t i1 ) and P(t i2 ) represents the relationship curve in which any two moments t are taken within a preset time period i1 ,t i2 The corresponding gas pressure.

5. The test method for rapidly determining the phase equilibrium conditions of gas hydrates in sediments according to claim 3, characterized in that: The gas pressure P of gas hydrate in equilibrium state eq，i for: Among them, P eq，i Indicates the gas pressure when the gas hydrate is in equilibrium.

6. A test system for rapidly determining the phase equilibrium conditions of gas hydrates in sediments, characterized in that: A system for implementing the test method for rapidly determining the phase equilibrium conditions of gas hydrates in sediments as claimed in any one of claims 1 to 5, comprising: a phase equilibrium test device, a data acquisition module, a data fitting module, a pressure calculation module and a circulation module; The phase equilibrium test device is used to perform a phase equilibrium test on gas hydrates; The data acquisition module is used to obtain a relationship curve of the gas pressure and reservoir temperature of the gas hydrate changing with time based on a phase equilibrium test, and to construct a mathematical model corresponding to the relationship curve; The data fitting module is used to select the gas pressure curve of a preset time period in the relationship curve, fit the change relationship of the gas pressure in the gas pressure curve using the mathematical model, and obtain the unit temperature pressure release rate and characteristic time under the action of the reservoir temperature corresponding to the preset time period; The pressure calculation module is used to calculate the gas pressure of the gas hydrate in an equilibrium state under the action of the reservoir temperature by using the unit temperature pressure release rate and the characteristic time; The circulation module is used to repeat the processing of the data fitting module and the pressure calculation module until the gas pressure of the gas hydrate in the equilibrium state is equal to the initial gas pressure.

7. The test system for rapidly determining the phase equilibrium conditions of gas hydrates in sediments according to claim 6, characterized in that: The phase equilibrium test device comprises: a reaction kettle, a gas supply subsystem, a vacuum subsystem, and a temperature-pressure control subsystem; The reactor has a built-in hydrate reservoir, a cavity is provided between the hydrate reservoir and the top cover of the reactor body, a methane gas inlet is provided at the top cover to connect with the gas supply subsystem and the vacuum subsystem, the gas supply subsystem and the vacuum subsystem are independent of each other by a horizontal valve, and when in use, only the horizontal valve needs to be opened to realize the connection between the gas supply subsystem and the vacuum subsystem and the reactor; The temperature-pressure control subsystem includes: a constant temperature water tank, a water tank, a pressure sensor and a temperature sensor; wherein the pressure sensor is arranged at the air inlet of the reactor, a temperature sensor is arranged in the reservoir and the cavity in the reactor and connected to the reactor by a quick connector, and the temperature of the reactor is controlled by circulating an ethylene glycol aqueous solution.

8. The test system for rapidly determining the phase equilibrium conditions of gas hydrates in sediments according to claim 6, characterized in that: The relationship curve between the gas pressure and reservoir temperature of gas hydrate obtained in the data acquisition module and the change with time includes: applying periodic reservoir temperature changes, wherein each cycle begins with the reservoir temperature suddenly increasing by a predetermined increment to a new level and remaining constant at that level for a period of time; In each cycle, the change of gas pressure with time is monitored and recorded, and a relationship curve between the gas pressure of gas hydrate and the reservoir temperature with time is obtained.

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