Experimental device and method for measuring gas-water relative permeability of hydrate-containing sediment by unsteady-state method

Abstract

The invention relates to an experimental device and method for measuring gas-water relative permeability of hydrate-containing sediments by an unsteady-state method, xenon is used for replacing methane gas to synthesize xenon hydrate, then methane gas is used for displacing water, in the displacement process, the displacement pressure is kept between the balance pressure of the xenon hydrate and the balance pressure of the methane hydrate, and the gas-water relative permeability of the hydrate-containing sediments is measured. Therefore, the saturation of the xenon hydrate in the measurement process is not changed, and no new methane hydrate is generated. The response rule of the gas and water relative permeability of the hydrate-containing sediment along with the saturation of the hydrate is quantitatively described through an unsteady state method, and the gas and water relative permeability of the hydrate-containing sediment can be measured under the indoor condition.

Description

Technical Field

[0001] The invention relates to the technical field of measuring physical property parameters of natural gas hydrate reservoirs, and in particular to an experimental device and method for measuring gas-water relative permeability of hydrate-containing sediments by a non-steady-state method. Background Art

[0002] Natural gas hydrate is an ice-like crystalline substance formed by natural gas and water under low temperature and high pressure conditions. It is an unconventional, clean natural gas resource with a wide distribution and large resource volume. However, there are a series of geological challenges and engineering difficulties that need to be overcome, and commercial exploitation still has a long way to go.

[0003] The dynamics of natural gas hydrate exploitation are quite different from those of conventional oil and gas reservoirs. Under the temperature and pressure conditions of the reservoir, natural gas hydrate exists in the solid phase. However, when the temperature is higher than the equilibrium temperature or the pressure is lower than the equilibrium pressure, the hydrate decomposes into gas phase and liquid phase, and the saturation, effective porosity, permeability, etc. of each phase in the reservoir also change accordingly. Therefore, the exploitation of natural gas hydrate involves a multi-phase and multi-component coupled seepage process. Natural gas hydrate seepage measurement generally includes steady-state method and unsteady-state method. Among them, the steady-state method refers to injecting gas and water into the rock sample at a certain flow rate ratio, and calculating the permeability based on Darcy's law after the flow stabilizes. During the steady-state measurement process, the distribution of gas and water in the rock sample is uniform, and the water saturation of the rock sample does not change. The unsteady-state method refers to the method of gas driving water at a constant pressure difference or constant speed. During the displacement process, the distribution of the two-phase saturation in the porous medium is uneven, and they are functions of distance and time.

[0004] Hydrates in the Shenhu Sea area of ​​the South my country Sea mainly exist in reservoirs rich in clay minerals. Clay minerals have small corresponding pore sizes and are swellable by water. As the hydrate saturation increases, the permeability of the hydrate reservoir decreases significantly, making it difficult to form a stable seepage flow. Therefore, it is very difficult to measure the reservoir permeability at a certain hydrate saturation using the steady-state method. In addition, when measuring the relative permeability of gas and water, hydrates may be generated or decomposed due to changes in temperature and pressure conditions during the experiment, resulting in the inability to maintain the hydrate saturation at a constant value.

[0005] In recent years, technicians have studied experimental measurement devices and methods for the permeability of hydrate-containing sediments, and obtained data on the variation of the permeability of certain hydrate-containing sediments with hydrate saturation. For example, CN105572014A discloses a synchronous transient measurement device and method for natural gas hydrate saturation and sediment permeability, including an inverted reactor, the bottom of which is respectively connected to a vacuum system, a confining pressure control system and a circulating sample preparation system, the top of which is respectively connected to a permeability transient measurement system, a hydrate saturation measurement system and a data acquisition system, the permeability transient measurement system, the hydrate saturation measurement system, and the data acquisition system are respectively connected to a computer; the reactor, the circulating sample preparation system and the permeability transient measurement system are all arranged in a temperature control system. The device can obtain a hydrate-containing sediment sample liquid under non-steady-state seepage conditions to measure absolute permeability.

[0006] CN108051354A discloses a method and device for measuring the permeability of low-permeability hydrate sediments based on pulse attenuation analysis, including a reaction vessel, an intermediate vessel at the downstream end of the reaction vessel, an ISCO plunger pump connected to each side of the reaction vessel, both pumps are connected to a gas supply cylinder, and a data acquisition system measures the upstream end pressure and the pressure difference between the two ends of the reaction vessel, as well as the temperature in the reaction vessel. The device can measure the absolute permeability of some fine-grained porous media with high hydrate saturation, thereby solving the problem that traditional measurement methods are difficult to form stable seepage in such media.

[0007] However, the above invention only describes the measurement of the absolute permeability of hydrate-containing sediments, and does not involve the measurement of the relative permeability of gas and water, which is extremely important for actual production. Therefore, it is urgent to propose an experimental device and method for the relative permeability of hydrate-containing sediments that can be easily implemented under indoor conditions. Summary of the invention

[0008] In view of the shortcomings of the prior art, the purpose of the present invention is to provide an experimental device and method for measuring the gas-water relative permeability of hydrate-containing sediments by a non-steady-state method, which can meet the development needs of hydrates in the South China Sea, and at the same time quantitatively describe the response law of the gas and water relative permeabilities of hydrate-containing sediments with hydrate saturation, thereby realizing the measurement of the gas and water relative permeabilities of hydrate-containing sediments.

[0009] In order to achieve the purpose of the invention, the present invention adopts the following technical solutions:

[0010] In a first aspect, the present invention provides a method for measuring the gas-water relative permeability of hydrate-containing sediments by a non-steady-state method, the method comprising the following steps:

[0011] (1) Calculating the pore volume of the reactor after the sediment is filled, and then sequentially injecting xenon gas and water into the reactor so that the xenon gas in the reactor completely generates xenon hydrate, and calculating the xenon hydrate saturation;

[0012] (2) Injecting methane into the reactor at a constant pressure greater than the reactor outlet pressure to displace water, recording the amount of water displaced, the time of water emergence, the cumulative gas production and the cumulative water production when water emerged, the cumulative gas production and the cumulative water production at different times after water emergence, and the displacement pressure difference, and calculating the gas and water relative permeabilities and water saturation of the hydrate-containing sediments;

[0013] In step (1) and step (2), the outlet pressure of the reactor is controlled to be greater than the equilibrium pressure of xenon hydrate and less than the equilibrium pressure of methane hydrate.

[0014] The method provided by the present invention aims at the problem that methane hydrate is easy to generate or decompose during the measurement of gas and water relative permeability, and the methane hydrate saturation cannot be kept at a constant value. Xenon gas is used to replace methane gas to synthesize xenon hydrate, and then methane gas is used to displace water. Since the equilibrium pressure of xenon hydrate is lower than that of methane hydrate, during the displacement process, the displacement pressure is kept between the equilibrium pressure of xenon hydrate and methane hydrate, which can ensure that the xenon hydrate saturation does not change during the measurement process, and no new methane hydrate is generated. The present invention quantitatively describes the response law of gas and water relative permeability of hydrate-containing sediments with hydrate saturation through a non-steady-state method, and can realize the measurement of gas and water relative permeability of hydrate-containing sediments under indoor conditions.

[0015] Preferably, before calculating the pore volume in step (1), the volume of the reactor is measured by a liquid injection method.

[0016] Preferably, the pore volume in step (1) is calculated by a liquid injection method.

[0017] The "liquid injection method" refers to injecting a liquid medium into the reactor until the pores of the reactor are completely filled. The volume of the injected liquid is recorded, and the volume of the reactor is calculated by measuring the difference between the initial volume of the liquid and the volume of the remaining liquid in the reactor.

[0018] Preferably, the sediment in step (1) comprises any one of quartz sand, clay mineral or muddy silt.

[0019] Preferably, in step (1), the temperature of the reactor is controlled so that the xenon gas in the reactor is completely converted into xenon hydrate.

[0020] Preferably, the xenon hydrate saturation calculation formula in step (1) is as follows:

[0021]

[0022] Among them, S h is the xenon hydrate saturation, expressed as a percentage; V h 、V pore and V g They are the volume of xenon hydrate, the pore volume after the reactor is filled with sediment, and the gas volume, all in cm 3 ;m h With M h are the mass and molar amount of xenon hydrate, in g and g / mol respectively; ρ h is the density of xenon hydrate, in g / cm 3 ; P and T are the experimental pressure and temperature, respectively, in MPa and K; Z is the gas compressibility factor; R is the ideal gas constant, in J / (mol·K).

[0023] Preferably, in step (2), methane is injected to displace water until no water is discharged from the outlet of the reactor.

[0024] Preferably, the cumulative gas production in step (2) is corrected from the measured value at the reactor outlet to the value under the average pressure, and the calculation formula is as follows:

[0025]

[0026] Where: V i is the cumulative gas production at time i, in cm 3 ; ΔV gi Indicates the gas production increment from time i-1 to time i, in cm 3 ; V i-1 Indicates the cumulative gas production at time i-1, in cm 3 ;P a represents atmospheric pressure, in MPa; ΔP represents displacement pressure difference, in MPa.

[0027] In the present invention, when the methane gas pressure changes from the inlet pressure of the reactor to the outlet pressure, the gas volume changes, so the average volume flow rate is used, and the cumulative gas production value measured at the reactor outlet pressure is corrected to the value at the average pressure through the above formula.

[0028] Preferably, the calculation formula of the water relative permeability of the hydrate-containing sediment in step (2) is as follows:

[0029]

[0030] Where: k rw Represents the relative permeability of water, expressed as a decimal; f w (S w ) represents the moisture content, expressed as a decimal; It represents the dimensionless cumulative total amount of gas and water produced, expressed as a fraction of the pore volume; I represents the flow capacity ratio.

[0031] Preferably, the moisture content f w (S w ) is calculated as follows:

[0032]

[0033] in: Represents the dimensionless cumulative water production, expressed as a fraction of the pore volume.

[0034] Preferably, the calculation formula of the flow capacity ratio I is as follows:

[0035]

[0036] Where: Q(t) represents the gas production water flow rate at the reactor outlet at time t, in cm 3 / s;Q w Indicates the water flow rate at the reactor outlet at the initial moment, in cm 3 / s; ΔP0 represents the initial driving pressure difference, in MPa; ΔP(t) represents the displacement pressure difference at time t, ΔP(t) = ΔP0, in MPa.

[0037] In the present invention, since the constant pressure method is used for displacement, ΔP(t)=ΔP0.

[0038] Preferably, the calculation formula for the gas relative permeability of the hydrate-containing sediment in step (2) is as follows:

[0039]

[0040] Where: k rg Indicates the relative permeability of gas, expressed as a decimal; μ g Indicates the viscosity of methane gas at the measured temperature, in mPa·s; μ w It indicates the viscosity of water at the measurement temperature, in mPa·s.

[0041] Preferably, the calculation formula for the water saturation of the hydrate-containing sediment in step (2) is as follows:

[0042]

[0043] Where: S we Indicates the water saturation at the reactor outlet, expressed as a percentage; S ws Indicates bound water saturation, expressed as a percentage.

[0044] Preferably, the irreducible water saturation S wsIt is the difference between the saturated water volume and the driven water volume.

[0045] In a second aspect, the present invention provides an experimental device for measuring the gas-water relative permeability of hydrate-containing sediments by a non-steady-state method. The method described in the first aspect is adopted through the experimental device to measure the gas-water relative permeability of hydrate-containing sediments. The experimental device includes a gas-liquid supply unit, an experimental reaction unit, and a gas-liquid composition testing unit connected in sequence along the material flow direction; and also includes a data acquisition unit, and the gas-liquid supply unit, the experimental reaction unit, and the gas-liquid composition testing unit are respectively connected to the data acquisition unit.

[0046] The experimental device provided by the present invention has a simple structure and is easy to operate. It can achieve the goal of quantitatively measuring and calculating the relative permeability of gas and water and water saturation of hydrate-containing sediments by gas-water displacement under constant pressure, and highly simulates the actual hydrate reservoir seepage process.

[0047] Preferably, the experimental reaction unit comprises a reactor, and the reactor is placed in a constant temperature water bath.

[0048] Preferably, a temperature sensor assembly is provided inside the reactor to measure the internal temperature of the reactor.

[0049] Preferably, the pressure difference between the two ends of the reactor is measured by a pressure difference sensor.

[0050] Preferably, the outlet pressure of the reactor is controlled by a back pressure valve.

[0051] Preferably, the gas-liquid supply unit includes a xenon gas storage device, a methane storage device, a first plunger pump, a second plunger pump and a horizontal flow pump. The xenon gas storage device is connected to the reactor through the first plunger pump, the methane storage device is connected to the reactor through the second plunger pump, the horizontal flow pump is connected to the reactor, and the horizontal flow pump is used to supply water to the reactor.

[0052] Preferably, the xenon gas storage device comprises a xenon gas high-pressure cylinder.

[0053] Preferably, the methane storage device comprises a methane high-pressure gas cylinder.

[0054] Preferably, a first pressure sensor is provided between the first plunger pump and the reactor, and a second pressure sensor is provided between the second plunger pump and the reactor. The first pressure sensor and the second pressure sensor are respectively used to monitor the inlet pressure of the reactor.

[0055] Preferably, a circulating water pipe extends from the constant temperature water bath device to the cylinders of the first plunger pump and the second plunger pump and performs cold water circulation, so that the temperature in the cylinder is kept consistent with the temperature in the reactor.

[0056] Preferably, the gas-liquid composition testing unit comprises a gas-liquid separator, the inlet of the gas-liquid separator is connected to the reactor, the gas outlet of the gas-liquid separator is provided with a gas flow meter, and the liquid outlet of the gas-liquid separator is provided with a liquid flow meter.

[0057] Preferably, the data acquisition unit comprises a data acquisition module, the input end of the data acquisition module is connected in parallel to the temperature sensor assembly, the differential pressure sensor, the first pressure sensor, the second pressure sensor, the gas flow meter and the liquid flow meter, and the output end of the data acquisition module is connected to a computer.

[0058] Compared with the prior art, the present invention has the following beneficial effects:

[0059] The method for measuring the relative permeability of gas and water of hydrate-containing sediments by a non-steady-state method provided by the present invention aims at the problem that methane hydrates are easily generated or decomposed during the measurement of gas and water relative permeabilities, and the methane hydrate saturation cannot be kept at a constant value. Xenon gas is used to replace methane gas to synthesize xenon hydrates, and then methane gas is used to displace water. During the displacement process, the displacement pressure is maintained between the equilibrium pressure of xenon hydrate and methane hydrate, so that the saturation of xenon hydrates does not change during the measurement process, and no new methane hydrates are generated. The present invention quantitatively describes the response law of the relative permeability of gas and water of hydrate-containing sediments with hydrate saturation through a non-steady-state method, and can realize the measurement of the relative permeability of gas and water of hydrate-containing sediments under indoor conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0060] Figure 1 It is a schematic structural diagram of an experimental device for measuring the gas-water relative permeability of hydrate-containing sediments by a non-steady-state method provided by the present invention.

[0061] Among them: 1, reactor; 2, constant temperature water bath device; 3, temperature sensor assembly; 4, differential pressure sensor; 5, back pressure valve; 6, xenon high-pressure gas cylinder; 7, methane high-pressure gas cylinder; 8, first plunger pump; 9, second plunger pump; 10, horizontal flow pump; 11, first pressure sensor; 12, second pressure sensor; 13, gas-liquid separator; 14, gas flow meter; 15, liquid flow meter; 16, data acquisition module; 17, computer. DETAILED DESCRIPTION

[0062] The technical solution of the present invention is further described below by specific implementation methods. It should be understood by those skilled in the art that the embodiments are only to help understand the present invention and should not be regarded as specific limitations of the present invention.

[0063] The present invention provides a method for measuring the gas-water relative permeability of hydrate-containing sediments by a non-steady-state method, the method comprising the following steps:

[0064] (1) measuring the volume of the reactor 1 by a liquid injection method, and then calculating the pore volume of the reactor 1 after the sediment is filled by the liquid injection method; injecting xenon gas and water into the reactor 1 in sequence, controlling the temperature of the reactor 1 so that the xenon gas in the reactor 1 completely generates xenon hydrate, and calculating the xenon hydrate saturation;

[0065] The xenon hydrate saturation calculation formula is as follows:

[0066]

[0067] Among them, S h is the xenon hydrate saturation, expressed as a percentage; V h 、V pore and V g They are the volume of xenon hydrate, the pore volume after the reactor is filled with sediment, and the gas volume, all in cm 3 ;m h With M h are the mass and molar amount of xenon hydrate, in g and g / mol respectively; ρ h is the density of xenon hydrate, in g / cm 3 ; P and T are the experimental pressure and temperature, respectively, in MPa and K; Z is the gas compressibility factor; R is the ideal gas constant, in J / (mol·K).

[0068] (2) Methane was injected into the reactor 1 at a constant pressure greater than the outlet pressure of the reactor 1 to displace water until no water came out of the outlet of the reactor 1. The amount of water displaced, the time of water emergence, the cumulative gas production and the cumulative water production when water appeared, the cumulative gas production and the cumulative water production at different times after water appeared, and the displacement pressure difference were recorded to calculate the relative permeability of gas and water and the water saturation of the hydrate-containing sediments.

[0069] In step (1) and step (2), the outlet pressure of the reactor 1 is controlled to be greater than the equilibrium pressure of xenon hydrate and less than the equilibrium pressure of methane hydrate.

[0070] The cumulative gas production in step (2) is corrected from the measured value at the outlet of reactor 1 to the value under the average pressure, and the calculation formula is as follows:

[0071]

[0072] Where: V i is the cumulative gas production at time i, in cm 3 ; ΔV gi Indicates the gas production increment from time i-1 to time i, in cm 3 ; V i-1 Indicates the cumulative gas production at time i-1, in cm 3;P a represents atmospheric pressure, in MPa; ΔP represents displacement pressure difference, in MPa.

[0073] The calculation formula of the water relative permeability of the hydrate-containing sediment in step (2) is as follows:

[0074]

[0075] Where: k rw Represents the relative permeability of water, expressed as a decimal; f w (S w ) represents the moisture content, expressed as a decimal; It represents the dimensionless cumulative total amount of gas and water produced, expressed as a fraction of the pore volume; I represents the flow capacity ratio.

[0076] The moisture content f w (S w ) is calculated as follows:

[0077]

[0078] in: Represents the dimensionless cumulative water production, expressed as a fraction of the pore volume.

[0079] The calculation formula of the flow capacity ratio I is as follows:

[0080]

[0081] Where: Q(t) represents the gas production water flow rate at the outlet of reactor 1 at time t, in cm 3 / s;Q w Indicates the water flow rate at the outlet of reactor 1 at the initial moment, in cm 3 / s; ΔP0 represents the initial driving pressure difference, in MPa; ΔP(t) represents the displacement pressure difference at time t, ΔP(t) = ΔP0, in MPa.

[0082] The calculation formula for the gas relative permeability of the hydrate-containing sediment in step (2) is as follows:

[0083]

[0084] Where: k rg Indicates the relative permeability of gas, expressed as a decimal; μ g Indicates the viscosity of methane gas at the measured temperature, in mPa·s; μ w It indicates the viscosity of water at the measurement temperature, in mPa·s.

[0085] The calculation formula for the water saturation of the hydrate-containing sediment in step (2) is as follows:

[0086]

[0087] Where: S we Indicates the water saturation at the outlet of reactor 1, expressed as a percentage; S ws Indicates bound water saturation, bound water saturation S ws It is the difference between the saturated water volume and the driven water volume, expressed as a percentage.

[0088] The method is used to measure the gas-water relative permeability of hydrate-containing sediments through an experimental device. The structural schematic diagram of the experimental device is shown in FIG. Figure 1 As shown, the experimental device includes a gas-liquid supply unit, an experimental reaction unit and a gas-liquid composition testing unit which are connected in sequence along the material flow direction; it also includes a data acquisition unit, and the gas-liquid supply unit, the experimental reaction unit and the gas-liquid composition testing unit are respectively connected to the data acquisition unit.

[0089] The experimental reaction unit includes a reactor 1, which is placed in a constant temperature water bath device 2; a temperature sensor assembly 3 is arranged inside the reactor 1 for measuring the internal temperature of the reactor 1; the pressure difference between the two ends of the reactor 1 is measured by a pressure difference sensor 4; and the outlet pressure of the reactor 1 is controlled by a back pressure valve 5.

[0090] The gas-liquid supply unit includes a xenon high-pressure gas cylinder 6, a methane high-pressure gas cylinder 7, a first plunger pump 8, a second plunger pump 9 and a horizontal flow pump 10. The xenon high-pressure gas cylinder 6 is connected to the reactor 1 through the first plunger pump 8, the methane high-pressure gas cylinder 7 is connected to the reactor 1 through the second plunger pump 9, and the horizontal flow pump 10 is connected to the reactor 1. The horizontal flow pump 10 is used to supply water to the reactor 1; a first pressure sensor 11 is arranged between the first plunger pump 8 and the reactor 1, and a second pressure sensor 12 is arranged between the second plunger pump 9 and the reactor 1. The first pressure sensor 11 and the second pressure sensor 12 are respectively used to monitor the inlet pressure of the reactor 1; a circulating water pipe is extended from the constant temperature water bath device 2 to the cylinders of the first plunger pump 8 and the second plunger pump 9 and cold water is circulated so that the temperature in the cylinder is consistent with the temperature in the reactor 1.

[0091] The gas-liquid composition test unit comprises a gas-liquid separator 13 , the inlet of the gas-liquid separator 13 is connected to the reactor 1 , the gas outlet of the gas-liquid separator 13 is provided with a gas flowmeter 14 , and the liquid outlet of the gas-liquid separator 13 is provided with a liquid flowmeter 15 .

[0092] The data acquisition unit includes a data acquisition module 16 , the input end of the data acquisition module 16 is connected in parallel to the temperature sensor assembly 3 , the pressure difference sensor 4 , the first pressure sensor 11 , the second pressure sensor 12 , the gas flow meter 14 and the liquid flow meter 15 , and the output end of the data acquisition module 16 is connected to a computer 17 .

[0093] Example 1

[0094] This embodiment provides a method for measuring gas-water relative permeability of hydrate-containing sediments using a non-steady-state method, the method comprising the following steps:

[0095] (1) The volume of reactor 1 was measured by liquid injection method and was 401.9 cm 3 Then, the pore volume of reactor 1 after filling with quartz sand sediment with an average particle size of 250 μm was calculated by the liquid injection method to be 117.6 cm 3 ; Inject 150cm into the reactor 1 3 The xenon gas and excess water are added, the temperature of the reactor 1 is controlled at 277K, and the outlet pressure of the reactor 1 is controlled at 0.5MPa, so that the xenon gas in the reactor 1 completely generates xenon hydrate, and the xenon hydrate saturation is calculated to be 7.3%;

[0096] (2) Methane was injected into the reactor 1 at a constant pressure of 1 MPa to displace water, and the displacement pressure difference was 0.5 MPa until no water came out of the outlet of the reactor 1. The cumulative water production when water appeared was recorded as 1050.8 cm 3 , the cumulative gas production is 202.1cm 3 The cumulative water production after 1000s is 1067.5cm 3 , the cumulative gas production is 368.8cm 3 The cumulative gas production corrected to the value at the average pressure is 416.4 cm 3 The relative permeability of water in the hydrate-containing sediments was calculated to be 0.7, the relative permeability of gas in the hydrate-containing sediments was 0.13, and the water saturation was 30%.

[0097] This embodiment uses a non-steady-state method to measure the relative permeability of gas and water and the water saturation of hydrate-containing sediments under indoor conditions.

[0098] Comparative Example 1

[0099] This comparative example provides a method for measuring the permeability of hydrate-containing sediments, which is carried out by adopting the method for measuring the natural gas hydrate saturation and sediment permeability disclosed in CN105572014A.

[0100] The measurement method provided in this comparative example only describes the measurement of the absolute permeability of hydrate-containing sediments, but cannot measure the relative permeability of gas and water.

[0101] In summary, the method for measuring the relative permeability of gas and water in hydrate-containing sediments by the non-steady-state method provided by the present invention aims at the problem that methane hydrates are easily generated or decomposed during the measurement of gas and water relative permeabilities, and the methane hydrate saturation cannot be kept at a constant value. Xenon gas is used to replace methane gas to synthesize xenon hydrates, and then methane gas is used to displace water. During the displacement process, the displacement pressure is maintained between the equilibrium pressure of xenon hydrate and methane hydrate, so that the saturation of xenon hydrates does not change during the measurement process, and no new methane hydrates are generated. The present invention quantitatively describes the response law of the relative permeability of gas and water in hydrate-containing sediments with hydrate saturation through the non-steady-state method, and can realize the measurement of the relative permeability of gas and water in hydrate-containing sediments under indoor conditions.

[0102] The applicant declares that the above is only a specific implementation mode of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention shall fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for measuring the relative permeability of gas and water in hydrate-containing sediments by a non-steady-state method, characterized in that: The method comprises the following steps: (1) Calculating the pore volume of the reactor after the sediment is filled, and then sequentially injecting xenon gas and water into the reactor so that the xenon gas in the reactor completely generates xenon hydrate, and calculating the xenon hydrate saturation; (2) Injecting methane into the reactor at a constant pressure greater than the reactor outlet pressure to displace water, recording the amount of water displaced, the time of water emergence, the cumulative gas production and the cumulative water production when water emerged, the cumulative gas production and the cumulative water production at different times after water emergence, and the displacement pressure difference, and calculating the gas and water relative permeabilities and water saturation of the hydrate-containing sediments; In step (1) and step (2), the outlet pressure of the reactor is controlled to be greater than the equilibrium pressure of xenon hydrate and less than the equilibrium pressure of methane hydrate.

2. The method according to claim 1, characterized in that Before calculating the pore volume in step (1), the volume of the reactor is measured by the liquid injection method; Preferably, the sediment in step (1) comprises any one of quartz sand, clay mineral or muddy silt; Preferably, in step (1), the temperature of the reactor is controlled so that the xenon gas in the reactor is completely converted into xenon hydrate; Preferably, the xenon hydrate saturation calculation formula in step (1) is as follows: Among them, S h is the xenon hydrate saturation, expressed as a percentage; V h 、V pore and V g They are the volume of xenon hydrate, the pore volume after the reactor is filled with sediment, and the gas volume, all in cm 3 ;m h With M h are the mass and molar amount of xenon hydrate, in g and g / mol respectively; ρ h is the density of xenon hydrate, in g / cm 3 ; p and T are the experimental pressure and temperature, respectively, in MPa and K; Z is the gas compressibility factor; R is the ideal gas constant, in J / (mol·K).

3. The method according to claim 1 or 2, characterized in that: Step (2) injecting methane to displace water until no water comes out of the outlet of the reactor; Preferably, the cumulative gas production in step (2) is corrected from the measured value at the reactor outlet to the value under the average pressure, and the calculation formula is as follows: Where: V i is the cumulative gas production at time i, in cm 3 ; ΔV gi Indicates the gas production increment from time i-1 to time i, in cm 3 ; V i-1 Indicates the cumulative gas production at time i-1, in cm 3 ;P a represents atmospheric pressure, in MPa; ΔP represents displacement pressure difference, in MPa.

4. The method according to claim 3, characterized in that The calculation formula of the water relative permeability of the hydrate-containing sediment in step (2) is as follows: Where: k rw Represents the relative permeability of water, expressed as a decimal; f w (S w ) represents the moisture content, expressed as a decimal; It represents the dimensionless cumulative total amount of gas produced water, expressed as a fraction of the pore volume; I represents the flow capacity ratio; Preferably, the moisture content f w (S w ) is calculated as follows: in: It represents the dimensionless cumulative water production, expressed as a fraction of the pore volume; Preferably, the calculation formula of the flow capacity ratio I is as follows: Where: Q(t) represents the gas production water flow rate at the reactor outlet at time t, in cm 3 / s;Q w Indicates the water flow rate at the reactor outlet at the initial moment, in cm 3 / s; ΔP0 represents the initial driving pressure difference, in MPa; ΔP(t) represents the displacement pressure difference at time t, ΔP(t) = ΔP0, in MPa.

5. The method according to claim 4, characterized in that The calculation formula for the gas relative permeability of the hydrate-containing sediment in step (2) is as follows: Where: k rg Indicates the relative permeability of gas, expressed as a decimal; μ g Indicates the viscosity of methane gas at the measured temperature, in mPa·s; μ w It indicates the viscosity of water at the measurement temperature, in mPa·s.

6. The method according to claim 4 or 5, characterized in that: The calculation formula for the water saturation of the hydrate-containing sediment in step (2) is as follows: Where: S we Indicates the water saturation at the reactor outlet, expressed as a percentage; S ws It represents bound water saturation, expressed as a percentage; Preferably, the irreducible water saturation S ws It is the difference between the saturated water volume and the driven water volume.

7. An experimental device for measuring the relative permeability of gas and water in hydrate-containing sediments by a non-steady-state method, characterized in that: The method described in any one of claims 1 to 6 is used to measure the gas-water relative permeability of hydrate-containing sediments through the experimental device, wherein the experimental device includes a gas-liquid supply unit, an experimental reaction unit, and a gas-liquid composition testing unit connected in sequence along the material flow direction; and also includes a data acquisition unit, and the gas-liquid supply unit, the experimental reaction unit, and the gas-liquid composition testing unit are respectively connected to the data acquisition unit.

8. The experimental device according to claim 7, characterized in that: The experimental reaction unit comprises a reaction kettle, and the reaction kettle is placed in a constant temperature water bath device; Preferably, a temperature sensor assembly is provided inside the reactor to measure the internal temperature of the reactor; Preferably, the pressure difference between the two ends of the reactor is measured by a pressure difference sensor; Preferably, the outlet pressure of the reactor is controlled by a back pressure valve.

9. The experimental device according to claim 8, characterized in that: The gas-liquid supply unit comprises a xenon storage device, a methane storage device, a first plunger pump, a second plunger pump and a horizontal flow pump, wherein the xenon storage device is connected to the reactor via the first plunger pump, the methane storage device is connected to the reactor via the second plunger pump, the horizontal flow pump is connected to the reactor, and the horizontal flow pump is used to supply water to the reactor; Preferably, a first pressure sensor is provided between the first plunger pump and the reactor, and a second pressure sensor is provided between the second plunger pump and the reactor, and the first pressure sensor and the second pressure sensor are used to monitor the inlet pressure of the reactor respectively; Preferably, a circulating water pipe extends from the constant temperature water bath device to the cylinders of the first plunger pump and the second plunger pump and performs cold water circulation, so that the temperature in the cylinder is kept consistent with the temperature in the reactor.

10. The experimental device according to claim 9, characterized in that: The gas-liquid composition test unit comprises a gas-liquid separator, the inlet of the gas-liquid separator is connected to the reactor, the gas outlet of the gas-liquid separator is provided with a gas flow meter, and the liquid outlet of the gas-liquid separator is provided with a liquid flow meter; Preferably, the data acquisition unit comprises a data acquisition module, the input end of the data acquisition module is connected in parallel to the temperature sensor assembly, the differential pressure sensor, the first pressure sensor, the second pressure sensor, the gas flow meter and the liquid flow meter, and the output end of the data acquisition module is connected to a computer.

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