Method and device for judging the occurrence state of hydrate in sediment based on relaxation rate

Abstract

The present application discloses a method and device for judging the occurrence state of hydrates in sediments based on relaxation rate, comprising the following steps: performing nuclear magnetic resonance on a sediment sample to obtain a nuclear magnetic resonance signal M of the sediment sample during the hydrate formation and decomposition process; obtaining the water content w of the sediment sample during the hydrate formation and decomposition process through the change of the nuclear magnetic resonance signal M; calculating the surface relaxation rate of the sediment under different hydrate content states during the hydrate formation and decomposition process according to the following formula: judging the occurrence state of hydrates in sediments according to the change of the surface relaxation rate of hydrate-containing sediments with the hydrate content; the present application uses the nuclear magnetic resonance theory in porous media to judge the occurrence state of hydrates in sediments according to the change law of relaxation rate during the hydrate formation and decomposition process in sediments, thereby providing important data support for hydrate exploitation.

Description

Technical Field

[0001] The present application relates to the technical field of hydrate occurrence state research, and in particular to a method and device for judging the occurrence state of hydrates in sediments based on relaxation rate. Background Art

[0002] Natural gas hydrate is a new type of clean and high-quality energy with a wide distribution and huge reserves. It is a solid substance with a cage-shaped crystal structure formed by certain small molecular gases (mainly methane) and water molecules under certain temperature and pressure conditions. Exploration data show that there are abundant natural gas hydrate resources on the seabed along my country's coast. The natural gas hydrate resources in the South China Sea alone reach 70 billion tons, which is equivalent to half of the total proven natural gas resources in my country. The hydrate content and its occurrence mode are the main factors affecting the mechanical properties of hydrate-containing sediments. The exploitation of hydrates will change the soil structure (hydrate content and occurrence state), weaken the seabed strata, and may cause large-scale engineering geological disasters such as seabed subsidence, instability, and landslides, and damage artificial structures such as offshore oil platforms, submarine oil and gas pipelines, and submarine optical cables. Therefore, how to quantitatively test the hydrate content and its occurrence state is a key step in the hydrate exploitation plan. At present, the hydrate saturation in sediments can be indirectly obtained by calculating the gas consumption, and the occurrence state of hydrates in sediments has always been a key difficulty in hydrate detection experiments. Summary of the invention

[0003] In order to solve the above problems, the present application provides a method and device for judging the occurrence state of hydrates in sediments based on relaxation rate. With the help of nuclear magnetic resonance theory in porous media, the occurrence state of hydrates in sediments is judged according to the change law of relaxation rate during the formation and decomposition of hydrates in sediments. The technical solution is as follows:

[0004] In a first aspect, the present application provides a method for determining the occurrence state of hydrates in sediments based on relaxation rate, comprising the following steps: performing nuclear magnetic resonance on a sediment sample to obtain a nuclear magnetic resonance signal M of the sediment sample during hydrate formation and decomposition; obtaining the water content w of the sediment sample during hydrate formation and decomposition through changes in the nuclear magnetic resonance signal M; and calculating the surface relaxation rate of the sediment under different hydrate content states during hydrate formation and decomposition according to the following formula:

[0005]

[0006] Among them, ρ i is the relaxation rate, i = 1 or 2, representing the longitudinal and transverse relaxation rates respectively, ρ w is the density of water at 20℃, S is the specific surface area of ​​sediment, T i is the relaxation time, where i = 1 or 2, representing the longitudinal or transverse relaxation time, respectively;

[0007] The occurrence state of hydrates in sediments can be determined based on the change of surface relaxation rate of hydrate-containing sediments with hydrate content.

[0008] For example, in the method for determining the occurrence state of hydrates in sediments based on relaxation rate provided in one embodiment, the water content w of the sediment sample is obtained by the change of the nuclear magnetic resonance signal M, and the water content w of the sediment sample satisfies the following calculation formula:

[0009]

[0010] Wherein, w0 is the water content of the sediment sample before hydrate formation, and M0 is the NMR signal of the sediment sample before hydrate formation.

[0011] For example, in the method for judging the occurrence state of hydrates in sediments based on relaxation rate provided in one embodiment, the hydrate content w of the hydrate-containing sediment is h Satisfy the following calculation formula:

[0012] w h =w0-w.

[0013] For example, in the method for judging the occurrence state of hydrates in sediments based on relaxation rate provided in one embodiment, when hydrates begin to form in the sediments, the surface relaxation rate of the hydrate-containing sediments is i With hydrate content w h When the surface relaxation rate of the sediment increases steadily and remains equal to that of the sediment without hydrate, it indicates that the hydrate exists in the sediment as a filling hydrate.

[0014] For example, in the method for judging the occurrence state of hydrates in sediments based on relaxation rate provided in one embodiment, when hydrates begin to form in the sediments, the surface relaxation rate of the hydrate-containing sediments is i With hydrate content w h When the value of hydrate increases and decreases, it indicates that the hydrate exists in the sediment as cemented hydrate.

[0015] For example, in the method for judging the occurrence state of hydrates in sediments based on relaxation rate provided in one embodiment, when hydrates begin to form in the sediments, the surface relaxation rate of the hydrate-containing sediments is i With hydrate content w h The increase in relaxation rate decreased instantly, and then the relaxation rate remained stable, indicating that the hydrate existed in the sediment as encapsulated hydrate.

[0016] For example, in the method for judging the occurrence state of hydrate in sediment based on relaxation rate provided in one embodiment, the method for obtaining the nuclear magnetic signal amount M0 of the sediment sample before the hydrate is formed includes the following steps:

[0017] S1: Soak the soil particles in distilled water, wash them, and then air-dry them to obtain dry soil;

[0018] S2 preparing the dry soil body into a loose soil sediment sample with a water content of w0;

[0019] S3: placing the sediment sample into a nuclear magnetic resonance instrument, applying a sequence to the sediment sample, inverting the original nuclear magnetic resonance data, and obtaining a distribution curve of the pore water nuclear magnetic resonance relaxation time of the sediment sample;

[0020] S4 calculates the peak area of ​​the nuclear magnetic relaxation time distribution curve to obtain the total nuclear magnetic signal M0 of the sediment sample.

[0021] For example, in the method for determining the occurrence state of hydrates in sediments based on relaxation rate provided in one embodiment, the method for obtaining the nuclear magnetic signal amount M of the sediment sample after the hydrate is formed includes the following steps:

[0022] The sediment sample is cooled and pressurized to the designed parameters. After the hydrate is formed and stabilized, S3-S4 are repeated to obtain the nuclear magnetic signal M of the sediment sample after the hydrate is formed.

[0023] A second aspect of the present application provides an electronic device, comprising: a memory and a processor, wherein the processor is used to implement the above-mentioned method for determining the occurrence state of hydrates in sediments based on relaxation rate when executing a computer management program stored in the memory.

[0024] A third aspect of the present application provides a computer-readable storage medium having a computer management program stored thereon, which, when executed by a processor, implements the above-mentioned method for determining the occurrence state of hydrates in sediments based on relaxation rate.

[0025] The beneficial effects of a method and device for judging the occurrence state of hydrates in sediments based on relaxation rate provided in some embodiments of the present application are as follows: With the help of nuclear magnetic resonance theory in porous media, the present application judges the occurrence state of hydrates in sediments according to the change law of relaxation rate during the formation and decomposition of hydrates in sediments, providing an important information basis for hydrate exploitation. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] In order to more clearly illustrate the embodiments of this specification 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 application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0027] Figure 1 is the curve diagram of relaxation rate changing with hydrate content;

[0028] Figure 2 This is a schematic diagram of the structure of hydrate filling type in sediments;

[0029] Figure 3 This is a schematic diagram of the structure of cemented hydrate in sediments;

[0030] Figure 4 Schematic diagram of the structure of hydrate inclusion in sediments. DETAILED DESCRIPTION

[0031] The following will be combined with the drawings in the embodiments of the present application to clearly and completely describe the technical solutions in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0032] Unless otherwise defined, the technical terms or scientific terms used in the present disclosure should be understood by people with ordinary skills in the field to which the present disclosure belongs. The "first", "second" and similar words used in the present disclosure do not indicate any order, quantity or importance, but are only used to distinguish different components. "Include" or "comprise" and similar words mean that the elements or objects appearing before the word cover the elements or objects listed after the word and their equivalents, without excluding other elements or objects. "Connect" or "connected" and similar words are not limited to physical or mechanical connections, but can include electrical connections, whether direct or indirect. "Up", "down", "left", "right" and the like are only used to indicate relative positional relationships. When the absolute position of the described object changes, the relative positional relationship may also change accordingly.

[0033] In a first aspect, the present application provides a method for determining the occurrence state of hydrates in sediments based on relaxation rate, comprising the following steps:

[0034] Perform nuclear magnetic resonance on the sediment sample to obtain the nuclear magnetic resonance signal M of the sediment sample during the hydrate formation and decomposition process;

[0035] Specifically, the method for obtaining the nuclear magnetic signal amount M0 of the sediment sample before hydrate formation includes the following steps:

[0036] S1: Soak the soil particles in distilled water, wash them, and then air-dry them to obtain dry soil;

[0037] S2 preparing the dry soil body into a loose soil sediment sample with a water content of w0;

[0038] S3: placing the sediment sample into a nuclear magnetic resonance instrument, applying a sequence to the sediment sample, inverting the original nuclear magnetic resonance data, and obtaining a distribution curve of the pore water nuclear magnetic resonance relaxation time of the sediment sample;

[0039] S4 calculates the peak area of ​​the nuclear magnetic relaxation time distribution curve to obtain the total nuclear magnetic signal M0 of the sediment sample.

[0040] The method for obtaining the nuclear magnetic signal amount M of the sediment sample after hydrate formation comprises the following steps:

[0041] The sediment sample is cooled and pressurized to the designed parameters. After the hydrate is formed and stabilized, S3-S4 are repeated to obtain the nuclear magnetic signal M of the sediment sample after the hydrate is formed.

[0042] The water content w of the sediment sample during the hydrate formation and decomposition process is obtained through the change of the nuclear magnetic resonance signal M;

[0043] Specifically, the water content w of the sediment sample satisfies the following calculation formula:

[0044]

[0045] Wherein, w0 is the water content of the sediment sample before hydrate formation, and M0 is the NMR signal of the sediment sample before hydrate formation.

[0046] Hydrate content of hydrate-containing sediments w h Satisfy the following calculation formula:

[0047] w h =w0-w.

[0048] The surface relaxation rate of sediments at different hydrate contents during hydrate formation and decomposition was calculated according to the following formula:

[0049]

[0050] Among them, ρ i is the relaxation rate, i = 1 or 2, representing the longitudinal and transverse relaxation rates respectively, ρ w is the density of water at 20℃, S is the specific surface area of ​​sediment, T iis the relaxation time, where i = 1 or 2, representing the longitudinal or transverse relaxation time respectively; the relaxation rate of the sediment sample before hydrate formation is calculated based on the water content w0 of the sediment sample before hydrate formation as ρ i0 .

[0051] like Figure 1 As shown in Figure 2, the occurrence state of hydrates in sediments can be determined based on the change in the surface relaxation rate of hydrate-containing sediments with the hydrate content. The occurrence state of hydrates in sediments is shown in Figure 2. Figure 2-4 As shown, including filling type, bonding type and wrapping type, Figure 2-4 In the figure, 4 is a hydrate, 5 is a solid particle, and 6 is water.

[0052] Specifically, Figure 1 As shown in Figure 2, when hydrates begin to form in the sediments, the surface relaxation rate of the hydrate-containing sediments is i With hydrate content w h The surface relaxation rate ρ of the sediment remains constant and is equal to that of the sediment without hydrate. i0 hour( Figure 1 The middle curve 1) indicates that hydrates are formed in the middle of the pores. The formation of hydrates has no obvious effect on soil-water interaction. The corresponding state of hydrates in sediments is Figure 2 Filled hydrate shown.

[0053] like Figure 1 As shown in Figure 2, when hydrates begin to form in the sediments, the surface relaxation rate of the hydrate-containing sediments is i With hydrate content w h When the increase of Figure 1 The middle curve 2) shows that with the increase of hydrate, the soil-water interaction gradually decreases, and the corresponding hydrate occurrence state in the sediment is Figure 3 The cemented hydrate shown.

[0054] like Figure 1 As shown in Figure 2, when hydrates begin to form in the sediments, the surface relaxation rate of the hydrate-containing sediments is i With hydrate content w h The increase in the relaxation rate decreases momentarily, and then the relaxation rate remains constant ( Figure 1 The middle curve 3) shows that hydrates are first formed on the surface of soil particles, and the soil-water interaction is instantly reduced. The corresponding hydrate state in the sediment is Figure 4 The encapsulated hydrate is shown.

[0055] This application uses the nuclear magnetic resonance theory in porous media to judge the occurrence state of hydrates in sediments according to the change law of relaxation rate during the formation and decomposition of hydrates in sediments, providing an important information basis for hydrate exploitation.

[0056] A second aspect of the present application provides an electronic device, comprising: a memory and a processor, wherein the processor is used to implement the above-mentioned method for determining the occurrence state of hydrates in sediments based on relaxation rate when executing a computer management program stored in the memory.

[0057] A third aspect of the present application provides a computer-readable storage medium having a computer management program stored thereon, which, when executed by a processor, implements the above-mentioned method for determining the occurrence state of hydrates in sediments based on relaxation rate.

[0058] Although the implementation scheme of the present application has been disclosed as above, it is not limited to the applications listed in the specification and implementation modes, and it can be fully applicable to various fields suitable for the present application. For those familiar with the art, additional modifications can be easily implemented. Therefore, without departing from the general concept defined by the claims and the scope of equivalents, the present application is not limited to the specific details and the illustrations shown and described herein.

Claims

1. A method for judging the occurrence state of hydrates in sediments based on relaxation rate, characterized in that: The following steps are involved: Perform nuclear magnetic resonance on the sediment sample to obtain the nuclear magnetic resonance signal M of the sediment sample during the hydrate formation and decomposition process; The water content w of the sediment sample during the hydrate formation and decomposition process is obtained through the change of the nuclear magnetic resonance signal M; The surface relaxation rate of sediments at different hydrate contents during hydrate formation and decomposition was calculated according to the following formula: Among them, ρ i is the relaxation rate, i = 1 or 2, representing the longitudinal and transverse relaxation rates respectively, ρ w is the density of water at 20℃, S is the specific surface area of ​​sediment, T i is the relaxation time, where i = 1 or 2, representing the longitudinal or transverse relaxation time, respectively; When hydrates begin to form in sediments, according to the surface relaxation rate ρ of hydrate-containing sediments, i With hydrate content w h The occurrence state of hydrate in sediments can be determined by the changes in When i Follow h When the surface relaxation rate of the sediment increases steadily and remains equal to that of the sediment without hydrate, it indicates that the hydrate exists in the sediment as a filling hydrate; When i Follow h When the value of hydrate increases and decreases, it indicates that the hydrate exists in the sediment as cemented hydrate; When i Follow h The increase in relaxation rate decreased instantly, and then the relaxation rate remained stable, indicating that the hydrate existed in the sediment as encapsulated hydrate.

2. The method for judging the occurrence state of hydrates in sediments based on relaxation rate according to claim 1, characterized in that: The water content w of the sediment sample is obtained by the change of the nuclear magnetic resonance signal M, and the water content w of the sediment sample satisfies the following calculation formula: Wherein, w0 is the water content of the sediment sample before hydrate formation, and M0 is the NMR signal of the sediment sample before hydrate formation.

3. The method for judging the occurrence state of hydrate in sediment based on relaxation rate according to claim 2, characterized in that: Hydrate content of hydrate-containing sediments w h Satisfy the following calculation formula: In h =w0-w。 4. The method for judging the occurrence state of hydrate in sediment based on relaxation rate according to claim 3, characterized in that: The method for obtaining the nuclear magnetic signal M0 of the sediment sample before hydrate formation comprises the following steps: S1: Soak the soil particles in distilled water, wash them, and then air-dry them to obtain dry soil; S2 preparing the dry soil body into a loose soil sediment sample with a water content of w0; S3: placing the sediment sample into a nuclear magnetic resonance instrument, applying a sequence to the sediment sample, inverting the original nuclear magnetic resonance data, and obtaining a distribution curve of the pore water nuclear magnetic resonance relaxation time of the sediment sample; S4 calculates the peak area of ​​the nuclear magnetic relaxation time distribution curve to obtain the total nuclear magnetic signal M0 of the sediment sample.

5. The method for judging the occurrence state of hydrate in sediment based on relaxation rate according to claim 4, characterized in that: The method for obtaining the nuclear magnetic signal amount M of the sediment sample after hydrate formation comprises the following steps: The sediment sample is cooled and pressurized to the designed parameters. After the hydrate is formed and stabilized, S3-S4 are repeated to obtain the nuclear magnetic signal M of the sediment sample after the hydrate is formed.

6. An electronic device, characterized in that: include: A memory and a processor, wherein the processor is used to implement the method for determining the occurrence state of hydrates in sediments based on relaxation rate as described in any one of claims 1 to 5 when executing a computer management program stored in the memory.

7. A computer-readable storage medium having a computer management program stored thereon, characterized in that: When the computer management program is executed by the processor, the method for determining the occurrence state of hydrates in sediments based on relaxation rate as described in any one of claims 1 to 5 is implemented.

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