A method for analyzing dynamic sensible heat in hydrate production process

Abstract

The present invention discloses a method for analyzing dynamic sensible heat during hydrate exploitation, which belongs to the field of simulation research serving the development of natural gas hydrate resources. A stable multiphase hydrate system in which liquid water, hydrate and gas phase coexist is synthesized in a high-pressure reactor using sediment samples, and the system is subjected to a decompression disturbance at a constant pressure to determine the comprehensive sensible heat of the system at any time. The dynamic sensible heat analysis is performed by combining the comprehensive sensible heat with the decomposition enthalpy of the stable multiphase hydrate system at any time when the equilibrium pressure drops, so as to further explore the influence of the dynamic sensible heat of the hydrate reservoir on the hydrate decomposition behavior. This scheme considers the comprehensive sensible heat of the hydrate phase and the liquid phase while considering the reservoir sediments. The comprehensive sensible heat is related to the contents of the three phases of the sediment phase, the hydrate phase and the liquid phase, as well as their own thermophysical properties and the dynamic temperature changes of the system. Related research based on this method can provide a reference for the site selection and development plan design of field hydrate development.

Description

Technical Field

[0001] The present invention belongs to the field of simulation research serving the development of natural gas hydrate resources, and specifically relates to an analysis method of dynamic sensible heat in a hydrate exploitation process. Background Art

[0002] The decompression decomposition process of natural gas hydrate is usually divided into two stages: decompression and constant pressure. The "thermal drive" of hydrate decomposition is different in different periods. In the decompression stage of hydrate, the system pressure drops from the in-situ pressure to the target production pressure value. During the process, the reservoir temperature gradually decreases, and the gas production rate is usually high. When the pressure drops to the decomposition pressure, the temperature also drops to the lowest point. At this time, the system establishes a new equilibrium again. During this period, the decompression driving force for the decomposition of hydrates is essentially the reservoir sensible heat generated by the temperature difference between the new equilibrium reservoir state and the in-situ state of the reservoir. The drop in system pressure is only an appearance, and the change in sensible heat behind it is the fundamental source of power. In the constant pressure decomposition stage, because the reservoir has dropped to the lowest temperature, the reservoir sensible heat generated by the decompression drive is exhausted. At this stage, hydrates only use the conduction heat of the upper and lower overburdens or the surrounding remote reservoirs in the decomposition area as the thermal power for the continuous decomposition of hydrates.

[0003] At present, the focus of hydrate depressurization production is mainly on the heat conduction effect, and there is less analysis on the sensible heat supply stage of hydrate decomposition. On the one hand, it is due to the objective limitation of the reactor size. On the other hand, in the focus on reservoir sensible heat, it is mostly limited to the reservoir sediment framework, and it is believed that reservoir sensible heat is only supplied by sediments. But in fact, in the process of hydrate decomposition, especially the first stage of depressurization - the pressure drop stage, the hydrates in the reservoir have not been completely decomposed, and the fluids in the reservoir pores have not been completely produced. At this time, the undecomposed hydrate phase and the unproduced liquid phase can also be used as effective components of sensible heat to supply hydrate decomposition. However, it should also be noted that the hydrate phase and liquid phase at this time are constantly changing with the progress of production. Therefore, how to propose a comprehensive dynamic sensible heat quantification method for these two phases with constantly changing design phases is crucial to further explore the sensible heat mechanism of hydrate decomposition. Summary of the invention

[0004] In view of the defects in the analysis of sensible heat supply of hydrate decomposition in the prior art, the present invention proposes a method for analyzing dynamic sensible heat in the process of hydrate extraction, and considers the comprehensive sensible heat calculation model of the reservoir when the multiphase dynamic changes of sediments, hydrates and water during the hydrate decomposition process, which provides a possibility for guiding the study of gas production and comprehensive sensible heat effect in the process of hydrate development.

[0005] The present invention is implemented by adopting the following technical scheme: a method for analyzing dynamic sensible heat in a hydrate mining process, comprising the following steps:

[0006] Step A: Determine the density of the sediment sample s ;

[0007] (1) Add V to the centrifuge tube y0 Deionized water, and use a high-precision electronic scale to weigh a certain amount of dry sediment sample, use the pipette tip to vertically and slowly add the sediment sample into the centrifuge tube, shaking slightly while adding, and wait until the deionized water level rises to the scale V y0 +V Δy When the weight of the sediment sample injected is recorded, m s1 ;

[0008] (2) Let the centrifuge tube stand for more than 24 hours, then weigh a certain amount of sediment sample, and continue to add sediment sample with the help of a pipette tip until the liquid level reaches V y0 +2V Δy Scale, record the mass of sediment sample injected for the second time m s2 , then the density of the sediment sample

[0009] Step B: synthesizing a stable multiphase hydrate system containing liquid water, hydrate and gas phase in a high pressure reactor using the sediment sample, and subjecting the stable multiphase hydrate system to a constant pressure P w0 Perform a depressurization disturbance and determine the comprehensive sensible heat of the system at any time t;

[0010] At any time t, the liquid phase m in the synthesis autoclave wt , hydrate phase m ht and gas phase gt The contents are:

[0011] m wt =ρ w V w0 +108x_mol-m wp

[0012] m ht =n h0 M h -M h x_mol

[0013] n gt =n g0 +n disg0 +x_mol-n gasp -m wp S disgpt -m wt S disgt

[0014] The comprehensive sensible heat supply of the system is:

[0015]

[0016] m h0 =n h0 M h ,m w0 =ρ w V w0

[0017] Among them, C pn is the specific heat capacity of the corresponding phase, n is the phase identifier, s represents the sediment phase, n=ω corresponds to the liquid phase in the system, n=h corresponds to the hydrate phase, C ps is the specific heat capacity of the sediment phase; x_mol is the corresponding hydrate decomposition amount from decomposition to time t, m wp is the water production measured by the decomposition water metering system during the hydrate decomposition process at any time t, n gasp is the cumulative free gas output of the decomposed water metering system and the gas collection and metering system during the hydrate decomposition process corresponding to any time t, S disgpt and S disgt In T t , P t The methane solubility corresponding to the water decomposition metering system and the hydrate synthesis reactor under the same conditions. w0 、n h0 With n g0 are the liquid water volume, the molar amount of hydrate and the molar amount of gas in the stable multiphase hydrate-containing system, ρ w With M h are the liquid density and the molar mass of the hydrate, T in_situ With P in_situ To stabilize the final temperature and pressure of the system, m s0 is the mass of sediment sample added to the high-pressure reactor, n disg0 To stabilize the content of dissolved methane gas in the system;

[0018] Step C: Dynamic sensible heat analysis:

[0019] (1) Determine the pressure as P in_situ For a stable multiphase hydrate-containing system, at any time t of decomposition under reduced pressure, the decomposition enthalpy of the hydrate is:

[0020] ΔE=(456.22-0.134T t )(mh0-m ht )

[0021] (2) Stable multiphase hydrate system consists of P in_situ Change to P w0At any moment in the whole process, compare the relationship between ΔQ and ΔE. If there exists:

[0022] 1) ΔQ ≥ ΔE, or 1 / 2ΔE < ΔQ < ΔE, then the hydrate decomposition of the system is mainly supplied by the comprehensive sensible heat of the reservoir;

[0023] 2) ΔQ ≤ 1 / 2ΔE, then the comprehensive sensible heat supply of the reservoir is not the dominant factor in the decomposition of hydrates in the system, and the determination of the main influence of its decomposition can be further analyzed by other factors such as heat conduction.

[0024] If the system consists of P in_situ Change to P w0 In the process of decomposition, the two situations of ΔQ and ΔE appear in obvious stages, and the comprehensive sensible heat of the reservoir for hydrate decomposition in the process of decompression is dominated by stages; otherwise, it is considered that the hydrate decomposition of the system is not controlled by sensible heat, and other action mechanisms including heat conduction and seepage are further considered.

[0025] Furthermore, in step B, a synthesis reactor with a known volume of V is filled with a mass of m s0 sediment, then regardless of whether hydrate is synthesized in the reactor or not, the pore volume of the system for:

[0026]

[0027] Among them, ρ s is the density of the sediment sample.

[0028] By injecting V gin of methane gas and V win The stable multiphase hydrate system formed by water, the temperature and pressure in the stable state is T in-situ and P in-situ , at this time the liquid water content in the system is V w0 The molar mass of the hydrate is n h0 , then:

[0029]

[0030]

[0031] n disg0 =V w0 S disg0

[0032]

[0033] Among them, ρ h0 is the density of hydrate, Z and S disg0 T in_situ , P in_situThe methane gas compression factor and methane solubility under the conditions are combined with the above four equations, according to the specific T in_situ and P in_situ That is, the volume V of the only liquid water in the stable multiphase hydrate system is obtained. w0 , the unique hydrate molar mass n h0 and gas molar mass n g0 Corresponding value.

[0034] Furthermore, in step B, the stable multiphase hydrate system is subjected to a constant pressure P w0 During the depressurization process, the reservoir stable pressure P in_situ To P w0 Set different depressurization rates.

[0035] Compared with the prior art, the advantages and positive effects of the present invention are:

[0036] This scheme first determines the density of the sediment, and then uses the sediment sample to synthesize a stable multiphase hydrate system in which liquid water, hydrates and gas phases coexist in a high-pressure reactor, and then depressurizes the stable multiphase hydrate system at a constant pressure to determine the comprehensive sensible heat of the system at any time. The dynamic sensible heat analysis is performed by combining the comprehensive sensible heat with the decomposition enthalpy of the stable multiphase hydrate system at any time when the equilibrium pressure drops, so as to guide the study of gas production and comprehensive sensible heat effect during hydrate development. It is suitable for the analysis of hydrate decomposition gas production after synthesizing a hydrate system in an unknown sediment sample, especially for the dynamic sensible heat calculation method, hydrate decomposition enthalpy and comprehensive sensible heat effect quantitative analysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] Figure 1 This is a schematic diagram of the process of the analysis method described in the embodiment of the present invention;

[0038] Figure 2 Schematic diagram of the synthesis and decomposition system of hydrate-containing sediments used to achieve comprehensive sensible heat quantification of reservoirs;

[0039] Among them: 1. Sediment sample; 2. Centrifuge tube with deionized water for experiment; 3. Centrifuge tube after adding a certain amount of sediment sample; 4. Centrifuge tube containing mixture after standing for 24 hours; 5. Centrifuge tube with sediment sample added continuously; 6. Hydrate synthesis reactor with volume V; 7. Decomposed water metering system during hydrate decomposition; 8. Gas collection and metering system during hydrate decomposition; 9. Pore water in synthesis reactor; 10. Sediment sample filled in synthesis reactor; 11. Hydrate in synthesis reactor; 12. Water produced during decomposition; 13. Gas produced during decomposition; 14. Balance; 15. Temperature sensor; 16. Pressure sensor. DETAILED DESCRIPTION

[0040] In order to be able to more clearly understand the above-mentioned purpose, features and advantages of the present invention, the present invention is further described below in conjunction with the accompanying drawings and Examples. It should be noted that, in the case of no conflict, the embodiments of the present application and the features in the embodiments can be combined with each other. In the following description, a lot of specific details are set forth to facilitate a full understanding of the present invention, but the present invention can also be implemented in other ways different from those described herein, and therefore, the present invention is not limited to the specific embodiments disclosed below.

[0041] This embodiment proposes a method for analyzing dynamic sensible heat during hydrate production, such as Figure 1 As shown, the following steps are included:

[0042] Step A, determining the density of the sediment sample;

[0043] First, add V y0 mL deionized water; weigh a certain amount of sediment sample for the experiment, and add the sediment sample vertically and slowly into the centrifuge tube with the help of a pipette tip, shaking it slightly while adding it to allow the sample to settle and soak into the liquid, and prevent the liquid from adhering to the centrifuge tube due to excessive shaking. y0 +V Δy )mL scale on the inner wall; wait until the deionized water level rises to the scale (V y0 +V Δy )mL, record the weight of the sample injected at this time m s1 , unit: g; let the centrifuge tube stand for more than 24 hours, then weigh a certain amount of sediment sample, and continue to add sediment sample with the help of the pipette tip until the liquid level reaches (V y0 +2V Δy )mL scale, record the mass of the sediment sample injected for the second time m s2 , unit is g. Then, the density of the sediment is:

[0044]

[0045] Step B, synthesizing a stable multiphase hydrate-containing system in which liquid water, hydrates and gas phases coexist using a sediment sample; and performing a depressurization disturbance on the stable multiphase hydrate-containing system;

[0046] (1) Build a stable system;

[0047] A certain amount of sediment sample is filled into a high-pressure reactor with a volume of V. In this scheme, the sediment sample can be filled gradually and filled up in batches under specific temperature conditions, or the sediment sample of a certain volume of the reactor can be filled and the mass of the filled sediment sample m is recorded. s0, unit: g. The sediment is used to synthesize a stable multiphase hydrate system in which liquid water, hydrate and gas coexist. At this time, it is necessary to record the amount of methane gas V injected before synthesis. gin (standard condition, unit L) and the volume V of the injected deionized water w0 (Unit: mL). When the hydrate synthesis is completed and stabilized, the final stable temperature and pressure of the synthesized system are recorded as T in_situ and P in_situ , in units of ℃ and MPa respectively. Then, the volume of liquid water V at this time can be calculated according to the following formula: w0 (Unit: mL), molar amount of hydrate and gas n h0 With n g0 , unit is mol.

[0048]

[0049]

[0050]

[0051] n disg0 =V w0 S disg0

[0052]

[0053] Among them, ρ h0 The density of the hydrate is 0.912 g / mL, M h The molar mass of the hydrate is 124.0 g / mol, Z and S disg0 T in_situ and P in_situ The calculation of the methane gas compression factor and the solubility of methane under the corresponding conditions is a relatively mature technology. For details, please refer to "A calculation and analysis method for hydrate saturation in experimental and numerical simulation processes" (patent number: ZL201910327973.9) for implementation, and no further details will be given here.

[0054] (2) To stabilize the system, a pressure reduction disturbance is performed to determine the comprehensive sensible heat of the system at any time t;

[0055] Apply a certain constant pressure P to the stable multiphase system. w0 The decompression disturbance, in the process of system pressure drop, the content of liquid water and hydrate is the change over time, the decomposed water volume and the corresponding temperature and pressure are the results of real-time measurement by the balance and temperature and pressure sensors. At any time t, the water production measured by the decomposed water metering system in the process of hydrate decomposition with a volume of V1 is m wp , unit: g, the corresponding temperature and pressure are Tgas and P gas The gas collection and metering system V2 during the hydrate decomposition process is connected to V1, and its temperature and pressure are also T gas and P gas The temperature and pressure of the autoclave at this time are recorded as P t With T t .

[0056] Similarly, according to the invention patent "A method for calculating and analyzing hydrate saturation in experimental and numerical simulation processes" (patent number: ZL201910327973.9), the corresponding hydrate decomposition amount x_mol (unit mol) at time t, the temperature T of the decomposition water metering system and the gas collection and metering system during the hydrate decomposition process can be obtained. gas 、Pressure P gas The output of free gas corresponding to the conditions n gasp , as well as decomposition water metering system and hydrate synthesis reactor T t , P t The methane solubility corresponding to the conditions is S disgpt and S disgt (All units are mol / g).

[0057] Then, at any time t, the liquid phase m in the synthesis high-pressure reactor system wt , hydrate phase m ht and gas phase gt The contents are:

[0058] m wt =ρ w V w0 +108x_mol-m wp

[0059] m ht =n h0 M h -M h x_mol

[0060] n gt =n g0 +n disg0 +x_mol-n gasp -m wp S disgpt -m wt S disgt

[0061] The comprehensive sensible heat supply of the system is calculated as:

[0062]

[0063] m w0=ρ w V w0 , m h0 =n h0 M h

[0064] Among them, C pn is the specific heat capacity of the corresponding phase, n is the phase identifier, s represents the sediment phase, n = ω corresponds to the liquid phase in the system, and n = h corresponds to the hydrate phase.

[0065] Step C: Analysis of dynamic sensible heat:

[0066] The system is composed of pressure P in_situ At any time t of the decline, the decomposition enthalpy of the hydrate is:

[0067] ΔE=(456.22-0.134T t )(m h0 -m ht )

[0068] The analysis and judgment criteria are:

[0069] The system consists of P in_situ Change to P w0 At any time during the whole process, compare the values ​​of ΔQ and ΔE. If there exists:

[0070] (1) ΔQ ≥ ΔE, or 1 / 2ΔE < ΔQ < ΔE, then the hydrate decomposition in the system is mainly supplied by the comprehensive sensible heat of the reservoir;

[0071] (2) ΔQ ≤ 1 / 2ΔE, then the reservoir comprehensive sensible heat supply is not the dominant factor in the system hydrate decomposition process;

[0072] In addition, if the system consists of P in_situ Change to P w0 During the process, the above two situations appear in obvious stages. For example, in the time period 0-t1, there is one kind of ΔQ≥ΔE, while t1-t2 is the second kind of ΔQ≤1 / 2ΔE, and t2-t3 is the first kind of ΔQ≥ΔE. This obvious staged appearance indicates that the sensible heat of hydrate decomposition in the process of decomposition under reduced pressure is dominated by stages; otherwise, it is considered that the hydrate decomposition of the system is not controlled by sensible heat, and other action mechanisms including heat conduction and seepage are further considered.

[0073] At this point, by proposing the above-mentioned comprehensive calculation method and analysis method of dynamic sensible heat in the hydrate decomposition process, the sensible heat action mechanism of hydrate in the mining process can be further determined.

[0074] In order to understand this solution more clearly, the following is a detailed description of this solution in combination with two implementation cases:

[0075] Example 1:

[0076] A. After drying, measure the density of sediment sample A obtained from hydrate drilling in the actual sea area;

[0077] S11. Inject 30 mL of homemade deionized water into a 45 mL centrifuge tube, and use a high-precision electronic scale to weigh a large mass of dry sediment sample A on a weighing paper, and record the weighed mass m. A1 ;

[0078] S12. With the help of a pipette tip, specifically, a portion of the tip of a pipette tip of appropriate size can be cut off so that the sediment sample can flow out smoothly without clogging the pipette tip, and the pipette tip is placed upright and suspended 0.7-1.0 cm above the liquid surface.

[0079] S13. With the help of weighing paper, slowly inject the weighed sample A into the tip of the pipette, so that the sediment A falls vertically into the deionized water. During the injection process, oscillate slightly while injecting, so that a small amount of sediment particles floating on the liquid surface sink into the liquid with the oscillation. As the sediment A is continuously injected, slowly and vertically raise the tip of the pipette, so that the tip of the pipette is always 0.7-1.0 cm above the liquid surface, to prevent the pipette from contacting the liquid surface and contaminating the sediment sample that has not yet been injected.

[0080] S14. When the liquid level in the pipette rises to 35 mL, stop injecting the sediment and weigh the remaining sediment again. Record the weight m at this time. A2 .

[0081] S15. After the pipette containing sediment in S12 is left to stand for 24 hours, S13-S14 are repeated again so that after a certain amount of sediment A is injected again, the liquid level of deionized water just reaches 40mL. At this time, the remaining amount of sediment m is recorded again. A3 .

[0082] S16. Then the density of sediment A is:

[0083]

[0084] B. Calculation method of comprehensive sensible heat:

[0085] S21. In a volume V A The synthetic reactor is filled with sediment A in layers, and the mass m of the sediment A filled is measured. sA0 . A system containing a certain amount of hydrate is synthesized by gas injection, water injection and temperature control.

[0086] When the S22.S21 system is stable, the temperature and pressure in the synthesis reactor 6 are T in_situ1 and P in_situ1And by controlling and recording the synthetic experimental conditions, the contents of hydrate, liquid water and free methane gas phase in the hydrate-containing system under the stable state are calculated as follows: m h01 、m w01 , n g01 , the corresponding units are: g, g, and mol. And the content of dissolved methane gas n under this stable condition is obtained disg01 , unit: mol.

[0087] S23. Apply P to S22 hydrate system w01 By adjusting the pressure drop rate, the system pressure can be set from P in_situ1 Down to P w01 When the system pressure is P in_situ1 Down to P w0 In the process, through Figure 2 The volume shown is V 1A The decomposed water metering system 7 in the hydrate decomposition process obtains the water production m at any time t wpA , and the corresponding volume at that moment is V 2A The temperature and pressure of the gas collection and metering system 8 during the hydrate decomposition process are T gas1 , P gas1 .

[0088] S24. According to the invention patent "A method for calculating and analyzing hydrate saturation in experimental and numerical simulation processes" (patent number: ZL201910327973.9), at any time t, the corresponding hydrate decomposition amount x_mol1 (unit: mol) in the hydrate synthesis reactor 6, the cumulative free gas output n in the decomposed water metering system 7 and the gas collection and metering system 8 during the hydrate decomposition process gaspA , and according to the temperature and pressure conditions T of the decomposed water metering system 7 gas1 With P gas1 The corresponding methane solubility S can be obtained disgpt1 and the temperature and pressure conditions T of the synthesis reactor 6 tA , P tA The methane solubility S corresponding to the conditions disgt1 , the amount of methane dissolved in water produced during the hydrate decomposition process is n disgpA (Unit: mol). Then, the corresponding water phase m in the hydrate synthesis reactor 6 wt , hydrate phase m ht And gas phase gt The contents of w01 +108x_mol1-m wpA )、(m h01 -M hx_mol1) and (n g01 +n disg01 +x_mol1-n gaspA -m wpA S disgpt1 -m wt S disgt1 ).

[0089] S25. At any time t, the comprehensive sensible heat of the system is calculated as:

[0090]

[0091] In the above formula, C pn is the specific heat capacity of the corresponding phase. The specific values ​​of sediment and deionized water can be measured by differential scanning calorimetry, and the specific heat of hydrate can refer to the measured values ​​in the literature.

[0092] C. Dynamic sensible heat analysis method:

[0093] S31. The system consists of P in_situ1 Down to P w01 In the process, if: ΔQ ≥ ΔE, or 1 / 2 < ΔQ < ΔE, the hydrate decomposition of the system is mainly supplied by the comprehensive sensible heat of the reservoir;

[0094] In S32.S31, ΔE corresponds to any time t, the temperature condition of the synthesis reactor T tA The specific value of is expressed as:

[0095] ΔE=(456.22-0.134T tA )(m h01 -m ht )

[0096] S33. If ΔQ≤1 / 2ΔE, the comprehensive sensible heat supply of the reservoir is not the dominant factor in the hydrate decomposition process of the system, and heat conduction is considered to be the main influencing factor of hydrate decomposition.

[0097] Example 2: A method for analyzing dynamic sensible heat in the process of hydrate extraction. Different from Example 1, the density measurement operation of the sediment sample is changed as follows:

[0098] S11. Inject 20 mL of homemade deionized water into a 45 mL centrifuge tube.

[0099] S12. In S11, use a pipette tip and a high-precision electronic scale to slowly add the dry sediment sample B to S11, shaking while adding, until the liquid level in S11 rises to 30 mL, and record the weight of the sample B added at this time (m). B1 .

[0100] S13. Leave S12 to stand for more than 24 hours, then continue to slowly add sediment B sample in the same way, shaking while adding, so that all sediment B particles are immersed in the liquid. Record the weight of sediment B sample injected when the liquid level rises to 40mL (m). B2 .

[0101] S14. Then the density of sediment B is:

[0102]

[0103] Next, perform system comprehensive sensible heat calculation and dynamic sensible heat analysis as described in Case 1:

[0104] S21. In a volume V B Fill the synthesis reactor with sediment sample B until the reactor is 4 / 5V B The position of the sample B is recorded. B0 .

[0105] S22. Into S21, continuously inject methane gas from bottom to top and inject deionized water from top to bottom, and record the amount of gas and deionized water injected, which are n gas0in 、V w0in .

[0106] S23. Lower the temperature of S22 to allow hydrate synthesis. After the system synthesis is stable, slowly increase the system temperature to ensure that only the temperature of the system increases but the pressure remains unchanged. Record the temperature and pressure of the system after stabilization, which are T in_situ2 and P in_situ2 At this time, the contents of sediment, liquid water and hydrate in the hydrate synthesis reactor are m B0 、V wB0 and n hB0 , the units are: g, mL, mol respectively.

[0107] S24. According to the invention patent "A method for calculating and analyzing hydrate saturation in experimental and numerical simulation processes" (patent number: ZL201910327973.9), the content of dissolved methane gas in the stable state of S23 can be calculated. disgB01 , in mol. Note that the pore volume at this time is Calculation according to Then, in this stable state, the content of free gas in the synthesis reactor 6 is: n gB0 =n gas0in -3m hB0 / 62-n disgB01 .

[0108] S25. Apply P to the S23 hydrate systemwB01 The pressure drop disturbance is caused by the system pressure P in_situ2 Down to P wB01 In the process, through Figure 1 The decomposed water metering system 7 during the hydrate decomposition process and the gas collection and metering system 8 during the hydrate decomposition process can measure the water production m at any time t. wpBt , and the corresponding temperature and pressure T of the gas collection and metering system 8 gasB1 , P gasB1 .

[0109] S26. According to the measured data of S25, the invention patent "A method for calculating and analyzing hydrate saturation in experimental and numerical simulation processes" (patent number: ZL201910327973.9) can be obtained that at any time t, the corresponding hydrate decomposition amount xB_mol (unit: mol) in the hydrate synthesis reactor 6 and the cumulative free gas output n gaspB (Unit: mol). In addition, according to the temperature and pressure conditions T of the gas collection and metering system 8 during the hydrate decomposition process gasB1 , P gasB1 The solubility S of methane under the corresponding conditions can be obtained disgptB1 , the temperature and pressure T of the synthesis reactor 6 Bt , P Bt The methane solubility S corresponding to the conditions disgtB1 , and the amount of dissolved methane in the water produced in the decomposition water metering system 7 during the hydrate decomposition process n disgpB =S disgptB1 *m wpBt , unit: mol. Then, the corresponding water phase in the hydrate synthesis reactor 6 is m wtB , hydrate phase m htB And gas phase gtB The contents are:

[0110] m wtB =V wB0 ρ w +108xB_mol-m wpBt

[0111] m htB =n hB0 M h -M h xB_mol

[0112] n gtB =n gB0 +n disgB01 +xB_mol-n gaspB -n disgpB -m wtB S disgtB1

[0113] S27. At any time t, the comprehensive sensible heat of the system is calculated as:

[0114]

[0115] Therefore, during the hydrate decomposition process, for any time t, there is a unique ΔQ value. By comparing the ΔQ and ΔE values, the mechanism of the comprehensive sensible heat in the system decomposition process can be further determined. Specifically:

[0116] Dynamic sensible heat analysis method:

[0117] Compare the values ​​of comprehensive sensible heat ΔQ and ΔE at any time, where

[0118] ΔE=(456.22-0.134T Bt )(n hB0 M h -m htB )

[0119] Similarly, if the values ​​of ΔQ and ΔE show stage-by-stage size differences, for example

[0120] At a certain stage, ΔQ ≥ ΔE, or 1 / 2 < ΔQ < ΔE, then the hydrate decomposition of the system in this stage is mainly supplied by the comprehensive sensible heat of the reservoir;

[0121] At a certain stage, ΔQ≤1 / 2ΔE is always present, indicating that the main thermodynamic force for hydrate decomposition in the system during this stage is not reservoir sensible heat, and heat conduction may play a leading role.

[0122] If during the entire decomposition process, ΔQ and ΔE do not show obvious regular stage-by-stage changes as above, then the decomposition of hydrates in the system is not caused by thermal mechanism, and other characteristics such as seepage should be considered.

[0123] The above description is only a preferred embodiment of the present invention and does not limit the present invention in other forms. Any technician familiar with the profession may use the technical content disclosed above to change or modify it into an equivalent embodiment with equivalent changes and apply it to other fields. However, any simple modification, equivalent change and modification made to the above embodiment based on the technical essence of the present invention without departing from the content of the technical solution of the present invention still falls within the protection scope of the technical solution of the present invention.

Claims

1. A method for analyzing dynamic sensible heat in a hydrate mining process, characterized in that: The following steps are involved: Step A: Determine the density of the sediment sample s ; Step B: synthesizing a stable multiphase hydrate system containing liquid water, hydrate and gas phase in a high pressure reactor using the sediment sample, and subjecting the stable multiphase hydrate system to a constant pressure P w0 Perform a depressurization disturbance and determine the comprehensive sensible heat of the system at any time t; At any time t, the liquid phase m in the autoclave wt , hydrate phase m ht and gas phase gt The contents are: m wt =ρ w V w0 +108x_mol-m wp m ht =n h0 M h -M h x_mol n gt =n g0 +n disg0 +x_mol-n gasp -m wp S disgpt -m wt S disgt The comprehensive sensible heat supply of the system is: ΔQ=C ps m s0 (T in_situ -T t )+∫[C pn (m n0 -m nt )dT t ] n=ω,h m h0 =n ho M h ,m w0 =ρ w V w0 Among them, C pn is the specific heat capacity of the corresponding phase, n is the phase identifier, s represents the sediment phase, n=ω corresponds to the liquid phase in the system, n=h corresponds to the hydrate phase, C ps is the specific heat capacity of the sediment phase; x_mol is the corresponding hydrate decomposition amount from decomposition to time t, m wp is the water production measured by the decomposition water metering system during the hydrate decomposition process at any time t, n gasp is the cumulative free gas output of the decomposed water metering system and the gas collection and metering system during the hydrate decomposition process corresponding to any time t, S disgpt and S disgt In T t , P t The methane solubility corresponding to the water decomposition metering system and the hydrate synthesis reactor under the conditions; V w0 、n h0 With n g0 are the liquid water volume, the molar amount of hydrate and the molar amount of gas in the stable multiphase hydrate-containing system, ρ w With M h are the liquid density and the molar mass of the hydrate, T in_sit With P in_situ To stabilize the final temperature and pressure of the system, m s0 is the mass of sediment sample added to the high-pressure reactor, n disg0 To stabilize the content of dissolved methane gas in the system; Step C: Dynamic sensible heat analysis: (1) Determine the pressure as P in_situ For a stable multiphase hydrate-containing system, at any time t of decomposition under reduced pressure, the decomposition enthalpy of the hydrate is: ΔE=(456.22-0.134T t )(m h0 -m ht ) (2) Stable multiphase hydrate system consists of P in_situ Change to P w0 At any moment in the whole process, compare the relationship between ΔQ and ΔE. If there exists: 1) ΔQ ≥ ΔE, or 1 / 2ΔE < ΔQ < ΔE, then the hydrate decomposition of the system is mainly supplied by the comprehensive sensible heat of the reservoir; 2) ΔQ ≤ 1 / 2ΔE, then the comprehensive sensible heat supply of the reservoir is not the dominant factor in the decomposition of hydrates in the system, and the determination of the main influence of its decomposition can be further analyzed by other factors such as heat conduction.

2. The method for analyzing dynamic sensible heat in the hydrate production process according to claim 1, characterized in that: In the step C, if the system consists of P in_situ Change to P w0 In the process of decomposition, the two situations of ΔQ and ΔE appear in obvious stages, and the comprehensive sensible heat of the reservoir for hydrate decomposition in the process of decompression is dominated by stages; otherwise, it is considered that the hydrate decomposition of the system is not controlled by sensible heat, and other action mechanisms including heat conduction and seepage are further considered.

3. The method for analyzing dynamic sensible heat in the hydrate production process according to claim 1, characterized in that: In step A, the following method is used to determine the density of the sediment sample: (1) Add V to the centrifuge tube y0 Deionized water, and use a high-precision electronic scale to weigh a certain amount of dry sediment sample, use the pipette tip to vertically and slowly add the sediment sample into the centrifuge tube, shaking slightly while adding, and wait until the deionized water level rises to the scale V y0 +V Δy When the weight of the sediment sample injected is recorded, m s1 ; (2) Let the centrifuge tube stand for more than 24 hours, then weigh a certain amount of sediment sample, and continue to add sediment sample with the help of a pipette tip until the liquid level reaches V y0 +2V Δy Scale, record the mass of sediment sample injected for the second time m s2 , then the density of the sediment sample 4. The method for analyzing dynamic sensible heat in the hydrate production process according to claim 1, characterized in that: In step B, a synthesis reactor with a known volume V is filled with a mass of m s0 sediment, then regardless of whether hydrate is synthesized in the reactor or not, the pore volume of the system for: Among them, ρ s is the density of the sediment sample.

5. The method for analyzing dynamic sensible heat in the hydrate production process according to claim 1, characterized in that: In step B, by injecting V gin of methane gas and V win The stable multiphase hydrate system formed by water, the temperature and pressure in the stable state is T in-situ and P in-situ , at this time the liquid water content in the system is V w0 The molar mass of the hydrate is n h0 , then: n disg0 =V w0 S disg0 Among them, ρ h0 is the density of hydrate, Z and S disg0 T in_situ , P in_situ The methane gas compression factor and methane solubility under the conditions are combined with the above four equations, according to the specific T in_situ and P in_situ That is, the volume V of the only liquid water in the stable multiphase hydrate system is obtained. w0 , the unique hydrate molar mass n h0 and gas molar mass n g0 The corresponding value of .

6. The method for analyzing dynamic sensible heat in the hydrate production process according to claim 1, characterized in that: In step B, the stable multiphase hydrate system is subjected to a constant pressure P w0 During the depressurization process, the reservoir stable pressure P in_situ To P w0 Set different depressurization rates.

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