Apparatus and method for exploiting hydrates using deep geothermal

Abstract

The application discloses a device and method for exploiting hydrate by using deep geothermal energy, and the device and method can save the cost of heat source, realize continuous supply of deep heat source and continuous production of hydrate by calculating the temperature of the heat source in the deep sand layer of the hydrate enrichment area, determining the depth of the heat source stratum, extracting the heat source in the deep sand layer to the production section, and heating the hydrate layer and directly using the deep heat source.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of natural gas hydrate exploitation, and particularly relates to a device and method for exploiting hydrates by using deep geothermal energy. BACKGROUND

[0002] Natural gas hydrate is one of the most promising alternative energy sources in the future. Since 2002, countries around the world have successively carried out 11 hydrate test productions around hydrate reservoirs, but none of them has achieved the goal of sustained and high-yield gas production. Countries have explored various hydrate exploitation methods in theory and technology, such as pressure reduction method, solid sulfurization method, thermal stimulation method, and chemical potential difference driving method. Among them, the pressure reduction method is considered to be the most promising technology for industrialized exploitation of hydrates in terms of technology and economy, and the pressure reduction strategy is adopted in almost every test production worldwide.

[0003] However, the decomposition of hydrates is an endothermic process, and the decomposition of hydrates in the pressure reduction process will cause a sharp drop in reservoir temperature, thereby inducing the secondary generation of hydrates or even the production of ice, which in turn inhibits the continuous decomposition of hydrates, ultimately resulting in reduced gas production efficiency, shortened gas production period, or even discontinued production. The existing methods continuously heat the formation by injecting hot water, hot steam, and the like, thereby solving the problem of temperature drop, but these methods require a large amount of cost and consume a lot of energy, and have low heat efficiency. SUMMARY

[0004] The present application aims to at least solve one of the technical problems existing in the prior art. To this end, the present application proposes a method for exploiting hydrates by using deep geothermal energy, which can determine the optimal heat extraction depth, use deep heat sources to heat the hydrate layer, and reduce the cost of heat sources, and has good heat exchange effect.

[0005] The present application also proposes a device for exploiting hydrates by using deep geothermal energy using the above method.

[0006] The method for exploiting hydrates by using deep geothermal energy according to the first aspect of the present application comprises the following steps:

[0007] calculating the temperature of the heat source in the deep sand layer of the hydrate enrichment area;

[0008] determining the heat extraction formation depth;

[0009] drilling a horizontal production section in the hydrate layer, wherein the production section is provided with a flow guide part in communication with the hydrate layer;

[0010] drilling a heat extraction section connected to the heat extraction formation depth downwardly, wherein a first flow valve is arranged between the heat extraction section and the production section, and a second flow valve is arranged between the production section and the production well;

[0011] closing the first flow valve, using the depressurization method to produce;

[0012] opening the first flow valve, closing the second flow valve, extracting the heat source into the production section, the heat source flows into the hydrate layer through the flow guide, and the hydrate layer is heated;

[0013] opening the second flow valve, reducing the formation pressure, and the decomposition gas generated by the decomposition of the hydrate under heat flows into the production section through the flow guide for production.

[0014] According to the method for exploiting hydrates by using deep geothermal energy according to the first aspect of the present application, at least the following beneficial effects are achieved: the method for exploiting hydrates by using deep geothermal energy according to the present application can calculate the temperature of the heat source in the deep sand layer of the hydrate-rich area, determine the depth of the heat extraction formation, extract the heat source in the deep sand layer to the production section, heat the hydrate layer, and directly utilize the deep heat source, which can save the cost of the heat source, realize the continuous supply of the deep heat source, and continuously produce the hydrates; by calculating the temperature of the heat source in the deep sand layer, the depth of the heat extraction formation can be determined, which can ensure that the extracted heat source has a good temperature, can effectively conduct heat, and improve the heat efficiency.

[0015] According to some embodiments of the present application, in the determination of the depth of the heat extraction formation, the following steps are included:

[0016] by the fluid extraction flow Q w and the wellbore cross-sectional area A of the production section p calculate the fluid velocity V per unit area w and the mass m of the fluid flowing through w ;

[0017] calculate the heat loss q1 of the fluid during the fluid extraction process;

[0018] calculate the heat transfer amount q2 of the fluid during the fluid extraction process;

[0019] determine the depth of the heat extraction formation by calculating the heat loss q1 of the fluid in the wellbore and the heat transfer amount q2 of the fluid.

[0020] According to some embodiments of the present application, the following steps are included:

[0021] the fluid extraction flow is Q w , d is the inner diameter of the wellbore of the production section, A p is the wellbore cross-sectional area of the production section, then

[0022]

[0023] m w = Q w · ρ w ;

[0024] calculating heat loss q1 of the fluid in the wellbore during the process, wherein C w is the specific heat capacity, T2 is the water temperature at the depth of the heat production formation, and T1 is the lowest temperature of the heat source flowing into the hydrate layer:

[0025] q1 = m w · C w · (T2-T1);

[0026] ΔT m is the average temperature difference, A is the pipe wall area, k is the total heat transfer coefficient, and l is the length of the well;

[0027] q2 = k·A·ΔT m ;

[0028] a = π·d·l;

[0029]

[0030] h is the heat transfer coefficient of the wellbore, a is the heat transfer coefficient of the fluid to the wellbore during the process of flowing in the wellbore, and λ is the thermal conductivity of the fluid at the corresponding temperature;

[0031]

[0032] Re is the Reynolds number, which is related to the inner diameter of the well:

[0033]

[0034] Since the heat loss q1 of the fluid in the wellbore should be equal to the heat transfer q2 during the process of the fluid,

[0035] q1 = q2;

[0036] m w · C w · (T2-T1) = k·A·ΔT m ;

[0037] The water temperature T2 at the depth of the heat production formation is calculated, the depth of the heat production formation is x, and the water temperature T2 at the depth of the heat production formation is calculated by

[0038] T2 = 3 + 0.1x;

[0039] Thus, the depth x of the heat production formation is obtained.

[0040] According to some embodiments of the present application, in the determination of the depth of the heat production formation by calculation, further comprising:

[0041] The lowest temperature T1 of the heat source flowing into the hydrate layer is 40℃.

[0042] According to some embodiments of the present application, in the calculation of the temperature of the heat source in the deep sand layer of the hydrate enrichment zone, further comprising:

[0043] By measured geothermal gradient G and measured bottom temperature T sf The heat source temperature T at D+1 meters below the bottom formation D+1 is calculated.

[0044] When D=0, T D is the temperature at 0 meters below the bottom formation, i.e. T D =T sf , and

[0045]

[0046] The heat source temperature T at D+1 meters below the bottom formation can be obtained. d+1

[0047] According to some embodiments of the present application, in the production using the depressurization method after the first flow valve is closed, further comprising:

[0048] The depressurization amplitude is 0.2 times the initial formation pressure, and the depressurization production lasts for 15 days.

[0049] According to some embodiments of the present application, further comprising:

[0050] Observing the change of the gas production during the depressurization production;

[0051] When the hydrate layer temperature decreases and the gas production decreases, the first flow valve is opened, the second flow valve is closed, and the heat source is extracted into the production section.

[0052] According to some embodiments of the present application, the heat source is extracted into the production section, comprising:

[0053] After the heat source is extracted into the wellbore filled with the production section, the first flow valve is closed, and the hydrate layer temperature change is observed for three days;

[0054] When the hydrate layer temperature no longer increases, the first flow valve is opened, the heat source is extracted into the production section until the wellbore is filled with the production section, the first flow valve is closed, and the hydrate layer temperature change is observed;

[0055] The above steps are repeated until the hydrate layer temperature reaches the standard of the depressurization production, and the depressurization production is performed.

[0056] The device for exploiting hydrates using deep geothermal energy according to the second aspect of the present application uses the method for exploiting hydrates using deep geothermal energy according to the first aspect of the present application, and further comprises:

[0057] A production well;

[0058] ​a production section connected to the production well, the production section being horizontally arranged in the hydrate layer, the production section being provided with a flow guide part in communication with the hydrate layer;

[0059] a heat extraction section connected to the production section at one end and connected to a heat extraction formation at the other end;

[0060] wherein a first flow valve is arranged between the heat extraction section and the production section, and a second flow valve is arranged between the production section and the production well.

[0061] According to the second aspect of the present application, the device for exploiting hydrates using deep geothermal energy has at least the following beneficial effects: the device for exploiting hydrates using deep geothermal energy includes a production well, a production section, and a heat extraction section. The production section is horizontally arranged in the hydrate layer and is provided with a flow guide part in communication with the hydrate layer. The production section exchanges hydrolysis gas with the hydrate layer through the flow guide part, which can realize continuous production of hydrates. The heat extraction section is connected to a heat extraction formation. The heat source in the deep formation is extracted into the production section through the heat extraction section, which directly uses the deep heat source to heat the hydrate layer, can save heat source cost, and realizes continuous supply of deep heat source. The first flow valve and the second flow valve are used to switch between pressure reduction production and heat source supply, which can save heat source cost, realize continuous supply of deep heat source, and continuous production of hydrates.

[0062] According to some embodiments of the present application, the heat extraction section includes a horizontal branch section connected to the production section and a vertical branch section in communication with the heat extraction formation.

[0063] Additional aspects and advantages of the present application will be in part apparent and in part pointed out hereinafter. BRIEF DESCRIPTION OF DRAWINGS

[0064] The above and / or additional aspects and advantages of the present application will become apparent and be readily appreciated from the following description, including the appended drawings, wherein:

[0065] Figure 1 is a flow chart of a method for exploiting hydrates using deep geothermal energy according to an embodiment of the present application;

[0066] Figure 2 is a structural schematic diagram of a device for exploiting hydrates using deep geothermal energy according to an embodiment of the present application;

[0067] Figure 3 is a structural schematic diagram of a device for exploiting hydrates using deep geothermal energy according to another embodiment of the present application;

[0068] Figure 4is a schematic view of a cross section of a production section according to an embodiment of the present application.

[0069] Reference signs:

[0070] Production well 100;

[0071] Production section 200, flow guide 210;

[0072] Heat extraction section 300, horizontal branch section 310, vertical branch section 320;

[0073] First flow valve 410, second flow valve 420, third flow valve 430;

[0074] Hydrate layer 500. DETAILED DESCRIPTION

[0075] Embodiments of the present application are described below in detail, examples of which are shown in the drawings, wherein the same or similar reference signs represent the same or similar elements or elements having the same or similar functions throughout. The embodiments described below by referring to the drawings are exemplary and are only used to explain the present application, and cannot be understood as a limitation of the present application.

[0076] In the description of the present application, it is understood that the orientation description, such as the orientation or position relationship indicated by up, down, front, back, left, right, inner, outer, etc. is based on the orientation or position relationship shown in the drawings, and is only for the purpose of facilitating the description of the present application and simplifying the description, and does not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as a limitation of the present application.

[0077] In the description of the present application, the meaning of several is one or more, and the meaning of multiple is more than two, greater than, less than, more than, etc. are understood as not including the number, and above, below, etc. are understood as including the number. If it is described as first, second, it is only for the purpose of distinguishing technical features, and cannot be understood as indicating or implying relative importance or implicitly indicating the number of indicated technical features or the order of indicated technical features.

[0078] In the description of the present application, unless otherwise explicitly limited, the words such as setting, installing, connecting, assembling, cooperating, etc. should be broadly understood, and the person skilled in the art can reasonably determine the specific meaning of the above words in the present application in combination with the specific content of the technical solution.

[0079] The following refers to Figures 1 to 3 A method for exploiting hydrates using deep geothermal energy according to an embodiment of the present application is described.

[0080] A method for exploiting hydrates using deep geothermal energy according to an embodiment of the present application is described with reference to Figure 1, comprising the following steps:

[0081] Step S1: calculating the temperature of the heat source in the deep sand layer of the hydrate enrichment zone. First, the distribution of the deep sand layer of the hydrate enrichment zone needs to be evaluated. For the distribution of the sand layer, the sedimentary facies related to the sandy sedimentary body such as the channel-levee is interpreted by using the seismic data, the sand body distribution in different depth ranges is identified, and the sand body plan distribution map is drawn. For the temperature of the heat source, the temperature of the heat source several meters below the seabed stratum is calculated by the measured geothermal gradient and the measured seabed temperature. It should be noted that the heat source mentioned in the present application includes hot water, hot gas and other heat fluids.

[0082] Step S2: determining the depth of the heat production stratum. After obtaining the temperature of the heat source, the optimal depth of the heat production stratum is determined according to the conditions of the hydrate layer 500.

[0083] Step S3: drilling a horizontal production section 200 in the hydrate layer 500, the production section 200 being provided with a flow guide part 210 in communication with the hydrate layer 500. After determining the depth of the heat production stratum, a set of sand layers near the depth of the heat production stratum is selected as the target heat production layer, and a horizontal production section 200 is formed by horizontal drilling in the hydrate layer 500, the production section 200 being provided with a flow guide part 210 in communication with the hydrate layer 500.

[0084] Step S4: drilling a heat production section 300 connected to the depth of the heat production stratum, a first flow valve 410 is arranged between the heat production section 300 and the production section 200, and a second flow valve 420 is arranged between the production section 200 and the production well 100. The first flow valve 410 is used to control the flow of the heat source from the heat production section 300 to the production section 200, and the second flow valve 420 is used to control the flow of the hydrolysis gas from the production section 200 to the production well 100.

[0085] Step S5: closing the first flow valve 410 and using the depressurization method for depressurization production. By closing the first flow valve 410, the heat source cannot flow from the heat production section 300 to the production section 200, and the formation pressure is reduced by the depressurization method. The hydrate is stable in the low-temperature and high-pressure environment, and the hydrate can be decomposed by reducing the formation pressure, so that the hydrolysis gas can be produced and transported to the production well 100, and the production operation is completed.

[0086] Step S6: open the first flow valve 410, close the second flow valve 420, extract the heat source into the production section 200, and the heat source flows into the hydrate layer 500 through the flow guide 210 to heat the hydrate layer 500. In the related art, the hydrate decomposition during the pressure reduction process can cause the temperature of the reservoir to drop sharply, thereby inducing the secondary generation of hydrates or even the production of ice, which in turn inhibits the continuous decomposition of hydrates, ultimately resulting in reduced gas production efficiency, shortened gas production period, or even termination. Opening the first flow valve 410 and closing the second flow valve 420 allows the heat source to flow from the heat extraction section 300 to the production section 200, and the second flow valve 420 blocks the heat source, which stays in the production section 200 and flows into the hydrate layer 500 through the flow guide 210 to heat the hydrate layer 500. Direct use of deep heat sources can save heat source costs.

[0087] Step S7: open the second flow valve 420, reduce the formation pressure, and the decomposition gas generated by the decomposition of hydrates under heat flows into the production section 200 through the flow guide 210 for production. After the temperature of the hydrate layer 500 rises, the second flow valve 420 is opened, the formation pressure is reduced, and the production continues through the pressure reduction method. The decomposition gas generated by the decomposition of hydrates under heat flows into the production section 200 through the flow guide 210 to complete the production operation.

[0088] The method for exploiting hydrates using deep geothermal energy according to the present application calculates the temperature of the heat source in the deep sand layer of the hydrate-rich area, determines the heat extraction formation depth, extracts the heat source in the deep sand layer to the production section 200, heats the hydrate layer 500, and directly uses the deep heat source to save heat source costs and achieve continuous supply of deep heat sources and continuous production of hydrates. By calculating the temperature of the heat source in the deep sand layer, the heat extraction formation depth can be determined to ensure that the extracted heat source has a good temperature and can effectively conduct heat to improve thermal efficiency.

[0089] According to some embodiments of the present application, in determining the heat extraction formation depth, the fluid extraction flow rate Q w and the wellbore cross-sectional area A p of the production section 200 are calculated to calculate the fluid velocity V w per unit area and the mass m w of the fluid flowing through the fluid, calculate the heat loss q1 of the fluid during the fluid extraction process, calculate the heat transfer q2 of the fluid during the fluid extraction process, and determine the heat extraction formation depth by calculating the heat loss q1 of the fluid in the wellbore and the heat transfer q2 of the fluid.

[0090] Specifically, the fluid extraction flow rate is Q w , d is the inner diameter of the wellbore of the production section 200, A p is the wellbore cross-sectional area of the production section 200, and then

[0091]

[0092] m w = Q w · p w ;

[0093] The heat loss q1 of the fluid in the wellbore during the process is calculated, wherein C w is the specific heat capacity, T2 is the water temperature at the depth of the heat-producing formation, and T1 is the lowest temperature of the heat source flowing into the hydrate layer 500:

[0094] q1 = m w · C w · (T2 - T1);

[0095] ΔT m is the average temperature difference, A is the pipe wall area, k is the total heat transfer coefficient, and l is the length of the well;

[0096] q2 = k · A · ΔT m ;

[0097] A = π · d · l;

[0098]

[0099] h is the heat transfer coefficient of the wellbore, a is the heat transfer coefficient of the fluid to the wellbore during the flow of the fluid in the wellbore, and λ is the thermal conductivity of the fluid at the corresponding temperature;

[0100]

[0101] Re is the Reynolds number, which is related to the inner diameter of the well:

[0102]

[0103] Since the heat loss q1 of the fluid in the wellbore should be equal to the heat transfer q2 during the process of the fluid,

[0104] q1 = q2;

[0105] m w · C w · (T2 - T1) = k · A · ΔT m ;

[0106] The water temperature T2 at the depth of the heat-producing formation x is calculated, and the depth of the heat-producing formation is x, from

[0107] T2 = 3 + 0.1x;

[0108] Thus, the depth of the heat-producing formation x is obtained.

[0109] According to some embodiments of the present application, in the process of determining the depth of the heat source in the hydrate layer 500 by calculation, the lowest temperature T1 of the heat source flowing into the hydrate layer 500 is 40℃. In some embodiments, the heat source is hot water. When the water temperature in the wellbore is 40℃, the heating effect on the hydrate is good, which can ensure that the extracted heat source has good temperature and can effectively conduct heat to improve the thermal efficiency.

[0110] According to some embodiments of the present application, in the process of calculating the temperature of the heat source in the sand layer deep in the hydrate enrichment area, the measured geothermal gradient G and the measured seabed temperature T sf The temperature T D+1 of the heat source 1 meter below the seabed formation is calculated.

[0111] When D = 0, T D is the temperature 0 meter below the seabed formation, that is, T D = T sf , and

[0112]

[0113] The temperature T D+1 of the heat source 1 meter below the seabed formation can be obtained.

[0114] According to some embodiments of the present application, in the process of closing the first flow valve 410 and using the depressurization method for production, the depressurization amplitude is 0.2 times the initial pressure of the formation, and the depressurization production is 15 days. By depressurizing the bottom layer pressure, the hydrate can be decomposed to form hydrolysis gas, and the depressurization amplitude of 0.2 times can promote the decomposition of the hydrate, while avoiding the sudden drop of the formation temperature caused by excessive depressurization. The depressurization production time is controlled to be 15 days, which can not only realize the full production of hydrolysis gas, but also can monitor the formation pressure and temperature changes in real time in a short period, quickly adjust the production strategy, improve the response flexibility, and prepare for the subsequent extraction of the heat source to heat the hydrate layer 500.

[0115] According to some embodiments of the present application, in the process of observing the change of the gas production in the depressurization production, when the temperature of the hydrate layer 500 decreases and the gas production decreases, the first flow valve 410 is opened, the second flow valve 420 is closed, and the heat source is extracted to the production section 200 and then left for three days. When the temperature of the hydrate layer 500 decreases and the gas production decreases, the first flow valve 410 is opened, the second flow valve 420 is closed, and the heat source is extracted and transported to the production section 200. The heat source is injected into the hydrate layer 500 through the flow guide part 210 uniformly distributed around the wellbore. The heat source is left in the production section 200 for 3 days to ensure that the heat source can effectively conduct heat and heat the hydrate layer 500. After the formation temperature rises, the hydrate decomposes to continue the production operation.

[0116] According to some embodiments of the present application, the extraction of the heat source into the production section 200 comprises:

[0117] After the heat source is extracted to the wellbore filled with the production section 200, the first flow valve 410 is closed, and the temperature change of the hydrate layer 500 is observed for three days;

[0118] After the temperature of the hydrate layer 500 no longer increases, the first flow valve 410 is opened, and the heat source is extracted to the wellbore filled with the production section 200, and then the first flow valve 410 is closed, and the temperature change of the hydrate layer 500 is observed for three days;

[0119] The above steps are repeated until the temperature of the hydrate layer 500 reaches the standard of the depressurization production, and then the depressurization production is performed.

[0120] In some embodiments, after the depressurization production, multiple heat source extraction operations are required to heat the hydrate layer 500. Specifically, after the heat source is extracted to the wellbore filled with the production section 200, the first flow valve 410 is closed, and the temperature change of the hydrate layer 500 is observed for three days. The heat source is injected into the hydrate layer 500 through the flow guide part 210 uniformly distributed around the wellbore. After the temperature of the hydrate layer 500 no longer increases is observed, the first flow valve 410 is opened, and the heat source is extracted to the wellbore filled with the production section 200, and then the first flow valve 410 is closed, and the temperature change of the hydrate layer 500 is observed for three days. The above steps are repeated until the temperature of the hydrate layer 500 reaches the standard of the depressurization production, and then the depressurization production is performed. By extracting the heat source into the production section 200 multiple times, the heat source can be used to provide continuous heat compensation for the hydrate decomposition around the production section 200, and the hydrate decomposition continues after the formation temperature rises to continue the production operation.

[0121] A method for exploiting hydrates using deep geothermal energy is described below in a specific embodiment. In the example of the South Qiongzhou Sea area of China, the hydrate enrichment area has a very high geothermal gradient, exceeding 100℃ / km. We first need to evaluate the distribution and temperature of the heat source in the deep sand layer of the hydrate enrichment area. In this embodiment, the inner diameter of the wellbore is 0.15m, the liquid flow rate is 300L / min, the heat transfer coefficient of the stainless steel wellbore is 27W / (m2·K), the geothermal gradient is 100℃ / km, and the sea floor temperature is 3℃. The heat source is extracted from the formation x meters below the sea floor (the temperature of the formation at this location is 3+0.1x) to the hydrate layer 500 200 meters below the sea floor through the wellbore. The temperature of the hydrate layer 500 is 23℃.

[0122] For the distribution of the sand layer, seismic data is used to interpret the sedimentary facies related to sandy sedimentary bodies such as channels and natural levees, and to identify the distribution of sand bodies at different depths. A sand body planar distribution map is drawn. This technology is a mature technology in the oil industry.

[0123] For the temperature of the heat source, the patent calculates the measured geothermal gradient G and the measured temperature T of the seabed sf of the heat source under the seabed stratum D+1 meters D+1 . D+1 of the heat source under the seabed stratum D+1 meters. When D=0, it means at the seabed, i.e. T D =T sf , sf is the measured temperature of the seabed, such as in the Qiongdongnan Sea, T sf =3℃, then according to T D+1 =T D +G / 1000, the temperature T D+1 of the heat source under the seabed stratum D+1 meters can be calculated.

[0124] After obtaining the distribution and temperature of the heat source in the deep sand layer, the optimal heat extraction stratum depth is determined according to the conditions of the hydrate layer 500.

[0125] The fluid extraction flow rate Q w and the wellbore cross-sectional area A p of the production section 200 are used to calculate the fluid velocity V w per unit area and the mass m w of the fluid flowing through, Q w =300[L / min]=5[L / s]=5×10 -3 [m 3 / s], V w is the fluid velocity per unit area, d is the inner diameter of the wellbore of the production section 200, A p is the wellbore cross-sectional area of the production section 200, and m w is the mass of the fluid flowing through. Assuming the fluid is water,

[0126]

[0127] m w =Q w ·ρ w =5×10 -3 [m 3 / s]·1000kg / m 3 =5[kg / s];

[0128] The heat loss q1 of the fluid during extraction is calculated as follows:

[0129] where C w is the specific heat capacity, with a value of 4180 J(kg·k), T2 is the water temperature at the heat extraction stratum depth x meters, i.e. 3+0.1x, and T1 is the lowest temperature of the heat source flowing into the hydrate layer 500, i.e. 40℃,

[0130] q1=mw • C w • (T2-T1) = 5 · 4180 · (3 + 0.1x - 40)

[0131] = 20900 · (0.1x - 37).

[0132] The heat transfer amount q2 of the fluid in the fluid extraction process is calculated, ΔT m is the average temperature difference, A is the pipe wall area, k is the total heat transfer coefficient, and l is the length of the well, so:

[0133] q2 = k · A · ΔT m ;

[0134]

[0135] where 40 is the required hot fluid temperature, 23 is the temperature of the hydrate layer 500. k is the total heat transfer coefficient, and l is the length of the well, so in this model l = x - 200, then:

[0136] A = π · d · l = 3.14 · 0.15 · (x - 200) = 0.471 · (x - 200);

[0137] h is the heat transfer coefficient of the wellbore, which is 27 W / (m 2 · k); a is the heat transfer coefficient of the fluid to the wellbore during flow in the wellbore, λ is the thermal conductivity of the fluid at the corresponding temperature, which is 0.64 W / (m·k), P r is a constant, which is set to 3.77, and Re is the Reynolds number, which is related to the inner diameter of the well:

[0138]

[0139] Therefore, for the specific settings of the model,

[0140]

[0141] Thus,

[0142]

[0143] Since the heat loss q1 of the fluid in the wellbore should be equal to the heat transfer amount q2 of the fluid process,

[0144] q1 = q2;

[0145] Therefore, 20900 · (0.1x - 37) = 26.38 · [0.471 · (x - 200)] · 8.5

[0146] The calculated heat extraction stratum depth x = 379.

[0147] It should be noted that the above calculation assumes that the heat source is hot water, if it is hot gas, the part of the above calculation involving specific heat capacity, density, thermal conductivity and other constants need to be replaced by the value of hot gas.

[0148] After determining the depth of the heat source layer as 379 meters, a set of sand layers near this depth is selected as the heat extraction target layer. Horizontal drilling is performed in the hydrate layer 500 to form the production section 200, and then the well trajectory is changed by building an angle to drill into the heat extraction target sand layer in the form of a near-vertical well to form the heat extraction section 300, and a submersible pump is placed in the heat extraction section 300. After the well is drilled, the depressurization production operation and the heat source throughput heating operation are started to achieve continuous supply of deep heat sources and continuous production of hydrates.

[0149] The following will be combined Figures 2 to 4 The device for exploiting hydrates using deep geothermal energy according to the embodiments of the present application is introduced below, which comprises a production well 100, a production section 200 and a heat extraction section 300. The production section 200 is connected to the production well 100 and is horizontally arranged in the hydrate layer 500. The production section 200 is provided with a flow guide part 210 that is in communication with the hydrate layer 500. One end of the heat extraction section 300 is connected to the production section 200, and the other end of the heat extraction section 300 is connected to the heat source layer. A first flow valve 410 is arranged between the production section 200 and the heat extraction section 300, and a second flow valve 420 is arranged between the production section 200 and the production well 100. The production section 200 is horizontally arranged in the hydrate layer 500 and is provided with a flow guide part 210 that is in communication with the hydrate layer 500. The production section 200 exchanges water and gas with the hydrate layer 500 through the flow guide part 210, which can achieve continuous production of hydrates. The heat extraction section 300 is connected to the heat source layer, and the heat source in the deep layer is extracted into the production section 200 through the heat extraction section 300, which directly uses the deep heat source to heat the hydrate layer 500, thereby saving the cost of heat sources and achieving continuous supply of deep heat sources. The first flow valve 410 and the second flow valve 420 are used to switch between depressurization production and heat source supply, which can save the cost of heat sources and achieve continuous supply of deep heat sources and continuous production of hydrates.

[0150] Reference Figure 3According to some embodiments of this application, the heat extraction section 300 includes a connected horizontal branch section 310 and a vertical branch section 320. The horizontal branch section 310 is connected to the production section 200, and the vertical branch section 320 is connected to the heat extraction stratum. Specifically, the horizontal branch section 310 is located approximately 10-20 meters below the production section 200. Both the horizontal branch section 310 and the production section 200 are located within the hydrate layer 500. A third flow valve 430 is installed between the horizontal branch section 310 and the production well 100. When the thickness of the hydrate layer 500 is greater than 30 meters, a dual-branch well approach is adopted for heat extraction and production. After depressurization production, the heat source is extracted to the horizontal branch section 310. Through multiple heat source extraction operations, the hydrate layer 500 is heated, continuously supplying heat to the hydrate layer 500 and providing continuous heat compensation for the decomposition of hydrates in the production section 200.

[0151] The embodiments of this application have been described in detail above with reference to the accompanying drawings. However, this application is not limited to the above embodiments. Within the scope of knowledge possessed by those skilled in the art, various changes can be made without departing from the spirit of this application.

Claims

1. A method for extracting hydrates using deep geothermal energy, characterized in that, Includes the following steps: Calculate the temperature of the heat source in the deep sand layer of the hydrate-rich zone; Determine the depth of the geothermal strata; A horizontal production section is formed by drilling in the hydrate layer, the production section being provided with a flow guide that communicates with the hydrate layer; Drilling downwards forms a heating section connected to the depth of the heating formation. A first flow valve is installed between the heating section and the production section, and a second flow valve is installed between the production section and the production well. Close the first flow valve and use the pressure reduction method for pressure reduction production; Open the first flow valve, close the second flow valve, and draw a heat source into the production section. The heat source flows into the hydrate layer through the guide section to heat the hydrate layer. The second flow valve is opened to reduce the formation pressure, and the decomposition gas formed by the thermal decomposition of hydrates flows into the production section through the guide section for production.

2. The method for extracting hydrates using deep geothermal energy according to claim 1, characterized in that, Determining the depth of the thermal extraction strata includes: Fluid extraction flow rate Q w The cross-sectional area A of the wellbore in the production section p Calculate the fluid velocity V per unit area w and the mass m of the fluid flowing through w ; Calculate the heat loss q1 of the fluid during the fluid extraction process; Calculate the heat transfer q2 of the fluid during the fluid extraction process; The depth of the thermal extraction formation is determined by calculating the heat loss q1 and the heat transfer q2 of the fluid inside the wellbore.

3. The method for extracting hydrates using deep geothermal energy according to claim 2, characterized in that, include: The fluid extraction flow rate is Q w d is the inner diameter of the wellbore in the production section, A p Let be the cross-sectional area of ​​the wellbore in the production section. m w =Q w ·r w ; During the calculation, the heat loss q1 of the fluid inside the wellbore is calculated, where C w T2 is the specific heat capacity, T2 is the water temperature at the depth of the heating formation, and T1 is the lowest temperature at which the heat source flows into the hydrate layer. q1=m w ·C w ·(T2-T1); ΔT m The average temperature difference is A, the pipe wall area is k, the overall heat transfer coefficient is k, and the length of the well is l. q2=k·A·ΔT m ; A = π·d·l; h is the heat transfer coefficient of the wellbore, a is the heat transfer coefficient of the fluid to the wellbore during the flow process in the wellbore, and λ is the thermal conductivity of the fluid at the corresponding temperature. Re is the Reynolds number, which is related to the inner diameter of the well. Since the heat loss q1 of the fluid inside the wellbore should be equal to the heat transfer q2 during the fluid process, q1 = q2; m w ·C w ·(T2-T1)=k·A·ΔT m ; The water temperature T2 at the depth of the heating formation is calculated, and the depth of the heating formation is x. T2 = 3 + 0.1x; Thus, the depth x of the geothermal stratum is obtained.

4. A method for extracting hydrates using deep geothermal energy according to claim 3, characterized in that, The process of determining the depth of the thermal extraction strata through calculation also includes: The lowest temperature T1 at which the heat source flows into the hydrate layer is 40°C.

5. A method for extracting hydrates using deep geothermal energy according to claim 1, characterized in that, The calculation of the heat source temperature in the deep sand layers of hydrate-rich areas also includes: Through the measured geothermal gradient G and the measured seabed temperature T sf The temperature T of the heat source at a depth of D+1 meters below the seabed strata D+1 Perform calculations; When D = 0, T D The temperature at 0 meters below the seabed is T. D =T sf ,Depend on The temperature T of the heat source at a depth of D+1 meters below the seabed can be calculated. D+1 .

6. A method for extracting hydrates using deep geothermal energy according to claim 1, characterized in that, In the process of closing the first flow valve and using the pressure reduction method for mining, the following is also included: The pressure reduction was 0.2 times the initial formation pressure, and production was carried out for 15 days with the pressure reduced.

7. A method for extracting hydrates using deep geothermal energy according to claim 1 or 6, characterized in that, Also includes: Observe the changes in gas production during the depressurization production process; When the temperature of the hydrate layer decreases and the gas production decreases, the first flow valve is opened and the second flow valve is closed to extract heat to the production section.

8. A method for extracting hydrates using deep geothermal energy according to claim 7, characterized in that, Extracting heat to the production section includes: After the heat source is drawn into the wellbore that fills the production section, the first flow valve is closed and the well is left to stand for three days to observe the temperature change of the hydrate layer. Once the temperature of the hydrate layer stops rising, open the first flow valve, extract the heat source to the production section until the wellbore is full, then close the first flow valve, let it stand, and observe the temperature change of the hydrate layer. Repeat the above steps until the temperature of the hydrate layer reaches the standard for depressurization production, then proceed with depressurization production.

9. An apparatus for extracting hydrates using deep geothermal energy, characterized in that, A method for extracting hydrates using deep geothermal energy according to any one of claims 1 to 8 includes: Production wells; The production section is connected to the production well and is horizontally arranged in the hydrate layer. The production section is provided with a guide section that communicates with the hydrate layer. A heat extraction section, one end of which is connected to the production section, and the other end of which is connected to the heat extraction stratum; A first flow valve is installed between the heat extraction section and the production section, and a second flow valve is installed between the production section and the production well.

10. The apparatus for extracting hydrates using deep geothermal energy according to claim 9, characterized in that, The heat extraction section includes connected horizontal and vertical branch sections. The horizontal branch sections are connected to the production section, and the vertical branch sections are connected to the heat extraction stratum.

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