Device and method for exploiting hydrate by using deep geothermal energy

Abstract

The invention discloses a device and a method for exploiting hydrates by using deep terrestrial heat, which can save the heat source cost by calculating the heat source temperature in a deep sand layer of a hydrate enrichment area, determining the depth of a heat collection stratum, extracting the heat source in the deep sand layer to a production section, heating the hydrate layer and directly utilizing the deep heat source. The continuous supply of a deep heat source and the continuous production of the hydrate are realized; the depth of the heat collection stratum is determined by calculating the temperature of the heat source in the deep sand layer, it can be guaranteed that the extracted heat source has the good temperature, heat can be effectively conducted, and the heat efficiency is improved.

Description

Technical Field

[0001] The present application relates to the technical field of natural gas hydrate exploitation, and particularly to an apparatus and method for exploiting hydrates using deep geothermal energy. Background Art

[0002] Natural gas hydrate is one of the most promising alternative energy sources in the future. Since 2002, various countries around the world have successively carried out 11 hydrate production tests on hydrate reservoirs, but none of them have achieved the goal of continuous and high-yield gas production. Various countries have conducted theoretical and technical explorations on various hydrate exploitation methods, such as pressure reduction method, solid state sulfidation method, thermal stimulation method, chemical potential difference driving method, etc. Among them, pressure reduction exploitation is considered to be a technology that is most promising for industrial exploitation of hydrates in terms of technology and economy, and a pressure reduction strategy has been adopted almost every time in the world.

[0003] However, the decomposition of hydrates is an endothermic process. During the pressure reduction process, the decomposition of hydrates will cause a sharp drop in the reservoir temperature, thereby inducing the secondary formation of hydrates or even the generation of ice, which in turn inhibits the continuous decomposition of hydrates, ultimately resulting in a decrease in gas production efficiency, a shortening of the gas production cycle, or even suspension. Existing methods continuously heat the formation by injecting hot water, hot steam and other different methods to solve the problem of temperature reduction, but these methods require a large amount of cost, consume a large amount of energy, and have low thermal efficiency. Summary of the Invention

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

[0005] The present application also proposes an apparatus for exploiting hydrates using deep geothermal energy using the above method.

[0006] A method for exploiting hydrates using deep geothermal energy according to an embodiment of the first aspect of the present application includes the following steps:

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

[0008] Determine the depth of the heat extraction formation;

[0009] Drill a horizontal production section in the hydrate layer, and the production section is provided with a diversion part communicating with the hydrate layer;

[0010] Drill downward to form a heat extraction section connected to the depth of the heat extraction formation, and 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] Close the first flow valve and carry out pressure reduction production using the pressure reduction method;

[0012] Open the first flow valve, close the second flow valve, extract the heat source into the production section, and the heat source flows into the hydrate layer through the diversion part to heat the hydrate layer;

[0013] Open the second flow valve, reduce the formation pressure, and the decomposition gas formed by the thermal decomposition of the hydrate flows into the production section through the diversion part for production.

[0014] A method for exploiting hydrates using deep geothermal energy according to an embodiment of the first aspect of the present application has at least the following beneficial effects: The method for exploiting hydrates using deep geothermal energy of the present application can save the heat source cost and realize the continuous supply of deep heat sources and the continuous production of hydrates by calculating the heat source temperature in the deep sand layer of the hydrate enrichment area, determining the depth of the heat extraction formation, extracting the heat source in the deep sand layer to the production section, heating the hydrate layer, and directly utilizing the deep heat source; by calculating the heat source temperature in the deep sand layer and determining the depth of the heat extraction formation, it can ensure that the extracted heat source has a good temperature, effectively conduct heat, and improve the thermal efficiency.

[0015] According to some embodiments of the present application, in determining the depth of the heat extraction formation, it includes:

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

[0021] The fluid extraction flow rate 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] The heat loss q1 of the fluid in the wellbore during the calculation process, where C w is the specific heat capacity, T2 is the water temperature at the depth of the heat extraction 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 flow 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 amount q2 during the fluid process,

[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 extraction formation is calculated. The depth of the heat extraction formation is x, and from

[0038] T2 = 3 + 0.1x;

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

[0040] According to some embodiments of the present application, in determining the depth of the heat extraction formation by calculation, it further includes:

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

[0042] According to some embodiments of the present application, in calculating the heat source temperature in the deep sand layer in the hydrate enrichment area, it further includes:

[0043] Based on the measured geothermal gradient G and the measured seabed temperature T sf calculate the heat source temperature T at D + 1 meters below the seabed formation; D+1 perform the calculation;

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

[0045]

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

[0047] According to some embodiments of the present application, during the exploitation using the pressure reduction method with the first flow valve closed, it further includes:

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

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

[0050] Observe the change in gas production during the pressure reduction production process;

[0051] After the temperature of the hydrate layer decreases and the gas production drops, open the first flow valve, close the second flow valve, and extract the heat source into the production section.

[0052] According to some embodiments of the present application, extracting the heat source into the production section includes:

[0053] After extracting the heat source into the wellbore filling the production section, close the first flow valve, stand still for three days, and observe the temperature change of the hydrate layer;

[0054] After the temperature of the hydrate layer no longer rises, open the first flow valve, extract the heat source into the production section until the wellbore filling the production section, then close the first flow valve, stand still and observe the temperature change of the hydrate layer;

[0055] Repeat the above steps until the temperature of the hydrate layer reaches the standard of pressure reduction production, and then perform pressure reduction production.

[0056] An apparatus for exploiting hydrates using deep geothermal energy according to the embodiments of the second aspect of the present application, using the method for exploiting hydrates using deep geothermal energy according to the embodiments of the first aspect, further includes:

[0057] Production well;

[0058] A production section, which is connected to the production well. The production section is horizontally arranged in the hydrate layer, and a diversion part communicating with the hydrate layer is provided in the production section.

[0059] A heat extraction section, one end of which is connected to the production section, and the other end of which is connected to a heat extraction formation.

[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] An apparatus for exploiting hydrates using deep geothermal energy according to an embodiment of the second aspect of the present application has at least the following beneficial effects: The apparatus for exploiting hydrates using deep geothermal energy of the present application includes a production well, a production section and a heat extraction section. The production section is horizontally arranged in the hydrate layer, and a diversion part communicating with the hydrate layer is provided in the production section. The production section exchanges hydrolysis gas with the hydrate layer through the diversion part, and can realize continuous production of hydrates; The heat extraction section is connected to the heat extraction formation, and the heat source in the deep formation is extracted into the production section through the heat extraction section, and the hydrate layer is directly heated by the deep heat source, which can save the heat source cost and realize continuous supply of the deep heat source; By switching between pressure reduction production and heat source supply through the first flow valve and the second flow valve, the heat source cost can be saved, and continuous supply of the deep heat source and continuous production of hydrates can be realized.

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

[0063] Additional aspects and advantages of the present application will be given in part in the following description, will become apparent in part from the following description, or will be learned through the practice of the present application. Description of the Drawings

[0064] The above and / or additional aspects and advantages of the present application will become apparent and easy to understand from the description of the embodiments in conjunction with the following drawings, wherein:

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

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

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

[0068] Figure 4It is a cross-sectional schematic view of the production section of an embodiment of the present application.

[0069] Reference numerals:

[0070] Production well 100;

[0071] Production section 200, diversion section 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 implementation manners

[0075] The embodiments of the present application will be described in detail below. The examples of the embodiments are shown in the drawings, where the same or similar reference numerals denote the same or similar elements or elements with 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 should not be construed as a limitation to the present application.

[0076] In the description of the present application, it should be understood that the orientation or positional relationship indicated by terms such as up, down, front, back, left, right, inside, outside, etc. is based on the orientation or positional relationship shown in the drawings, and is only for the convenience of describing the present application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be construed as a limitation to the present application.

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

[0078] In the description of the present application, unless otherwise clearly defined, words such as "set", "install", "connect", "assemble", "fit", etc. should be understood in a broad sense, and those skilled in the art can reasonably determine the specific meanings 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 Describe a method for exploiting hydrates using deep geothermal energy in an embodiment of the present application.

[0080] A method for exploiting hydrates using deep geothermal energy in an embodiment of the present application, referring to Figure 1, including the following steps:

[0081] Step S1: Calculate the heat source temperature in the deep sand layer of the hydrate enrichment area. First, it is necessary to evaluate the distribution of the deep sand layer in the hydrate enrichment area. For the distribution of the sand layer, seismic data is used to interpret sedimentary facies related to sandy sedimentary bodies such as channels - natural levees, identify the distribution of sand bodies in different depth ranges, and draw a planar distribution map of the sand bodies. For the temperature of the heat source, based on the measured geothermal gradient and the measured seabed temperature, the heat source temperature at several meters below the seabed formation is calculated. It should be noted that the heat source mentioned in this application includes hot fluids such as hot water and hot gas.

[0082] Step S2: Determine the depth of the heat extraction formation. After obtaining the heat source temperature, determine the optimal depth of the heat extraction formation according to the conditions of the hydrate layer 500.

[0083] Step S3: Drill a horizontal production section 200 in the hydrate layer 500, and the production section 200 is provided with a diversion part 210 communicating with the hydrate layer 500. After determining the depth of the heat extraction formation, select a set of sand layers near the depth of the heat extraction formation as the heat extraction target layer, and implement horizontal drilling in the hydrate layer 500 to form a horizontal production section 200, and the production section 200 is provided with a diversion part 210 communicating with the hydrate layer 500.

[0084] Step S4: Drill downward to form a heat extraction section 300 connecting to the depth of the heat extraction formation, and a first flow valve 410 is arranged between the heat extraction 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 rate of the heat source from the heat extraction section 300 to the production section 200, and the second flow valve 420 is used to control the flow rate of the hydrolyzed gas from the production section 200 to the production well 100.

[0085] Step S5: Close the first flow valve 410 and use the pressure reduction method for pressure reduction production. Close the first flow valve 410, and the heat source will not flow from the heat extraction section 300 to the production section 200. By using the pressure reduction method to reduce the formation pressure, the hydrate is stable in a low - temperature and high - pressure environment. By reducing the formation pressure, the hydrate can be decomposed, and the hydrolyzed gas is produced and transported to the production well 100 to complete the production operation.

[0086] Step S6: Open the first flow valve 410, close the second flow valve 420, extract the heat source into the production section 200. The heat source flows into the hydrate layer 500 through the diversion part 210 to heat the hydrate layer 500. In the related art, during the pressure reduction process, the decomposition of hydrates will cause a sharp drop in the reservoir temperature, thus inducing the secondary formation of hydrates or even the generation of ice, which in turn inhibits the continuous decomposition of hydrates, ultimately resulting in a decrease in gas production efficiency, a shortening of the gas production cycle, or even suspension. Open the first flow valve 410, close the second flow valve 420, and extract the heat source from the heat extraction section 300 to the production section 200. The second flow valve 420 blocks the heat source, and the heat source will stay in the production section 200 and flow into the hydrate layer 500 through the diversion part 210 to heat the hydrate layer 500. By directly using the deep heat source, the heat source cost can be saved.

[0087] Step S7: Open the second flow valve 420, reduce the formation pressure, and the decomposition gas formed by the thermal decomposition of hydrates flows into the production section 200 through the diversion part 210 for production. After the temperature of the hydrate layer 500 rises, open the second flow valve 420, reduce the formation pressure, and continue production by the pressure reduction method. The decomposition gas formed by the thermal decomposition of hydrates flows into the production section 200 through the diversion part 210 to complete the production operation.

[0088] A method for exploiting hydrates using deep geothermal energy in the present application determines the depth of the heat extraction formation by calculating the heat source temperature in the deep sand layer in the hydrate enrichment area, extracts the heat source in the deep sand layer to the production section 200 to heat the hydrate layer 500, directly utilizes the deep heat source, can save the heat source cost, realize the continuous supply of the deep heat source and the continuous production of hydrates; by calculating the heat source temperature in the deep sand layer and determining the depth of the heat extraction formation, it can ensure that the extracted heat source has a good temperature, can effectively conduct heat, and improve the thermal efficiency.

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

[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, then

[0091]

[0092] m w =Q w ·ρ w ;

[0093] The heat loss q1 of the fluid in the wellbore during the calculation process, where C w is the specific heat capacity, T2 is the water temperature at the depth of the heat extraction formation, and T1 is the lowest temperature at which the heat source flows to 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 from the fluid to the wellbore during the fluid flow 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 amount q2 during the fluid process,

[0104] q1 = q2;

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

[0106] Calculate the water temperature T2 at the depth of the heat extraction formation. The depth of the heat extraction formation is x, and from

[0107] T2 = 3 + 0.1x;

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

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

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

[0111] When D = 0, T D is the temperature at 0 meters below the seabed formation, that is, T D = T sf , from

[0112]

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

[0114] According to some embodiments of the present application, when the first flow valve 410 is closed and the pressure reduction method is used for production, the pressure reduction amplitude is 0.2 times the initial formation pressure, and the pressure reduction production is carried out for 15 days. By reducing the formation pressure, it can promote the decomposition of hydrates to form hydrolyzed gas. The pressure reduction amplitude of 0.2 times can not only promote the decomposition of hydrates, but also avoid the sudden drop of formation temperature caused by excessive pressure reduction. The pressure reduction production time is controlled within 15 days, which can not only ensure the full progress of hydrolyzed gas production, but also monitor the changes of formation pressure and temperature 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, during the pressure reduction production process, observe the change of gas production. When the temperature of the hydrate layer 500 decreases and the gas production decreases, open the first flow valve 410, close the second flow valve 420, extract the heat source to the production section 200 and then let it stand for three days. When the temperature of the hydrate layer 500 decreases and the gas production decreases, at this time, open the first flow valve 410, close the second flow valve 420, extract and transport the heat source into the production section 200. The heat source is injected into the hydrate layer 500 through the uniformly distributed diversion part 210 around the wellbore. The heat source stands in the production section 200 for 3 days to ensure that the heat source can effectively conduct heat, heat the hydrate layer 500, and wait for the formation temperature to rise before continuing the production operation of hydrate decomposition.

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

[0117] After extracting the heat source into the wellbore that fills the production section 200, close the first flow valve 410, let it stand for three days, and observe the temperature change of the hydrate layer 500.

[0118] After the temperature of the hydrate layer 500 stops rising, open the first flow valve 410, extract the heat source into the production section 200 until the wellbore that fills the production section 200, then close the first flow valve 410, let it stand and observe the temperature change of the hydrate layer 500.

[0119] Repeat the above steps until the temperature of the hydrate layer 500 reaches the standard for pressure reduction production, and then carry out pressure reduction production.

[0120] In some embodiments, after pressure reduction production, multiple heat source extraction operations are required to heat the hydrate layer 500. Specifically, after extracting the heat source into the wellbore that fills the production section 200, close the first flow valve 410, let it stand for three days, and the heat source is injected into the hydrate layer 500 through the diversion part 210 evenly distributed around the wellbore. Observe the temperature change of the hydrate layer 500 during the standing period. After observing that the temperature of the hydrate layer 500 stops rising, open the first flow valve 410, extract the heat source into the production section 200 until the wellbore that fills the production section 200, then close the first flow valve 410, let it stand and observe the temperature change of the hydrate layer 500. Repeat the above steps until the temperature of the hydrate layer 500 reaches the standard for pressure reduction production, and then carry out pressure reduction production. By extracting the heat source into the production section 200 multiple times, it is possible to use the heat source to provide continuous heat compensation for the decomposition of hydrates around the production section 200, and wait for the hydrate decomposition to continue the production operation after the formation temperature rises.

[0121] The following uses a specific embodiment to introduce a method for exploiting hydrates using deep geothermal energy in the present application. Taking the Qiongdongnan Sea area of China as an example, the geothermal gradient in the hydrate enrichment area is very high, exceeding 100 °C / km. First, we 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 0.15 m, the liquid flow rate is 300 L / min, the heat transfer coefficient of the stainless steel wellbore is 27 W / (m2·K), the geothermal gradient is 100 °C / km, the seabed temperature is 3 °C, and the heat source is extracted from the formation x meters below the seabed (the formation temperature at this point is 3 + 0.1x) to the hydrate layer 500 200 m below the seabed, and the temperature of the hydrate layer 500 is 23 °C.

[0122] For the distribution of the sand layer, using seismic data, interpret sedimentary facies related to sandy sedimentary bodies such as channels - natural levees, identify the sand body distribution in different depth ranges, and draw a planar distribution map of the sand body. This technology is a mature technology in the petroleum industry.

[0123] For the temperature of the heat source, this patent calculates it through the measured geothermal gradient G and the measured seabed temperature T sf of the heat source temperature T at D + 1 meters below the seabed formation D+1 . T D+1 is the heat source temperature at D + 1 meters below the seabed formation. When D = 0, it means at the seabed, that is, T D = T sf , T sf is the measured seabed temperature. For example, in the Qiongdongnan Sea area, T sf = 3°C, then according to T D+1 = T D + G / 1000, the heat source temperature T at D + 1 meters below the seabed formation can be calculated D+1 .

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

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

[0126]

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

[0128] Calculate the heat loss q1 of the fluid during the fluid extraction process:

[0129] Among them, C w is the specific heat capacity, with a value of 4180 J / (kg·K), T2 is the water temperature at x meters of the heat extraction formation depth, that is, 3 + 0.1x, T1 is the lowest temperature of the heat source flowing into the hydrate layer 500, that is, 40°C,

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

[0131] = 20900·(0.1x - 37).

[0132] Calculate the heat transfer quantity q2 of the fluid during the fluid extraction process, ΔT m is the average temperature difference, A is the tube wall area, k is the total heat transfer coefficient, l is the length of the well, and we get:

[0133] q2 = k·A·ΔT m ;

[0134]

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

[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, with a value of 27 W / (m 2 ·k); a is the heat transfer coefficient of the fluid to the wellbore during the fluid 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, set to 3.77, 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, we obtain

[0142]

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

[0144] q1 = q2;

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

[0146] Calculating gives the depth x of the heat extraction formation as x = 379.

[0147] It should be noted that in the above calculations, it is assumed that the heat source is hot water. If it is hot gas, then the parts involving constants such as specific heat capacity, density, and thermal conductivity in the above calculations need to be replaced with the values of hot gas.

[0148] After determining that the depth of the heat extraction formation is 379 meters, a set of sand layers is selected as the heat extraction target layer near this depth. A horizontal well is drilled in the hydrate layer 500 to form the production section 200, and then the well trajectory is changed by directional drilling, and the well is drilled into the heat extraction target sand layer in the form of a near-vertical well to form the heat extraction section 300. A submersible pump is placed in the heat extraction section 300. After the well drilling is completed, the pressure reduction production operation and the heat source huff and puff heating operation are started to achieve continuous supply of the deep heat source and continuous production of hydrates.

[0149] The following combines Figures 2 to 4 An apparatus for exploiting hydrates using deep geothermal energy according to an embodiment of the present application is introduced, including 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 the production section 200 is horizontally arranged in the hydrate layer 500. The production section 200 is provided with a diversion part 210 communicating 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 extraction formation; a first flow valve 410 is arranged between the heat extraction 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 production section 200 is horizontally arranged in the hydrate layer 500, and the production section 200 is provided with a diversion part 210 communicating with the hydrate layer 500. The production section 200 exchanges hydrolysis gas with the hydrate layer 500 through the diversion part 210, and can realize continuous production of hydrates; the heat extraction section 300 is connected to the heat extraction formation, and the heat source in the deep formation is extracted into the production section 200 through the heat extraction section 300, and the hydrate layer 500 is directly heated by using the deep heat source, which can save the heat source cost and realize continuous supply of the deep heat source; by switching between pressure reduction production and heat source supply through the first flow valve 410 and the second flow valve 420, the heat source cost can be saved, and continuous supply of the deep heat source and continuous production of hydrates can be realized.

[0150] Refer to Figure 3, according to some embodiments of the present 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 communicates with the heat extraction formation. Specifically, the horizontal branch section 310 is located about 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 provided between the horizontal branch section 310 and the production well 100. When the thickness of the hydrate layer 500 is more than 30 meters, a double-branch well method is adopted for heat extraction and production. After pressure-reducing production, the heat source is extracted to the horizontal branch section 310, and the hydrate layer 500 is heated through multiple heat source extraction operations to continuously supply heat to the hydrate layer 500, providing continuous heat compensation for the decomposition of hydrates in the production section 200.

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

Claims

1. A method for exploiting hydrates using deep geothermal energy, characterized in that: The following steps are involved: Calculate the heat source temperature in the deep sand layer of the hydrate-rich area; Determine the depth of the heat extraction formation; Drilling in the hydrate layer to form a horizontal production section, wherein the production section is provided with a diversion portion communicating with the hydrate layer; Drilling downward to form a heat extraction section connected to the depth of the heat extraction formation, setting a first flow valve between the heat extraction section and the production section, and setting a second flow valve between the production section and the production well; Close the first flow valve and use the pressure reduction method to perform pressure reduction production; Opening the first flow valve, closing the second flow valve, extracting a heat source into the production section, and allowing the heat source to flow into the hydrate layer through the guide portion to heat the hydrate layer; The second flow valve is opened to reduce the formation pressure, and the decomposed gas formed by the thermal decomposition of the hydrate flows into the production section through the guide part for production.

2. The method for exploiting hydrates using deep geothermal energy according to claim 1, characterized in that: In determining the depth of the thermal formation, the following factors are included: Extraction flow rate Q through the fluid w and the cross-sectional area of ​​the wellbore in the production section A 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 fluid extraction; Calculate the heat transfer q2 of the fluid during fluid extraction; The depth of the heat extraction formation is determined by calculating the heat loss q1 of the fluid in the wellbore and the heat transfer q2 of the fluid.

3. The method for exploiting 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 is the wellbore cross-sectional area of ​​the production section, then m w =Q w ·r w ; The heat loss of the fluid in the wellbore during the calculation process is q1, where C w is the specific heat capacity, T2 is the water temperature at the depth of the heat extraction 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 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; 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 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 in the wellbore should be equal to the heat transfer q2 in the fluid process, q1=q2; m w ·C w ·(T2-T1)=k·A·ΔT m ; The water temperature T2 at the depth of the heat extraction formation is calculated. The depth of the heat extraction formation is x, and the T2 = 3 + 0.1x; Thus, the depth x of the heat extraction formation is obtained.

4. The method for exploiting hydrates using deep geothermal energy according to claim 3, characterized in that: The calculation to determine the depth of the heat extraction stratum also includes: The minimum temperature T1 at which the heat source flows into the hydrate layer is 40°C.

5. The method for exploiting hydrates using deep geothermal energy according to claim 1, characterized in that: The calculation of the heat source temperature in the deep sand layer of the hydrate-rich area also includes: The measured geothermal gradient G and the measured seafloor temperature T sf The temperature of the heat source T at D+1 meter below the seabed D+1 Perform calculations; When D = 0, T D is the temperature at 0 meters below the seafloor, that is, T D =T sf ,Depend on The heat source temperature T at D+1 meter below the seabed can be obtained D+1 .

6. The method for exploiting hydrates using deep geothermal energy according to claim 1, characterized in that: The process of closing the first flow valve and using the pressure reduction method to perform mining also includes: The pressure reduction range is 0.2 times of the initial formation pressure, and the pressure reduction production lasts for 15 days.

7. A method for exploiting 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 process; When the temperature of the hydrate layer 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.

8. The method for exploiting hydrates using deep geothermal energy according to claim 7, characterized in that: Extracting heat source into the production section includes: After the heat source is extracted until the wellbore of the production section is filled, 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; When the temperature of the hydrate layer stops rising, the first flow valve is opened, and the heat source is pumped to the production section until the wellbore of the production section is filled, and then the first flow valve is closed, and the temperature change of the hydrate layer is observed while the temperature is kept still. Repeat the above steps until the temperature of the hydrate layer reaches the standard for depressurization production, and then carry out depressurization production.

9. A device for exploiting hydrates using deep geothermal energy, characterized in that: The method for exploiting hydrates using deep geothermal energy according to any one of claims 1 to 8 comprises: Production wells; A production section, the production section is connected to the production well, the production section is horizontally arranged in the hydrate layer, and the production section is provided with a diversion part communicating 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 a heat extraction stratum; 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.

10. The device for exploiting hydrate using deep geothermal energy according to claim 9, characterized in that: The heat extraction section comprises a connected horizontal branch section and a vertical branch section, wherein the horizontal branch section is connected to the production section, and the vertical branch section is connected to the heat extraction stratum.

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