[0024] Attached Figure 2-4 , To further describe the present invention:
[0025] (1) Use a large drilling rig to drill a 10-inch diameter deep well;
[0026] (2) Use logging equipment to stop drilling when the measured formation temperature reaches 40 degrees, and measure the well depth;
[0027] (3) Replace the 7-inch bit and continue drilling down;
[0028] (4) Stop drilling when the measured formation temperature reaches 75-80 degrees and measure the well depth;
[0029] (5) Calculate the length of the 7-inch well depth and the 10-inch well depth;
[0030] (6) Run 7-inch casing to the bottom of the well, with a length of about 1000-1600 meters;
[0031] (7) At the same time, with thermal insulation and protection layer, the casing shall reach the junction of 10 inches and 7 inches, the length is about 1000 meters;
[0032] (8) Carry out cementing work at the bottom of the well; (9) Carry out cementing work at the top of the well;
[0033] (10) Run a 3-inch temperature-isolated suction pipe from the 7-inch casing to the bottom of the well, with a length of about 2000-2500 meters;
[0034] (11) Install outlet and return water flow interfaces at the wellhead;
[0035] (12) Install a 10kw circulating water pump h and a variable frequency speed motor; (13) Install a make-up water tank on the top of the building;
[0036] (14) Connect various water pipelines and conduct pipeline insulation treatment after leak detection;
[0037] (15) Add softened water or superconducting liquid to the system until the entire system is filled;
[0038] (16) Start trial operation.
[0039] Reference attached figure 1 with 5 6. One of the heat preservation methods is to add heat insulation material b between the two circulating pipes (a, c) in the casing d and the wall of the casing pipe. Refer to the attachment figure 1 , The substance can be: polyurethane thermal insulation materials, HJ composite silicate thermal insulation mortar, foam products and other thermal insulation materials.
[0040] Another heat preservation method is to use double-layer hollow pipe e. figure 2 , The central interlayer of the tube e is filled with helium, an inert gas, which has a better heat insulation effect, so that the high-temperature water after heating can carry the temperature to the use area, and solves the problem of short-circuiting of the temperature of the high and low temperature differences. ; Reference attached image 3 , There is a heat supply return pipe f at the outlet and return water flow device interface on the upper part of the hot well.
[0041] The main technical content is:
[0042](1) The casing used in the area with ineffective temperature collection depth of about 1000 meters below the ground should be subjected to outer insulation treatment. In addition, an outer protective layer i (not shown in the figure) such as iron sheet is added to the insulation layer g (also called the yellow jacket insulation layer) to protect the outer temperature insulation material layer of the softer casing, so as to keep warm when the casing is running. The layer is not scratched by the stratum rock, and has a thermal insulation effect for future use. The function of the temperature barrier is to prevent the circulating return water with a temperature of 35° from being absorbed by the 1000-meter low-temperature formation when it flows back into the well, reducing the total energy loss of the return water and improving the heat recovery efficiency. The thermal insulation materials outside the casing can be used: polyurethane thermal insulation materials, centrifugal glass wool felt, HJ composite silicate thermal insulation mortar, foamed asbestos products and other thermal insulation materials. HJ composite silicate thermal insulation mortar is the first choice for the outer thermal insulation of the casing due to its excellent water resistance and low cost.
[0043] (2) Choose a suitable temperature isolation pumping pipe. In order to solve the short-circuit problem of the high and low temperature difference of the water flow temperature, we design and use a double-layer hollow pipe e. The central interlayer of the pipe is filled with helium, an inert gas. To better heat insulation. The high-temperature water after heating can carry the temperature to reach the use area.
[0044] (3)Using the principle of U-tube, we can use low-power circulating water pump h to achieve warm water circulation with a height difference of 2000-3000 meters. The circulating water pump h is the power source of the system. It only needs to overcome the water in the pipeline. The energy of resistance when flowing can realize the circulation of water in the entire system. Therefore, even high-rise buildings do not need high-lift, high-power water pumps, and hot water circulation is still realized, saving electricity and energy.
[0045] (4) In order to prevent the failure of the water pump caused by the lack of water in the system, the water supply tank needs to be designed to avoid system damage. The make-up tank is generally placed on the top floor of the building, above the pump.
[0046] (5) In order to achieve a better heat extraction effect, we can also use superconducting liquid instead of softened water as the heat carrier.
[0047] The theoretical basis for the realization of the present invention is as follows:
[0048] (1) Newton's law of cooling: The law followed when objects with a higher temperature than the surrounding environment transfer heat to the surrounding medium to gradually cool down. When there is a temperature difference between the surface of an object and the surroundings, the heat lost from a unit area per unit time is proportional to the temperature difference, and the proportional coefficient is called the heat transfer coefficient. Newton's law of cooling was determined by Newton experimentally in 1700. It is in good agreement with reality when forced convection occurs, and it is only valid when the temperature difference is not too large under natural convection. The law is Heat transfer One of the basic laws of using dry calculations convection How much calories.
[0049] Temperature difference Δt=|tw-tf| q=hΔt Φ=qA=AhΔt=Δt/(1/hA)
[0050] The 1/hA is called convection heat transfer resistance.
[0051] Conclusion: According to this principle, we can think that when the temperature of the circulating water in the downhole casing is lower than the temperature of the deep underground rock, the heat energy in the rock will be transferred to the circulating water through the casing wall.
[0052] (2) Fourier's law is a basic law in heat transfer.
[0053] Used to calculate the amount of heat conduction, the relevant formula is as follows:
[0054] Φ=-λA(dt/dx) q=-λ(dt/dx) where Φ is the thermal conductivity, the unit is W, λ is the thermal conductivity A is the heat transfer area, the unit is m^2, t is the temperature, the unit is K, x are the coordinates on the heat conduction surface, the unit is mq is the heat flux, the unit is W/m^2, the negative sign indicates that the direction of heat transfer is opposite to the direction of the temperature gradient, and λ is the physical parameter of the thermal conductivity of the material (the greater the λ , The better the thermal conductivity)
[0055] Conclusion: According to Fourier's law combined with Newton's law of cooling, we can calculate the heat transfer of formation rocks to water.
[0056] (3) Geothermal and heat conduction
[0057] In the current field of dry hot rock geothermal energy development and utilization, thermodynamic research on the use of water flowing in deep well casings for thermal energy extraction is being carried out. In the dry hot rock geothermal development system, the first concern is the process of large-scale heat conduction in the liquid-containing geothermal rock mass. The geothermal rock mass can be considered as a geothermal area composed of a number of approximately perpendicular and interconnected fissures and relatively impermeable rock masses. The present invention focuses on the heat conduction of the heat energy of the deep rock through the well wall surface to the water flow in the pipe.
[0058] The basic forms of heat conduction in rocks include heat conduction and heat convection. Among them, the understanding of the heat conduction process is very mature. Thermal convection is the transfer of heat energy through water flow in rock fractures. The mechanism of heat convection is that in a fluid, the movement of the fluid material causes the various parts to mix, resulting in heat transfer. Fluid movement can be caused by external factors (for example, using a fan or water pump, etc.). This situation can be called forced heat transfer. If the fluid movement is caused by the density difference caused by the temperature difference, it can be called free or natural heat transfer. In deep underground dry-hot rock areas, heat conduction is the main geothermal transfer mechanism. However, the extraction of thermal energy to the surface is achieved by the transfer of heat from the rock to the water flow in the well wall. For a single-phase fluid without chemical reaction, the classic heat conduction equation is as follows:
[0059] ∂ p ∂ t + ▿ ( ρv ) = 0 - - - ( 1 )
[0060] ρ [ ∂ v ∂ t + v 0 ▿ v ] = - ▿ ρ + μ ▿ 2 v + ρF - - - ( 2 )
[0061] ρc [ ∂ T ∂ t + v 0 ▿ T ] = k ▿ 2 T + Q 0 - - - ( 3 )
[0062] Where: v, T, t, p, F and Q 0 Respectively represent speed, temperature, time, pressure, physical strength and heat generation; while ρ, μ, c and k represent physical properties such as density, dynamic viscosity, specific heat, and thermal conductivity.
[0063] Another form of heat propagation called radiation is ignored in the basic form of heat conduction in rocks. For solid heat conduction, there is no velocity term, so the above equations can be reduced to only energy equations:
[0064] ρc ∂ T ∂ t = k ▿ 2 T + Q 0 - - - ( 4 )
[0065] The derivative of equations (1)~(3) implies the following Fourier basic empirical formula:
[0066] q = - kA ▿ T - - - ( 5 )
[0067] In the formula: q is the thermal conductivity, and A is the area perpendicular to the heat flow.
[0068] For many heat propagation problems, it is difficult to apply equations (1) to (3), so the semi-empirical method is usually used to fit the experimental data with a certain form of equation. The equation thus obtained usually expresses a standard dimensionless parameter (quantity) relationship. These parameters come from further analysis of the above equations, or from the dimensional analysis of the physical and characteristic parameters involved in the problem. Regarding the current water fluid situation, the relevant dimensionless variables Reynolds number (Re) and Prandtl number (Pr) are given by the following formula:
[0069] Re=UL/v (6)
[0070] Pr=v/α (7)
[0071] In the formula: U is the characteristic flow velocity, L is the characteristic length depending on the geometric size of the problem, v is the dynamic viscosity number, and α is the thermal diffusion coefficient.
[0072] For the problem of thermal convection, Nusselt number (Nu) is also involved, which is defined as follows: Nu=hL/k (8)
[0073] In the formula: h is an important heat convection conduction parameter, and its value represents the degree of heat conduction caused by heat convection. The effect of h can be seen from Newton's law:
[0074] q=hAΔT (9) where: ΔT is the temperature difference between the rock surface and the fluid.
[0075] (4) Thermal conductivity of rock
[0076] The ability of a rock to conduct heat is called thermal conductivity and is often expressed by thermal conductivity. According to the second law of thermodynamics, the heat in an object continuously flows from a high temperature point to a low temperature point through thermal conduction, so that the temperature in the object gradually becomes uniform. Suppose that on the plane of area A, the temperature only changes along the x direction. At this time, the heat flow (Q) passing through A is proportional to the temperature gradient dT/dx and the time dt, namely
[0077] Q = - kA dT dx dt
[0078] In the formula: k is the thermal conductivity (W/(m·K)), meaning that when dT and dx are equal to 1, the heat passing through a unit area of rock per unit time.
[0079] Thermal conductivity is an important thermal property index of rock, and its size depends on the mineral composition, structure and water-bearing state of the rock. The thermal conductivity of common rocks is shown in Table 3-4. It can be seen from the table that the k = 1.61~6.07W/(m·K) of rock at room temperature. In addition, the thermal conductivity of most sedimentary rocks and metamorphic rocks is anisotropic, that is, the thermal conductivity along the bedding direction is higher than that of the vertical bedding direction. The thermal conductivity is about 10%-30% higher on average. The thermal conductivity of rocks is often measured in the laboratory by the unstable method.
[0080] According to research, there is the following relationship between the specific heat capacity (C) and thermal conductivity (k) of rocks:
[0081] k=λρC
[0082] In the formula: ρ is the density of the rock; λ is the thermal diffusivity of the rock (cm 2 /s).
[0083] The thermal diffusivity reflects the sensitivity of the rock to temperature changes. The larger the λ, the faster the rock's response to temperature changes, and the greater the influence of temperature. The thermal diffusivity of common rocks is shown in the table
[0084] Table 3-5 Thermal characteristic parameters of several rocks
[0085] Table 3-5 Thermal characteristic parameters of several rocks
[0086]
[0087] (4) Characteristics of water
[0088] Water exists in a liquid state at room temperature and has the common characteristics of general liquids. Compared with other liquids, it has many unique properties.
[0089] (1) Water does not expand and contract with heat in the range of 0~4℃, but expands and shrinks with cooling, that is, the temperature increases, the volume decreases, and the density increases.
[0090] (2) Among all liquids, water has the largest specific heat capacity, which is 4.18 Joules/gram degree. Therefore, water can be used as a high-quality heat exchange medium for cooling, heat storage, and heat transfer.
[0091] (3) At room temperature (0-100°C), water can undergo three-phase changes of solid, liquid, and gas. It is convenient to use the phase heat of water to convert energy.
[0092] (4) In liquids, except for mercury (Hg), water has the largest surface energy.
[0093] (5) Water solubility and reaction ability is very strong. Many substances not only have great solubility in water, but also have the greatest degree of ionization.
[0094] (6) The conductivity of water increases as the salt content in the water increases.
[0095] Conclusion: Water can be used as a heat transfer medium.
[0096] (5) Introduction to the properties of superconducting liquid:
[0097] 1. The starting temperature is low, and it only needs 35℃ to start the temperature transmission. The water temperature rises very slowly, and the transmission is slower. Generally, it takes one to two hours to start the water heating to reach room temperature. Superconducting heating can heat the radiator in only 3-5 minutes, and its transfer speed is several times that of water heating, and it can transfer more than 15-20 meters per minute.
[0098] 2. There will be no freezing at minus 40℃, and there is no hidden danger of equipment freezing.
[0099] Conclusion: Superconducting liquid can replace water as the heat transfer medium for circulation.
[0100] (6) Comparison of thermal conductivity of materials
[0101]
[0102] (7) Heat capacity of water and rocks
[0103] The comparison value of the energy consumed when the temperature difference between the heating water in and out of the 40,000 square meter building is 15 degrees per hour and the heat capacity per unit volume of rock can be compared to Table 5 for analysis
[0104] Table 4 shows the relationship between the heat exchange temperature difference between water and rock per unit time and the heat capacity contained in it
[0105] Specific heat
[0106] From Table 4, we can preliminarily think that the heat capacity provided by the rock with a shaft radius of 1 meter and a volume range of 800-1600 meters long is 2-20 times the required heat capacity per unit volume and unit time of circulating water, which is sufficient to meet the circulation. The thermal energy of the water compensates for the need.
