JPH0492074A - Extraction heat increasing method for geothermal extraction method by single undermining well - Google Patents

Abstract

PURPOSE:To increase extraction heat by cooling suddenly a high-temperature stratum, forming a cracking belt caused by stress generated in the case a bed- rock is contracted, and lessening fluidized resistance in the cracking belt to make it easy to generate convection. CONSTITUTION:An insulating pipe 16 is inserted up to the predetermined depth to form a cracking belt into an undermining well. After that, low temperature water is poured to the inside of the insulating pipe 16 from a water tank 17 of the ground through a pump 18. Then, the water is returned to the ground through a circular void between an undermining wall and the insulating pipe. A stratum is suddenly cooled by the returned low temperature water, and the cracking belt 19 is formed in the stratum by thermal stress generated in that time. After the water reduced to the ground is cooled by a cooler 20, it is stored in the water tank 17 and is circulated to use.

Description

[Detailed description of the invention] [Industrial application field] Extraction of only thermal energy without extracting steam or hot water existing in high-temperature geological formations for direct use of heat such as heating or for power generation. In this method, the heat pipe 3 is inserted deep into the high temperature area.

Between the inner wall of the metal protection tube and the outer surface of the heat pipe,
Fill with water to promote heat transfer. Thermal energy extracted by the heat pipe is transferred to the working fluid via an above-ground heat exchanger 4. The heat transferred to the working fluid is used for direct heat utilization, such as heating, or for power generation.

Such a geothermal extraction method using a single well is simple and has the advantage of being able to obtain extremely clean energy because it extracts only thermal energy.

However, since the thermal conductivity of the geological formation is low, if heat is transferred only by thermal conduction in the geological formation, the amount of heat extracted will be limited even if the formation is at a fairly high temperature. When the permeability of the stratum is good and stratum fluids such as steam and water convect in the stratum around the wellbore, heat is transferred only by thermal conduction, and a conceptual diagram of the fracturing method is shown in Figure 4. , 5 is a well, and a metal protection pipe 6 is constructed except for the part where a crack is formed. First, the wellbore cuts N7 and 8 are cut off below the location where the crack is to be formed. It is usually made of rubber, is inflated by mechanical or hydraulic force, and is pressed against the mine wall. After doing this, high pressure is released from the above-ground water tank 9. However, in order to increase the amount of heat extracted by the geothermal extraction method using a single well, it is necessary to sorb the water permeability of the strata surrounding the well and make convection more likely to occur. In order to improve the permeability of a geological formation, it is necessary to create cracks in it and form a crack zone.

As a method for creating cracks in the strata, the so-called water fragmentation method is used, in which high-pressure water is injected into the strata5 and the pressure is used to create cracks in the strata. water 1], and eventually a crack 13 is formed in the stratum due to this pressure.

In this hydraulic fracturing method, (1) If the stratum has a certain degree of permeability, the water that is injected will escape and it will be difficult to create cracks. For this reason, it can only be applied when the permeability of the stratum is extremely poor. ■The cracks that occur are very thin;
The flow resistance in the cracks is large, so convection occurs, and a large effect of increasing the amount of extracted heat cannot be expected.
■ Cracks often develop in specific directions depending on the condition of the ground and the properties of the strata, making it difficult to effectively create a crack zone around the 5 wells. It is difficult to create cracks evenly over a long section of the wellbore in one operation because they occur at the weakest of the six existing fringes or weak points in the wellbore. In order to form a crack zone in a long section, there are problems such as the cost of partitioning the wellbore, and it is not necessarily an effective method for creating a crack zone.[Object of the Invention] 12. Formation of turtle cracks around the wellbore prior to heat extraction operations without using hydraulic fracturing. There are few cases in which it is difficult to reliably divide the mine into sections using conventional methods. It may not be possible.

■Existing devices for partitioning wells have low heat resistance, making them difficult to apply when the geological formations are at high temperatures. ■Since a large amount of high-pressure water is injected into the geological formation, a large high-pressure pump is required, and a device to partition the well is also essential.

Moreover, the work is complicated and requires a large number of works.

Therefore, it can be applied even when a large amount of water is good. In addition, because the high-temperature strata are rapidly cooled and crack zones are formed due to the stress generated when the rock contracts, the thickness of the cracks formed is larger than with hydraulic fracturing.

Therefore, the flow resistance in the crack zone becomes small, and convection becomes more likely to occur. In other words, a greater effect of increasing the amount of extracted heat can be expected. Thermal stress generated in the geological formation when cooling a wellbore is large near the wellbore wall and decreases as the distance goes further, so an effective ζ-crack zone can be formed around the wellbore. Furthermore, in order to form a long section G crack zone using the hydraulic fracturing method, repeat step 1 while cutting the well into short sections. Although it is necessary to perform hydraulic fracturing,
In this method, since the section in which the crack zone is formed is long, there is a possibility that the crack zone can be formed in a predetermined section in one operation.

In the hydraulic fracturing method, it is not necessary to divide the drag A into sections, and compared to the hydraulic fracturing method, a large amount of equipment is not required, and the work is simple, so it is thought that the cost will be low.

As a result of the above, it becomes possible to easily form a large crack zone in a high-temperature geological formation at low cost. The position where the crack zone is formed can be changed simply by changing the method of increasing the amount of heat extracted by formation. Since crack zones are formed by cooling the strata, the higher the temperature of the strata, the easier the formation of crack zones. In addition, the only equipment exposed to high temperatures is the insulated pipe, and since the heat-resistant performance of the insulated pipe is high, it can be applied to strata at such high temperatures that hydraulic fracturing is difficult to apply. The hydraulic fracturing method requires a large, high-pressure pump, but according to the present invention, only low-temperature water is circulated within the mine, so this is an example of the high-pressure pump method.
In the figure, 14 is a well drilled into a high-temperature stratum. In the section where the crack zone is planned to be formed, the strata are exposed, but in other sections, the pit wall is protected by a metal protection pipe 15. A thermally insulated tube 16 is inserted into this wellbore to the depth at which the fracture zone is to be formed. As this heat insulating pipe, a vacuum heavy heat insulating pipe, a ceramic pipe, a ceramic/metal composite pipe, etc. can be considered. Thereafter, low-temperature water is injected into the inside of the heat insulating pipe 16 from the water tank 17 on the ground using the pump 18. Since the tube is insulated, the injected water reaches the lower end of the tube at almost the same temperature. This water is
The water then returns to the ground through an annular gap between the mine wall and the insulated pipe. The geological formation is rapidly cooled by the circulating low-temperature water, but cracks 4119 are formed in the geological formation due to the thermal stress generated at this time. The water that has returned to the ground 1 is then returned to the ground while cooling the mine wall. The temperature of the water at this time is represented by a solid line from point C to point A in the figure. A crack zone occurs in an area where there is a large difference between the temperature of this flowing water and the temperature of the stratum. As the temperature of the refluxing water increases and the difference between it and the temperature of the strata decreases, cracks will no longer form.
- In order to form a crack zone over a long section with multiple operations, an example of the temperature distribution in the tunnel expected in this case is shown in the second example.
The depth of the wellbore and the insertion depth of the insulated pipe in the case of figure 0 shown in the figure are approximately 3,000 m. In figure 9, the temperature represented by the broken line from point A to point B is the temperature before injecting low-temperature water. This is the temperature distribution of the strata. Water injected into an insulated pipe reaches the bottom end of the pipe at almost the same temperature. The temperature distribution of the water in the heat-insulated pipe at this time is shown by a solid line from point A to point C. The injected water can then pass through the annular gap between the pit wall and the insulated pipe, forming a crack zone most effectively at the lower end of the insulated pipe. It is therefore conceivable to move the position of the lower end of the tube and cool it repeatedly in order to ensure the formation of a crack zone over a long section of the wellbore.

After forming a crack zone in the strata surrounding the well in this way, heat is extracted using a geothermal extraction method using a single well.
In some cases, after the crack zone is formed, a metal protection tube may be used to protect the section where the crack zone is formed.

In addition, in this example, the stratum is exposed in the section where the crack zone is formed, but the entire length of the well C, including the section where the crack zone is formed, is covered by a metal shield. After constructing lcR,
It is also conceivable to form crack zones according to the invention. The protection tube is made of metal and has high thermal conductivity, so it is
7L, even a geological cooler is possible.

Note that heat extraction is performed after the creation of a crack zone, but when using a shield pipe, C4° is used to create the crack zone, and after removing the insulated pipe, G':O
In the case of using a borehole shaft heat exchanger, which is inserted to extract heat, there are cases in which the insulated tube used for forming the crack zone is used as an inner tube for heat extraction, and It is also possible to inject low-temperature water into the annular space between the pipes and return it to the ground through the insulated pipes. Since the crack band formation effect is considerably smaller than that in the case of the method, it is considered that the crack band formation effect is inferior.

forming a crack zone around the pit.
This method solves the same whisker points associated with the conventional crack zone formation method, and aims to inexpensively and reliably increase the amount of extracted heat in geothermal extraction '7+' * from shore to well. It is also conceivable to inject water into the crack zone after formation. This operation can be carried out before or after the installation of the metal protection tube, or during the heat extraction operation.

[Brief explanation of drawings]

FIG. 1 is an explanatory diagram showing an example of the force method for forming cracks in the strata surrounding a wellbore according to the present invention. FIG. 2 is an explanatory diagram showing an example of temperature distribution in a well that is expected when a crack is formed in a geological formation according to the present invention, and FIG. 1 is an explanatory diagram showing an example of a geothermal extraction method using a single well. In addition, FIG. 4 is an explanatory diagram showing an example of forming cracks in the strata around a wellbore by a conventional method. Heat exchanger Fig. 1 13 - Crack 15 - Metal protective tube 17 - Water tank 19 - Crack zone. Well insulation pipe tank cooler

Claims (1)

[Claims] In single-well geothermal extraction, before the heat extraction operation,
An insulated pipe with a high degree of insulation performance is inserted into the well, and water at a lower temperature than the surface is sent through the insulated pipe to the lower end of the insulated pipe, and the water is sent to the ground through the annular gap between the well wall and the inner pipe. It is characterized by rapidly cooling the deep, high-temperature strata by circulating the current up to Method for increasing extraction heat amount.