A method for constructing injection wells for the heat exchange space of fractures in deep dry hot rock formations

Abstract

This invention discloses a method for constructing an injection well in the heat exchange space of a deep hot dry rock formation fracture. The method includes: after drilling to the formation floor of the hot dry rock formation, performing open-hole logging to determine the location, thickness, temperature, and physical properties of the hot dry rock formation; running a pressure-bearing, corrosion-resistant casing into the borehole and cementing it with cement slurry; then drilling a horizontal section in the lower part of the hot dry rock formation, using a corrosion-resistant screen for completion. After completion, a fluxing rod is run into the hot dry rock formation, and the target amount of liquid CO2 injected is determined based on the formation thickness, reservoir properties, and well spacing; liquid CO2 is injected sequentially into the hot dry rock formation under high pressure using the fluxing rod in a segmented injection manner, and after reaching the target amount of liquid CO2, the wellhead is shut off for a preset time. This invention improves well completion processes and injects liquid CO2 under high pressure. By injecting liquid CO2 under high pressure, a fracture network is formed in the hot dry rock formation, which communicates with the fracture network of the production well, thereby ultimately improving the heat exchange efficiency of the hot dry rock formation.

Description

1. Description of a Method for Constructing an Injection Well for a Heat Exchange Space in a Deep Hot Dry Rock Formation Technical Field This invention relates to the field of hot dry rock engineering heat extraction technology, and particularly to a method for constructing an injection well for a heat exchange space in a hot dry rock formation. Background Art With the increasing global demand for clean and renewable energy, hot dry rock (HDR), as a geothermal resource with enormous development potential, has received widespread attention. Hot dry rock resources are mainly found at depths of 3-10 km in the upper part of the Earth's crust, containing enormous thermal energy. To effectively develop and utilize this resource, it is necessary to establish an Enhanced Geothermal System (EGS). An EGS is an artificial heat exchange space formed deep underground through artificial fracturing, drilling, and other means, allowing the thermal energy in the high-temperature underground rock to be transferred to the surface through media such as water and CO2, and then used for power generation, heating, and other purposes. However, due to the large burial depth, high temperature, and complex geological conditions of hot dry rock resources, the construction technology of EGS faces many challenges. Currently, international research on EGS technology mainly focuses on how to effectively form and maintain heat exchange spaces in formation fractures. Although there have been some successful trials and demonstration projects, EGS technology is still in the development stage, especially in the construction of heat exchange spaces in deep dry hot rock formations, where many problems remain to be solved. The inventors have discovered that the geological conditions of deep dry hot rock formations are complex, and parameters such as rock type, stress state, and fracture distribution are difficult to predict accurately, increasing the uncertainty of fracture formation and propagation. Changes in underground physical conditions such as temperature and pressure can also significantly affect fracture formation and stability. Existing hydraulic fracturing techniques are difficult to effectively form and maintain stable fracture networks in deep dry hot rock formations. Deep dry hot rock formations typically have harder rocks, requiring higher pressure and energy to form fractures. The direction and extent of fracture propagation are difficult to control, potentially leading to fractures extending in unexpected directions or even forming uncontrollable fracture systems. In view of the above problems, this invention is proposed to provide a method for constructing an injection well in the fracture heat exchange space of a deep hot dry rock formation to overcome or at least partially solve the above problems. The method may include: after drilling to the formation floor of the hot dry rock formation, performing open-hole logging to determine the location, thickness, temperature, and reservoir properties of the hot dry rock formation; inserting a pressure-bearing, corrosion-resistant casing into the drilled borehole and cementing it with cement slurry; drilling a horizontal well section in the lower part of the hot dry rock formation, the length of which is calculated based on the required heat exchange power. The horizontal well section is completed using a corrosion-resistant screen pipe.A syringe plunger is lowered into the hot dry rock formation to prepare for liquid CO2 injection into the injection well. The target amount of liquid CO2 to be injected into the hot dry rock formation is determined based on its thickness, temperature, reservoir properties, and well spacing. Liquid CO2 is then injected sequentially into the hot dry rock formation under high pressure using the syringe plunger in a segmented injection manner until the target amount of liquid CO2 is reached. Afterward, the wellhead is closed for a preset time. Optionally, the method may further include: deploying a number of injection and production wells within the same rock body containing the hot dry rock formation, based on geological interpretation results of the study area; and performing the aforementioned casing installation, cementing, horizontal drilling, syringe plunger injection, and high-pressure injection operations on all injection wells. After the preset wellhead closure time, the wellhead of the injection well is opened, and CO2 is pumped out through the injection well. Optionally, after pumping CO2 out through the injection well, the process may further include: repeating the high-pressure injection operation described above on the injection well until the target amount of liquid CO2 is reached, and then closing the wellhead for a preset time. Optionally, cementing the well with cement slurry may include: filling the space around the casing with cement using a forward grouting method until the cement slurry returns to the surface. Optionally, after lowering the injection rod string into the hot dry rock formation, the process may further include: installing a surface high-pressure liquid CO2 injection device. Optionally, determining the target amount of liquid CO2 injected into the hot dry rock formation based on the thickness, temperature, reservoir properties, and well spacing of the hot dry rock formation may include: determining the target amount of liquid CO2 injected into the hot dry rock formation based on the thickness, temperature, porosity included in the reservoir properties, and well spacing of the hot dry rock formation. Optionally, liquid CO2 is injected sequentially into the hot dry rock formation under high pressure via the injection rod in a segmented injection manner. After reaching the target amount of liquid CO2 injected, the wellhead is shut off for a preset time. This high-pressure injection of liquid CO2 is repeated until the target water injection volume and the target gas injection volume are reached, at which point the wellhead is shut off for a preset time. Optionally, the preset time is 7-10 days. Optionally, the length of the horizontal well section is 1-2 kilometers. Optionally, the reservoir physical properties include porosity, permeability, and / or pore distribution.The beneficial effects of the above-mentioned technical solutions provided in the embodiments of the present invention include at least the following: The embodiments of the present invention provide a method for constructing an injection well in the heat exchange space of a deep dry hot rock formation fracture. The method may include: after drilling to the bottom plate of the dry hot rock formation, performing open-hole logging to determine the location, thickness, temperature, and reservoir physical parameters of the dry hot rock formation; after inserting a pressure-bearing and corrosion-resistant casing into the borehole after drilling, cementing the well with cement slurry; drilling a horizontal well section in the lower part of the dry hot rock formation, the length of which is calculated based on the required heat exchange power. The horizontal well section is completed using corrosion-resistant screen pipes; an injection rod string is run into the hot dry rock formation to prepare for liquid CO2 injection; based on the thickness, temperature, reservoir properties, and well spacing of the hot dry rock formation, the target water and gas injection volumes are determined; liquid CO2 is sequentially injected into the hot dry rock formation under high pressure using a slug injection method through the injection rod string, and the wellhead is shut off for a preset time after the target amount of liquid CO2 is reached. This embodiment of the invention improves the well completion process and the sequence of liquid CO2 injection, thereby achieving the cyclical exploitation of heat from the hot dry rock formation (HK 30135236 A 4). High-pressure injection increases the amount of liquid CO2 injected into the hot dry rock formation, forming a fracture network within the formation that communicates with the fracture network of the production well, ultimately improving the heat exchange efficiency of the hot dry rock formation. Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention can be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings. The technical solutions of the invention will be further described in detail below with reference to the accompanying drawings and embodiments. Description of Drawings The accompanying drawings are used to provide a further understanding of the invention and constitute a part of the specification. They are used together with the embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings: Figure 1 is a flowchart of a method for constructing an injection well for heat exchange space in a deep dry hot rock formation fracture, provided in an embodiment of the invention. Detailed Description Exemplary embodiments of the present disclosure will now be described in more detail with reference to the accompanying drawings. Although exemplary embodiments of the present disclosure are shown in the drawings, it should be understood that the present disclosure may be implemented in various forms and should not be limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the disclosure to those skilled in the art.In the description of this invention, it should be noted that the terms "center," "upper," "lower," "left," "right," "vertical," "horizontal," "inner," "outer," "far," "near," "front," and "rear," etc., indicating orientation or positional relationships, are based on the orientation or positional relationships shown in the accompanying drawings and are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention. Furthermore, the terms "first," "second," and "third" are used for descriptive purposes only and should not be construed as indicating or implying relative importance. In the description of this invention, it should be noted that unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances. This invention provides a method for constructing an injection well in the heat exchange space of a deep hot dry rock formation fracture. Referring to Figure 1, the method may include the following steps: Step S10: After drilling to the bottom plate of the hot dry rock formation, open-hole logging is performed to determine the location, thickness, temperature, and reservoir properties of the hot dry rock formation. In this step, a drilling rig is used for drilling. After the drill bit reaches the bottom plate of the hot dry rock formation in the study area, the drill string is pulled up to perform open-hole geophysical exploration. The geophysical exploration can then determine the location, thickness, temperature, and reservoir properties of the hot dry rock formation. The reservoir properties may include, but are not limited to, the following parameters: porosity, permeability, and / or pore distribution. Step S11: After inserting a pressure-bearing, corrosion-resistant casing into the drilled borehole, cementing is performed using cement slurry. In this step, casing is lowered into the borehole after drilling is completed. The inventors selected a pressure-bearing, corrosion-resistant casing, which, compared to ordinary casings used in existing technologies, not only enables liquid CO2 injection under high pressure but also prevents corrosion of the pressure-bearing, corrosion-resistant casing by dissolved CO2 water. Simultaneously, cement slurry is used for cementing, providing a sealing condition for the high-pressure liquid CO2 injection in the following steps. In practice, the cementing operation uses a forward grouting method to fill the space around the casing with cement until the cement slurry returns to the surface, completing the cementing operation. Of course, after the cementing operation is completed, the cementing quality needs to be inspected to ensure the entire construction process of the injection well in the fracture heat exchange space of deep dry hot rock formations is inspected multiple times, improving the safety factor.Step S12: Drill a horizontal well section in the lower part of the hot dry rock formation. The length of the horizontal well section is calculated based on the required heat exchange power. The horizontal well section uses corrosion-resistant screen pipe for completion. HK 30135236 A 6 Step S13: Run the injection rod string into the horizontal well section of the hot dry rock formation to complete the preparation work for liquid CO2 injection. This step involves running the injection rod string into the horizontal well section of the hot dry rock formation formed after step S12, and injecting liquid CO2 into the hot dry rock formation through the injection rod string. Step S14: Install the surface high-pressure liquid CO2 injection equipment. This step involves installing the surface equipment after the underground equipment is assembled. Step S15: Determine the target amount of liquid CO2 to be injected into the hot dry rock formation based on the thickness, temperature, reservoir properties, and well spacing of the hot dry rock formation. In practice, this step involves determining the target amount of liquid CO2 to be injected into the hot dry rock formation based on its thickness, temperature, reservoir properties (including porosity), and well spacing. This step is a calculation; before injecting liquid CO2, the amount of liquid CO2 to be injected into the well needs to be determined to ensure sufficient fracture network formation in the hot dry rock formation near the well. It should be noted that this step only needs to be performed before step S16, but can be performed after step S14 or after step S10. That is, the calculation of the target amount of liquid CO2 can be performed after obtaining data such as the location, thickness, temperature, and reservoir properties of the hot dry rock formation from geophysical exploration wells. This embodiment of the invention does not specifically limit the timing of step S15. Step S16: Liquid CO2 is injected under high pressure into different parts of the horizontal section of the hot dry rock formation using a segmented injection method via an injection rod. After reaching the target amount of injected liquid CO2, the wellhead is closed for a preset time. In this step, the inventors use a segmented injection method to inject liquid CO2, injecting it multiple times until the target amount of injected liquid CO2 is reached. After the injection is completed, the wellhead is closed for a preset time, which can be 7-10 days before CO2 discharge, allowing the fracture network in the horizontal section of the hot dry rock formation to fully develop. In this embodiment of the invention, the inventors fully consider the expansion effect of liquid CO2 in the hot dry rock formation, increasing the injection volume of liquid CO2, thereby promoting the formation of the fracture network in the hot dry rock formation. Step S17: Based on the geological interpretation results of the study area where the hot dry rock strata are located, deploy a number of injection wells and production wells for the same rock mass containing the hot dry rock strata, and perform the above-mentioned HK 30135236 A 7 casing installation, cementing, perforation, injection rod insertion, and high-pressure injection operations on all injection wells. This step involves performing the above operations on all rock masses containing the injection wells within the study area to achieve the exploitation of the entire rock mass.Step S18: After the wellhead is closed for a preset time, the wellhead of the injection well is opened, and CO2 is pumped out through the injection well pump. Step S19: The injection well construction method for the heat exchange space of deep dry hot rock formations provided in the embodiments of the present invention improves the well completion process and the order of liquid CO2 injection, thereby realizing the fracture network transformation of the dry hot rock formation. The amount of liquid CO2 injected into the dry hot rock formation is increased by high-pressure injection, thereby ultimately improving the development degree of the fracture network. The comparative embodiments of the above embodiments of the present invention are as follows: Comparative Embodiment 1: Step 1: After drilling to the bottom plate of the dry hot rock formation, open-hole logging is performed to determine the location, thickness, temperature, and reservoir physical parameters of the dry hot rock formation. Step 2: After running ordinary casing into the borehole after drilling, cementing is performed using cement slurry. Step 3: After well washing, lower the perforating gun into the borehole to the hot dry rock formation, penetrate the casing, and then penetrate the uranium ore layer at a predetermined distance to establish communication between the casing and the hot dry rock formation. Step 4: Lower the injection rod string into the hot dry rock formation to complete preparations for injection well fracturing. Step 5: Install the surface fracturing equipment. Step 6: Determine the fracturing fluid volume based on the thickness of the hot dry rock formation, its reservoir properties, and the well spacing. Step 7: Inject fracturing fluid into the hot dry rock formation using the injection rod string and seal the wellhead for a predetermined time. Step 8: Open the wellhead of the injection well and pump out the fracturing fluid. Comparative Example 2: Step 1: After drilling to the bottom plate of the hot dry rock formation, perform open-hole logging to determine the location, thickness, temperature, and reservoir properties of the hot dry rock formation. HK 30135236 A 8 Step 2: After drilling, run a pressure-bearing, corrosion-resistant casing into the borehole and cement it with cement slurry. Step 3: Drill a horizontal section in the lower part of the hot dry rock formation. The length of the horizontal section is calculated based on the required heat exchange power. The horizontal section uses corrosion-resistant screen pipe for completion. Step 4: Run the injection rod string into the horizontal section of the hot dry rock formation to complete the preparation work for injection well fracturing. Step 5: Install the surface fracturing equipment. Step 6: Determine the fracturing fluid volume based on the thickness of the hot dry rock formation, the reservoir properties of the uranium ore layer, and the well spacing. Step 7: Inject fracturing fluid into the hot dry rock formation through the injection rod string and seal the wellhead for a preset time. Step 8: Open the wellhead of the injection well and pump out the fracturing fluid through the injection well pump. Comparative Example 3, Step 1: After drilling to the bottom plate of the hot dry rock formation, open-hole logging is performed to determine the location, thickness, temperature, and reservoir properties of the hot dry rock formation. Step 2: After running a pressure-bearing, corrosion-resistant casing into the drilled hole, cementing is performed using cement slurry. Step 3: A horizontal well section is drilled in the lower part of the hot dry rock formation. The length of the horizontal well section is calculated based on the required heat exchange power.The horizontal well section uses corrosion-resistant screen pipe for completion. Step 4: Run the injection rod string into the hot dry rock formation to complete the preparation work for injection well fracturing. Step 5: Install the surface fracturing equipment. Step 6: Determine the amount of fracturing fluid to be injected into the hot dry rock formation based on the thickness, reservoir properties, and well spacing of the hot dry rock formation. Step 7: Inject fracturing fluid into the horizontal well section of the hot dry rock formation in stages through the injection rod string, and seal the wellhead for a preset time. Step 8: Open the wellhead of the injection well and pump out the fracturing fluid through the injection well pump. Comparative Example 4: Step 1: After drilling to the bottom plate of the hot dry rock formation, open-hole logging is performed to determine the location, thickness, and reservoir properties of the hot dry rock formation. Step 2: After running a pressure-bearing corrosion-resistant casing into the drilled hole, cementing is performed using cement slurry. Step 3: Drill a horizontal well section in the lower part of the hot dry rock formation. The length of the horizontal well section is calculated based on the required heat exchange power. The horizontal well section uses corrosion-resistant screen pipe for completion. Step 4: Run the injection rod string into the hot dry rock formation to complete the preparation work for injection well construction. Step 5: Install the surface high-pressure liquid CO2 injection equipment. Step 6: Determine the target amount of liquid CO2 to be injected into the hot dry rock formation based on its thickness, temperature, reservoir properties, and well spacing. Step 7: Inject liquid CO2 into the horizontal well section of the hot dry rock formation in stages using the injection rod string, and seal the wellhead for a preset time. Step 8: Open the wellhead of the injection well and pump out CO2 through the injection well pump. This embodiment of the invention is mainly aimed at deep hot dry rock formations, where existing fracturing technologies are difficult to effectively form and maintain a stable fracture network. Deep formations typically have harder rocks, requiring higher pressure and energy to form fractures. Traditional EGS (Enhanced Geochemical Seismic Systems) construction may have negative impacts on groundwater, soil, and the ecological environment, such as groundwater pollution and surface subsidence. If fractures are not properly controlled, they may also trigger geological disasters such as earthquakes. Due to the high temperature and pressure conditions in deep strata, the stability and durability of the fracture heat exchange space face challenges. Fractures may deform or close at high temperatures, affecting heat exchange efficiency. This invention employs a method of directly injecting liquid CO2 into dry hot rock strata in a segmented manner under high pressure. This significantly increases the amount of liquid CO2 injected into the dry hot rock strata, thereby improving the development of the fracture network and ultimately enhancing the heat exchange effect. Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. This disclosure is not limited to the precise structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this disclosure is limited only by the appended claims.Thus, if these modifications and variations of the present invention fall within the scope of the claims of the present invention and their equivalents, the present invention also intends to include these modifications and variations. HK 30135236 A 1 Claim 1: A method for constructing an injection well in the heat exchange space of a deep dry hot rock formation fracture, characterized by comprising: drilling to the formation floor of the dry hot rock formation, performing open-hole logging to determine the location, thickness, temperature, and reservoir properties of the dry hot rock formation; inserting a pressure-bearing, corrosion-resistant casing into the drilled borehole, and cementing the well with cement slurry; drilling a horizontal well section in the lower part of the dry hot rock formation, the length of which is calculated based on the required heat exchange power. The horizontal well section is completed using a corrosion-resistant screen pipe. A syringe plunger is lowered into the hot dry rock formation to prepare for the injection of liquid CO2 into the injection well; the target amount of liquid CO2 to be injected into the hot dry rock formation is determined based on the formation's thickness, temperature, reservoir properties, and well spacing; liquid CO2 is injected into the formation under high pressure using the syringe plunger in a segmented injection manner until the target injection volume and target liquid CO2 volume are reached, at which point the wellhead is closed for a preset time. 2. The method according to claim 1, further comprising: deploying a number of injection wells and production wells for the same hot dry rock body where the hot dry rock formation is located, based on geological interpretation results of the study area; performing the aforementioned casing installation, cementing, syringe plunger installation, and high-pressure liquid CO2 injection operations on all injection wells; and opening the wellhead of the injection well after the preset wellhead closure time, pumping CO2 out through the injection well. 3. The method according to claim 2, characterized in that, after pumping CO2 out through the injection well, it further includes: repeating the above-mentioned high-pressure injection operation on the injection well to reach the target amount of liquid CO2, and then closing the wellhead for a preset time; 4. The method according to claim 1, characterized in that, cementing the well with cement slurry includes: filling the space around the casing with cement using a forward grouting method to cement the well until the cement slurry returns to the surface. HK 30135236 A 2 5. The method according to claim 1, characterized in that, after the injection rod is lowered into the hot dry rock formation, it further includes: installing a surface high-pressure liquid CO2 injection device; 6. The method according to claim 1, characterized in that, determining the target amount of liquid CO2 injected into the hot dry rock formation based on the thickness, temperature, reservoir properties of the hot dry rock formation, and well spacing includes: determining the target amount of liquid CO2 injected into the hot dry rock formation based on the thickness, temperature, porosity included in the reservoir properties of the hot dry rock formation, and well spacing.7. The method according to claim 1, characterized in that liquid CO2 is injected sequentially into the hot dry rock formation under high pressure through the injection rod in a segmented injection manner, and after reaching the target amount of injected liquid CO2, the wellhead is closed for a preset time. 8. The method according to claim 7, characterized in that the preset time is 7-10 days. 9. The method according to claim 1, characterized in that the length of the horizontal well section is 1-2 kilometers. 10. The method according to any one of claims 1-9, characterized in that the reservoir physical properties include: porosity, permeability, and / or pore distribution. HK 30135236 A 1 Specification Drawings Figure 1 HK 30135236 A.