A medium-deep geothermal well structure and a construction method thereof

Abstract

The application discloses a kind of middle deep geothermal well structure and its construction method, a kind of middle deep geothermal well structure includes inner tube, borehole and input end, the inside of borehole is provided with outer tube, and the gap between borehole and outer tube is filled with cementing cement, inner tube is coaxially inserted into outer tube, one end of input end is connected with the upper port of outer tube, the other end of input end is connected with ground water injection equipment;The construction method of a kind of middle deep geothermal well structure, specific steps are as follows: step one, borehole and well logging procedure;Step two, lower outer tube;Step three, fill cementing cement;Step four, lower inner tube, and ground extraction equipment is connected with inner tube, ground water injection equipment is connected and input end is connected.By the way of setting thread groove on inner tube, the flow trajectory of heat-conducting medium is changed, the circulation time of heat-conducting medium in the heat reservoir rock mass heating zone is prolonged, the heat conduction is more sufficient, so as to achieve the purpose of improving heat exchange efficiency.

Description

Technical Field

[0001] This invention belongs to the field of geothermal well construction technology, and specifically provides a medium-deep geothermal well structure and its construction method. Background Technology

[0002] As a renewable and clean energy source, geothermal energy is receiving increasing attention in the context of global carbon emission reduction.

[0003] The common method of geothermal energy extraction is to extract heat from deep underground formations through wells. There are two main methods: one is to directly extract underground hot water and then utilize it; the other is to use heat exchange, which involves transferring heat from the formation to the surface through a heat transfer medium. Among these methods, the "heat extraction without water extraction" approach is more in line with the principle of recyclability and is currently the focus of research.

[0004] In traditional heat exchange and extraction schemes, both the inner and outer casings of the well are straight pipes, made of steel or alloy pipes, which can achieve basic heat exchange effect, but there is still much room for improvement in heat exchange efficiency.

[0005] Therefore, it is necessary to explore a geothermal well structure scheme with relatively low construction costs and higher heat exchange efficiency. Summary of the Invention

[0006] To solve the above-mentioned technical problems, the technical solution adopted by the present invention is: a medium-deep geothermal well structure, including an inner tube, a borehole and an input end, an outer tube is provided inside the borehole, and the gap between the borehole and the outer tube is filled with cementing cement, the inner tube is coaxially inserted into the outer tube, one end of the input end is connected to the upper port of the outer tube, and the other end of the input end is connected to the surface water injection equipment.

[0007] The rock walls surrounding the borehole are divided into low-temperature rock mass, hot reservoir rock mass, and hot reservoir rock mass heating zone according to the formation temperature.

[0008] The inner tube is divided into two parts: a straight section and a flow-turbulence section. The outer wall of the flow-turbulence section is provided with a threaded groove.

[0009] The turbulence section is located in the thermal reservoir rock mass.

[0010] Furthermore, the threaded grooves are three in number and are distributed in a centrally symmetrical manner.

[0011] Furthermore, the borehole is a straight pipe, with the end of the outer pipe extending to the bottom of the borehole, completely covering the entire borehole section.

[0012] Furthermore, the borehole is a variable diameter pipe, and the end of the outer pipe extends to the boundary between the low-temperature rock mass and the hot reservoir rock mass.

[0013] A construction method for a medium-deep geothermal well structure, the specific steps of which are as follows:

[0014] Step 1: Drilling and logging procedures;

[0015] Step 2: Insert the outer tube;

[0016] Step 3: Fill with cementing material;

[0017] Step 4: Lower the inner pipe and connect the ground extraction equipment to the inner pipe, and connect the ground water injection equipment to the input end.

[0018] Furthermore, during step two, the outer tube is lowered to the deepest point of the borehole, and then step three is carried out.

[0019] Furthermore, during step two, the outer pipe is lowered to the boundary between the low-temperature rock mass and the hot reservoir rock mass, and then step three is carried out.

[0020] Furthermore, in step three, the cementing process is as follows:

[0021] Cement is injected into the gap between the outer casing and the borehole to fix the outer casing in place.

[0022] Furthermore, step three also includes performing secondary drilling, and the specific construction process of step three is as follows:

[0023] Continue injecting cement until the borehole is completely filled with the thermal reservoir rock mass and the heating zone of the thermal reservoir rock mass;

[0024] The drilling equipment is replaced with a smaller diameter drill bit, and secondary drilling is carried out on the solidified cement to form a variable diameter borehole.

[0025] The beneficial effects of using this invention are:

[0026] By setting threaded grooves on the inner tube, the flow trajectory of the heat transfer medium is changed, the circulation time of the heat transfer medium in the heating zone of the thermal reservoir rock mass is extended, and the heat transfer is more complete, thereby improving the heat exchange efficiency.

[0027] The inner tube is made of polymer material, which reduces the weight of the tube and improves the heat insulation effect of the inner tube, thus avoiding the problem of significant heat loss during the upward movement of the heat transfer medium inside the inner tube. Attached Figure Description

[0028] Figure 1 This is a schematic diagram of the structure of the present invention;

[0029] Figure 2 This is a schematic diagram of the threaded groove portion of the inner tube of the present invention;

[0030] Figure 3This is a radial cross-sectional view of the threaded groove portion of the inner tube of the present invention;

[0031] Figure 4 This is a schematic diagram of the second embodiment of the present invention;

[0032] The reference numerals in the attached drawings include: 1-inner pipe; 101-threaded groove; 2-drill hole; 201-low temperature rock mass; 202-thermal reservoir rock mass; 203-heating zone of thermal reservoir rock mass; 204-outer pipe; 205-cementing cement; 3-input end; Detailed Implementation

[0033] The present invention will now be described in detail with reference to the accompanying drawings.

[0034] Example 1

[0035] Reference Figure 1 and Figure 3 A medium-deep geothermal well structure includes an inner tube 1, a borehole 2, and an input end 3. An outer tube 204 is installed inside the borehole 2, and the gap between the borehole 2 and the outer tube 204 is filled with cementing cement 205. The inner tube 1 is coaxially inserted into the outer tube 204. One end of the input end 3 is connected to the upper port of the outer tube 204, and the other end of the input end 3 is connected to the surface water injection equipment.

[0036] The rock walls surrounding borehole 2 are divided into low-temperature rock mass 201, hot reservoir rock mass 202, and hot reservoir rock mass heating zone 203 according to the formation temperature.

[0037] Reference Figure 2 The inner tube 1 is divided into two parts: one part is a conventional straight section, and the other part is a turbulence section. The outer wall of the turbulence section is provided with a threaded groove 101.

[0038] The turbulence section is located in the 202 thermal reservoir rock mass;

[0039] The inner tube 1 is made of a polymer material with low thermal conductivity and good heat insulation properties.

[0040] There are three threaded grooves 101, which are centrally symmetrically distributed, that is, the included angle between adjacent threaded grooves 101 is 120°.

[0041] A height difference is left between the end of the inner tube 1 and the bottom of the borehole 2.

[0042] Preferably, the inner tube 1 is made of PB, PERT, PPR or PE material, the wall thickness is usually 10 to 12 mm, and the depth of the threaded groove 101 is 8 to 10 mm.

[0043] Example 2

[0044] Compared to Embodiment 1, the difference in this embodiment is as follows:

[0045] Reference Figure 1 Specifically, borehole 2 is a straight pipe (ideally, borehole 2 can be completed in one drilling operation, therefore...). Figure 1 This is for illustrative purposes only. In actual construction, depending on the geological conditions, multiple drilling operations such as two-stage drilling and three-stage drilling may be carried out. The inner diameter of borehole 2 varies with the needs of multiple drilling operations. Furthermore, the end of the outer pipe 204 extends to the bottom of borehole 2, completely covering the entire section of borehole 2.

[0046] Example 3

[0047] Compared to Embodiment 1, the difference in this embodiment is as follows:

[0048] Reference Figure 4 Specifically, borehole 2 is a variable diameter pipe, and the end of the outer pipe 204 extends to the junction of the low-temperature rock mass 201 and the hot reservoir rock mass 202.

[0049] Example 4

[0050] A construction method for a medium-deep geothermal well structure, the specific steps of which are as follows:

[0051] Step 1: Drilling and logging procedures;

[0052] Conventional drilling procedures were carried out, and logging procedures were carried out after the drilling procedures were completed to obtain downhole temperature data. Based on the temperature changes, the rock mass surrounding borehole 2 was divided into low-temperature rock mass 201, hot reservoir rock mass 202, and hot reservoir rock mass heating zone 203.

[0053] Step 2: Insert the outer tube 204;

[0054] Lower the outer tube 204 into the deepest part of borehole 2;

[0055] Step 3: Fill with cement 205;

[0056] Inject cement 205 into the gap between the outer pipe 204 and the borehole 2 to fix the outer pipe 204.

[0057] Step 4: Lower the inner pipe 1 and connect the ground extraction equipment to the inner pipe 1, and connect the ground water injection equipment to the input end 3;

[0058] The inner pipe 1 located at a depth of 201 in the low-temperature rock mass is a straight pipe, while the inner pipe 1 located at a depth of 202 in the hot reservoir rock mass and 203 in the heating zone of the hot reservoir rock mass is a turbulence pipe.

[0059] The inner tube 1 is lowered to a point approximately 50m from the bottom of borehole 2.

[0060] As the heat transfer medium flows downward, it is guided by the threaded groove 101, and its flow trajectory is spiral. Compared with the straight flow trajectory, the spiral flow trajectory has a longer path. Under the premise that the flow velocity of the heat transfer medium is constant, the residence time of the heat transfer medium at the heating zone 203 of the hot reservoir rock mass is greatly extended, allowing the heat in the formation to be more fully transferred to the heat transfer medium, thereby improving the heat exchange efficiency.

[0061] Example 5

[0062] Compared to Embodiment 4, the difference in this embodiment is that:

[0063] Reference Figure 4 Specifically, during the implementation of step two, the outer pipe 204 is lowered to the junction of the low-temperature rock mass 201 and the hot reservoir rock mass 202;

[0064] Step 3: Fill with cement 205 and perform secondary drilling;

[0065] During the process, cement 205 is continuously injected until borehole 2 is completely filled in the section of the hot reservoir rock mass 202 and the hot reservoir rock mass heating zone 203. Then, the drilling equipment is replaced with a small diameter drill bit (smaller in diameter than the drill bit used in the drilling process). After the cement 205 solidifies, a second drilling is carried out to drill a variable diameter borehole in the cement 205 of the hot reservoir rock mass 202 and the hot reservoir rock mass heating zone 203.

[0066] Among them, the variable diameter borehole is coaxial with the outer tube 204;

[0067] In this scheme, the purpose of injecting cement 205 into the thermal reservoir rock mass 202 and the thermal reservoir rock mass heating zone 203 is to fill the fractures in the rock mass, so as to avoid groundwater directly mixing into the heat transfer medium during the heat exchange process, which would deviate from the original intention of the heat exchange and heat extraction scheme of "extracting heat without extracting water". At the same time, in the thermal reservoir rock mass heating zone 203, the heat transfer medium is in direct contact with the rock mass covered with a thin layer of cement 205. Its heat transfer effect is necessarily better than the scheme of heat transfer through the outer pipe 204 and cement 205, which further improves the heat exchange efficiency.

[0068] The above content is only a preferred embodiment of the present invention. For those skilled in the art, many changes can be made in the specific implementation and application scope based on the concept of the present invention. As long as these changes do not depart from the concept of the present invention, they all fall within the protection scope of the present invention.

Claims

1. A construction method for a medium-deep geothermal well structure, the medium-deep geothermal well structure comprising an inner pipe, a borehole and an input end, wherein an outer pipe is installed inside the borehole and the gap between the borehole and the outer pipe is filled with cementing cement, the inner pipe is coaxially inserted into the outer pipe, one end of the input end is connected to the upper port of the outer pipe, and the other end of the input end is connected to a surface water injection device; The rock walls surrounding the borehole are divided into low-temperature rock mass, hot reservoir rock mass, and hot reservoir rock mass heating zone according to the formation temperature. The inner tube is divided into two parts: a straight section and a flow-turbulence section. The outer wall of the flow-turbulence section is provided with a threaded groove. The turbulence section is located in the thermal reservoir rock mass; Its features are, The specific steps for constructing the medium-deep geothermal well structure are as follows: Step 1: Drilling and logging procedures; Step 2: Insert the outer tube; During step two, the outer pipe is lowered to the boundary between the low-temperature rock mass and the hot reservoir rock mass, and then step three is carried out. Step 3: Fill with cementing material; Step three also includes performing secondary drilling. The specific construction process of step three is as follows: Continue injecting cement until the borehole is completely filled with the thermal reservoir rock mass and the heating zone of the thermal reservoir rock mass; The drilling equipment is replaced with a smaller diameter drill bit, and secondary drilling is carried out on the solidified cement to form a variable diameter borehole; Step 4: Lower the inner pipe and connect the ground extraction equipment to the inner pipe, and connect the ground water injection equipment to the input end.

2. The construction method for a medium-deep geothermal well structure according to claim 1, characterized in that: The threaded grooves are three in number and are distributed in a centrally symmetrical manner.

3. The construction method for a medium-deep geothermal well structure according to claim 1, characterized in that: The borehole is a variable diameter pipe, and the end of the outer pipe extends to the boundary between the low-temperature rock mass and the hot reservoir rock mass.

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