Deep geothermal cluster type concentrated exploration and mining well laying method and drilling structure

Abstract

The present application relates to a kind of deep geothermal cluster type concentrated exploration and mining well distribution method and drilling structure, belong to the technical field of geothermal exploitation. Including the following steps: (1) according to the thickness of heat reservoir stratification, temperature and seepage field variation law, using equilateral triangle principle, the plane coordinates of each well bottom water taking point of cluster type concentrated distribution are determined;(2) all geothermal wells are first drilled vertically, then dispersed radially, and the single well trajectory is a structure of "straight section-directional build-up section-one-inclined straight well section-directional build-up section two-inclined section two". The drilling structure is sequentially from top to bottom: pump chamber pipe, well pipe, filter pipe and sedimentation pipe. The present application also provides a drilling structure explored and mined by the above method. The present application uses equilateral triangle principle for stratified cluster type concentrated geothermal well target distribution, which is beneficial to determine the minimum impact area of project geothermal exploitation, beneficial to improve the utilization rate of mineral area geothermal resources, and realize the rational utilization of deep geothermal resources.

Description

Technical Field

[0001] This invention relates to the technical field of geothermal extraction, specifically to a method for clustered exploration and extraction well placement and drilling structure for deep geothermal resources. Background Technology

[0002] Geothermal energy, as a clean and renewable high-quality energy source, is an ideal heat source for winter heating, achieving low-carbon, stable, and efficient heating effects. It is also one of the current clean heating methods in winter. Compared with traditional heating, geothermal heating has the following advantages: (1) Clean and low-carbon: There is no coal or gas combustion process, and almost no pollutants such as CO2, SO2, and dust are produced, reducing air pollution from the source of winter heating. (2) Stable and reliable: Geothermal resources are not affected by seasons, weather, or diurnal changes, and are supplied at a constant temperature all year round, with no risk of heating interruption. (3) Low operating cost: Medium-deep geothermal heating only requires a small amount of electricity for water pumping and heat exchange. The energy efficiency ratio (COP) of shallow ground source heat pumps can reach more than 4 (consuming 1 kWh of electricity and outputting more than 4 kWh of heat energy). The long-term operating cost is much lower than that of gas and electric heating. (4) Renewable resources: As long as the principle of "harvesting and irrigation balance and closed utilization" is followed, geothermal reservoirs can be continuously replenished, and the service life of the heating system can reach more than 30 years, which is a long-term renewable energy utilization method.

[0003] In recent years, with the development of geothermal development and utilization technologies, a number of deep geothermal heating replacement projects have been promoted and implemented in cities in cold winter regions. Previously, geothermal clean energy heating replacement projects adopted a decentralized well layout model and drilling technology. To meet the requirements of reasonable well spacing design and avoid thermal breakthrough, multiple drilling sites were usually required, with the area of ​​a single well site generally exceeding 2000 m². 2 However, the dense urban buildings make it difficult to meet the requirements for drilling sites, which seriously restricts the development and utilization of geothermal clean energy. There is an urgent need for a method and construction technology that can centrally deploy wells to solve the well deployment problem in geothermal development and promote the centralized development and utilization of geothermal resources in urban areas. Summary of the Invention

[0004] To address the technical problems of the existing decentralized well placement method for geothermal exploration and production, this invention provides a method and drilling structure for centralized exploration and production of deep geothermal clusters, in order to solve the above-mentioned problems.

[0005] The technical solution of this invention is as follows:

[0006] Firstly, the present invention provides a method for concentrated exploration and production well placement in deep geothermal clusters, as detailed below:

[0007] (1) Layout of geothermal wellheads: Based on the thickness of the geothermal reservoir, temperature and seepage field variation law, calculate the reasonable well spacing; use the principle of equilateral triangle to determine the plane coordinates of the bottom water intake points of each well in the cluster layout; based on the determined plane coordinates of the bottom water intake points of each well and the burial depth of the geothermal reservoir at the water intake points, determine the underground space coordinates of the bottom water intake points of each well in the cluster layout.

[0008] (2) Based on the determined underground spatial coordinates of each well target point in the clustered layout, the spatial trajectory of the clustered geothermal wells is determined by applying the directional well spatial trajectory design method. All geothermal wells are first drilled vertically and then penetrated deep underground, and then radially dispersed in a clustered pattern. The trajectory of a single well is a structure of “straight section - directional ramping section 1 - inclined straight section 1 - directional ramping section 2 - inclined straight section 2”. The drilling structure from top to bottom is: pump chamber pipe, well pipe, filter pipe and sedimentation pipe.

[0009] Furthermore, in step (1), the layout scheme of the surface wellheads is as follows: the number of rows of surface wellheads is 1 to 3, and the distance between two adjacent wells is 3 to 5m.

[0010] Further optimization involves the following arrangements: when the number of surface wellheads is less than 6, they are arranged in one row; when the number of surface wellheads is between 6 and 15, they are arranged in two rows; and when the number of surface wellheads is greater than 15, they are arranged in 2 to 3 rows. This ensures that drilling in the surface pump room sections does not interfere with each other, making full use of surface space.

[0011] Furthermore, in step (2), the extraction and recharge wells are arranged in a cross pattern, and the ratio of extraction wells to recharge wells is 1:1.2~1.6.

[0012] Furthermore, in step (2), the specific structure of the single-well trajectory is as follows: the surface section of the geothermal well is designed as a vertical well section with a depth ≤600m; below the vertical well section is a directional ramping section with a length of 300~500m and an inclination angle ≤45°; below the directional ramping section to a depth of 200m from the top of the target geothermal reservoir is a slanted vertical well section; a directional ramping section is set again at a depth of 200m from the top of the target geothermal reservoir with an inclination angle of 60°~65°; after entering the target geothermal reservoir, it is a slanted vertical well section II until the designed drilling depth.

[0013] The well trajectory adopted in this invention, which is "straight section - directional ramping section one - inclined straight section one - directional ramping section two - inclined straight section two", not only meets the relevant requirements for geothermal reservoir extraction and reinjection, but also minimizes the length of the well section with an inclination angle of 45°~60°. Furthermore, the well section with an inclination angle of 45°~60° is set in the caprock section of the geothermal reservoir, which is usually mudstone. The drilled rock cuttings are not easy to settle and are easy to carry, thus solving the problem that rock cuttings in the well section with an inclination angle of 45°~60° tend to settle into beds, affecting drilling efficiency and downhole safety.

[0014] Secondly, the present invention provides a drilling structure using the above-mentioned deep geothermal cluster-type centralized exploration and production, which includes, from top to bottom, a pump chamber pipe; the pump chamber pipe is connected to a well pipe extending obliquely downward; the bottom end of the well pipe is connected to a filter pipe; a packer is installed between the bottom end of the well pipe and the filter pipe; the packer is installed on the outside of the well pipe; a rubber umbrella is installed above the packer and on the outside of the well pipe to stop water flow; and a sedimentation pipe is installed below the filter pipe.

[0015] The drilling structure provided by this invention employs a packer + rubber umbrella water-stop structure, achieving precise separation of each thermal reservoir. The packer can quickly achieve water-stopping, and the wear-resistant mesh of the rubber umbrella causes the umbrella opening to flip outward, making the umbrella tube tightly adhere to the borehole wall. This effectively holds back debris that collapses from the borehole wall over time, forming a rock plug to achieve a permanent water-stopping effect, preventing water-stopping failure due to packer malfunction over a long period. Furthermore, compared to the previous packer + cement cementing structure, the packer + rubber umbrella water-stopping structure avoids the poor controllability of cement cementing water-stopping and the potential impact on the thermal reservoir, thus protecting the thermal reservoir.

[0016] Furthermore, the pump chamber pipe overlaps the well pipe by 30m, and cement slurry is used for well cementing and water sealing.

[0017] Furthermore, the overlapping portion of the pump chamber pipe and the well pipe is a straight section; the well pipe, from top to bottom, consists of directional ramping section one, inclined straight well section one, and directional ramping section two; the filter pipe and sedimentation pipe are inclined straight section two.

[0018] Furthermore, the length of the rubber umbrella is 300mm; the minimum inner diameter of the rubber umbrella is 2mm smaller than the outer diameter of the well pipe; and the maximum outer diameter of the rubber umbrella is 10mm larger than the borehole diameter.

[0019] Furthermore, the outer wall of the umbrella tube is covered with a layer of high abrasion-resistant mesh, which is a rubber-coated nylon mesh with water-reducing properties.

[0020] The beneficial effects of this invention are as follows:

[0021] This invention provides a method for clustered centralized exploration and production well layout for deep geothermal resources. The number of wellheads on the surface is 1-3 rows, with a spacing of 3-5 meters between adjacent wells. This method helps save surface space while ensuring the smooth implementation of geothermal drilling projects. The method involves alternating the layout of extraction and reinjection wells, with a extraction-to-injection ratio of 1:1.2-1.6, which facilitates balanced extraction and injection. Furthermore, this invention employs the equilateral triangle principle in the layered layout of the bottom water intake points for clustered centralized geothermal extraction wells. This helps determine the minimum impact area for geothermal extraction and injection, improves the utilization rate of geothermal resources in the mining area, and achieves the rational utilization of deep geothermal resources.

[0022] This invention also features a layered design of well groups and the exposure of high-quality target thermal reservoirs at high angles. The selection of target thermal reservoirs can effectively avoid problems such as sand production in water production wells and low reinjection volume in reinjection wells in the later stages. The exposure of target thermal reservoirs at high angles is equivalent to increasing the contact length between the well and the target thermal reservoir and increasing the flow area, thereby increasing the water production and reinjection volume, and realizing high-quality and efficient utilization of deep thermal reservoirs. Attached Figure Description

[0023] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0024] Figure 1 This is a schematic diagram of the layout of water intake points at the bottom of the cluster-type centralized geothermal well in Embodiment 1 of the present invention. In the figure, 1-1 to 1-15 are water intake points 1-1 to 1-15; the straight-line distance between water intake point 1-2 and water intake point 1-4 is 450m; the straight-line distance between water intake point 1-4 and water intake point 1-5 is 450m. A is the surface wellhead area of ​​the cluster-type centralized geothermal well.

[0025] Figure 2 yes Figure 1 The enlarged view in section A is a schematic diagram of the arrangement of wellheads in the clustered centralized geothermal well extraction in Embodiment 1 of the present invention. Here, 1'-1 to 1'-15 are wellheads 1'-1 to 1'-15; the water intake point corresponding to wellhead 1'-1 is 1-1, the water intake point corresponding to 1'-2 is 1-2, and so on, with the water intake point corresponding to 1'-15 being 1-15.

[0026] Figure 3 This is a schematic diagram of the spatial layout of the clustered centralized geothermal wells of this invention.

[0027] Figure 4 This is a schematic diagram of the single-well structure of the cluster-type centralized geothermal well of the present invention. In the diagram, 1-pump chamber pipe, 2-well pipe, 3-rubber umbrella, 4-packer, 5-filter pipe, 6-sedimentation pipe. Detailed Implementation

[0028] To enable those skilled in the art to better understand the technical solutions of this invention, the technical solutions of the embodiments of this invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this invention, and not all embodiments. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort should fall within the scope of protection of this invention.

[0029] Example 1

[0030] A method for concentrated exploration and production well placement in deep geothermal clusters is as follows:

[0031] (1) Geothermal wellheads are installed on Platform 2 of the northern block of the Clean Heat Source Replacement Project EPC project in the western urban area of ​​Pingyuan County. The project designs 14 exploration and production wells, with a configuration of 6 production wells and 8 reinjection wells (6 production wells paired with 8 reinjection wells), and a production-to-injection ratio of 1:1.33. A clustered, centralized well layout is adopted, with the 14 geothermal exploration and production wellheads arranged in two rows with a spacing of 4.5m between wellheads. For details on the wellhead layout, please refer to [link to details]. Figure 2 . Figure 2 In the design, wellhead 1'-3 is a vertical well, while wellheads 1'-1, 1'-2, 1'-4 to 1'-15 are exploration and production wells.

[0032] (2) Based on the determined underground spatial coordinates of each well target point in the clustered layout, the schematic diagram of the layout of the water intake points at the bottom of the geothermal wells is detailed below. Figure 1 Using the directional well spatial trajectory design method, the spatial trajectory of clustered geothermal wells was determined, targeting three main geothermal reservoirs with a vertical depth of 1290-1530m. First, a vertical well section of 350-450m was drilled. Then, directional drilling was performed in the first directional ramp section, 350-450m in length and with an inclination angle of 40°-42°. Drilling continued in the first directional ramp section until it reached a depth of 200m from the top of the target geothermal reservoir. Next, directional drilling was performed in the second directional ramp section, with an inclination angle of 60°-61°. Drilling continued in the second directional ramp section into the target geothermal reservoir until the designed completion depth, with a spacing of >400m between wells in the target geothermal reservoir section.

[0033] The deep geothermal cluster-type centralized exploration and production drilling structure includes, from top to bottom, a pump chamber pipe 1; the pump chamber pipe 1 is connected to a well pipe 2 extending obliquely downwards; the pump chamber pipe 1 and well pipe 2 overlap by 30m and are cemented for water sealing; the pump chamber pipe 1 is located in the vertical well section; the bottom end of the well pipe 2 is connected to a filter pipe 5; a packer 4 is installed between the bottom end of the well pipe 2 and the filter pipe 5; the packer 4 is installed on the outside of the well pipe 2; a rubber umbrella 3 is installed above the packer 4 and on the outside of the well pipe 2; the rubber umbrella 3 has a length of 300mm; the minimum inner diameter of the rubber umbrella 3 is 2mm smaller than the outer diameter of the well pipe; the maximum outer diameter of the rubber umbrella 3 is 10mm larger than the borehole, serving as a water-stopping function; the outer wall of the rubber umbrella 3 is covered with a layer of high wear-resistant mesh, which has the characteristic of vertical shrinkage after being soaked in water for 6 hours. A sedimentation pipe 6 is installed below the filter pipe 5. The filter pipe 5 and sedimentation pipe 6 are located in the inclined straight section two.

[0034] The extraction well can draw 80-90m of water per well. 3 / hour, single well water extraction of 60~70m³ 3 / hour, 100% of the geothermal tailwater is reinjected.

[0035] Example 2

[0036] A method for concentrated exploration and production well placement in deep geothermal clusters is as follows:

[0037] (1) Geothermal wells were laid out at the site of the Xiajin County Geothermal Clean Energy Heating Project. The project designed 8 exploration and production wells with a configuration of 3 production and 5 injection (3 production wells and 5 injection wells), with a production-to-injection ratio of 1:1.6. The wells were arranged in a cluster-style centralized layout, with the 8 geothermal exploration and production wells arranged in a single row and the well spacing was 6m.

[0038] (2) Based on the determined underground spatial coordinates of each target point of the clustered geothermal wells, the spatial trajectory of the clustered geothermal wells is determined by applying the directional well spatial trajectory design method. The target is six major geothermal reservoirs with a vertical depth of 1150~1600m. First, a vertical well section with a vertical depth of 350~450m is drilled. Then, directional drilling is carried out in the first directional ramp section, with a length of 300~400m and an inclination angle of 33°~40°. Then, the first directional ramp section is drilled until it stops at a depth of 200m from the top of the target geothermal reservoir. The second directional ramp section is drilled again with an inclination angle of 60°~62°. The second directional ramp section is drilled after entering the target geothermal reservoir until the designed completion depth is reached. The distance between each well in the target geothermal reservoir section is >400m.

[0039] The structure of the deep geothermal cluster-type centralized exploration and production well is the same as that in Example 1.

[0040] The extraction well yields 90-120m of water per well. 3 / hour, single well water extraction of reinjection well 50~70m 3 / hour, 100% of the geothermal tailwater is reinjected.

[0041] Example 3

[0042] A method for concentrated exploration and production well placement in deep geothermal clusters is as follows:

[0043] (1) Geothermal wells were laid out at the site of the Dezhou Finance and Economics Smart Agriculture Energy Transformation Project. The project designed 10 exploration and production wells with 4 production and 6 injection wells (4 production wells and 6 injection wells). The production and injection ratio was 1:1.5. The wells were laid out in a cluster. The 10 geothermal exploration and production wells were arranged in a single row with a well spacing of 5m.

[0044] (2) Based on the determined underground spatial coordinates of each target point of the clustered geothermal wells, the spatial trajectory of the clustered geothermal wells is determined by applying the directional well spatial trajectory design method. The target is three main geothermal reservoirs with a vertical depth of 1200-1500m. First, a vertical well section with a vertical depth of 350-450m is drilled. Then, directional drilling is carried out in the first directional ramp section, with a length of 350-450m and an inclination angle of 38°-40°. Then, the first directional ramp section is drilled until it stops at a depth of 200m from the top of the target geothermal reservoir. The second directional ramp section is drilled again with an inclination angle of 60°-61°. The second directional ramp section is drilled after entering the target geothermal reservoir until the designed completion depth is reached. The distance between each well in the target geothermal reservoir section is >400m.

[0045] The structure of the deep geothermal cluster-type centralized exploration and production well is the same as that in Example 1.

[0046] The extraction well yields 80-100m of water per well. 3 / hour, single well water extraction of reinjection well 50~70m 3 / hour, 100% of the geothermal tailwater is reinjected.

[0047] Example 4

[0048] A method for concentrated exploration and production well placement in deep geothermal clusters is as follows:

[0049] (1) Geothermal wells were laid out at the No. 1 energy station of the Dongying Economic and Technological Development Zone Geothermal Clean Heating Project. The project designed 20 exploration and production wells with 8 production wells and 12 injection wells (8 production wells and 12 injection wells). The production-injection ratio was 1:1.5. The wells were laid out in a cluster-style centralized layout. The 20 geothermal exploration and production wells were arranged in two rows with a well spacing of 4.5m.

[0050] (2) Based on the determined underground spatial coordinates of each target point of the clustered geothermal wells, the spatial trajectory of the clustered geothermal wells is determined by applying the directional well spatial trajectory design method. The target is nine major geothermal reservoirs with a vertical depth of 1320~2200m. First, a vertical well section with a vertical depth of 350~450m is drilled. Then, directional drilling is carried out in the first directional ramp section, with a length of 300~400m and an inclination angle of 41°~42°. Then, the first directional vertical well section is drilled until it stops at a depth of 200m from the top of the target geothermal reservoir. The second directional ramp section is drilled again with an inclination angle of 60°~62°. The second directional vertical well section is drilled after entering the target geothermal reservoir until the designed completion depth is reached. The distance between each well in the target geothermal reservoir section is >400m.

[0051] The structure of the deep geothermal cluster-type centralized exploration and production well is the same as that in Example 1.

[0052] The extraction well yields 80-100m of water per well.3 / hour, single well water extraction of reinjection well 50~70m 3 / hour, 100% of the geothermal tailwater is reinjected.

[0053] Example 5

[0054] A method for concentrated exploration and production well placement in deep geothermal clusters is as follows:

[0055] (1) Geothermal wells were laid out at the North Station of the Clean Energy Comprehensive Utilization Project in Zhanhua District, Binzhou City. The project designed 8 exploration and production wells with 3 production and 5 injection wells (3 production wells and 5 injection wells). The production and injection ratio was 1:1.6. The wells were laid out in a cluster. The ground wells of the 8 geothermal exploration and production wells were arranged in a single row with a well spacing of 4.5m.

[0056] (2) Based on the determined underground spatial coordinates of each target point of the clustered geothermal wells, the spatial trajectory of the clustered geothermal wells is determined by applying the directional well spatial trajectory design method. The target is four main geothermal reservoirs with a vertical depth of 1020~1260m. First, a vertical well section with a vertical depth of 350~450m is drilled. Then, directional drilling is carried out in the first directional ramp section, with a length of 300~400m and an inclination angle of 36°~38°. Then, the first directional vertical well section is drilled until it stops at a depth of 200m from the top of the target geothermal reservoir. The second directional ramp section is drilled again with an inclination angle of 60°~61°. The second directional vertical well section is drilled after entering the target geothermal reservoir until the designed completion depth is reached. The distance between each well in the target geothermal reservoir section is >400m.

[0057] The structure of the deep geothermal cluster-type centralized exploration and production well is the same as that in Example 1.

[0058] The extraction well can draw 80-90m of water per well. 3 / hour, single well water extraction of 50~60m³ 3 / hour, 100% of the geothermal tailwater is reinjected.

[0059] Although the present invention has been described in detail with reference to the accompanying drawings and preferred embodiments, the present invention is not limited thereto. Various equivalent modifications or substitutions can be made to the embodiments of the present invention by those skilled in the art without departing from the spirit and essence of the invention, and such modifications or substitutions should all be within the scope of the present invention. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in the present invention should also be covered within the protection scope of the present invention.

Claims

1. A method for concentrated exploration and production well placement in deep geothermal clusters, characterized in that, Specifically as follows: (1) Layout of geothermal wells: Based on the thickness, temperature and seepage field of the geothermal reservoir, calculate the reasonable well spacing and use the principle of equilateral triangles to determine the plane coordinates of the bottom water intake points of each well in the cluster layout; based on the determined plane coordinates of the target points and the deep burial of the geothermal reservoir, determine the underground space coordinates of the target points of each well in the cluster layout. (2) Based on the determined underground spatial coordinates of each well target point in the clustered layout, the spatial trajectory of the clustered geothermal wells is determined by applying the directional well spatial trajectory design method. All geothermal wells are first drilled vertically and then penetrated deep underground, and then radially dispersed in a clustered pattern. The trajectory of a single well is a structure of "straight section - directional ramping section one - inclined straight section one - directional ramping section two - inclined straight section two". The drilling structure from top to bottom is: pump chamber pipe, well pipe, filter pipe and sedimentation pipe.

2. The method for concentrated exploration and production well placement in deep geothermal clusters as described in claim 1, characterized in that, In step (1), the specific layout scheme of the surface wellheads is as follows: the number of rows of surface wellheads is 1 to 3, and the distance between two adjacent wells is 3 to 5m.

3. The method for concentrated exploration and production well placement in deep geothermal clusters as described in claim 2, characterized in that, When the number of surface wellheads is less than 6, they are arranged in one row; when the number of surface wellheads is 6 ≤ number of surface wellheads ≤ 15, they are arranged in two rows; when the number of surface wellheads is greater than 15, they are arranged in 2 to 3 rows.

4. The method for concentrated exploration and production well placement in deep geothermal clusters as described in claim 1, characterized in that, In step (2), the extraction and recharge wells are laid out alternately, and the ratio of extraction wells to recharge wells is 1:1.2~1.

6.

5. The method for concentrated exploration and production well placement in deep geothermal clusters as described in claim 1, characterized in that, In step (2), the specific structure of the single well trajectory is as follows: the surface section of the geothermal well is designed as a vertical well section with a depth of ≤600m; below the vertical well section is a directional ramping section with a length of 300~500m and an inclination angle of ≤45°; below the directional ramping section to a depth of 200m from the top of the target geothermal reservoir is a slanted vertical well section; a directional ramping section is set again at a depth of 200m from the top of the target geothermal reservoir with an inclination angle of 60°~65°; after entering the target geothermal reservoir, it is a slanted vertical well section II until the designed drilling depth.

6. A drilling structure for exploration and production using the deep geothermal cluster-type centralized exploration and production well layout method as described in claim 1, characterized in that, The system comprises, from top to bottom, a pump chamber pipe; the pump chamber pipe is connected to a well pipe extending obliquely downwards; the bottom end of the well pipe is connected to a filter pipe; a packer is installed between the bottom end of the well pipe and the filter pipe; the packer is installed on the outside of the well pipe; a rubber umbrella is installed above the packer and on the outside of the well pipe; and a sedimentation pipe is installed below the filter pipe.

7. The drilling structure as described in claim 6, characterized in that, The pump chamber pipe overlaps the well pipe by 30m, and cement grout is used for cementing and water sealing.

8. The drilling structure as described in claim 6, characterized in that, The overlapping section between the pump chamber pipe and the well pipe is a straight section; the well pipe, from top to bottom, consists of directional ramping section one, inclined straight well section one, and directional ramping section two; the filter pipe and sedimentation pipe are inclined straight section two.

9. The drilling structure as described in claim 6, characterized in that, The length of the rubber umbrella is 300mm; the minimum inner diameter of the rubber umbrella is 2mm smaller than the outer diameter of the well pipe; the maximum outer diameter of the rubber umbrella is 10mm larger than the borehole.

10. The drilling structure as described in claim 6, characterized in that, The outer wall of the umbrella tube is covered with a layer of high abrasion-resistant mesh, which is a rubber-coated nylon mesh with water-reducing properties.

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