A method for reverse well construction of a large diameter shaft in deep surface soil

Abstract

The invention discloses a method for reverse well construction of a large-diameter wellbore in a deep surface soil layer, comprising the following steps: (A) preparation for wellbore construction; (B) using a rotary drilling rig to excavate a surface soil section to form a pilot well, and the pilot well is excavated to a bedrock section; (C) backfilling the pilot well with concrete; (D) constructing a pilot hole at the full well depth; (E) expanding the well at the bedrock section to form a well; (F) expanding the surface soil section; and (G) supporting the well wall. The invention combines the advantages of a rotary drilling rig and a reverse well drilling rig through newly designed construction steps to form a set of safe, reliable, short-term and low-cost wellbore construction technology. The invention replaces the surface soil layer with concrete or quasi-concrete with suitable strength so that the reverse well drilling technology is suitable for the full well depth, thereby achieving the purpose of safely, quickly and economically constructing the wellbore.

Description

Technical Field

[0001] The present invention relates to the technical field of well construction in the coal industry, and more specifically to a method for constructing a large-diameter wellbore inverted well in a deep surface soil layer. Background Art

[0002] The well construction plan in the coal mining industry generally includes two sections, namely the topsoil section and the rock section.

[0003] For the topsoil section, in the coalfields in western my country, due to the shallow topsoil layer (most shafts have a topsoil layer thickness of less than 150m), when constructing large-diameter shafts, owners tend to prefer the common method of drilling wells after comprehensively comparing the construction costs and construction period. However, when drilling wells through the topsoil, water gushing and hole collapse often occur, and the safety is very poor. In addition, there are freezing method, drilling method, curtain method and caisson method. The freezing method is highly safe, but the construction cost is high and requires appropriate hydrogeological conditions. The drilling method has a high degree of mechanization and high safety, but the process is cumbersome and the construction period is long. Other construction methods such as the curtain method and caisson method are rarely used due to various conditions.

[0004] For rock sections, a raise boring machine can be used to drill a slag hole (when there is a horizontal tunnel at the bottom), and then blast it to enlarge it or use a raise boring machine to expand the hole. During raise boring, because the formation is subjected to the drilling pressure of the drilling rig, the topsoil layer is difficult to stand on its own under this drilling pressure and often collapses and buries the drill. Therefore, raise boring is generally suitable for rock layers and is not suitable for construction in topsoil layers. However, for hard rock, the rock breaking efficiency of raise boring is much lower than the construction efficiency of blasting. Therefore, it is difficult to construct a large-diameter vertical shaft with the existing raise boring technology, and only a small-diameter vertical shaft can be constructed. Therefore, the vertical shafts attached to hydropower stations, metal mines and traffic tunnels generally use raise boring machines to drill small-diameter raise borings (referring to a shaft with a net diameter of less than 5m), and then blast it to enlarge it. The large-diameter (referring to a shaft with a net diameter greater than or equal to 5m) raise boring technology is more suitable for the coal mining industry with low rock strength.

[0005] However, no matter what method is used to expand the rock section, the ordinary method of drilling the well in the topsoil section ultimately determines that in the current large-diameter wellbore construction technology, there will always be risks of accidents such as water gushing and quicksand causing well flooding and hole collapse, resulting in poor safety and harsh working environment. Summary of the invention

[0006] To this end, the technical problem to be solved by the present invention is to provide a method for constructing a large-diameter wellbore in a deep surface soil stratum. Compared with the conventional well drilling method, the present invention is a wellbore construction process that is safer and more reliable, has a shorter construction period and lower engineering costs.

[0007] In order to solve the above technical problems, the present invention provides the following technical solutions:

[0008] The method for constructing a large-diameter shaft inverted well in a deep surface soil layer comprises the following steps:

[0009] (A) Preparation work for shaft construction;

[0010] (B) The rotary drilling rig excavates the topsoil section to form a pilot well, and the pilot well is excavated to the bedrock section;

[0011] (C) Concrete backfill pilot shaft;

[0012] (D) Full-depth pilot hole construction;

[0013] (E) Reverse well expansion in bedrock section to form a well;

[0014] (F) Expansion of the topsoil section;

[0015] (G) Well support.

[0016] Furthermore, in step (B), the diameter of the pilot shaft is 2.4m-2.6m.

[0017] Furthermore, in step (C), the strength of the concrete is C20.

[0018] Furthermore, in step (E), the hole is expanded from bottom to top in the bedrock section to the portion adjacent to the topsoil section, leaving 10m to 15m of bedrock, and no longer expanding the hole to a larger diameter.

[0019] Furthermore, in step (F), the large diameter drill bit used in the bedrock section is removed, and a small diameter reaming drill bit is installed to continue to reaming the topsoil section concrete from bottom to top, and a portion of the concrete is left to form a retaining wall.

[0020] Furthermore, the thickness of the reserved retaining wall is 0.4m-0.6m.

[0021] Furthermore, in step (F), after the construction of the small-diameter expansion drill is completed, the surface soil section is manually brushed to a large pilot well to the designed diameter of the wellbore and supported to form the final wellbore.

[0022] Furthermore, in step (G), the bedrock section is supported by bolting and spraying to form the final wellbore.

[0023] Furthermore, there is a tunnel at the bottom of the shaft, through which the drill bit is transported and the gangue is removed.

[0024] Furthermore, in step (D), the pilot hole is inclination-measured while drilling, and the drilling deviation rate is ≤0.5%.

[0025] The technical solution of the present invention achieves the following beneficial technical effects:

[0026] The invention combines the advantages of rotary drilling rigs and raise boring rigs through newly designed construction steps to form a safe and reliable wellbore construction process with a short construction period and low engineering cost; the invention replaces the topsoil layer with concrete or quasi-concrete with suitable strength so that the full well depth is suitable for the raise boring process, thereby achieving the purpose of safely and quickly building the wellbore;

[0027] Compared with the conventional well drilling method, this technology greatly improves the safety of artificial well drilling in the surface soil, and also realizes the use of reverse drilling technology at full well depth in the surface soil and bedrock sections at a lower cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] Figure 1 The construction of the present invention is shown in FIG. Figure 1 ;

[0029] Figure 2 The construction of the present invention is shown in FIG. Figure 2 ;

[0030] Figure 3 The construction of the present invention is shown in FIG. Figure 3 ;

[0031] Figure 4 The construction of the present invention is shown in FIG. Figure 4 ;

[0032] Figure 5 The construction of the present invention is shown in FIG. Figure 5 ;

[0033] Figure 6 The construction of the present invention is shown in FIG. Figure 6 ;

[0034] Figure 7 The construction of the present invention is shown in FIG. Figure 7 ;

[0035] Figure 8 It is a construction flow chart of an engineering example of the present invention.

[0036] The reference numerals in the figure are as follows: 1-bottom tunnel; 2-bedrock section; 3-topsoil section; 4-backfilled concrete, 5-guide hole, 6-large diameter drill bit, 7-small diameter drill bit, 8-wall protection. DETAILED DESCRIPTION

[0037] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the accompanying drawings in the embodiments of the present invention.

[0038] like Figures 1 to 7 As shown, Figure 1 The middle one is a pilot well being dug by a rotary drilling rig. Figure 2 This is a schematic diagram of the pilot shaft after concrete backfilling. Figure 3 After the full depth pilot hole construction is completed, Figure 4 Bedrock Section 2 reverse well expansion; Figure 5 Reverse well expansion in the topsoil section, Figure 6 The topsoil section chute is enlarged. Figure 7 Schematic diagram of the wellbore support construction in the bedrock section;

[0039] The method for constructing a large-diameter shaft inverted well in a deep surface soil layer comprises the following steps:

[0040] (A) Preparation work for shaft construction;

[0041] (B) The rotary drilling rig excavates the topsoil section 3 to form a pilot well, and the pilot well is excavated to the bedrock section 2;

[0042] (C) Concrete is backfilled into the pilot well to form plain concrete piles; the backfilled concrete 4 enhances the bearing capacity of the topsoil section 3 as the foundation, solves the problem that the topsoil section 3 cannot rigidly support the raise boring machine, solves the problem that the topsoil section 3 collapses and cannot stand on its own when the raise boring machine expands the hole, and solves the problem that the working surface is unstable when the topsoil section is manually expanded;

[0043] (D) Full depth pilot hole 5 construction;

[0044] (E) 2nd well expansion in bedrock section, 1st well expansion;

[0045] (F) Expansion of topsoil section 3;

[0046] (G) Well support;

[0047] This construction method is applied to the construction of a shaft with a tunnel at the bottom of the excavation. The lower opening of the full-depth pilot hole 5 is connected to the bottom tunnel 1, and the reaming drill bit and waste rock are transported through the bottom tunnel 1;

[0048] The present method overcomes the high risk of common well sinking methods, the high cost of freezing methods, and the long construction period of drilling methods, and integrates rotary drilling into reverse drilling technology, combining the respective advantages of the two technologies to form a wellbore construction technology that is safe, reliable, has a short construction period, and has low engineering costs; combined with the construction method of the present application, this wellbore construction technology can also be named topsoil rotary drilling and artificial brushing full-well depth reverse drilling technology.

[0049] Furthermore, in step (B), the operation steps involved are the same as those of the rotary bored piles in the pile foundation industry, including measuring and positioning, laying out casing and checking the center line of the hole, drilling with the drilling rig in place, and finally cleaning the hole. However, when drilling the pilot well, the required drilling diameter is 2.4m-2.6m. Considering the slag sliding effect, the operating area of ​​the working surface when brushing, and the economic benefits, the best pilot well drilling diameter is 2.5m, and the pilot well is excavated to a distance below the bedrock. Figures 1 to 4 A schematic diagram of the location of the pilot well can be seen in the figure.

[0050] Furthermore, in step (C), the operating steps included are the same as those of the rotary bored piles in the pile foundation industry, including installing concrete conduits, pouring concrete and curing concrete to the designed strength. The best concrete design strength is C20. Too high strength is not conducive to hole expansion, and too low strength is not conducive to the remaining concrete retaining wall 8.

[0051] Furthermore, step (D) includes the basic step of constructing a guide hole 5 with a raise boring machine, and the diameter of the guide hole 5 is generally within 50 mm; in addition, the guide hole 5 is required to be inclination-measured while drilling to ensure that the borehole deviation rate is ≤0.5%. Figure 3 It is a schematic diagram after the construction of the guide hole 5 is completed.

[0052] Furthermore, in step (E), the basic steps of hole enlargement construction by the raise boring machine are included, namely, installing the raise boring machine and using a large diameter drill bit 6 to enlarge the hole, wherein the hole enlargement diameter is equal to the net diameter of the wellbore plus the thickness of the anchor mesh spraying support; the large diameter drill bit 6 enlarges the hole from bottom to top in the bedrock section 2 to the part adjacent to the topsoil section 3, and 10m to 15m of bedrock is reserved, and no large diameter enlargement is performed, and the supporting effect of the reserved bedrock on the topsoil section increases the stability of the topsoil section. Figure 4 This is a schematic diagram of the process of a large-diameter drill bit falling to the bottom tunnel after completing the hole expansion in the bedrock section.

[0053] Furthermore, in step (F), the large-diameter drill bit 6 used in the bedrock section 2 is removed, and a small-diameter reaming drill bit is installed. The reaming diameter is equal to the concrete pile diameter minus the thickness of the concrete retaining wall 8 that needs to be retained. The concrete of the topsoil section 3 is continued to be expanded from bottom to top, and part of the concrete is reserved to form the retaining wall 8. The thickness of the reserved retaining wall 8 is 0.4m-0.6m. A circle of retaining wall 8 forms a well ring. The well ring, together with the bedrock reserved in step (E), enhances the stability of the topsoil section 3, prevents the topsoil section from collapsing, and prevents the reverse drilling rig from tilting or falling. Figure 5 The well ring formed by the reserved concrete retaining wall 8 can be seen.

[0054] Furthermore, in step (F), the manual enlargement of the pilot well includes the basic steps of enlarging the wellbore, such as building a simple derrick, installing a hoisting device, and manually enlarging the pilot well from top to bottom by using a pneumatic pick or blasting method; when encountering large-diameter boulders during the enlargement of the pilot well in the surface soil section 3, they generally need to be broken to prevent them from falling from the pilot well and damaging the surrounding rock or maintenance structure around the well. After the pilot well is enlarged, it is supported and formed into a final wellbore according to the design requirements. Figure 6 The middle is a construction diagram of manually brushing a large pilot well in the surface soil section after the simple well frame is installed.

[0055] Furthermore, in step (G), the bedrock section 2 is supported by anchor spraying to form the final wellbore. Anchor spraying support is a conventional support method after well raising construction, which will not be described in detail here. Figure 7 This is a schematic diagram of construction using a hanging platform.

[0056] The present invention applies the rotary drilling rig generally used for pile driving to the construction of the topsoil layer of the wellbore, and the conventional large rotary drilling rig can meet the construction requirement of a drilling diameter of 2.5m. The rotary drilling rig is also known as a rotary drilling rig, commonly known as a pile driver; the rotary drilling rig is a comprehensive drilling rig, which uses a short spiral drill bit for dry excavation, and can also use a rotary drill bit for wet excavation under the condition of mud wall protection 8; the rotary drilling rig can cooperate with a hammer to drill and break the hard stratum and then perform hole digging operations. The rotary drilling rig adopts a multi-layer telescopic drill rod, which has less drilling auxiliary time, low labor intensity, no need for mud circulation and slag removal, and a fast hole-making speed. The application of rotary drilling rigs in wellbore construction has also further improved the mechanization level of the well construction industry.

[0057] Project Examples

[0058] The following is an illustration of a specific well construction case, and a comparison with the two existing well construction methods in terms of economy, safety and construction period.

[0059] Shaft design parameters: shaft depth 588m, of which the topsoil section 3 is 100m deep and the rock section is 488m deep; the shaft net diameter is 7.0m; the topsoil section 3 is reinforced concrete shaft wall with a thickness of 800mm, and the rock section is anchor spray support with a thickness of 150mm.

[0060] (a) If Figures 1 to 8 As shown, a large-diameter wellbore reverse well construction method in deep surface soil strata is adopted, specifically, the following steps are included:

[0061] (A) Preparation for wellbore construction, including geological data analysis, drilling of inspection holes before construction, determination of wellhead location, layout of wellhead site, etc., and various measures to meet the needs of wellbore construction;

[0062] (B) Install a rotary drilling rig, which excavates the topsoil section 3 to form a pilot well. The pilot well diameter is preferably 2.5 m. The pilot well is excavated to the bedrock section 2 and extends about 10 m into the bedrock section. After the pilot well construction is completed, the rotary drilling rig is removed;

[0063] (C) Concrete backfilling the pilot well to form plain concrete piles, the concrete grade is C20, the particle size of coarse aggregate is 5mm-20mm as the best, and backfilling to the ground level;

[0064] (D) Install the raise drilling machine and construct a full-depth pilot hole 5, the diameter of the pilot hole is 50 mm, and the pilot hole is connected to the bottom tunnel;

[0065] (E) The large-diameter drill bit 6 is transported from the bottom tunnel to the pilot hole 5, and the large-diameter drill bit 6 is installed on the drill pipe. The bedrock section 2 is reversed and expanded. Once the well is expanded, the expanded hole diameter is equal to the designed net diameter of the wellbore plus the thickness of the anchor mesh spraying support, that is, 7.30m; the pilot hole 5 is expanded to 10m from the bottom of the pilot well and stopped;

[0066] (F) Remove the large-diameter drill bit 6 and install the small-diameter drill bit 7; continue to expand the topsoil section 3 from bottom to top, the expanded hole diameter is equal to the concrete pile diameter minus the thickness of the concrete retaining wall 8 to be retained, and the required retaining wall 8 is 0.5m thick, corresponding to the 2.5m pilot well mentioned above. In this example, the diameter of the small-diameter drill bit 7 is 1.5m, and finally a slag guide well with a diameter of 1.5m is formed in the topsoil section 3;

[0067] After the construction of the small-diameter drill bit 7 is completed, the small-diameter drill bit 7 is removed and the raise drilling rig is withdrawn, and the holes expanded by the large and small-diameter drill bits 7 are manually brushed; specifically, a simple derrick and a lifting plate are installed at the wellhead, and the topsoil is excavated manually with a pneumatic pick or a small excavator. The concrete retaining wall 8 can be demolished as it is excavated by blasting, and the slag falls from the slag guide shaft to the lower wellhead. The section height is determined according to the strength of the corresponding soil layer; then the formwork and steel bars are lowered using a lifting device, and concrete is poured to form a reinforced concrete well wall support in the topsoil section 3. According to the design requirements, the reinforced concrete well wall is 800mm thick and the net diameter of the inner wall is 7.0m.

[0068] (G) The bedrock section 2 is supported by anchor spraying to form the final wellbore. Anchor spraying support is a conventional technology and will not be described in detail here. According to the design requirements, the thickness of the anchor spraying support structure is 150 mm.

[0069] (II) The plan that is suitable from the owner's perspective (referred to as Plan A) is as follows: the ordinary well drilling method is used in the topsoil layer. After the topsoil well is built, a small drilling rig is placed at the bottom of the topsoil well to drill a small hole downward to drain the slag, manually brush the large rock section of the well, and then anchor spray.

[0070] (III) Suitable scheme for large-diameter reverse drilling (referred to as Scheme B), the well construction process is as follows: the surface soil section 3 adopts the ordinary well drilling method. After the surface soil well shaft is built, the built well shaft is backfilled with concrete, and then the reverse drilling technology is used for the full well depth.

[0071] The comparison of the three methods in terms of main steps, economy, safety and construction period is shown in the following table:

[0072]

[0073] Economic comparison: Both Schemes A and B use the common well sinking method to construct the topsoil section of the wellbore, and both use anchor spraying to support the bedrock section. These costs are the same and lower than the construction cost of the topsoil section of this scheme. Scheme B requires an additional 3,900m 3 The backfill concrete cost is increased, and the corresponding crushing and slag transportation costs are increased. The backfill concrete volume in the present invention is about 490m 3 , which is much less than the concrete construction cost in Scheme B; in addition, when the bedrock section is enlarged, the cost of reverse drilling and hole enlargement is also higher than the cost of enlargement by artificial blasting. By comparison, it can be seen that the cost of well construction in the three schemes is: Scheme B> the present invention> Scheme A.

[0074] Comparison of construction period: Both Schemes A and B use the common well-drilling method to construct the wellbore in the topsoil section. The topsoil section of the present invention uses a rotary drilling rig, reverse well, and brushing, but all three use anchor spraying to support the bedrock section. In the absence of a slag well, when the common well-drilling method is used to construct unstable topsoil, only the derrick foundation construction and derrick installation take about 60 days. In addition, when drilling wells, it is necessary to deal with gushing water, collapsed holes, and hoisting slag, etc., and the progress is very slow; while the rotary drilling rig can generally complete the construction of piles in 100 meters of topsoil in 7 days, and including the preparation time, it generally takes 3 days to reverse well and expand the concrete of the topsoil section; when anchoring and spraying the bedrock section and brushing the topsoil section, only a simple derrick needs to be installed, and the installation can generally be completed in 3 days. After comprehensive comparison, the construction period of the scheme of the present invention is much shorter than the construction period of Scheme A and Scheme B. The number of days for the wellbore construction period of the three schemes is: Scheme of the present invention < Scheme A < Scheme B.

[0075] Safety comparison: In Schemes A and B, when the artificial blasting method is used to brush the large bedrock section, there is no water gushing in the wellbore. In addition, the wind speed and wind direction can be adjusted to control the possible gas accumulation, that is, the construction safety at this time is greatly improved, so the key safety hazard of this project lies in the construction of the wellbore in the surface soil section. When the surface soil layer is artificially excavated, there are often accidents such as water gushing and quicksand that cause well flooding and hole collapse, so the ordinary well drilling method has poor safety and a bad working environment. Both Schemes A and B use ordinary well drilling methods, so the safety of both schemes is relatively low. The scheme of the present invention first uses a rotary drilling rig to dig a pilot well in the surface soil section, then backfills the pilot well with concrete, and then uses a reverse drilling process to the full depth of the well; after the bedrock section is expanded, a small diameter drill bit is replaced to drill the concrete of the surface soil section to form a slag well, and then the large slag well is manually brushed to the designed diameter of the wellbore and supported, and finally the rock section is anchored and sprayed for support. The backfilled concrete forms a plain concrete pile, which realizes the safe, economical and fast treatment of the topsoil layer, and enhances the bearing capacity of the surface of the topsoil section, so that the full well depth is suitable for the reverse drilling process, and the purpose of safely and quickly building the wellbore is achieved. By comparison, it can be seen that the safety comparison of the three schemes is: the present invention>Scheme B>Scheme A.

[0076] Compared with the common method of drilling wells for treating the topsoil section, the present invention can safely, economically and quickly treat the topsoil layer so that the full well depth is suitable for the reverse drilling process, thereby achieving the purpose of safely and quickly building a wellbore; the present invention greatly improves the safety of artificial drilling of wells in the topsoil, and also realizes the use of the reverse drilling process for the full well depth of the topsoil and bedrock sections at a lower cost.

[0077] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived therefrom are still within the scope of protection of the claims of this patent application.

Claims

1. A method for constructing a large-diameter shaft in a deep surface soil layer, characterized in that: The steps include: (A) Preparation work for shaft construction; (B) a rotary drilling rig excavates the topsoil section (3) to form a pilot well, and the pilot well is excavated to the bedrock section (2); in step (B), the diameter of the pilot well is 2.4m-2.6m; (C) Concrete backfill pilot shaft; the strength of the concrete is C20; (D) Construction of full-depth pilot hole (5); (E) The bedrock section (2) is expanded from bottom to top to the part adjacent to the surface soil section (3), leaving 10m to 15m of bedrock, and no longer expanding the diameter; (F) Expanding the topsoil section (3); removing the large-diameter drill bit (6) used in the bedrock section (2), installing a small-diameter expansion drill bit, and continuing to expand the topsoil section (3) concrete from bottom to top, leaving part of the concrete to form a retaining wall (8); the thickness of the retained retaining wall (8) is 0.4m-0.6m; (G) Well support.

2. The method for constructing a large-diameter shaft in reverse well in a deep surface soil layer according to claim 1, characterized in that: In step (F), after the construction of the small diameter expansion drill is completed, the surface soil section (3) is manually brushed to a large pilot well to the designed wellbore diameter and supported to form the final wellbore.

3. The method for constructing a large-diameter shaft in reverse well in a deep surface soil stratum according to claim 1, characterized in that: In step (G), the bedrock section (2) is supported by bolting and spraying to form the final wellbore.

4. The method for constructing a large-diameter shaft in reverse well in a deep surface soil layer according to claim 1, characterized in that: There is a tunnel at the bottom of the shaft, through which the drill bit is transported and the waste rock is removed.

5. The method for constructing a large-diameter shaft in reverse well in a deep surface soil stratum according to claim 1, characterized in that: In step (D), the pilot hole (5) is inclination-measured while drilling, and the drilling deviation rate is ≤0.5%.

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