CN101749005B - Underground Borehole Protection Technology - Google Patents

Abstract

The invention provides a protection process of an underground drilling hole, which comprises the following steps of: as for a directional drilling hole (8), arranging a horizontal drilling hole supporting pipe or filling a mixed foaming firming agent in the drilling hole at a horizontal segment after finishing the well cementation of a drilling hole sleeve pipe (9) at a vertical segment; and/or as for a vertical drilling hole (1), firstly reinforcing the hole bottom of the drilling hole, then arranging a drilling hole protection device (10) or filling the mixed foaming firming agent. In the invention, an open hole segment is effectively protected after drilling is finished, thereby not only ensuring that the drilling hole is not blocked before utilized, but also ensuring that the protection measures of the drilling hole can not influence the free flow of a fluid between the drilling hole and a coal layer when in utilization.

Description

Underground Borehole Protection Technology

technical field

The invention relates to the construction of small-scale deep underground projects, in particular to the protection technology for preventing borehole diameter shrinkage, hole collapse, silting, blockage, etc. in underground coal seams.

Background technique

In the process of coalbed methane mining and underground coal gasification, especially in the wellless underground coal gasification, it is necessary to continuously extend the gasification channel to provide new gasifiable coal resources, which requires continuous replenishment from the ground to the coal seam in advance drilling. Usually, due to the relatively small diameter of the borehole, if the completed borehole is not well protected, it is easy to be blocked due to stratum creep, debris spalling, water gushing, etc. During the construction of underground coal gasification boreholes, the coal seam There are drilling casings inside and below the above part of the borehole, and the outside of the pipe is cemented by grouting cement, while the part entering the coal seam and the part below the borehole is usually exposed, which is convenient for fluid to enter and exit the coal seam. Due to the relatively small diameter of the borehole (generally less than 1000mm), the soft coal seam, the inability to use it immediately after completion, and various factors, the coal seam section drilling and horizontal directional drilling are prone to diameter shrinkage, hole collapse, and silting, etc. The drilling holes are not perfect during use, need to be processed again, and even the drilling holes are scrapped. This makes it necessary to protect the open hole section after the drilling is completed. When implementing protection, it is necessary to ensure that the drilled hole is not blocked before use, and to ensure that the protection measures of the drilled hole do not affect the flow of fluid in the drilled hole when it is used. and free flow between coal seams.

Contents of the invention

Aiming at the above technical problems, the present invention discloses a borehole protection process suitable for underground coal gasification, including: for directional drilling, after completing the drilling casing cementing in the vertical section, lowering the borehole into the horizontal section Drilling support pipe or filling with mixed foaming curing agent; for vertical drilling, it is necessary to evaluate the drilling depth of the drilling protection device (different from the drilling support pipe in the horizontal section) to reinforce the bottom of the drilling hole , and then lower into the drilling protection device or fill and mix the foaming curing agent. For the protection process of directional drilling and vertical drilling, one or both can be selected, preferably both.

The protection measures for the horizontal section of directional drilling are relatively simple. After the completion of directional drilling and drilling and cementing above the coal seam, the drilling support pipe is lowered into the horizontal section of the drilling or filled with a mixed foaming curing agent.

The supporting pipes for running into the horizontal section are usually segment by segment, which are connected in series when running in, and laid without interruption in the horizontal drilling.

The support pipe has a certain mechanical strength and does not hinder the circulation of gas between the coal seam and the borehole during the utilization of the borehole. The material can be an ordinary steel pipe (screen pipe) with a certain number of small holes, a glass steel pipe, or Combustible plastic pipes, bamboo or wood, etc., but not limited to the above types, it is important to keep the boreholes from being blocked, and the fluid can flow freely between the borehole and the coal seam with or without simple treatment during use .

Said filling and mixing the foaming and curing agent into the horizontal section borehole is polyurethane foam. The polyurethane foaming process is very mature. Here, the semi-prepolymer method is used to make a part of polyether polyol (white material) and diisocyanate (black material) into a prepolymer, and then another part of polyether or poly Polyhydric alcohol, diisocyanate, water, catalyst, surfactant, other additives, etc. are added, injected into the drilled hole in the horizontal section through a thin tube at high speed, and then mixed for foaming. Rigid polyurethane foam has a certain mechanical strength, and can support the wall of the borehole without collapsing after filling, and the foam is flammable, and it can be exposed when the foam is burned off the coal seam when the borehole is used.

And the protection technology of vertical borehole, can be to go into borehole protection device 10 or fill mixed foaming solidifying agent to the coal seam section borehole.

The drilling protection device 10 can shield the exposed coal seam between the lower end of the drilling casing 7 and the bottom of the hole, preventing water, rock debris, sludge, coal, etc. from falling into the hole and causing blockage. The drilling protection device has certain mechanical strength and anti-leakage. The material can be but not limited to glass fiber reinforced plastics, bamboo, wood piles or plastic bladders, etc., but it should meet the requirements that the circulation of gas in and out of the coal seam will not be affected after simple treatment during drilling.

At first, it is the protection process of entering the drilling protection device 10 into the coal seam section borehole, and the specific content is as follows:

Drill a vertical borehole from the ground to the underground coal seam, drill to the depth _H2 at the lower end of the drilling casing 7, inject cement slurry to cement the borehole above the _H2 position, and continue drilling to the coal seam after waiting for solidification Inside the bottom plate 5, according to the pre-drilling coring and well logging data, the position of the coal seam, the thickness of each coal seam, the quality of coal, the thickness of each layer of gangue, the characteristics of the coal seam floor, etc. are determined, and the drilling casing 7 and the drilling protection device 10 times are estimated. into position. The specific calculation can refer to the following formula or similar algorithm:

Borehole protection device 10 lower end position depth:

H ₁ =H ₀ +∑(h ₁ , h ₂ ... h _n )+∑(M ₁ , M ₂ ... M _n )-c

Among them: H ₁ is the depth of the lower end of the drilling protection device (m), H ₀ is the depth of the coal seam roof (m), h _n is the thickness of each gangue layer (m), M _n is the thickness of each net coal seam (m), c It is an empirical constant with a value range of 0.5 to 1.5.

Drilling casing 7 lower end position depth:

H ₂ = H ₁ -∑(h ₁ , h ₂ …h _n )-∑(M ₁ *A ₁ , M ₂ *A ₂ …M _n *A _n )-b

Among them: H ₂ is the depth of the lower end of the drilling casing (m), A _n is the ash content of each clean coal seam (%), b is an empirical constant, and its value ranges from 1 to 2.

After calculating the relevant parameters, inject cement into the bottom of the borehole to the position H ₁ of the lower end of the borehole protection device 10 to reinforce the bottom of the borehole 6; The open hole section is lowered into the drilling protection device 10 .

The borehole protection device 10 usually adopts hard pipes such as glass steel pipes, bamboo, and wooden piles, preferably glass steel pipes, and the hard pipes and the borehole casing 7 are partially overlapped or socketed together to protect the coal seam in the open hole section.

The drilling protection device 10 can also be a plastic bladder, which can be inflated and deflated to realize the protection of the drilling wall and the insertion and removal of the bladder. Specifically: if the drilling protection device 10 is a plastic bladder, it needs to be equipped with an inflatable device, which will not be inflated during the lowering process, and will be inflated to fill the bare hole section after it is lowered to the expected position, so as to support the hole wall to avoid collapse. When the drilling needs to be enabled, the volume becomes smaller by deflation, and the drilling protection device 10 is taken out, and the drilling can be used.

If the drilling protection device 10 is hard, its length should be slightly longer than the bare hole section, and its diameter should be slightly smaller than the diameter of the drilling casing 7. The lower end reaches the position _H1 at the bottom of the drilling hole, and a part of the upper end overlaps the drilling casing 7. Or it is socketed together with the drilling casing 7 .

The material of the protection device has a certain hardness, which can support the wall of the borehole from collapsing, is easy to cut or can be burned and broken at a certain temperature, and the protection device 10 is preferably hollow.

In addition, the drilling protection device 10 may also be in the form of being socketed with the drilling casing 7 . That is, a drill hole can be drilled from the ground to the coal seam floor, and the lower end position of the drilling casing 7, the lower end insertion position of the drilling protection device 10, and the amount of grouting cement required for hole bottom reinforcement can be calculated according to the drilling data and the above calculation formula , inject cement slurry into the borehole according to the amount, and wait for it to set. On the ground, a drilling protection device 10 of suitable length is connected with the drilling casing 7. The lower end of the protection device is closed, and a window 15 is arranged on the side to facilitate cementing cement return. After the cement slurry reinforced at the bottom of the hole is set, the drilling casing connected with the drilling protection device is lowered into the drilling hole, and the drilling protection device is lowered to the bottom of the hole. Cement slurry is injected into the drilling casing 7, and the mud returns to the ground from the protection device 10 and the outer wall of the casing 7 through the window 15 at the bottom of the drilling protection device 10, and the cementing is completed.

Before the implementation of underground coal gasification or during the gasification process, the coal seam near the borehole wall can be in contact with the outside atmosphere through the borehole through technical means, such as cutting, perforating, burning or installing the borehole protection device. Proposed drilling, including but not limited to the above.

In addition, it is also possible to protect the borehole by filling and mixing the foaming curing agent, specifically: mixing several fluids and then foaming and curing to support the borehole, such as the above-mentioned polyurethane foam filling process, that is, after the fluids are mixed The foam cures to a rigid polyurethane foam. Through several fluid delivery pipes, the fluid is transported to the drilling section that needs to be supported, and then mixed in a certain proportion. After mixing, the foam will fill the drilling section, and after a certain period of time, it will solidify into a support material with a certain pressure-bearing capacity. It can burn or defoam and soften when encountering high temperature (above 250°C).

By adopting the borehole protection process of the present invention, the drilled boreholes can be placed for a long time before being reused, and complicated borehole cleaning is not required during reuse, only the borehole protection device needs to be destroyed downhole.

The present invention will be described in detail below in conjunction with the accompanying drawings and embodiments.

Description of drawings

Figure 1 is a longitudinal sectional view of directional drilling and vertical drilling after drilling protection is implemented

Figure 2 is a longitudinal sectional view of the vertical borehole after the borehole protection is implemented

Figure 3 is a longitudinal sectional view of the borehole using the sleeve protection process

In the figure, 1—vertical drilling; 2—surface soil layer; 3—rock formation, coal seam roof; 4—coal seam; 5—coal seam floor; 6—reinforcement at the bottom of the drilling hole; Casing; 8--directional drilling; 9--directional drilling casing; 10--drilling protection device; 11--horizontal drilling support pipe; 12-supporting pipe connection section; 13--drilling The socket part of the protection device and the drilling casing; 14--closed end; 15--window. the

Among them, Figure 1 is the abstract drawing.

Detailed ways

The present invention will be described in detail below in conjunction with the accompanying drawings. The following are only preferred embodiments of the present invention, and the scope of the present invention cannot be limited thereto. That is, all equivalent changes and modifications made according to the scope of the patent application of the present invention should still fall within the scope covered by the patent of the present invention.

Embodiment one:

In this embodiment, directional drilling and vertical drilling will be constructed, and the drilling protection process for both will be implemented. Here, specific implementation steps are given in conjunction with FIG. 1 .

First, build a vertical borehole 1 from the ground to the coal seam floor 5 through the surface soil layer 2, rock formation, coal seam roof 3 and coal seam 4, and estimate the position of the lower end of the borehole casing according to the previous drilling data and the calculation formula provided by the present invention. The depths of H ₂ and H ₁ at the lower end of the drilling protection device to the ground are 277 meters and 289 meters respectively in the Gonggou coalfield of ENN Ulanqab test base for underground coal gasification without wells. When drilling to the expected lower end position _H2 of the drilling casing, the drilling casing 7 is lowered into the borehole 1, and the drilling casing and the formation are cemented together by grouting cement, that is, well cementing. After the well cementing is completed, continue to drill into the inside of the coal seam floor 5, and calculate the amount of grouting cement required for hole bottom reinforcement according to the depth of the drilled hole entering the coal seam floor 5, the diameter of the borehole, and the position _H1 of the lower end of the borehole protection device. Inject the cement slurry into the borehole and wait for it to solidify to form reinforcement at the bottom of the borehole 6 .

Secondly, construct directional borehole 8 at a certain distance from borehole 1. Once spud to the bottom of the coal seam roof, build-up will start until the middle and upper part of the coal seam is completed. Casing 9 and implement grouting and cementing. After the cementing is completed, the second drilling continues to build up to the middle and lower part of the coal seam. At this time, the drilling tends to move forward horizontally. Enter the directional drilling target point in the vertical drilling 1 to the middle and lower part of the coal seam, continue the construction of the directional drilling 8 until the directional drilling 8 and the vertical drilling 1 are opened, and take out the drilling equipment.

Then, the horizontal drilling support pipe 11 (here, the screen pipe) is lowered into the second-opened deflection and horizontal section drilling. The screen pipe is a steel pipe with a certain number of small holes, and each screen pipe section passes through a small section of glass fiber reinforced plastic. The pipe 12 is connected or screwed, and the screen pipe is laid from the end of an open section of the borehole 8 to the bottom of the vertical borehole 1.

Finally, lower the drilling protection device 10 into the exposed section of the coal seam of the vertical borehole 1. The protection device here is an inflatable bladder, which is in a deflated state during the lowering process. Until the volume size is similar to the shape of the bare hole section, fix the gas pipeline at the wellhead and cut off the connection with the inflatable device on the ground. When the drilling is about to be put into use, the gas in the leather bag is released through the air pipe, and the volume decreases, and the skin bag can be taken out, and the well-protected drilling can be utilized.

Embodiment two:

The implementation steps of the vertical drilling protection process will be described with reference to FIG. 2 .

First, use a drilling rig to drill a hole 1 from the ground to the coal seam floor 5 through the surface soil layer 2, the rock layer, the coal seam roof 3, and the coal seam 4. Referring to the previous drilling work in the Ulanchabu Gonggou coalfield, the coal seam is roughly buried. The depth, thickness and other conditions have been grasped, and it can be estimated that the lower end position H ₂ of the drilling casing is 277 meters deep and the lower end position H ₁ of the drilling protection device is 289 meters deep. When drilling to the expected lower end position H ₂ of the drilling casing , wash the well, run the drilling casing 7 into the borehole 1 to the bottom of the hole (the lower end of the drilling casing 7), inject cement slurry for cementing, and consolidate the drilling casing 7 and the formation together. After waiting for solidification, the drill is started again to drill into the coal seam floor, and the amount of cement slurry needed to reinforce the bottom of the hole is estimated according to the position H ₁ of the lower end of the borehole protection device 10 , the borehole diameter and the borehole depth.

Secondly, wash the borehole. After cleaning the mud used for drilling, inject the estimated amount of mud to reinforce the bottom of the hole and wait for solidification to form the bottom reinforcement of the borehole 6 .

Finally, after the hole bottom reinforcement construction is completed, the drilled hole below the lower end of the drilled casing 7 and the bottom of the reinforced hole 6 is exposed. Lower the borehole protection device 10 (here, a glass steel pipe) into the borehole of the exposed section of the coal seam, and ensure that the upper end of the borehole protection device 10 overlaps with the lower end of the borehole casing 7 to avoid cuttings and sand , formation water, etc. enter the borehole protection device 10 from the upper end. When the drilling needs to be used, the glass steel pipe can be taken out or burned directly at the bottom of the hole.

Embodiment three:

Herein, the implementation method of the sleeved borehole protection process is described in detail with reference to FIG. 3 .

First, build a vertical borehole 1 from the ground to the underground coal seam, pass through the surface soil layer 2, the rock layer, the coal seam roof 3, and the coal seam 4, and drill into or even penetrate the coal seam floor 5. According to the drilling data and coal seam For the coring situation, it is estimated that the lower end position H ₂ of the borehole casing is 277 meters deep and the lower end position H ₁ of the borehole protection device is 289 meters deep, and then the amount of grouting cement required for hole bottom reinforcement is estimated based on the borehole diameter and drilling depth .

Secondly, wash the borehole. After cleaning the mud used for drilling, inject the estimated amount of mud to reinforce the bottom of the hole and wait for solidification to form the bottom reinforcement of the borehole 6 .

Finally, according to the calculation results, one end of the borehole protection device 10 with a suitable length (glass steel pipe is used here) is socketed together with the borehole casing 7. The socketed part is shown at position 13 in Figure 3, and one end is closed. Two small windows 15 are opened on the side of the end 14, the closed end 14 is on the bottom, the drilling casing is lowered into the borehole 1, and the cementing slurry is injected into the casing, under pressure, the cement slurry passes through the small window to the drill hole. The space outside the hole casing 7 is circulated, and the space between the hole casing 7 and the drilling protection device 10 and the rock formation is filled by pressing and discharging, and the cementing and the protection of the coal seam section drilling are completed after waiting for solidification.

When the borehole needs to be utilized, the perforating equipment is lowered into the borehole protection device 10 of the coal seam section, the borehole protection device 10 and the nearby cement sheath are shot, and the fluid between the coal seam and the borehole can circulate freely.

Claims (10)

1. a method for underground borehole protection, is characterized in that, comprises the steps: Step A, drilling a vertical borehole (1) from the ground to the underground coal seam, drilling to a depth of _H2 at the lower end of the borehole casing (7), and cementing the borehole above the position of _H2 ; Step B, continue to drill into the coal seam floor (5), estimate the drilling casing (7) and the drilling protection device (10) into the position, the bottom of the drilling hole to the drilling protection device 10 lower end position H ₁ Drill holes for reinforcement (6); Step C, the remaining section of the borehole in the coal seam is in the state of open hole at this time, and the drill hole protection device (10) is lowered into the open hole section in the vertical borehole (1) or filled with a mixed foaming curing agent; Step D, remove or destroy the borehole protection device (10) or fill the mixed foaming curing agent before implementing underground coal seam gasification or during the gasification process, so that the coal seam can be in contact with the outside atmosphere, so far the borehole protection device (10) ) or the drilling protection effect of filling and mixing the foaming curing agent ends. 2. The method according to claim 1, characterized in that, between step B and step C, further comprising the following steps: Step 1, implement directional drilling (8), once spud to the bottom of the coal seam roof and begin to deflect until the middle and upper part of the coal seam is completed, the direction is to the vertical drilling (1) direction, and the drilling casing ( 9) and implement grouting and cementing; Step 2. After the cementing is completed, the second drilling continues to build up to the middle and lower part of the coal seam. At this time, the drilling tends to move forward horizontally; in the vertical borehole (l), drill the target point of the directional drilling to the middle of the coal seam. Bottom, continue the construction of directional drilling (8), until get through directional drilling (8) and vertical drilling (1), take out drilling equipment; Wherein, for the directional drilling (8), the horizontal drilling support pipe is lowered into the horizontal section drilling or filled with a mixed foaming curing agent. 3. The method according to claim 2, characterized in that: the material of the support pipe is ordinary steel pipe, glass steel pipe, combustible plastic pipe, bamboo or wood; the material of the drilling protection device (10) is glass steel, bamboo, wood Stakes or plastic skins. 4. The method according to claim 3, characterized in that: when the drilling protection device (10) adopts a hard pipe, the hard pipe and the drilling casing (7) are partially overlapped or socketed to shield the bare hole section coal seam. 5. The method according to claim 3, characterized in that: if the drilling protection device (10) is a hard pipe, its length is slightly longer than the bare hole section, and its diameter is slightly smaller than the diameter of the drilling casing (7). The lower end reaches the position _H1 at the bottom of the borehole, and a part of the upper end overlaps with the drilling casing (7). 6. The method according to claim 3, characterized in that: when the drilling protection device (10) adopts a sleeve type, the drilling protection device (10) is connected with the drilling casing (7) to protect The lower end of the device (10) is closed, and the side is perforated. 7. The method according to claim 1, characterized in that: using filling and mixing foaming curing agent to protect the borehole is to mix several fluids and then foam and solidify to support the borehole. 8. The method according to claim 7, characterized in that: the filling and mixing foaming curing agent is rigid polyurethane foam. 9. The method according to claim 3, characterized in that: the drilling protection device (10) adopts a plastic bladder, which realizes the protection of the drilling and the insertion and removal of the bladder by inflation and deflation. 10. According to any one of the methods described in claims 1-9, it is characterized in that: for the vertical borehole (1), the borehole protection device (10) is lowered into the borehole protection device (10) or the drill is reinforced before filling the mixed foaming curing agent. Hole bottom (6).

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