A combined drilling method for gob filling in steeply inclined multi-seam coal mines

Abstract

The present invention relates to the technical field of drilling treatment for steeply inclined goafs, and in particular to a combined drilling method for filling steeply inclined multi-seam goafs, which includes the following steps: S1: Select appropriate drilling equipment according to the filling treatment requirements of the steeply inclined multi-seam goaf; S2: Before drilling construction, prepare an emergency plan for the loss of drilling fluid during hole flushing; S3: Construct a grouting curtain at the boundary through directional drilling along the coal seam dip; S4: Drill vertical holes on the ground and achieve the treatment of the shallow goaf through the hole grouting step; S5: Drill directional holes along the coal seam normal and complete the treatment of the deep goaf through the hole grouting step; S6: Drill nearly horizontal holes along the coal seam strike to detect and reinforce the grouting treatment effect. The combined drilling hole-forming process of the present invention can ensure the safe and efficient hole-forming of grouting holes and fully guarantee the grouting effect; especially for steeply inclined multi-seam goafs, there are many complex connecting crosshead roadways in the mine. By adopting the combined drilling process, the grouting filling quality can be significantly improved.

Description

Technical Field

[0001] The present invention relates to the technical field of drilling treatment in steeply inclined goafs, and particularly to a drilling construction method that can achieve rapid, safe, and efficient drilling in the goaf of steeply inclined broken coal seams, especially a combined drilling method for filling steeply inclined multi-seam goafs. Background Art

[0002] Coal seams with an inclination angle below 8° are nearly horizontal coal seams, coal seams with an inclination angle between 8° and 25° are gently inclined coal seams, coal seams with an inclination angle between 25° and 45° are inclined coal seams, and coal seams with an inclination angle above 45° are steeply inclined coal seams. In the prior art, the technologies for drilling and mining the goafs of nearly horizontal coal seams, gently inclined coal seams, etc. have been relatively mature, and there are a certain number of existing technical solutions.

[0003] At present, there are also some publicly known technologies for drilling in steeply inclined strata. For example, in the patent document with the patent application number CN201010152658.6, a patented technology for directional inclined hole drilling in steeply inclined strata is disclosed. However, it is mainly an improvement in the process of directional inclined hole drilling for the core drilling construction environment of ordinary steeply inclined strata, rather than for the special environment of the broken strata in the goaf of steeply inclined coal seams that have undergone coal mining and formed goafs.

[0004] In the prior art, the filling and drilling technologies for the special environment of the broken strata in the goaf of steeply inclined coal seams that have undergone coal mining and formed goafs are still relatively insufficient. The main reasons are that there are problems such as great construction risks, complex geological environments, and high construction difficulties in the special environment of the broken strata in the goaf of steeply inclined coal seams.

[0005] As is well known, most of the mined goafs of steeply inclined coal seams in China are close-proximity multi-seam goafs. When mining the lower coal seam in a steeply inclined close-proximity coal seam group, the water-conducting fissure zone usually develops to the upper coal seam during mining, resulting in the connection of the goafs of the upper and lower coal seams during mining and affecting the mining of the upper coal seam. When mining the upper coal seam first, different from nearly horizontal coal seams, the floor fissure zone of the goaf of steeply inclined coal seams is likely to develop to the lower layer, affecting the mining of the lower coal seam.

[0006] The mining-induced fissures in steeply inclined coal-bearing strata are well developed, and the surface subsidence and deformation are significant, often showing trough-shaped collapses. Especially in the outcrop area of the coal seam, pumping and caving collapses usually occur, and the mining of steeply inclined close-proximity coal seam groups is likely to form a large-scale surface water accumulation area. It causes great damage to surface buildings and structures, which also puts forward higher requirements for grouting and subsidence reduction in coal mining subsidence areas. Moreover, the large-scale water accumulation area significantly restricts the drilling layout form and drilling construction technology.

[0007] In addition, in the existing technology, the traditional drilling method for the gob area of steeply inclined coal seams (i.e., the traditional vertical drilling process) is mainly adopted. Whether it is the national standard specification or the engineering construction practice, the traditional vertical drilling process applied to the gob area of steeply inclined coal seams is basically the same as that of the gob area of nearly horizontal coal seams. There are no obvious changes in both the layout method of vertical grouting holes and the drilling structure and drilling process parameters; both adopt the square or triangular uniform distribution form for hole layout and the two-opening drilling structure.

[0008] This construction process has a large amount of work, the hole-forming construction process for passing through multiple gob areas is complex, and the drilling trajectory is difficult to control, resulting in a long hole-forming cycle and low efficiency; moreover, the radiation area of single-hole grouting filling is small, the grouting efficiency is low, the trajectory of conventional vertical drilling is uncontrollable, the difficulty of forming holes in the strata passing through multiple coal seam gob areas is large, and the hole layout is limited by large-scale surface water accumulation.

[0009] In addition, when using the above vertical drilling process and arranging grouting holes in a square or triangular uniform manner, the following problems also exist in this drilling process and method:

[0010] (1) When mining steeply inclined coal seams, due to the large inclination angle of the coal seams, the angle formed by the direction of the rock gravity and the direction of the rock bedding plane becomes smaller, so the force of gravity along the bedding direction is greatly increased. This causes a series of characteristics different from those when mining gently inclined coal seams in the movement of surrounding rocks, the shape of roof caving, and the deformation characteristics of roadways. Especially due to the particularity of the development form of the water-conducting fissure zone in the overlying strata and the different distribution characteristics of the remaining voids in the gob area, the conventional drilling process and hole layout form lack pertinence, the grouting filling efficiency is not high, and there is a greater possibility of potential grouting quality problems.

[0011] (2) Due to the particularity of the occurrence state of steeply inclined coal seams, they generally have experienced strong geological changes. The geological structure is relatively complex and the occurrence is unstable. It is difficult to form holes with the conventional vertical drilling, the difficulty of controlling the drilling trajectory is large, and the hole-forming efficiency is low.

[0012] (3) In the steeply inclined coal-bearing strata, mining-induced fissures are developed, surface subsidence and deformation are significant, and trough-shaped collapses often occur; especially in the outcrop area of the coal seam, the phenomenon of pumping and caving collapses usually occurs, and large-scale surface water accumulation areas are easily formed during the mining of steeply inclined close coal seam groups. It causes great damage to surface buildings and structures, which also puts forward higher requirements for grouting and subsidence reduction in the coal mining subsidence area, and the large-scale water accumulation area significantly limits the hole layout form and drilling construction process. The conventional vertical drilling process can no longer meet the requirements of grouting treatment for the gob area of steeply inclined coal seams.

[0013] (4) At present, most of the gob areas of steeply inclined coal seams mined in China are close multi-coal seam gob areas. For the gob area of steeply inclined close coal seam groups, it is difficult to form holes with the conventional vertical drilling, the drilling speed is slow, drilling accidents are likely to occur, and the grouting efficiency is low.

[0014] (5) Steeply inclined coal seams have their own characteristics in mine development, mining methods, roof management methods, layout of mining area roadways, and stope mining technology. The significant differences in the layout of the goaf working face and roadways result in different forms of grouting borehole layout. Conventional vertical boreholes are arranged at a certain interval along the dip, which is prone to grouting blind spots and potential grouting quality hazards. Moreover, due to the limited accuracy of the borehole trajectory of conventional vertical boreholes, it is difficult to accurately hit the mining area roadways, which may create weak areas in grouting quality.

[0015] For this reason, the present invention hereby proposes a method for realizing rapid, safe, and efficient drilling construction for the goaf of steeply inclined multi - coal seams, which can effectively solve many dilemmas and deficiencies faced by traditional vertical borehole grouting filling and better solve the problems existing in the prior art. Summary of the Invention

[0016] One of the technical solutions adopted by the present invention to solve the above - mentioned technical problems is: a combined drilling method for filling the goaf of steeply inclined multi - coal seams, including the following steps:

[0017] S1: Select appropriate drilling equipment according to the burial depth of the goaf, overlying rock lithology, borehole type, and borehole structure requirements;

[0018] S2: Before drilling construction, make an emergency plan for the loss of drilling fluid during borehole flushing;

[0019] S3: During construction, construct a grouting curtain at the boundary of the treatment area through a directional borehole along the dip of the coal seam (Process a);

[0020] First, construct a curtain borehole along the dip of the coal seam at the boundary of the treatment of the goaf of steeply inclined coal seams. When the goafs at different levels above and below are connected, the construction penetrates the goafs at multiple levels during construction. During drilling, an advancing - type sectional hole - forming process is adopted, and it is constructed at the boundary of the treatment scope of the coal - mining subsidence area.

[0021] The directional borehole along the dip of the coal seam adopts an advancing sectional hole - forming process. One borehole can penetrate the goafs at multiple levels simultaneously, with high curtain construction efficiency.

[0022] S4: After the construction of the grouting curtain at the boundary is completed, construct a surface vertical borehole (Process b) and achieve the treatment of the shallow - part goaf of steeply inclined multi - coal seams within the treatment area through the borehole grouting step;

[0023] The surface vertical borehole (Process b) designed here has a simple borehole structure, few ineffective grouting sections, high hole - forming efficiency, and low cost, and can well complete the effective grouting of the goafs with relatively shallow burial depths and coal seam outcrop areas in the internal steeply inclined multi - coal seam goafs.

[0024] S5: While the surface vertical borehole (Process b) is being carried out, construct a directional borehole along the normal direction of the coal seam (Process c) and complete the treatment of the deep - part goaf through the borehole grouting step;

[0025] The drilling structure is a multi-branch inclined directional borehole. For the goaf in the lower horizon with a large buried depth or the goaf where vertical borehole construction is not feasible due to surface water accumulation, the directional borehole along the coal seam normal direction (Process c) is used to complete the treatment of the deep goaf. This solves the problems in the traditional process, such as the high difficulty of constructing vertical boreholes from the surface, penetrating multiple goafs, formation fragmentation, high borehole accident rate, and difficulty in forming holes. In this specific area, the normal directional borehole is adopted. The directional borehole enters the goaf from a relatively intact formation outside the working face, improving the hole-forming efficiency. Moreover, the multi-branch directional borehole is used to improve the grouting efficiency of the directional filling borehole and reduce the ineffective grouting hole section.

[0026] Here, the surface vertical borehole (Process b) and the directional borehole along the coal seam normal direction (Process c) are constructed synchronously, enabling simultaneous grouting of the goafs at different mining levels above and below, greatly shortening the treatment period and improving the treatment efficiency.

[0027] S6: After the treatment of the surface vertical borehole (Process b) and the directional borehole along the coal seam normal direction (Process c) is completed, construct the nearly horizontal borehole along the coal seam strike (Process d) to detect and reinforce the grouting treatment effect.

[0028] Since the technology of constructing a long-distance nearly horizontal borehole in the broken formation of the goaf is relatively difficult, the construction of the nearly horizontal borehole along the coal seam strike (Process d) should be started after the grouting of the surface vertical borehole (Process b) and the directional borehole along the coal seam normal direction (Process c) is completed.

[0029] The borehole structure of the nearly horizontal borehole along the coal seam strike (Process d) is a long-distance nearly horizontal borehole. When the width of the goaf working face along the dip is large, horizontal branch boreholes are arranged in a retreating manner along the main borehole.

[0030] The difference from the nearly horizontal coal seam multi-branch directional borehole (i.e., its effect) is that the branch boreholes of the directional borehole along the strike of the steeply inclined coal seam are concentrated on one side of the main borehole and are vertically offset in spatial position. To improve the grouting effect, the side drilling points of each branch borehole gradually retreat upward; while the side drilling points of the branch boreholes of the nearly horizontal coal seam multi-branch directional borehole are arranged alternately on both sides of the main borehole, and the branch borehole trajectories are distributed on both sides of the main borehole. The side drilling point positions can be in a forward manner or a retreating manner.

[0031] The nearly horizontal boreholes along the coal seam strike (Process d) are constructed along the coal seam strike. The nearly horizontal section of the boreholes is relatively long, and they are mainly horizontally drilled in the broken strata of the goaf. The hole-forming is difficult. It is necessary to first carry out pre-grouting through the vertical boreholes of Process b and the normal directional boreholes of Process c. After the strata are filled and reinforced to a certain extent, the construction is carried out. The main borehole sections of Process d are all in the goaf, and the grouting filling efficiency is high. It can carry out supplementary grouting and effect detection on the weak areas of grouting quality existing after grouting with Process a, Process b, and Process c. Therefore, it is also used as a borehole for grouting quality detection. Each horizontal directional borehole along the goaf strike controls a line, and the lines form a plane, which has a higher detection efficiency than the point-type detection of vertical boreholes, fully ensuring that there is no blind area in grouting filling.

[0032] Preferably, in any of the above solutions, the borehole grouting steps are as follows:

[0033] Drill and construct along the designed trajectory of the current strata. When the circulating fluid completely leaks, drill against the leakage for 10 - 20 m, use the drill pipe to press water to wash the borehole for 30 min, and then lift out the drill tool.

[0034] Install the borehole mouth grouting device and start pressure grouting of the cement fly ash composite slurry. During grouting, record the changes in grouting flow rate and pressure; stop grouting after the grouting pressure reaches the design standard.

[0035] After standing for 12 - 24 h, remove the borehole mouth grouting device, lower the drill tool and start flushing the borehole. After washing the residual slurry in the borehole clean, lift out the drill tool.

[0036] Install the borehole mouth grouting device and pressure grout the cement slurry to reinforce the borehole wall; end this stage of grouting when the grouting pressure reaches the final hole standard, and wait for coagulation for 48 - 72 h.

[0037] After the waiting for coagulation is over, lower the drill tool to conduct a trial drill to detect the strength of the cement slurry. When the strength reaches the design requirements, continue drilling along the designed trajectory until the circulating fluid completely leaks. According to the integrity of the borehole wall, drill against the leakage for 10 - 20 m, lift the drill and grout until the borehole is formed.

[0038] After the borehole is formed, install the borehole mouth grouting device and pressure grout the cement fly ash composite slurry. When the grouting flow rate and grouting pressure reach the design final hole standard, end the grouting. When the grouting volume of the borehole exceeds 1.5 times the designed grouting volume and still does not reach the design final hole standard, the grouting parameters should be adjusted. After grouting is completed, remove the borehole mouth device and seal the hole to the hole mouth.

[0039] Preferably, in any of the above solutions, during the construction of the directional boreholes along the coal seam dip (Process a), when there are multiple working face goafs at different levels in the coal seam at the boundary of the treatment area, the forward segmented hole-forming method should be adopted until entering the goaf at the boundary of the treatment area.

[0040] In the nearly horizontal boreholes along the coal seam strike (process d), when the dip width of the working face is large and only one borehole arranged along the coal seam strike cannot fully cover the goaf of the same working face, the main hole of the directional drill shall be arranged at the upper part of the working face. After the main hole is grouted, branch boreholes shall be arranged below the main hole, and each branch borehole shall be drilled forward from top to bottom to form a hole.

[0041] In addition, considering that the dip width of the steeply inclined coal seam working face in China is generally small, 1-2 branch boreholes can be arranged for the same working face.

[0042] Preferably in any of the above schemes, when there are multiple working face goafs at different mining levels in the same coal seam, enter the goaf along the normal direction of the coal seam, start drilling and grouting from the lower goaf first, and after completion, gradually construct upward.

[0043] Preferably in any of the above schemes, when local filling is required for the goaf of the steeply inclined coal seam in a certain mining area, a low-fluidity slurry is used to construct an isolation curtain at the boundary of the grouting filling area to build a grouting boundary curtain and prevent the slurry from spreading to the goaf outside the filling area; among them, the boundary refers to the upper and lower boundaries of the current treatment area along the vertical direction and the two side boundaries along the strike.

[0044] Preferably in any of the above schemes, the drilling method for constructing the curtain includes the following steps:

[0045] According to the estimated value of the diffusion range of the grouting slurry, reasonably set the distance between the curtain borehole and the design filling area boundary. The distance between the curtain borehole trajectory and the filling boundary should not be too close;

[0046] Put aggregate into the curtain borehole, and the borehole diameter ≥ 110mm;

[0047] The directional borehole trajectory of the designed grouting section should preferably be linear along the coal seam strike or dip. The included angle of the broken line type should not be less than 120°, and the curvature radius of the curved borehole trajectory should not be less than 50m; to avoid abnormal termination of grouting caused by the blockage of the borehole by the aggregate slurry;

[0048] To ensure the accuracy of the borehole trajectory, the angle of encountering the layer should not be less than 30°;

[0049] When reaching the filling area boundary, the grouting slurry is changed to a high-concentration thick slurry, and a certain proportion of fine aggregate is added. The aggregate particle size in the nearly horizontal borehole ≤ 3mm, and the addition proportion is within the range of 15%-50% to significantly reduce the fluidity of the slurry;

[0050] When necessary, add a setting accelerator of 2% of the cement weight to reduce the setting time of the slurry;

[0051] During the curtain grouting process, grout in a low-pressure and flow-limiting manner, strictly control the grouting pressure and the unit grouting flow rate. When the single grouting volume is large, adopt intermittent grouting.

[0052] Different from nearly horizontal coal seams, the caving zone and fracture zone of steeply inclined coal seams usually develop to the Quaternary system, and even cause pumping and collapse in the outcrop area of the coal seam. In this case, it is very difficult to construct the upper boundary curtain of the filling area. Moreover, due to the extremely large dip angle of the coal seam, the conventional grouting slurry continuously flows downward by its own weight and it is very difficult to stay at the bottom of the designed filling area to accumulate a certain height. Therefore, it is also very difficult to construct the bottom boundary curtain. To ensure the successful construction of the boundary curtain wall, the above-mentioned boundary curtain drilling method is adopted.

[0053] In any of the above solutions, preferably, when encountering a hole section with hole collapse, drill sticking or serious loss of flushing fluid during the drilling process and it is impossible to carry out normal drilling operations and difficult to achieve one-time hole formation, the downhole sectional drilling method is adopted to ensure safe hole formation;

[0054] After single sectional hole formation, press water to wash the hole and start grouting. After the grouting is completed, wait for coagulation for 36 - 72h, and then start the next sectional drilling construction.

[0055] In any of the above solutions, preferably, at the end stage of grouting, the grouting pressure is increased to 3 - 4MPa, and the selected slurry concentration should not be too thick, so as to improve the reinforcement effect of the grouting slurry on the broken hole wall, effectively prevent hole collapse accidents, and ensure the reinforcement effect of the formation of the sectional hole wall of the drill hole.

[0056] In any of the above solutions, preferably, when sectional grouting of the drill hole is carried out, at the end stage of each section of grouting, the cement-based composite slurry is adjusted to pure cement slurry added with a coagulant accelerator to accelerate the slurry coagulation speed, reduce the waiting coagulation time for the next section of drilling of the drill hole, and improve the drilling hole formation efficiency.

[0057] In any of the above solutions, preferably, when drilling in soft and broken strata or horizontal sections, a flexible drill string combination is adopted, four low drilling parameters are selected, short trips are made, and the drilling method of gradually increasing the displacement from a small displacement to a normal displacement is used, combined with the refined control technology of the wellbore trajectory, to achieve water drilling in soft coal seams to prevent wellbore instability and collapse; prevent the collapse of the wellbore of horizontal wells in soft coal seams / strata.

[0058] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0059] 1. By adopting the combined drilling hole formation process of the present invention, it can ensure the safe and efficient hole formation of grouting drill holes and fully guarantee the grouting effect; especially for the gob areas of steeply inclined multi-seam coal mines, there are generally many complex connecting crosshead roadways in the mine. By adopting the combined drilling process, it can effectively eliminate the grouting blind areas caused by various roadways and significantly improve the grouting filling quality.

[0060] 2. Due to the different occurrence states of the goaf in steeply inclined broken coal seams and the goaf in nearly horizontal coal seams, and the essential differences in geological conditions, the drilling holes of this method for grouting in the goaf of steeply inclined coal seams (belonging to the mined broken strata) are difficult to carry out drilling construction. At present, the existing technologies for directional drilling in goaf treatment are not applicable and cannot achieve safe and efficient grouting filling when used for the treatment of the goaf in steeply inclined broken coal seams. For the grouting of the goaf in steeply inclined multi - coal seams, the main grouting target section of the drilling hole is located from the water - conducting fissure zone in the roof of the goaf to the goaf. During the drilling process, there are adverse situations such as passing through broken strata and serious leakage of drilling fluid. The drilling hole needs to penetrate through extremely broken strata for a long distance in steeply inclined coal seams. However, through this process method, rapid, safe and efficient drilling construction can be achieved.

[0061] 3. In this method, increasing the drilling hole spacing in the middle and lower parts of the goaf, appropriately reducing the drilling hole spacing in the middle and upper parts of the goaf or arranging multi - branch directional drilling holes along the coal seam bedding can effectively reduce the drilling accidents in the broken strata of the roof and floor of steeply inclined coal seams. Except for the roof rock strata caving and moving, under certain conditions, there is also a probability of problems such as rolling and slippage of the floor rock strata.

[0062] 4. When it is necessary to enter the goaf from the strata outside the coal seam working face in this method, arrange multiple rows of drilling holes along the coal seam strike, design the drilling hole trajectory to drill perpendicular to the coal - bearing strata, and use directional drilling to measure the drilling hole trajectory while drilling, and adjust the drilling hole trajectory at any time to make the drilling hole enter the water - conducting fissure zone along the normal direction of the coal - bearing strata, so as to significantly reduce the probability of drilling hole deviation, reduce the number of hole deviation corrections, and ensure that the drilling hole is quickly formed according to the designed trajectory. It can effectively solve the problem that the dip angle of the strata in the goaf of steeply inclined broken coal seams is very large. Using the traditional drilling hole layout form, the drilling hole trajectory always forms a certain angle with the strata, and the angle passing through different strata changes, resulting in great difficulty in controlling the drilling hole trajectory, and it is easy to cause the drilling hole to deviate in trajectory when passing through different strata interfaces. Especially when the hardness difference between the upper and lower layers is obvious, it is difficult to ensure the construction of the drilling hole along the designed trajectory.

[0063] 5. By arranging directional grouting drilling holes along the coal seam, accurately controlling the trajectory of the directional drilling hole and dynamically correcting the deviation during the drilling process, not only can the hidden dangers of grouting quality caused by drilling hole deviation be avoided, but also the problem that the projected area of the goaf in steeply inclined coal seams along the horizontal direction is small due to the particularity of the occurrence of the goaf in steeply inclined coal seams can be solved. The treatment area is a long and narrow area with a small projected distance along the dip and a large projected length along the strike. When arranging grouting drilling holes in the long and narrow treatment area, the spacing of the drilling holes along the dip is small, and the control accuracy of the trajectory of conventional vertical drilling holes is low. The deviation of the drilling hole may cause the targets of two drilling holes to be close or even coincide, affecting the grouting filling effect.

[0064] 6. This process utilizes a multi-step, multi-drilling approach to achieve comprehensive drilling results. Multiple directional drill holes are arranged along the coal seam's inclination and strike, ensuring full grouting coverage of the goaf. This ensures high grouting efficiency and effectively avoids blind spots. Conventional vertical drill holes, however, are arranged at regular intervals along the inclination, which can easily create blind spots and pose quality risks. Furthermore, due to the limited accuracy of the drilling trajectory, conventional vertical drill holes struggle to accurately target the mining area's roadways, potentially creating weak grouting areas. BRIEF DESCRIPTION OF THE DRAWINGS

[0065] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly describes the drawings required for the specific embodiments or the description of the prior art. Similar elements or components are generally identified by similar reference numerals throughout the drawings. Elements or components in the drawings are not necessarily drawn to scale.

[0066] Figure 1 This is a cross-sectional view of the existing steeply inclined coal seam.

[0067] Figure 2 This is a schematic diagram of the existing steeply inclined goaf.

[0068] Figure 3 This is a schematic diagram of the drilling layout of process b and process d of the present invention from a planar top-down perspective.

[0069] Figure 4 Schematic diagram of the drilling layout of process a, process b, process c, and process d of the present invention from a planar top-down perspective.

[0070] Figure 5 This is a schematic diagram of the layout of process b and process d of the present invention from a frontal perspective.

[0071] Figure 6 for Figure 1 Schematic diagram of the layout distribution of drilling holes of various processes under the cross-sectional state.

[0072] in, Figure 1 The F in stands for ground. DETAILED DESCRIPTION

[0073] The following embodiments of the technical solution of the present invention are described in detail with reference to the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention and are therefore only used as examples and are not intended to limit the scope of protection of the present invention. Figures 1-6 As shown in .

[0074] There are three differences between the goaf of steeply inclined coal seams and the goaf of traditional nearly horizontal coal seams:

[0075] (1) The occurrence states of the gob areas in steeply inclined coal seams and gently inclined coal seams are different. The most important difference is the coal seam dip angle. Steeply inclined coal seams are mostly unstable and complex coal seams, and the engineering geological conditions are complex.

[0076] Generally speaking, steeply inclined coal seams have experienced strong geological tectonic movements. The geological structure is relatively complex and the occurrence is unstable.

[0077] The gob areas of gently inclined coal seams in the same mining area are generally within the same elevation range, and the planar projection area is large. The working face of a steeply inclined coal seam is generally arranged along a certain elevation in a mining area, and isolation coal pillars are left between different elevations. Therefore, the working face of a steeply inclined coal seam is generally shorter along the dip and longer along the strike, and the planar projection is slender and strip-shaped.

[0078] Due to the large coal seam dip angle, the development morphology of the "three zones" of the overlying strata of the coal seam is significantly different from that of gently inclined coal seams. Moreover, the floor failure of the gob area of a steeply inclined coal seam is generally more serious and needs to be grouted for treatment. The development ranges of the water-conducting fissure zones of the two are different.

[0079] (2) The dip angle of a steeply inclined coal seam is very large. Generally, the working conditions of the working face of a steeply inclined coal seam are poor, and the coal seam thickness is small. The height of a mining area is generally 80 - 200 m, and the strike length of a double-wing mining area is generally 400 - 600 m. The mining area is generally divided into sections along the dip, but the inclined length of the section is generally small, depending on the selected coal mining method, ranging from only 15 - 20 m at the small end to 50 - 60 m at the large end. The width of the coal pillar between sections is generally 3 - 5 m. This also results in a smaller planar projection range of the gob area along the dip. If the grouting borehole spacing of the gob area of a gently inclined coal seam is still used, the actual distance between two grouting boreholes in the gob area is very large, and there is a high risk of grouting quality. (Example: For the gob area of a steeply inclined coal seam with a burial depth of 500 and a dip angle of 75°, when the borehole deviates by 1°, the grouting borehole deviates more than 30 m along the floor of the gob area. According to the specification, the grouting hole spacing is only 10 - 30 m. It can be seen that the borehole deviation amount is greater than the borehole spacing.)

[0080] (3) Due to geological structure factors, there are usually multiple gob areas in steeply inclined coal seams, and most of them are connected between different layers. Compared with the gob area of gently inclined coal seams, the strata are more fragmented and the fragmented hole sections are longer, making it difficult to form boreholes.

[0081] The void distribution in the gob area of gently inclined coal seams generally conforms to the "O"-ring theory, with a small middle area and a large surrounding area near the coal pillars. In the gob area of a steeply inclined coal seam, the void ratio is small at the lower part of the floor and large at the higher part of the floor, and there are usually large cavities, which are prone to cause the phenomenon of drill string dropping.

[0082] Due to the severe surface deformation of steeply inclined coal seams, higher technical requirements are placed on directional drilling, including controlling the accuracy of the drilling trajectory, reducing the spacing between branch drill holes, and increasing the cement content of the grouting slurry in the coal seam outcrop area.

[0083] The patterns of surface subsidence and deformation are inconsistent. The maximum subsidence and deformation in goafs of near-horizontal coal seams is usually in the middle of the goaf. For fully mined goafs, the surface subsidence takes on a basin-like shape. However, for goafs of steeply inclined coal seams, the maximum surface subsidence and deformation occurs not in the middle of the goaf, but rather in the upper middle section of the working face, toward the coal seam outcrop.

[0084] The pressure exerted by the overlying strata on the coal seam roof changes with the increase of the coal seam inclination. The vertical component of the overlying strata exerted on the roof of the steeply inclined coal seam goaf is smaller than that of the gently inclined one, while the component acting along the inclination is larger. Due to the different stress states of the roof strata, the development morphology of the water-conducting fracture zone caused by mining is also different. The morphology of the water-conducting fracture zone in the nearly horizontal coal seam is generally "saddle-shaped" or "arch-shaped", and the upper and lower arch angles of the roof rock stratum damage zone in the steeply inclined coal seam goaf are larger on the upper side and smaller on the lower side. As the angle increases, the funnel shape of the roof damage gradually becomes smaller, and the lower arch angle gradually tapers out.

[0085] In addition, the main target area for treatment of coal mining subsidence areas is the water-conducting fracture zone in the goaf area. However, the development morphology of the water-conducting fracture zone in the goaf area of steeply inclined coal seams is different, so traditional technology cannot be effectively applied to the effective treatment of the goaf area of steeply inclined coal seams.

[0086] To this end, in this embodiment, a combined drilling method for filling steeply inclined multi-coal seam goaf is designed, comprising the following steps:

[0087] S1: Select appropriate drilling equipment based on the depth of the goaf, overburden lithology, drilling type, and drilling structure requirements;

[0088] S2: Before drilling construction, prepare an emergency plan for drilling fluid leakage;

[0089] S3: During construction, a grouting curtain is constructed at the boundary of the treatment area by directional drilling along the coal seam trend (process a);

[0090] First, curtain drilling is carried out along the coal seam inclination at the boundary of the steeply inclined coal seam goaf area. When the upper and lower goaf areas are connected, the construction passes through multiple levels of goaf areas. The forward segmented drilling process is used during drilling, and construction is carried out at the boundary of the coal mining subsidence area control range.

[0091] Directional drilling is carried out along the inclination of the coal seam, and the drilling adopts the forward segmented drilling process. One borehole penetrates multiple levels of goaf at the same time, and the curtain construction efficiency is high.

[0092] S4: After the boundary construction grouting curtain is completed, construct surface vertical boreholes (Process b) and achieve the treatment of shallow steeply inclined multi-seam goafs in the treatment area through the borehole grouting step;

[0093] The surface vertical boreholes (Process b) designed herein have a simple borehole structure, few ineffective grouting sections, high hole-forming efficiency and low cost, and can well complete the effective grouting of shallowly buried and outcrop goafs in the steeply inclined multi-seam goafs inside.

[0094] The vertical boreholes adopt a three-opening wellbore structure (where the three-opening structure parameters: borehole diameter (casing diameter) 311.1mm / 273, 244.5mm / 177.8, 152mm / 110; or the first opening 311.1mm / 244.5, the second opening 215.9 / 168.3mm, the third opening 149.2 / 114.3mm). When stuck-pipe or hole-burying accidents occur in the broken formation, it is convenient to handle.

[0095] After the casting of the hole-opening casing is completed, a pressure test should be carried out 48 hours after waiting for coagulation. The test pressure is generally 3.5 - 4.5 MPa, the test time should not be less than half an hour, the pressure loss should not exceed 0.5 MPa, and the next grouting step can be carried out only when the test result is qualified. This step can ensure the subsequent sectional grouting effect and avoid the grouting slurry flowing into the surface soil layer between the casing and the hole wall or gushing out from the ground surface. When encountering a large area of water accumulation area, multiple-branch inclined directional boreholes need to be arranged outside the water accumulation area to solve the problem that vertical drilling cannot be directly adopted.

[0096] S5: While the surface vertical boreholes (Process b) are being constructed, construct normal-to-seam directional boreholes (Process c) and complete the treatment of deep goafs through the borehole grouting step;

[0097] The borehole structure is a multiple-branch inclined directional borehole. For the goafs of the lower coal seams with large burial depths or the surface water accumulation areas where borehole construction conditions are not available, the normal-to-seam directional boreholes (Process c) complete the treatment of deep goafs. It solves the problems in the traditional process that it is difficult to construct vertical boreholes from the ground surface, penetrate multiple goafs, the formation is broken, the borehole accident rate is high, and it is difficult to form holes. In this specific area, normal directional boreholes are used to enter the goaf from a relatively complete formation outside the mining face area, improving the hole-forming efficiency, and using multiple-branch directional boreholes to improve the grouting efficiency of the directional filling boreholes and reduce the ineffective grouting hole sections.

[0098] When constructing perpendicular to the coal seam direction, it vertically penetrates the upper three zones and the lower three zones of the goaf, ensuring the effective grouting filling of the upper three zones of the roof and the lower three zones of the floor of the steeply inclined coal seam and improving the grouting treatment quality;

[0099] Install a casing for protecting the borehole wall in the bedrock section immediately below the casing near the borehole opening. The casing for protecting the borehole wall is preferably an equal-diameter expandable casing. After it is lowered into the predetermined section, the casing is expanded to the aperture size, which can achieve the plugging of complex sections without increasing the borehole order, so as to avoid the problems of borehole collapse during grouting and subsequent repeated hole cleaning in particularly fractured formations. The casing for protecting the borehole wall should pass through the fractured formation, and cement slurry is poured between the casing for protecting the borehole wall and the borehole wall to fix the casing.

[0100] The casing for protecting the borehole wall should not penetrate deeply into the grouting section of the goaf. When it enters within the water-conducting fissure zone of the goaf, a perforated pipe is connected to the end of the casing.

[0101] Here, the surface vertical borehole (process b) and the directional borehole along the normal direction of the coal seam (process c) are constructed synchronously, which can realize the simultaneous grouting of the goafs at different horizontal levels above and below, greatly shortening the treatment period and improving the treatment efficiency.

[0102] S6: After the treatment of the surface vertical borehole (process b) and the directional borehole along the normal direction of the coal seam (process c) is completed, construct a nearly horizontal borehole along the strike of the coal seam (process d) to detect and reinforce the grouting treatment effect.

[0103] When the directional borehole is arranged along the strike of the coal seam, each branch hole is in the same coal seam and is constructed from one side to the other side.

[0104] In the dip direction of the borehole, reduce the plane spacing of the boreholes to ensure that the target point spacing of the boreholes passing through the goaf does not exceed 30m.

[0105] Along the dip of the coal seam, when the coal seam dip angle is greater than 45°, it can be calculated that the plane spacing of the target points of the vertical grouting boreholes should not be greater than 21m. When using vertical coal seam directional boreholes or bedding directional boreholes, the target point spacing of two adjacent branch boreholes does not exceed 30m.

[0106] During construction, the borehole penetrates through the goafs of multiple working faces at different mining levels along the dip of the same mining coal seam at one time, and grouts in a downward manner along the dip of the mining coal seam to improve the grouting efficiency of the borehole.

[0107] In process a, when it is necessary to construct a curtain at the bottom boundary of the treatment area, nearly horizontal boreholes along the strike can be arranged in the goaf at the bottom boundary, and a curtain is constructed along the strike treatment boundary to form a curtain boundary, that is, the bottom boundary of the treatment area. A low-fluidity grouting slurry is used to form the curtain.

[0108] Using a low-fluidity grouting slurry to form the curtain can effectively prevent the overflow and loss of the slurry, greatly improving the grouting efficiency while avoiding excessive waste of the slurry.

[0109] For steeply inclined multi - seam gob areas, the projection in the horizontal direction is relatively small. However, for boreholes with a relatively large burial depth, such as a borehole with a burial depth of 500 m, a deviation of 1°, and a horizontal offset of 8.7 m, if the horizontal offset is 8.7 m, it is very likely to deviate from the steeply inclined gob area, especially the local gob area of an isolated working face, resulting in waste of boreholes and delay of the construction period. Therefore, it is specified that the deviation distance of the vertical grouting borehole shall not be greater than the coal seam thickness.

[0110] In addition, in the steeply inclined multi - seam gob area, the main hole of the directional borehole vertically penetrates the gob areas of multiple coal seams at different mining levels in sequence, and the inclined bedding branch holes are arranged along the inclination directions of multiple coal seams at different mining levels. A multi - branch directional borehole group can simultaneously take into account the grouting filling of the gob areas of multiple coal seams at different mining levels, so as to further improve the grouting filling efficiency and construction efficiency.

[0111] Since the technology of constructing long - distance nearly horizontal boreholes along the broken strata of the gob area is relatively difficult, after the vertical boreholes on the ground (process b) and the directional boreholes along the normal direction of the coal seam (process c) are grouted, the construction of the nearly horizontal boreholes along the strike of the coal seam (process d) can be started.

[0112] The borehole structure of the nearly horizontal borehole along the strike of the coal seam (process d) is a long - distance nearly horizontal borehole. When the gob area working face has a large width along the inclination, the horizontal branch boreholes are arranged in a retreating manner along the main hole.

[0113] The difference from the nearly horizontal coal - seam multi - branch directional borehole (i.e., its effect) is that the spatial positions of the branch boreholes of the directional borehole along the strike of the steeply inclined coal seam are distributed in a vertically staggered manner. To improve the grouting effect, the side - drilling points of each branch borehole gradually retreat upward; while the side - drilling points of the branch boreholes of the nearly horizontal coal - seam multi - branch directional borehole are arranged alternately on both sides of the main hole, and the branch borehole trajectories are distributed on both sides of the main hole. The side - drilling point positions can be in a forward - type or a retreating - type.

[0114] The nearly horizontal borehole along the strike of the coal seam (process d) is constructed along the strike of the coal seam. The nearly horizontal section of the borehole is relatively long, and it mainly drills horizontally in the broken strata of the gob area. The hole - forming is difficult. It is necessary to first carry out pre - grouting through the vertical borehole of process b and the normal - direction directional borehole of process c, and after filling and strengthening the strata to a certain extent, then construct. The main borehole sections of process d are all in the gob area, and the grouting filling efficiency is high. It can carry out supplementary grouting for the weak areas of grouting quality existing after grouting by processes a, b, and c. Therefore, it is also used as a grouting quality inspection borehole. Each horizontal directional borehole along the gob area strike controls a line, and from lines to a surface, the detection efficiency is higher than that of the point - type detection of vertical boreholes, fully ensuring that there is no blind area in grouting filling.

[0115] When the directional drilling is arranged along the coal seam strike, the branch holes are not at the same height. It is advisable to construct the branch holes sequentially from top to bottom. After the upper branch boreholes are grouted, the strata of the adjacent lower branch holes are reinforced, and the drilling and hole-forming efficiency of the subsequent branch holes gradually increases. Moreover, the spacing of the subsequent branch holes can be adjusted immediately according to the grouting volume of the previous branch holes, reducing the drilling construction cost and shortening the treatment period. When the grouting boreholes are arranged along the coal seam, multiple-branch inclined directional drilling is arranged to improve the drilling and grouting construction efficiency.

[0116] In addition, large-scale advancing grouting is carried out in the goaf at a certain mining level in the steeply inclined coal seam to improve the drilling and grouting efficiency; in this case, fewer boreholes can be used to complete the grouting and filling construction of the working face goaf at the same mining level; the advancing sectional drilling technology is adopted in the goaf, and the drilling and grouting processes are carried out alternately during construction.

[0117] Preferably in any of the above schemes, the above-mentioned borehole grouting steps are as follows:

[0118] Carry out drilling construction along the designed trajectory of the current strata. When complete loss of the circulating fluid occurs, drill while topping off the loss for 10 - 20 m, flush the borehole with water under pressure using the drill pipe for 30 min, and then withdraw the drill string.

[0119] Install the borehole mouth grouting device and start pressure grouting the cement fly ash composite slurry. During grouting, record the changes in grouting flow rate and pressure; stop grouting after the grouting pressure reaches the design standard.

[0120] After standing for 12 - 24 h, remove the borehole mouth grouting device, lower the drill string to start flushing the borehole, flush the residual slurry in the borehole clean, and then withdraw the drill string.

[0121] Install the borehole mouth grouting device and pressure grout the cement slurry to reinforce the borehole wall; end the grouting of this section when the grouting pressure reaches the end-hole standard, and wait for setting for 48 - 72 h.

[0122] After the waiting for setting is over, lower the drill string to conduct a trial drill to detect the strength of the cement slurry. After the strength meets the design requirements, continue drilling along the designed trajectory until complete loss of the circulating fluid occurs. According to the integrity of the borehole wall, drill while topping off the loss for 10 - 20 m, lift the drill and grout until the borehole is formed.

[0123] After the borehole is formed, install the borehole mouth grouting device and pressure grout the cement fly ash composite slurry. End the grouting when the grouting flow rate and grouting pressure reach the design end-hole standard. When the grouting volume of the borehole exceeds 1.5 times the design grouting volume and still does not reach the design end-hole standard, the grouting parameters should be adjusted. After grouting is completed, remove the borehole mouth device and seal the hole to the hole mouth.

[0124] Preferably, in any of the above solutions, during the construction of the directional borehole along the dip of the coal seam (Process a), when there are multiple goafs of working faces at different levels in the boundary coal seam of the treatment area, the forward segmented hole-forming method should be adopted until entering the goaf at the boundary of the treatment area;

[0125] In the nearly horizontal borehole along the strike of the coal seam (Process d), when the dip width of the working face is large and only one borehole arranged along the strike of the coal seam cannot fully cover the goaf of the same working face, the main hole of the directional drill should be arranged at the upper part of the working face. After the main hole is grouted, branch holes should be arranged below the main hole, and each branch hole is drilled forward from top to bottom in sequence.

[0126] In addition, considering that the dip width of the steeply inclined coal seam working face in China is generally small, 1 - 2 branch holes can be arranged for the same working face.

[0127] Preferably, in any of the above solutions, when there are multiple goafs of working faces at different mining levels in the same coal seam, first construct the main hole in the lowest working face. After the main hole grouting is completed, 1 - 2 branch holes are respectively arranged in each goaf of the working face from bottom to top in sequence; each branch hole is drilled backward from bottom to top along the main hole trajectory in sequence.

[0128] Preferably, in any of the above solutions, when local filling is required for the goaf of the steeply inclined coal seam in a certain mining area, a low-fluidity slurry is used to construct an isolation curtain at the boundary of the grouting filling area to build a grouting boundary curtain and prevent the slurry from spreading to the goaf outside the filling area.

[0129] Preferably, in any of the above solutions, the drilling method for constructing the curtain includes the following steps:

[0130] According to the estimated value of the diffusion range of the grouting slurry, reasonably set the distance between the curtain borehole and the boundary of the designed filling area. The trajectory of the curtain borehole should not be too close to the filling boundary;

[0131] Inject aggregate into the curtain borehole, and the borehole diameter ≥ 110mm;

[0132] Design the borehole trajectory of the grouting section to be nearly horizontal or inclined downward along the coal seam, and the inclination angle ≤ 30°, so as to avoid abnormal termination of grouting caused by the blockage of the borehole by the aggregate slurry;

[0133] When filling the boundary of the treatment area, the grouting slurry is changed to a thick slurry, adding a certain proportion of fine aggregate. The particle size of the aggregate in the nearly horizontal borehole ≤ 3mm, and the addition proportion is within the range of 15% - 50%, so as to significantly reduce the fluidity of the slurry;

[0134] If necessary, add a coagulant of 2% of the cement weight to reduce the setting time of the slurry;

[0135] During the curtain grouting process, grouting is carried out in a low-pressure and flow-limiting manner, strictly controlling the grouting pressure and the unit grouting flow rate. When the single grouting volume is large, intermittent grouting is adopted.

[0136] Different from nearly horizontal coal seams, the caving zone and fracture zone of steeply inclined coal seams usually develop to the Quaternary system, and even cause pumping and collapse in the outcrop area of the coal seam. In this case, there are great technical difficulties in constructing the boundary curtain of the designed filling area. Moreover, due to the extremely large dip angle of the coal seam, the conventional grouting slurry continuously flows downward by its own weight and it is very difficult to stay at the bottom of the designed filling area to accumulate a certain height. Therefore, it is also very difficult to construct the boundary curtain at the bottom. To ensure the successful construction of the boundary curtain wall, the above-mentioned boundary curtain drilling method is adopted.

[0137] Preferably in any of the above solutions, when there are hole sections with hole collapse, drill sticking or serious loss of flushing fluid during the drilling process and normal drilling operations cannot be carried out and it is difficult to achieve one-time hole formation, the downhole sectional drilling method is adopted to ensure safe hole formation;

[0138] After single sectional hole formation, pressure water washing of the hole starts grouting. After the grouting is completed, wait for coagulation for 36 - 72h, and then start the construction of the next sectional drilling.

[0139] The specific sectional length is comprehensively determined according to the formation fragmentation degree, drilling equipment capacity and grouting technology; generally, the sectional length is about 10 - 50m. When the formation is severely fragmented, the one-time sectional drilling length is appropriately reduced.

[0140] The technological steps of sectional hole formation grouting are as follows: sectional drilling, hole washing, grouting, waiting for coagulation, sectional drilling, hole washing again, grouting again, until the designed hole depth, and finally grouting in the goaf.

[0141] Preferably in any of the above solutions, in the end stage of grouting, the grouting pressure is increased to 3 - 4MPa, and the selected slurry concentration should not be too thick, so as to improve the reinforcement effect of the grouting slurry on the broken hole wall, effectively prevent hole collapse accidents, and ensure the reinforcement effect of the formation of the sectional hole wall of the drill hole.

[0142] Preferably in any of the above solutions, when sectional grouting of the drill hole is carried out, at the end stage of each section of grouting, the cement-based composite slurry is adjusted to pure cement slurry with a coagulant added to accelerate the slurry coagulation speed, reduce the waiting coagulation time for the next sectional drilling of the drill hole, and improve the drilling hole formation efficiency.

[0143] Preferably in any of the above solutions, when drilling in soft and broken formations or horizontal sections, a flexible drill string combination is adopted, four low drilling parameters are selected, short trips are made, and the drilling method of gradually increasing the displacement from a small displacement to the normal displacement is used, combined with the refined control technology of the wellbore trajectory, to achieve clear water drilling in soft coal seams to prevent wellbore instability and collapse; prevent the collapse of the wellbore of horizontal wells in soft coal seams / formations.

[0144] The drilling flushing fluid is prepared for the purpose of preventing cave-ins and leakage, ensuring normal drilling, and improving drilling efficiency.

[0145] In this invention, the various processes adopted are independent from the drilling perspective and can be applied to different processes for different regions and different drilling construction stages in steeply inclined multi-seam goafs. For goaf filling grouting, first, curtain holes are arranged at the boundary of the designated treatment area, and curtain grouting is carried out to prevent excessive loss of grout; directional holes along the coal seam dip are used as curtain grouting holes; after the curtain grouting is completed, filling grouting starts inside the treatment area; in the treatment area, shallow vertical holes are first constructed, and then normal directional holes are constructed to specifically grout the deep goaf. Finally, when the injectability of the hole significantly decreases, directional holes along the strike are constructed, and through water pressure tests and grouting, the grouting quality is detected and deficiencies are checked and filled.

[0146] Adopting the combined drilling hole-forming process of this invention can ensure the safe and efficient hole-forming of grouting holes and fully guarantee the grouting effect; especially for steeply inclined multi-seam goafs, there are generally many complexly connected crossheading roadways in the mine. By using the combined drilling process, the grouting blind areas caused by various roadways can be effectively eliminated, and the grouting filling quality can be significantly improved.

[0147] Due to the different occurrence states and essential differences in geological conditions between steeply inclined fractured multi-seam goafs and nearly horizontal coal seam goafs, the holes drilled by this method for grouting in steeply inclined coal seam goafs (belonging to the mined fractured strata) are difficult to carry out drilling construction. At present, the existing technologies for directional drilling in goaf treatment are not applicable and cannot achieve safe and efficient grouting filling when used for treating steeply inclined fractured coal seams; for grouting in steeply inclined multi-seam goafs, the main grouting target interval of the hole is located from the water-conducting fissure zone in the goaf roof to the goaf. During the drilling process, there are adverse situations such as passing through fractured strata and serious leakage of the drilling flushing fluid. Steeply inclined coal seams need to penetrate extremely fractured strata over a long distance, and through this process method, rapid, safe, and efficient drilling construction can be achieved.

[0148] In this method, the drilling spacing is increased in the middle and lower parts of the goaf, and the drilling spacing is appropriately reduced in the middle and upper parts of the goaf or multi-branch directional boreholes are arranged along the bedding of the coal seam, which can effectively reduce the drilling accidents in the broken strata of the roof and floor of steeply inclined coal seams. In addition to the roof rock caving and movement, under certain conditions, there is also a probability of problems such as rolling and slippage of the floor rock; when entering the goaf from the strata outside the mining face, multiple rows of boreholes are arranged along the normal direction of the coal seam, the drilling trajectory is designed to be perpendicular to the coal-bearing strata for drilling, and the directional drilling can measure while drilling and adjust the drilling trajectory at any time, so that the borehole enters the water-conducting fissure zone along the normal direction of the coal-bearing strata, so as to significantly reduce the probability of borehole deviation, reduce the number of borehole deviation corrections, and ensure that the borehole is quickly drilled according to the designed trajectory. It can effectively solve the problem that the dip angle of the strata in the goaf of steeply inclined broken coal seams is very large. Using the traditional drilling layout form, the drilling trajectory and the strata always form a certain angle, and the angle passing through different strata changes, resulting in great difficulty in controlling the drilling trajectory, and it is easy to cause the drilling trajectory to deviate when passing through different strata interfaces. Especially when the hardness difference between the upper and lower layers is obvious, it is difficult to ensure the construction of the borehole along the designed trajectory. By arranging directional grouting boreholes along the coal seam, accurately controlling the trajectory of the directional borehole, and dynamically correcting the deviation during the drilling process, not only can the hidden danger of grouting quality caused by borehole deviation be avoided, but also the problem that the horizontal projection area of the goaf of steeply inclined coal seams is small due to the particularity of the occurrence of the goaf of steeply inclined coal seams can be solved. The treatment area is a long and narrow area with a small projection distance along the dip and a large projection length along the strike. When arranging grouting boreholes in the long and narrow treatment area, the spacing of the boreholes along the dip is small, the control accuracy of the conventional vertical drilling trajectory is low, and the borehole deviation may cause the targets of two boreholes to be close or even coincide, affecting the grouting filling effect.

[0149] In this process method, multiple steps and various drilling methods are used in combination to achieve comprehensive drilling effects. Multi-branch directional boreholes are arranged along the strike, dip, and normal directions of the coal seam respectively, which can ensure full-coverage grouting filling of the goaf, with high grouting efficiency and effectively avoid the generation of grouting blind areas. The conventional vertical boreholes are arranged at a certain interval along the dip, and it is easy to appear grouting blind areas, resulting in hidden dangers of grouting quality. Moreover, due to the limited accuracy of the drilling trajectory of the conventional vertical boreholes, it is difficult to accurately hit the mining roadway, and grouting weak areas may be generated.

[0150] The above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention; for those skilled in the art of this technology, any alternative improvement or transformation of the embodiments of the present invention falls within the protection scope of the present invention.

[0151] For those not detailed in the present invention, they are all well-known technologies to those skilled in the art.

Claims

1. A combined drilling method for filling steeply inclined multi-coal seam goaf, characterized in that: The steps include: S1: Select appropriate drilling equipment based on the depth of the goaf, overburden lithology, drilling type, and drilling structure requirements; S2: Before drilling construction, prepare an emergency plan for drilling fluid leakage; S3: During construction, a grouting curtain is constructed at the boundary of the treatment area by directional drilling along the coal seam trend; S4: After the boundary construction and grouting curtain are completed, vertical drilling is carried out on the construction surface and the shallow steeply inclined multi-coal seam goaf area in the treatment area is treated through drilling and grouting steps; S5: While vertical drilling is being carried out on the surface, directional drilling is carried out along the normal direction of the coal seam and deep goaf treatment is completed through drilling and grouting steps; S6: After the surface vertical drilling and directional drilling along the normal direction of the coal seam are completed, near-horizontal drilling along the coal seam strike is carried out to test and reinforce the grouting treatment effect; During directional drilling along the coal seam inclination, when there are multiple working face goafs at different levels in the coal seam at the boundary of the treatment area, the forward segmented drilling method should be adopted until the goaf at the boundary of the treatment area is reached. Drill holes nearly horizontally along the coal seam strike. When the working face has a large dip width and only one borehole along the coal seam strike cannot fully cover the goaf of the same working face, the directional drill main hole should be arranged at the upper part of the working face. After the main hole is grouting, branch holes should be arranged below the main hole. Each branch hole should be drilled in a forward direction from top to bottom. The drilling method for constructing the grouting curtain comprises the following steps: According to the estimated value of the grouting slurry diffusion range, the distance between the curtain drilling hole and the boundary of the designed filling area should be reasonably set. The curtain drilling trajectory should not be too close to the filling boundary. Curtain drilling for aggregate casting, drilling hole diameter ≥110mm; The directional drilling trajectory of the designed grouting layer section should be straight along the strike or dip of the coal seam. The angle of the broken line should not be less than 120°, and the curvature radius of the curved drilling trajectory should not be less than 50m. To ensure the accuracy of the drilling trajectory, the layer angle should not be less than 30°; When filling the boundary of the area, the grouting slurry is changed to a high-concentration thick slurry, mixed with a certain proportion of fine aggregate. The aggregate particle size in the nearly horizontal borehole is ≤3mm, and the mixing ratio is within the range of 15%-50%; Then add 2% of the cement weight of the accelerating agent to reduce the setting time of the slurry; During the curtain grouting process, low-pressure and flow-limiting grouting is adopted, and the grouting pressure and grouting unit flow rate are strictly controlled. When the single grouting volume is large, intermittent grouting is adopted.

2. A combined drilling method for filling steeply inclined multi-coal seam goaf according to claim 1, characterized in that: When there are multiple working face goafs at different levels in the same coal seam, enter the deep goaf along the normal direction of the coal seam, start drilling and grouting from the lower goaf, and after completion, gradually construct upwards.

3. A combined drilling method for filling steeply inclined multi-coal seam goaf according to claim 2, characterized in that: When the goaf of a steeply inclined coal seam in a certain mining area needs to be partially filled, a low-fluidity slurry is used to construct an isolation curtain at the boundary of the grouting filling area to build a grouting boundary curtain to prevent the slurry from spreading to the goaf outside the treatment area; the boundary refers to the upper and lower boundaries of the current treatment area in the vertical direction.

4. A combined drilling method for filling steeply inclined multi-coal seam goaf according to claim 3, characterized in that: When encountering a hole collapse, drill stuck or serious leakage of flushing fluid during the drilling process, and normal drilling operations cannot be carried out, or it is difficult to complete the hole in one go, downward segmented drilling is used to ensure safe hole formation. After drilling a single section, pressurize the hole with water and start grouting. After grouting is completed, wait for 36-72 hours to set before starting the next section drilling construction.

5. A combined drilling method for filling steeply inclined multi-coal seam goaf according to claim 4, characterized in that: At the end of grouting, the grouting pressure is increased to 3 MPa, and the selected slurry concentration should not be too thick, and the mass concentration is controlled below 70%.

6. A combined drilling method for filling steeply inclined multi-coal seam goaf according to claim 5, characterized in that: When drilling and grouting in sections, at the end of each grouting section, the cement-based composite slurry is adjusted to pure cement slurry with the addition of an accelerator.

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