Advanced treatment method for multilayer limestone flood of coal seam floor

Abstract

The invention belongs to the technical field of coal seam floor flood prevention and control, and particularly relates to a coal seam floor multi-layer limestone flood advanced treatment method which comprises the following steps: S1, analyzing the hydrogeologic characteristics of a coal seam floor in a to-be-treated area and verifying the hydrogeologic characteristics through drilling so as to reveal the occurrence condition of coal seam floor limestone and determine a treatment target horizon; the treatment target horizon comprises a main aquifer and an indirect aquifer, and whether a water inrush threat exists or not is judged; s2, carrying out multi-branch horizontal drilling on the treatment target horizon with the water inrush threat; and S3, grouting, plugging and reinforcing are conducted on the main horizontal bare holes and the branch horizontal bare holes in the main water-bearing layer and the indirect water-bearing layer correspondingly. By means of the method, advanced treatment of multilayer limestone flood disasters of the coal seam floor is achieved, so that the water inrush threat of a roadway and a working face in the excavation process is reduced, and underground safety production is guaranteed.

Description

Technical Field

[0001] The invention belongs to the technical field of coal seam floor flood prevention and control, and specifically relates to a method for preemptive control of multi-layer limestone floods on coal seam floors. Background Art

[0002] At present, the effective measures for coal seam floor flood control are generally to carry out grouting transformation of the aquifer, that is, mainly to grouting transformation and reinforcement of the conductive and water-bearing rock strata of the coal seam floor into an impermeable layer, so as to increase the thickness of the coal seam floor impermeable layer and enhance the comprehensive water-blocking capacity of the coal seam floor rock strata to prevent the outburst of karst water in the floor.

[0003] The common underground management method in mines is to manage water while mining. However, due to the limitations of underground, there are technical problems such as small water management range and large blind spots. In recent years, the technology of advanced ground management of coal seam floors has been widely promoted, but most of the existing advanced water management technologies are aimed at managing a single aquifer, lacking targeted management of multiple aquifers in the coal seam floor, and often ignoring the threat of water inrush from the lower aquifers to the tunnels and working faces. In addition, in some areas, the coal seam floors have developed multiple aquifers with large water volume and strong water-richness. In addition, the potential hidden structure of the stratum makes it very easy for the aquifers to communicate in series, posing a great threat of water inrush to the working face and tunnels of the mine. It is difficult to achieve the expected water blocking effect by advanced management of a single aquifer. Summary of the invention

[0004] In order to overcome the shortcomings and deficiencies of the prior art, the purpose of the present invention is to provide a method for advance control of multi-layer limestone water disasters in the coal seam floor. Before the working face and the tunnel are excavated, the aquifer in the coal seam floor is explored in advance, multi-layer and multi-branch control drilling is carried out through drilling control and monitoring technology, and grouting reinforcement is carried out on the multi-layer control drilling, thereby achieving advance control of multi-layer limestone water disasters in the coal seam floor, reducing the threat of water inrush in the tunnel and working face during mining, and ensuring safe production underground.

[0005] To achieve the above object, the present invention provides the following technical solutions: A method for preemptive treatment of multi-layer limestone flooding in a coal seam floor comprises the following steps: Step S1: Analyze the hydrogeological characteristics of the coal seam floor in the area to be treated and verify them through drilling to reveal the occurrence of limestone in the coal seam floor; During the drilling process, the target layer for treatment is determined by the consumption of drilling fluid. The target layer for treatment includes the main aquifer and the indirect aquifer. The water inrush coefficient of the coal seam floor in the area to be treated is calculated according to various parameters of the target layer for treatment to determine whether there is a water inrush threat. Step S2: performing multi-branch horizontal drilling on the target layer with water inrush threat, wherein the multi-branch horizontal drilling comprises the following steps: Step S21: before the mine working face and mining tunnel are excavated, a drilling site is selected on the ground of the area to be treated, at least two secondary landing points are selected, and treatment drilling is opened according to the preset trajectory of the wellbore through drilling control monitoring technology, wherein the treatment drilling includes an injection well 2 for exposing the indirect aquifer and an injection well 3 for exposing the main aquifer; Step S22: The first drilling of the injection well 2 and the injection well 3 uses a roller drill bit to rotate and drill to a certain depth of stable bedrock, and lowers the primary casing; the second drilling of the injection well 2 and the injection well 3 uses a PDC drill bit to rotate and drill through the coal seam floor to a certain depth of the indirect aquifer and the main aquifer, and lowers the secondary casing; the third drilling of the injection well 2 and the injection well 3 uses a PDC drill bit to rotate and drill forward in the indirect aquifer and the main aquifer to open a main horizontal open hole; Step S23: a plurality of branch horizontal open holes are opened in the main aquifer and the indirect aquifer, wherein one end of each branch horizontal open hole is connected to the main horizontal open hole and the other end thereof extends in the main aquifer and the indirect aquifer respectively; Step S3: Grouting is performed in the main horizontal open holes and each branch horizontal open hole in the main aquifer and the indirect aquifer respectively to grout and seal the target layer for treatment.

[0006] Preferably, in step S22, the injection well 2 and the injection well 3 are first opened by using a Φ311.15mm roller drill bit to rotate and drill to a depth of 10m in stable bedrock, and a primary casing is lowered, and the size of the primary casing is not less than Φ244.5*8.05mm; the injection well 2 and the injection well 3 are second opened by using a Φ215.9mm PDC drill bit to rotate and drill through the coal seam floor to a depth of more than 2m in the indirect aquifer and the main aquifer, respectively, and a secondary casing is lowered, and the size of the secondary casing is not less than Φ177.8*8.94mm; the injection well 2 and the injection well 3 are third opened by using a Φ152.4mm PDC drill bit to rotate and drill forward in the indirect aquifer and the main aquifer to open a main horizontal open hole.

[0007] Preferably, in step S23, the number of branches of the branch horizontal open holes is between 10 and 15 and the distance between adjacent branch horizontal open holes is between 50 and 55 m.

[0008] Preferably, the branch horizontal open holes of the injection well 2 and the branch horizontal open holes of the injection well 3 should be arranged alternately, and the branch horizontal open holes are radial.

[0009] Preferably, each branch horizontal open hole of the injection 3 well is located between adjacent branch horizontal open holes corresponding to the injection 2 well.

[0010] Preferably, the full-angle change rate in the preset wellbore trajectory is 5 to 9°.

[0011] Preferably, the drilling control and monitoring technology includes drilling well trajectory control technology, gamma logging, mud logging, and geological guidance technology. The drilling control and monitoring technology is used to comprehensively monitor, analyze, and adjust the treatment drilling well in real time to ensure that the treatment target layer is effectively exposed and the grouting reinforcement effect of the treatment target layer is guaranteed.

[0012] Preferably, fly ash or clay is added to the cement slurry used for grouting and plugging reinforcement of the target layer for treatment.

[0013] Preferably, when the area to be treated is anticline landform, when the preset trajectory of the wellbore is preset, the treatment drilling is arranged along the axial direction of the anticline core, the wellhead of the treatment drilling is set at the high point of the formation, and the branch horizontal open holes extend from the core to the wing; when the area to be treated is syncline landform, when the preset trajectory of the wellbore is preset, the treatment drilling is arranged along the extension direction of the two wings of the syncline, the wellhead of the treatment drilling is set at the high point of the formation, and the branch horizontal open holes extend from the core of the syncline on both wings.

[0014] Preferably, when the area to be treated is a fault zone, a divided-plate construction is implemented for a fault whose fault drop is greater than 1.5 times the thickness of the target layer for treatment, and the divided-plate construction includes: according to the fault characteristics, the upper and lower plates that are disconnected due to the fault are respectively arranged with the treatment drilling wells, and when the fault zone is grouting reinforced, the arranged treatment drilling wells should pass through the fault zone and continue to drill for not less than 50m; for a fault whose fault drop is less than 1.5 times the thickness of the target layer for treatment, when the treatment drilling well is constructed through the fault, it is carried out from the rising plate to the descending plate, and the trajectory is lowered vertically to the lower part of the target layer for treatment in advance during construction, and the upper part of the target layer for treatment of the descending plate is connected after passing through the fault.

[0015] Compared with the prior art, the present invention has the following beneficial effects: 1. In this application, the hydrogeological characteristics of the coal seam floor in the treatment area are analyzed and verified through multiple drilling holes, so as to obtain the multi-layer treatment target layer (including the main aquifer and the indirect aquifer) that needs to be treated in advance, and the water inrush coefficient of the treatment target layer is calculated to determine whether there is a water inrush threat, so as to carry out multi-layer and multi-branch grouting reinforcement on the treatment target layer, thereby overcoming the technical shortcomings of the prior art of ignoring the water inrush threat of the lower aquifer of the layer to be treated to the tunnel and the working face.

[0016] 2. This application aims at the situation that there are multiple aquifers in the coal seam floor in the area to be treated, and the aquifers are all highly water-rich and pose obvious threats of water inrush to the mine. Double-layer or multi-layer grouting reinforcement management is used to fully cover the coal seam floor aquifers to eliminate the threats of water inrush from the floor aquifers to the mine.

[0017] 3. Most existing drilling technologies only use a single borehole inclination measurement and logging technology. In addition, the geological structure of the target layer for treatment is not clearly developed, and the stratigraphic direction is unclear. This technology makes it difficult to conduct effective in-layer drilling of the target layer for treatment. The full and effective exposure of the target layer for treatment is the key to the advanced treatment of the aquifer in this application, and directly affects the grouting reinforcement effect of the aquifer. Therefore, this application comprehensively adopts a variety of drilling control and monitoring technologies (such as drilling well trajectory control technology, gamma logging, logging, and geological guidance technology) to monitor, judge, and adjust the drilling well in real time to ensure the effective exposure of the target layer for treatment, achieve precise landing of the target layer for treatment and real-time in-layer drilling, and the target layer drilling rate reaches more than 85%, thereby ensuring the grouting reinforcement effect of the target layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a stratigraphic column diagram of the area to be treated in Example 1 of the present invention.

[0019] Figure 2 This is a schematic diagram of the wellbore structure of the control drilling according to Example 1 of the present invention.

[0020] Figure 3 This is a multi-layer and multi-branch horizontal drilling layout diagram of Example 1 of the present invention.

[0021] Figure 4 This is a vertical projection diagram of the multi-layer and multi-branch horizontal drilling trajectory of Example 1 of the present invention.

[0022] Figure 5 This is a horizontal projection diagram of the multi-layer and multi-branch horizontal drilling trajectory of Example 1 of the present invention.

[0023] Figure 6 This is a projection diagram of a stereoscopic projection diagram of a multi-layer and multi-branch horizontal drilling trajectory of Example 1 of the present invention.

[0024] Figure 7 This is a comparison chart of drilling fluid consumption before and after the treatment of the L2 limestone layer in Example 1 of the present invention.

[0025] Figure 8 This is a comparison chart of drilling fluid consumption before and after the treatment of the L8 limestone layer in Example 1 of the present invention.

[0026] In the figure: 1. L8 limestone layer, 2. L2 limestone layer, 3. 21 coal seam, 4. Injection well 2, 5. Injection well 3, 6. Stable bedrock, 7. Primary casing, 8. Secondary casing, 9. Main horizontal open hole, 91. Branch horizontal open hole. DETAILED DESCRIPTION

[0027] The present invention is further described in detail below in conjunction with specific implementation cases. It should be noted that the following embodiments are only for explanation and do not limit the scope of protection of the present invention. Example 1

[0028] The method for preemptive control of multi-layer limestone flooding in coal seam floors is applied in the preemptive control project of multi-layer limestone flooding in Zhongma Mine in Jiaozuo, Henan.

[0029] A method for preemptive treatment of multi-layer limestone flooding in a coal seam floor comprises the following steps: Step S1: Analyze the hydrogeological characteristics of the coal seam floor in the area to be treated and verify them through drilling to reveal the occurrence of limestone in the coal seam floor; determine the treatment target layer by the consumption of drilling fluid during the drilling process, the treatment target layer includes the main aquifer and the indirect aquifer, the indirect aquifer may include multiple, and in this embodiment, the indirect aquifer obtained by drilling is one; calculate the water inrush coefficient of the coal seam floor in the area to be treated according to various parameters of the treatment target layer, and judge whether there is a water inrush threat; 1. Regarding the occurrence of limestone in the coal seam floor: Analyze the hydrogeological characteristics of the coal seam floor in the area to be treated and drill the area to be treated, and reveal the stratigraphic column diagram (such as Figure 1 ), see Figure 2 As shown, in this embodiment, the occurrence of coal seam floor limestone includes the Carboniferous Taiyuan Formation L8 limestone layer 1 and the Carboniferous Taiyuan Formation L2 limestone layer 2 located below the 21 coal seam 3.

[0030] 2. Determination of governance target levels: (1) Analysis of the L8 limestone layer The distance between L8 limestone layer 1 and the bottom plate of L1 coal seam 3 is 20.38-35.33m, and the thickness of L8 limestone layer 1 is 9.31-12.04m. The karst fissures in this stratum are relatively developed. When the first borehole was drilled to 16m from the top plate of L8 limestone layer 1, the drilling fluid consumption of the first borehole was significantly greater than that of the overlying strata, that is, the drilling fluid consumption increased significantly from 490-620m, and the maximum consumption was nearly 10m³ / h; when the second borehole set in parallel was exposed to the top plate of L8 limestone layer 1, a large amount of drilling fluid was consumed, that is, the maximum consumption was 30m³ / h from 456-476m, and the drilling fluid consumption decreased significantly after drilling through L8 limestone layer 1. It can be seen that L8 limestone layer 1 is the main aquifer of the coal seam bottom plate, with developed interlayer fissures and strong water-richness.

[0031] (2) Analysis of the L2 limestone layer The distance between L2 limestone layer 2 and the bottom plate of L8 limestone layer 1 is 59.70m, and the distance between L2 limestone layer 2 and the bottom plate of coal seam 3 is 92.12m. The thickness of L2 limestone layer 2 is 10.69m. When drilling hole 2 exposed L2 limestone layer 2, the consumption of drilling fluid was significantly greater than that of the overlying rock layer. There was a large leakage of drilling fluid from L8 limestone layer 1 to the bottom plate of L2 limestone layer 2, and the water level of the aquifer was +68.14m. L2 limestone layer 2 is an indirect aquifer of the coal seam bottom plate, with relatively developed interlayer fissures and strong water richness.

[0032] Combining previous geological exploration data with actual drilling revelations, there are multiple limestone layers between L8 limestone layer 1 and L2 limestone layer 2, but most of them are unstable and thin, and do not have the conditions to be transformed into impermeable layers. Among them, L8 limestone layer 1 is the main aquifer of the coal seam floor, so L8 limestone layer 1 needs to be covered and managed in the entire area. L2 limestone layer 2 is an indirect aquifer of the coal seam floor. In addition, the water pressure of the deeper limestone is large and the impermeable layer is thin. It is very easy to form water inrush during mining activities. Therefore, L2 limestone layer 2 should also be reinforced.

[0033] In summary, L8 limestone layer 1 and L2 limestone layer 2 were identified as the target layers for treatment, and multi-layer and multi-branch horizontal drilling and grouting plugging technology was implemented.

[0034] 3. Determination of water inrush coefficient and water inrush threat: According to the 2018 No. 6 document of the "Detailed Rules for Water Control in Coal Mines", the water level of the indirect aquifer L2 limestone layer 2 is +68.14m, the thickness of the coal seam floor aquifer is 20.38m, and the lowest mining elevation of the No. 1 coal seam 3 in the area is -330m. According to the formula of the "Detailed Rules for Water Control in Coal Mines" (Appendix 5-2), it is calculated as follows: T=P / M Where: M——Reinforcement depth and outer distance m; T——water inrush coefficient, taken as 0.1MPa / m; P——actual water head value, taken as 5.6MPa (L2 limestone layer 2); The water inrush coefficient of the coal seam floor is T=0.2748MPa / m>0.1MPa / m, which poses a great threat of water inrush.

[0035] Step S2: multi-branch horizontal drilling is performed on the target layer with water inrush threat. The multi-branch horizontal drilling includes the following steps: Step S21: Before the mine working face and mining tunnel are excavated, the drilling site is selected on the ground of the area to be treated, at least two secondary landing points are selected (the standard landing point is between 220m and 270m), and the treatment drilling is opened according to the preset trajectory of the wellbore through the drilling control monitoring technology. The treatment drilling includes the injection well 2 4 for exposing the indirect aquifer (i.e., the L2 limestone layer 2) and the injection well 3 5 for exposing the main aquifer (i.e., the L8 limestone layer 1) (see Figure 2 shown); Step S22: The first drilling of the injection well 2 and the injection well 3 uses a roller drill bit to rotate and drill to a certain depth in the stable bedrock, and lowers the primary casing; the second drilling of the injection well 2 and the injection well 3 uses a PDC drill bit to rotate and drill through the coal seam floor to a certain depth in the indirect aquifer and the main aquifer, and lowers the secondary casing; the third drilling of the injection well 2 and the injection well 3 uses a PDC drill bit to rotate and drill forward in the indirect aquifer and the main aquifer to open a main horizontal open hole; Specifically, in step S22, the injection well 2 4 and the injection well 3 5 are first opened by using a Φ311.15mm roller drill bit to rotate and drill to 10m in the stable bedrock 6, and lower the primary casing 7, the size of the primary casing 7 is not less than Φ244.5*8.05mm; the injection well 2 4 and the injection well 3 5 are second opened by using a Φ215.9mm PDC drill bit to rotate through the 21 coal seam 3 and drill to the indirect aquifer (i.e., the L2 limestone layer 2) and the main aquifer (i.e., the L8 limestone layer 1) at a depth of more than 2m, and lower the secondary casing 8, the size of the secondary casing 8 is not less than Φ177.8*8.94mm; the injection well 2 4 and the injection well 3 5 are third opened by using a Φ152.4mm PDC drill bit to rotate and drill forward in the indirect aquifer (i.e., the L2 limestone layer 2) and the main aquifer (i.e., the L8 limestone layer 1) to open a main horizontal open hole 9, so as to complete the horizontal section construction.

[0036] About the preset trajectory of the wellbore: Since the vertical depth of the target layer in the treatment area is shallow and the horizontal footage is long, maintaining an appropriate full-angle change rate (i.e., dogleg degree) and smoothness of the treatment drilling trajectory can effectively reduce the friction of the open hole and the drilling torque, which is beneficial to the treatment drilling construction. Therefore, when designing the preset drilling trajectory, the full-angle change rate (i.e., dogleg degree) is designed to be 5-9°.

[0037] About drilling control detection technology: Drilling control and monitoring technologies include wellbore trajectory control technology, gamma logging, mud logging, and geological guidance technology. Through the drilling control and monitoring technology, real-time monitoring, analysis, and adjustment are carried out during the drilling of Injection 2 Well 4 and Injection 3 Well 5 to ensure that the target strata for treatment are effectively exposed and the grouting reinforcement effect of the target strata for treatment is guaranteed.

[0038] Drilling wellbore trajectory control technology: The drilling wellbore trajectory control technology uses the screw drill as the downhole power, and monitors the drilling trajectory parameters of Note 2 Well 4 and Note 3 Well 5 in real time through the MWD wireless measurement while drilling system. The measured data is compared and analyzed with the preset wellbore trajectory using directional software. The purpose of controlling the drilling trajectory is achieved by adjusting the direction of the screw elbow, and the actual drilling trajectory is extended along the preset wellbore trajectory. The forward direction of the actual drilling trajectory is monitored by the inclinometer while drilling.

[0039] Gamma logging: Real-time monitoring of the rock formations encountered is carried out through azimuth gamma, and real-time analysis is performed based on the signals received on the ground. Then, the well inclination and azimuth are adjusted to achieve in-line drilling of the target formations for treatment, thus ensuring the effective exposure of the target formations for treatment.

[0040] Mud logging includes cuttings logging and drilling logging.

[0041] Rock cuttings logging: For stable bedrock 6 and the second opening, 1 bag of sand samples shall be collected every 1m until drilling is completed. Each bag of samples shall be no less than 200g, and they shall be bagged after sun drying or drying, and then identified and the stratigraphic profile shall be established. The rock cuttings logging table shall be sorted and summarized on site, and a preliminary judgment and division of the stratigraphic formation shall be made. For the third opening, the horizontal section of the target layer shall be collected with no less than 200g of samples per bag, and 1 bag of sand samples shall be collected every 2m until drilling is completed. The rock cuttings logging table shall be sorted and summarized on site, and a preliminary judgment and division of the stratigraphic formation shall be made.

[0042] Drilling logging: Drilling logging starts from the second drilling, and records a drilling point every 1m. This is to facilitate the determination of coal seam burial depth and thickness. Try to keep the relative stability of the drilling parameters to improve the effectiveness of drilling parameters in reflecting the formation lithology, and record the non-geological factors that cause false drilling. The number of missed drilling points in the whole well shall not exceed 0.5% of the total number, and the drilling points of the target layer section shall not be missed. The length of the drill tool and the well depth must be checked frequently. The drill tool must be measured and the well depth must be calibrated before each drilling. The well depth error shall not exceed 0.1m.

[0043] Geological steering technology: using the geological parameters collected in real time near the drill bit, the target layer is predicted and identified in advance, and the borehole trajectory of injection well 2 4 and injection well 3 5 is adjusted as needed to guide the drill bit to accurately drill the target layer. The key to geological steering lies in the real-time measurement and interpretation of the formation parameters near the drill bit, the borehole trajectory parameters and the drill bit working parameters.

[0044] Step S23: A plurality of branch horizontal open holes 91 are opened in the main aquifer (i.e., the L8 limestone layer 1) and the indirect aquifer (i.e., the L2 limestone layer 2), wherein one end of each branch horizontal open hole 91 is connected to the main horizontal open hole 9 and the other end thereof extends into the main aquifer and the indirect aquifer, respectively.

[0045] For details, see Figure 3 , 4 As shown in Figures 5 and 6, in step S23, the number of branches of the branch horizontal open hole 91 is 10-15 and the spacing between adjacent branch horizontal open holes 91 is between 50-55m. A group of boreholes (i.e., including a main horizontal open hole 9 and 10-15 branch horizontal open holes 91) is opened in the L8 limestone layer 1, and a group of boreholes (i.e., including a main horizontal open hole 9 and 10-15 branch horizontal open holes 91) is opened in the L2 limestone layer 2. It should be noted that the branch horizontal open hole 91 can be further branched according to the specific conditions of the coal seam floor in the area to be treated.

[0046] A group of boreholes in the L8 limestone layer 1 and a group of boreholes in the L2 limestone layer 2 are arranged vertically in space, and the spacing between the L2 limestone layer 2 and the L8 limestone layer 1 determines the vertical spacing between the two groups of boreholes. The branch horizontal open holes 91 of the injection well 4 and the branch horizontal open holes 91 of the injection well 5 should be staggered, and the branch horizontal open holes 91 of each group of boreholes are radial. Furthermore, each branch horizontal open hole 91 of the injection well 5 is located between the adjacent branch horizontal open holes 91 corresponding to the injection well 4, so as to achieve a better grouting reinforcement effect. The construction sequence should give priority to the construction of the boreholes in the lower L2 limestone layer 2, and then the construction of the boreholes in the upper L8 limestone layer 1, that is: first construct the injection well 4, and then the injection well 5.

[0047] Step S3: Grouting is performed in the main horizontal open holes and each branch horizontal open hole in the main aquifer and the indirect aquifer respectively to seal and reinforce the target strata for treatment.

[0048] Specifically, the present application adopts injection well 2 to carry out grouting reinforcement on the main horizontal open hole 9 and the branch horizontal open hole 91 in the L2 limestone layer 2, and adopts injection well 3 to carry out grouting reinforcement on the main horizontal open hole 9 and the branch horizontal open hole 91 in the L8 limestone layer 1.

[0049] Furthermore, the present application aims at the possible unexplored hidden structures and vertical water channels in the target strata for treatment, as well as the relatively developed cracks, large pores, and long-term lack of pressure during the grouting process, which leads to ineffective diffusion of the grouting slurry. In this embodiment, fly ash or clay is added to the cement slurry used for grouting and plugging reinforcement of the target strata for treatment, which can effectively reduce the diffusion range of the slurry and avoid the ineffective diffusion of the slurry in the coal seam floor, resulting in the target strata for treatment cannot be effectively reinforced and treated.

[0050] The effect of the advanced treatment of the target layer in this embodiment was verified. By comparing the formation loss (i.e., drilling fluid consumption) before and after grouting reinforcement treatment, it was found that the main aquifer and indirect aquifer were well filled and reinforced after grouting, the cracks were effectively blocked, and the formation loss was significantly reduced. The comparative analysis results are shown in Figure 7 and Figure 8 .

[0051] See also Figure 7 As shown in FIG. 1 , it is a comparison chart of drilling fluid consumption before and after the treatment of L2 limestone layer 2. The lower one is the drilling fluid consumption change curve after treatment, and the upper one is the drilling fluid consumption change curve before treatment. Figure 8 As shown, it is a comparison chart of drilling fluid consumption before and after the treatment of L8 limestone layer 1. The lower one is the drilling fluid consumption change curve after the treatment, and the upper one is the drilling fluid consumption change curve before the treatment.

[0052] It can be seen that the opening of double-layer directional multi-branch horizontal wells and the use of grouting reinforcement management have achieved good results, and effective and advanced management of multi-layer limestone flooding in the coal seam floor has been achieved. Example 2

[0053] The difference between this embodiment and embodiment 1 is that the treatment area contains anticline landforms. When multi-branch horizontal drilling is carried out on the treatment target layer of the anticline landform, the treatment drilling (including injection well 2 and injection well 3) is arranged along the axis direction of the anticline core, and the wellhead of the treatment drilling is set at the high point of the formation. The main horizontal open hole 9 and the branch horizontal open hole 91 extend from the core to the wing. Example 3

[0054] The difference between this embodiment and embodiment 1 is that the treatment area contains syncline landforms. When multi-branch horizontal drilling is carried out on the treatment target layer of the syncline landform, the treatment drilling (including injection well 2 and injection well 3) is arranged along the extension direction of the two wings of the syncline, and the wellhead of the treatment drilling is set at the high point of the formation. The main horizontal open hole 9 and the branch horizontal open hole 91 extend from the core of the two wings of the syncline. Example 4

[0055] The difference between this embodiment and embodiment 1 is that the treatment area contains a fault zone.

[0056] When multi-branch horizontal drilling is carried out for the target layer of the fault zone, the fault with a fall greater than 1.5 times the thickness of the target layer is divided into different plates. The divided plate construction includes: according to the fault characteristics, the upper and lower plates separated by the fault are arranged with treatment drilling wells (including injection well 2 and injection well 3) respectively. When the fault zone is reinforced by grouting, the arranged treatment drilling wells should pass through the fault zone and continue to drill for no less than 50m; For faults with a fault drop less than 1.5 times the thickness of the target layer for treatment, drilling through the fault is carried out from the rising plate to the descending plate. During construction, the trajectory is lowered vertically to the lower part of the target layer for treatment in advance, and then connected to the upper part of the target layer for treatment on the descending plate after passing through the fault.

[0057] The above embodiments of the present invention do not describe all the details in detail, nor limit the present invention to the above embodiments. Various changes, modifications, substitutions and variations made by ordinary technicians in this field without departing from the principles and purpose of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preemptive flood control of multi-layer limestone on coal seam floor, characterized by: The following steps are involved: Step S1: Analyze the hydrogeological characteristics of the coal seam floor in the area to be treated and verify them through drilling to reveal the occurrence of limestone in the coal seam floor; determine the treatment target layer by the consumption of drilling fluid during the drilling process, the treatment target layer includes the main aquifer and the indirect aquifer, calculate the water inrush coefficient of the coal seam floor in the area to be treated according to various parameters of the treatment target layer, and judge whether there is a water inrush threat; Step S2: performing multi-branch horizontal drilling on the target layer with water inrush threat, wherein the multi-branch horizontal drilling comprises the following steps: Step S21: before the mine working face and mining tunnel are excavated, a drilling site is selected on the ground of the area to be treated, at least two secondary landing points are selected, and treatment drilling is opened according to the preset trajectory of the wellbore through drilling control monitoring technology, wherein the treatment drilling includes an injection well 2 for exposing the indirect aquifer and an injection well 3 for exposing the main aquifer; Step S22: The first drilling of the injection well 2 and the injection well 3 uses a roller drill bit to rotate and drill to a certain depth of stable bedrock, and lowers the primary casing; the second drilling of the injection well 2 and the injection well 3 uses a PDC drill bit to rotate and drill through the coal seam floor to a certain depth of the indirect aquifer and the main aquifer, and lowers the secondary casing; the third drilling of the injection well 2 and the injection well 3 uses a PDC drill bit to rotate and drill forward in the indirect aquifer and the main aquifer to open a main horizontal open hole; Step S23: a plurality of branch horizontal open holes are opened in the main aquifer and the indirect aquifer, wherein one end of each branch horizontal open hole is connected to the main horizontal open hole and the other end thereof extends in the main aquifer and the indirect aquifer respectively; Step S3: Grouting is performed in the main horizontal open holes and each branch horizontal open hole in the main aquifer and the indirect aquifer respectively to grout and seal the target layer for treatment.

2. The method for preemptive treatment of multi-layer limestone flooding in coal seam floors according to claim 1, characterized in that: In step S22, the injection well 2 and the injection well 3 are first opened by using a Φ311.15mm roller drill bit to rotate and drill to a depth of 10m in the stable bedrock, and a primary casing is lowered, and the size of the primary casing is not less than Φ244.5*8.05mm; the injection well 2 and the injection well 3 are second opened by using a Φ215.9mm PDC drill bit to rotate through the coal seam floor and drill to a depth of more than 2m in the indirect aquifer and the main aquifer, respectively, and a secondary casing is lowered, and the size of the secondary casing is not less than Φ177.8*8.94mm; the injection well 2 and the injection well 3 are third opened by using a Φ152.4mm PDC drill bit to rotate and drill forward in the indirect aquifer and the main aquifer to open a main horizontal open hole.

3. The method for preemptive treatment of multi-layer limestone flooding in coal seam floors according to claim 1, characterized in that: In step S23, the number of branches of the branch horizontal open holes is between 10 and 15 and the distance between adjacent branch horizontal open holes is between 50 and 55 m.

4. The method for preemptive treatment of multi-layer limestone flooding in coal seam floors according to claim 3 is characterized by: The branch horizontal open holes of the injection well 2 and the branch horizontal open holes of the injection well 3 should be arranged alternately, and the branch horizontal open holes are radial.

5. The method for preemptive treatment of multi-layer limestone flooding in coal seam floors according to claim 4, characterized in that: Each branch horizontal open hole of the injection 3 well is located between adjacent branch horizontal open holes corresponding to the injection 2 well.

6. The method for preemptive treatment of multi-layer limestone flooding in coal seam floors according to claim 1, characterized in that: The full angle change rate in the preset wellbore trajectory is 5 to 9 degrees.

7. The method for preemptive treatment of multi-layer limestone flooding in coal seam floors according to claim 1, characterized in that: The drilling control and monitoring technology includes drilling well trajectory control technology, gamma logging, mud logging, and geological guidance technology. Through the drilling control and monitoring technology, the treatment drilling wellbore is comprehensively monitored, evaluated, and adjusted in real time to ensure that the treatment target layer is effectively exposed and the grouting reinforcement effect of the treatment target layer is guaranteed.

8. The method for preemptive treatment of multi-layer limestone flooding in coal seam floors according to claim 1, characterized in that: Fly ash or clay is added to the cement slurry used for grouting and plugging reinforcement of the target layer.

9. The method for preemptive treatment of multi-layer limestone flooding in coal seam floors according to claim 1, characterized in that: When the area to be treated is an anticline landform, when the wellbore preset trajectory is preset, the treatment drilling is arranged along the axis direction of the anticline core, the wellhead of the treatment drilling is set at the formation high point, and the branch horizontal open hole extends from the core to the wing; When the area to be treated is a syncline landform, when the wellbore preset trajectory is preset, the treatment drilling is arranged along the extension direction of the two wings of the syncline, the wellhead of the treatment drilling is set at the high point of the formation, and the branch horizontal open holes extend from the core of the two wings of the syncline.

10. The method for preemptive treatment of multi-layer limestone flooding in coal seam floors according to claim 1, characterized in that: When the area to be treated is a fault zone, a fault with a fault drop greater than 1.5 times the thickness of the target layer to be treated is subjected to a separate plate construction, wherein the separate plate construction includes: according to the fault characteristics, the upper and lower plates separated by the fault are respectively arranged with the treatment wells, and when the fault zone is grouting reinforced, the arranged treatment wells should pass through the fault zone and continue to be drilled for no less than 50m; For faults with a fault drop less than 1.5 times the thickness of the target layer for treatment, when constructing the treatment drilling through the fault, it is carried out from the rising plate to the descending plate. During construction, the trajectory is lowered vertically to the lower part of the target layer for treatment in advance, and after passing through the fault, it is connected to the upper part of the target layer for treatment on the descending plate.

Images