Sandstone layer water level protection method based on ground directional drilling hydraulic curtain

Abstract

The invention discloses a sandstone layer water level protection method based on a ground directional drilling hydraulic curtain. The sandstone layer water level protection method comprises the following steps that firstly, hydrogeological conditions of a coal mine area and hydrogeological conditions of a water source area protection area are analyzed respectively; the hydrogeological conditions of the coal mine area comprise a water-resisting layer-containing space structure, a burial depth and a mining method of mining coal seam overlying strata of a coal mining working face of the coal mine area; the cretaceous system sandstone aquifer is recharged between the water source area protection area and the coal mine area through the nearly-horizontal directional recharge drill holes, a strip-shaped high-water-level hydraulic curtain wall is formed, runoff of underground water of the cretaceous system sandstone aquifer in the water source area protection area to the coal mine area can be controlled, and the underground water level protection target can be achieved. Compared with water-preserved coal mining methods such as layering, height limiting, striping, filling and paralleling, the technical problem of how to reduce the influence of coal mining on the water-containing water level of water supply of a water source area while ensuring efficient mining of coal resources in the prior art is effectively solved.

Description

Technical Field

[0001] The present invention belongs to the field of underground water resources and environmental protection in coal mining areas, and relates to a water level protection method, in particular to a water level protection method for sandstone layers based on a ground directional drilling hydraulic curtain Background Art

[0002] Due to the large-scale pumping of groundwater in the deep mining areas of the Jurassic coalfields in the western region, a groundwater drawdown funnel centered on the coal mining and excavation space has been formed, resulting in the runoff and drainage of the aquifer within the protection area of the peripheral water source to the coal mining area under the action of the hydraulic gradient. Since there is no stable water-resisting layer between the Cretaceous sandstone aquifer and the overlying Quaternary pore aquifer, it is easy to cause a significant drop in the water levels of the Cretaceous sandstone aquifer and the Quaternary pore aquifer in the water source protection area, resulting in problems such as the inability of the water intake wells in the water source area to supply water (the pumping wells dry up due to the drop in the water level) and even ground ecological degradation. The development of coal resources in the western mining area is the most important pillar to support the regional national economic development. Ensuring the groundwater level of the water source area under normal coal mining conditions is an important aspect of realizing the coordinated exploitation of coal and water resources and ecological protection

[0003] In the western region, the main mining coal seams are located in the Jurassic Yan'an Formation coal seams. Due to the control of the regional monoclinic structure, the burial depth of the main mining coal seams shows an obvious trend of being shallower in the east and deeper in the west, with a general burial depth of more than 600 m and a maximum of over 800 m. The overlying strata of the coal seam are, from bottom to top, the Jurassic Yan'an Formation and Zhiluo Formation sandstone aquifers, the Anding Formation sandy mudstone relatively water-resisting layer, the Cretaceous sandstone aquifer, and the Quaternary pore aquifer

[0004] Since there is no stable water-resisting layer between the Cretaceous sandstone aquifer and the overlying Quaternary pore aquifer, the Cretaceous sandstone aquifer and the near-surface Quaternary pore aquifer (collectively referred to as the water conservation target layer) together constitute an important water supply aquifer and ecological protection layer for water sources such as Chagannaoer and Ganzhumiao in Ordos City. That is, the near-surface Cretaceous sandstone aquifer is designated as the target aquifer for the protection of underground water resources in the western coal mining areas of China

[0005] A large number of actual measurement results show that in coal mining areas, first, when the mining-induced water-conducting fissures formed by coal seam mining in the mining area directly expose the Cretaceous sandstone aquifer, the groundwater in this aquifer directly flows away along the mining-induced water-conducting fissures; second, even if the mining-induced water-conducting fissures formed by coal seam mining do not directly break through the relatively water-resistant Jurassic Anding Formation below the Cretaceous sandstone aquifer, after coal seam mining, the groundwater in the lower Jurassic Zhiluo Formation and Yan'an Formation aquifers directly leaks and the water level drops suddenly, resulting in a large water head difference (or water level difference) between the upper Cretaceous sandstone aquifer and the Jurassic Zhiluo Formation and Yan'an Formation sandstone aquifers within the surrounding area of the coal seam mining area. Under the action of the large water head difference, it will also cause a large amount of cross-flow leakage of groundwater between the near-surface Quaternary pore aquifer and the Cretaceous sandstone aquifer and a significant drop in the groundwater level. Therefore, a low water level area is formed in the coal mining area, while the water levels of the near-surface Quaternary pore aquifer and the Cretaceous sandstone aquifer (collectively referred to as the water conservation target layer) in the water source protection area are relatively high. Under the action of the hydraulic gradient, it causes the groundwater resources of the water conservation target layer in the water source protection area to runoff and discharge to the coal mining area, which easily leads to problems such as the decline of the water level of the Cretaceous sandstone aquifer in the water source protection area, the inability of the water intake wells in the water source area to supply water, and even the degradation of the ground ecology.

[0006] At present, the water resource protection coal mining methods mainly focus on optimizing the coal mining technology. By means of coal mining methods such as "stratified, height-limited, strip, backfilling, and parallel", the development height of water-conducting fractures is inhibited, but there are technical problems of high cost and low coal resource recovery rate. And through grouting reinforcement, constructing underground continuous curtain impervious walls, etc., they have also been gradually applied to the engineering practice of protecting the near-surface strongly water-rich Quaternary aquifer. However, under the conditions of large buried depth and large thickness of the water conservation aquifer, there are problems such as construction difficulty and excessive investment cost. Protecting the groundwater level of aquifers with ecological significance and water supply significance during the development process of coal resources in ecologically fragile areas is the core of water conservation coal mining and has reached a consensus in the field of water conservation coal mining. How to reduce the impact of coal mining on the water level of the water supply aquifer in the water source area while ensuring the efficient exploitation of coal resources is a long-term technical problem that is difficult to solve in this field. Summary of the Invention

[0007] Aiming at the deficiencies of the existing technology, the purpose of the present invention is to provide a method for protecting the water level of sandstone layers based on a hydraulic curtain of surface directional drilling to solve the technical problem of how to reduce the impact of coal mining on the water level of the water supply aquifer in the water source area while ensuring the efficient exploitation of coal resources in the existing technology.

[0008] To solve the above technical problems, the present invention is realized by adopting the following technical solutions:

[0009] A method for protecting the water level of sandstone layers based on a hydraulic curtain of surface directional drilling, comprising the following steps:

[0010] Step 1: Analyze the hydrogeological conditions of the coal mining area and the water source protection area respectively;

[0011] The hydrogeological conditions of the coal mining area include the spatial structure, burial depth, and mining method of the aquitard and aquifer in the overlying strata of the coal seam in the coal mining face of the coal mining area;

[0012] The hydrogeological conditions of the water source protection area include the spatial structure of the aquitard and aquifer in the water source protection area, as well as the thickness and pore structure of the Cretaceous sandstone aquifer from which water is taken in the water source protection area;

[0013] Step 2: Construct a nearly horizontal directional recharge borehole on the ground;

[0014] Construct a group of nearly horizontal directional recharge boreholes in the Cretaceous sandstone aquifer on the ground between the boundary of the water source protection area and the boundary of the coal mining area;

[0015] The nearly horizontal directional recharge borehole has one main hole, and a plurality of branch holes are arranged at equal intervals on the main hole, and the plurality of branch holes are parallel to each other;

[0016] Step 3: Recharge the water body;

[0017] Continuously inject the recharge water into the Cretaceous sandstone aquifer through the nearly horizontal directional recharge borehole to form a "high water level" hydraulic curtain wall;

[0018] The recharge water includes mine water, surface water, and groundwater that meet the recharge standard after treatment, and the water quality of the mine water, surface water, and groundwater is better than the water quality of the groundwater in the recharge layer.

[0019] The present invention further includes the following technical features:

[0020] In Step 2, estimate the vertical spacing d, m between adjacent branch holes in the nearly horizontal directional recharge borehole according to Formula (1) and Formula (2);

[0021]

[0022] d = 2R (2)

[0023] Where:

[0024] Q is the recharge water volume, m 3 / d;

[0025] M is the thickness of the recharge aquifer, m;

[0026] K is the permeability coefficient of the recharge aquifer, m / d;

[0027] r w is the radius of the recharge well borehole, m;

[0028] R is the recharge influence radius, m;

[0029] $H_0$ is the initial static water level of the aquifer under the condition of no recharge after being affected by coal seam mining, in m;

[0030] $h$ w is the water level after recharge of the aquifer, in m;

[0031] $d$ is the vertical spacing of the recharge branch holes, in m.

[0032] In step two, calculate the number $N$ of branch holes in the nearly horizontal directional recharge boreholes during construction;

[0033] $N = M / d - 1\ (3)$

[0034] Where:

[0035] $M$ is the thickness of the recharge aquifer, in m, and $M / d$ is rounded to an integer, $M / d\geq2$.

[0036] Step three specifically includes the following steps:

[0037] Step 3.1, recharge the recharge water into the Cretaceous sandstone aquifer at a certain pressure through the nearly horizontal directional recharge boreholes obtained in step two;

[0038] Step 3.2, when the water level of the Cretaceous sandstone aquifer after recharge rises to the bottom plate of the Quaternary pore phreatic aquifer, adopt unpressurized recharge, that is, form a "high water level" hydraulic curtain wall.

[0039] It also includes: observing the groundwater level between the water source protection area and the coal mining area through observation wells. When the water level rises to the high water level and a "high water level" hydraulic curtain wall is formed, continuously inject water into the Cretaceous sandstone aquifer without pressure or at low pressure;

[0040] The observation wells are arranged on both sides of the nearly horizontal directional recharge boreholes and are parallel to the nearly horizontal directional recharge boreholes.

[0041] The distance between the observation wells and the directional recharge boreholes is 5 - 10 m.

[0042] Compared with the prior art, the beneficial technical effects of the present invention are:

[0043] (Ⅰ) Between the water source protection area and the coal mining area, recharge the Cretaceous sandstone aquifer through nearly horizontal directional recharge boreholes to form a strip-shaped "high water level" hydraulic curtain wall, which can control the runoff of groundwater in the Cretaceous sandstone aquifer in the water source protection area to the coal mining area, and can achieve the groundwater level protection goal. Compared with the water conservation coal mining methods such as "stratification, height limit, strip, filling, parallel", it effectively solves the technical problem in the prior art of how to reduce the influence of coal mine mining on the water level of the water source supply aquifer while ensuring the efficient exploitation of coal resources.

[0044] (Ⅱ) In the present invention, the water body forms a "high water level" hydraulic curtain wall by means of natural recharge or low-pressure recharge, and the water level of the Cretaceous sandstone aquifer can be simply controlled by the recharge pressure, making the construction process relatively simple, the operation cost low, and the operation convenient.

[0045] (Ⅲ) Without changing the coal mining process, this application obviously has the technical advantages of low cost and high coal resource recovery rate. Description of the Drawings

[0046] Figure 1 It is a schematic cross-sectional view of the water level of the Cretaceous sandstone aquifer during normal mining in the coal mining area;

[0047] Figure 2 It is a schematic plan view of the directional water injection boreholes between the coal mining area and the protection area;

[0048] Figure 3 It is a schematic cross-sectional view of the directional water injection boreholes between the coal mining area and the protection area;

[0049] Figure 4 It is a schematic cross-sectional view of the water level rising effect of the aquifer under the directional borehole water injection curtain between the coal mining area and the protection area.

[0050] The following further elaborates on the specific content of the present invention in conjunction with the embodiments. Specific Embodiments

[0051] It should be noted that all components in the present invention, without special instructions, are components known in the art.

[0052] The following gives specific embodiments of the present invention. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent transformations made on the basis of the technical solutions of this application fall within the protection scope of the present invention.

[0053] The present invention provides a method for protecting the water level of sandstone layers based on a ground directional borehole hydraulic curtain. Refer to Figures 1 to 4 , which includes the following steps:

[0054] Step 1: Analyze the hydrogeological conditions of the coal mining area and the hydrogeological conditions of the water source protection area respectively;

[0055] The hydrogeological conditions of the coal mining area include the spatial structure, burial depth, and mining method of the aquiclude and aquifer in the overlying strata of the coal seam mined in the coal mining area working face;

[0056] The hydrogeological conditions of the water source protection area include the spatial structure of the aquiclude and aquifer in the water source protection area, as well as the thickness and pore structure of the Cretaceous sandstone aquifer from which water is taken in the water source protection area;

[0057] Step 2: Construct nearly horizontal directional recharge boreholes on the construction ground;

[0058] Construct a set of nearly horizontal directional recharge boreholes in the Cretaceous sandstone aquifer on the ground between the boundary of the water source protection area and the boundary of the coal mining area;

[0059] The nearly horizontal directional recharge borehole has one main hole, and multiple branch holes are arranged at equal intervals on the main hole, and the multiple branch holes are parallel to each other;

[0060] Step 3: Recharge water body;

[0061] Continuously inject the recharge water into the Cretaceous sandstone aquifer through the nearly horizontal directional recharge boreholes to form a "high water level" hydraulic curtain wall;

[0062] The recharge water includes mine water, surface water and groundwater that meet the recharge standard after treatment, and the water quality of mine water, surface water and groundwater is better than the groundwater quality of the recharge layer.

[0063] In Step 3, the "high water level" hydraulic curtain wall can control the runoff loss of groundwater in the protection area aquifer to the coal mining space and achieve the groundwater level protection goal.

[0064] Between the water source protection area and the coal mining area, recharge the Cretaceous sandstone aquifer through nearly horizontal directional recharge boreholes to form a strip-shaped "high water level" hydraulic curtain wall, which can control the runoff of groundwater in the Cretaceous sandstone aquifer in the water source protection area to the coal mining area and can achieve the groundwater level protection goal. Compared with the water-preserving coal mining methods such as "stratification, height limitation, strip, filling, parallel", it effectively solves the technical problem of how to reduce the impact of coal mining on the water level of the water source area while ensuring the efficient extraction of coal resources in the prior art.

[0065] The water body is formed into a "high water level" hydraulic curtain wall by natural recharge or low-pressure recharge, and the water level of the Cretaceous sandstone aquifer can be simply controlled by the recharge pressure, so that the construction process is relatively simple, the operation cost is low, and the operation is simple.

[0066] The present invention further includes the following technical features:

[0067] In Step 2, estimate the vertical spacing d, m between adjacent branch holes in the nearly horizontal directional recharge borehole according to Formula (1) and Formula (2);

[0068]

[0069] d = 2R (2)

[0070] Where:

[0071] Q is the recharge water volume, m 3 / d;

[0072] M is the thickness of the recharge aquifer, in m;

[0073] K is the permeability coefficient of the recharge aquifer, in m / d;

[0074] r w is the radius of the recharge well bore, in m;

[0075] R is the radius of influence of recharge, in m;

[0076] H0 is the initial static water level of the aquifer under the influence of coal seam mining and before recharge, in m;

[0077] h w is the water level of the aquifer after recharge, in m;

[0078] d is the vertical spacing of the recharge branch holes, in m.

[0079] In the above technical solution, according to the on-site construction parameters and on-site tests, the recharge water volume Q, the thickness M of the recharge aquifer, the permeability coefficient K of the recharge aquifer, and the radius r of the recharge well bore w , the initial static water level H0 of the aquifer under the influence of coal seam mining and before recharge, and the water level h of the aquifer after recharge w and other parameter values can be obtained. Substituting the parameters into formula (1) can obtain the value of the radius of influence of recharge R, and then the well spacing of the recharge well can be obtained through formula (2).

[0080] In step two, calculate the number N of branch holes in the nearly horizontal directional recharge borehole during construction;

[0081] N = M / d - 1 (3)

[0082] Where:

[0083] M is the thickness of the recharge aquifer, in m, and M / d is rounded to an integer, M / d ≥ 2.

[0084] Step three specifically includes the following steps:

[0085] Step 3.1, recharge the recharge water into the Cretaceous sandstone aquifer at a certain pressure through the nearly horizontal directional recharge borehole obtained in step two;

[0086] Step 3.2, when the water level of the Cretaceous sandstone aquifer after recharge rises to the bottom plate of the Quaternary pore phreatic aquifer, adopt unpressurized recharge, that is, form a "high water level" hydraulic curtain wall.

[0087] In the above technical solution, because the sandstone layer structure is relatively dense, the permeability is general, and the water absorption capacity of the recharge water is limited, so low-pressure recharge is adopted first during the recharge process; but due to the loose pore structure and strong permeability of the Quaternary strata, unpressurized recharge is adopted later.

[0088] In Step 3.1, the water injection pressure at the ground orifice is greater than or equal to 1.5*D / 100, with the unit of MPa, where D is the buried depth of the water injection borehole in meters, so as to form a "high water level" hydraulic curtain wall with the long-distance nearly horizontal water injection borehole as the center line between the boundary of the water source protection area and the boundary of the coal mining area.

[0089] In Step 3.2, by observing the change of the groundwater level in the recharge layer, when the water level of the Cretaceous sandstone aquifer after recharge rises to the bottom plate of the Quaternary pore phreatic aquifer, unpressurized or low-pressure continuous recharge is adopted. The water injection pressure at the ground orifice is 0 to (D - Ms) / 100, with the unit of MPa, where D is the buried depth of the water injection borehole and Ms is the buried depth of the bottom plate of the overlying Quaternary strata in meters. That is, the water injection pressure at the ground of the water injection hole is greater than the hydrostatic pressure of the water injection layer but not greater than the hydrostatic pressure generated by the buried depth of the water injection layer, so as to ensure the continuous injection of the recharge water and prevent the recharge water from overflowing the ground surface. Thus, a dynamic and stable "high water level" hydraulic curtain wall with the long-distance nearly horizontal water injection borehole as the center line is formed between the boundary of the water source protection area and the boundary of the coal mining area.

[0090] It also includes: observing the groundwater level between the water source protection area and the coal mining area through observation wells. When the water level rises to the high water level and a "high water level" hydraulic curtain wall is formed, continuously injecting water into the Cretaceous sandstone aquifer without pressure or at low pressure;

[0091] The observation wells are arranged on both sides of the nearly horizontal directional recharge borehole and are parallel to the nearly horizontal directional recharge borehole.

[0092] In the above technical solution, after the "high water level" hydraulic curtain wall is formed, continuously injecting water into the Cretaceous sandstone aquifer without pressure can effectively ensure the stability of the formed high water level hydraulic curtain wall and prevent the recharge water from running off or even overflowing the ground surface through the highly permeable Quaternary strata.

[0093] The distance between the observation well and the directional recharge borehole is 5 - 10 m.

[0094] In the above technical solution, the observation wells can reflect the groundwater level between the water source protection area and the coal mining area in real time, and the interval distance of 5 - 10 m is optimal.

Claims

1. A sandstone layer water level protection method based on ground directional drilling hydraulic curtain, characterized in that: The following steps are involved: Step 1: Analyze the hydrogeological conditions of the coal mining area and the hydrogeological conditions of the water source protection area respectively; The hydrogeological conditions of the coal mining area include the spatial structure, burial depth and mining method of the aquiclude of the overburden of the mining coal seam at the coal mining face in the coal mining area; The hydrogeological conditions of the water source protection area include the spatial structure of the aquiclude in the water source protection area, as well as the thickness of the Cretaceous sandstone aquifer and the pore structure of the water-bearing medium from which water is drawn from the water source; Step 2: Drilling holes for directional recharging near the horizontal surface of the construction ground; A group of nearly horizontal directional recharge boreholes were constructed in the Cretaceous sandstone aquifer between the boundary of the water source protection area and the boundary of the coal mining area; The nearly horizontal directional recharging drilling hole has a main hole, and a plurality of branch holes are arranged at equal intervals on the main hole, and the plurality of branch holes are parallel to each other; Step 3: water recharging; The recharge water is continuously injected into the Cretaceous sandstone aquifer through a near-horizontal directional recharge borehole to form a "high water level" hydraulic curtain wall; The recharge water includes mine water, surface water and groundwater that meet the recharge standard after treatment, and the water quality of the mine water, surface water and groundwater is better than the water quality of the recharge layer groundwater.

2. The sandstone layer water level protection method based on the ground directional drilling hydraulic curtain as claimed in claim 1 is characterized in that: In step 2, the vertical spacing d, m, between adjacent branch holes in the nearly horizontal directional recharge borehole is estimated according to formula (1) and formula (2); d=2R (2) in: Q is the amount of recharge water, m 3 / d; M is the thickness of the recharge aquifer, m; K is the permeability coefficient of the recharge aquifer, m / d; r w is the radius of the reinjection well borehole, m; R is the reinjection influence radius, m; H0 is the initial static water level of the aquifer without recharge after the impact of coal mining, m; h w is the water level after aquifer recharge, m; d is the vertical spacing of the reinjection branch holes, m.

3. The sandstone layer water level protection method based on the ground directional drilling hydraulic curtain as claimed in claim 2 is characterized in that: In step 2, the number N of branch boreholes in the nearly horizontal directional recharging borehole is calculated; N=M / d-1 (3) in: M is the thickness of the recharge aquifer, m, and M / d is rounded to the nearest integer, M / d≥2.

4. The sandstone layer water level protection method based on the ground directional drilling hydraulic curtain as claimed in claim 1 is characterized in that: Step three specifically includes the following steps: Step 3.1, recharging the recharge water at a certain pressure into the Cretaceous sandstone aquifer through the nearly horizontal directional recharge borehole obtained in step 2; In step 3.2, when the water level of the Cretaceous sandstone aquifer after recharging rises to the bottom plate of the Quaternary porous phreatic aquifer, pressureless recharging is adopted to form a "high water level" hydraulic curtain wall.

5. The sandstone layer water level protection method based on the ground directional drilling hydraulic curtain as claimed in claim 1, characterized in that: Also includes: The groundwater level between the water source protection area and the coal mining area is observed through observation wells. When the water level rises to a high level and forms a "high water level" hydraulic curtain wall, water is continuously injected into the Cretaceous sandstone aquifer without pressure or at low pressure. The observation wells are arranged on both sides of the nearly horizontal directional reinjection borehole and are parallel to the nearly horizontal directional reinjection borehole.

6. The sandstone layer water level protection method based on the ground directional drilling hydraulic curtain as claimed in claim 5, characterized in that: The observation well and the directional recharge borehole are spaced 5 to 10 m apart.

Images