Method for Constructing Artificial Water-Conducting Channel Through Pulse Hydraulic Fracturing of Drainage Boreholes in Roof Aquifer

The application claims priority to Chinese patent application No. 202410577064.1, filed on May 10, 2024, the entire contents of which are incorporated herein by reference.

The present disclosure relates to the technical field of coal mining, and specifically relates to a method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer.

During coal mining, drainage of water from mine roof aquifers is common and challenging. As the focus of coal mining gradually shifts to central and western regions of China, the depth of coal mining gradually increases, and the degree of hydrogeological survey in most mining areas is low. Exploring the water-bearing characteristics of roofs through geophysical prospecting and drilling usually has the defects of “difficult and inaccurate exploration”, and it is difficult to accurately identify the distribution, continuity and other characteristics of water-bearing areas in the roof of coal seam, which leads to lack of effective technical support for the prevention and control of roof water hazards during mining, and makes the drainage of water from mine roof aquifers more complicated and challenging. Particularly during mining, a roof aquifer of a deep mine features a greater water pressure, drastic water level changes, and enhanced groundwater permeability, and water hazards of the mine roof aquifer make mining become increasingly challenging.

If the roof aquifer is not reasonably predicted, evaluated and treated in a targeted manner, mine construction and mining will be severely impacted. Currently, a comprehensive theoretical foundation has been established in the fields of assessment of roof water hazards such as water inrush, aquifer water abundance assessment, and hydrogeological parameter calculation, which enables to accurately predict and evaluate roof water hazards. However, in complex geological conditions such as good water abundance of roof sandstone fissures of the coal seam, heterogeneous aquifer distribution and water conductivity, strong localization, and poor rock permeability, the accuracy of geophysical prospecting cannot meet engineering needs. Drilling pre-drainage is somewhat blind, and the drainage of water from roof sandstone fissures by increasing drainage boreholes has the defects of large quantities and long construction period. Traditional treatment methods such as drilling pre-drainage, grouting reinforcement, and hole sealing and leakage plugging usually yield limited results, including failure to fully drain and control water from roof sandstone fissures. During the mining of the working face, phenomena such as large-scale water seepage of the roof may still occur, which affects the normal operation and safe production of the mine.

Especially for geological conditions such as good water abundance of the coal seam roof, heterogeneous water conductivity and water-bearing characteristics, and strong localization, the conventional method of underground drilling pre-drainage is ineffective in draining the water from roof sandstone fissures. Currently, the method of underground drilling pre-drainage is mainly employed for prospecting and drainage of water from roof sandstone fissures of the coal seam characterized by good water abundance, heterogeneous water conductivity and water-bearing characteristics, and the permeability of sandstone is controlled by the in-situ sandstone rock mass structure. Under normal conditions, the permeability of dense and intact rock masses is poor, and the drilling drainage effect is not ideal. During the mining of the working face, phenomena such as large-scale water seepage of the roof may still occur, which will affect the normal operation and safe production of the working face. Therefore, there is an urgent need to achieve efficient drainage of water from roof sandstone fissures of the coal seam characterized by good water abundance, heterogeneous water conductivity and water-bearing characteristics.

In view of this, the present disclosure is provided.

Sufficient drainage of the mine is fundamental to achieve smooth mining and ensure safe operation. Before mining of the working face, a certain number of prospecting boreholes are usually arranged to effectively control roof water hazards and ensure safe mining of the working face. The prospecting boreholes have functions of both advance exploration and drainage. To fully drain water from the water-rich areas of the roof, the drainage borehole arrangement scheme needs to be designed based on the distribution and continuity of water-bearing areas and water-rich areas of the roof in the mining area, and other hydrogeological characteristics. Drainage boreholes are generally divided into trans-stratal straight boreholes and directional long boreholes.

Under the complex geological conditions such as good water abundance of roof sandstone fissures, discontinuity of the water-bearing areas, and poor permeability of dense and intact sandstone rock masses, drilling boreholes to fully drain water from all discontinuous water-bearing areas not only is labor-intensive but also fails to ensure that the water from roof sandstone fissures is fully drained. The core of solving the above problem is to construct an artificial water-conducting channel in the sandstone fissure aquifer through advance arrangement of drainage boreholes and other technical means, so as to improve the permeability of the dense and intact sandstone rock masses. The artificial water-conducting channel formed in the sandstone fissure aquifer through arrangement of drainage boreholes is connected to the discontinuous water-bearing areas and water-rich areas, and water from roof sandstone fissures is diverted to the drainage boreholes through the artificial water-conducting channel, which achieves effective drainage of the boreholes and expansion of the radiation range of single-borehole drainage.

The boreholes usually used for exploration are relatively limited, which cannot meet the needs of draining water from numerous and discontinuous roof sandstone fissures. Therefore, to effectively drain water from the roof sandstone fissures, it is necessary to design and add drainage boreholes. Arrangement and fracturing of inclined drainage boreholes in a long-short alternating manner not only enable connection to all water-bearing areas within a fracture propagation radius through a single borehole, and effectively increase an area of water drainage from the roof. Additionally, inclined arrangement of drainage boreholes ensures that during the mining process, the water from roof fissures that is not fully drained will flow to the drainage boreholes along the mining-induced fissures due to the rock stratum movement caused by mining, thereby achieving advance water drainage from the working face.

Fracturing refers to the process of injecting a high-pressure fluid (such as water, gas, or the like) through a borehole, which causes the borehole wall to fracture and expand under the action of fluid-solid coupling. An effective technical approach to efficiently drain the water from roof sandstone fissures is to pre-fracture the roof drainage boreholes to form fractures in the sandstone fissure aquifer so as to construct an artificial water-conducting channel. The pumping displacement of conventional hydraulic fracturing is constant, the hydraulic fracture propagation direction is controlled by a three-dimensional geostress field and is perpendicular to the direction of a minimum principal stress, and few hydraulic fractures are formed. In pulse pump fracturing, a high-pressure pulse pump outputs high-frequency pulse pressure water to impact the rock borehole walls, which causes fatigue damage to the rock, and reduces the impact of the geostress field on the initiation and propagation direction of hydraulic fractures, with a dense fracture network formed in the rock.

Therefore, a method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer is provided. The method not only avoids the arrangement of excessive drainage boreholes and significantly improves the drainage efficiency of the prospecting and drainage boreholes, but also facilitates advance drainage during the mining process. The method enables effective control of mine water hazards even under unfavorable geological conditions, thereby ensuring safe production of the mine.

An objective of the present disclosure is to provide a method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer, so as to solve the problems raised in the above background art.

To achieve the above objective, the present disclosure provides the following technical solution:

A method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer, includes the following steps:

Preferably, in the step S:

Preferably, in the step S:

Preferably, in the step S:

Preferably, in the step S:

Preferably, in the step S:

Preferably, in the step S:

Preferably, in the step S:

Preferably, in the step S:

Preferably, in the step S:

Preferably, in the step S:

Preferably, the spherical orifice water shutoff valve and the return flowmeter are connected, the return flowmeter is fixed to a roadway sidewall through a steel band clamp, the return flowmeter is connected to the orifice drainage hose, and the orifice drainage hose is connected to the drainage ditches of the two entries.

Preferably, in the step S:

Preferably, in the step S:

Preferably, in the step S:

Compared with the prior art, a method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer provided in the present disclosure not only avoids the arrangement of excessive drainage boreholes and significantly improves the drainage efficiency of the prospecting and drainage boreholes, but also facilitates advance drainage during the mining process. The method enables effective control of mine water hazards even under unfavorable geological conditions, thereby ensuring safe production of the mine.

Additionally, pulse hydraulic fracturing of drainage boreholes in roof sandstone fissure aquifers has dual functions of drainage and mine pressure control, which not only optimizes the drainage of water from water-bearing areas of the roof sandstone fissures, but also enables to pre-fracture the coal seam roof, reduces a caving interval of the roof during the mining of the working face, and reduces the mine pressure manifestation during the mining of the working face.

To make the above objectives, features, and advantages of the present disclosure easier to understand, preferred examples are specially given below and described below in detail with reference to the accompanying drawings.

The technical solutions in the examples of the present disclosure will be clearly and completely described below in combination with the accompanying drawings in the examples of the present disclosure. Apparently, the examples described are merely some rather than all of the examples of the present disclosure. The assemblies in the examples of the present disclosure described and illustrated in the accompanying drawings usually can be arranged and designed according to various different configurations. Therefore, the following detailed description of the examples of the present disclosure provided in the accompanying drawings is not intended to limit the protection scope of the present disclosure, but only to represent the selected examples of the present disclosure. All other examples acquired by those skilled in the art without making creative efforts based on the examples of the present disclosure fall within the protection scope of the present disclosure.

To fully drain water from roof sandstone fissures, reduce water seepage of the roadway during the mining of the working face, and ensure the normal operation and safe production of the working face, the present disclosure provides a method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer in an example. Specifically, a method for constructing an artificial water-conducting channel through segmented pulse hydraulic fracturing of trans-stratal parallel straight boreholes in a roof aquifer is used to solve the problem of low efficiency of conventional drainage of water from a sandstone fissure aquifer of the roof. The specific steps of the method are as follows:

In case of excessive water outflow from the drainage borehole, adjust the spherical orifice water shutoff valvein time to control the water outflow from the drainage borehole and achieve fully controllable drainage.

As shown in, numerous low-lying areas are distributed on the roof of a coal seam of a mine, which are characterized by extensive water accumulation, discontinuous distribution, strong localization, and heterogeneous stratigraphic distribution. During the mining process, mining-induced destabilization of the roof may cause sudden release of water in the low-lying areas, which may affect the operation area of the working face of a coal mine.

In case of excessive water outflow from the drainage borehole, adjust the spherical orifice water shutoff valvein time to control the water outflow from the drainage borehole and achieve fully controllable drainage.

To solve the problems, the present disclosure provides a method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer in an example. Specifically, a method for constructing an artificial water-conducting channel through segmented pulse hydraulic fracturing of directional long boreholes in a roof aquifer is used to fully drain water from roof sandstone fissures. The specific steps of the method are as follows:

In case of excessive water outflow from the drainage borehole, adjust the spherical orifice water shutoff valvein time to control the water outflow from the drainage borehole and achieve fully controllable drainage.

Since the vast majority of trajectories of the directional long boreholes are in the roof sandstone aquifer, segmented pulse hydraulic fracturing of the directional long boreholes causes significant modification of the aquifer and formation of many artificial water-conducting fissures in the aquifer. Therefore, the drainage coverage of a single borehole is large. Additionally, the borehole strike is parallel to the advancing direction of the working face, which enables the boreholes to also play a role in advance directional drainage during the mining of the working face.

Since the abandoned mine goaf has a large area and an elevated stratigraphic position, it is very difficult to accurately locate a water accumulation area of the goaf through geophysical prospecting. To solve this problem, the present disclosure provides a method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer in an example. According to the method, a plurality of groups of single-inclined trans-stratal boreholes are arranged near the abandoned mine goaf for segmented pulse hydraulic fracturing to drain the water accumulated in the abandoned mine goaf. The specific steps of the method are as follows:

In case of excessive water outflow from the drainage borehole, adjust the spherical orifice water shutoff valvein time to control the water outflow from the drainage borehole and achieve fully controllable drainage.

In case of excessive water outflow from the drainage borehole, adjust the spherical orifice water shutoff valvein time to control the water outflow from the drainage borehole and achieve fully controllable drainage.

In the present disclosure, sufficient drainage of the mine is fundamental to achieve smooth mining and ensure safe operation. Before mining of the working face, a certain number of prospecting boreholes are usually arranged to effectively control roof water hazards and ensure safe mining of the working face. The prospecting boreholes have functions of both advance exploration and drainage. To fully drain water from the water-rich areas of the roof, the drainage borehole arrangement scheme needs to be designed based on the distribution and continuity of water-bearing areas and water-rich areas of the roof in the mining area, and other hydrogeological characteristics. Drainage boreholes are generally divided into trans-stratal straight boreholes and directional long boreholes.

Under the complex geological conditions such as good water abundance of roof sandstone fissures, discontinuity of the water-bearing areas, and poor permeability of dense and intact sandstone rock masses, drilling boreholes to fully drain water from all discontinuous water-bearing areas not only is labor-intensive but also fails to ensure that the water from roof sandstone fissures is fully drained. The core of solving the above problem is to construct an artificial water-conducting channel in the sandstone fissure aquifer through advance arrangement of drainage boreholes and other technical means, so as to improve the permeability of the dense and intact sandstone rock masses. The artificial water-conducting channel formed in the sandstone fissure aquifer through arrangement of drainage boreholes is connected to the discontinuous water-bearing areas and water-rich areas, and water from roof sandstone fissures is diverted to the drainage boreholes through the artificial water-conducting channel, which achieves effective drainage of the boreholes and expansion of the radiation range of single-borehole drainage.

The boreholes usually used for exploration are relatively limited, which cannot meet the needs of draining water from numerous and discontinuous roof sandstone fissures. Therefore, to effectively drain water from the roof sandstone fissures, it is necessary to design and add drainage boreholes. Arrangement and fracturing of inclined drainage boreholes in a long-short alternating manner not only enable connection to all water-bearing areas within a fracture propagation radius through a single borehole, and effectively increase an area of water drainage from the roof. Additionally, inclined arrangement of drainage boreholes ensures that during the mining process, the water from roof fissures that is not fully drained will flow to the drainage boreholes along the mining-induced fissures due to the rock stratum movement caused by mining, thereby achieving advance water drainage from the working face.

Fracturing refers to the process of injecting a high-pressure fluid (such as water, gas, or the like) through a borehole, which causes the borehole wall to fracture and expand under the action of fluid-solid coupling. An effective technical approach to efficiently drain the water from roof sandstone fissures is to pre-fracture the roof drainage boreholes to form fractures in the sandstone fissure aquifer so as to construct an artificial water-conducting channel. The pumping displacement of conventional hydraulic fracturing is constant, the hydraulic fracture propagation direction is controlled by a three-dimensional geostress field and is perpendicular to the direction of a minimum principal stress, and few hydraulic fractures are formed. In pulse pump fracturing, a high-pressure pulse pump outputs high-frequency pulse pressure water to impact the rock borehole walls, which causes fatigue damage to the rock, and reduces the impact of the geostress field on the initiation and propagation direction of hydraulic fractures, with a dense fracture network formed in the rock.

Therefore, a method for constructing an artificial water-conducting channel through pulse hydraulic fracturing of drainage boreholes in a roof aquifer is provided. The method not only avoids the arrangement of excessive drainage boreholes and significantly improves the drainage efficiency of the prospecting and drainage boreholes, but also facilitates advance drainage during the mining process. The method enables effective control of mine water hazards even under unfavorable geological conditions, thereby ensuring safe production of the mine.

In the above examples, the drainage boreholes include the prospecting and drainage boreholes used for geophysical prospecting and drainage and drainage boreholes used for advance drainage and construction of an artificial water-conducting channel through pulse hydraulic fracturing, and the drainage boreholes are divided into trans-stratal straight boreholes and directional trans-stratal long boreholes.

The borehole arrangement scheme includes borehole arrangement parameters and borehole arrangement forms.