**1.1 Analysis of recent research and publications on drilling wells for degassing gas-bearing coal seams**

Currently, ensuring the methane safety of coal mining is carried out by two ways. The first way is the land-based method of extracting methane. It provides early degassing of mine fields through wells drilled from the surface and increases the efficiency of methane extraction due to cavern formation or hydraulic fracturing. In Russia, such work was initiated by Academician A.A. Skochinsky about 60 years ago in the Karaganda basin. More than 50 million tons of coal reserves were processed on 10 mine fields through 140 wells. To date, more than 30 million tons of coal have been mined in the early degassing zones.

Degassing of mine fields through wells drilled from the surface was also used in a number of mines in Ukraine. Such work was also carried out at the "Zasyadko" and "Sukhodolskaya-Vostochnaya" mines.

#### *Advanced Technology of Drilling and Hydraulic Loosening in Coal Bed Methane Using… DOI: http://dx.doi.org/10.5772/intechopen.105812*

However, this method of degassing does not provide the necessary efficiency from the standpoint of ensuring outburst hazard. This is due to the fact that, for economic reasons, wells are drilled at a distance of 200 or 300 m from each other and between them there are non-degassed sections of mine fields.

Note that the ground-based method of extracting methane continues to improve. Thus, in China, new technologies are being developed for degassing deep-seated coal seams [3] and multilateral radial borehole hydraulic fracturing "initiating the development of a fracture, increasing the permeability of coal and increasing the volume of gas drainage in the opening zone" (i.e. the technology increases fractures, enhancing coal permeability and raising gas drainage volume in the uncovering area.) [4].

The second way is the degassing of a coal seam from underground workings by static injection of liquid into it was an effective addition to the first method of extracting methane and reduced the problem of outburst hazard.

An analysis of the methods and means of combating gas and dust factors in countries with the most developed coal industry shows that to date, injection of liquid into coal seams is the fundamental method. Due to the preliminary moistening of the coal mass, dust formation and the intensity of gas emission during the destruction of coal are reduced.

In the world practice of conducting mining operations in these areas, a large amount of scientific and technical research has been carried out, on the basis of which regulatory documents have been developed that regulate the conduct of work, their control and evaluation of efficiency. At the same time, an increase in the depth of field development, changes in mining and geological conditions and properties of the coal rock massif have led to a significant decrease in the effectiveness of preventive measures. Analysis of studies shows that under conditions of great depths, the possibilities of fluid injection in a static mode have been exhausted. The widely used methods of hydraulic loosening and hydraulic pressing of the marginal part of outburst-prone formations become insufficiently effective. When fluid is injected, there are cases of spontaneous water breakthrough into the mined-out space and premature hydraulic pressing of the edge part of the formation with the threat of provoking a gas-dynamic phenomenon.

Considering that the equipment and technology for the use of hydraulic loosening and hydraulic pressing are almost the same (they differ only in the parameters of holes or wells and the effect achieved), their main disadvantage can be considered an uncontrolled process of fracturing, which reduces the efficiency of fluid filtration throughout the thickness of the layers and interlayers that make up the coal seam. In addition, the increase in the efficiency of measures related to the injection of liquid into the coal rock mass is constrained by the mining and geological factor—the presence of rocks prone to soaking, collapse, and heaving, and the mining factor—the formation of unloading zones and increased rock pressure in front of the working face. The fluid permeability coefficient k in these zones has directly opposite values, from the free flow of fluid flow through fractures, to the virtual absence of fluid filtration at all (see **Figure 1**).

There is a clear inverse relationship between the water permeability of coal seams and the value of rock pressure *P*. In case of increase in rock pressure, it decreases and, conversely, as the rock pressure decreases, the water permeability of the formation increases. In the marginal, unloaded zone of the formation, the permeability of coal has a maximum value. As the distance from the bottom of the working to the depth of the array, it increases and in the zone of maximum stresses it is practically equal to zero. Further, as the rock pressure decreases, the filtration properties of the formation

**Figure 1.** *Water permeability of coal* k *and the rock pressure* P *from the distance* X *of the working face.*

increase and approach a constant natural value. As practice has shown, when the filtration chamber is located in the unloaded zone, the injected fluid is filtered through cracks into the mined-out space, and when the chamber is located in the zone with increased rock pressure, due to the low water permeability of coal, an uncontrolled process of hydraulic pressing occurs. In this case, the provoking of explosion of methane and coal dust is possible.

The solution to this problem became possible after a number of experimental studies of pulsed fluid injection. In recent years, significant results in this direction have been obtained at the Institute of Geotechnical Mechanics of the National Academy of Sciences of Ukraine (IGTM NASU) in the development of methods and hydropulse action means. The solution to this problem is based on the use of the phenomenon of a periodically stalled cavitation flow of the injected fluid passes through a cavitation hydraulic vibrator.

The cavitation hydraulic vibrator, as an integral part of the drilling tool, was developed by the Institute of Technical Mechanics of the National Academy of Sciences of Ukraine (ITM NASU). This was a new direction in the development of well drilling technologies with submersible impact machines that create dynamic loads on the rock cutting tool using the effects of hydrodynamic cavitation [5]. The drilling tool with a cavitation hydraulic vibrator (for dynamic loads creation in the range of sound frequencies close to the natural frequency of the rock being destroyed) has undergone a full range of experimental studies on hydraulic and drilling stands [6]. An adequate mathematical model of the hydraulic vibrator dynamics has been developed. The model describes complex dynamic processes in the flow channel of the hydraulic vibrator and the vibrator interaction with the drill string structure [7]. The main results of the new technology with the use of the hydrovibrator are presented in [8].

The above studies allowed IGTM NASU in a short time to develop a new method and technology for hydropulse loosening of coal seams [9], as well as a device [10], which implements this method. A significant amount of laboratory research was carried out to substantiate the geometric and operating parameters of the hydrovibrator. At the enterprise of the "Krasnodonugol" PJSC, the hydropulse device was tested under industrial conditions. The new technological schemes and criteria for evaluating the effectiveness of fluid pulsed injection into outburst-hazardous coal seams were developed.

Below are the main results of research into the new technology effectiveness for drilling and loosening outburst hazardous coal seams in a special stand and in industrial coal mining.

*Advanced Technology of Drilling and Hydraulic Loosening in Coal Bed Methane Using… DOI: http://dx.doi.org/10.5772/intechopen.105812*
