**3. Efficiency of hydraulic vibrator operating modes during pilot works on impulse loosening of outburst hazardous coal seams**

For pilot testing the effectiveness of the hydraulic vibrator in loosening outburst hazardous coal seams by the manner prescribed by the rules [16], mining experimental sites were selected. The regulatory and technical documentation necessary for the work was developed, agreed, and approved. Mining and experimental studies of the hydraulic vibrator were carried out in difficult mining and geological conditions of the "Sukhodolskaya-Vostochnaya" and the "Molodogvardeiskaya" mines of "Krasnodonugol" Open Joint Stock Company. The schematic diagram of the hydraulic vibrator and its placement in the well is shown in **Figure 13**.

#### **Figure 13.**

*Schematic diagram of the hydraulic vibrator for hydropulse loosening of coal seams. 1 is manometer; 2 is channel for measuring back pressure; 3 is fluid flow separator; 4 is sealer (ls is hydrovibrator sealing length); 5 is tee; 6 is hydraulic vibrator; 8 is filtration part of the well.*

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

The hydraulic vibrator for hydropulse loosening of coal seams works as follows. The high-pressure water flow through the fluid flow distributor 3 and the tee 5 enters the inlet of the hydraulic vibrator 6. It converts the stationary fluid flow into a pulsating flow, which propagates into the well filtration part 8 and is transferred to the coal mass. The pulse repetition rate lies in the range from 1 to 7 kHz. Impact fluid pressure self-oscillations, reducing the internal and contact coal friction, initiate the development of shear deformation and cracking in differently inclined planes.

The equipment for hydroimpulse loosening of coal seams consists of: the pumping unit 4, the pulse loosening device, including the hydraulic vibrator 10, the Taurus-type sealer 9, the high-pressure hoses 7, and control equipment (the fluid flow meter, pressure gauges 7 and 8). The equipment was installed according to the scheme in **Figure 14**.

Mining and experimental work were carried out in two stages. At the first stage, the hydraulic loosening work was carried out by standard (static injection) [16]. The second stage of the hydraulic loosening work was made by the hydraulic impulse method. According to the results of the studies, the parameters of the two methods were compared and the effectiveness of hydroloosening was evaluated. The results of control and efficiency evaluation were documented in the protocol of mining and experimental work.

The formation hydraulic loosening according to the standard procedure was stopped after the pressure drop in the well was not less than 30% of the maximum pressure. The hydropulse action and evaluation of its effectiveness were carried out under the control of the system of sound catching equipment (ZUA - 98). The hydraulic loosening also stopped when the generator switched to "idle mode." The scope of studies to evaluate hydroimpulse loosening compared to static loosening and to establish the rational working hydrodynamic parameters of pulse loosening of outburst-hazardous coal seams in "Krasnodonugol" mines of amounted to 34 hydroloosening cycles according to the standard mining methodology and 20 hydroloosening cycles in the operation mode of pulsed fluid injection.

As an example, **Figure 15** shows the processes of change in time of the inlet average pressure of the hydraulic vibrator and the pressure in the well during loosening of the outburst-prone formation at a depth of 1300 m of the "Sukhodolskaya-Vostochnaya" mine (a). Fluid injection was carried out through the well with the diameter of 42 mm and the length of 7 m with sealing for the length of *ls* =5m (see **Figure 13**).

#### **Figure 14.**

*Schematic diagram of equipment installation in the face preparatory development during hydraulic loosening of coal seams. 1 is water supply; 2 is valve; 3 is flow meter; 4 is pumping unit; 5 is control valve; 6, 8 are pressure gauges for measuring fluid pressure; 7 is high-pressure sleeve; 9 is sealer; 10 is hydraulic vibrator; 11 is well filtration part; 12 is mining face.*

**Figure 15.** *The time dependence of the inlet hydrovibrator average pressure* Pp *and pressure head at the filtration part of the well* Pb *at a depth of 1300 m (a) and of 617 m (b).*

A similar loosening process is also presented here for outburst-prone layer at a depth of 617 m of the "Molodogvardeiskaya" mine (b). Fluid injection was carried out through a well with the diameter of 42 mm and the length of 6 m with sealing for the length of *ls* = 4 m (see **Figure 14**).

Based on instrumental measurements of injection and water pressure head in the "Sukhodolskaya-Vostochnaya" mine, the following operation modes of hydropulse loosening of the coal seam were established:


#### **Figure 16.**

*The seismogram at the active operation mode of coal seam hydropulse loosening. 1 is the coal seam crack development signal; 2 is the acoustic signal of the operation range of hydraulic impulse loosening: 3 is the acoustic signal of the pumping unit.*

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

• the mode of the completion of the active operation process, with a drop in the pressure of the fluid pressure head in the filtration part of the well with from about 30% or 50% of nominal pressure head level (from 32 to 36 min).

After the completion of the active operation process of cracking, hydropulse loosening becomes ineffective.

The seismogram at the active operation mode of hydropulse loosening of the reservoir by the ZUA-98 equipment is shown in **Figure 16**.

The nature of the time dependence of the acoustic signal of the pressure head oscillations in the well (see the curve 2 in **Figure 16**) during pulse loosening indicates operation of the hydrovibrator in the mode of periodically stalled cavitation. As a result, a system of cracks develops in the coal seam (see the curve 1 in **Figure 16**), which sharply reduces its hydraulic resistance upon completion of the active stage of hydropulse loosening.

The results of pulse loosening of the outburst-prone coal seam of the "Molodogvardeiskaya" mine are shown in **Figure 15b**. As in the previous case, there are three modes of loosening the coal seam:


The results of monitoring the loosening regimes (initial, active, and final stages) of this coal seam are detailed in [17].

A pilot test of the effectiveness of a hydraulic vibrator when loosening outbursthazardous coal seams showed that the pressure of fluid back-up in a well is a fundamental criterion for controlling the completion of the hydroloosening process. The unloading zone of the coal seam at the same time increased from 4 to 8 m. The transformation of the static fluid injection mode into a hydropulse effect on the formation made it possible to achieve:


An analysis of the results of the study of the hydraulic loosening parameters under static and pulsed fluid injection modes at the "Sukhodolskaya-Vostochnaya" and "Molodogvardeiskaya" mines has made a comparative assessment of their effectiveness (see **Table 3**). In the static mode (without cavitation self-oscillations), the fluid


#### **Table 3.**

*Comparative assessment of the efficiency of static and pulse modes of fluid injection (\* is case of fluid broke through the working face along the coal seam).*

injection pressure *Р<sup>p</sup>* was determined within ranges from 0.75 to 1*:*0*γH*, where γ and *H* are the average overlying rocks specific gravity and the formation depth. The required volume of injected fluid was determined by calculation in accordance with the instruction [U]. Under hydropulse action, the pressure *Р<sup>p</sup>* range is less than 0ð Þ *:*75 *γH*, and the injected fluid volume was measured by the flow meter upon completion of the hydraulic loosening process.

Visual observations showed that for case of \*(see **Table 3**.) during static injection of fluid at the "Molodogvardeiskaya" mine, after 15 min of hydraulic action, fluid broke through the working face along the coal seam. This did not allow to pump the standard fluid volume of 1.28 m<sup>3</sup> . For operation in hydrovibrator mode with pulsed fluid injection, no fluid released into the working face from the coal seam.

An analysis of the data given in the table shows that, in accordance with the accepted conditions of hydraulic loosening and evaluation of its effectiveness, the use of hydropulse action allowed, on average, to reduce the time of fluid injection into the reservoir and the volume of fluid injected into the reservoir by more than two times.

## **4. Conclusions**

The advanced technology of drilling and coal seam hydraulic loosening by pulsed fluid injection using a cavitation hydrovibrator has a number of advantages compared with the technology of static fluid injection. The technology achievements consist in the possibility of discrete-pulse impact on the coal seam and lead to a significant increase in the permeability of coal, a decrease in its hydraulic resistance, and an increase in injectivity. This allows researchers to increase the rate of injection of fluid supplied to the coal mass while reducing time costs. As a result, the efficiency of hydraulic loosening increases, the zones of moistening and unloading of the formation increase, the gas emission of methane is intensified, the level of dust formation and the resistance of coal to cutting during its destruction are reduced.

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

The hydraulic vibrator has a number of advantages over other well-known impulse hydraulic means, such as:

