Journal of Mining Science, Vol. 31, No. 3, May-June, 1995

DUST C O N D I T I O N S O F S T O P E S E C T I O N S I N Z O N E S O F " F O R C E A C T I O N " O N KI2 C O A L S E A M S

A. E. Perezhilov, E. Ya. Dikolenko,

UDC 622.907:519.2

V. S. Khar'kovskii, and A. V. Krysin

In order to increase the daily loading per stope, accelerate preliminary workings, and create safe conditions for conducting mining operations on the floor of the Saranskaya mine of the Karagandaugol' Production Association, wells were &flied from the surface for hydraulic fracturing ("disjointing") of the series of coal seams KT, KIo, Kll, and K12. The indexes of the "force actions"* on the coal seams are listed in Table 1, and data on the takeoff of methane from the wells driIled into the seams are presented in Table 2. As the object of investigation of dust conditions in certain worked sections, the characteristics of which are shown in Table 3, we selected seam K12, which is high-gas and blowout-hazardous, and is classed in groups 4-6 with respect to dust level. The K12 seam consists of 20 bands of coal interlayered with argillites with a thickness of 0.2-2.5 cm, with inclusion of pyrite interlayers with the coal. The seam was worked by regular longwalls along the strike. The dust control measures that are being implemented in the stopes of the mine consist of wetting the coal in place and the use of a typical watering system mounted on the combines. With the aim of evaluating the dust conditions of the stope sections that are shown schematically in Fig la, surveys were performed at characteristic points of the test areas of these sections (Fig. lb), both inside and outside the zones of the force actions on the K]2 coal seam. Dust samples were taken on AFA filters by means of an At~RA aspirator, following known procedures. In these test areas of the longwall, coal samples were taken for laboratory determinations of moisture content, hardness, and porosity, using standard methods. It was established by underground investigation that the efficiency of prewetting the K12 seam varied from 20% to 45 %. This great variation of efficiency of the method is due mainly to nonuniformity of water distribution through the seam and f'filing of large cracks and pores in the zone near the well, and also escape of part of the water into the adjacent mine workings, including losses due to leaks at the wellhead as a result of prolonged degassing of the seam. Moreover, the quality of moisture saturation of the coal was low, owing to time-limited capillary impregnation of the seam and the current lack of any method for real-time monitoring to determine the junction of hydraulic action zones between neighboring injection wells. The efficiency of a typical watering system in working coal reserves that had been prepared for stoping was 50% on the average, thus confirming the results of earlier studies. Analysis of the experimental data demonstrated that outside the hydraulic fracture zones of the seam, with a coal moisture content of 3.3% and coal hardness from 0.91 to 1.05, the dust content of the air at a distance of 5-8 m from the combine along the course of the ventilation stream averaged 2000 mg/m3. In the sections of hydraulic fracturing of the K12 seam through surface wells, no prewetting operation was performed on the coal in place.

*This literal translation of the Russian term denotes any method of applying external force, including hydraulic pressure -Translator. MGGU, Moscow. Rosugol' Company, Moscow. Polytechnic Institute, Karaganda. Karaganda Scientific-Research Institute of Coal (KNIUI), Karaganda. Translated from Fiziko-Tekhnicheskie Problemy Razrabotld Poleznykh Iskopaemykh, No. 3, pp. 74-79, May-June, 1995. Original article submitted June 22, 1994.

1062-7391/95/3103-0221512.50 ©1995 Plenum Publishing Corporation

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Fig. 1. *As in Russian original - Translator. This graphic material provides a good illustration of the character of the interrelation between dust content of the air ahead of the stoping combine along the course of the ventilation flow and the position of the test sections of the longwall relative to the line of the surface wells No. 3-bis (Fig. 2a), .No. 1 (Fig. 3a), No. 4 (Fig. 4a), and No. 5 (Fig. 5), the moisture content of the coal (Fig. 2b and Fig. 4b), the hardness of the coal (Fig. 3b), and the porosity of the coal (Fig. 3c). In Figs. 1-5, the numbers denote the number of observations in application to the particular conditions. An analysis of the results from these studies reveals a clear trend toward a shift of the minimum dust content of air in longwalls relative to the line of surface wells amounting to 70-100 m (see Figs. 2a, 4a, and 5); this is related to pneumatic displacement of the working liquid into the depth of the rock mass and takeoff of methane by the seam wells (see Table 2). With increasing moisture content of the coal, the dust content of the air in the stopes in Combine coalmining through the upper layer of the K12 seam decreases nonlinearly (see Figs. 2b and 4b); with increasing hardness of the coal, the dust conditions at the working sites become poorer (see Fig. 3b). With increasing pore volume in the zones of hydraulic fracturing of the coal seam through surface wells and takeoff of methane through seam wells, there is no clear trend in the variation of dust conditions on the longwall (see Fig. 3c), and additional studies are needed. As shown by experience, however, in zones o f uncompleted hydraulic fracturing wells, the efficiency of hydraulic fracturing in terms of the dust factor is higher than when pumping out a working fluid previously injected into the seam and degassing the coat seam; this is related to draining of the seam, particularly in the coal zone close to the well.

222

TABLE 1

Mean values

Volume injected Well No.

1

2 3-bis 4

Depth of occurrSeam ~eam ence of . index :hick- seam m .to~, ~ess, ' m m

K7

K10 KI1 K12 s

):7

KI0 Kll Kz2

6121 3102 7011 3586 6876 2899 7870 7883 2145 9881 6903 2068 200C 6282

469 4O7 472 409 485 422 549 484 444 414 550 487 452 419

5,6 7,0 5,2 7,2 5,2 6,0 5,2 5,0 2,8 4,8 5,2 5,8 2,4 7,6

Klo Kt2 Kzo Kt2 Kzo K12

" well injection heroical sur- : rate, i)iters/sec gent factat I HCI), (DB) 3trees kg water chemical agent 120 81 1 I0 142 165 185 69 182 -230 102 74 -212

600 300 200 100

440 120 730 6(]0

-765 580 120 20 160

Steadystate pressure Method of well completion* at welthead, MPa

65,2 ) 69.6 66,2 I 72,5 61,2 58,2 56,7 56,2 72,5 36,5

lS 12 19 9 11

30,0 40,4

3 14

37,0 28,0 34,0 --

57,7 87.0 72,5 I 61,0 67,5 30,0

9 13

58,0

12

43,5

Drilling of water takeoff wells into line of I-IF well

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52,9

Pneumatic displacement

10 9

I Drilling of water takeoff wells into line of HF well, and suction

*There was no takeoff of liquid and gas to the surface.

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223

TABLE 2 No.

Q_u.~.tity of methane Number o! Total length Average o.f removed, million m 3 wells of_;,v__ells:m output well, m~/min

Section Outside zone of well No. 3-bis Welt No. 3-bis Between wells No. 3-bis and 2 Well No. 2 Well No. 1 Well No. 4 Between wells No. 4 and 5 Well No. 5 Outside zone of well No. 5 Total

4680

26 21 20 19 21 19 12 13 21

1,81 2,37 1,70 2,56 2,56 1,81 1,27 1,84 1,74

2940 3600 2660 2100 1520 2160 2340 3780

1,8 1,5 1,1 1,2 1,6 2,4 0,8 1,5 1,0 12,9

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TABLE 3 Dip angle ot Workable seam, deg thickness of seam, m

Type o f mechanization of coal mining

Length of longwaII in zone, m

2K-52, props SGV-2, VDU- 1,4

70--200

Name of longwatl

Zone of well

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