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Applicability of surface directional wells for upper Silesia Basin coal seams’ drainage ahead of mining
International Journal of Mining Science and Technology 24 (2014) 353–362
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International Journal of Mining Science and Technology journal homepage: www.elsevier.com/locate/ijmst
Applicability of surface directional wells for upper Silesia Basin coal seams’ drainage ahead of mining Jura Bartłomiej ⇑, Skiba Jacek, Wierzbinski Krystian Central Mining Institute, Katowice 40-155, Poland
a r t i c l e
i n f o
Article history: Received 10 October 2013 Received in revised form 15 November 2013 Accepted 8 December 2013 Available online 30 April 2014 Keywords: Coal Methane drainage Methane hazard forecasting Numerical modeling Deposit simulation
a b s t r a c t Methods of exploitation drainage, which is presently applied in polish hard coal mines in Upper Silesian Coal Basin (Poland), are not effective enough, high risk of methane hazard can be observed, and production capacity of the mining plant is not fully used. Methane hazard, which may occur during planned coal exploitation, is presented in this paper. Following parameters are taken into consideration in the forecasts: coal extraction parameters, geological and mining conditions, deposit’s methane saturation degree and impact of coal exploitation on the degasification coefficient of the seams, which are under the influence of relaxation zone. This paper presents the results of the analysis aiming to verify applicability of drainage ahead of mining of the coal seams by using surface directional wells. Based on the collected data (coal seams’ structural maps, profiles of the exploratory wells, geological cross-sections), the lab tests of drilling cores and direct wells’ tests, static model of the deposit was constructed and suitable grid of directional wells from the surface was designed. Comparison of forecasted methane emission volume between the two methods is investigated. The results indicated the necessity of performing appropriate deposit’s stimulations in order to increase effectiveness of drainage ahead of mining. Ó 2014 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
1. Introduction Fundamental changes took place in last decade in development of directional drilling technology. It resulted in significant increasing of interest in coalbed methane recovery. The main reason for this is to search for new sources of energy and its economical utilization. Problem is becoming more complex when methane drainage of coal panel for future exploitation is taken into account. Methane drainage of coal beds from the surface before mining, paneling and future exploitation may have significant impact on the methane hazard in the future mining area. Efficient methane drainage method of the strata ahead of mining, as well as the seams located in the zone of mining-induced destressed area may result in more effective methane hazard elimination, without limitation for mining capacity of the coal mine. Presented concept of methane drainage ahead of mining is referring to the coal seams located in the boundary of mining acreage P-1 covering the acreage of 15.8 km2. Presently, there are no mining activities in P-1 mining acreage. Methane drainage ahead of mining assumes drilling directional wells from the surface prospective management of the coal deposit contains exploitation of ⇑ Corresponding author. Tel.: +48 32 3246607. E-mail address: [email protected] (B. Jura).
10 coal seams starting from the shallower-one occurring at the depth of 860 m (Seam 9) down to the seam 18 in the depth 1140 m. Thickness of above coal seams varies from 1.1 to 1.9 m and in the future longwall system with the fall of the roof will be used for mining. The example of designed cutting of the coal Seam 9 into individual coal panels is shown as Fig. 1. Designed development of the mining acreage P-1 includes construction of the shaft in its peripheral (i.e., in northern-east) part and hollowing the cross-cuts from already exploited mining field (shaft #V district) located to the west. The balance resources of the coal deposits within P-1 mining acreage were estimated as 304 million tons, and they contain 24 coal seams documented down to the depth 1300 m. The commercial reserves were estimated at 80 million tons.
2. Characteristics of geological and gas conditions within mining acreage P-1 The geological construction of the subject mining acreage down to the 1.300 m consists of Quaternary formations (holocene and plejstocene), and Tertiary formations (miocene) as well as productive carbon. The Quaternery and Tertiary formations constitute overburden for the coal-bearing carbon formations. They exist at whole acreage
http://dx.doi.org/10.1016/j.ijmst.2014.03.012 2095-2686/Ó 2014 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
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Fig. 1. Boundary of the mining acreage P-1 with the location of exploratory surface wells and designed cutting of the coal Seam 9 into individual coal panels.
of deposit. The Quaternery formation was developed as aluvial sediments-dusts, muds, gravels, sands and clays, which thickness varies from 10 to 62 m and increases towards southern-west direction. The Tertiary formations are overlying directly productive carbon formation. It was developed as the loams, margle shale and loams grown over with the dust sands. In northern part of the acreage thickness of the Tertiary formations varies from 150 up to 250 m and its southern part is more than 670 m. The roof of the productive carbon in the northern part of the deposit occurs from the depth 200 down to 280 m. Towards the south the roof suddenly declines to depth of 680 m. The lithological profile mudstones and clay stones are dominant (they constitute 60–80%) over the sandstones and numerous hard coal layers. The sandstones exist as a 15–25 m thin strata. In majority, these are fine-grained and dusty sandstones. The coal layers are rarely thicker than 2 m. The carbon formations are descending towards northern-east direction, and locally their extent direction is changing into parallel to altitude. The angle of dip is not very big, in most cases not higher than 10°. At the subject acreage, there are clearly two directions of tectonic dislocations: meridionally and parallel of altitude. The most important are: Fault ‘‘P-II’’ which constitutes northern-western boundary of the deposit and throws down the layers by 60–100 m. In the southern-western part of the acreage, the course of this fault was interpreted based on the mining works performed in the adjacent mother mining acreage. Fault ‘‘S’’ with its course SW-NE throw of the layers towards NW. The high of the throw varies from 10 to 60 m. Methane content of the coal seams for exploitation (Seam 9– Seam 18) varies between 5 up to 20 m3/tccs (tccs means per ton of clean coal substance) of methane content of the layers increases towards north, i.e., where the coal seams are located. Significant drop of beds’ methane saturation takes place in the southern-western part of the acreage, which is adjacent to the acreage where the coal exploitation is taking place right now (mother-mining acreage located towards west from P-1 mining acreage). Fig. 2 shows distribution of methane content based on the example of Seam 9.
Similar methane content distribution can be observed in the remaining coal seams. 3. Visualization of structural and facial changes based on the 3D static model of the P-1 deposit (property model) Analysis of the structural and facial changes was conducted based on the spatial static model of deposit P-1. The construction of geological model was made based on the PETREL software (by Schlumberger) [2]. Applied software enabled to conduct extensive analysis of available geological data both from the exploratory wells and from seismic tests. For the mining acreage P-1 cartographic mapping of the seam maps tops’ coordinates and attributing them to already imported ‘‘orto-photomaps’’ was strictly connected with initial conversion of GIS data. The required digitalization of the seams’ maps including designed exploitation was made based on the available modules of the software. For mapping purposes of the seams’ contour-lines point-by-point’’ method was used with attributing certain values of depth ordinates (Fig. 3). For non-linear geological disturbances, i.e., faults, the method of ‘‘open polygons’’ was used in 2D. The boundary of mining acreage P-1 was mapped using method of ‘‘closed polygons’’. Besides, for the modeling of deposits within the acreage P-1, it was required to establish spatial model of dislocations (fault model). For this purposes, the available procedure ‘‘pillar gridding’’ was used. Based on the well tops data and digitized structural maps, geological boundaries (horizons) constructed as a result of transformation of the surface were also introduced into the model. Spatial 3D model was constructed based on the so-called 2D grids of the structural acreage of seams’ roof and floor (see Fig. 4). When constructing the geological model, a comprehensive data base was elaborated including full identification of all exploratory wells’ parameters. The spatial coordinates of the roof and floor of all established surfaces zone and all exploratory wells were constructed in each seam. After importing the database into PETREL software, the adequate zones between the seams meant for exploitation were established (see Fig. 5).
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Fig. 2. Methane content distribution in Seam 9.
Fig. 3. Digitalization of the coal seams maps-contour lines.
The zones were constructed from certain parameters of thickness and depth, and the maps of thicknesses were created. Ultimately, necessary corrections between the coal seams (established based on the maps) and the profiles of the drilling wells were made. In order to optimize size of the model, its boundaries were narrowed down to the faults located at the limits of mining acreage P1. The log data of the drilling wells were associated with the coal seams and surrounding layers, which were established based on the structural maps of the seams. In order to calculate coal resources in the seams for the exploitation and volumes of remaining surrounding formations (sandstones, shale) limited by the mining acreage, the function ‘‘make zones–calculation performed in selected stratigraphic interval’’ was used (see Fig. 6). Based on the created database, it was possible to estimate the following items: volume of individual layers in the segments and within mining acreage, and gas resources in several coal seams (limited by horizontal and vertical TVT-total vertical thickness). Sediment logical profiles of the drilling wells were used to construct facial model of the mining acreage. In order to verify continuity of modeled layers the ‘‘fence diagram’’ was analyzed by spatial facial model (Fig. 7).
4. Analysis of methane hazard during coal seams exploitation Analysis of methane hazard was conducted based on the forecasted methane emission into the environment of designed longwalls in the Seam 9. The coal seam can be characterized by high methane content of clean coal substance (5–13 m3/tccs) and is the first seam for exploitation in mining acreage P-1 (see Fig. 8). The exploitation will take place in not-relaxed and not-drained deposit conditions. Besides, Seam 9 comparing with other balance coal seams is the shallower-one. When considering that methane saturation of deposit is increasing towards north, and especially in the Seam 9 (Fig. 2), the results of the hazard analysis were shown based on the example of the longwalls designed in the lower methane conditions. In the northern part of the Seam 9 the following longwalls were located: PN-1, PN-2, PN-3, PN-4, PN-5, and PN6. Forecasted methane emissions to the environment of above longwalls were determined based on the algorithm described as a dynamic forecast of absolute methane-bearing capacity. Above algorithm was defined as the instruction #14 of Central Mining Institute and is commonly used in polish hard coal mines to analyze forecasted methane hazard in the designed longwalls [1].
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Fig. 4. An example of establishing the surfaces.
Fig. 5. An example of establishing the zone.
The prognosis was prepared in accordance with the results of elaborated geological model and based on the information concerning coal Seam 9 development. The results of coal seams’ methane content tests were used for calculation (Table 1, Seam 7, Seam 8, Seam 9, Seam 10, Seam 11, Seam 12) and not marked in the exploratory wells. According to the research performed by Experimental Mine ‘‘Barbara’’, it was assumed that the initial methane content of the coal seams is changing in the linear way with the depth of their occurrence. Scale of methane content changes depending on difference methane contents in the individual seams and distance between them. It is referring to both increasing methane content and decreasing-one together with the depth of occurrence. For the seams of which methane content is not certain, its value was assumed based on the interpolation of the values from adjacent seams. The assumptions concerning length of designed longwalls (220–240 m), range of mining-induced zone of the Seam 9 on the degassing of the underlying and overlaying seams is: 55–60 m for the floor seam and 148–162 m for the roof seam. Mining-induced zone have impact on the roof seams (undermined), which names are: Seam 7 and Seam 8 with the thicknesses 0.8 and 0.7 m, and 18 unmarked seams with total thickness below
7 m as well as floor seams (overmined), i.e., Seam 10, Seam 11, Seam 12 and 4 unmarked coal seams with total thickness of 1.5 m. Degasification degree of surrounding seams was calculated according to the instruction #14 elaborated by Central Mining Institute [1]. The results of degasification degree of analyzed seams are shown in Fig. 9. As shown in the graph, pretty high exploitation degasification (above 30%) will also cover underlying Seam 10. The results of the calculations of total methane resources in the roof and floor seams under the mining-induced zone as well as the desorption resources, which as forecasted to be released during Seam 9 exploitation into the environment of longwall PN-1, are shown in the Table 2. As presented estimations are only due to the exploitation of the Seam 9 by the longwall PN-1, during whole exploitation period 9.3 106 m3 of methane will be released, and about 40% of total methane emission in the environment of longwall will come from the exploited Seam 9 (3.8 106 m3 methane), about 40% from the roof seams (3.5 106 m3 methane) and about 20% from the floor seams (about 2.0 106 m3 methane), including about 600,000 m3 methane from Seam 10. Total results of forecasted absolute methane-bearing capacity for the designed longwalls PN-1, PN-6 in the Seam 9 are shown in the Table 3.
B. Jura et al. / International Journal of Mining Science and Technology 24 (2014) 353–362
Fig. 6. Database for the purposes of calculation the resources.
Fig. 7. Fence diagram.
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Fig. 8. General view of 3D geological model of P-1 deposit with the wells and fault.
Table 1 Parameters of coal seams occurrence and values of methane content of the coal seams in the area of designed longwalls PN-1, PN-6 in the Seam 9. #
Seam ID
Distance from the Seam 9 (m)
Location in relation to Seam 9
Methane content of clean coal substance (m3CH4/tccs)
1 2 3 4 5 6 7 8 9 10 11
n. m. Seam n.m. Seam n.m. n.m. n.m. Seam Seam Seam Seam
160.8 117.1 87.8 70.6 53.3 17.2 5.6 0.0 24.2 37.3 54.8
above above above above above above above
7.9 11.5 13.2 13.3 10.4 7.7 11.7 13.3 13.0 20.2 12.6
7 8
9 10 11 12
below below below
Note: n.m. means not marked.
The results of forecasted methane emissions into the environment of designed longwalls are shown in Table 3 for confirming high methane hazard, which will occur in the underground activity during coal exploitation. In the conditions of such high methane emissions (41–53 m3/min) to the environment of the longwalls, fighting above hazard only with the ventilation methods will not
100
80
n.m. n.m. n.m. Seam 8
60
n.m. n.m. 40
20
0
-20
-40
n.m. n.m. n.m. n.m. 20 40 60 Desorption degree (%) Seam 10 n.m. Seam 11
80
n.m. n.m. Seam 12
-60
-80
Fig. 9. Degreeof degasification of the coal seams located within the range of mining-induced zone of Seam 9.
Table 2 Methane resources in the individual, surrounding coal seams (for the longwall PN-1 in Seam 9). Seam/Group of seam ID (a) Roof seams (undermined) 10 n.m. seams and Seam 7 Seams above Seam 8 Seam 8 n.m. n.m. n.m. n.m. n.m. n.m. n.m. n.m. Total (b) Floor seams (overmined) n.m. Seam 10 n.m. n.m. SEAM 11 n.m. Seam 12 Sum
Total methane resource (m3CH4)
Desorbable methane resource (m3CH4)
154323
144921
132111 251412 258147 764768 1187817 549514 521733 2142144 1015685 6977653
121082 216358 214374 453802 575548 261606 240155 915407 398502 3541755
732494 828238 214010 291711 488782 89934 24146 2669314
486883 597329 157761 219132 393640 74418 21237 1950399
Note: n.m. means not marked.
be efficient enough. Even when designing ventilation of the longwalls in ‘‘Y’’ system (with freshing air-flow), which is the most effective in the conditions of high methane hazard and when providing intensive ventilation of the roadways during the exploitation, it will still be necessary to implement methane drainage. When assuming relatively strong ventilation of the mining area, i.e., 1500 m3/min of air as a freshing air-flow of the return air and 1500 m3/min as a volumetric flow in the longwall with no inflow of methane from other sources, e.g., from developed roadways into the fresh air inflow pumped to the longwalls, in order to keep methane concentration at the end of the mining acreage below 1.5% CH4, it is necessary to design methane drainage with the efficiency at least: 34% in the longwall PN-6, 43% in the longwall PN-5, and 47–49% in the longwalls PN-1, PN-2, PN-3, and PN-4. Required drainage efficiency for the exploitation drainage will be possible to reach in the longwalls: PN-5 and PN-6 due to relatively high, i.e., 40% share of methane emissions coming from the undermined seams (from the roof) in the forecasted absolute methane-bearing capacity of designed longwalls in the Seam 9 (Table 2). However remaining methane, in the longwalls still have to be decreased. Besides, assumed air-flow volumes in the longwall area, in the real conditions can be difficult to achieve due to small
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B. Jura et al. / International Journal of Mining Science and Technology 24 (2014) 353–362 Table 3 Forecast of absolute methane-bearing capacity for the designed longwalls: PN-1, PN-6 in the Seam 9. No.
Longwall
Seam
1 2 3 4 5 6
PN-1 PN-2 PN-3 PN-4 PN-5 PN-6
Seam Seam Seam Seam Seam Seam
9 9 9 9 9 9
Year of exploitation
Length (m)
Life of the longwall (m)
Estimated max. output (t/day)
Forecasted methane-bearing capacity (m3/min)
2025–2026 2026 2026–2027 2027–2028 2028–2029 2029–2030
230 220 230 220 240 230
950 1300 1500 1600 1680 1780
3300 3200 3300 3000 2700 2300
52.7 50.4 52.9 51.3 47.2 40.7
5. Design of directional surface wells to drainage methane from the prospective coal seams ahead of their mining The concept of methane drainage using surface directional wells contains drainage of two shallower coal seams i.e., Seam 9 and Seam 10 is constructed for the exploitation in Mining Acreage P-1. In above seams, methane resources were estimated based on the geological model (description in point 3) and they amount as follows: 190 106 m3 methane in Northern part of Seam 9; 197 106 m3 methane in Northern part of Seam 10; 72 106 m3 methane in Eastern part of Seam 9; and 52 106 m3 methane in eastern part of Seam 10. Design of drainage when taking into consideration drilling of 16 pairs of the wells from the surface in the following configuration contains vertical well and directional well. Apart from this, from each directional well, 4–6 branches are getting into lateral wells in the coal seams covered by drainage ahead of mining. Fig. 10 shows vertical cross-section through single set of the wells, which consists of directional well (N1h), vertical well (N1) and laterals conducted along the Seam 9 and Seam 10.
Fig. 10. Vertical cross section showing designed surface wells: N1 h (directional well) and N1 (vertical well) and 2 laterals conducted in the Seam 9 and Seam 10.
cross-sections of designed longwalls (2.5–3 m2), which are the result of small thickness of the Seam 9. Pumping through the longwall about 1500 m3/min of air will not be very good as it will result in overcrossing (>5 m/s) air speed in the exploitation workings. As a result, there will increase of air dustiness and when designing ventilation in ‘‘Y’’ system-potential increase of spontaneous fire hazard.
N4h
N5h
N6h
8291
d1
d1
N7h
N4 N2h
N1h
N7
N5 N6
2029
N8h
11
12
8292
12
2028 N2
11
12 N3h N1
d1
I
PN-6
N8
13
11
d1
12 d1 11
III
PN-5
d1
2030
11 12
N3
PN-4
2026
2037
IV
12
2029
2026
2027
PN-1
12
2028
8293
12
11
PN-2
11
11
PN-3
2026
8290
Fig. 11. Designed drainage wells ahead of mining in the Seam 9 (northern part) (Note: dashed line: directional wells, continuous line: lateral sections).
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Fig. 12. Spatial set of the wells meant for methane drainage ahead of mining.
Fig. 13. General view of the geological model of the P-1 mining acreage together with exploratory wells and with the directional and vertical wells meant for methane drainage ahead of mining.
The lateral sections were designed within the boundaries of designed coal exploitation of Seam 9. They cover northern part of P-1 mining acreage with its 6 panels (longwalls: PN-1, . . ., PN-6, as shown in Fig. 11). The lateral sections were oriented crosswise to the length of designed longwalls. The length of individual lateral sections varies from 610 up to 1260 m. In the coal seam, plane distance between individual laterals was assumed as maximum 200 m. As a target, it was assumed to drill totally 62.2 km of 152 mm diameter lateral wells in the coal seams. Fig. 12 shows the spatial set of the wells meant for methane drainage ahead of mining. They consist of vertical wells and directional wells with lateral sections. At noted in Fig. 13, it is shown the general view of the geological model of the P-1 mining acreage together with exploratory wells and with the directional and vertical wells meant for methane drainage ahead of mining.
6. Analysis of methane drainage using surface directional wells Analysis of methane drainage using directional wells was made based on the results of numerical calculations for the period of 5 years. The simulations were performed in AnsysCFX software, which belongs to the group of computational fluid dynamics
0s 1 .5 h 3h 2 days 14 days 6 months
1 .1 e-002 1 .0 e-002 9 .0 e-003 8 .0 e-003 7 .0 e-003 6 .0 e-003 5 .0 e-003 4 .0 e-003 3 .0 e-003 2 .0 e-003 1 .0 e-003 0 .0 e+000
14 months 25 months 30 months 64 months 0
2500 5000 (m) 1250 3750
Fig. 14. Drop of methane content of the Seam 9 in the vertical plane perpendicular to the axis of horizontal well.
(CFD) software using in their computations method of finite element method (FEM) [3]. For the calculations, it was assumed that the drainage process will have isothermal course. It was assumed that the temperature of gas will be the same as the surrounding rock mass at 41 °C and
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Total methane intake from the wells (m3)
Fig. 15. Results of calculations of the dynamics of methane inflow changes (kg/s) in the individual lateral sections N1, . . ., N8 designed in northern part of Seam 9.
7000000 6000000
Seam10 (E)
5000000 4000000 Seam 10 (N)
3000000 2000000
Seam 9 (E)
1000000
0
0. 5
1. 0
1.5
2.0
2.5
Seam 9 (N) 3. 0 3.5
4.0
4.5
5.0
Period of time (year)
Fig. 16. Comparison of the results of total methane intake (m3CH4) from individual parts of the seams covered by surface drainage.
the conditions for the methane filtration and desorption from the coalbeds will be non-stationary. The coal was treated as a dry, porous medium (without water) with the porosity c = 0.05 and permeability K = 2 10 15 m2. For the Seam 9, it was assumed, that methane content will be 12.75 m3/tccs, and for the Seam 10 it will be 13.70 m3/tccs. The sorption kinetics constant k was assumed 0.0001 and deposit pressure from Langmuir isotherm, which was established during the well tests. The results of the calculations for the northern part of Seam 9 were presented at Figs. 14 and 15. Fig. 14 shows graphically drop of methane content of the seam in time. The changes of saturation were shown in the vertical plane perpendicular to the axis of horizontal well. At the graph (Fig. 15), it is shown dynamics of methane inflow changes (kg/s) in the individual lateral sections N1–N8. The numerical calculations show that the relatively higher intake of methane can be achieved from the drainage wells designed in the northern part of Seam 9 and Seam 10. The simulations indicate that during the initial stage of drainage (first 24 h) methane
intake from single lateral section located in the northern part can be 0.018–0.034 kg/s (1.6–3.1 m3/min) for the Seam 9 and 0.027– 0.051 kg/s (2.5–4.7 m3/min) for the Seam 10, which is from 2 to 12 times higher comparing with the intake coming from the similar wells located in the eastern part (E). In the eastern part (E) after 4–22 months there is a drop of methane flow from the individual lateral section down to 0.001 kg/s (0.1 m3/min), which is the same as in the northern part. Drop of methane flow in the northern part down to 0.002 kg/s (0.2 m3/min) occurs only after 16–24 months. Fig. 16 shows the results of the calculations of total methane intake by lateral sections of the wells, with division on the wells designed in the eastern and northern parts of the Seam 9 and Seam 10. Results show that total methane intake from designed wells in 5 years will be 14.4 106 m3, including 4.95 106 m3 from Seam 9 (N), 6.20 106 m3 from Seam 10 (N), 1.63 106 m3 from Seam 9 (E), and 1.65 106 m3 from Seam 10 (E). Assuming methane resources within the boundaries of designed longwalls in the northern part of the Seam 9, degasification degree was determined of within the boundaries of the longwalls PN1, . . ., PN-6, as shown in Table 4. Our research shows that average degree of degasification of the Seam 9 and Seam 10 in northern part for designed longwalls PN1, . . ., PN-6 in Seam 9 reaches 12%. Based on above calculations, it can be concluded its influence on decreasing forecasted methane content of designed longwalls. After another analysis of methane hazard in the longwalls PN-1, . . ., PN-6, it can be concluded that absolute methane-bearing capacity after implementation of surface drainage ahead of mining will reach: 47.4 m3/min for the longwall PN-1, 45.4 m3/min for the longwall PN-2, 47.6 m3/min for the longwall PN-3, 46.1 m3/min for the longwall PN-4, 42.6 m3/min for the longwall PN-5, and 36.8 m3/min for the longwall PN-6. After comparing above values (Table 4) with the forecasted values without drainaging from the surface (Table 3) it can be concluded, that during coal exploitation after drainage from the surface, forecasted methane hazard will be decreased by 10%. It can be expected that methane hazard in the designed longwalls will be still high, due to the fact that methane hazard fighting with ventilation methods is applicable only when the methane-bearing capacity is not exceeding 27 m3/min. In order to provide safe coal exploitation within mining Acreage P-1, it will be necessary then to apply conventional drainage (apart from drainage ahead of mining) using drainage boreholes from underground workings. Minimum drainage effectiveness should reach at least 27% for longwall PN-6 and 44% for longwall PN-3.
7. Conclusions The results of methane-bearing capacity for the designed longwalls from PN-1 to PN-6 show high methane hazard during coal exploitation in Seam 9 of the mining acreage P-1. When
Table 4 Degree of degasification of the Seam 9 and Seam 10 in the northern part, for the longwalls: PN-1, . . ., PN-6 in Seam 9. #
Designed Longwall
Seam
1. 2. 3. 4. 5. 6.
PN-1 PN-2 PN-3 PN-4 PN-5 PN-6
Seam Seam Seam Seam Seam Seam
9 9 9 9 9 9
Methane resources in the Seam 9 and Seam 10 within the boundaries of the longwall (m3)
Methane intake from Seam 9 and Seam 10 within the boundaries of the longwallsin 5 years time (m3)
Degree of Seam 9 and Seam 10 degasification (%)
9.0 106 11.8 106 14.2 106 14.6 106 16.6 106 17.0 106
1.1 106 1.4 106 1.7 106 1.8 106 2.0 106 2.0 106
12.2 11.8 11.9 12.3 12.0 11.7
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considering daily coal output at the level of 2300–3300 t/day, forecasted methane emissions into the environment of the longwalls varies between 41 up to 53 m3/min. High forecasted methane content of above longwalls justified the importance of the drainage ahead of mining concept of the seams located in the exploitation-induced zone. After performing the simulation of methane intake by designing 62 km directional wells from surface drainage ahead of mining, it can be concluded that during first 5 years, forecasted methane intake will reach 14.4 106 m3. Assumed method of drainage will result in degassing degree of 12% of the Seam 9 and Seam 10 within the boundaries of designed longwalls PN-1, . . ., PN-6. The result could not ensure safe exploitation within Mining Acreage P-1. Apart from drainage ahead of mining it will be necessary to apply
conventional drainage using drainage boreholes in the underground activity. Simulation results of non-relaxed rock-mass proved possibility to apply appropriate techniques of deposit simulation for increasing efficiency of drainage ahead of mining. References [1] Instruction # 14. Technical handbook. Dynamic forecast of the absolute methane-bearing capacity of the longwalls. Katowice: Central Mining Institute; 2000. [2] Introduction Course. Petrel (v.2005). Schlumberger Information, Solutions; 2006. [3] ANSYS Release 10.0. ANSYS, Inc., User’s guide; 2005.
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International Journal of Mining Science and Technology journal homepage: www.elsevier.com/locate/ijmst
Applicability of surface directional wells for upper Silesia Basin coal seams’ drainage ahead of mining Jura Bartłomiej ⇑, Skiba Jacek, Wierzbinski Krystian Central Mining Institute, Katowice 40-155, Poland
a r t i c l e
i n f o
Article history: Received 10 October 2013 Received in revised form 15 November 2013 Accepted 8 December 2013 Available online 30 April 2014 Keywords: Coal Methane drainage Methane hazard forecasting Numerical modeling Deposit simulation
a b s t r a c t Methods of exploitation drainage, which is presently applied in polish hard coal mines in Upper Silesian Coal Basin (Poland), are not effective enough, high risk of methane hazard can be observed, and production capacity of the mining plant is not fully used. Methane hazard, which may occur during planned coal exploitation, is presented in this paper. Following parameters are taken into consideration in the forecasts: coal extraction parameters, geological and mining conditions, deposit’s methane saturation degree and impact of coal exploitation on the degasification coefficient of the seams, which are under the influence of relaxation zone. This paper presents the results of the analysis aiming to verify applicability of drainage ahead of mining of the coal seams by using surface directional wells. Based on the collected data (coal seams’ structural maps, profiles of the exploratory wells, geological cross-sections), the lab tests of drilling cores and direct wells’ tests, static model of the deposit was constructed and suitable grid of directional wells from the surface was designed. Comparison of forecasted methane emission volume between the two methods is investigated. The results indicated the necessity of performing appropriate deposit’s stimulations in order to increase effectiveness of drainage ahead of mining. Ó 2014 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
1. Introduction Fundamental changes took place in last decade in development of directional drilling technology. It resulted in significant increasing of interest in coalbed methane recovery. The main reason for this is to search for new sources of energy and its economical utilization. Problem is becoming more complex when methane drainage of coal panel for future exploitation is taken into account. Methane drainage of coal beds from the surface before mining, paneling and future exploitation may have significant impact on the methane hazard in the future mining area. Efficient methane drainage method of the strata ahead of mining, as well as the seams located in the zone of mining-induced destressed area may result in more effective methane hazard elimination, without limitation for mining capacity of the coal mine. Presented concept of methane drainage ahead of mining is referring to the coal seams located in the boundary of mining acreage P-1 covering the acreage of 15.8 km2. Presently, there are no mining activities in P-1 mining acreage. Methane drainage ahead of mining assumes drilling directional wells from the surface prospective management of the coal deposit contains exploitation of ⇑ Corresponding author. Tel.: +48 32 3246607. E-mail address: [email protected] (B. Jura).
10 coal seams starting from the shallower-one occurring at the depth of 860 m (Seam 9) down to the seam 18 in the depth 1140 m. Thickness of above coal seams varies from 1.1 to 1.9 m and in the future longwall system with the fall of the roof will be used for mining. The example of designed cutting of the coal Seam 9 into individual coal panels is shown as Fig. 1. Designed development of the mining acreage P-1 includes construction of the shaft in its peripheral (i.e., in northern-east) part and hollowing the cross-cuts from already exploited mining field (shaft #V district) located to the west. The balance resources of the coal deposits within P-1 mining acreage were estimated as 304 million tons, and they contain 24 coal seams documented down to the depth 1300 m. The commercial reserves were estimated at 80 million tons.
2. Characteristics of geological and gas conditions within mining acreage P-1 The geological construction of the subject mining acreage down to the 1.300 m consists of Quaternary formations (holocene and plejstocene), and Tertiary formations (miocene) as well as productive carbon. The Quaternery and Tertiary formations constitute overburden for the coal-bearing carbon formations. They exist at whole acreage
http://dx.doi.org/10.1016/j.ijmst.2014.03.012 2095-2686/Ó 2014 Published by Elsevier B.V. on behalf of China University of Mining & Technology.
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Fig. 1. Boundary of the mining acreage P-1 with the location of exploratory surface wells and designed cutting of the coal Seam 9 into individual coal panels.
of deposit. The Quaternery formation was developed as aluvial sediments-dusts, muds, gravels, sands and clays, which thickness varies from 10 to 62 m and increases towards southern-west direction. The Tertiary formations are overlying directly productive carbon formation. It was developed as the loams, margle shale and loams grown over with the dust sands. In northern part of the acreage thickness of the Tertiary formations varies from 150 up to 250 m and its southern part is more than 670 m. The roof of the productive carbon in the northern part of the deposit occurs from the depth 200 down to 280 m. Towards the south the roof suddenly declines to depth of 680 m. The lithological profile mudstones and clay stones are dominant (they constitute 60–80%) over the sandstones and numerous hard coal layers. The sandstones exist as a 15–25 m thin strata. In majority, these are fine-grained and dusty sandstones. The coal layers are rarely thicker than 2 m. The carbon formations are descending towards northern-east direction, and locally their extent direction is changing into parallel to altitude. The angle of dip is not very big, in most cases not higher than 10°. At the subject acreage, there are clearly two directions of tectonic dislocations: meridionally and parallel of altitude. The most important are: Fault ‘‘P-II’’ which constitutes northern-western boundary of the deposit and throws down the layers by 60–100 m. In the southern-western part of the acreage, the course of this fault was interpreted based on the mining works performed in the adjacent mother mining acreage. Fault ‘‘S’’ with its course SW-NE throw of the layers towards NW. The high of the throw varies from 10 to 60 m. Methane content of the coal seams for exploitation (Seam 9– Seam 18) varies between 5 up to 20 m3/tccs (tccs means per ton of clean coal substance) of methane content of the layers increases towards north, i.e., where the coal seams are located. Significant drop of beds’ methane saturation takes place in the southern-western part of the acreage, which is adjacent to the acreage where the coal exploitation is taking place right now (mother-mining acreage located towards west from P-1 mining acreage). Fig. 2 shows distribution of methane content based on the example of Seam 9.
Similar methane content distribution can be observed in the remaining coal seams. 3. Visualization of structural and facial changes based on the 3D static model of the P-1 deposit (property model) Analysis of the structural and facial changes was conducted based on the spatial static model of deposit P-1. The construction of geological model was made based on the PETREL software (by Schlumberger) [2]. Applied software enabled to conduct extensive analysis of available geological data both from the exploratory wells and from seismic tests. For the mining acreage P-1 cartographic mapping of the seam maps tops’ coordinates and attributing them to already imported ‘‘orto-photomaps’’ was strictly connected with initial conversion of GIS data. The required digitalization of the seams’ maps including designed exploitation was made based on the available modules of the software. For mapping purposes of the seams’ contour-lines point-by-point’’ method was used with attributing certain values of depth ordinates (Fig. 3). For non-linear geological disturbances, i.e., faults, the method of ‘‘open polygons’’ was used in 2D. The boundary of mining acreage P-1 was mapped using method of ‘‘closed polygons’’. Besides, for the modeling of deposits within the acreage P-1, it was required to establish spatial model of dislocations (fault model). For this purposes, the available procedure ‘‘pillar gridding’’ was used. Based on the well tops data and digitized structural maps, geological boundaries (horizons) constructed as a result of transformation of the surface were also introduced into the model. Spatial 3D model was constructed based on the so-called 2D grids of the structural acreage of seams’ roof and floor (see Fig. 4). When constructing the geological model, a comprehensive data base was elaborated including full identification of all exploratory wells’ parameters. The spatial coordinates of the roof and floor of all established surfaces zone and all exploratory wells were constructed in each seam. After importing the database into PETREL software, the adequate zones between the seams meant for exploitation were established (see Fig. 5).
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Fig. 2. Methane content distribution in Seam 9.
Fig. 3. Digitalization of the coal seams maps-contour lines.
The zones were constructed from certain parameters of thickness and depth, and the maps of thicknesses were created. Ultimately, necessary corrections between the coal seams (established based on the maps) and the profiles of the drilling wells were made. In order to optimize size of the model, its boundaries were narrowed down to the faults located at the limits of mining acreage P1. The log data of the drilling wells were associated with the coal seams and surrounding layers, which were established based on the structural maps of the seams. In order to calculate coal resources in the seams for the exploitation and volumes of remaining surrounding formations (sandstones, shale) limited by the mining acreage, the function ‘‘make zones–calculation performed in selected stratigraphic interval’’ was used (see Fig. 6). Based on the created database, it was possible to estimate the following items: volume of individual layers in the segments and within mining acreage, and gas resources in several coal seams (limited by horizontal and vertical TVT-total vertical thickness). Sediment logical profiles of the drilling wells were used to construct facial model of the mining acreage. In order to verify continuity of modeled layers the ‘‘fence diagram’’ was analyzed by spatial facial model (Fig. 7).
4. Analysis of methane hazard during coal seams exploitation Analysis of methane hazard was conducted based on the forecasted methane emission into the environment of designed longwalls in the Seam 9. The coal seam can be characterized by high methane content of clean coal substance (5–13 m3/tccs) and is the first seam for exploitation in mining acreage P-1 (see Fig. 8). The exploitation will take place in not-relaxed and not-drained deposit conditions. Besides, Seam 9 comparing with other balance coal seams is the shallower-one. When considering that methane saturation of deposit is increasing towards north, and especially in the Seam 9 (Fig. 2), the results of the hazard analysis were shown based on the example of the longwalls designed in the lower methane conditions. In the northern part of the Seam 9 the following longwalls were located: PN-1, PN-2, PN-3, PN-4, PN-5, and PN6. Forecasted methane emissions to the environment of above longwalls were determined based on the algorithm described as a dynamic forecast of absolute methane-bearing capacity. Above algorithm was defined as the instruction #14 of Central Mining Institute and is commonly used in polish hard coal mines to analyze forecasted methane hazard in the designed longwalls [1].
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Fig. 4. An example of establishing the surfaces.
Fig. 5. An example of establishing the zone.
The prognosis was prepared in accordance with the results of elaborated geological model and based on the information concerning coal Seam 9 development. The results of coal seams’ methane content tests were used for calculation (Table 1, Seam 7, Seam 8, Seam 9, Seam 10, Seam 11, Seam 12) and not marked in the exploratory wells. According to the research performed by Experimental Mine ‘‘Barbara’’, it was assumed that the initial methane content of the coal seams is changing in the linear way with the depth of their occurrence. Scale of methane content changes depending on difference methane contents in the individual seams and distance between them. It is referring to both increasing methane content and decreasing-one together with the depth of occurrence. For the seams of which methane content is not certain, its value was assumed based on the interpolation of the values from adjacent seams. The assumptions concerning length of designed longwalls (220–240 m), range of mining-induced zone of the Seam 9 on the degassing of the underlying and overlaying seams is: 55–60 m for the floor seam and 148–162 m for the roof seam. Mining-induced zone have impact on the roof seams (undermined), which names are: Seam 7 and Seam 8 with the thicknesses 0.8 and 0.7 m, and 18 unmarked seams with total thickness below
7 m as well as floor seams (overmined), i.e., Seam 10, Seam 11, Seam 12 and 4 unmarked coal seams with total thickness of 1.5 m. Degasification degree of surrounding seams was calculated according to the instruction #14 elaborated by Central Mining Institute [1]. The results of degasification degree of analyzed seams are shown in Fig. 9. As shown in the graph, pretty high exploitation degasification (above 30%) will also cover underlying Seam 10. The results of the calculations of total methane resources in the roof and floor seams under the mining-induced zone as well as the desorption resources, which as forecasted to be released during Seam 9 exploitation into the environment of longwall PN-1, are shown in the Table 2. As presented estimations are only due to the exploitation of the Seam 9 by the longwall PN-1, during whole exploitation period 9.3 106 m3 of methane will be released, and about 40% of total methane emission in the environment of longwall will come from the exploited Seam 9 (3.8 106 m3 methane), about 40% from the roof seams (3.5 106 m3 methane) and about 20% from the floor seams (about 2.0 106 m3 methane), including about 600,000 m3 methane from Seam 10. Total results of forecasted absolute methane-bearing capacity for the designed longwalls PN-1, PN-6 in the Seam 9 are shown in the Table 3.
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Fig. 6. Database for the purposes of calculation the resources.
Fig. 7. Fence diagram.
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Fig. 8. General view of 3D geological model of P-1 deposit with the wells and fault.
Table 1 Parameters of coal seams occurrence and values of methane content of the coal seams in the area of designed longwalls PN-1, PN-6 in the Seam 9. #
Seam ID
Distance from the Seam 9 (m)
Location in relation to Seam 9
Methane content of clean coal substance (m3CH4/tccs)
1 2 3 4 5 6 7 8 9 10 11
n. m. Seam n.m. Seam n.m. n.m. n.m. Seam Seam Seam Seam
160.8 117.1 87.8 70.6 53.3 17.2 5.6 0.0 24.2 37.3 54.8
above above above above above above above
7.9 11.5 13.2 13.3 10.4 7.7 11.7 13.3 13.0 20.2 12.6
7 8
9 10 11 12
below below below
Note: n.m. means not marked.
The results of forecasted methane emissions into the environment of designed longwalls are shown in Table 3 for confirming high methane hazard, which will occur in the underground activity during coal exploitation. In the conditions of such high methane emissions (41–53 m3/min) to the environment of the longwalls, fighting above hazard only with the ventilation methods will not
100
80
n.m. n.m. n.m. Seam 8
60
n.m. n.m. 40
20
0
-20
-40
n.m. n.m. n.m. n.m. 20 40 60 Desorption degree (%) Seam 10 n.m. Seam 11
80
n.m. n.m. Seam 12
-60
-80
Fig. 9. Degreeof degasification of the coal seams located within the range of mining-induced zone of Seam 9.
Table 2 Methane resources in the individual, surrounding coal seams (for the longwall PN-1 in Seam 9). Seam/Group of seam ID (a) Roof seams (undermined) 10 n.m. seams and Seam 7 Seams above Seam 8 Seam 8 n.m. n.m. n.m. n.m. n.m. n.m. n.m. n.m. Total (b) Floor seams (overmined) n.m. Seam 10 n.m. n.m. SEAM 11 n.m. Seam 12 Sum
Total methane resource (m3CH4)
Desorbable methane resource (m3CH4)
154323
144921
132111 251412 258147 764768 1187817 549514 521733 2142144 1015685 6977653
121082 216358 214374 453802 575548 261606 240155 915407 398502 3541755
732494 828238 214010 291711 488782 89934 24146 2669314
486883 597329 157761 219132 393640 74418 21237 1950399
Note: n.m. means not marked.
be efficient enough. Even when designing ventilation of the longwalls in ‘‘Y’’ system (with freshing air-flow), which is the most effective in the conditions of high methane hazard and when providing intensive ventilation of the roadways during the exploitation, it will still be necessary to implement methane drainage. When assuming relatively strong ventilation of the mining area, i.e., 1500 m3/min of air as a freshing air-flow of the return air and 1500 m3/min as a volumetric flow in the longwall with no inflow of methane from other sources, e.g., from developed roadways into the fresh air inflow pumped to the longwalls, in order to keep methane concentration at the end of the mining acreage below 1.5% CH4, it is necessary to design methane drainage with the efficiency at least: 34% in the longwall PN-6, 43% in the longwall PN-5, and 47–49% in the longwalls PN-1, PN-2, PN-3, and PN-4. Required drainage efficiency for the exploitation drainage will be possible to reach in the longwalls: PN-5 and PN-6 due to relatively high, i.e., 40% share of methane emissions coming from the undermined seams (from the roof) in the forecasted absolute methane-bearing capacity of designed longwalls in the Seam 9 (Table 2). However remaining methane, in the longwalls still have to be decreased. Besides, assumed air-flow volumes in the longwall area, in the real conditions can be difficult to achieve due to small
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B. Jura et al. / International Journal of Mining Science and Technology 24 (2014) 353–362 Table 3 Forecast of absolute methane-bearing capacity for the designed longwalls: PN-1, PN-6 in the Seam 9. No.
Longwall
Seam
1 2 3 4 5 6
PN-1 PN-2 PN-3 PN-4 PN-5 PN-6
Seam Seam Seam Seam Seam Seam
9 9 9 9 9 9
Year of exploitation
Length (m)
Life of the longwall (m)
Estimated max. output (t/day)
Forecasted methane-bearing capacity (m3/min)
2025–2026 2026 2026–2027 2027–2028 2028–2029 2029–2030
230 220 230 220 240 230
950 1300 1500 1600 1680 1780
3300 3200 3300 3000 2700 2300
52.7 50.4 52.9 51.3 47.2 40.7
5. Design of directional surface wells to drainage methane from the prospective coal seams ahead of their mining The concept of methane drainage using surface directional wells contains drainage of two shallower coal seams i.e., Seam 9 and Seam 10 is constructed for the exploitation in Mining Acreage P-1. In above seams, methane resources were estimated based on the geological model (description in point 3) and they amount as follows: 190 106 m3 methane in Northern part of Seam 9; 197 106 m3 methane in Northern part of Seam 10; 72 106 m3 methane in Eastern part of Seam 9; and 52 106 m3 methane in eastern part of Seam 10. Design of drainage when taking into consideration drilling of 16 pairs of the wells from the surface in the following configuration contains vertical well and directional well. Apart from this, from each directional well, 4–6 branches are getting into lateral wells in the coal seams covered by drainage ahead of mining. Fig. 10 shows vertical cross-section through single set of the wells, which consists of directional well (N1h), vertical well (N1) and laterals conducted along the Seam 9 and Seam 10.
Fig. 10. Vertical cross section showing designed surface wells: N1 h (directional well) and N1 (vertical well) and 2 laterals conducted in the Seam 9 and Seam 10.
cross-sections of designed longwalls (2.5–3 m2), which are the result of small thickness of the Seam 9. Pumping through the longwall about 1500 m3/min of air will not be very good as it will result in overcrossing (>5 m/s) air speed in the exploitation workings. As a result, there will increase of air dustiness and when designing ventilation in ‘‘Y’’ system-potential increase of spontaneous fire hazard.
N4h
N5h
N6h
8291
d1
d1
N7h
N4 N2h
N1h
N7
N5 N6
2029
N8h
11
12
8292
12
2028 N2
11
12 N3h N1
d1
I
PN-6
N8
13
11
d1
12 d1 11
III
PN-5
d1
2030
11 12
N3
PN-4
2026
2037
IV
12
2029
2026
2027
PN-1
12
2028
8293
12
11
PN-2
11
11
PN-3
2026
8290
Fig. 11. Designed drainage wells ahead of mining in the Seam 9 (northern part) (Note: dashed line: directional wells, continuous line: lateral sections).
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Fig. 12. Spatial set of the wells meant for methane drainage ahead of mining.
Fig. 13. General view of the geological model of the P-1 mining acreage together with exploratory wells and with the directional and vertical wells meant for methane drainage ahead of mining.
The lateral sections were designed within the boundaries of designed coal exploitation of Seam 9. They cover northern part of P-1 mining acreage with its 6 panels (longwalls: PN-1, . . ., PN-6, as shown in Fig. 11). The lateral sections were oriented crosswise to the length of designed longwalls. The length of individual lateral sections varies from 610 up to 1260 m. In the coal seam, plane distance between individual laterals was assumed as maximum 200 m. As a target, it was assumed to drill totally 62.2 km of 152 mm diameter lateral wells in the coal seams. Fig. 12 shows the spatial set of the wells meant for methane drainage ahead of mining. They consist of vertical wells and directional wells with lateral sections. At noted in Fig. 13, it is shown the general view of the geological model of the P-1 mining acreage together with exploratory wells and with the directional and vertical wells meant for methane drainage ahead of mining.
6. Analysis of methane drainage using surface directional wells Analysis of methane drainage using directional wells was made based on the results of numerical calculations for the period of 5 years. The simulations were performed in AnsysCFX software, which belongs to the group of computational fluid dynamics
0s 1 .5 h 3h 2 days 14 days 6 months
1 .1 e-002 1 .0 e-002 9 .0 e-003 8 .0 e-003 7 .0 e-003 6 .0 e-003 5 .0 e-003 4 .0 e-003 3 .0 e-003 2 .0 e-003 1 .0 e-003 0 .0 e+000
14 months 25 months 30 months 64 months 0
2500 5000 (m) 1250 3750
Fig. 14. Drop of methane content of the Seam 9 in the vertical plane perpendicular to the axis of horizontal well.
(CFD) software using in their computations method of finite element method (FEM) [3]. For the calculations, it was assumed that the drainage process will have isothermal course. It was assumed that the temperature of gas will be the same as the surrounding rock mass at 41 °C and
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Total methane intake from the wells (m3)
Fig. 15. Results of calculations of the dynamics of methane inflow changes (kg/s) in the individual lateral sections N1, . . ., N8 designed in northern part of Seam 9.
7000000 6000000
Seam10 (E)
5000000 4000000 Seam 10 (N)
3000000 2000000
Seam 9 (E)
1000000
0
0. 5
1. 0
1.5
2.0
2.5
Seam 9 (N) 3. 0 3.5
4.0
4.5
5.0
Period of time (year)
Fig. 16. Comparison of the results of total methane intake (m3CH4) from individual parts of the seams covered by surface drainage.
the conditions for the methane filtration and desorption from the coalbeds will be non-stationary. The coal was treated as a dry, porous medium (without water) with the porosity c = 0.05 and permeability K = 2 10 15 m2. For the Seam 9, it was assumed, that methane content will be 12.75 m3/tccs, and for the Seam 10 it will be 13.70 m3/tccs. The sorption kinetics constant k was assumed 0.0001 and deposit pressure from Langmuir isotherm, which was established during the well tests. The results of the calculations for the northern part of Seam 9 were presented at Figs. 14 and 15. Fig. 14 shows graphically drop of methane content of the seam in time. The changes of saturation were shown in the vertical plane perpendicular to the axis of horizontal well. At the graph (Fig. 15), it is shown dynamics of methane inflow changes (kg/s) in the individual lateral sections N1–N8. The numerical calculations show that the relatively higher intake of methane can be achieved from the drainage wells designed in the northern part of Seam 9 and Seam 10. The simulations indicate that during the initial stage of drainage (first 24 h) methane
intake from single lateral section located in the northern part can be 0.018–0.034 kg/s (1.6–3.1 m3/min) for the Seam 9 and 0.027– 0.051 kg/s (2.5–4.7 m3/min) for the Seam 10, which is from 2 to 12 times higher comparing with the intake coming from the similar wells located in the eastern part (E). In the eastern part (E) after 4–22 months there is a drop of methane flow from the individual lateral section down to 0.001 kg/s (0.1 m3/min), which is the same as in the northern part. Drop of methane flow in the northern part down to 0.002 kg/s (0.2 m3/min) occurs only after 16–24 months. Fig. 16 shows the results of the calculations of total methane intake by lateral sections of the wells, with division on the wells designed in the eastern and northern parts of the Seam 9 and Seam 10. Results show that total methane intake from designed wells in 5 years will be 14.4 106 m3, including 4.95 106 m3 from Seam 9 (N), 6.20 106 m3 from Seam 10 (N), 1.63 106 m3 from Seam 9 (E), and 1.65 106 m3 from Seam 10 (E). Assuming methane resources within the boundaries of designed longwalls in the northern part of the Seam 9, degasification degree was determined of within the boundaries of the longwalls PN1, . . ., PN-6, as shown in Table 4. Our research shows that average degree of degasification of the Seam 9 and Seam 10 in northern part for designed longwalls PN1, . . ., PN-6 in Seam 9 reaches 12%. Based on above calculations, it can be concluded its influence on decreasing forecasted methane content of designed longwalls. After another analysis of methane hazard in the longwalls PN-1, . . ., PN-6, it can be concluded that absolute methane-bearing capacity after implementation of surface drainage ahead of mining will reach: 47.4 m3/min for the longwall PN-1, 45.4 m3/min for the longwall PN-2, 47.6 m3/min for the longwall PN-3, 46.1 m3/min for the longwall PN-4, 42.6 m3/min for the longwall PN-5, and 36.8 m3/min for the longwall PN-6. After comparing above values (Table 4) with the forecasted values without drainaging from the surface (Table 3) it can be concluded, that during coal exploitation after drainage from the surface, forecasted methane hazard will be decreased by 10%. It can be expected that methane hazard in the designed longwalls will be still high, due to the fact that methane hazard fighting with ventilation methods is applicable only when the methane-bearing capacity is not exceeding 27 m3/min. In order to provide safe coal exploitation within mining Acreage P-1, it will be necessary then to apply conventional drainage (apart from drainage ahead of mining) using drainage boreholes from underground workings. Minimum drainage effectiveness should reach at least 27% for longwall PN-6 and 44% for longwall PN-3.
7. Conclusions The results of methane-bearing capacity for the designed longwalls from PN-1 to PN-6 show high methane hazard during coal exploitation in Seam 9 of the mining acreage P-1. When
Table 4 Degree of degasification of the Seam 9 and Seam 10 in the northern part, for the longwalls: PN-1, . . ., PN-6 in Seam 9. #
Designed Longwall
Seam
1. 2. 3. 4. 5. 6.
PN-1 PN-2 PN-3 PN-4 PN-5 PN-6
Seam Seam Seam Seam Seam Seam
9 9 9 9 9 9
Methane resources in the Seam 9 and Seam 10 within the boundaries of the longwall (m3)
Methane intake from Seam 9 and Seam 10 within the boundaries of the longwallsin 5 years time (m3)
Degree of Seam 9 and Seam 10 degasification (%)
9.0 106 11.8 106 14.2 106 14.6 106 16.6 106 17.0 106
1.1 106 1.4 106 1.7 106 1.8 106 2.0 106 2.0 106
12.2 11.8 11.9 12.3 12.0 11.7
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considering daily coal output at the level of 2300–3300 t/day, forecasted methane emissions into the environment of the longwalls varies between 41 up to 53 m3/min. High forecasted methane content of above longwalls justified the importance of the drainage ahead of mining concept of the seams located in the exploitation-induced zone. After performing the simulation of methane intake by designing 62 km directional wells from surface drainage ahead of mining, it can be concluded that during first 5 years, forecasted methane intake will reach 14.4 106 m3. Assumed method of drainage will result in degassing degree of 12% of the Seam 9 and Seam 10 within the boundaries of designed longwalls PN-1, . . ., PN-6. The result could not ensure safe exploitation within Mining Acreage P-1. Apart from drainage ahead of mining it will be necessary to apply
conventional drainage using drainage boreholes in the underground activity. Simulation results of non-relaxed rock-mass proved possibility to apply appropriate techniques of deposit simulation for increasing efficiency of drainage ahead of mining. References [1] Instruction # 14. Technical handbook. Dynamic forecast of the absolute methane-bearing capacity of the longwalls. Katowice: Central Mining Institute; 2000. [2] Introduction Course. Petrel (v.2005). Schlumberger Information, Solutions; 2006. [3] ANSYS Release 10.0. ANSYS, Inc., User’s guide; 2005.