Geochemical analyses of ground air within the hole exploitation of Hard Coal Mine KWK Morcinek

Transkrypt

1 GOSPODARKA SUROWCAMI MINERALNYMI Tom Zeszyt 3/1 JAN MACUDA*, LUDWIK ZAWISZA* Geochemical analyses of ground air within the hole exploitation of Hard Coal Mine KWK Morcinek Introduction One of the most serious environmental hazards related with high methane coal exploitation are gas exhalations from the overburden, and gas migration in the annular space, geologic wells and technical wells drilled in the coal extraction area. Methane migration in rock layers has a diffusion and effusion character. Their share in total gas migration in the rock environment depends on the microstructure of rocks. The effusion phenomena dominate in tectonically loosened zones and in fractured rocks, whereas diffusion effect prevails in compact, low porous rocks [7, 8]. Natural methane exhalations are usually connected with definite geologic conditions in the coal extraction area, bedding of layers, degree of tectonic deformations, thickness and filtration properties of overburden rocks over the coal seams. The methane outflows to the surface in the shaft area are mainly connected with the untight casing; in the case of geologic and technological wells the outflows were caused by insufficient tightness of the cement plug in the annular space [6, 8]. Methane outflows around the shafts and wells are more easily identifiable and controllable than their counterparts. However, their course is relatively more intense. In extreme cases, this may lead to surface gas exhalations, and the resultant explosion hazard. Geochemical measurements were performed for a quantitative and qualitative assessment of workings in the closed Coal Mine Morcinek. * AGH-University of Science and Technology, Kraków, Poland.

2 Geological and technical characteristic of the closed Coal Mine Morcinek In the period of November 1986 to October 1998 the coal beds were goaf-exploited in the Coal Mine Morcinek. The coal levels 404/1-2 to 416/1-2 were exploited at a depth of 650 to 1100 m b.s. Their thicknesses ranged between 1.30 and 4.20 m. The total of ca mln ton of coal and ca. 9 mln m 3 of waste rock were produced from these levels [1]. When closing the Coal Mine Morcinek, cm of workings at the levels 650, 800, 950 and 1100 m were liquidated. Depending on the area, either dam or blow-out prevention plugs were applied. The technology was selected mainly in view of the methane, water and fire hazards. The thickness of plugs made during closing operations depended on the cross-section of the working, and was 10 to 15 m for backfilling plugs and 5 to 10 m for blow-out prevention plugs [1]. Owing to the large coal leftovers and possibility of resuming coal production, the closed shafts were filled with fine backfilling material having good filtration parameters for protecting the shaft s casing against deformations and slides. Sand and granite ground materials were used for this purpose. Part of the technical equipment was dismounted before the closing of shafts begun. Water-tight dams were construed at the shaft bottom cutting off the shaft inlets from the remaining workings; the outlets were closed tight with iron-reinforced plates with supply holes, and shafts equipped with methane-removal blow-out and fire-protection devices. Ventilation canal outlets were cut off with dams [1]. The main system was gradually dewatered by cutting off drainage holes leading to Dêbowiec beds, depression holes were liquidated and the main and auxiliary pump plants were gradually closed. High coal concentration in the large part of the mining area caused considerable degrading of area. Exploitation of levels 406/1, 406/2, 407/3, 410/1 and 416/1-2, of total thickness ca m, has caused a land subsidence of ca. 7.5 m. 2. Methodics of geochemical measurements The quantitative and qualitative assessment of methane content in soil air was based on geochemical image of two closed shafts nos. I and II and well Kaczyce-1, for coal-bed methane intaking [2, 3, 4, 5]. Geochemical analyses were performed in two stages. The first one was realized in the period 22 June to 24 June 2005, whereas the second stage was between 21 June and 24 June At each stage over 9 measurements were made around the mentioned objects [3, 7]. Measuring probes were distributed radially every 120 with the increasing distance between specific measuring points (2, 5 and 10 m) at each of the three probing directions. In the mining shafts area some of the measuring probes were distributed discordantly with the planned array. This was caused by the concrete plates inbuilt in the basement.

3 Measuring probes were made with the use of a Borro AB Geotechniques Sweden percussion kit. After drilling a hole to a depth of 2.5 m, the filtration columns were installed. Then the system was sealed, freed of air with a suction pump and closed tight. After 24 hours the soil air was sampled from the wells to aspirators or glass containers and transported to the laboratory. The chromatography analysis of soil air was made with the use of a gas chromatograph HP 5890 Series II by Hewlett Packard with a detector FID and a capillary column. The equipment was calibrated with mixtures by MULTAX. The results of chemical analyses of soil air are presented in Tables 1 and 2, and the distribution of methane content around the well Kaczyce-1 and shafts nos. I and II in Figs. 1 to TABLE 1 Results of surface geochemical measurements performed in the area of the Coal Mine Morcinek on 22 to 24 June 2005 TABELA 1 Wyniki powierzchniowych pomiarów geochemicznych przeprowadzonych w okolicy Kopalni Wêgla Morcinek w dniach czerwca 2005 r. Name of analyzed object Measuring point no. CH 4 content [vol.% ] Well Kaczyce - 1 Shaft no. I Shaft no. II

4 346 TABLE 2 Results of surface geochemical measurements performed in the area of the Coal Mine Morcinek on 21 to 24 June 2006 TABELA 2 Wyniki powierzchniowych pomiarów geochemicznych przeprowadzonych w okolicy Kopalni Wêgla Morcinek w dniach czerwca 2006 r. Name of analyzed object Measuring point no. CH 4 content [vol.%] Well Kaczyce - 1 Shaft no. I Shaft no. II Closing remarks The analysis of the results of methane content in soil air around the well Kaczyce-1 and shafts nos. I and II (Tables 1 and 2) and in maps of methane content (Figs. 1 to 4) reveals that they were low. At the first stage of measurements performed in June 2005 the methane content in the area of the well Kaczyce-1 was 0 to 0.279%, and the maximum value was observed in the exploration well no. 1. The methane content near the shaft no. I was 0 to 0.01%, and no methane was found in the soil air of the shaft no. II.

5 347 Fig. 1. Map of methane content [vol.%] in soil air in the area of the well Kaczyce-1. State as of 23 June 2005 Rys. 1. Mapa zawartoœci metanu [obj. %] w powietrzu glebowym w okolicy odwiertu Kaczyce-1. Stan na 23 czerwca 2005 r. Fig. 2. Map of methane content [vol.%] in soil air in the area of the well Kaczyce-1. State as of 24 June 2006 Rys. 2. Mapa zawartoœci metanu [obj. %] w powietrzu glebowym w okolicy odwiertu Kaczyce-1. Stan na 24 czerwca 2006 r.

6 348 Fig. 3. Map of methane content [vol.%] in soil air in the area of Shaft I and Shaft II within the Coal Mine Morcinek. State as of 23 June 2005 Rys. 3. Mapa zawartoœci metanu [obj. %] w powietrzu glebowym na terenie Szybów I i II Kopalni Wêgla Morcinek. Stan na 23 czerwca 2005 r.

7 349 Fig. 4. Map of methane content [vol.%] in soil air in the area of Shaft I and Shaft II within the Coal Mine Morcinek. State as of 24 June 2006 Rys. 4. Mapa zawartoœci metanu [obj. %] w powietrzu glebowym na terenie Szybów I i II Kopalni Wêgla Morcinek. Stan na 24 czerwca 2006 r.

8 350 At the second stage of measurements performed in June 2006 the methane content in the soil air around the well Kaczyce-1 was also low 0 to %, to increase in the area of the shaft no. 2.0 to 0.04%. The observed methane content values around these objects may speak for the leaky the casing and migration of methane from the closed workings to the surface. Low methane quantities in soil air do not create outburst direct hazard; however, in favorable conditions methane may accumulate in undersurface technological installations and cellars of the buildings, exceeding the low explosiveness values. REFERENCES [1] B i e l e w i c z R., G ó r n i k M., W a t o r L., 1998 Dokumentacja okreœlaj¹ca zmiany warunków hydrogeologicznych w rejonie likwidowanej KWK Morcinek. MG i JSW S.A. Katowice. [2] D z i e n i e w i c z M., G ó r e c k i W., S e c h m a n H., 1997 Powierzchniowe badania geochemiczne w rejonie Abramów Nasutów. Nafta-Gaz Nr 11. [3] M a c u d a J., Z a w i s z a L., 2006 Monitoring œrodowiska gruntowo-wodnego w rejonie likwidowanych kopalñ. Mat. Konf. Szko³y Eksploatacji Podziemnej. Kraków. [4] S c h m i t z R.A. et al., 1996 A Risk Based Management Approach to Problem of Gas Migration. SPE paper [5] S t o p a J., R y c h l i c k i S., W o j n a r o w s k i P., 2001 Analiza wp³ywu eksploatacji na ekshalacje gazu ze z³ó. Wiertnictwo Nafta Gaz, t. 18/1. Kraków. [6] Szl¹zak J., Szl¹zak N., Borowski M., Obracaj D., 2006 Program komputerowy do obliczania rozk³adu prêdkoœci powietrza i stê enia metanu w zrobach œcian zawa³owych. Mat. Konf. Szko³y Eksploatacji Podziemnej. Kraków. [7] Zawisza L., Macuda J., Nagy S., 2006 Protection of urbanized mining areas in the mine s closing processes. Polish Journal of Environmental Studies; 2006, vol. 15, no. 15C. [8] Z a w i s z a L., M a c u d a J., 2007 Ocena zagro eñ dla œrodowiska naturalnego wystêpuj¹cych przy poszukiwaniu i rozpoznawaniu oraz eksploatacji z³ó wêglowodorów. Praca niepublikowana: AGH Kraków. ANALIZY GEOCHEMICZNE POWIETRZA GRUNTOWEGO W EKSPLOATACJI OTWORU W KOPALNI WÊGLA KAMIENNEGO KWK MORCINEK S³owa kluczowe Zamkniêcie kopalni, metan, zagro enie metanowe, monitorowanie geochemiczne Streszczenie Zamkniêcie kopalni wêgla kamiennego prowadzi do powstania iloœciowych i jakoœciowych zmian pewnej liczby czynników œrodowiskowych. Woda i grunt nale ¹ do œrodowisk najbardziej zagro onych przez negatywny wp³yw operacji zamkniêcia kopalni. Do najwa niejszych zagro eñ nale ¹ emisje metanu i dwutlenku wêgla ze z³ó wêglowych. Intensyfikacja przep³ywu gazu na powierzchniê terenu najczêœciej wynika z czêœciowego lub ca³kowitego zatrzymania pompowania wód w kopalni. Powoduje to zmiany struktury karbonowych formacji

9 351 wodonoœnych, a w efekcie tak zwany efekt t³okowy. W zamkniêtych kopalniach efekt ten mo e byæ znacznie bardziej nasilony po zatrzymaniu wentylacji w starych wyrobiskach. W opracowaniu podano wyniki analizy geochemicznej w zamkniêtej kopalni wêgla KWK Morcinek. Badanie mia³o na celu ocenê skali wystêpowania gazów kopalnianych w strefie powierzchniowej oraz szczegó³owe zasady monitorowania geochemicznego. GEOCHEMICAL ANALYSES OF GROUND AIR WITHIN THE HOLE EXPLOITATION OF HARD COAL MINE KWK MORCINEK Key words Closing of mines, methane, methane hazard, geochemical monitoring Abstract Closing of hard coal mines leads to quantitative and qualitative changes of a number of environmental factors. Water and ground are one of the most endangered environments under the negative impacts of mines closing operations. Among the most important hazards are methane and carbon dioxide emissions from the coal beds. Intensification of gas flow to the surface area is most frequently caused partial or entire stopping of mine s waters pumping. This results in reconstruction of the Carboniferous aquifer, and consequently, the so-called piston effect. In the closed mined this effect may be considerably intensified after stopping ventilation of the abandoned workings. The results of geochemical analyses within a closed Coal Mine KWK Morcinek are presented in the paper. The investigations were aimed at evaluation of the scale of occurrence of mine s gases in the surface zone and principles of its detailed geochemical monitoring.

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