A Secondary Zone of Coal-bed Methane in (South Poland) Potential for Methane Exploitation[1]

International Journal of Coal Geology 86 (2011) 157–168

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International Journal of Coal Geology

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The occurrence of a secondary zone of coal-bed methane in the southern part of theUpper Silesian Coal Basin (southern Poland): Potential for methane exploitation

Sławomir Kędzior ⁎University of Silesia, Faculty of Earth Sciences, Będzińska 60, 41-200 Sosnowiec, Poland

⁎ Tel.: +48 32 36 89 371.E-mail address: [email protected].

0166-5162/$ – see front matter © 2011 Elsevier B.V. Aldoi:10.1016/j.coal.2011.01.003

a b s t r a c t

Article history:Received 8 April 2010Received in revised form 11 January 2011Accepted 12 January 2011Available online 21 January 2011

Keywords:Coal-bed methaneCarboniferous roofGeological structureCoal permeabilityGas fuelUpper Silesian Coal Basin

Coal-bed methane (CBM) exploitation in the Upper Silesian Coal Basin has, in spite of earlier failures, againaroused investor interest. Carboniferous coal seams at depths of 200–500 m are characterized by coalpermeability values (estimated at 27–230 mD) and degrees of methane saturation (almost 100%) that suggestfuture successful exploitation. Based on the results of geological surveys archived in the Polish GeologicalInstitute, the shallow CBM zone is defined as a gas horizon distinct from a deep CBM zone. The disposition ofthe shallow zone follows the topography of the Upper Carboniferous paleorelief, and, is deemed the mostimportant factor controlling methane distribution within this zone. The most favorable places for CBMaccumulation within the shallow coal seams are erosional highs and the slopes of Upper Carboniferous ridgesassociated with fault zones. The thickness of the zone (N200 m) and methane contents (N8 m3/t coal daf) arehighest in these places. The nearly-full saturation of the coal seams with methane reflects the involvement oftwo genetic types of gas — indigenous late-stage microbial methane and thermogenic methane derived fromthe deeper coals. The favorable geological characteristic of this shallow CBM zone is a potential source ofenergy for Upper Silesia.

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© 2011 Elsevier B.V. All rights reserved.

1. Introduction

A shallow zone of secondary coal-bed methane (CBM) inuppermost-Carboniferous coal seams occurs at depths from 200 to500 m in the southern part of the Upper Silesian Coal Basin (USCB). Anoverlying hermetic cover of Miocene claystones and mudstonesfacilitates gas concentration in these seams. Recently, this zone hasbecome the subject of attention by investors interested in exploitingthe methane. The secondary accumulation appears to offer betterprospects for CBM production than deeper-lying coal seams. Attemptsto recover gas from the deeper seams a decade ago were unsuccessful(Kędzior, 2009b). In October 2006, the Ministry of Environmentgranted Euro-Energy Resources Inc. a concession to explore andevaluate the occurrence of CBM within the USCB Main Syncline(Kędzior et al., 2007).

The possibility of recovering CBM through surface boreholes fromshallow coal prompted the present study of the secondary zone as anautonomous CBM horizon independent of the deep (primary) methanezone described bymany (e.g., Borowski, 1968; Kędzior, 2009b; Kotarbaet al., 1995; Kotas, 1994; Kwarciński and Hadro, 2008; Niemczyk, 1984;Tarnowski, 1989). This paper analyzes the present-day distribution ofmethane in the shallow Carboniferous coal seams in relation to

geological setting and coal parameters, e.g., permeability, that wouldinfluence CBM borehole production.

The area in question is situated in the southern part of the USCBbetween the cities Pawłowice to the west and Pszczyna to the east. Itincludes the undeveloped coal deposits of Pawłowice, Warszowice–Pawłowice and the southernpart ofKobiór–Pszczyna (Fig. 1). It lieswithinthe southern flank of the Main Syncline between two large regional faultzones — those of Jawiszowice to the north and Bzie–Czechowice to thesouth (Fig. 1). The Carpathian thrust is 10–20 km further to the south.

2. The geological context and methane content

2.1. Lithostratigraphy

The main elements of the geology of the area are the Carboniferouscoal-bearing strata, Miocene strata and Quaternary sediments. TheCarboniferous sequence includes several lithostratigraphical series(Fig. 2), the most important of which is the Mudstone Series (LowerPennsylvanian — Westphalian A and B) with a thickness reachingN1300 m(Buła andKotas, 1994). Towards the east, the CracowSandstoneSeries (Middle Pennsylvanian—Westphalian B and C) appears at the top.

Clays of the Miocene Skawina Formation discordantly overlyingthe coal-bearing strata within the entire area are molasse of theCarpathian Foredeep. The thickness of these strata varies from ca200 m to the north to b700 m to the south in the area. The Quaternarysediments are comprised of glacial and fluvio-glacial deposits that arethickest in river valleys.

Fig. 1. Location of the study area in the southern part of the USCB. 1 — the boundaries of the area, 2 — main city, 3 — Łaziska Sandstones, 4 — Mudstone Series, 5 — regional faults.

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2.2. Tectonics

The areaof interest is locatedwithin thedisjunctive part of theUSCB inwhich the two regional fault zones of Jawiszowice and Bzie–Czechowiceare themost important tectonic elements (Fig. 1). Both dislocations are oflarge size with throws of several hundredmeters in a southerly direction,which commonly divide into several fault surfaces. They are probably ofVariscan age but were reactivated in the Miocene due to Alpine folding(Teper and Sagan, 1995). Apart from these, there are many smaller faultstrending SW–NEwhich,with others orthogonal to them, build a systemoftectonic blocks of diverse sizes. The disposition of the blocks is not

Fig. 2. Simplified lithostratigraphic division of the CarboniferousModified after Buła and Kotas, 1994; Kandarachevová et al., 200

accurately defined as the only geological constraints are from boreholedata.

The dip of the Carboniferous beds is low — several degrees to thenorth and north-east. Only in the vicinity of the main dislocationsdoes the dip locally increase to b40 degrees.

2.3. The Carboniferous erosion surface

The varied topography of Carboniferous surface is a key feature ofthe area (Fig. 3). Ridge-like elevations and valley depressions

rocks.9; Kędzior, 2009b with series description after Kotas, 1995.

Fig. 3. The topography of the Carboniferous erosion surface. 1 — main faults, 2 — borehole, 3 — elevation of the Carboniferous erosion surface (m above sea level).Source: Archive of the Polish Geological Institute.

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constitute a latitudinal system coincident with the direction of themain faults (Bogacz et al., 1984; Buła et al., 2007; Jura, 2001).

The most important morphological elements of this erosionsurface are (Jura, 2001):

• the Żory ridge of varied topography located close to the JawiszowiceFault Zone.

• the Pawłowice Ridge is the most important morphological element inthe area. In contrast to the gentle north slope of this ridge, the southernslope is steep and characterized by numerous small valleys. Moreover,the ridge constitutes amorphological feature ofN500 mrelativeheightwhich coincides with the surface of the Bzie–Czechowice Fault Zone(Fig. 3).

• The asymmetric Strumień Valley which runs parallel to the Bzie–Czechowice dislocation and the Pawłowice ridge to the south.

These varied features reflect long-term pre-Miocene differentialerosion of the Carboniferous strata and differences in their resistance toerosion (e. g. Buła et al., 2007). The possible role of Pre-Miocene tectonicmovements that contributed to the formation of the CarpathianForedeep, cannot be discounted.

2.4. Coal rank and maceral composition

High- and medium volatile bituminous coals dominate in the area(ASTM D Standard Classification of Coals by Rank) and the coal rankdecreases towards the east. The vitrinite reflectance (Ro) decreases from1.0 to 1.5% in the Warszowice–Pawłowice area to 0.8–1.0% aroundKobiór–Pszczyna (Jurczak-Drabek, 1996). The average calorific value forthe coal is 26 MJ/kg (Kotas et al., 1983).

Vitrinite group macerals predominate (70–80%) in coal seamshosted in the Mudstone Series. In seams within the Upper SilesianSandstone Series, the proportion of inertinite group maceralsincreases from ~10–15% to ~30–40%. Liptinite group macerals rarelyexceed 10% and decrease to zero with depth.

2.5. Hydrogeology

The aquifers in the area occur within permeable sandstones andconglomerates isolated from each other by impermeable mudstones andclaystones. In the coal-bearing Carboniferous strata, the most water-richare the Łaziska Sandstones of the Cracow Sandstone Series and the Rudaand Saddle Sandstones of theUpper Silesian Sandstone Series. The ŁaziskaSandstones, with a limited thickness b200 m and occurring only in theKobiór–Pszczyna area have a filtration coefficient of ca 10−6 to 10−4 m/s(Różkowski, 1991). For the sandstones of the Upper Silesian SandstoneSeries, comprising 50–75% of the thickness of the Series, the coefficient is10−5 m/s (Różkowski, 1991). The Carboniferous Mudstone Series is amonotonous complex of impermeable claystones in which small water-bearing horizonswithin sandstone inserts display high pressures inmanycases. In the Miocene sediments, those with water are exclusively sandyinserts with filtration coefficients of ~8.0 10−8 to 2.4 10−6 m/s in theimpermeable clays of the Skawina Formation.

The waters in Carboniferous and Miocene hosts are weakly minera-lized (HCO3–Cl–SO4–Na or SO4–HCO3–Na) to depths of b200–300 m.Salinity increases rapidly below that depth (Kędzior, 2009b). The deepwaters are considered to reflect the infiltration of Miocene sea water andof meteoric waters into then-exposed Carboniferous rocks (Pluta andZuber, 1995).

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Infiltration of meteoric waters into the Carboniferous rocks ceasedwith the deposition of the impermeable Miocene cover. Relict waterstrapped in the sandy inserts in the Miocene clays are also sealed.

2.6. Methane occurrence

The study area is characterized by high- and variable CBM contents.Other rocks (e.g., sandstones) also contain methane. In coal seams, themethane primarily occurs as sorbedmethanemainly in coalmicropores(e.g. Lamberson and Bustin, 1993). Free methane, in much lesserquantity, fills macropores and fractures in both coal and sandstones,which is typical for conventional, natural gas deposits.

The spatial distribution of CBM in the coal series was shaped by pre-Miocene burial and uplift processes (Kędzior, 2009b). Uplift of the coalseries after late-Carboniferous times led to the erosion of the upper part ofthe series and facilitated the infiltration of meteoric waters. The resultingdeep degasification involved only the upper few hundred meters of rockthough, in places, it extended down to N1000 m depending on locallithology and structural conditions (Kotarba and Ney, 1995). Later,migrating methane would be trapped in the degassed coal seams andsandstones under the impermeable Miocene cover, which is the case inthe southern part of the USCB.

The present-day distribution of coal-bed methane within the areaincludes (Fig. 4):

• a shallowzoneof highmethane content (b4.5–20 m3/t coaldaf) in coaland other rocks with a typical thickness bca 250 m holding late-stagesecondary methane.

• an intermediate zone of decreasing methane content (ca 1 m3/t coaldaf).

• a deep primary zone of high methane content (N4.5 to 10–20 m3/tcoal daf) which is thicker andmore extensive than the shallow zone,

Fig. 4. Variation in coal-bed methane contents with depth. daf — dry ash-free.Modified after Kotas, 1994.

the maximum depth of this zone is not fully defined but locallyextends below 1500 m.

In some boreholes, the shallow secondary zone is significantlythicker than 250 m and in some cases, it links up with the deepprimary zone (Fig. 5). Where this happens, the entire Carboniferousprofile is methane-enriched. Methane also occurs in sandstones lyingat the Miocene and Carboniferous boundary within weatheredCarboniferous rocks and in the Miocene strata.

Themethane occurring in the deep primary zone is considered to bethermogenic (e.g., Kotarba, 2001). The methane in the shallow zonemight have migrated from deeper-lying coals (e.g., Hemza et al., 2009;Kotarba et al., 1995) or it might be secondary, late-stage microbialmethane produced by archaebacteria (Kotarba and Pluta, 2009) or both.

In general, the area is characterized by high gas contents thatcommonly exceed 4.5 m3/t coal daf. In the shallow zone, the predominantgas is methane (N80–90%), typically accompanied by ethane (ca 1% andmore depending on depth). In the primary zone, propane (1–2%) appearsbelow a depth of 1000 m. Within the intermediate zone of decreasingmethane content, the amount of nitrogen in the gas increases. Methanepredominance improves the quality of the gas as a fuel.

Almost all working coal mines in the area (e.g., Brzeszcze–Silesia,Krupiński, Pniówek and Zofiówkamines) are among themost gas-richmines in the USCB. Methods of methane production and utilizationare updated continuously. During 1997–2006, seven mines collectedN1.5 billion m3 of coal-mine methane (CMM), almost 1.2 billion m3 ofwhich was used as a local fuel and the remainder vented into theatmosphere (Kędzior, 2009a).

3. Processes involved in the development of CBM zones and sorptioncapacity of coal

3.1. Methane origin

Themethane in the coal bearing formations originated from the coalseams and from the type III dispersed organicmatter in other rocks (e.g.,Jasper et al., 2009; Kotarba, 2001; Semyrka et al., 1995). Methane(microbial) can also be generated by archaebacteria introduced bymeteoricwaters (e.g. Flores, 2008; Kotarba andPluta, 2009). In theUSCB,as in other basins (e.g., Wei et al., 2007), the generation of the methanewas probably a multi-stage process (e.g., Kędzior, 2009b).

Initially, the methane, higher gaseous hydrocarbons (C2 to C5) andcarbon dioxide in the coal-bed gasses were generated during thebituminous stage of coalification that lasted no longer than several Maandwas completed by the end of the Variscan orogeny (Kotarba, 2001).

Fig. 5. An example of the shallow CBM zone linking with the deep primary zone.G — methane content, h — elevation.Source: Archive of the Polish Geological Institute.

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Some authors (e.g., Kotas, 1990) have proposed that heatflowextendedthe coalification process into the Mesozoic or Paleogene. Today, thesegasses occur in the primarymethane zone at a depth N1000 m. Vitrinitereflectance data (1.5–1.7%) shows that the coal seams attained the gaswindow stage of thermal maturity and were able to generate methaneand other coalbed gasses.

Another stage of methane generation occurred shortly before orearly in the Miocene when the coal-bearing Pennsylvanian strata wasexposed and subjected to weathering and erosion (Kędzior, 2009b).Those conditions facilitated their infiltration bymeteoric waters alongwith methanogens and nutrients, required for methane-producingbacteria and other gas-producing organisms (Kotarba and Pluta,2009).

Isotopic studies on the coal-bed gasses of shallow-zone (Kotarba andPluta, 2009) show that coal-bed gasses with δ13C ranging about−70‰occur to a depth of 200 mwithin the Pennsylvanian strata, and that thegasses predominate in the shallow CBM zone. Only thermogenic gassesoccur in the primary CBM zone below a depth of ca 650 m (Kędzior,2009b; Kotarba and Pluta, 2009).

Therefore, there is evidence indicating thatmethane in the shallowCBM zone was generated by bacteria in or about Miocene times. Thisorigin would match that of gasses occurring in other coal basins (e.g.,Aravena et al., 2003; Flores, 2008) or that of conventional natural gasin the Polish part of the Carpathian Foredeep (e.g., Kotarba, 1999).

The shallow- and deep CBM zones are clearly separated by themethane minimum in profiles of many boreholes in the Pawłowicearea. The different origins of the gasses in the twomethane-rich zonesmay partly explain this.

3.2. Methane migration

The process of coal-bed methane migration reflects changes inpressure and temperature conditions. Rock burial and uplift result inpore-pressure and rock-temperature changes that lead to changes insorption capacity (e.g., Hildenbrand et al., 2006; Khavari-Khorasaniand Michelsen, 1999). Methane driven from coal seams at hightemperatures is adsorbed by seams at lower temperatures.

Asmethanemigrates towardsareasof lowerpressure, thedestinationswere erosional highs in the Carboniferous surface and slopes. Thus, today,elevated methane contents preferentially characterize seams in theseplaces. Both thermogenic and microbial methane migrated through theCarboniferous rocks. Microbial methane migrated only short distanceswithin the area immediately below the roof of the coal series.Thermogenic methane moved upwards over a much greater distancefrom its deeper source along faults and other breaks (e.g. Alsaab et al.,2009; Staniek, 1986; Tarnowski, 1989). The connection between theoccurrenceof coal-bedgasses in theweathered topofCarboniferous seriesand deeper-lying high rank coals has been recognized in the Czech part ofthe USCB (Hemza et al., 2009; Kandarachevová et al., 2009) and in thePolish part around Jastrzębie (Borowski, 1968; Kędzior, 2009b).

3.3. Methane accumulation

The Miocene clays complex overlying the Carboniferous coalbearing strata, as well as claystones and mudstones of the Załęże Bedsat the top of the Carboniferous sequence enabled CBM accumulationin the shallow zone (Kędzior, 2009b).

CBM isnot exclusive to the coal seams in theuppermost Carboniferousstrata. Freemethane also occurs inweathered breccia in those same strataand close by in sandstones of the Dębowiec Formation (e.g., Poborski,1960). In these cases, methane is typically linkedwithwater. The free gasin theMiocene deposits raises the question, if the secondary CBM zone, inwhichsorbedmethanepredominates, is part of a largermethanecomplex,also embracing coal seams, gaseous sandstones and conglomerates at thetop of the Carboniferous complex andMiocene rocks. This possibilitymaygain support from the fact thatmethane of similarmicrobial origin to that

in the shallow CBM zone occurs in conventional gas deposits in theCarpathian Foredeep (e.g., Kotarba, 1999) and also by the occurrence ofgas resources in Miocene sandstones in nearby Dębowiec Śląski andPogórz. The problem of coexisting coal-bedmethane and free natural gasinMiocenedepositshasbeen longdiscussed(e.g., Kędzior, 2008b;Kotarbaand Pluta, 2009; Obuchowicz, 1963; Poborski, 1960).

3.4. Sorption capacity and methane saturation in coal

Coal sorption capacity, i.e., the total gas capable of being adsorbedat given temperatures and pressures, is a parameter controlled by coaltype, temperature and pore pressure (Kędzior, 2009b). Manystudies incoal basins elsewhere have shown that coal rank and the content ofvitrinite and inertinitemacerals, arepositively influential (e.g., Buschet al.,2004; Gentzis et al., 2008; Lamberson and Bustin, 1993; Laxminarayanaand Crosdale, 1999), whereas some authors did not find any correlationbetween maceral composition and sorption capacity (e.g. Krooss et al.,2002). There also seems to be a rank dependence of the influence ofmaceral composition on sorption capacity of coal (Crosdale et al., 1998).Negative influences are temperature and moisture content (e.g.,Hildenbrand et al., 2006). In the USCB, similar studies (e.g., Borowskiand Sosnowski, 1977;Hemza et al., 2009; Jurczak-Drabek andKwarciński,2003) reached broadly similar conclusions. However, in the case of USCBcoals, sorption capacity is mainly controlled by the inertinite group(fusinite and semifusinite; Jurczak-Drabek and Kwarciński, 2003). In thesub-area of interest here, coal parameters controlling sorption capacityfavor methane accumulation (Table 1); the total content of vitrinite andinertinite groupmacerals is high (69–88%), the ash content is low (b16%)and the rock temperature is moderate (21–34 °C).

The difference between the sorption capacity of coal and its present-day methane content defines the degree of methane saturation. In thestudy area, a considerable degree of undersaturation is evident (30–70%;Kwarciński and Hadro, 2008). Based on research elsewhere (e.g.,Hildenbrand et al., 2006), this undersaturation is probably the result ofthegeological history that included long-termbasinuplift and, during theMesozoic and Paleogene, caused major coal-seam degasification afterwhich no significant new gas was generated (see Sections 2.6 and 5.2.).Only the shallow parts of coal seams are almost fully methane saturated(80–100%; see Kędzior, 2009b). This significant level of saturation mayreflect the generation of late-stage microbial methane in the uppermostpart of coal-bearing series during the Miocene, augmented by thermo-genic methane from deeper levels (see Sections 3.2 and 5.2).

4. Experimental

4.1. Source material

This work is based on the results of research carried out duringexploratory drilling for coal and coal-bed methane between 1970and 2007. The geological documentations for the coal deposits inWarszowice–Pawłowice, Pawłowice and Kobiór–Pszczyna areas arearchived by the Polish Geological Institute (PGI). Some additional dataon the reservoir parameters (permeability) of coal were obtainedfrom samples collected from borehole Kaczyce 2/07, and from mineopenings at Zofiówka mine several kilometers outside of the area.

4.2. Methane-content determination

In themajority of the boreholes, methane content was determined byvacuum degasification in hermetic containers — the method used by theKatowiceGeological Enterprise (KPG). Themethod involves thedegassingof coal samples in one litermetal containers under 7–10mmHg pressure(Borowski; Niemczyk; Niemczyk and Daniel in Kędzior, 2009b). In threeexploratory boreholes drilled for CBM, the US Bureau of Mines (USBM)methodwas applied. In contrast to the KPGmethod, thismethod involvesthe degassing of whole sections of core in 30 or 60 foot gas containers

Table 1Coal-seam parameters and methane contents in the shallow CBM zone in the southern USCB.Sources: The archives of the Polish Geological Institute and * Semyrka et al. (1995).

Borehole Stratigraphy Number ofseams

Depth(m)

Rock temperature(°C)

*VitrinitereflectanceRo (%)

*Maceral composition (%) *Mineral matter(%)

Methane content(m3/t coal daf)

Vitrinite(V)

Inertitnite(I)

V+I Liptinite(L)

Piasek IG-1 CracowSandstone andMudstoneSeries (S)

4 325–520 21 0.9 70.9 8.0 78.9 6.8 14.3 4.0

Łąka IG-1 Mudstone S 2 438–508 23 0.7 76.1 8.6 84.7 5.9 9.4 4.5Studzionka IG-1 Mudstone S 3 693–723 33 0.9 70.2 17.7 87.9 8.6 3.5 6.0Krzyżowice IG-1 Mudstone S 1 539–540 24 0.8 77.2 11.6 88.8 6.6 4.6 6.7WarszowicePawłowice TXA

Mudstone S 7 300–380 24 0.8 68.2 9.0 77.2 6.6 16.2 6.7

WarszowicePawłowice 9*

Mudstone S 1 692–693 33 0.9 52.0 27.0 79.0 17.0 4.0 10.5

WarszowicePawłowice 19*

Mudstone S 3 315–341 24 0.8 55.0 14.0 69.0 17.0 14.0 8.4

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under atmospheric pressure for, in many cases, several months. Bothmethods account for gas lost during gas sampling, desorbed gas andresidual gas (Kędzior, 2009b;McLennanet al., 1995). TheUSBMmethod ismore precise than the KPG method, but takes a much longer time. Dataprovided by Twardowski (1997) show that both methods give similarresults. In total, 1319 methane measurements from 87 boreholes wereused.

4.3. Permeability of coal

With the prospect of borehole CBMexploitation from the shallow coalseams in the area, measurements of coal permeability were made. To aconsiderable degree, the success of CBM exploitation is controlled by thisparameter (e.g., Scott, 2002). As no extensive research on coalpermeability has been carried out in the USCB, and in spite of dataprovidedbyAmoco, TexacoandPol-TexMethane, theOil andGas Institutein Cracowwas commissioned to carryout analyses of coal permeability onsamples from the recently-drilled borehole Kaczyce 2/07 and from theopenings at Zofiówka mine.

TheOil andGas Institutemeasurements included in the determinationof coal permeability were made using an apparatus belonging to theTemco Company Inc., that involved nitrogen flowing through the coalsample. In the determination of permeability, the Darcy equation wasapplied.

5. Results and discussion

5.1. The secondary, shallow methane zone determination

For every borehole in the study area, graphs showing the variationin methane content with depth were prepared (Fig. 8). Selectedboreholes in which the shallowmethane zone is best developed showthe following features, which act as limiting criteria (Kędzior, 2008a):

• the bottom of the zone is defined by a methane content of 4.5 m3/tcoal daf,

• apart from a small numbers of cases, where the limit of 4.5 m3/t coaldaf also defines the top, the overlying Miocene cover constitutes thetop of the zone,

• the average methane content within the zone is N2.5 m3/t coal daf• the minimum thickness of a coal seam is 0.6 m• a maximum depth of 700 m (ca −450 m above sea level) — appliesonly where the shallow zone links up with the deep methane zone.

These features are in accordance with the balance criteria for CBMas a main mineral commodity applied in Poland (Directive of Minister

of Environment, December 18th. 2001). The maximum depth of thezone was assumedwith the possibilities of borehole CBM exploitationin mind. Based on experiences elsewhere, depths from 200 to 800 mare optimal for profitable CBM well exploitation (e.g., Kędzior et al.,2007; Pashin, 2010). The remaining criteria are based on knowledgeof methane flows in coal seams. The minimum value of 4.5 m3/t coaldaf is recognized as enabling industrial CBM production (Hunt andStelle, 1991), whereas 2.5 m3/t coal daf enables spontaneous gasdesorption from coal (Kandora and Grzybek in Twardowski, 1997).

The thickness of the shallowmethane zone and the average methanecontent within it are shown in Figs. 6 and 7. On the map of averagemethane contents (Fig. 7), vitrinite reflectance (Ro) and the rocktemperatures are also shown; these parameters control the sorptioncapacity of coal (e.g., Crosdale et al., 1998).

5.2. The degree of development of the shallow CBM zone

Research on the extension and layout of the shallow CBM zone wascarried out in the Warszowice–Pawłowice, Pawłowice and Kobiór–Pszczyna areas (Figs. 6 and 7). The key parameters of the zone arepresented in Table 2. The vertical variation in methane content is shownin Fig. 8.

The zone is most continuous and methane-rich in the Warszowice–Pawłowice and Pawłowice areas (Table 2; Figs. 6 and 7). The maximummethane content was recorded in the Warszowice–Pawłowice 11borehole (average content — 12.5 m3/t coal daf; maximum content —20.2 m3/t coal daf). This borehole is located ca 500 m to the north of theBzie–Czechowice Fault Zone on its upthrow side within the southernslope of the Pawłowice Ridge. It is also sited on the upthrow side of asmall SSW–NNE fault associated with the Bzie–Czechowice Fault Zone(Fig. 7). Theminimum averagemethane content (3.8 m3/t coal daf) wasrecorded in the Pszczyna 73 borehole in the Kobiór–Pszczyna areawhere the zone is discontinuous in character (Figs. 6 and 7).

In the Warszowice–Pawłowice and Pawłowice areas, the shallowcoal seams lie within claystones andmudstones of theMudstone Serieswhich constitute, withMiocene clays, a hermetic seal for CBM (Kędzior,2009b). In the Kobiór–Pszczyna area, porous Łaziska Sandstones in theuppermost Carboniferous strata explain why methane contents of coalseams are relatively low in these strata, compared to the seams withinthe claystones andmudstones. They also explain the shift of the shallowmethane zone to the shales beneath the Łaziska Sandstones in the latterarea (Fig. 9).

The shallow CBM zone is best developed in the boreholes locatedwithin some erosional highs, flat surfaces and, in particular, on theslopes of the Pawłowice Ridge (Figs. 3, 6 and 7). The highest methane

Fig. 6. The thickness of CBM shallow zone in the southern part of the USCB. 1 —main faults, 2 — approximate boundary of the Łaziska Sandstones, 3 — thickness of the shallow CBMzone (m).Source: Archive of the Polish Geological Institute.

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contents (N8 m3/t coal daf) occur in the Warszowice–Pawłowice 11,15 and 18 boreholes sited in the vicinity of the valley on the southslope of the Pawłowice Ridge and in Warszowice–Pawłowice 19, 22and 25 near the pass in the Pawłowice Ridge above the same valley(Fig. 3). In contrast, the zone is less developed in the vicinity of the localhigh on the Pawłowice Ridge outlined by the Pawłowice 2–9 boreholesand in the environs of horizontal surfaces between the Żory andPawłowice ridges (Warszowice–Pawłowice 39–43 and Świerklany 5;Figs. 6 and 7). The development of the zone is probably related to theinvolvement of methane of microbial origin. Archaebacteria introducedinto the rock-mass with meteoric water generated methane as a resultof carbon dioxide reduction. Water infiltration was probably mostsignificant on the southern steep slope of the Pawłowice Ridge and inthe local valleys; the high methane contents of coal seams in theseplaces are the result (Fig. 10).

In general, the shape of the Carboniferous surface controls the extentof the shallow zone in the Warszowice–Pawłowice and Pawłowiceareas. The most gaseous parts are the slopes of the Pawłowice ridge,particularly where broken by valleys and the passes above them(Kędzior, 2008a; Figs. 6, 7 and 10). In Warszowice–Pawłowice 13 and18, the shallow zone even links with the deep primary zone.

Tectonic factors are also likely involved in the configuration of theshallow methane zone. The highest methane contents and the greatestzone thicknesses appear in boreholes near the Bzie–Czechowice andJawiszowice fault zones.

The increased thickness of the shallowCBMzone in thevicinity of theregional Bzie–Czechowice and Jawiszowice faults, and in associatedfaults and ridges, shows the importance of these structures in methanemigration (Kędzior, 2009b; Staniek, 1986; Figs. 8 and12, see Section3.2).The two CBM zones also overlap near these structures (Figs. 6 and 7). As

migrating thermogenic methane probably mixed with indigenousmicrobial methane, the gas in the secondary shallow zone is likely tobe a combination of both methane types. Available data do not allow amore precise conclusion.

5.3. Coal permeability

The cleat system of coal determines its permeability and, thus, itsability to conduct fluids. Two methods of permeability measurementwere used in this study. The first was carried out in-situ during drillingby the Amoco and Texaco Companies and the second in the laboratoryon coal samples taken by the author from the Kaczyce 2/07 boreholeand from the openings of Zofiówka Mine. Both gave similar results(Fig. 11). A general trend of decreasing permeability with depth wasnoted; as pore pressure increases, the cleats close. This trend has beenrecognized elsewhere (e.g., BoddenandEhrlich, 1998;Gentzis et al., 2008;Pashin, 2010; Scott, 2002). In the USCB, measured coal permeabilitiesaverage between 1 and 3 mD (Kędzior, 2009b; McCants et al., 2001; VanBergen et al., 2006); this low permeability is insufficient for profitablemethane exploitation.

The trend noted above suggests that high coal permeability mightcharacterize the Carboniferous series where the shallow CBM zoneexists (Fig. 11). Estimated values range between 27 and 230 mD at adepth of 200–500 m (J. Hadro et al., Internal Report, October 2006).However, no suchvalueshavebeenactuallymeasured to-date in the area.

Studies on coal permeability elsewhere (e. g., Gentzis et al., 2007,2008) demonstrate the strong negative influence of tectonic stress oncoal permeability. Themain direction of coal permeability should reflectthe orientation of any regional tectonic stress (e.g., Gentzis et al., 2008;Wolf et al., 2008). In the area of interest here, a present-day W–E

Fig. 7. The average methane content within the shallow CBM zone. 1 — main faults, 2 — approximate boundary of Łaziska Sandstones, 3 — rock temperature (°C), 4 — vitrinitereflectance (%). G — average methane content (m3/t coal daf).Source: Archive of the Polish Geological Institute.

164 S.ł Kędzior / International Journal of Coal Geology 86 (2011) 157–168

horizontal stress (Pozzi, 1996) could be having a negative effect on coalpermeability.

Gas and rock outbursts that occurred in the vicinity of the Bzie–Czechowice Fault Zone in openings in the nearby Pniówek and Zofiówkacoal mines provide evidence that the permeability of coal that has beensubject to local stress can be greatly enhanced.Microscope examinationof samples from the outbursts reveals structurally deformed coalnetworked by new fractures (Jakubów et al., 2006). However, thetectonic context needs to be more completely understood here.

A linear correlation between average cleat spacing and hostvitrain-layer thickness has been shown elsewhere (Dawson andEsterle, 2010). In the area, vitrinite groupmacerals predominate in thecoal at depths of 200–500 m (average 70%: Table 1). This couldinfluence coal permeability, as vitrinite-rich coals have a denser cleatnetwork compared to dull, inertinite-rich coal (Bustin, in Gentziset al., 2008).

5.4. Potential methods of methane exploitation

Methanemay be recovered bymeans of independent gaswells andfrom the methane drainage systems in coal mines. The first methodwas tested in the area by Texaco during the nineties. Deeper coalseams (N1000 m) with low permeability (ca 1–3 mD; see Section 5.3)were tested. Gas yields from the boreholes of 200–350 m3 per day(Texaco reports, December 1998) were insufficient to encourageexploitation. The shallow CBM zone, lying at depths between 200 and500 m, is quite dense and continuouswith a thickness between 150 and200 m, locally more (Section 5.1). With an estimated coal permeabilityof 27–230 mD and almost full methane saturation (80–100%), this zone

is a more favorable prospect. Moreover, the cost of drilling shallowboreholes (b700 m deep) would be lower.

The Euro Energy Resources Company, granted a concession to exploretheCBMpotential of the central part ofUSCBMain Syncline (Kędzior et al.,2007), is currently undertaking a prefeasibility study on CBM recoveryfrom the secondary CBM zone. The use of horizontal wells and under-balanced drilling technology is being considered as it has provedsuccessful elsewhere (Gentzis et al., 2008; Kwarciński and Hadro, 2008).Even though the company estimates that ca 5.2 billion m3 ofmethane arepresent in the shallow CBM zone in the area (J. Hadro et al., Project ofGeological Surveys, EurEnergy Resources, June 2006), implementation ofthese recovery methods faces problems. The seams in the MudstoneSeries are irregularly developed with variable thicknesses rarely N2m(L. Mandrela, Z. Pękała, unpublished report, Katowice GeologicalEnterprise, May 2002). In addition, inserts b50 cm thick of other rockstend to split up the seams and a lack of lithological or paleontologicalmarkers inhibits correlation. Thus, the scope of the feasibility study wasextended almost to the base of the Mudstone Series.

There are other problems. Crucial for horizontal drilling is the problemof the fault zones dividing the coal series into blocks. These blocks mustnot be too small. Borehole data alone cannot adequately map thedislocations or provide an estimate of block size. Thus, geophysicalmethods, e.g., 3D seismics, are being considered. Underground watercaptured from the boreholes is a further problem. Due to its salinity, thiswater should be re-injected deep into the rock mass. In this case, thepermeable Miocene Dębowiec Formation comprising sand and gravelwith the filtration coefficient averaging ca 5 10−7 m/s, could accept thenecessary quantities (B. Niemczyk, Internal Report, Katowice GeologicalEnterprise, May–Sept. 1998).

Table 2Parameters of the CBM shallow zone in the southern USCB.Source: The archives of the Polish Geological Institute.

Borehole The CBM shallow zone Methane content (m3/t coal daf)

Elevation of base (m above sea level) Thickness of zone (m) Average Maximum

Kobiór–Pszczyna 121 −300.0 353.3 4.2 4.6Krzyżowice 28 −170.2 177.9 7.6 9.6Krzyżowice 30 −317.9 320.0 7.1 7.4Krzyżowice IG-1 −286.3 26.7 6.7 6.7Łąka IG-1 −247.0 83.0 4.5 5.2Pawłowice 1 −279.4 250.0 4.4 5.7Pawłowice 11 −102.6 170.0 5.7 5.7Pawłowice 12 −276.4 53.0 3.9 5.0Pawłowice 13 −419.6 247.0 4.6 6.1Pawłowice 15 −479.5 56.0 5.0 6.3Pawłowice 17 −174.7 200.0 4,6 7.6Piasek IG-1 −255.0 216.0 4.0 5.2Pszczyna 28 −113.0 190.3 4.1 4.9Pszczyna 29 −80.0 152.2 5.6 5.6Pszczyna 73 −115.0 225.8 3.8 5.3Studzionka IG-1 −653.9 255.0 6.0 8.7Suszec 12 −449.4 528.0 6.3 6.5Suszec 13 −149.9 228.8 5.9 6.5Suszec 16 −49.1 76.0 4.3 5.2Warszowice 4/91 −361.3 436.8 5.8 9.3Warszowice Pawłowice 2 −449.9 420.4 8.2 10.8Warszowice–Pawłowice 9 −449.6 77.0 10.5 10.5Warszowice–Pawłowice 11 −439.5 216.0 12.5 20.2Warszowice–Pawłowice 12 −575.1 150.0 10.5 13.6Warszowice Pawłowice 13 −440.0 221.0 7.3 8.1Warszowice Pawłowice 15 −430.2 255.0 8.7 13.6Warszowice Pawłowice 18 −449.6 435.0 9.2 18.7Warszowice–Pawłowice 19 −160.1 134.0 8.4 11.5Warszowice–Pawłowice 20 −133.3 130.0 4.7 4.7Warszowice–Pawłowice 22 −99.7 85.0 8.1 8.4Warszowice–Pawłowice 23 −450.0 422.2 5.3 5.3Warszowice Pawłowice 25 −147.4 125.0 8.0 12.8Warszowice Pawłowice 26 −115.8 76.0 7.4 9.0Warszowice Pawłowice 27 −99.1 100.0 7.2 8.2Warszowice Pawłowice 29 −449.4 465.0 7.2 8.8Warszowice Pawłowice 30 −83.1 50.0 8.7 8.7Warszowice Pawłowice 37 −450.4 340.0 10.0 14.0Warszowice Pawłowice 38 −248.2 130.0 7.7 7.7Warszowice Pawłowice 45 −244.3 347.0 4.8 5.3Warszowice Pawłowice 88/2/96 −449.3 400.0 7.1 8.4Warszowice Pawłowice TXA −143.9 130.0 6.7 7.9

A B C

Fig. 8. Variation in methane contents with depth. Legend as in Fig. 5.Source: Archive of Polish Geological Institute.

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Fig. 9. The Łaziska Sandstones and the location of the shallow CBM zone in the Kobiór–Pszczyna area. 1— Łaziska Sandstones (Cracow Sandstone Series), 2—Mudstone Series,3— shallow CBM zone, 4— coal seam, 5— expected direction ofmethanemigration, 6—

line of methane content=4.5 m3/t coal daf. B–C Fault — Bzie–Czechowice Fault Zone.B–C — Bzie–Czechowice, CBM — coal-bed methane.Source: Archive of the Polish Geological Institute.

Fig. 11. Vertical variation in coal permeability within the southern part of the USCB.Modified after J. Hadro et al., unpublished report, October 2006.

166 S.ł Kędzior / International Journal of Coal Geology 86 (2011) 157–168

In spite of these various problems, the area seems to have morepotential for successful CBM recovery than neighboring areas or theremainder of the USCB. The most important favorable factors are theshallow depth of themethane-saturated seams, their almost completesaturation and the thickness of the secondary CBM zone.

The building of newmine openings at PniówekMine in the Pawłowicearea is planned. The collection of methane through the mine drainagesystem may be feasible there, as in neighboring mines (see Section 2.6).The well production of longwall gob gas might be considered; this hasproved successful elsewhere (e.g., Karacan, 2009). As methane has beendrained and collected at the PniówekandZofiówkamines in the vicinity, awell-developed gas distribution network already exists there.

6. Conclusions

(1) A shallow secondary CBM zone ca 100–200 m thick occurs at adepth of 200–500 m in uppermost-Carboniferous coal-bearingstrata. It is separated from the deep primary CBM zone by areduced-methane concentration interval.

(2) The topography of the Carboniferous erosion surface controlsthe distribution of the secondary methane; gas preferentiallyoccupies topographic slopes and highs.

(3) In the eastern part of the area, the shallow zone is weaklydeveloped as porous and permeable Łaziska sandstones therehave allowed methane to escape.

Fig. 10. Influence of the Bzie–Czechowice fault on the distribution of the CBM shallow zonmethane.Source: Archive of the Polish Geological Institute.

(4) The shallowCBMzoneprobably comprises amixture of late-stagemicrobial methane and migrated thermogenic methane fromdeeper coals. As a result, the coal seams are almost fully saturatedwith methane (80–100%) and the zone is especially thick nearstructures that facilitated migration, e.g., the Bzie–CzechowiceFault Zone.

(5) The estimated greater permeability of the shallow coal seams(27–230 mD) compared to that of the deeper coals (1–3 mD)makes the shallow CBMzone an attractive prospect, even thoughthere are serious geological difficulties to be overcome.

(6) Future exploitation of the methane may involve independentgas-well production and/or gas collection fromdrainage systemsin future coal mines.

Acknowledgements

This workwas partly financed by theMinistry of Science and HigherEducation (Grant noNN307 427834). The author thanks the staff of theArchive of the Polish Geological Institute for their assistance andcommitment as the materials for this study were collected. Thanks arealso due to Karbonia PL and Zofiówka Mine for making drill coreavailable and to the Oil and Gas Institute in Cracow for petrophysicalanalyses. Marek Hałczyński from Bobrek–Centrum mine is thanked forhis assistance in preparing the maps on Figs. 3, 6 and 7 and PádhraigKennan of University College Dublin for assistancewith themanuscript.

e in the Pawłowice area. Legend as in Fig. 9. B–C — Bzie–Czechowice, CBM — coal-bed

167S.ł Kędzior / International Journal of Coal Geology 86 (2011) 157–168

The author also wishes to thank the anonymous reviewers for theirvaluable suggestions and comments.

References

Alsaab, D., Elie,M., Izart, A., Sachsenhofer, R.F., Privalov, V.A., Suárez-Ruiz, I., 2009. Distributionof thermogenic methane in Carboniferous coal seams of the Donets Basin (Ukraine):applications to exploration of methane and forecast of mining hazards. InternationalJournal of Coal Geology 78, 27–37.

Aravena, R., Harrison, S.M., Barker, J.F., Abercrombie,H., Rudolph,D., 2003.Origin ofmethanein the Elk Valley coalfield, southeastern British Columbia, Canada. Chemical Geology195, 219–227.

Bodden, R.W., Ehrlich, R., 1998. Permeability of coals and characteristic of desorptiontests: implications for coalbed methane production. International Journal of CoalGeology 35, 333–347.

Bogacz, W., Kotarba, M.J., Krach, J., 1984. Structural features of the coal-bearing strata inthe southern part of the Rybnik Coal District (Southern Poland). GeologorumPoloniae 54 (3/4), 361–377 (in Polish with English abstract).

Borowski, J., 1968. The problem of coalification of coal seams and methane originagainst a background of volcanism in the south part of the Upper Silesian Basin.Przegląd Górniczy 4, 165–172 (in Polish).

Borowski, J., Sosnowski, M., 1977. Phenomena associatedwith a great depth of coal seamsin north-eastern part of Rybnik Coal Area. Przegląd Górniczy 9, 402–407 (in Polish).

Buła, Z., Kotas, A., 1994. Geological Atlas of the Upper Silesian Coal Basin, Part IIIStructural Geological Maps. Geological Institute, Poland, Warsaw.

Buła, Z., Habryn, R., Piątkowska, A., Doktór, S., Graniczny, M., Kowalski, Z., 2007. Structuralpattern of sedimentary formations from Upper Silesia and westernMałopolska in thelight of remote sensing data. PrzeglądGeologiczny55, 582–588 (in Polishwith Englishabstract).

Busch, A., Gensterblum, Y., Krooss, B.M., Littke, R., 2004. Methane and carbon dioxideadsorption–diffusion experiments on coal: upscaling and modeling. InternationalJournal of Coal Geology 60, 151–168.

Crosdale, P.J., Beamish, B.B., Valix, M., 1998. Coalbed methane sorption related to coalcomposition. International Journal of Coal Geology 35, 147–158.

Dawson, G.K.W., Esterle, J.S., 2010. Controls on coal cleat spacing. International Journalof Coal Geology 82, 213–218.

Flores, R.M., 2008. Microbes, methanogenesis, and microbial gas in coal. InternationalJournal of Coal Geology 76, 1–2.

Gentzis, T., Deisman, N., Chalaturnyk, R.J., 2007. Geomechanical properties andpermeability of coals from the Foothills and Mountain regions of western Canada.International Journal of Coal Geology 69, 153–164.

Gentzis, T., Goodarzi, F., Cheung, F.K., Laggoun-Défarge, F., 2008. Coalbed methaneproduction from the Manville coals in Alberta, Canada: a comparison of two areas.International Journal of Coal Geology 74, 237–249.

Hemza, P., Sivek,M., Jirásek, P., 2009. Factors influencing themethane content of coal bedsof theCzechpartof theUpper SilesianCoalBasin, CzechRepublic. International Journalof Coal Geology 79, 29–39.

Hildenbrand, A., Krooss, B.M., Busch, A., Gaschnitz, R., 2006. Evolution ofmethane sorptioncapacity of coal seams as a function of burial history — a case study from CampineBasin, NE Belgium. International Journal of Coal Geology 66, 179–203.

Hunt, A.M., Stelle, D.J., 1991. Coalbed methane development in the Appalachian Basin.Quarterly Review of the Methane from Coal Seams Technology 1–4, 10–19.

Jakubów, A., Tor, A., Wierzbicki, M., 2006. Some structural properties of coal samplecollected from outburst masses from “Zofiówka” coal mine. XIII InternationalScientific–Technical Conference: Natural Mining Hazards 2006, Depth of Mining andMining Hazards. Główny Instytut Górnictwa, Katowice, pp. 86–93 (in Polish withEnglish abstract).

Jasper, K., Krooss, B.M., Flajs, G., Hartkopf-Fröder, Chr, Littke, R., 2009. Characteristics oftype III kerogen in coal-bearing strata from the Pennsylvanian (Upper Carboniferous)in the Ruhr Basin, Western Germany: comparison of coals, dispersed organic matter,kerogen concentrates and coal-mineral mixtures. International Journal of CoalGeology 80, 1–19.

Jura, D., 2001. Morphotectonics and Evolution of Discordances of Different Age Present inthe Top Surface of the Carboniferous of the Upper Silesian Coal Basin. WydawnictwaUniwersytetu Śląskiego, Katowice. (in Polish with English abstract).

Jurczak-Drabek, A., 1996. Petrographical atlas of coal deposits. Upper Silesian CoalBasin. Geological Institute, Warsaw.

Jurczak-Drabek, A., Kwarciński, J., 2003. Relationship between hard coal sorption capacityof methane and petrographic composition of hard coal (Upper Silesian Coal Basin).ZeszytyNaukowePolitechniki Śląskiej s. Górnictwo 257, 75–84 (in Polishwith Englishabstract).

Kandarachevová, J., Sedláčková, L.,Hýlová, L., Jirásek, J., Sivek,M., 2009. Lateraldevelopmentof coalification in the Czech part of the Upper Silesian Coal Basin and its connectionwith gas deposits. International Journal of Coal Geology 78, 225–232.

Karacan, C.Ö., 2009. Reconciling longwall gob reservoirs and venthole productionperformances using multiple rate drawdown test analysis. International Journal ofCoal Geology 80, 181–195.

Kędzior, S., 2008a. The geological aspect of the occurrence of high coalbed methanezone in Pawłowice area (Upper Silesian Coal Basin). Biuletyn PaństwowegoInstytutu Geologicznego 429, 69–73 (in Polish with English abstract).

Kędzior, S., 2008b. Geological and resources characterization of natural gas (freemethane) deposits occurring in the Upper Silesian region from the localexploitation point of view. Górnictwo Odkrywkowe 2–3, 77–80 (in Polish withEnglish abstract).

Kędzior, S., 2009a. The problem of emission and development of coal mine methane anexample from chosen coal mines of the southern part of the Upper Silesian CoalBasin. Górnictwo Odkrywkowe 2–3, 79–83 (in Polish with English abstract).

Kędzior, S., 2009b. Accumulation of coal-bed methane in the south-west part of theUpper Silesian Coal Basin (southern Poland). International Journal of Coal Geology80, 20–34.

Kędzior, S., Hadro, J., Kwarciński, J., Nagy, S., Młynarczyk, M., Rostkowski, R., Zalewska, E.,2007. The natural conditions of the occurrence and exploitation methods of coal-bedmethane in chosen coal basins in the USA and the possibilities of development of thatgas exploitation in Poland— a report on training trip to theUSA. PrzeglądGeologiczny55, 565–570 (in Polish).

Khavari-Khorasani, G., Michelsen, J.K., 1999. Coal-bed gas content and gas under-saturation. In: Mastalerz, M., Glikson, M., Golding, S.D. (Eds.), Coal-bed Methane:Scientific, Environmental and Economic Evaluation. Kluwer Academic Publishers,Boston, pp. 207–231.

Kotarba, M.J., 1999. Generation and accumulation of hydrocarbons and geochemicalcharacteristics of organic matter in autochthonous Miocene strata of the CarpathianForedeep. In: Peryt, T.M. (Ed.), Prace PIG, CLXVIII: Analysis of the Tertiary Basin of theCarpathian Foredeep. Polish Geological Institute, pp. 277–296 (in Polish and Englishabstract).

Kotarba, M.J., 2001. Composition and origin of gases in the Upper Silesian and LublinCoal Basins, Poland. Organic Geochemistry 32, 163–180.

Kotarba,M., Ney, R., 1995. Hydrocarbons inUpper Carboniferous coal-bearing series of theUpper Silesian Coal Basin. In: Ney, R., Kotarba, M. (Eds.), Study of Models and theBalance of Generation and Accumulation of Gases in Coal-bearing Series of the UpperSilesian Coal Basin. Publication Centrum PPGSMiE PAN, Kraków, pp. 7–24 (in Polish).

Kotarba, M.J., Pluta, I., 2009. Origin of natural waters and gases within the UpperCarboniferous coal-bearing and autochthonous Miocene strata in South-Westernpart of the Upper Silesian Coal Basin, Poland. Applied Geochemistry 24, 876–889.

Kotarba, M., Pękała, Z., Daniel, J., Więcław, D., Smolarski, L., 1995. The deep distribution ofmethane content andhigherhydrocarbons inUpper Carboniferous coal-bearing strataof Upper Silesian Coal Basin. In: Ney, R., Kotarba, M.J. (Eds.), Study of Models and theBalance of Generation and Accumulation of Gases in Coal-bearing Series of the UpperSilesian Coal Basin. Publication CentrumPPGSMiE PAN, Kraków, pp. 61–74 (in Polish).

Kotas, A., 1990. Upper Silesian Coal Basin. In: Osika, R. (Ed.), Geology of Poland. : MineralDeposits, vol. VI. Geological Institute,Wydawnictwa Geologiczne, Warszawa, pp. 77–92.

Kotas, A. (Ed.), 1994. Coal-bed Methane Potential of the Upper Silesian Coal Basin,Poland. : Prace PIG CXLII. Polish Geological Institute, Warszawa.

Kotas, A., 1995. Moravian–Silesian–Cracovian region. Upper Silesian Coal Basin. In:Zdanowski, A., Żakowa, H. (Eds.), The Carboniferous System in Poland. : PracePaństwowego Instytutu Geologicznego CXLVIII. Polish Geologcal Institute, pp. 124–133.

Kotas, A., Buła, Z., Gądek, S., Kwarciński, J., Malicki, R., 1983. Geological Atlas of the UpperSilesian Coal Basin. Part II Coal quality maps. Wydawnictwa Geologiczne, Warsaw.

Krooss, B.M., Van Bergen, F., Gensterblum, Y., Siemons, N., Pagnier, H.J.M., David, P., 2002.High-pressuremethaneandcarbondioxideadsorptionondryandmoisture-equilibratedPennsylvanian coals. International Journal of Coal Geology 51, 69–92.

Kwarciński, J., Hadro, J., 2008. Coalbedmethane in the Upper Silesian Coal Basin. PrzeglądGeologiczny 56, 485–490 (in Polish with English abstract).

Lamberson, M.N., Bustin,M.R., 1993. Coal-bedmethane characteristics of Gates Formationcoals, northeastern British Columbia; effect of maceral composition. The AmericanAssociation of Petroleum Geologists Bulletin 77, 2062–2076.

Laxminarayana, C., Crosdale, P.J., 1999. Role of coal type and rank on methane sorptioncharacteristic of Bowen Basin, Australia Coals. International Journal of Coal Geology40, 309–325.

McCants, C.Y., Spafford, S., Stevens, S.H., 2001. Five-spot production pilot on tightspacing: rapid evaluation of a coalbed methane block in the Upper Silesian CoalBasin, Poland. Proceedings of the 2001 International Coalbed Methane Symposium,Tuscaloosa, Alabama, May 14–18, 193–204.

McLennan, J.D., Schafer, P.S., Pratt, T.J., 1995. A Guide to Determining Coalbed GasContent. Gas Research Institute (GRI Reference Number, GRI-94/0396), Chicago IL,pp. 10–19.

Niemczyk, B., 1984. Determination from results of drilling of gas potential in coal depositsand practical confirmation of the method from the “Krupiński” mine. TechnikaPoszukiwań Geologicznych 4, 37–42 (in Polish with English abstract).

Obuchowicz, Z., 1963. Petroleum and gas deposits in Carpathian Foredeep. AnnalesSocietatis Geologorum Poloniae 33, 397–411 (in Polish with Russian abstract).

Pashin, J.C., 2010. Variable gas saturation in coalbed methane reservoirs of the BlackWarrior Basin: implications for exploration and production. International Journal ofCoal Geology 82, 135–146.

Pluta, I., Zuber, A., 1995. Origin of brines in the Upper Silesian Coal Basin (Poland)inferred from stable isotope and chemical data. Applied Geochemistry 10,447–460.

Poborski, C., 1960. In a cause of methane origin in Carboniferous strata of the south partof Rybnik Mining District. Przegląd Górniczy 7–8, 360–369 (in Polish).

Pozzi, M., 1996. Optical anisotropy of coal in seams of Jastrzębie area as a symptom oftectonic stresses. Zeszyty Naukowe Politechniki Śląskiej, 229. Gliwice. (in Polishwith Englich abstract).

Różkowski, A., 1991. Silesian and Krakow region. In: Malinowski, J. (Ed.), Geology ofPoland. : Hydrogeology, vol. VII. Geological Institute, PublishingHouse,WydawnictwaGeologiczne, Warszawa, pp. 177–189 (in Polish).

Scott, A.R., 2002. Hydrogeologic factors affecting gas content distribution in coal beds.International Journal of Coal Geology 50, 363–387.

Semyrka, G., Kowalski, A., Kosakowski, P., Więcław, D., 1995. Petrographical, chemicaland geochemical description of coals from chosen areas of the Upper Silesian CoalBasin. In: Ney, R., Kotarba, M.J. (Eds.), Publication Centrum PPGSMiE PAN 75–98 (inPolish).

168 S.ł Kędzior / International Journal of Coal Geology 86 (2011) 157–168

Staniek, L., 1986. Methane migration in the Upper Silesian Coal Basin by disjunctivedislocations. Zeszyty Naukowe Politechniki Śląskiej, s. Górnictwo 140, 50–54 (inPolish with English abstract).

Tarnowski, J., 1989.Geological conditionsofmethaneoccurrence in theUpper SilesianCoalBasin (USCB). Zeszyty Naukowe Politechniki Śląskiej, z., 166. Dział WydawnictwPolitechniki Śląskiej, Gliwice (in Polish with English summary).

Teper, L., Sagan, G., 1995. Geological history and mining seismicity in Upper Silesia(Poland): mechanics of Joined and Faulted Rock II. In: Rossmanith, H.P. (Ed.),Rotterdam-Brookfield, Balkema, pp. 939–943.

Twardowski, K., 1997. Assessment ofMethane-content inHard Coals in theUpper SilesianCoal Basin Based on the Results of Bore-holesMeasurements.Wydawnictwo CentrumPPGSMiE, Kraków. (in Polish).

Van Bergen, F., Pagnier, H., Krzystolik, P., 2006. Field experiment of enhanced coalbedmethane–CO2 in the Upper Silesian basin of Poland. Environmental Geosciences13, 201–224.

Wei, C., Qin, Y.,Wang, G.G.X., Fu, X., Jiang, B., Zhang, Z., 2007. Simulation study onevolutionof coalbed methane reservoir in Qinshui basin, China. International Journal of CoalGeology 72, 53–69.

Wolf, K.A.A., Van Bergen, F., Ephraim, R., Pagnier, H., 2008. Determination of the cleatangle distribution of the RECOPOL coal seams, using CT-scans and image analysison drilling cuttings and coal blocks. International Journal of Coal Geology 73,259–272.