• Nie Znaleziono Wyników

Composition and orlgln of gaseous hydrocarbons in the Miocene strata of the Polish part of the Carpathian Foredeep

N/A
N/A
Protected

Academic year: 2021

Share "Composition and orlgln of gaseous hydrocarbons in the Miocene strata of the Polish part of the Carpathian Foredeep"

Copied!
8
0
0

Pełen tekst

(1)

Przegląd Geologiczny, vol. 46, nr 8/2, 1998

Composition and orlgln of gaseous hydrocarbons in the Miocene strata

of the Polish part of the Carpathian Foredeep

Maciej

J.

Kołarba

*

The results oj molecular and stable carbon isotope analyses oj methane, ethane and propane, and stable hydro gen isotope analyses oj methane to explain the origin oj gaseous hydrocarbons accumulated in the whole Badenian and Early Sarmatian sequence oj the Carpathian F oredeep, at the depths jrom 161 to 2,670 meters. Composition oj tested gases is dominated by methane which concentration usually exceeds 98 vol. %. Methane was generated during carbon dioxide reduction pathway ojmicrobial processes. Higher gaseous hydrocarbons (mainly ethane and propane) which are usually minor constituents (concentrations less than 0.2 vol. %), were generated during diagenetic processes and at the initial stage oj the low-temperature thermogenic processes. Only the gas encountered in the Tarnów-45 we li, in the bottom part oj Upper Badenian sequence atypical, high-temperature, thermogenic gas generated jrom the oil-prone, marine organie matter (type II kerogen) which remains at transjormation level corresponding to 1.1-1.6% in vitrinite reflectance scale. This gas has migrated jrom the Mesozoic basement where such thermogenic gases were encountered. Natural gas accumulated in the Upper Jurassie carbonate trap ojthe Lubaczów field is typically microbial and has migratedjrom the autochthonous Miocene strata along the jault zone.

Key words: petroleum explo ration, natural gas, methane, genesis, stable isotopes, carbon, Miocene, reservoir rocks, Carpathian Foredeep, Poland

Introduction

Previous molecular and isotopic studies (mainly stable carbon isotope analyses of methane) of the natural gases accumulated in autochthonous Miocene strata of the Polish part of the Carpathian Foredeep revealed that methane which dominated in the composition of these gases was generated during microbial (bacterial) processes (Głogoczo­ wski, 1976; Calikowski, 1983; Kotarba et al., 1987; Jawor

& Kotarba, 1991, 1993; Kotarba 1992; Kotarba & Jawor, 1993). The microbial methane is of vital economic impor-tance as its reserves constitute about 20% of overall world gas reserves (Rice & Claypool1981; Riee 1992).

The studies on molecular composition and stable carbon isotope composition of methane, ethane and propane, and stable hydro gen isotope composition of methane aim to recog-nize the generation conditions of gases accumulated within the autochthonous Miocene strata of the Carpathian Foredeep. Totally, 59 gas samples were taken from accumulations within the autochthonous Miocene strata of the Carpathian Foredeep in which: 4 samples from Lower Badenian strata, 25 samples from Upper Badenian strata and 30 samples from Lower Sarmatian strata. Data from 20 wells, mostly the isotopic analyses of methane, has been partly published in Kotarba et al. (1987) and Kotarba (1992). Locations of the gas sampling sites are presented in Fig. 1.

The study has been undertaken as a part of research projects of the Carpathian Foredeep financed by the State Committee for Scientific Research in Warsaw (grant No. 9 9214 92 03) and N ational Fund for Environmental Protec-tion and Water Management (grant No. 2.14.0100.00.0).

Geological setting and gas occurrence

The Carpathian Foredeep is one of the largest sedimen-tary basins in the Central Europe. It is a tectonic through of Alpine age filled with the Miocene marine molasse. The

*University of Mining and Metallurgy, Departrnent of Fossil Fuels, al. Mickiewicza 30, 30-059 Kraków, Poland,

ernail: kotarba@uci.agh.edu.pl

trough extends along the front of the Carpathian orogenic arc from Vienna (Austria) in the west towards the Iron Gate (Danube) in Romania in the south-east (Fig. 1) and partly also underlies the Carpathian nappes. The Carpathian Fore-deep is divided into the two basins: outer and inner (Ney et al., 1974; Oszczypko, 1996, 1997) (Fig. 1). The folded Miocene strata of the Stebnik and Zgłobice units known from the inner basin in the Polish part of the Carpathian Foredeep (Ney, 1968; Oszczypko, 1996, 1997) are thought to be unimportant for petroleum exploration. The eastem part of the outer basin (east from Kraków) is filled with Badenian and Lower Sarmatian sediments of the following thicknesses: Lower and Middle Badenian - from O to 300 m, Upper Badenian - from O to 1,700 m, and Lower Sarmatian - from O to 2,900 m (Ney et al., 1974). Most ofthe known gas field s occur within the Upper Badenian and Lower Sarmatian strata. Both the Upper Badenian and the Lower Sarmatian are represented by c1ay-sandy, mainly deltaie facies. Sedimentation rate ofUpper Badenian sediments was maximum 1,500 mIMa, and for the Lower Sarmatian ones it reached 5,000 mIMa. On the other hand, the Lower and Middle Badenian strata comprise shallow-water psammitic, argillaceous and chemical sediments. The autochthonous Miocene sediments of the outer basin of the Carpathian Foredeep have not be affected by Alpine orogenie move-ments and rest almost horizontally up on the Precambrian-Paleozoic-Mesozoic basement (Oszczypko, 1982, 1996).

The gas fields discovered in the autochthonous Miocene strata of the Polish part of the Carpathian Foredeep contain practieally only the methane and small amounts of higher gaseous hydrocarbons. Cumulative production between 1945 and 1997 yielded about 80*109 cubic meters of gas. The remaining proved reserves of about 70* 109 cubic meters are available. Undiscovered resources are estimated to be about 190*109 cubic meters. The production of natural gas from the autochthonous Miocene reservoirs has started in 1924 from the Daszawa field (recently in the Ukraine). Since 1945, about 70 gas fie1ds have been discovered in the Polish part of the Carpathian Foredeep, and the most important is the Przemyśl-Jaksmanice deposit of initial reserves about 80* 1 09 cubic meters.

(2)

SLOVAKIA

o

I 20 ! 40km

D

outer part ot the

Carpathian Foredeep

D

strata autochthonous Miocene , -~ 'Miocene strata northern range ot

-7 ~ isobaths ot the basa I surface .,- ot Miocene strata (km)

inner part ot the Carpathian Foredeep

D

the Carpathians Miocene strata ... _---' on the Carpathians ~ margin ot the ~ -.. Carpathian overthrust

interred southern range ot Miocene strata

interred range ot recent remnants ot inner basin

RESERVOIRS (TESTED WELLS): • Lower Sarmatian

O Upper Badenian

D Lower Badenian b:. Lower Badenian

and Upper Jurassic

Fig. 1. Sketch map of the central and eastern parts of the Polish Carpathian Foredeep and location of studied wells

Experimental

Gas sampies were collected on1l from the wellheads. Sampies were collected to l or 2 dm metal containers.

The molecular composition of natura! gases was analy-sed in a set of columns on Helwett Packard 5990, Chrom-5 and Chrom-41 gas chromatographs with flame ionization and thermal conductivity detectors.

Stable isotope analyses were carried on with the Finni-gan Delta, Micromass MM 602C and MI-1201 mass spec-trometers. The stable carbon and hydro gen isotope data are presented in the 8-notation relative to the PDB and the SMOW standards, respectively. The analytical precision is estimated to be ±0.2%0 for carbon and ±3%0 for hydrogen.

Methane, ethane and propane were separated chromato-graphically for stable isotope analyses. After separation each gas was combusted over hot copper oxide (850°C). The resulting CO2 fraction was purified and directly analyzed for

813C content, whereas the water resulting from the

combu-stion of methane was reduced to gaseous hydro gen in a uranium fumace at 800°C or with zinc method (Florkowski, 1985).

Origin of natural gases based on molecular and isotopic compositions

Methane is one of chemical compounds in which the stable carbon and hydrogen isotope compositions are sensi-tive indicators of the gas origin and migration. Carbon in methane shows wide range of 8'3C values. Isotopically he a-viest methane was encountered in the gas accompanyin~ the thermal spring s in the Yellowstone National Park (8' C

=

-10.4%0, Schoell, 1983, 1988; Whiticar 1994). Diversified

chemical, physical and biological processes cause common, significant differences between the isotopic compositions of the source organic matter and the daughter gases. Principal role in the geochemical identification of the gases is playc:d by the genetic factor. Analyses of stable carbon and

(3)

hydro-Przegląd Geologiczny, vol. 46, nr 8/2, 1998

_I 1 1 1 1

o Upper 8adenian MIGRATlON

[AJ

\ D Lower 8adenian

~Ą/,

t -

-\ 6 Lower 8adenian lON

\

and Upper Jurassie

\ MIGRATlON

-I -I~/ -\

f

-[AJ

I ~ -100 I ~ o Fig. 2. Genetic / ~ u characterization of / &

-

/ c;:

(A) Badenian and Q

-80 /1 d" ~ / / 1 u (B) Sarmatian ga-

e-t

MICROBIAL METHANE

fi

/1"/ \ U-116. cfY \ , /' o I / ... t , I $,' ;' ~-"--~-,\ ~ in terms of

-ses ę TRANSITlON :J: ~ ~LU-3 , Lu-22 " I -12 I T-45 I

tJt

I ,

MIXING D Ro-2 \- - -./- - - -C? II«:-O~I

, , \ \ / «II : THERMOGENIC v / ~ / - , , , , - -- --- -- \ GASES \ / - - \ ---J

:/

; ' I I I L - I I I I 00 ::;, \ [. Lower Sarmatian J (J 104 ~ + \ CD 103 : . . . ~ fMICROBIAL METHANE •• ~ 102

rr

WBu-2 :J: \ (J " , MIXING 1 \ I I MIGRATlON

t

OJ(IDĄ/,

P

lON MIGRATlON I 1

~

-0I3C(CH4) versus -60 / - ' : . , Q -(J FERMENTATION /.--CHJ(C2H6+C3HS).

-

/ MIXING / / -... Compositional (J I'ljl::, C") GIY/i-t°G fields from Whiti-

Vo

-40 , c<JS

t::/

2N/c

car (1994) '- '- '- OT -45 '--20 ' --100

--

Q -80 ~

e--

ę :J: II 101 r- -Fig. 3. Genetic characterization of (A) Badenian and

(B) Sarmatian ga-ses from the Car-pathian Foredeep in terms of oI3C(CH4) versus oD(CH4). Compo-sitional fields from Whiticar et al. (1986) -60 U J: (J -20 _-30 Q ~ Q

-_-40 ę :J:

~-50

(J C")

Vo

-60 -70 -20 _-30 Q ~

e---40 ę :J:

~-50

(J C")

Vo

-60 -70 \ ---J I I 1 1 I -90 -80 -70 -60 -50 o Upper 8adenian D Lower 8adenian 6 Lower 8adenian

and Upper Jurassie

Q) '"" O 6l .,.<;1)0 "9(b oQ U- o 0 0 & • Lower Sarmatian Pr-14

••

.

..

.

,

...

,

.

.

.

,

1 I -40 -30 -50 -40 -30 -20 013C(C2H6)

(%0)

Fig. 4. Genetic characterization of (A) Badenian and (B)

Sarrnatian gases from the Carpathian Foredeep in terms of oI3C(CH4) versus o13C(C2H6). Positions of vitrinite reflec-tance curves for types II and III kerogen after Berner & Faber (1996)

-

Q ~ Q

--

00 :J: C") (J

U

C")

Vo

-

Q ~ Q

--

00 J: C") (J

-(J C")

Vo

-20 -30 -40 -20

~

-30

Pr-14 -40 ~ (J C")

Vo

-40 -20 -350 -250 -150

00

(CH4 )

(%0)

o o o 8~ DCO

oo~

o o

°

S

0.6 . BI-5 . Oc-1

.

,

.

•• -I

,

0.6 Bu-2 -50 -40 013C(C2Hs) 2.4 2.0 .6 1.2 / o T-45 0\0 1.0 «-~ 0.8 / o Upper 8adenian D Lower 8adenian 6 Lower 8adenian

and Upper Jurassie

2.4 1.0 «-0

0/

0.8

/

[ • Lower Sarmatian -30 -20

(%0)

Fig. 5. Genetic characterization of (A) Badenian and (B) Sarrnatian gases from the Carpathian Foredeep in terms of o13C(C2H6) versus oI3C(C3Hs). Positions of vitrinite reflectance curve for types IIIIII kerogen after Berner & Faber (1997)

(4)

-30 -40

-

CI ?:fi?

-O -50 M

7<J

-60 -70

Fig. 6. Stable carbon isotope composition of methane, ethane and propane of (A) Badenian and (B) Sarmatian gases from the Carpathian Foredeep

0.2 0.4 0.6 0.8 1.0

1/n (CnH2n+2)

0.2 0.4 0.6 0.8 1.0

1/n (CnH2n+2)

gen isotopes in methane enables the identifieation of the souree organie matter from whieh gases were generated during mierobial or thermogenic proeesses (e.g., Bemer &

Faber, 1996, 1997; Kotarba, 1995; Stahl, 1977, 1979). The 813C values of methanes generated from the marine (type II kerogen) and the terrestrial organie matter (type III kerogen) differ by 13-14%0 in the fulI range of transformation proees-ses. This differenee results from different ehemical struetu-res of both types of the souree organie matter. Methane generated during thermogenie proeesses from the sapropelie organie matter shows 813C values from -55 to -30%0 whereas that produeed from the humie organie matter has 813C from -30 to -20%0. On the eontrary, the mierobialIy generated met-hane reveals typiealIy very low 813C vaIues even below

-100%0. Microbial gases ean be generated in the two proees-ses: methane fermentation and earbon dioxide reduetion. Stable hydro gen eomposition 8D of mierobial methane va-ries from -380 to -150%0 (SehoelI, 1983, 1988; Whitiear et al., 1986). Correlation of stable earbon isotope eomposition of methane with the hydroearbon index CHC = ClL/(C2H6 + C3Hg) and with the stable hydrogen isotope eomposition of

methane enables the distinetion between various genetie types of methane, various generation proeesses and determi-nes the maturation degree of the souree organie matter (Whitiear, 1994).

Results of stable earbon isotope analyses of ethane and propane alIowed the preparation of more precise genetie c1assifieation of natural gases, i.e. the distinguishing of genetie groups and enabled the identifieation of migration and mixing of either genetieally different gases or gases produeed from the same souree organie matter but during the sueeessive generation stages (SehoelI, 1988; Whitiear, 1994; Bemer & Faber, 1996, 1997; Kotarba et al., 1994). Both the ethane and propane are praetiealIy absent during microbial proeesses and appear in larger quantities only during thermogenie transformation of the organie matter. Both gases are enriehed in heavy earbon isotope 13C in

eomparison with the methane generated in the same proeess. Both the experimental data and theoretieal ea1culation

de-monstrated that stabIe earbon isotope studies of methane, ethane and propane are essential for determination of the type and the maturation degree of the souree organie matter in vitrinite refleetanee scale (Berner & Faber, 1996, 1997; SehoelI1988, Whitiear, 1994).

Results and disscussion

Analytieal results shown in Tab. 1 will be eommented on separately for the gases aeeumulated within the Badenian and the Lower Sarmatian strata.

Depth of sampled gas aeeumulations in the Badenian strata varies from 170 to 2,640 meters (Tab. 1). Values of geoehemieal parameters for the gas aeeumulated in Bade-nian strata from the Polish part of the Carpathian Foredeep are given below:

hydroearbon index CHC [CHJ(C2H6+C3Hg)] from 26 to

962, i-C4HIO/n-C4H6 index from 0.5 to 16.0, CDMI index

{CDMI

=

[CO~(C02+CH4)] 100 (%)} from 0.01 to 0.94%, 813C(ClL) from -69.0 to -35.7%0, 8D(CH4) from -215 to

-151%0, 813C(C2H6) from -50.5 to -28.1%0, and 813

C(C3Hg)

from -31.8 to -23.8%0.

Most of the analysed gases were eolleeted from the Upper Badenian strata (Tab. 1). OnIy in the Roźwieniea

field gas is aeeumulated in the Lower (and partly Middle) Badenian sequenee, in the Lubaezów and Uszkowee depo-sits it oeeurs in Lower Badenian strata and in the topmost parts of Upper Jurassie earbonates.

Gases aeeumulated in Badenian reservoirs of the Carpa-thian Foredeep are methane-dominated (its eoneentation usualIy exeeeds 98 vol. %). Results of moleeular analyses and stabIe earbon isotope analyses of methane, ethane and propane, and stable hydro gen isotope analyses of methane (Figs 2A to 6A) indieate that the gaseous hydroearbons were generated during mierobial and diagenetie proeesses, and in the initial phase of the low-temperature thermogenie proees-ses. The only exeeption is gas from the Tamów-45 whieh is typiealIy thermogenie. This gas was generated from the oil-prone, marine organie matter (type II kerogen) whieh has

(5)

Przegląd Geologiczny, vol. 46, nr 8/2, 1998

Tab. 1. Geochemical indices and stable carbon and hydrogen composition of natural gases reservoired within autochthonous Miocene strata

Accumulation Geochemical indices Stable isotopes (%0)

Well depth CHe i-C4/n-C4 CDMI 813C 8D 813C 813C

(m) (Clli) (Clli) (C3Hs) (C3HS)

Reservoirs: Lower Sarmatian

Blizna-5 (El-S) 603- 623 410 4.0 0.08 -63.7 -188 -36.9 -22.8

Buszkowiczki-2 (Bu-2) 2199-2215 123 2.1 0.39 -64.4 -199 -37.6 -31.7

Husów-1 (H-l) 1934-1939 510 2.0 0.20 -65.2 -202 -48.0 -30.1

Husów-lI (H-lI) 1882-1901 220 2.5 0.04 -66.0 -197 -42.9 n.a.

Husów-26 (H-26) 1937-1987 380 4.7 0.07 -67.3 n.a. n.a. n.a.

Husów-52 (H-52) 965-1055 602 1.8 0.11 -64.3 -204 -48.5 -29.5 Husów-53 (H-53) 1330-1375 457 4.0 0.05 -67.8 -194 -41.5 -30.8 Husów-90a (H-90a) 239- 243 1240 0.5 0.43 -69.4 -202 -52.0 -30.7 Jaksmanice-19a (J-19a) 900--1101 678 2.3 0.10 -66.0 -198 -51.9 -30.7 Jarosław-53 (Jw-53) 1188-1205 274 4.3 0.11 -67.0 -214 -47.2 -30.8 Jodłówka-17 (Jo-17) 2444-2621 234 2.3 0.04 -63.7 -195 -39.6 -30.1 Kańczuga-7 (Ka-7) 1075-1134 275 1.8 0.04 -67.4 -198 -46.3 -31.6 Korzeniów-9 (Kw-9) 161- 164 1270 0.5 0.10 -72.6 -179 -50.0 -25.9 Krasne-l2 (Kr-12) 884- 892 928 2.3 0.21 -66.0 -204 -51.4 -30.6 Krasne-21 (Kr-21) 902- 913 372 2.0 0.15 -65.3 -210 -42.7 -31.0

Kuryłówka-3 (Ku-3) 675- 680 208 - 0.11 -65.0 -184 -33.4 n.a.

Leżajsk-7 (Le-7) 420-- 485 509 - 0.15 -68.6 n.a. n.a. n.a. Leżajsk-8 (Le-8) 416- 440 539 - 0.47 -68.8 -202 -50.2 n.a.

Lipnica-2 (Li-2) 360-- 395 1667 - 0.10 -69.4 -180 -40.7 n.a.

Ocieka-1 (Oc-l) 600-- 620 349 - 0.09 -64.9 -196 -38.0 -25.5

Pruchnik-12 (Pk-12) 855- 900 353 6.0 0.08 -68.0 -200 -45.6 -28.8

Pruchnik-13 (Pk-13) 1248-1255 378 10.0 0.06 -67.8 -202 -45.2 n.a.

Przeworsk-9a (Pr-9a) 266- 283 650 - 0.10 -70.8 n.a. n.a. n.a.

Przeworsk-11a (Pr-11a) 415- 432 693 - 0.09 -71.2 -201 -53.3 n.a.

Przeworsk-14 (Pr-14) 404- 421 590 3.7 0.11 -69.2 -202 -57.4 -31.5

Smolarzyny-1 (Sm-l) 375- 455 392 5.5 0.04 -66.2 n.a. n.a. n.a.

Smolarzyny-5 (Sm-S) 395- 420 390 - -0.05 -66.5 n.a. n.a. n.a.

Tarnogród-7 (Tr-7) 1085-1103 538 1.7 0.07 -64.6 -202 -42.2 -30.2

Trześnik -1 (Tk-1) 188- 190 1450 - 0.13 -70.9 -197 -50.9 -29.4

Wola Różanecka-9 (WR-9) 940-- 945 656 2.3 0.08 -64.2 -188 -50.2 -30.6 Reservoirs: U~~er Badenian

Borek-9 (Bk-9) 515- 542 434 1.0 0.05 -63.4 -215 -39.9 -28.6 Brzezowiec-lI (Be-lI) 839- 900 663 3.3 0.04 -66.4 -198 -49.9 -30.5 Dąbrówka-20 (Db-20) 807- 809 186 1.6 0.03 -62.7 -210 -39.2 -31.2 Grabina-2 (Gr-2) 350-- 357 856 2.5 0.09 -66.6 -188 -50.5 -30.0 Husów-B (H-13) 2398-2442 357 2.6 0.01 -67.8 -194 -41.5 -30.8 Husów-70 (H-70) 2419-2455 446 2.9 0.08 -67.6 -195 -43.8 -23.8 Jaśniny-6 (Ja-6) 817- 841 458 2.7 0.05 -65.5 -204 -46.4 -29.1 Jaśniny-l2 (Ja-12) 461- 523 889 - 0.05 -68.6 n.a. n.a. n.a. Kielanówka-1 (Ki-l) 2320-2348 218 6.3 0.05 -64.9 -208 -38.7 -26.2

Kielanówka-3 (Ki-3) 2306-2320 217 5.0 0.04 -64.9 n.a. n.a. n.a.

Łąkta-lO (Lk-10) 1876-2355 260 3.5 0.10 -66.5 -178 -44.6 -31.0

Nieznanowice-5a (Ni-5a) 310-- 388 947 2.5 0.06 -66.2 -175 -48.7 -31.8

Nosówka-14 (N-14) 2300-2520 272 3.4 0.04 -68.1 -204 -39.6 -31.4

Pilzno-13 (Pi-B) 210-- 216 868 - 0.11 -67.3 n.a. n.a. n.a.

Pilzno-14 (Pi-14) 170-- 195 580 - 0.94 -69.0 -199 -48.1 -30.9 Przemyśl-123 (P-123) 2375-2432 253 3.5 0.18 -65.6 -205 -40.2 -29.4 Przemyśl-186 (P-186) 2590-2610 304 2.7 0.48 -64.7 -195 -43.0 -30.6 Przemyśl-227 (P-227) 2597-2640 323 2.2 0.52 -65.2 -192 -46.2 -31.4 Raciborsko-1 (Ra-1) 528- 535 244 16.0 0.07 -60.7 -196 -39.2 -30.3 Rysie-3 (Ry-3) 601- 624 872 - -0.05 -66.3 -199 -45.4 -27.8 Rzeszów-5 (Rz-5) 2243-2257 497 2.8 0.15 -65.0 -192 -46.8 -30.3

Rzeszów-16 (Rz-16) 2231-2249 394 4.8 0.05 -67.3 n.a. n.a. n.a.

Tarnów-45 (T-45) 1365-1384 42 0.5 0.61 -35.7 -151 -28.1 -27.2

Tarnów-63 (T-63) 462- 468 206 1.4 0.10 -61.1 -206 -38.6 -29.4

Wygoda-l (Wy-l) 592- 625 962 1.5 0.08 -64.6 -189 -46.3 -29.7

Reservoirs: Lower Badenian

Roźwienica-2 (Ro-2) 1870-1873 26 0.8 0.08 -67.3 -206 -51.1 -31.2 Reservoirs: Lower Badenian and U~~er Iurassic

Lubaczów-3 (Lu-3) 992-1041 102 0.6 0.28 -67.3 -198 n.a. n.a.

Lubaczów-22 (Lu-22) 1020-1045 76 1.0 0.36 -66.6 -201 -38.8 -29.0

(6)

SSE

TARNÓW

NNW:SW

, SMĘGORZÓW

NE

(m) ~---~--~~~~~---~---~---~ S-3 OT-11 ,

Insignificant changes in values of geochemical indices and isotopic ra-tios (Tab. land Fig. 9) with the depth suggest quite uniform generation conditions of microbial methane in the whole Badenian succession. Mo-reover, the lack of dependence of stable carbon isotopic compositions of ethane and propane with the depths (Tab. 1, Fig. 9) also indicates the simi-lar generation conditions of these

ga-ses within the fuli Badenian sequence.

O~---+----M~1-~---r---+---~

-2000

D Flysch Carpathians

D folded Miocene (Zgłobice Unit)

D autochthonous Miocene • Upper Cretaceous

o

5 10km ~I ---~, ---~, Dupper Jurassie D Triassic

D Lower Carboniferous and Devonian

Precambrian

Depths of sampled gas accumu-lations in the Lower Sarmatian strata are between 161 and 2,621 meters (Tab. 1). Geochemical indices and isotopic ratios of the gas reservoired within the Lower Sarmatian of the Polish part of the Carpathian Fore-deep are given below (Tab. 1):

hydrocarbon index [CHe

=

Fig. 7. Geological cross section through the Tarnów, Dąbrowa Tarnowska and Smęgorzów CHJ(C2H6+C3Hg

)] from 123 to

fields with isotopic data after Kotarba & Jawor (1993) 1,667, i-C4HIO/n-C4HIO ratio: from

0.5 to 10.0, CDMI index {CDMI =

).

(m 200 o -200 -400 -600 -800

sw

L 40 L4 - r -• L.. Dupper Badenian D Lower Badenian Dupper Jurassie L-22 I

NE

II \ MIGRATlON OF MIOCENE GAS ~ ~-\.,

illJ

r

Fig. 8. Geological cross section through the Lubaczów field with

isotopic data

attained maturation degree corresponding to 1.1 to 1.6% in the vitrinite reflectance scale (Figs 4A and 5A). The gas has migrated together with the oil to the autochthonous Miocene complex from the Upper Jurassic carbonates (Fig. 7) where several discovered deposits accumulating oil and gas

produ-ced from this genetic type of organic matter (Kotarba &

Jawor, 1993). In the Tamów-47 well even the oil shows were

encountered in the bottom part of the autochthonous Mio-cene sequence which is a curiosity in the Carpathian

Fore-deep (Kotarba & Jawor, 1993). Methane reservoired in the

other deposits originated from the microbial carbon dioxide

reduction (Fig. 3). In both the Roźwienica (Ro-2 sample)

and the Lubaczów deposits (Lu-3 and Lu-22 sampIes) very small admixture of diagenetic (and/or low-temperature ther-mogenic) methane has been identified (Tab. 1, Fig. 2A). In the Lubaczów deposit gas filled also the trap in the Upper Jurassic carbonates. Genetically, this gas is typical microbial methane which migrated to the Upper Jurassic trap from the

autochthonous Miocene strata along the fault zone (Fig. 8).

[C02/(C02+CH4)] 100 (%)} from

0.04 to 0.47%, OJ3C(C&) from -72.6 to -63.7%0, oD(C&)

from -214 to -179%0, 013C(C2H6) from -57.4 to -33.4%0, and

oJ3C(C3Hg) from -31.7 to -22.8%0.

Composition of theses gases is also methane-dominated (Tab. 1). Results of stable carbon isotope analyses in metha-ne, ethane and propametha-ne, and stable hydrogen isotope analyses in methane (Figs 2B to 6B) point out that the hydrocarbons were generated during the carbon dioxide reduction of mic-robi al processes as well as, sporadically, in the initial phase of thermogenic processes. Methane was produced during microbial carbon dioxide reduction (Figs 2B and 3B). The only exception is the gas from the Buszkowiczki field (Bu-2 sample) where very small amounts of diagenetic and/or low-temperature thermogenic methane was found

(Tab. 1, Fig. 5B). Minor ethane and propane were

gene-rated in both the diagenetic processes and in the initial phase of the low-temperature thermogenic processes (Figs 4B and 5B). The highest contents of thermogenic pro-pane were reported from the Blizna and the Ocieka depo-sits (Bl-5 and Oc-l samples, Fig. 5B) whereas the largest concentration of diagenetic ( microbial) ethane was found in the Przeworsk depo sit (Pr-14 sample, Figs 4B and 5B).

Similarly to the Badenian gases, minor changes of geo-chemical indices and isotopic ratios with the depth (Fig. 9) indicate the alike generation conditions of microbial metha-ne within the full thickmetha-ness of the Lower Sarmatian succes-sion. Additionally, lack of correlation between the stable carbon isotope composition of ethane and propane with the depth (Tab. land Fig. 9D) also points to the similarity of diagenetic and/or low-temperature thermogenic processes in the full thickness of Lower Sarmatian succession.

Conclusions

The Miocene gas deposits of the Carpathian Foredeep are dominated by methane generated by the microbial carb-on dioxide reducticarb-on. This process, un1ike the methane fermentation, occurs in the marine environment. Small amounts ofhigher gaseous hydrocarbons (mainly ethane and propane) were produced during the initial phase

(7)

oflowtem500 1000

-I

;; 1500 -c. Q) C 2000 r-2500 t -500 -1000

-I

..c 1500

-..

c. Q) C 2000 t -2500 r-I I I

~ot

lAI

~. Cb

o

-• -• Q)

o

D

o

.0j-M.L,. • •

••

...

o • 00 ~ .<0 I I I 10 100 1000 -CHe

=

CHJ(C2H6+C3Hs) I I I ·:~o

.~"

op

8

.~o

f#.

-I

T-45 C -~

-o

;g

~ -I I I I -70 -60 -50 -40

,.

-..

o o o

o

• Lower Sarmatian O Upper Badenian D Lower Badenian L,. Lower Badenian

and Upper Jurassie

0.5 1.0 1.5 CDMI=[COi(C02+CH4)]100 (%) I I I -~.

[Q]

~ O

000

-O O

- ..~

~~

-•

O - -D. t - -O • ( b O O O O

oc!

-I I I -35 -30 -25

Przegląd Geologiczny, vol. 46, nr 8/2, 1998 bial gas which migrated from auto-chthonous Miocene strata along the fauIt zone.

References

BERNER U. & FABER E. 1996 - Empiri-cal carbon isotope/maturity relationships for gases from algal kerogens and terrigenous or-ganic matter, based on dry, open-system py-rolysis. Org. Geochem., 24: 947-955. BERNER U. & FABER E. 1997 - Carbon isotope/maturity relationships for gases from

algal kerogens and terrigenous organic mat-ter. Geol. Jahrbuch, D 103: 129-145. CALIKOWSKI A. 1983 - Badania geoche-miczne gazów ziemnych miocenu na obsza-rze Husów-Kraków. Pr. Inst. Gór. Naft. i Gazow., 45: 74-81.

FLORKOWSKI T. 1985 - Sample prepara-tion for hydrogen isotope analysis by mass spectrometry. Intr. J. Appl. Radiat. Isot., 36: 991-992.

GŁOGOCZOWSKI J.J. 1976 -

Zagadnie-nie genezy i migracji gazu ziemnego w mio-cenie SE części Przedgórza Karpat. Prz.

Geol., 24: 372-380.

JAWOR E. & KOTARBA M.J. 1991 - Ge-neza gazu ziemnego akumulowanego w pa-leozoiczno-mezozoicznych utworach

podłoża miocenu zachodniej i środkowej czę­

ści zapadliska przedkarpackiego - interpre-tacja geologiczna i izotopowa. Nafta, 47: 149-155.

JAWORE.&KOTARBAM.J. 1993-Ge-neza gazu ziemnego zakumulowanego w utworach cenomanu i miocenu w złożu Brze-zowiec. Nafta, 49: 47-52.

813C(CH4) (%0) 813C(C3Hs) (%0)

KOTARBA M.J. 1992 - Bacterial geses in Polish part of the Carpathian Foredeep and the Flysch Carpathians: isotopic and geologi-cal approach. [In:] Bacterial Gas, Vially R.

(ed.). Technip, Paris: 133-146.

Fir,. 9. (A) Hydrocarbon index, (B) carbon dioxide-methane index, (C) b'3C(CR.) and (D)

b' C(C3Hs) versus depth

KOTARBA M.J. 1995 - Geochemia

trwa-łych izotopów w poszukiwaniach

nafto-wych. Prz. Geol., 43: 988-992.

perature thermogenic and/or diagenetic processes. Both the molecular and isotopic compositions of gases accumulated in the autochthonous Badenian and Lower Sarmatian strata are practically similar which indicates homogeneity of ge-neration processes within the full thickness of Miocene suc-cession. Both the high sedimentation rate and the rhythmic and cyc1ic deposition ofMiocene c1ays and sands facilitated the gas accumulation and formation of muItihorizontal gas fields (Kotarba et al., 1998a). Microbial gases generated in a particular c1aystone/mudstone horizon migrated to the overlying sandstone horizon which, in turn, was covered by another c1aystone/mudstone bed. The only exception is the gas from the Tarnów-45 well reservoired in the bottom part of Lower Badenian sequence. This is the typical ther-mogenic gas produced from oil-prone, marine organic mat-ter (type II kerogen) which remains at the maturation stage corresponding to 1.1 to 1.6% in vitrinite reflectance scale whereas the whole Miocene sequence is dominated by the type III (humic), low-matured kerogen of maximum vitrinite

reflectance 0.6% Ro (Kotarba et al., 1998b). Hence, the gas

reservoired within the Badenian strata in the Tarnów-45 well had to migrate from the Mesozoic basement where such

thermogenic hydrocarbons are common (Kotarba & Jawor,

1993). Natural gas from the Lubaczów field accumulated in Upper Jurassic carbonate trap is therefore, a typical

micro-KOTAR BA M.J., BURZEWSKI W., WIL-CZEK T., SŁUPCZYŃSKI K., KOSAKO-WSKI P. & BOTOR D. 1998a - Model of gaseous hydrocarbons genera-tion in the Miocene strata of the Polish part of the Carpathian Foredeep. Prz. Geol., 46: 737-742.

KOTARBA M.J. & JAWOR E. 1993 - Petroleum generation, mi gra-tion and accumulagra-tion in the Miocene sediments and Paleozoic-Mesozo-ic basement complex of the Carpathian foredeep between Cracow and Pilzno (Poland). [In:] Generation, accumulation and production ofEuro-pe' s hydrocarbons. III. Special publication of the European Association ofPetroleum Geologists, Spencer A.M. (ed.). Springer, Heidelberg, 3:

295-301.

KOTARBA M.J., SOLARSKI W., STECKO Z. 1994 - Zastosowanie analizy trwałych izotopów węgla w etanie i propanie w poszukiwaniach naftowych. Mat. Symp. Badania geochemiczne i petrofizyczne w poszuki-waniach ropy naftowej i gazu ziemnego. Wyd. IGNiG, Kraków: 92-102. KOTARBA M.J., SZAFRAN S. & ESPITALIE J. 1987 - A study or or-ganic matter and naturai gases of the Miocene sediments Polish part of the Carpathian Foredeep. Chem. Geol., 64: 197-207.

KOTARBA M.J., WILCZEK T., KOSAKOWSKI P., KOWALSKI A. &

WIĘCŁAW D. 1998b - A study of organic matter and habitat of

ga-seous hydrocarbons in the Miocene strata of the Polish part of the Car-pathian Foredeep. Prz. Geol., 46: 742-750.

NEY R. 1968 - Rola rygla krakowskiego w geologii zapadliska przed-karpackiego i rozmieszczeniu złóż ropy i gazu. PI. Geol. Kom. Nauk Ge-ol. PAN Oddz. w Krakowie, 45: 7-82.

NEY R., BURZEWSKI W., BACHLEDA T., GÓRECKI W., JAKOB-CZAK K. & SŁUPCZYŃSKI K. 1974 - Zarys paleogeografii i rozwoju litologiczno-facjalnego utworów miocenu zapadliska przedkarpackiego. Pr. Geol. Kom. Nauk Geol. PAN Oddz. w Krakowie, 82: 3-65. OSZCZYPKO N. 1982 - Explanatory notes to lithotectonic molasse profiles of the Carpathian Foredeep and in the Polish part of the Western Carpathians. Veroff. Zentralinst. Phys. Erde Akad. Wiss. DDR, 66: 95-115.

(8)

OSZCZYPKO N. 1996 - Mioceńska dynamika polskiej części zapadli-ska przedkarpackiego. Prz. GeoI., 44: 1007-1018.

OSZCZYPKO N. 1997 - The Early-Middle Miocene Carpathian peri

-pheral foreland basin (Western Carpathians, Poland). Prz. GeoI., 45: 1054-1063.

RICE D.D. 1992 - Controls, habitat, and resource potential of ancient bacterial gas. [In:] Bacterial Gas, Vially R. (ed.). Technip, Paris: 91-117.

RICE D. D. & CLAYPOOL J. 1981 - Generation, accumulation and re-source potential ofbiogenic gas. Amer. Ass. Petrol. GeoI. BulI., 65: 5-25. SCHOELL M. 1983 - Genetic characterization of naturai gases. Amer. Ass. Petrol. GeoI. BulI., 67: 2225-2238.

SCHOELL M. 1988 - Multiple origins of methane in the Earth. Chem.

Geol., 71: 1-10.

STAHL W. 1977 - Carbon and nitrogen isotopes in hydrocarbon re-search and exploration: Chem. GeoI., 20: 121-149.

STAHL W. 1979 - Carbon isotopes in petroleum geochemistry. [In:] Lectures in Isotope Geology, Jager E. & Hunziker J.e. (eds). Berlin, Springer: 274-282.

WHITICAR M.J. 1994 - Correlation of natural gases with their sour-ces. [In:] The petroleum system - from source to trap, Magoon L.B. & Dow W.G. (eds). Amer. Ass. Petro!. GeoI. Mem., Tulsa, 60:

261-283.

WHITICAR M.J., FABER E. & SCHOELL M. 1986 - Biogenic meta-ne formation in marimeta-ne and fresh water environment, C02 reduction vs. acetate fermentation - Isotopic evidence. Geochim. Cosmochim. Acta, 50: 693-709.

Tectonics of the consolidated basement of the Polish Carpathians

Wojciech

Ryłko*,

Adam

Tomaś*

Based on the results ojmagnetotelluric soundings a sketch ojthe main tectonic elements ojthe consolidated basement ojthe Polish Flysch Carpathians and a number oj longitudinal profiles and cross-sections have been drawn. The sketch as well as the sections allowedjor developing a concept about major tectonic pattern oj the consolidated basement in this part oj the Carpathians. Morphology oj the consolidated basem en t suiface oj the Carpathians is very diversified. Depth to the top oj the basem en t suiface varies jrom several hundred meters in the western part ojthe Carpathians to around 20 km in the south-eastern part. Generally, the surjace dropsfrom the north-west toward the south-east. The drop is not uniform, and it has a discontinuous character.

In the tectonics oj the consolidated basement oj the Carpathians, in the territory oj Poland, three major elements influencing its structure are distinguished. These are two transverse, generally SW-NE orientedjault zones (A-A and B-B), where the basem en t is dipping eastward. The third element, oj a comparable meaning to the other two, is a longitudinal zone oj the basem en t dipping southward -"regional basement slope".

The jirst oj these large jault zones, the transverse and western-most one (A-A), runs from Babia Góra to the region oj Rzeszotary. The dislocated area lying to south-east oj the jault zone is lowered by about 8.5 km in its southern part and about 2 km in its northern part.

The second, transverse B-B jault zon e jollows the Wysowa-Sędziszów Małopolski line. The dislocated area lying to the east oj this jault zone is lowered by several kilometers to maximum oj 12 km in the southern part. The entire eastern block is moved along thejault 40 km

to the north. The B-B zone separates the central block jrom the eastern one. The third major tectonic element is the described earlier zone ojthe regional basement slope (Fig. 2). It is a longitudinal element which remodels the consolidated basement ojthe Carpathians in the southern direction. Along this zone, there is an abrupt block-wise lowering ojthe consolidated basem en t to the south.

The two transverse dislocation zone A-A and B-B, discussed earlier, divide the consolidated basement oj the Polish Carpathians into three regions. The western region located to the west oj the A-A zone, the central region between the A-A and B-B zones, and eastern region located to the east oj the last zone (B-B). The consolidated basement oj the western region is relatively shallow, at the depth jrom one to jour kilometers. This region is technically calm. The central and eastern blocks are two-joZd, separated by the regional basement slope into the elevated northern part and lowered southern part.

An outlined general jramework oj the tectonics oj the consolidated basement oj the Polish Carpathians is a present-day representation, yet itwas jinally jormed in the Neogene. We can assume that in the Early Neogene (probably at the turn oj the Oligocene and Miocene) the northern plate collided with the Carpathian block. In the Lower Miocene, along the boundary between the northern plate and the Carpathian block, the latter was dropped jrom a jew kilometers in the west to several kilometers in the east. After the lower Miocene, probably at the Middle/Upper Miocene interjace, the Carpathian block started to disjoin. It was jractured along the A-A zon e and, in its eastern part, rotationally shifted by about 40 km to the north-east. In the west, the western block was jonned. The eastern part, apart from be ing shifted and rotated, was additionally lowered by a jew kilometers towards the south. In the Upper Miocene a jracture along the B-B zon e took place, and, as in the previous stage, the eastern part was rotationally transjerred by ca 40 km to the north-east. Thus, the net shift, along the A-A and B-B line was about 80 km. The eastern part was divided along the B-B line into the central and eastern blocks. The eastern block, moreover, is lowered by ajew kilometers to the south. This process is accompanied by a development oj a set oj oblique slip jaults ojvarious directions.

Key words: areal geology, Polish Carpathians, magnetotelluric surveys, deep sounding, basement tectonics, jault zones, regional

patterns, Neogene

Introduction

In the area of the Polish Flysch Carpathians, magneto-telluric research has been continued since 1975 under the initiative and commission of the Polish Geological Institute.

*Polish Geological Institute, Carpathian Branch, ul. Skrzatów 1, 31-560 Kraków, Poland

Magnetotelluric and telluric coverage of the entire area of the Carpathians was carried out from 1986 to 1990. In this period 518 magnetotelluric soundings were made along 61 profiles. These profile s were located perpendicular to the axis of the Carpathian arc. All magnetotelluric work was rendered by the Agency for Geophysical Research

(Przed-siębiorstwo Badań Geofizycznych) in Warsaw. First

Cytaty

Powiązane dokumenty

Mesodiagenesis in cluded quartz and K-feld - spar overgrowths, albitisation, crystallisation of do lo mite and an ker ite and coarsely crys tal line cal cite, dis so

The study in cluded also re la tion ships be tween re sults of the com pre hen sive in ter pre ta tion: po ros ity (PHI), wa ter sat u ra tion in flushed zone (SWXO) and un in

The geo chem i cal study of car bon ates and sulphates oc cur - ring within the Badenian anhydrite sec tion of the Wola Różaniecka 7 (SE Po land) sup ports ear lier con

The old est de pos its known from the Koszalin–Chojnice Zone are up per Llanvirnian and Caradocian strata (Bednarczyk, 1974; Modliński, 1987; Podhalańska and Modliński, 2006),

Nu mer ous deep bore holes and re flec tion seis - mic pro files have pro vided data on the struc ture of the top of the crys tal line base ment in the coastal area of the Bal

Al though the pro por tion al ity of meth ane to eth ane in nat u - ral gas is not sim u lated in the thermogenic gases gen er ated by hy drous py rol y sis and in other py rol

The oils ac cu mu lated in the Mid dle Cam brian sand stones from the Pol ish part of the Bal tic re gion re veal very sim i lar geo chem i cal char ac ter is tics and were gen

Non-rep re sen ta tive, in di vid ual re sults of porosimetric mea - sure ments in the Lower Cam brian Żarnowiec For ma tion of the Mobergella Zone and Holmia Zone do not en able