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Off. Geochem. Vo l. I1, No. 6. pp. 505-512, 1987 0146-6380/87 $3.00+ 0.00Printed in Gr eat Britain. All rights reserved Copyright ~ 1987 Pergamon Journals Ltd

Pyrolysis GC characterization o f whole rock and kerogen concentTatesamples o f immature Jurass ic source rocks from NW Germany

CARot . Aatz~os3a an d PETER J. MOLLER*Institut ffir Erd61 und Organische Geochem ie (ICH-5), K FA Jfilich Gm bH , D -517 0 Jii lich, F.R.G.

Received 25 November 1986; accepted 7 April 1987)A ~tra ct --N ine rock samples f rom three Jurassic st ra t igraphic uni ts of a shallow core from N W Germanywe re analyzed by pyrolysis-gas chromatography. The units contain a m ixed Ty pe-ll /I l l kerogen(Dogger-c0, a hydrogen-rich Ty pe-II kerogen (Lias-~), and a hydrogen-poor Ty pe-Ill kerogen (Lias-6).All of the kerogen was imm ature (Ro = 0.5%). Tw o sets of kerogen concentrates ( A D : HC I/HF followedby a density separation, and A : only acid treatment) prepared from the rock samples were also analyzedto make a detailed comparison of the pyrolysates of rock and corresponding kerogen-concentrates.Hydrogen-index (HI) values of the kerogen concentrates prepared from organic-carbon poo r rock werenearly 200% higher than H I values of the rock samples. Changes in HI w ere minimal for the samplescontaining T ype -II kerogen. The A and A D samples from the Con-poor rock y ielded pyrolysates withn-alkane series o f very different molecular lengths. Pyrograms of the rock samp les had n-aikane seriesextending to n-C~(; the chromatograms of the A samples reached the n-Ct4--nC.x range. The A D samplesfrom C o,l-poor rock an d all three sample types from the Cm-rich rock had n-alkane series up to n-C_~.The benzene/hexane and toluene/heptane ratios fo r the Cm -po or rock and A samples were far higher thanfor the A D sam ples, which had ratios similar to those o f all three sample types from the Co ~-rich rocks.These results indicate that choice of kerogen preparation method is cri tical whe n Co~-poor samples areanalyzed.Key words : kerogen, source rock, pyrolysis-gas chromatography, hydrogen index, n-alkanes

INTRODUCTIOND u r i n g t h e p a s t d e c a d e , p y r o l y s i s h a s b e c o m e ac o m m o n a n a l y t i c m e t h o d i n g e o c h e m i c a l r e s e a r c h .T h e h y d r o g e n i n d e x ( H I ) o b t a i n e d b y R o c k - E v a lpyro lys i s (Esp i t al i~ e t a l . , 1977) has become a s t an-d a r d m e a s u r e o f k e r o g e n q u a l i t y , a n d p y r o l y t i c a n a l -y s e s h a v e b e e n u s e d t o c h a r a c t e r i z e k e r o g e n ( L a t t e ra n d D o u g l a s , 1 98 0 ), e v a lu a t e s o u r c e r o c k s ( C l a y p o o la n d R e e d , 1 9 76 ), S t u d y t h e e f f ec t s o f t h e r m a l m a t -u r a t i o n ( P e t e r s e t a i . , 1983) , and to he lp de t e rmineg e n e r a ti o n a n d m i g r a t i o n h i s to r ie s o f h y d r o c a r b o n s( H u c a n d H u n t , 1 9 80 ).

W i t h t h e g r o w i n g u s e o f p y r o l y t i c an a l y s e s i no r g a n i c g e o c h e m i s t r y , i n c r e a s e d a t t e n t i o n h a s a l s ob e e n g iv e n t o s o m e o f t h e i n h e r e n t a n a l y t i c a l i n c o n -sistencies. Espitali~ e t a L ( 1 9 8 0 ) r e p o r t e d t h a t r o c k sa n d t h ei r c o r r e s p o n d i n g k e r o g e n c o n c e n t r a te s d i d n o ta l w a ys y ie ld t h e s am e a m o u n t o f h y d r o c a r b o n s p ~ rg r a m o f o r g a n i c c a r b o n , a n d t h a t c e r t a i n m i n e r a l sc a u s e d c a ta l y ti c c r a c k i n g o f h y d r o c a r b o n s w h e n p y -r o l y z e d w i t h k e r o g e n c o n c e n t r a t e s . K a t z ( 1 9 8 3 )f o u n d t h a t t h e R o c k - E v a l h y d r o g e n i n d e x ( H I ) a n do x y g e n i n d e x ( O I ) c o u l d b e s i g n i fi c a n tl y a f f e ct e d b ym i n e r a l c o m p o s i t i o n a n d o r g a n i c c a r b o n c o n t e n t .F u r t h e r i n v e s t i g a t i o n s u s i n g r o c k s a n d k e r o g e n c o n -c e n t r a t e s m i x e d w i t h m i n e r a l s s h o w e d t h a t t h e*Present address: Universitfi t Bremen, Fachbereich Geo-wissenschaften, Postfach 330 440, D-2800 Bremen 33,F.R.G.

a m o u n t o f h y d r o c a r b o n s a d s o r b e d b y m i n e r a ls i sre l a t ed t o t he na tu re a nd spec if ic su r face a rea o f t hemine ra l s (Esp i ta l i~ e t a l . , 1984) . A n inc reasse i n l owm o l e c u l a r w e i g h t h y d r o c a r b o n s ( l i g h t e r t h a n n - C ) 0 )a n d a d e c r e a s e i n h i g h e r m o l e c u l a r w e i g h t h y d r o -c a r b o n s w a s r e p o r t e d b y D c m b i c k i e t a l . (1983) whent h e y c o m p a r e d r o c k t o k e r o g e n - c o n c e n tr a t e p y r o l y -sates, but Espitali~ e t a i . ( 1 9 8 4 ) f o u n d t h a t r o c kp y r o l y s a t e s y i e l d e d a s l i g h t l y r e d u c e d q u a n t i t y o fl i g h t h y d r o c a r b o n s a n d a g r e a t l y r e d u c e d q u a n t i t y o fh e a v y h y d r o c a r b o n s a s c o m p a r e d t o t h e p y r o l y s a te o fc o r r e s p o n d i n g k e r o g e n c o n c e n t r a t e s .

T h e n a t u r e o f t h e r o c k s a m p l e c a n s i g n i f ic a n t lya f f e c t t h e p y r o l y s a t e : K a t z ( 1 9 8 3 ) f o u n d t h a t t h ep y r o l y s a t e s o f T y p e - I k e r o g e n s w e r e l es s a f f e ct e d b ym i n e r a l s t h a n w e r e t h e p y r o l y s a te s o f T y p e - I I I k er -o g e n s , a n d s u g g e s t e d t h a t T y p e - I k e r o g e n s m a y b ea b l e t o o v e r s a t u r a t e t h e r e t e n ti o n c a p a c i t y o f am i n e r a l m a t ri x . A c c o r d i n g t o D e m b i c k i e t a l . (1983),w h e n c a r b o n c o n t e n t i n a r o c k e x c e e ds 1 0 % r e t e n t io na n d / o r c r a c k i n g e ff e ct s a r e u n i m p o r t a n t . E v e n w i t hT y p e - I k e r o g e n s , h o w e v e r , O r r ( 1 9 8 1 ) f o u n d t h a tp y r o l y s a t e c o m p o s i t i o n a n d q u a n t i t y c a n b e s u b s t a n -t i a l l y a f fec t ed by ce r t a in mine ra l s such a s smec t i t e s .

I n s p i te o f t h e e x te n s iv e w o r k w h i c h h a s b e e n d o n ei n p y r o ly s i s , a n u m b e r o f p r o b l e m s r e q u i r e f u r t h e rw o r k . K e r o g e n - c o n c e n t r a t e a n d w h o l e r o c k s a m p l e scan p roduce ve ry d i f fe ren t pyro lysa t e s , d i f fe ren t i nc o m p o s i t i o n a s w e l l a s q u a n t i t y . M a n y c o m p a r a t i v es t u d ie s o f k e r o g e n c o n c e n t r a t e a n d r o c k s a m p l e s ,h o w e v e r , h a v e b e e n d o n e u s i n g o n l y F I D a n a l y s i s o f

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506 CAROL ARNOSTIand PETER J. MCLLERp y r o l y s a t e c o m p o s i t i o n , w i t h o u t p r i o r c h r o -m a t o g r a p h i c s e p a r a t i o n . A f l a m e - i o n i z a t i o n d e t e c t o ra lone , t hough , does no t y i e ld t he de t a i l ed i n fo rm a t iona b o u t p y r o l y s a t e c o m p o s i t i o n w h i c h c a n b e g a i n e df r o m a g a s c h r o m a t o g r a p h . F u r t h e r m o r e , m o s t s t u d -i es have been ca r r i ed ou t wi th j us t o ne sam p le t ypeor w i th s i ng le sam ple s , i n s t ead o f wi th a n en t i r e se r ie so f r o c k a n d c o r r e s p o n d i n g k e r o g e n c o n c e n t r a te s a m -ples.

A f u r t h e r p r o b l e m c o n c e r n s t h e k e r o g e n c o n c e n -t r a t i o n p r o c e s s : m a n y d i f f e r e n t p r o c e d u r e s c a n b eused , wi th va ry ing ef fect s on t he ke ro gen and m ine r -a l s ( see , fo r exam ple , D ura nd and Nica i se , 1980) .E l i m i n a t io n o f p y r i t e i s a m a j o r p r o b l e m f o r an u m b e r o f r ea s o n s . F o r e x a m p l e , c er t a in t y p e s o fp y r i te m a y h a v e a p r o t e c ti v e c o a t i n g o f o r g a n i cm a t t e r , so e l im ina t i on o f py r i t e i s no t po ss ib l e wi th -ou t a l t e r i ng t he o rgan i c m a t t e r . Seve re chem ica lt r e a t m e n t o f t h e ro c k , a c o m m o n t e c h n i q u e f o r p y r i t er e m o v a l , c a n l e a d t o c h a n g e s i n k e r o g e n s t r u c t u r e ,pa r t i cu l a r l y w hen the rock i s im m a tu re (R0 < 0 .5% ) .A dens i t y sepa ra t i on can be used t o e l im ina t e py r i t e ,bu t c lose ly a ssoc i a t ed o rgan i c m a t t e r m ay be l os t.E ven a f t e r a dens i t y sepa ra t i on , py r i t e e l im ina t i on i sno t nece ssa r i l y com ple t e , s i nce som e ve ry f i ne pyr i t em a y b e l e f t i n t h e s u p e r n a t a n t f r a c t i o n ( D u r a n d a n dN i c a is e , 1 9 8 0 ) . W i t h o u t t h e d e n s i t y s e p a r a t i o n ,t h o u g h , t h e m i n e r a l s r e m a i n i n g i n t h e s a m p l e m a yr e t a i n o r c r a c k t h e h e a v i e r h y d r o c a r b o n s .

T he ob j ec t i ve o f t h i s s t udy was t o sys t em a t i ca l l yc o m p a r e a se ri es o f r o c k a n d c o r r e s p o n d i n g k e r o g e n -c o n c e n t r a t e p y r o l y s a t e s w i th t h e u s e o f p y r o l y s i s - G C .T h e d i f f e r e n c e s i n k e r o g e n c o n c e n t r a t e s p r e p a r e dw i t h a n d w i t h o u t a d e n s i t y s e p a r a t i o n w e r e a l s ostudied.

S MPLES ND E X P E R IM E N T L M E T H O D S

In t h is s t ud y , t he p y ro lysa t e s o f a se ri es o f who le -r o c k a n d c o r r e s p o n d i n g k e r o g e n - c o n c e n t r a t e s a m p l e swere sys t em a t i ca l l y com pared ; t h ree d i f f e ren t ke r -ogen t ypes a re r ep re sen t ed i n t he sam ple se r i e s . T wok e r o g e n - c o n c e n t r a t i o n p r o c e d u r e s w e r e u s e d in o r d e rto de t e rm ine t he ef fec ts o f a dens i t y sepa ra t i on on t hek e r o g e n c o n c e n t r a t e s.

T h e n i n e r o c k s a m p l e s u s e d i n t h e s t u d y a r e f r o ma s h a l l o w c o r e h o l e d r i ll e d n e a r H a m e l n , N W G e r -m a n y , w h i c h c o n t a i n e d t h r e e s t r a t i g r a p h i c u n i t s o fJu ra ss i c age : Dogger -o r (Aa len i an ) , L i a s -E (T oa rc i an ,Pos idon ia sha l e ) , and L ias -t~ (P l i ensbach i an ) . T hrees a m p l e s w e r e t a k e n f r o m e a c h o f t h e t h r e e s t r a t i-g r a p h i c u n i t s. R o c k - E v a i p y r o l y s i s s tu d i e s o f t h e c o r ehave shown tha t t he Dogge r -~ t con t a ins a m ixedT y p e - I I / l l I k e r o g e n , t h e L i a s- E a h y d r o g e n - r i c h T y p e -I I k e r o g e n , a n d t h e L i a s -6 a h y d r o g e n - p o o r T y p e - I l lke rogen . Vi t r in i t e r e f le c t ance va lue s o f abo u t 0 .5 %i n d i c a t e t h a t t h e k e r o g e n i s i m m a t u r e ( R u l l k r t t e r J . ,W . K a l k r e u t h , U . M a n n , P . J . M i i l l e r , M . R a d k e , R .G. Schae fe r , H . - J . Sehenk and E . -G. Wi t t e 1985 ,K F A / I C H - 5 - R e p o r t N o . 5 0 3 2 8 5 , J i i l i c h ) .

T h e r o c k s a m p l e s w e r e g r o u n d a n d e x t r a c t e d w i t hd i c h l o r o m e t h a n e . A p o r t i o n o f e a c h s a m p l e w a s s e ta s ide fo r ana lys i s a s 'who le rock . T o d i sso lvec a r b o n a t e s , a s m a l l a m o u n t o f e t h a n o l a n d 2 0 0 m l o fH C I ( 1 2 .5 % ) w a s a d d e d t o t h e r es t o f e a c h s a m p l e( a p p r o x . 3 0 g ) , a n d t h e m i x t u r e w a s s t i r r e d a n dhea t ed a t 50~C fo r 75 m in . 500 m i o f wa te r was t hena d d e d , a n d d e c a n t e d o n t h e f o l lo w i n g d a y . A f t e rf u r t h e r w a s h i n g a n d c e n t r i f u g in g , 3 5 0 m l o f aH F / H C I - s o l u t i o n (2 p a rt s 4 8 % H F , 1 p a r t 3 2 % H C I )was added t o t he r e s idue , and t he m ix tu re was s t i r r edf o r 9 6 h o u r s a t r o o m t e m p e r a t u r e t o d i s s o l v e a l u m i -nos i l i c a t e s . Af t e r m ul t i p l e wash ings and cen t r i fug ing ,o n e p o r t i o n o f e a c h s a m p l e w a s d r i e d a n d w e i g h ed f o ruse a s A (ac id con cen t ra t i on ) sam ple s . 150 m l o fZ n B r2 s o l u t i o n ( d e n s it y 1 . 9 5 g c m - ~ ) w a s a d d e d t ot h e r e m a i n d e r o f e a c h s a m p l e . T h e m i x t u r es w e r es t i r r ed , c en t r i fuged , vacuum -f i l t e red , and washedwi th de ion i zed wa te r , and t he r e su l t i ng so l i d m a te r i a lw a s d r i e d a n d w e i g h e d f o r u s e a s A D ( a ci d - a n ddens i t y - sepa ra t i on ) sam ple s .

O r g a n i c c a r b o n w a s d e te r m i n e d b y d r y c o m b u s t i o nw i th a L E C O - I R 1 12 c a r b o n a n a l y z er ; c a r b o n a t e -C O 2 w a s e x p e l l e d b e f o r e h a n d f r o m t h e w h o l e - r o c ks a m p l e s b y t r e a t m e n t w i t h d i l u t e d H C I a t a p p r o x i -m a t e l y 8 0 C . T o t a l c a r b o n w a s m e a s u r e d o n u n -t r e a t e d w h o l e - r o c k s u b s a m p l e s a n d c a r b o n a t ec a r b o n - - d e t e r m i n e d b y d i f f e r e n c e - - w a s ex p r e s se d asC a C O 3 , a s s u m i n g c a l c i t e w a s t h e p r e d o m i n a t e c a r -b o n a t e p h a s e . T o t a l s u l f u r w a s d e t e r m i n e d b y d r yc o m b u s t i o n i n o x y g e n a n d i n f r a r e d d e t e c t i o n o f t h ee v o l v e d S O 2 . R o c k - E v a l p y r o l y s i s w a s c a r r i e d o u tw i t h a G e o c o m R o c k - E v a l I I , u s i n g t h e p r o c e d u r edescr ibed by Espi ta l i~ e t a l (1977).

P y r o l y s i s - g a s c h r o m a t o g r a p h y w a s c a r r i e d o u tw i t h a m o d i f i e d C h e m i c a l D a t a S y s t e m s ( C D S )8 2 0 G S u n i t. T h e s a m p l e ( 2 . 0 -6 0 . 0 m g , d e p e n d i n g o no r g a n i c c a r b o n c o n t e n t ) w a s p l ac e d i n a q u a r t z t u b e ;q u a r t z w o o l w a s u se d f o r e n d p l u g s . A d h e r e d h y d r o -c a r b o n s w e r e r e m o v e d b y h e a t i n g t h e s a m p l e a t2 5 0 C f o r 1 0 m i n a n d c h a n n e l i n g a n y e v o l v e d m a t e -r i a l d i r ec t l y t o t he purge ven t . T he pyro lys i s t em -p e r a t u r e p r o g r a m w a s t h e n s t a r te d : 3 m i n a t t h ein it i al t em p e ra tu re o f 250C, and t hen t he i n t e r f acewas hea t ed a t a r a t e o f 25C/m in t o t he f ina l t em -p e r a t u r e o f 5 9 0 C , w h i c h w a s h e l d f o r 6 m i n u t e s . T h epyro lysa t e was co l l e c t ed i n a l i qu id -n i t rogen coo l edt rap.

T he pyro lysa t e was ana lyzed i n a Va r i an Se r i e s3 7 00 ga s c h r o m a t o g r a p h w i th a 6 0 m D u r a b o n d D B 5c o l u m n ( 0. 32 m m i .d .) a n d a V a r i a n F I D d e t e c t o r a n di n t e g r a to r . T h e l i q ui d n i t r o g e n w a s r e m o v e d f r o m t h et r a p , w h i c h w a s h e a t e d w i t h i n 2 m i n t o 3 3 0 C a n dh e l d a t t h a t t e m p e r a t u r e f o r 1 6 m i n . T h e c h r o -m a t o g r a p h t e m p e r at u r e p r o g r a m w a s b e g u n s im u l ta -neous ly . T he co lu m n was he ld fo r 5 m in a t t he i n i ti a lt e m p e r a t u r e o f 4 C a n d t h e n h e a t e d a t a r a t e o f4 : C / m i n t o t h e fi na l t e m p e r a t u r e o f 3 4 0 C , w h i c h w a sh e l d f o r 2 5 m i n . B l a n k s a m p l e s a n d s t a n d a r d h y d r o -c a r b o n m i x t u r e s w e r e r u n p e r i o d i c al l y t o e n s u r e t h a t

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W hole rock and kerogen-concentrate samples of Jurass ic rocks 507Table I . Elementa l ana lys i s and Rock-Eval resul ts for whole-rock ( I-9) and kerogen-concentrate samples [ IA-9A:concentrates obta ined by acid treatment HCI/HF); IAD--9AD: concentrates obta ined by acid treatment fo l lowed b ydens i ty separat ion]Sample Dep th CaCO ~ S, . Co ,g S C Tm~Unit (m) (%) (%) (%) (g w) S: ~ (C ) HF

Who ~ rock ex t r ac ted1 ~ Dog ger-a 16.36 15.2 1.52 1.22 1.25 2.432 Dogg er-~ 22.70 12.4 1.19 1.36 0.88 2.773 Dogg er-~ 27.90 10.2 0.69 I . I 1 0.62 1.794 Lias-c 30.70 38.0 3.09 9.48 0.33 49.505 Lias-~ 33.10 29.2 2.97 12.10 0.25 66.106 Lias- 40.00 38.6 3.30 9,51 0.35 54.407 Lias-6 45.30 0.7 3.47 0.86 4.03 0.918 Lias-6 52.15 1.2 3.28 0.88 3.73 0,579 Lias -6 55.30 1.4 4.78 0.86 5.56 0.49Kerogen. ac id-concent ratwnI-A Do gger-~ 16.36 - - 8.20 14.05 0.58 55.102-A Dogger -~ 22.70 - - 10.20 13.45 0.76 44.403-A Dogg er- a 27.90 7.60 13.75 0.55 60.604-A Lias-~ 30.70 - - 13.30 49.70 0.27 341.005-A Lias~ 33.10 - - 11.20 54.05 0.21 298.606-A Lias- 40.00 - - 14.00 50.65 0.28 293.607-A Lias-6 45.30 - - 18.60 6.38 2.92 c8-A Lias-6 52.15 - - 15.50 7.50 2.07 c9-A Lias-fi 55.30 - - 21.90 5.50 3.98 c

Kerogen ac i d - and density-concentrationt- AD Dog ser -a 16.36 5.30 56.30 0.09 219.102-AD Dogg er- a 22.70 - - 8.00 52.50 0,15 190.803-AD Dogg er- a 27.90 - - 7.80 56.25 0.14 235.104-AD Lias- 30.70 -- 11.40 61.00 0.19 369.205-A D Lias- 33.10 -- 10.40 64.85 0.16 382.506-A D Lias-~ 40,00 - - 10.70 64.10 0.17 342.707-AD Lias-6 45.30 - - 3.40 26.40 0.13 79.808-AD Lias-6 52.15 5.40 40.65 0.13 104.009-AD Lias-6 55.30 - - 5.70 35.20 0.16 74.50

431 199429 204430 161418 522423 546422 572424 106428 64425 57431 392431 330431 441430 686434 552432 580

t

414 389427 363422 418428 605435 590430 535424 302433 256428 212*S2: Pyro lys is y i e ld mg H C/g rock) .b i ll : Hy d r o g e n in d e x m g HC / g Co,s).CContaminated by unident i f ied c om pou nd s ) . Product y i e ld ca lcula t ionsin A an d A D samples w ere very s imi lar for the Lias-6. showed that quant i ty o f hydrocarbons per g Co~

t h e C D S a n d c h r o m a t o g r a p h u n i t w e r e f u n c t i o n i n gp rop er l y .

M a j o r p e a k s w e r e i d e n t i f i e d b y c o m p a r i s o n o fr e t e n t i o n t i m e s w i t h a s t a n d a r d m i x t u r e o f a l i p h a t i ca n d a r o m a t i c c o m p o n e n t s . T h e i d en ti fi ed p e a k s w e r en - C s t h r o u g h n - C 2 9 , b e n z e n e , t o l u e n e , a n d t h em , p - x y l e n e s . A n e x t e r n a l - s t a n d a r d c o n v e r s i o n f a c t o rw a s u s e d t o c o n v e r t p e a k a r e a c o u n t s i n t o c o n c e n -t r a t io n u n it s , l - P h e n y l h e x a n e w a s a d d e d t o t h e s a m -p l e s a s in t e r n a l r e fe r e n c e c o m p o u n d ( I . S . i n F i g s 2and 5) .

RESULTS AND INTERPRETATIONElemen ta l an d Rock E va l resu l ts

R e s u l t s o f t h e c a r b o n , s u l f u r , a n d R o c k - E v a la n a l y s e s a r e l is t e d i n T a b l e ( R o c k s a m p l e s a r el a b e le d 1 - 9 , a c i d - c o n c e n t r a t i o n s a m p l e s a r e I A - 9 A ,a n d a c i d a n d d e n s i t y s e p a r a t i o n s a m p l e s a r e l a b e l e dI A D - 9 A D ) . T h e t h r e e s t r a ti g r a p h ic u n i t s a r e d i s-t i n c t l y d i f f eren t f rom on e an ot h er :- - - T h e D o g g e r - a r o c k s a m p l e s a r e c h a r a c t e r i z e d b y

m o d e r a t e c a r b o n a t e (1 0 - 1 5 % C a C O 3 ) , su l fu r( 0 . 7 -1 . 5 % ) , a n d o r g a n i c c a r b o n c o n t e n t ( 1 . 1 -

. 4 % ) , a n d c o n t a i n a m i x e d T y p e - I I / I I I k e r o g e n( H I : 1 6 1 - 2 0 9 m g H C / g C o n ) .- - T h e L ia s- s a m p l e s h a v e h ig h c a r b o n a t e ( 2 9 - 3 9 %C a C O 3 ) , m o d e r a t e l y h i g h su l f u r ( 2 . 9 - 3 . 3 % ) , a n d

q u i t e h i g h o r g a n i c c a r b o n c o n t e n t ( 9 . 5 - 1 2 . 1 % ) ,a n d c o n t a i n a T y p e - l l k e r o g e n (H I : 5 2 3 -5 7 2 m g H C / g C o rg ).

- - T h e L i a s -d s a m p l e s a r e c h a r a c t e r i z e d b y l o wc a r b o n a t e (0 . 7 - 1 . 4 % C a C O 3 ) , h ig h s u lf u r ( 3 . 3 -4 . 8 % ) , a n d v e r y l o w o r g a n i c c a r b o n c o n t e n t( 0 . 9 9 % ) , a n d c o n t a i n a T y p e - I l l k e r o g e n ( H I :5 7 - 1 0 6 m g H C / g C o ,g ).A s e x p e c t e d , a l l A a n d A D s a m p l e s h a d C o t v a l u e s

s u b s t a n t i a l l y h i g h e r t h a n t h o s e o f t h e r o c k s a m p l e s ,b u t t h e re l a t i ve i n crease i n Cot s wa s great es t f or t h eD o g g er -: c a n d L i a s -6 s a m p l e s . T h e o r g a n i c c a r b o nc o n t e n t o f t h e L i a s < A D s a m p l e s , f o r e x a m p l e , w a so n a v e r a g e s i x t i m e s h i g h e r t h a n t h e C o , , c o n t e n t o ft h e r o c k s a m p l e s . F o r t h e D o g g e r - a s a m p l e s , t h eavera ge i n cr ease i n Co~gc o n t e n t w a s b y a f a c t o r o f 4 5 ,a n d f o r t h e L i a s - 6 s a m p l e s b y a f a c t o r o f 3 9 .

A l t h o u g h C o~ g v a l u e s o f t h e D o g g e r - ' , a n d L i a s -6s a m p l e s i n c r e a s e d a f t e r a c i d - tr e a t m e n t , a n d i n c r e a s e dagai n su b s t an t i a l l y a f t er t h e d en s i t y s ep arat i on , l argei n c r e a s e s i n h y d r o g e n - i n d e x v a l u e s a r e e v i d e n t s o l e l ya f t e r a c i d - t r e a t m e n t . D e n s i t y - s e p a r a t i o n h a d l i t t l ef u r t h e r e f f ec t o n h y d r o g e n i n d e x v a l u e s ; t h e H I o f t h eA a n d A D s a m p l e s a re q u i t e s i m i la r ( F i g . 1 ) . I ns e v e r a l c a s e s , t h e H I v a l u e s o f t h e A s a m p l e s s li g h t lye x c e e d e d t h o s e o f t h e c o r r e s p o n d i n g A D s a m p l e s .F o r t h e Co ~ , - r i ch L i as- ~ samp l es , a su b s t an t i a l i n -c r e a s e i n C or g v a l u e f r o m t h e r o c k t o t h e A D s a m p l e s

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O

0 4 0

Doqger-aL+ Ker-o Ker-ADLJO -~

o I I 10 2 0 0 40 O 6 0 OH y d r o g e n i n d e x r ag H C / g C : , ;)

Fig. 1. Hydrogen index values of who le-rock and kerogen-concentrate samples (Ker-A and Ker-AD) plotted versusdepth in well Wenzen-1001. Samples from Co,f poo r rocks(Dogger-~: 16-28 m, Lias-6:45--55 m) produced the greatestdifferences in HI values between who le-rock and kerogen-concentrate samples.

was accom pan ied by l i tt l e chan ge i n HI va lue s ; t he HIv a lu e s a g r e e w i th i n + 7 % f o r a ll t h r ee t y p e s o fs a m p l e s ( r o c k , A , A D ) , e x c l u d i n g o n e h i g h e r v a l u e( sample 4A) ,

The d i f f e rences i n HI va lue s be tween t he rock andk e r o g e n - c o n c e n t r a t e s a m p l e s a g r e e w i t h t h e r e su l ts o fEspitali+ et al. (1980) , Horsf ie ld and Douglas (1980) ,a n d O r r ( 1 9 8 1 ) , w h o a l s o f o u n d t h a t p r o d u c t y i e l d s( H I v a l u e s ) o f k e r o g e n c o n c e n t r a t e s e x c ee d t h o s e o fwho le - rock sample s , and sample s f rom Corg-poorrocks p roduced t he g rea t e s t d i f f e rences i n y i e lds .

One reason for the la rge increase in re la t ive Co~gcon ten t a f t e r t he dens i t y sepa ra t i on i s mos t l i ke ly t hesubs t an t i a l l o ss o f su l fu r i n t he fo rm o f py r i te ; t he S /Cra t i os d rop d rama t i ca l l y , e spec i a l l y fo r t he L i a s -6sample s , 7A D-- 9A D (Tab le 1 ). Because H I va lues a reunre l a t ed t o su l fu r con t e n t , t he l oss o f py r i t e le avesH I v a l ue s u n c h a n g e d , e x c e p t f o r t h e s a m p l e s i n w h i c hr e m o v a l o f p y r i t e w a s a c c o m p a n i e d b y t h e l o s s o fs i g n if i ca n t a m o u n t s o f o r g a n i c m a t t e r .Pyrolysis GC

C h r o m a t o g r a p h i c a n a l y s i s o f t h e p y r o l y s a te sb r o u g h t o u t a n u m b e r o f o t h e r di f fe r e nc e s b e tw e e nthe sample t ypes . Aga in , t he d i f f e rences be tweenr o c k , a c i d s e p a r a t i o n , a n d a c i d - d e n s i t y s e p a r a t i o ns a m p l e s d e p e n d e d l a r g e ly o n t h e n a t u r e o f t h e r o c k .The mos t s t r i k ing d i f f e rence .be tween t he Dogge r -~r o c k , A , a n d A D p y r o l y s a t e s is t h e l e n g th o f th e i rn -a lk ane se ri es an d t he r e l a ti ve p ropo r t i on s o f l owm o l e c u l a r w e i g h t a r o m a t i c h y d r o c a r b o n s . F i g u r e 2s h o w s th e g a s c h r o m a t o g r a m s o f r o c k , A , a n d A D

s a m p l e s f r o m o n e o f t h e D o g g e r - ' , s a m p l e s ( 2 7 . 9 m )a n d F i g . 3 th e c a r b o n - n o r m a l i z e d y i e ld s o f n - a lk a n e s( s o l i d c o l u m n s ) a n d a r o m a t i c h y d r o c a r b o n s ( c l e a rc o l u m n s ) . T h e w h o l e - r o c k p y r o l y s a t e s h o w e d a l m o s tn o n - a l k a n e s b e y o n d n - C ~ s , t h e A p y r o l y s a t e a d d i -t io n a l l y sh o w s t r a c e a m o u n t s o f n - a l k a n e s u p t o C 2 : ,a n d t h e A D p y r o l y s a t e h a s a l o n g s er ie s o f n - a l k a n e se x t e n d i n g a p p r o x i m a t e l y t o t / - C 2 9 . T h e c a r b o n -n o r m a l i z e d y i e ld s o f l o w m o l e c u l a r w e i g h t n - a l k a n e sa re s imi l a r fo r a l l t h ree sample t ypes whe rea s t hey i e lds o f benzene and t o luene dec rea se i n t he o rde rr o c k - A - A D ( F i g . 3) . T h e t w o o t h e r D o g g e r - ~ s am p l e sp r o d u c e d p y r o l y s a t e s v e r y s i m i l a r t o t h o s e s h o w nh er e. T h e r a ti o s o f b e n z e n e / h e x a n e a n d t o l u e n e / h e p -t a n e t h u s a p p e a r t o b e a f f e c t e d b y t h e k e r o g e nc o n c e n t r a t i o n p r o c e d u r e . T h e y a r e h i g h e s t i n t h ew h o l e - r o c k p y r o l y s a t e s a n d l o w e s t in t h e A D p y r o l y -s a te s ( T a b l e 2 , s a m p l e s I - 3 ) . T h e m , p - x y l e n e / o c -t ane r a t i os do no t show a c l ea r t r end .The L ia s - f i sample s showed s imi l a r t r ends a s t heD o g g e r - ~ s a m p l e s, b u t h a d g e n e r a ll y l o w e r n - a l k a n ey i e lds ( a s we l l a s l ower HI va lue s ) . The who le - rockp y r o l y s a t e h a d a l m o s t n o n - a l k a n e s b e y o n d n - C t t ,t h e A p y r o l y s a t e s h o w e d n - a l k a n e s u p t o n - C 2 2 , a n dt h e A D p y r o l y s a t e u p t o n - C 2 4 ( F i g . 4) . T h e h i s t o -g r a m s i n F i g . 4 a r e f r o m s a m p l e 9 ( 5 5 . 3 m ) , b u ta ll o f t h e L ia s -3 s am p l e s ( 7 - 9 ) p r o d u c e d v e r ys imi l a r py ro lysa t e s . Aga in , t he benzene /hexane andt o l u e n e / h e p t a n e r a t i o s d e c r e a s e i n t h e o r d e r r o c k - A -A D ( T a b l e 2 , s a m p l e 7 - 9 ) .

P y r o g r a m s f r o m s a m p l e 5 o f t h e L ia s- E g r o u p ( F i g .5 ) s h o w t h a t t h e r o c k , A , a n d A D s a m p l e s y i e l d e dv e r y si m i la r p y r o l y s a t e s . T h e q u a n t i t y o f t h e r o c ksamp le (F ig . 5a ) i s f a r g rea t e r t han t he quan t i t y o f t heA a n d A D s a m p l e s, s o m a n y o f th e p e a k s i n F ig . 5 aa re l a rge r t han t hose i n F igs 5b and 5c . Howeve r , t hec a r b o n - n o r m a l i z e d d a t a ( F i g. 6 ) s h o w t h a t t h e d is t ri -bu t i on o f t he n -a lk ane se r ie s and t he r e la t i ve p ro por -t io n s o f l o w m o l e cu l a r w e ig h t a r o m a t i c c o m p o u n d sare simi lar in a l l three sample types.

T h e a p p e a r a n c e o f t h e l o n g n - a l k a n e s er ie s i n t h eD o g g e r - x a n d - - l e s s p r o n o u n c e d - - i n t h e L ia s -5 A Dsample pyro lysa t e s i nd i ca t e s t ha t t he re i s a d i f f e rencein h y d r o c a r b o n c o m p o s i t i o n b e tw e e n t h e A a n d A Ds a m p l e s , e v e n t h o u g h h y d r o c a r b o n q u a n t i t y ( r e p r e -sen t ed by HI ) i s s im i l a r . The d i f f e rences i n HI va lue sb e t w e e n t h e r o c k a n d k e r o g e n - c o n c e n t r a t e s a m p l e sm i g h t b e r e l a te d t o t h e r e m o v a l o f m i n e ra l m a t t e rd u r i n g t h e k e r o g e n c o n c e n t r a t i o n p r o c e s s . A n o t h e rposs ib l e exp l ana t i on fo r t he ve ry l a rge d i f f e rences i nH I v a l u es is t h a t h y d r o g e n - p o o r o r g a n i c m a t t e r ( s u c ha s N S O c o m p o u n d s o r i n e r t in i te m a t e r i a l) c o u l d h a v ebeen p re fe ren t i a l l y l o s t du r ing t he ke rogen concen-t r a t i on p rocedure . The f ac t t ha t t he Co , , -poorDogge r - ,~ and L ia s -5 sample s ( i n wh ich o rgan i c ca r -b o n r e c o v e r y w a s l e a s t c o m p l e t e ) s h o w e d v e r y l a r g ed i ff e re n c es b e t w e e n r o c k a n d k e r o g e n - c o n c e n t r a t e H Iv a l u e s s u p p o r t s t h e i d e a t h a t p r i m a r i l y h y d r o g e n -p o o r o r g a n i c m a t t e r w a s l o s t , O n t h e o t h e r h a n d , i fchanges i n HI va lue s had been so l e ly due t o p re fe ren -

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Whole rock and kerogen-concentrate samples of Jurassic rocks 509

I S (a) ROCKHICoFg

12

(52.8 mg)= 167 mg HC /g CoFg: I . I I

| S

Corg : 13.8

x 1 0 ] . o . . ~ . . ~12 2, , . ~ . i , . . . . . . o _ _

(b) KER-A (2.4 mg)HI = 441 mg HC/g CoFg

].s. (c) KER-AD (3,1 mg)

x HI = h18 mg HC/g Corg1~ / 14

Fig. 2. Capillary gas chromatograms of pyrolysates for whole-rock (a) and kerogen-concentrate samples(b and c) of Dogger-,~ sample 3, Selected n-alkanes indicated by carbo n numbers. Cm, CI2, and C ,n-alkane peaks in the whole-rock and K er-A pyrolysates enlarged by co-eluting unknown com pound(s),B = benzene; T = Toluene; X = m ,p-xylene; I .S. = internal reference compound , l-phenylhexane.

t ia l l o ss o f h y d r o g e n - p o o r o r g a n i c m a t t e r , t h e n t h el e n g th o f t h e n - a l k a n e s e ri es s h o u l d n o t h a v e v a r i e db y sa m p l e t y p e . F o r t h e r o c k s a m p l e s a n d t h e As a m p l e s ( i n w h i c h m i n e r a l r e m o v a l w a s i n c o m p l e t e ),m i n e r a l m a t t e r m a y h a v e a f f e c t e d p y r o l y s a t e c o m -pos i t i on by ca t a ly t i c o r c rack ing e f fec t s , a s de sc r ibedby Espi ta l i6 e t a l (1980) , Dembick i e t a l . (1983) , ando t h e r s . F o r t h e A s am p l e s , p y r o l y s a t e c o m p o s i t i o n( a s s ee n i n t h e p y r o g r a m s ) w a s m o r e g r e a t l y a f fe c t edt h a n p y r o [ y s a t e q u a n t i t y ( H I ) , w h e r e a s b o t h c o m -p o s i t i o n a n d q u a n t i t y o f t h e p y r o l y s a t e w a s a f fe c t edf o r t h e D o g g e r - ~ a n d L i a s - 6 r o c k s a m p l e s .

T h e f a c t th a t t h e D o g g e r - , t a n d L i a s -6 A a n d A Ds a m p l e p y r o g r a m s w e r e d i f f e r e n t i n s p i t e o f t h e i r

s i m i la r H I v a l u e s i n d i c a te s t h a t i n C o g - p o o r s a m p le s ,t h o r o u g h r e m o v a l o f m i n e r al m a t t e r - - b y d e n s it ys e p a r a t i o n , f o r e x a m p l e w i s n e c e s s a r y in o r d e r t orecove r s i gn i f i can t quan t i t i e s o f h ighe r molec u l a rwe igh t hy dro ca rb ons . The s imi l ar i ti e s o f t he L ia s -Er o c k , A , a n d A D c h r o m a t o g r a m s s h o w t h a t f o rs a m p l e s r i c h i n o r g a n i c c a r b o n , t h e i n f l u e n c e o fm i n e r a l c o n t e n t o n p y r o l y s a t e c o m p o s i t i o n i s m i n -i m i z e d b e ca u s e t h e r e l a ti v e a m o u n t o f o r g a n i c m a t t e ri s h igh.

S U M M A R Y A N D C O N C L U S I O N ST h e D o g g e r - , , a n d L i a s- 6 A D s a m p l e s w h i c h h a dr e la t iv e l y h ig h o r g a n i c - c a r b o n c o n t e n t , w e r e i n m a n y

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510 CAROL ARNO STI an d PETER J. MI~'LLER

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43210

0 0 ( ] ( ~ e f - - ~ . 27 g mB

L * o s - 8 . S S . 3 m

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L 32E1

8

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0 4 6 7 8 9 1 1 1 3 l S 1 7 1 9 2 1 2 3 2 5 2 7 2 9C o r b o n n u m b e r

F i g. 3 . C a r b o n - n o r m a l i z e d p y r o l y s i s - G C y i e l d s o f n - a l k a n e s( s o l i d c o l u m n s ) a n d a r o m a t i c c o m p o u n d s ( c l e a r c o l u m n s )for who le -rock and kerogen-concentrate sam ples o f Dog ger-:~ samp le 3 . Ct0 , C] , . an d Ct4 n-a lk ane y ie lds in terpolatedfrom border ing n-a lkane peaks .

54 r

2 Xt

0 I | I i I IG 7 e 9 - i 1 { 3 15 i ? 1 9 2 12 ~3 2 5 2 7 2 9C o r b o n n u m b e r

Fig. 4. Carbon-normalized pyrolysis-GC yields of n-alkanes( s o l i d c o l u m n s ) a n d a r o m a t i c c o m p o u n d s ( c l e a r c o l u m n s )f o r w h o l e - r o c k a n d k e r o g e n - c o n e e n t r a t e sa m p l e s o f L i a s -6sam ple 9 . C~0 , Ct . ,, and Ct4 n-a lk ane y ie lds in terpolatedfrom border ing n-a lkane peaks .

ways s imi l a r t o a ll t h ree sample t ypes o f t he Corg -r ichL ia s- E s a m p l e g r o u p . T h e D o g g e r - ~ a n d L i a s -6 s a m -p le s had a nu m ber o f d i s t inc t d i f f e rences be tween t her o c k , A , a n d A D s a m p l e s . H y d r o g e n i n d e x v a l u e sh y d r o c a r b o n y i el d ) o f t h es e r o c k s a m p l e s o n t h e

o n e h a n d a n d t h e i r A a n d A D s a m p l e s o n t h e o t h e rd i ff e re d b y c l o s e t o 2 0 0 m g H C / g C o r g . T h eb e n z e n e / b e x a n e a n d t o l u e n e / h e p t a n e r a t i o s w e r emuch l a rge r fo r t he Dogge r - , , and L ia s - f i rock and As a m p l e s t h a n f o r t h e A D s a m p l e s , w h i c h h a d v a l u e s

Table 2. Aromatic, aliphati c ratios for selected low- molecular-weight hydrocarbons released by pyrolysis of whole-rockand kerogen-concentrate samplesWhole rock Kerogen-A Kerogen-ADSample

Unit B/6 T,7 X/'8 B,6 T/7 X/8 B/6 T/7 X/8I Do g~ r- x 2.5 3.2 1.6 1.3 2.5 1.6 1.0 1.5 3.42 Dogger-~ 4.2 3.3 1.7 t.4 2.1 1.5 1.0 2.1 1.23 Dog ~r -~ 3.5 2.7 1.6 1.5 2.8 t.5 0.7 1.6 1.2

Mean: 3.4 3.1 1.6 1.4 2.5 1.5 0.9 1.7 1.9Std. dev: 0.9 0.3 0.I 0.1 0.4 0.1 0.2 0.3 1.34 Lias-E 0.8 1.6 1.7 0.6 1.4 1.7 0.8 2.2 2.15 Lias -, 0.6 1.5 1.8 0.6 1.8 1.8 0.6 1.3 1.66 Lias-~ 0.5 1.0 1.6 I. t 1.8 1.5 0.8 1.4 1.6

Mean: 0.6 1.4 1.7 0.8 1.7 1.7 0.7 1.6 1.8Std. dev: 0.2 0.3 0.1 0.3 0.2 0.2 0.1 0.5 0.37 Lias-6 5.6 6.0 3.1 3.9 3.7 1.6 2.3 2.4 1.38 Lias-6 5.6 3.6 1.3 2.8 2.8 1.5 2.9 4.8 2.39 Lias-6 5.4 3.8 1.7 3.3 3.6 1.5 2.5 2.9 1.5

Mean: 5.5 4.5 2.0 3.3 3.4 1.5 2.6 3.4 1.7Std. dev: 0.1 1.3 0.9 0.6 0.5 0.1 0.3 1.3 0.5Kerogen-A: Concentrate obtained by acid treatment (HCI and HF).Kerogen-AD: Concentrate obtained by acid treatment followed by density separation.B/6: Benz0ne/hcxane weight rati o.T'7: Toiuen/heptane weight ratio,X/8: Xylene/octane weight ratio.

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W hole rock and kerogen-concentrate samples of Jurassic rocks 511

B T X 1 ,I a) ROCK 28.6 mg)

Ii Corg = 12,1

lT X 1.5.

I b )

1 4

2 0

KER-A (2.1 mg)HI = 552 mg HC/g CorgCorg = 54.1

X 1

(C) KER-AD (2.2mg)I.S. HI = 590 mgHC/g Corgi~ ] Corg = 64.9

1 4 1

] j~ . ' .-~,~4: ,~. ' -~-,~ Ll-.J.a.j.a.~._

Fig. 5. Capillary gas chromatograms of pyrolysates for whole-rock (a) and kerogen-eoncentrate samples(b and c) of Lias- sample # 5. Selected n-alkanes indicated by c arbon numbers. B = benzene;T = T oluene; X = m , p-xylene; l .S. = internal reference compound, l-phenylhexane.

c l o se t o t h o s e o f t h e L i a s - , s a m p l es . L e n g t h o f th en - a l k a n e s e ri es i n t h e D o g g e r - ~ A a n d A D s a m p l e se x c e e d e d t h a t o f t h e i r c o r r e s p o n d i n g r o c k s a m p l e s .T h e L ia s- ~ s a m p l e s g a v e r o u g h l y c o m p a r a b l e r e s u lt sf o r ro c k , A , a n d A D s a m p l e s . H y d r o g e n i n d e x v a l ue s ,b e n z e n e / h e x a n e a n d t o l u e n e / h e p t a n e r a t i o s , a n dl e n g th o f t h e n - a l k a n e s e ri es w e r e a p p r o x i m a t e l y t h esam e .

A l t h o u g h t h e p y r o g r a m s o f th e D o g g e r - ~ a n dL ia s - f i AD sam ple s we re s im i l a r t o t he L i a s -~ pyro -g r a m s , h y d r o c a r b o n y i e ld p e r g r a m o f o rg a n i c c a r b o n(HI ) d i f f e red g rea t l y . For t he Dogge r -~ and L ia s - f is a m p l e s, t h e r e a r e i n d i c a t io n s t h a t o r g a n i c m a t t e r w a sl o s t a l o n g w i t h s u l f u r ( p y r i t e ) a n d o t h e r i n o r g a n i c

s u b s t a n c e s d u r i n g t h e k e r o g e n c o n c e n t r a t i o n p r o -c c d u r e , a n d e s p e c ia l ly d u r i n g t h e d e n s i t y s e p a r a t io n .

S e v e r al p r a c t ic a l c o n c l u s i o n s c a n b e d r a w n f r o mth i s s t udy : T h e na tu re o f a sam p le se t ( e spec ia l l yo r g a n i c c a r b o n a n d s u l f u r c o n t e n t ) s h o u l d b e t a k e ni n t o c o n s i d e r a t i o n w h e n p l a n n i n g a p y r o l y s i s a n a l -ys is . I f a sam ple se t is o rgan i c -ca rbo n r i ch , t hen t hed i f f e r e n c e s b e t w e e n r o c k a n d k e r o g e n - c o n c e n t r a t ep y r o l y s a t e s a r e n o t v e r y s i g n i fi c an t ; b u t f o r o r g a n i c -c a r b o n p o o r s a m p l e s , w h o l e - r o c k a n d k e r o g e n -c o n c e n t r a t e p y r o l y s i s w i ll p r o d u c e v e r y d i f fe r e n t p y -ro lysa t e s .

L e n g t h o f t h e n - a l k a n e s e r i es a n d a r o m a t i c /a l i pha t i c r a t i os c an be s i gn i f i c an t l y d i f f e ren t fo r

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