Chapter 9 Metals
in
Crude
Oils,
Asphaltenes,
Bitumen,
and
Kerogen in Molasse Basin, Southern Germany Alfred V. Hirner
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Mineralogisch-Petrographisches Institut der Universität, Theresienstrasse 41, D-8000 München 2, Federal Republic of Germany
In the course of organic geochemical investigations in the Southern German Molasse Basin, the use of trace element studies on maltene, asphaltene and kerogen fractions of crude oils, bitumens and potential source rocks for o i l - o i l and oil-source rock correlations has been tested. The Ni, V and Co contents of crude oil-maltenes and -asphaltenes enabled the differentiation of two o i l families to be made in conjunction with other geochemical analyses. Elemental concentrations in the asphaltene fraction of bitumen and in the kerogen of potential source rocks are similar to those in the corresponding crudes. However, these correlations are not true for Zn and I. It could be shown that Ni in kerogen is associated with the organic phase, whereas Ti is derived from the mineral matrix. Organic substances p l a y a dominant r o l e i n geochemical c y c l i n g , e s p e c i a l l y i nthe l o c a l c o n c e n t r a t i o n o f t r a c e metals (1-3). Metalo r g a n i c a n d o r g a n o m e t a l l i c s p e c i e s i n s e d i m e n t s may o r i g i n a t e f r o m t h e b i o m a s s w i t h o u t m a j o r c h e m i c a l c h a n g e s , o r t h e y may b e f o r m e d d u r i n g sedimentation and/or d i a g e n e s i s from o r g a n i c molecules and metal ions d e r i v e d from d i f f e r e n t b i o g e n i c (biomass) and a b i o g e n i c sources (weathering o f m i n e r a l s ) . T h u s , i n many o f t h e s e g e o chemical cycles i n o r g a n i c as w e l l as organic a s s o c i a t i o n s o f t h e metals are i n v o l v e d , and o f t e n they d i r e c t l y o r i n d i r e c t l y i n t e r a c t w i t h each o t h e r . Complex s i t u a t i o n s r e s u l t , and c o r r e l a t i o n s between metal c o n c e n t r a t i o n s and e i t h e r i n o r g a n i c o r o r g a n i c sediment f r a c t i o n s may n o t a l w a y s b e f o u n d . For example, i n A u s t r a l i a no i l s h a l e s n i c k e l i s a s s o c i a t e d w i t h the o r g a n i c as w e l l as t h e i n o r g a n i c f r a c t i o n s w i t h no a p p a r e n t p r e f e r e n c e ( 4 ) . In o r g a n i c geochemical e x p l o r a t i o n however, o n l y those metals a r e o f s i g n i f i c a n c e , whose c o n c e n t r a t i o n s a r e c l o s e l y a s s o c i a t e d w i t h the o r g a n i c matter. The c o o r d i n a t i o n c h e m i s t r y a n d abundance o f these metals i n crude o i l s p r o v i d e u s e f u l i n f o r m a t i o n on the o r i g i n , m i g r a t i o n , and m a t u r a t i o n o f p e t r o l e u m ( 5 ) .
0097-6156/87/0344-0146$06.00/0 © 1987 American Chemical Society
Filby and Branthaver; Metal Complexes in Fossil Fuels ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
9.
HIRNER
Metab in Mo fasse Basin, Southern
Germany
147
In t h i s s t u d y , f o r m e r i n v e s t i g a t i o n s (6) a r e e x t e n d e d t o t h e m a l t e n e a n d a s p h a l t e n e f r a c t i o n s o f S o u t h e r n German c r u d e o i l s a s w e l l as t h e b i t u m e n and k e r o g e n f r a c t i o n s o f p o t e n t i a l s o u r c e r o c k s of these crudes.
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Samples and
Methods
S e v e r a l geochemical i n v e s t i g a t i o n s o f crude o i l s have r e v e a l e d the e x i s t e n c e o f o n l y two o i l f a m i l i e s i n t h e S o u t h German M o l a s s e B a s i n (6-8) . A l l c r u d e s f o u n d a t t h e s t r a t i g r a p h i e base o f t h e T e r t i a r y b e l o n g t o one g r o u p . The o i l s i n M e s o z o i c r e s e r v o i r s i n t h e w e s t e r n p a r t o f t h e b a s i n a r e s u p p o s e d t o be o f a d i f f e r e n t o r i g i n . Based on t h e s e r e s u l t s , r e p r e s e n t a t i v e samples f r o m each o i l f a m i l y have been s e l e c t e d : M e s o z o i c o i l s : F r o n h o f e n 12, P f u l l e n d o r f 6, O s t r a c h 8 T e r t i a r y b a s e o i l s : M o n c h s r o t , A r l e s r i e d , D a r c h i n g 1, H o h e n r a i n 4. C a r b o n i s o t o p i c s t u d i e s g a v e some e v i d e n c e f o r S a n n o i s i a n a n d R u p e l i a n s e d i m e n t s as p o t e n t i a l s o u r c e r o c k s f o r t h e T e r t i a r y base o i l s (9), a l t h o u g h the samples i n v e s t i g a t e d were s t i l l immature. T h e r e f o r e , t h e b o r e c o r e samples T e i s i n g 1 and H o h e n r a i n 2 have been included i n t h i s study. The c o n c e n t r a t i o n s o f V, C r , F e , Co, N i , Z n , S e , B r , A g a n d I were d e t e r m i n e d b y i n s t r u m e n t a l n e u t r o n a c t i v a t i o n a n a l y s i s as a l r e a d y d e s c r i b e d ( 6 ) ; T i i n k e r o g e n was d e t e r m i n e d b y X - r a y s p e c t r o metry. The a s p h a l t e n e s w e r e s e p a r a t e d b y p r e c i p i t a t i o n w i t h p e t r o l e u m e t h e r 40/60. Trace element c o n c e n t r a t i o n s o f the maltenes (= d e a s p h a l t e d o i l s ) w e r e c a l c u l a t e d b y d i f f e r e n c e , u s i n g t h e a n a l y t i c a l r e s u l t s o f t h e t o t a l o i l and t h e a s p h a l t e n e f r a c t i o n . The c o r e samples were e x t r a c t e d w i t h c h l o r o f o r m / m e t h a n o l (2:1 v/v) f o r t h r e e days. The m a l t e n e a n d t h e a s p h a l t e n e f r a c t i o n s o f t h e e x t r a c t s w e r e analysed separately. Trace element c o n c e n t r a t i o n s To i n d i c a t e t h e c o n c e n t r a t i o n r a n g e s o f t r a c e e l e m e n t s i n S o u t h e r n G e r m a n o i l s a n d k e r o g e n s , p r e v i o u s d a t a (6_, JLO) h a v e b e e n c o m p i l e d a s s h o w n i n F i g u r e 1. T r a c e e l e m e n t c o n c e n t r a t i o n s r a n g e o v e r more t h a n s i x o r d e r s o f magnitude, i . e . from s e v e r a l p a r t s per b i l l i o n to s e v e r a l weight percent. With the e x c e p t i o n o f I, the elements are e n r i c h e d i n the a s p h a l t e n e f r a c t i o n b y a b o u t one o r d e r o f m a g n i t u d e o n t h e a v e r a g e , i n d i c a t i n g an i n c r e a s e o f the m e t a l - b i n d i n g c a p a c i t y w i t h i n c r e a s i n g p o l a r i t y and m o l e c u l a r w e i g h t o f the o r g a n i c m o l e c u l e o r , a l t e r n a t i v e l y , an i n c r e a s e i n m e t a l - t r a p p i n g c a p a c i t y o f a s p h a l t e n e s . Se, Zn, Fe a n d C r a r e e n r i c h e d i n t h e k e r o g e n f r a c t i o n c o m p a r e d t o t h e asphaltenes. W i t h r e s p e c t t o N i , V a n d Co, h o w e v e r , t h e s e two f r a c t i o n s o v e r l a p , a r g u i n g f o r a common o r i g i n o f t h e s e e l e m e n t s i n both f r a c t i o n s . I t must be c o n s i d e r e d , h o w e v e r , t h a t t h e k e r o g e n f r a c t i o n c a n n e v e r be c o m p l e t e l y f r e e o f i n o r g a n i c c o n t r i b u t i o n s .
American Chemical Society,
Library 1155 16th St., N.W. Filby and Branthaver; Metal Complexes in Fossil Fuels Washington, O.C. 2003S
ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
148
M E T A L C O M P L E X E S IN FOSSIL FUELS
001 -τη
0-1 ,
I
ppm 10
1 ' • • • • mi
I
100 ι
ι • ι Mii|
1000 1
Ni
I
10000 1
I
ι — ι crude oils ββιββ^ΕΕΕίίΕΕΕΕ^Ηΐί^ββ
V
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• r-
Ni
W^*M»»»»»»»»,A
CO
Se
~^/////////m
CO
^^^^^^^^^^^^^^^^
Se
""WMMM
W/
1
Zn Fe
Zn Fe
w////Aàw//AwmmM»A
Cr
'
0 01
"
0-1
.
Cr
v^>^ i^^^^ ^ mm
(n = 49)
m& asphaltenes ( n = 19 ) • • kerogens ( n = 23 )
V
m
I • I I I I I ll 10 100 ppm
.
I
1000
.
10000
I
F i g u r e 1. Ranges o f t r a c e e l e m e n t c o n c e n t r a t i o n s i n c r u d e a s p h a l t e n e s a n d k e r o g e n f r o m S o u t h e r n G e r m a n y (6_, ICQ .
Filby and Branthaver; Metal Complexes in Fossil Fuels ACS Symposium Series; American Chemical Society: Washington, DC, 1987.
oils,
9.
HIRNER
Meîab
in Molasse Basin, Southern
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Results o f correlation
Germany
149
studies
C o m p a r e d t o t h e T e r t i a r y - b a s e o i l s , t h e M e s o z o i c c r u d e o i l s show s i g n i f i c a n t l y l o w e r c o n t e n t s o f N i , V a n d Co i n t h e m a l t e n e a s w e l l as i n t h e a s p h a l t e n e f r a c t i o n ( F i g u r e 2 ) . This r e s u l t i s i n accordance w i t h t h e presumed a s s o c i a t i o n o f these elements w i t h t h e o r i g i n a l source m a t e r i a l (biomass). However, o v e r l a p p i n g ranges a r e o b s e r v e d i n t h e c a s e o f Zn a n d I , i n d i c a t i n g a n u n k n o w n a s s o c i a t i o n b e t w e e n compounds o f t h e s e e l e m e n t s o r j u s t a c o n t r i b u t i o n f r o m i n o r g a n i c matter ( m i n e r a l s ) . Other arguments f o r t h e l a t t e r h y p o t h e s i s a r e t h e s t r o n g e n r i c h m e n t ( 7 - t o 1 5 - f o l d ) o f Zn i n t h e m a l t e n e s a n d a s p h a l t e n e s o f t h e e x t r a c t e d b i t u m e n , w h e r e a s N i a n d Co i n t h e a s p h a l t e n e f r a c t i o n o f t h e b i t u m e n show s i m i l a r a b u n d a n c e s a s i n t h e crude o i l asphaltenes. B e c a u s e o f t h e e n r i c h m e n t o f t h e p o l a r compounds i n t h e n o n - m i g r a t e d bitumen compared t o t h e m i g r a t e d c r u d e s , a n d b e c a u s e N i a n d Co a r e c o n c e n t r a t e d i n t h e p e t r o l e u m h e a v y e n d s , the observed enrichment (2- t o 6-fold) o f these elements i n t h e bitumen maltenes compared t o t h e o i l maltenes i s u n d e r s t a n d a b l e . I n F i g u r e 2, d a t a f o r Co a n d Zn o b t a i n e d f r o m p r e v i o u s s t u d i e s are i n c l u d e d f o r comparison. T h i s c o u l d n o t be done f o r N i a n d V i n the f i g u r e s used because t h e u s u a l low c o n c e n t r a t i o n s o f these e l e m e n t s i n S o u t h e r n German c r u d e o i l s p r e c l u d e d s h o w i n g b o t h d a t a s e t s o n t h e same g r a p h . Concerning Cr c o n c e n t r a t i o n s , a l l bitumen f r a c t i o n s (1.2 t o 11.1 ppm) l i e w i t h i n t h e r a n g e o f o i l a s p h a l t e n e s ( 0 . 9 t o 2 2 . 7 p p m ) . A l s o , t h e Ag contents o f bitumen maltenes a r e w i t h i n t h e crude o i l r a n g e ( 0 . 0 2 t o 0.32 ppm). Whereas Fe i n b i t u m e n m a l t e n e s (35 t o 38 ppm) i s a s a b u n d a n t as i n crudes, t h e bitumen a s p h a l t e n e s (700 t o 2100 ppm) a r e e n r i c h e d c o m p a r e d t o t h e o i l a s p h a l t e n e s (
