Metal Complexes in Fossil Fuels - American Chemical Society

Chapter 5 Application of Metal Complexes in Petroleum to Exploration Geochemistry 1

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Jan F. Branthaver and Royston H. Filby 1

Western Research Institute, Box 3395, University Station, Laramie, WY 82070 Department of Chemistry and Nuclear Radiation Center, Washington State University, Pullman, WA 99164-1300

Downloaded by NORTH CAROLINA STATE UNIV on January 12, 2013 | http://pubs.acs.org Publication Date: July 6, 1987 | doi: 10.1021/bk-1987-0344.ch005

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Metal complexes are part of the organic constituents of fossil fuels and source rocks of fossil fuels. The most studied metal complexes associated with petroleum and its source rocks are nickel (II) and vanadyl VO(II) porphyrins of the desoxophylloerythroetioporphyrin (DPEP) and etioporphyrin (etio) types. The relative abundances of the Ni(II) and VO(II) species and the DPEP/etio ratios of metalloporphyrin suites have been used as indicators of source rock maturity and in oil -source rock and o i l - o i l correlations. The nature of the ligands complexed with metals other than nickel and vanadium in petroleum is not known. However, the total metal content of a crude o i l can provide a distinctive "fingerprint" which has been used to correlate related oils and to correlate oils with source rocks. The effects of migration and maturation processes experienced by petroleum on metalloporphyrin and trace element distributions have received l i t t l e attention. Geochemists have l o n g attempted t o improve t h e i r u n d e r s t a n d i n g o f t h e d e t a i l s o f t h eo r i g i n and m i g r a t i o n o f petroleum. The s t u d y o f element r a t i o s , i s o t o p e r a t i o s , and biomarkers i n petroleum and s o u r c e r o c k s h a s y i e l d e d much i n f o r m a t i o n a b o u t t h e t r a n s f o r m a t i o n of organic matter i n t o crude o i l . The i d e n t i f i c a t i o n o f m e t a l l o p o r p h y r i n s i n s h a l e s a n d p e t r o l e u m (1-3J) p r o v i d e d c o n v i n c i n g e v i d e n c e that petroleum i s d e r i v e d from p l a n t - d e r i v e d o r g a n i c matter and i s not a b i o g e n i c . The c o r r e l a t i o n o f c r u d e o i l s w i t h t h e i r p r e s u m e d s o u r c e r o c k s i s an o b j e c t i v e o f geochemical s t u d i e s and i s o f value i n petroleum exploration. Geochemical data a r e u s e f u l i n developing c o r r e l a t i o n s among d i f f e r e n t c r u d e o i l s w i t h i n a p r o d u c i n g a r e a . These d a t a c a n be h e l p f u l i n e l u c i d a t i n g t h e f r e q u e n t l y c o m p l e x s t r a t i g r a p h y o f petroleum bearing formations, p a r t i c u l a r l y those that a r e h e a v i l y faulted. I t i s r e a s o n a b l e t o assume t h a t t h e m e t a l l o p o r p h y r i n s a n d the s u i t e o f t r a c e metals o f a source rock l e a v e s an i m p r i n t on i t s d e r i v e d crude o i l s w h i c h might n o t be t o o g r e a t l y a l t e r e d d u r i n g

0097-6156/87/0344-0084$06.00/0 © 1987 American Chemical Society

In Metal Complexes in Fossil Fuels; Filby, R., et al.; ACS Symposium Series; American Chemical Society: Washington, DC, 1987.

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BRANTHAVER A N D FILBY

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Exploration Geochemistry

migration. I f so, i t might prove p o s s i b l e t o e s t a b l i s h c o r r e l a t i o n s among c r u d e o i l s a n d s o u r c e r o c k s b a s e d o n r e l a t i v e a m o u n t s o f m e t a l s and c o m p a r i s o n s o f m e t a l l o p o r p h y r i n t y p e s . I f , however, the d i s t r i bution o fmetals o r porphyrin s u i t e s o f a crude o i l are s i g n i f i c a n t l y a l t e r e d d u r i n g m i g r a t i o n o r a f t e r emplacement i n r e s e r v o i r s i n a n u n p r e d i c t a b l e f a s h i o n , then they w i l l not be u s e f u l i n c o r r e l a t i o n studies. Other areas i n which m e t a l l o p o r p h y r i n andmetal d i s t r i b u t i o n data should provide u s e f u l i n f o r m a t i o n are i nthe r e c o n s t r u c t i o n o f d e p o s i t i o n a l environments o f sediments and the e s t i m a t i o n o f t h e m a t u r i t y o f organic matter i n p o t e n t i a l source rocks.


Metalloporphyrins

i n M a t u r i t y and C o r r e l a t i o n

Studies

Crude o i l s and p e t r o l e u m source r o c k s o f t e n c o n t a i n measurable amounts o f m e t a l l o p o r p h y r i n s , p r i n c i p a l l y o f the e t i o p o r p h y r i n ( e t i o ) , d e s o x o p h y l l o e r y t h r o e t i o p o r p h y r i n (DPEP), and benzoporphyrin (benzo) types. The s t r u c t u r e s o f t h e s e compounds a r e i l l u s t r a t e d i n t h e p a p e r b y C h i c a r e l l i et_ a l . ( 4 ) i n t h i s v o l u m e . Although metallop o r p h y r i n s were t h e f i r s t compounds o f c o n c l u s i v e b i o l o g i c a l o r i g i n Cl-3) i d e n t i f i e d i n p e t r o l e u m , t h e r e p o r t e d u s e o f t h e s e compounds in o i l - o i l ando i l - s o u r c e rock c o r r e l a t i o n s t u d i e s , maturation s t u d i e s , and i n d e p o s i t i o n a l environment r e c o n s t r u c t i o n h a s been v e r y l i m i t e d compared t o the a p p l i c a t i o n o f h y d r o c a r b o n b i o m a r k e r s steranes, t r i t e r p a n e s , etc.) . A major reason f o r t h i s l i m i t e d use h a s been the a n a l y t i c a l d i f f i c u l t y e n c o u n t e r e d i n the i s o l a t i o n and s e p a r a t i o n o f t h e complex m i x t u r e s o f N i ( I I ) o r V O ( I I ) h o m o l o g u e s of each o f the geoporphyrin types p r i o r t o the development o f r o u t i n e m a s s s p e c t r o m e t r i c (MS) a n d h i g h r e s o l u t i o n H P L C m e t h o d s . A more f u n d a m e n t a l r e a s o n , however, f o r the l i m i t e d a p p l i c a t i o n o f m e t a l l o p o r p h y r i n s a s b i o m a r k e r s h a s been the i n c o m p l e t e understanding of the p o r p h y r i n - b i o l o g i c a l p r e c u r s o r r e l a t i o n s h i p and o f the r e l a t i o n s h i p between d e p o s i t i o n a l environment andp o r p h y r i n e v o l u t i o n . A l s o , the d i a g e n e t i c / c a t a g e n e t i c r e a c t i o n s o f the m e t a l complexes i n source rocks and t h e i r subsequent i n c o r p o r a t i o n i n t o bitumens and petroleum i s incompletely understood. The r e c e n t ( p o s t - 1 9 7 9 ) d e t e r minations o f absolute porphyrin s t r u c t u r e s by nuclear Overhauser e f f e c t (nOe) NMR, X - r a y d i f f r a c t i o n , a n d MS/MS h a v e made p o s s i b l e t h e i d e n t i f i c a t i o n o f many g e o c h e m i c a l l y s i g n i f i c a n t m e t a l l o p o r p h y r i n s 05-7) a n d t h e i r p r e c u r s o r s . A l t h o u g h t h e f i r s t r e a c t i o n scheme proposed t o account f o r the t r a n s f o r m a t i o n o f c h l o r o p h y l l s i n t o g e o p o r p h y r i n s , r e f e r r e d t o a s t h e T r e i b s scheme ( 8 ) , h a s u n d e r g o n e s i g n i f i c a n t m o d i f i c a t i o n s i n c e 1936, t h e c o n v e r s i o n o f c h l o r o p h y l l - a t o C32DPEP m e t a l l o p o r p h y r i n s i n m a t u r i n g s e d i m e n t s h a s b e e n c o n f i r m e d b y t h e d e t e r m i n a t i o n o f t h e s t r u c t u r e o f t h e V O ( I I ) a n d N i ( I I ) C32DPEP c o m p l e x e s (.5-7) a n d b y t h e i d e n t i f i c a t i o n o f i n t e r m e d i a t e s ( 9 ) . T h e geochemical e v o l u t i o n o f the m e t a l l o p o r p h y r i n s h a s been r e c e n t l y r e v i e w e d b y B a k e r a n d Louda (9) a n d b y F i l b y a n d V a n B e r k e l i n t h i s volume (10). —

Several studies confirm that porphyrin species are u s e f u l i n d i c a t o r s o f sediment m a t u r i t y (11-15). However, r o u t i n e a p p l i c a t i o n o f p o r p h y r i n d i s t r i b u t i o n d a t a i n m a t u r i t y s t u d i e s i s hampered b y t h e t i m e - c o n s u m i n g a n d e x p e n s i v e n a t u r e o f t h e mass s p e c t r o s c o p i c a n a l y s i s of metalloporphyrin types. P r o g r e s s h a s b e e n made i n a p p l y i n g p o r p h y r i n d i s t r i b u t i o n s t o m a t u r i t y s t u d i e s (and t o c o r r e l a t i o n s t u d i e s ) b y t h e d e v e l o p m e n t o f r a p i d HPLC t e c h n i q u e s w h i c h p e r m i t


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M E T A L C O M P L E X E S IN FOSSIL FUELS


d e t e r m i n a t i o n of amounts of m e t a l l o p o r p h y r i n s h a v i n g s p e c i f i c c a r b o n numbers w i t h o u t r e c o u r s e t o mass s p e c t r o m e t r y and w h i c h , i n c e r t a i n cases, separate s t r u c t u r a l isomers (16-21). Other problems are not s o l e l y o f an o p e r a t i o n a l n a t u r e , s u c h as an i n c o m p l e t e understanding o f t h e e f f e c t s o f c a t a g e n e t i c p r o c e s s e s i n v o l v i n g k e r o g e n and m i n e r a l c o m p o n e n t s o f s e d i m e n t s on p o r p h y r i n d i s t r i b u t i o n s , t h e l i m i t e d knowl e d g e o f the i n f l u e n c e o f s e d i m e n t a r y and e a r l y d i a g e n e t i c c o n d i t i o n s (pH, E h , m e t a l s p e c i a t i o n , e t c . ) o n N i ( I I ) a n d V O ( I I ) c h e l a t i o n o f f r e e - b a s e p o r p h y r i n s , and the r e l a t i v e s t a b i l i t i e s o f t h e m e t a l l o porphyrins. S o l u t i o n s to these problems are being v i g o r o u s l y pursued i n some o i l c o m p a n y g e o c h e m i s t r y programs. The u s e o f %DPEP ( i . e . , [ D P E P / ( D P E P + e t i o ) ] x 1 0 0 ) d e t e r m i n e d f r o m HPLC c h r o m a t o g r a m s a s a m e a s u r e o f s o u r c e r o c k m a t u r i t y h a s b e e n s u g g e s t e d b y B a r w i s e a n d P a r k ( 1 3 ) , who f o u n d a l i n e a r r e l a t i o n s h i p b e t w e e n %DPEP a n d v i t r i n i t e r e f l e c t a n c e (% R ) i n s e v e r a l source rocks. T h e y c o n c l u d e d t h a t t h e %DPEP i s a v e r y s e n s i t i v e measure of m a t u r i t y . T h e s e a u t h o r s , h o w e v e r , do n o t make i t c l e a r w h e t h e r t h e p o r p h y r i n r a t i o was m e a s u r e d o n t h e d e m e t a l l a t e d N i ( I I ) o r V O ( I I ) p o r p h y r i n s o r o n t h e t o t a l p o r p h y r i n c o n t e n t o f t h e samples. B e c a u s e %DPEP may v a r y d i f f e r e n t l y w i t h m a t u r i t y f o r N i ( I I ) a n d V O ( I I ) p o r p h y r i n s , t h e N i ( I I ) a n d V O ( I I ) s p e c i e s s h o u l d be s e p a r a t e d p r i o r t o HPLC a n a l y s i s o f t h e d e m e t a l l a t e d s p e c i e s . M a c k e n z i e et_ a l . ( 1 2 ) a l s o h a v e u t i l i z e d t h e r e l a t i v e a b u n d a n c e s o f t h e N i ( I I ) and V O ( I I ) p o r p h y r i n s and t h e D P E P / e t i o r a t i o s o f b o t h metal s e r i e s to determine m a t u r i t y l e v e l s i n the Toarcian shales of the P a r i s B a s i n . Q

The u s e o f m e t a l l o p o r p h y r i n d i s t r i b u t i o n s i n d e p o s i t i o n a l e n v i r o n m e n t r e c o n s t r u c t i o n h a s b e e n d e s c r i b e d b y M o l d o w a n e_t a l . ( 1 5 ) who s t u d i e d a L o w e r T o a r c i a n s h a l e s e q u e n c e f r o m t h e P a r i s B a s i n t h a t was o f c o n s t a n t , r e l a t i v e l y l o w , m a t u r i t y ( i . e _ . , p r e - " o i l window"). The s h a l l o w e r M i d d l e L i a s s h a l e s c o n t a i n e d e s s e n t i a l l y o n l y V O ( I I ) p o r p h y r i n s and were d e p o s i t e d u n d e r h i g h l y r e d u c i n g c o n d i t i o n s , whereas the deeper Lower L i a s s h a l e s were d e p o s i t e d u n d e r s u b - o x i c c o n d i t i o n s and c o n t a i n e s s e n t i a l l y 100% N i ( I I ) porphyrins. A t r a n s i t i o n zone between t h e s e d e p o s i t i o n a l e n v i r o n ments c o n t a i n e d b o t h N i ( I I ) and V O ( I I ) p o r p h y r i n s . A l t h o u g h Lewan ( 2 2 ) h a s d i s c u s s e d t h e g e n e r a l e f f e c t s o f pH, E h , H2S p r o d u c t i o n , e t c . on p o r p h y r i n e v o l u t i o n i n s e d i m e n t s , few q u a n t i t a t i v e d a t a a r e available. Compared t o t h e a p p l i c a t i o n o f h y d r o c a r b o n b i o m a r k e r s t o o i l - o i l o r o i l - s o u r c e r o c k c o r r e l a t i o n , t h e number o f r e p o r t e d p o r p h y r i n studies i s limited. Table I l i s t s the major p u b l i s h e d s t u d i e s . The f i r s t s y s t e m a t i c use of p o r p h y r i n s i n o i l - s o u r c e r o c k c o r r e l a t i o n was a c o m p a r i s o n o f N i ( I I ) a n d V O ( I I ) p o r p h y r i n c o n c e n t r a t i o n s i n O z o u r i , G a b o n , o i l s a n d s o u r c e r o c k s b y V a n E g g e l p o e l ( 2 3 ) who was a b l e t o show t h a t t h e o i l s a r e m i x t u r e s d e r i v e d f r o m s e v e r a l s o u r c e s . A major f r a c t i o n of each of the o i l s i s b e l i e v e d be d e r i v e d f r o m one p a r t i c u l a r a r g i l l a c e o u s s o u r c e r o c k . He a l s o p o i n t e d o u t t h e d i f f i c u l t i e s i n v o l v e d i n determining the m e t a l l o p o r p h y r i n contents of crude o i l s u s i n g U V - v i s i b l e spectrometry of whole o i l s . Polar organic m a t e r i a l (i.e.., asphaltenes, r e s i n s ) modifies VO(II) p o r p h y r i n s p e c t r a and c h a n g e s t h e m o l a r a b s o r p t i v i t y o f t h e m e t a l c o m p l e x (24^, 25) . A m o r e d e t a i l e d s t u d y u s i n g U V - v i s i b l e s p e c t r o m e t r y was made o f the V O ( I I ) p o r p h y r i n s f r o m the M a r a c a i b o B a s i n o i l s and s o u r c e r o c k s



5.



87

by G r a n s c h a n d E i s m a ( 2 6 ) . These a u t h o r s c o r r e l a t e d C r e t a c e o u s a n d T e r t i a r y o i l s (Boscan, L a P a z , e t c . ) w i t h the o r g a n i c - r i c h L a Luna shale (Cretaceous) using the VO(II) porphyrin concentrations o f t h e o i l s and rock e x t r a c t s . The r e l a t i v e l y abundant V O ( I I ) p o r p h y r i n s of the western Venezuelan o i l s and source rock e x t r a c t s permits r e l i a b l e a n a l y s i s by U V - v i s i b l e spectrometry. Few o t h e r d e t a i l e d b a s i n - w i d e s t u d i e s u s i n g e i t h e r MS o r HPLC t e c h n i q u e s h a v e b e e n published (see Table I ) . Most o f t h e c o r r e l a t i o n s t u d i e s r e p o r t e d i n Table I i n v o l v e a comparison o f N i ( I I ) and VO(II) porphyrins, o r a comparison o f DPEP/etio p o r p h y r i n r a t i o s o f the subject m a t e r i a l s . Strong and F i l b y (24) determined t h e etio/DPEP r a t i o s o f VO(II) p o r p h y r i n s i n A t h a b a s c a , P e a c e R i v e r , a n d C o l d L a k e o i l sand b i t u m e n s a n d showed t h a t these bitumens have etio/DPEP c h a r a c t e r i s t i c o f o i l s t h a t have migrated from deeper source rocks p r i o r t o the b i o d e g r a d a t i o n that subsequently occurred i nt h e i r shallow r e s e r v o i r s . They c o n c l u d e d on t h e b a s i s o f i n c r e a s i n g e t i o / D P E P r a t i o t h a t t h e o r i g i n a l s o u r c e r o c k o r p r e - m i g r a t i o n depth sequence corresponds t o t h e i r p r e s e n t r e s e r v o i r d e p t h s e q u e n c e , i..e_., Cold Lake > Peace R i v e r > Athabasca S i m i l a r t o t h e e t i o / D P E P v a r i a t i o n s , b u t more p r o n o u n c e d , were t h e v a r i a t i o n s i nthe r a t i o s o f e t i o t o minor p o r p h y r i n s e r i e s , such a s t e t r a h y d r o b e n z o (THBD), benzo-DPEP, a n d b e n z o - e t i o p o r p h y r i n s . This r a i s e s t h e p o s s i b i l i t y t h a t t h e m i n o r s e r i e s p o r p h y r i n s ( e . j * . , THBD, b e n z o ) may h a v e v a l u e i n c o r r e l a t i o n s t u d i e s , p a r t i c u l a r l y s i n c e these p o r p h y r i n s have r e c e n t l y been d e t e c t e d i n s e d i m e n t s a s t h e f r e e bases (27,28) w i t h a s y e t - t o - b e determined p r e c u r s o r s a n d d i a g e n e t i c pathways. The s i m i l a r p a t t e r n s o b s e r v e d f o r a l l t h e e t i o / o t h e r porphyrin r a t i o s w i t h depth argues against formation o f e t i o - p o r p h y r i n s i n t h e s e o i l s b y a d i r e c t DPEP t o e t i o c o n v e r s i o n b e c a u s e t h e r e i s n o a p p a r e n t g e n e t i c r e l a t i o n s h i p b e t w e e n DPEP a n d the minor s e r i e s p o r p h y r i n s . Non-Porphyrin

Complexes a n d Geochemical C o r r e l a t i o n s

The g e o c h e m i c a l s i g n i f i c a n c e a n d u t i l i t y o f n o n - p o r p h y r i n n i c k e l a n d vanadium complexes i n crude o i l s i s d i f f i c u l t t o a s s e s s because no d i s c r e t e complexes have been i d e n t i f i e d and t h e i r o r i g i n i s obscure. The f a c t t h a t t h e m o s t a b u n d a n t o r g a n i c a l l y c o m b i n e d n o n - p o r p h y r i n metals i n crude o i l asphaltenes a r e normally n i c k e l and vanadium suggests, however, a g e n e t i c r e l a t i o n s h i p between t h e p o r p h y r i n and non-porphyrin s p e c i e s . Yen (29) h a ssuggested t h a t t h e non-porphyrin c o m p l e x e s may i n f a c t b e m e t a l l o p o r p h y r i n d e g r a d a t i o n p r o d u c t s t h a t remain i n asphaltene s t r u c t u r e s . Branthaver (30) h a s determined that Ni/V r a t i o s a r e s i m i l a r throughout s e v e r a l g e l permeation c h r o m a t o g r a p h y (GPC) f r a c t i o n s o f B o s c a n c r u d e o i l . Porphyrin c o n t e n t s v a r y g r e a t l y among t h e s e f r a c t i o n s . I none f r a c t i o n , a l l m e t a l s a r e a c c o u n t a b l e a s p o r p h y r i n s , w h i l e i n a n o t h e r most m e t a l s are apparently non-porphyrinic. Other f r a c t i o n s a r e i n t e r m e d i a t e . T h i s would f u r t h e r support a g e n e t i c r e l a t i o n s h i p between p o r p h y r i n s and n o n - p o r p h y r i n s i f t h e s e f i n d i n g s were v e r i f i e d i n o t h e r c r u d e s . A l t h o u g h n o n - p o r p h y r i n n i c k e l a n d v a n a d i u m s p e c i e s may o c c u r i n crude o i l s , a s p h a l t s , e t c . , there i s l i t t l e i n f o r m a t i o n on t h e i r o c c u r r e n c e i nt h e bitumens o f source r o c k s w i t h w h i c h o i l s c o u l d be correlated. T h e r e may, i n f a c t , b e a c o r r e l a t i o n b e t w e e n n i c k e l a n d



Rock

Rock

Oil-Source

Oil-Source

Basin

Suite of o i l s :

Oil-Oil

no

Venezuela, Boscan Maracaibo Basin

Oil-Oil

Venezuela Lake

W.

Oil-Oil

location

oils

Maracaibo

S e n l i , and o t h e r c o n t i n e n t a l oil fields, China

Boscan o i l , Venezuela (Maracaibo Basin)

o i l , Gabon

Rock

Oil-Source

Ozouri

W. V e n e z u e l a L a k e (Lake Maracaibo)

Rock

Oil-Source

Applications of Porphyrins

Region-Occurrence

I.

Correlation

Table

and O i l - S o u r c e

show s i m i l a r i t i e s

HPLC c h r o m a t o g r a m s u s e d t o c o r r e l a t e sequence o f o i l s a t d i f f e r e n t l e v e l s of m a t u r i t y

HPLC f i n g e r p r i n t s of Boscan o i l s

Attempts c o r r e l a t i o n o f Cretaceous and T e r t i a r y o i l s with r e s e r v o i r depth b a s e d o n VOP c o n t e n t s

16

L8

26

73

A p p l i c a t i o n of DPEP/etio r a t i o s c o r r e l a t i o n w i t h source rocks

for

18

23

U s e d HPLC d e m e t a l l a t e d p o r p h y r i n c h r o m a t o g r a m s t o show c o r r e l a t i o n o f Boscan o i l s t o La Luna shale

Spectroscopic determination of NiP a n d VOP o f o i l s a n d k n o w n s o u r c e rock

26

Reference

Rock C o r r e l a t i o n s

C o r r e l a t e s Cretaceous and T e r t i a r y crudes w i t h L a Luna source r o c k on b a s i s o f VOP c o n t e n t s

Comments

in Oil-Oil



Grosmont F o r m a t i o n A l b e r t a , Canada

A l b e r t a o i l sand

Oil-Oil

deposits

bitumen,

C o r r e l a t i o n of Athabasca, Cold Lake, and Peace R i v e r o i l sands on b a s i s o f D P E P , e t i o , THBD, a n d b e n z o p o r p h y r i n abundances

D P E P / e t i o r a t i o s o f VOP u s e d t o c o r r e l a t e bitumen i n Devonian Grosmont Formation with Cretaceous Athabasca deposit

to correlate

Oil-Oil

DPEP/etio r a t i o s used degraded o i l s

Colombia

Oil-Oil

oils

HPLC c h r o m a t o g r a m s u s e d t o d e t e r m i n e m a t u r i t y sequence o f S h e n g l i o i l s (approx. DPEP/etio r a t i o s )

China

Shengli O i l Field,

C o r r e l a t e s m i g r a t e d o i l s on p r o p o r t i o n s o f p o l a r / n o n - p o l a r VOP a n d D P E P / e t i o ratios

Oil-Oil

USSR

U s e d VOP c o n t e n t s a n d D P E P / e t i o r a t i o s to d i s t i n g u i s h between J u r a s s i c and Cretaceous bitumoids

Surgut O i l F i e l d ,

E a s t C a u c a s u s F o o t h i l l s , USSR (bitumoids and crude o i l s )

W.

Oil-Oil

Oil-Oil


M E T A L C O M P L E X E S I N FOSSIL F U E L S

90


vanadium s p e c i e s i n kerogens from m a t u r i n g sediments and those p r e sent i n crude o i l a s p h a l t e n e s . R e c e n t l y , s e v e r a l a u t h o r s (31-34) demonstrated that o i l shale kerogen concentrates c o n t a i n s u b s t a n t i a l q u a n t i t i e s o f o r g a n i c a l l y combined n i c k e l and vanadium. Van B e r k e l and F i l b y (32) measured m i n e r a l - f r e e c o n c e n t r a t i o n s o f n i c k e l and v a n a d i u m o f 2 1 3 0 a n d 7 0 0 yg/g> r e s p e c t i v e l y , i n New A l b a n y o i l - s h a l e k e r o g e n a n d 3 5 0 a n d 3 2 6 0 Ug/g» r e s p e c t i v e l y , i n t h e W o o d f o r d o i l - s h a l e kerogen. A l t h o u g h t h e y showed t h a t b o t h k e r o g e n s g e n e r a t e d N i ( I I ) and V O ( I I ) p o r p h y r i n s on p y r o l y s i s , o n l y a s m a l l f r a c t i o n o f t h e t o t a l m e t a l was r e l e a s e d f r o m t h e k e r o g e n . I t was n o t p o s s i b l e t o d e t e r m i n e what f r a c t i o n o f t h e n i c k e l a n d v a n a d i u m i n t h e k e r o g e n was porphyrinic. During kerogen c a t a g e n e s i s , molecules a s s o c i a t e d w i t h petroleum a s p h a l t e n e s a r e thought t o form as i n t e r m e d i a t e s i n the c o n v e r s i o n o f k e r o g e n t o h y d r o c a r b o n s ( 3 5 ) , a s s h o w n i n F i g u r e 1. T h u s , a n a s p h a l tene m o i e t y formed from kerogen p r o b a b l y c o n t a i n s N i ( I I ) and V O ( I I ) porphyrin s u i t e s s i m i l a r to those present i n the parent kerogen, a n d may a l s o c o n t a i n t h e n o n - p o r p h y r i n c o m p l e x e s t h a t may b e p a r t o f the k e r o g e n s t r u c t u r e . Recent work (32) i n d i c a t e s t h a t t h e m e t a l l o p o r p h y r i n s p r o b a b l y a r e n o t bonded by a l i p h a t i c l i n k a g e s t o t h e k e r o g e n b u t may b e s t r o n g l y c h e m i s o r b e d , o r t r a p p e d i n t h e p o l y m e r i c structure. K e r o g e n s may t h u s r e t a i n p o l a r n i c k e l a n d v a n a d i u m n o n p o r p h y r i n s p e c i e s i n a s i m i l a r f a s h i o n a n d t h e s e may b e p a r t o f asphaltene s t r u c t u r e s a f t e r f o r m a t i o n from the maturing kerogen. Thus, t h e a s p h a l t e n e s o f s o u r c e r o c k bitumens and r e s u l t i n g crude o i l s may c o n t a i n n o n - p o r p h y r i n m e t a l c o m p l e x e s t h a t a r e c h a r a c t e r i s t i c of t h e s o u r c e - r o c k kerogens and t h e i r g e o c h e m i c a l h i s t o r y and thus o f p o t e n t i a l use i n c o r r e l a t i o n studies. An a l t e r n a t i v e o r i g i n f o r t h e n o n - p o r p h y r i n c o m p l e x e s i n a s p h a l t e n e s may b e t h a t t h e a s p h a l t e n e s e v o l v i n g from kerogen i n source r o c k s complex Ni2+, V0^+ and o t h e r i o n s from m i n e r a l s u r f a c e s . I f t h i s i s the case, the non-porphyrin m e t a l s i n c r u d e o i l a s p h a l t e n e s may s t i l l r e f l e c t t h e s o u r c e r o c k e n v i r o n m e n t ( b u t n o t n e c e s s a r i l y t h e k e r o g e n c o m p o s i t i o n ) and be o f value i n correlation studies. The g e o c h e m i c a l r e l a t i o n s h i p b e t w e e n n o n - p o r p h y r i n m e t a l complexes and p o r p h y r i n s i n crude o i l s and kerogens and t h e i r p o t e n t i a l f o r u s e i n c o r r e l a t i o n s t u d i e s s h o u l d be f u r t h e r i n v e s t i g a t e d . Metal Distributions

i n Exploration

Studies

T h e r e h a v e been a number o f a t t e m p t s t o c l a s s i f y p e t r o l e u m a n d s o u r c e r o c k kerogens by examining e n t i r e m e t a l s u i t e s i n t h e s e m a t e r i a l s . In t h e s e s t u d i e s , p o r p h y r i n c o n t e n t s a r e n o t d e t e r m i n e d . For the m e t a l s o t h e r t h a n n i c k e l a n d v a n a d i u m , i t i s n o t known t h a t t h e chelating ligands are porphyrinic. T h e s e s t u d i e s p a r a l l e l many s i m i l a r i n v e s t i g a t i o n s of c o a l s , from which i t i s u s u a l l y i m p o s s i b l e to e x t r a c t s i g n i f i c a n t amounts o f m e t a l c h e l a t e s , b u t w h i c h o f t e n c o n t a i n s u b s t a n t i a l q u a n t i t i e s o f m e t a l s t h a t a p p e a r t o be a s s o c i a t e d with organic matter (36). Several e a r l y workers attempted to use V/Ni r a t i o s as i n d i c a t o r s o f m a t u r a t i o n ( o r a g e ) o f c r u d e o i l s , b u t many o f t h e c o n c l u s i o n s a r e contradictory. Hodgson (37) measured n i c k e l , vanadium and i r o n i n some W e s t e r n C a n a d a o i l s a n d c o n c l u d e d t h a t t h e V / N i r a t i o d e c r e a s e d w i t h i n c r e a s i n g m a t u r a t i o n from a s p h a l t i c Cretaceous t o l e s s a s p h a l t i c deeper Devonian o i l s . Hodgson (37) a l s o c o n c l u d e d t h a t n i c k e l ,


5.


91


KEROGEN


ι

HYDROCARBONS F i g u r e 1. S c h e m a t i c d i a g r a m o f f o r m a t i o n o f a s p h a l t e n e a g g r e g a t e from kerogen showing N i ( I I ) and VO(II) p o r p h y r i n s and o t h e r m e t a l c o m p l e x e s , ML^, -M-, i n s t r u c t u r e . C o m p l e x e s a r e shown a s s o c i a t e d and bonded t o t h e s t r u c t u r e i n d i f f e r e n t modes.



92


v a n a d i u m , and i r o n were d e r i v e d f r o m t h e o r i g i n a l s o u r c e m a t e r i a l . B a l l et. a l . ( 3 8 ) a n d H y d e n ( 3 9 ) , h o w e v e r , c o n c l u d e d t h a t t h e V / N i r a t i o i n c r e a s e d w i t h r e s e r v o i r r o c k age. Much o f t h i s d i s a g r e e m e n t p r o b a b l y a r i s e s from the i n a b i l i t y to d i s t i n g u i s h between the p o r p h y r i n and n o n - p o r p h y r i n f o r m s o f t h e m e t a l s i n t h e s e o i l s and the p r o b a b l e v a r i a t i o n i n the t r a c e m e t a l assemblages o f the source rocks. Bonham ( 4 0 ) s t u d i e d t h e m e t a l c o n t e n t s o f a n u m b e r o f A m e r i c a n c r u d e o i l s o f v a r i o u s a g e s , w i t h e m p h a s i s on P e n n s y l v a n i a n c r u d e s from the Andarko b a s i n o f Oklahoma. He f o u n d t h a t t h e v a n a d i u m a n d n i c k e l c o n t e n t s o f t h e o i l s d i f f e r e d s i g n i f i c a n t l y f r o m one b a s i n t o another. Bonham c o u l d n o t , o n t h e b a s i s o f m e t a l s u i t e s , c o r r e l a t e b e t w e e n o i l p o o l s i n t h e same p r o d u c i n g s t r a t a o f i n d i v i d u a l b a s i n s o r e v e n d i f f e r e n t i a t e b e t w e e n t h e same p r o d u c i n g s t r a t a . Neverthel e s s , he c l a i m e d t h a t t h e m e t a l s u i t e s p r o v i d e d i n f o r m a t i o n a b o u t t h e p a l e o g e o g r a p h y o f t h e b a s i n s . S e v e r a l a t t e m p t s h a v e b e e n made to c o r r e l a t e t r a c e m e t a l d i s t r i b u t i o n s w i t h t h e a g e s o f r e s e r v o i r r o c k s o r o t h e r geochemical p r o p e r t i e s (41-45) o f R u s s i a n o i l s . T h u s , K o t o v a et_ a^L. ( 4 1 ) s h o w e d that n i c k e l , vanadium, copper, g a l l i u m , and germanium v a r i e d s y s t e m a t i c a l l y w i t h age and d e p t h o f reservoir rocks. I n m o s t o f t h e s e s t u d i e s , l i t t l e a t t e n t i o n was p a i d t o t h e n a t u r e o f t h e m e t a l s p e c i e s i n t h e o i l s (£.£., m i n e r a l forms, e n t r a i n e d aqueous phase, e t c . ) . The s t u d y b y C h a k h m a c h k e v et a l . (43) i s s i g n i f i c a n t b e c a u s e t h e s e a u t h o r s a t t e m p t c o r r e l a t i o n s between s y n g e n e t i c and p a r a a u t o c h t h o n o u s ( s i c ) b i t u m e n s o f J u r a s s i c a n d T r i a s s i c s o u r c e r o c k s a n d o i l s f r o m p r o d u c i n g s t r a t a o f t h e same age. In t h i s study, t r a c e element d i s t r i b u t i o n s were used as p a r a m e t e r s f o r o i l - s o u r c e r o c k and o i l - o i l c o r r e l a t i o n s whereas VO(II) p o r p h y r i n s were used to determine source r o c k m a t u r i t y . The DPEP/etio r a t i o s of VO(II) p o r p h y r i n s i n the bitumen decreased w i t h depth. T r a c e element c o n t e n t s o f o i l s and b i t u m e n s were s i m i l a r f o r s u i t e s o f t h e same a g e , i n d i c a t i n g t h a t t h e o i l s may be s y n g e t i c w i t h t h e T r i a s s i c a n d J u r a s s i c h o s t r o c k s , J L . e _ . , t h a t t h e r e a r e two hydrocarbon sources. M a s t et_ a l . ( 4 6 , 4 7 ) d e t e r m i n e d t h e v a n a d i u m c o n t e n t s o f a l a r g e number o f P a l e o z o i c c r u d e o i l s f r o m I l l i n o i s by n e u t r o n a c t i v a t i o n analysis. L i k e Bonham, t h e s e i n v e s t i g a t o r s f o u n d t h a t v a n a d i u m d i s t r i b u t i o n i n the o i l s provided paleogeographic i n f o r m a t i o n . R e l a t i v e l y h i g h vanadium c o n c e n t r a t i o n s were found i n c r u d e s accumul a t e d i n some d e f o r m a t i o n a l l y h i g h s t r u c t u r a l t r a p s . These t r a p s a r e b e l i e v e d t o h a v e f o r m e d a t a t i m e c l o s e t o when t h e s o u r c e r o c k s o f t h e s t u d y c r u d e s b e g a n g e n e r a t i n g o i l . The a u t h o r s c o n t e n d t h a t t h e i r d a t a s u p p o r t t h e s u g g e s t i o n o f Weeks (48) t h a t h e a v y o i l s a r e formed from s o u r c e r o c k s b e f o r e l i g h t o i l s . I t h a s b e e n shown t h a t the i n i t i a l s t a g e s of kerogen d e c o m p o s i t i o n i n v o l v e a decrease i n oxygen t o c a r b o n , n i t r o g e n t o c a r b o n , and s u l f u r t o c a r b o n r a t i o s (49); hence, carbon-heteroatom bonds of source r o c k kerogens break m o r e r e a d i l y u n d e r t h e r m a l s t r e s s t h a n do c a r b o n - c a r b o n b o n d s . T h u s , o i l s i n i t i a l l y f o r m e d f r o m s o u r c e r o c k s w i l l be r e l a t i v e l y r i c h i n s u l f u r , n i t r o g e n , and oxygen. T h e s e o i l s w o u l d be l e s s e x t e n s i v e l y c r a c k e d than those formed l a t e r i n the o i l g e n e r a t i o n process. These e a r l i e r formed, h e a v i e r o i l s would c o n t a i n most o f the m e t a l complexes, which would accumulate i n those t r a p s e x i s t i n g a t t h e o n s e t o f h e a v y o i l g e n e r a t i o n . The p a u c i t y o f i n f o r m a t i o n o n t h e t r a c e e l e m e n t c o n t e n t s o f b i t u m e n s and k e r o g e n s , h o w e v e r , means a d i s t i n c t i o n between the i n h e r i t a n c e o f a t r a c e element "fingerprint"



5.



93

of t h e kerogen i n t h e heavy bitumen a n d t h e c o m p l e x a t i o n o f m e t a l i o n s f r o m t h e m i n e r a l m a t r i x b y t h e e v o l v i n g b i t u m e n c a n n o t b e made at t h i s time. M c l v e r (50) d e t e r m i n e d t h e n i c k e l a n d vanadium c o n t e n t s o f Wind R i v e r B a s i n , Wyoming, c r u d e s o f v a r y i n g a g e s b y X - r a y f l u o r e s c e n c e . He f o u n d t h a t a l l o f t h e C r e t a c e o u s o i l s h a d V / N i r a t i o s t h a t w e r e d i s t i n c t l y d i f f e r e n t from those o f t h e P a l e o z o i c o i l s t h a t were studied. These d i f f e r e n c e s were a l s o r e f l e c t e d i n o t h e r p r o p e r t i e s of t h e c r u d e s . Mclver interpreted these data t o i n d i c a t e d i f f e r e n c e s i n t h e environments o f d e p o s i t i o n o f t h e source r o c k s o f t h e two petroleum s u i t e s , which i s r e f l e c t e d i nthe composition o f the o i l s . H o d g s o n et_ a l . ( 5 1 ) u s e d t h e v a n a d i u m a n d n i c k e l c o n t e n t s o f A l b e r t a crudes t o determine m i g r a t i o n pathways. Their data indicate that within a given o i l f i e l d , distance o fmigration i s r e f l e c t e d in the metal contents o f an o i l pool. They s u g g e s t a d s o r p t i o n o f m e t a l c h e l a t e s and o t h e r p o l a r m a t e r i a l s on r o c k s d u r i n g m i g r a t i o n as a major determinant o f m e t a l c o n t e n t s o f a p e t r o l e u m d e p o s i t . T h i s c h r o m a t o g r a p h i c e f f e c t may b e s i m i l a r t o t h a t a c t i n g o n t h e porphyrin species ofmigrating o i l s . Radchenko (52) m a i n t a i n e d t h a t vanadium i n crude o i l a n d b i t u mens i s o f s e c o n d a r y o r i g i n . Radchenko i n v o k e d b a c t e r i a l a c t i o n i n r e s e r v o i r s t o a c c o u n t f o r many o f t h e u n u s u a l p r o p e r t i e s o f h e a v y bitumens, i n c l u d i n g h i g h vanadium c o n t e n t s . A c c o r d i n g t o Radchenko, the v a n a d i u m c o n t e n t o f a c r u d e o i l w o u l d t h u s n o t a l w a y s be r e l a t e d to t h e t r a c e element s u i t e o f t h e s o u r c e r o c k o f t h e c r u d e , n o r would m i g r a t i o n e f f e c t s n e c e s s a r i l y be s i g n i f i c a n t . A l - S h a h r i s t a n i and A l - A t y i a (53) measured t h e n i c k e l and vanadium c o n t e n t s o f crudes from t h r e e f i e l d s i n I r a q . Their study was d e s i g n e d t o r e s o l v e a c o n t r o v e r s y o v e r t h e o r i g i n o f t h e o i l s o f northern Iraq. One s c h o o l o f t h o u g h t ( 4 8 ) m a i n t a i n s t h a t t h e s o u r c e r o c k s from which t h e o i l s a r e d e r i v e d a r e contemporaneous w i t h t h e l a t e r Cretaceous and e a r l y T e r t i a r y r e s e r v o i r s i n which they a r e found. Another s c h o o l o f thought (54) contends t h a t t h e o i l s were d e r i v e d from e a r l y Cretaceous r o c k s and i n i t i a l l y accumulated i n middle Cretaceous traps. Later, during extensive f o l d i n g and f r a c t u r i n g d u r i n g t h e T e r t i a r y , m u c h o f t h e o i l m i g r a t e d (i.£., s e c o n d a r y migration) v e r t i c a l l y into Tertiary reservoirs. A l - S h a h r i s t a n i and A l - A t y i a r e a s o n e d t h a t i f a l l t h e o i l s came f r o m t h e same s o u r c e r o c k s , b u td i d n o t m i g r a t e f a r , n i c k e l andvanadium c o n t e n t s and v a n a d i u m t o n i c k e l r a t i o s s h o u l d b e s i m i l a r , r e f l e c t i n g a common source. H o w e v e r , i f e x t e n s i v e v e r t i c a l m i g r a t i o n o f some o f t h e o i l s h a d o c c u r r e d , i t was r e a s o n e d t h a t t h e s e o i l s would have l o w e r m e t a l s c o n t e n t s , b u t s i m i l a r v a n a d i u m t o n i c k e l r a t i o s , when c o m p a r e d with the o i l s remaining i nthe middle Cretaceous traps. The n i c k e l and vanadium d a t a o b t a i n e d b y A l - S h a h r i s t a n i a n d A l - A t y i a were i n t e r p r e t e d b y them t o c o n f i r m t h e t h e o r y o f v e r t i c a l m i g r a t i o n f r o m middle Cretaceous t o l a t e Cretaceous and e a r l y T e r t i a r y traps. A b u - E l g h e i t et_ CLL. ( 5 5 ) c o n c l u d e d t h a t t h r e e G u l f o f S u e z M i o c e n e o i l s could be d i s t i n g u i s h e d from f i v e Western Desert Cretaceous o i l s on the b a s i s o f V/Ni contents and that the V/Ni r a t i o decreased w i t h i n c r e a s i n g age (not given). They a l s o c l a i m e d t h a t t h e V/Sb and N i / S b r a t i o s c o u l d a l s o be used t o d i s t i n g u i s h t h e two g r o u p s o f oils. However, t h e s m a l l number o f samples s t u d i e d a n d t h e l a r g e v a r i a t i o n s i n t h e V/Sb a n d N i / S b r a t i o s i n t h e g r o u p s makes t h e conclusions speculative.



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S a b a n e_t a l _ . ( 5 6 ) i n v e s t i g a t e d t r a c e e l e m e n t s u i t e s o f o i l s o f the P a n n o n i a n B a s i n and c o n c l u d e d t h a t t h e V / N i r a t i o i s r e l i a b l e f o r o i l - o i l correlations. They a l s o e x p r e s s r e s e r v a t i o n s about t h e use of V/Ni f o r d e t e r m i n i n g a b s o l u t e ages o f o i l s , c i t i n g numerous c o n f l i c t i n g s t u d i e s i n the l i t e r a t u r e . Connor and G e r r i l d (57) s t u d i e d t r a c e e l e m e n t d i s t r i b u t i o n s and o t h e r p r o p e r t i e s o f a number o f c r u d e s i n t h e E l k H i l l s , C a l i f o r n i a , field. T h e y w e r e among t h e f i r s t g e o c h e m i s t s t o a n a l y z e o i l - o i l c o r r e l a t i o n d a t a by s t a t i s t i c a l t e c h n i q u e s s u c h as m u l t i p l e discriminant function analysis. They were a b l e t o c l a s s i f y t h e E l k H i l l s o i l s i n t o t h r e e d i s t i n c t types u s i n g these methods. Hitchon e t a l . ( 5 8 ) a n d H i t c h o n a n d F i l b y ( 5 9 ) m e a s u r e d 22 e l e m e n t s i n A l b e r t a B a s i n c r u d e o i l s a n d a p p l i e d Q- a n d R-mode f a c t o r a n a l y s i s to the d a t a . They c o n c l u d e d t h a t t h e t r a c e element d i s t r i b u t i o n s were c o n t r o l l e d by o i l m a t u r a t i o n p r o c e s s e s r a t h e r t h a n by m i g r a t i o n processes. They found t h a t a major f r a c t i o n o f the c u m u l a t i v e v a r i a n c e c o u l d be a s s i g n e d t o s u l f u r , v a n a d i u m , s e l e n i u m , and n i c k e l . H i t c h o n and F i l b y (60) u s e d m u l t i p l e - d i s c r i m i n a n t f u n c t i o n a n a l y s i s to r e - e v a l u a t e t h e A l b e r t a o i l t r a c e element d a t a , and were a b l e t o c l a s s i f y the A l b e r t a crudes i n t o three f a m i l i e s . The e l e m e n t s f o u n d t o be d i s c r i m i n a t i n g w e r e s u l f u r , c o b a l t , v a n a d i u m , s e l e n i u m a n d bromine. S t a t i s t i c a l treatment of the t r a c e element data y i e l d e d c l a s s i f i c a t i o n s of the c r u d e s t h a t were s i m i l a r to t h o s e d e t e r m i n e d by t h e more e x p e n s i v e and t i m e consuming methods o f h y d r o c a r b o n and s u l f u r b i o m a r k e r a n a l y s i s used by Deroo e t a l . ( 6 1 ) . The a d v e n t o f a n a l y t i c a l t e c h n i q u e s s u c h a s I C P s p e c t r o m e t r y permits the convenient q u a n t i t a t i v e a n a l y s i s of t r a c e element s u i t e s of f o s s i l f u e l s . D a t a n e e d no l o n g e r be c o n f i n e d t o t h o s e e l e m e n t s , s u c h as v a n a d i u m and n i c k e l , w h i c h a r e f o u n d i n s u b s t a n t i a l c o n c e n trations. C u r i a l e (62) has l a u n c h e d a c o m p r e h e n s i v e program t o a n a l y z e a l a r g e number o f h e a v y c r u d e o i l s and s o l i d b i t u m e n s f o r several trace elements. The o b j e c t i v e s o f t h e s t u d y a r e t o d e t e r m i n e w h e t h e r o r n o t t r a c e m e t a l d a t a c a n be u s e d t o e s t a b l i s h g e n e t i c r e l a t i o n s h i p s among b i t u m i n o u s s u b s t a n c e s a n d t o d i s c o v e r i n t e r n a l r e l a t i o n s h i p s among e l e m e n t s i n t h e m e t a l s u i t e s . The u l t i m a t e purpose i s to e v a l u a t e the u t i l i t y of metal data i n s o l v i n g problems i n f o s s i l f u e l geochemistry. I n more t h a n a hundred heavy o i l s and s o l i d b i t u m e n s s t u d i e d , C u r i a l e (62) found t h a t a n e g a t i v e r e l a t i o n s h i p e x i s t s between API g r a v i t y and c o n c e n t r a t i o n s o f cadmium, chromium, molybdenum, n i c k e l and v a n a d i u m , and t h a t a p o s i t i v e c o r r e l a t i o n b e t w e e n t h e l a s t f o u r m e t a l s and a s p h a l t e n e c o n t e n t e x i s t s . This suggests that these four m e t a l s a r e a s s o c i a t e d w i t h heavy f r a c t i o n s o f p e t r o l e u m and b i t u m e n s . The same c o r r e l a t i o n s w e r e n o t o b s e r v e d f o r c o b a l t , c o p p e r , i r o n , manganese, and z i n c . T h e s e m e t a l s may h a v e d i f f e r e n t m o d e s o f c o o r d i n a t i o n than the other metals. U s i n g data from t h i s study, C u r i a l e was a b l e t o d e m o n s t r a t e a g e n e t i c r e l a t i o n s h i p b e t w e e n c r u d e o i l s and s o l i d b i t u m e n s . The l a t t e r m a t e r i a l s a r e d e r i v e d f r o m t h e f o r m e r by a p r o c e s s t h a t c o n s e r v e s m e t a l s . S o l i d b i t u m e n s do n o t h a v e a mode o f o r i g i n d i f f e r e n t f r o m p e t r o l e u m . I n t h i s manner, C u r i a l e used metals data to p r o v i d e a s o l u t i o n to a geochemical problem. C u r i a l e (63) r e p o r t s on f u r t h e r s t u d i e s u s i n g t r a c e e l e m e n t data i n t h i s volume. E l l r i c h e_t a l . ( 6 4 ) s t u d i e d t h e c o n c e n t r a t i o n s o f 12 t r a c e e l e m e n t s i n 45 c r u d e o i l s f r o m 17 o i l f i e l d s i n t h e M o l a s s e B a s i n o f


5.


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S. G e r m a n y . They found t h a t t h e y c o u l d c l a s s i f y the o i l s i n t o t h r e e f a m i l i e s on the b a s i s o f n i c k e l , vanadium, and s u l f u r c o n t e n t s . They a l s o showed t h a t t h e i o d i n e c o n t e n t s o f t h e c r u d e s c o u l d b e c o r r e l a t e d w i t h the i o d i n e contents o f the formation waters. Hirner (65), i n t h i s volume, r e p o r t s on a c o n t i n u a t i o n o f t h i s study o f the t r a c e e l e m e n t d i s t r i b u t i o n s i n German o i l s a n d a l s o i n c l u d e s t h e m e t a l contents o f source rock kerogens i n the c o r r e l a t i o n study.


M i g r a t i o n and A l t e r a t i o n Processes: t i o n s o f M e t a l Complexes

T h e i r E f f e c t s on the

Distribu-

The e f f e c t s o f c r u d e o i l m i g r a t i o n o n m e t a l l o p o r p h y r i n o r t r a c e m e t a l a b u n d a n c e s h a v e n o t b e e n f u l l y i n v e s t i g a t e d , a l t h o u g h some o f t h e e a r l y t r a c e m e t a l s t u d i e s a l r e a d y c i t e d have attempted t o c o r r e l a t e V/Ni r a t i o s w i t h m i g r a t i o n process (51-53). C h a k h m a c h k e v «et a l . ( 6 6 ) attempted t o simulate g e o l o g i c m i g r a t i o n o f porphyrins i n t h e laboratory by passing an o i l w i t h high VO(II) porphyrin content through c l a y - s a n d columns. These a u t h o r s found t h a t p o l a r V O ( I I ) p o r p h y r i n s were r e t a i n e d on the column r e l a t i v e t o n o n - p o l a r V O ( I I ) porphyrins (not defined) andthat the DPEP/etio r a t i o i nthe i n i t i a l e f f l u e n t s were lower than the crude o i l r a t i o , a s expected from polarity considerations. B u r k o v a et_ a l . ( 2 2 ) u s e d D P E P / e t i o r a t i o s o f V O ( I I ) p o r p h y r i n s f r o m C r e t a c e o u s - J u r a s s i c W. S u r g u t o i l s t o c o r r e l a t e o i l s that hadmigrated t o d i f f e r e n t degrees. Silverman ( 6 8 ) s h o w e d t h a t p o r p h y r i n c o n t e n t s o f some V e n e z u e l a n o i l s e m p l a c e d at v a r i o u s p o i n t s along a m i g r a t i o n path decreased w i t h d i s t a n c eo f migration. The e f f e c t s o f m i g r a t i o n p r o c e s s e s a r e d i s c u s s e d i n more d e t a i l b y F i l b y a n d V a n B e r k e l (10) i n t h i s v o l u m e . The t r a c e m e t a l a b u n d a n c e s i n s o u r c e r o c k b i t u m e n s a r e u n d o u b t e d l y a f f e c t e d when p e t r o l e u m i s g e n e r a t e d f r o m t h e r o c k s . M i g r a t i o n i s believed t o r e s u l t i n a decrease i n asphaltene and r e s i n content of a m i g r a t e d o i l . Thus t h e abundances o f most m e t a l s w h i c h a r e concentrated i nthe asphaltenes should decrease w i t h d i s t a n c eo f m i g r a t i o n , b u t t h e i r r e l a t i v e c o n c e n t r a t i o n s may b e u n a f f e c t e d . T h i s c o n c l u s i o n w a s r e a c h e d b y L e w a n (9) who s t u d i e d t h e e f f e c t s o f m i g r a t i o n on the n i c k e l a n d vanadium c o n t e n t s o f crude o i l s compared w i t h source rock bitumens. However, i f c h r o m a t o g r a p h i c e f f e c t s do change t h e m e t a l l o p o r p h y r i n o r t r a c e m e t a l d i s t r i b u t i o n s o f m i g r a t e d o i l s , i t s t i l l may be p o s s i b l e t o " r e c o n s t r u c t " t h e p o r p h y r i n o r t r a c e m e t a l d i s t r i b u t i o n s c h a r a c t e r i s t i c o f the bitumen i nthe source rock through a n a l y s i s o f the crude o i l a s p h a l t e n e s . S e v e r a l a u t h o r s h a v e shown t h a t b i o m a r k e r s c a n b e t r a n s p o r t e d a n d p r o t e c t e d f r o m biodégradation a s a consequence o f being i n c o r p o r a t e d asphaltene s t r u c t u r e s i n a crude o i l andc a nbe l i b e r a t e d b y a s p h a l t e n e p y r o l y s i s (70,71). In a s i m i l a r manner, p o r p h y r i n s o r o t h e r t r a c e m e t a l s p e c i e s r e t a i n e d w i t h i n t h o s e a s p h a l t e n e m i c e l l e s w h i c h s u r v i v e m i g r a t i o n may n o t have been s u b j e c t e d t o c h r o m a t o g r a p h i c f r a c t i o n a t i o n d u r i n g m i g r a t i o n . The e f f e c t s o f biodégradation ( a n d a s s o c i a t e d w a t e r w a s h i n g ) o n p o r p h y r i n and t r a c e m e t a l d i s t r i b u t i o n s a l s o have not been f u l l y investigated. A s m e n t i o n e d e a r l i e r , B a r w i s e a n d P a r k (16) c o n c l u d e d that biodegraded o i l s from a m a t u r a t i o n sequence had VO(II) p o r p h y r i n d i s t r i b u t i o n s (e.g., DPEP/etio r a t i o s ) s i m i l a r t o those o f r e l a t e d non-degraded o i l s o f s i m i l a r m a t u r i t y , a l t h o u g h no q u a n t i t a t i v e d a t a were p r e s e n t e d . Palmer (72) s t u d i e d t h e V O ( I I ) p o r p h y r i n s



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from a s e r i e s of g e n e t i c a l l y r e l a t e d o i l s from Colombia c o n s i s t i n g of a h i g h l y d e g r a d e d seep o i l ; a r e s e r v o i r b i o d e g r a d e d o i l ; and n o n degraded o i l s . She f o u n d t h a t t h e D P E P / e t i o r a t i o s , t h e s e r i e s m a x i m a (C^i f o r DPEP, C 2 9 f o r e t i o ) , a n d t h e c a r b o n n u m b e r r a n g e s were v e r y s i m i l a r f o r the o i l s . She d i d n o t i c e , h o w e v e r , t h a t i n t h e most degraded seep o i l t h e V O ( I I ) p o r p h y r i n s were e n r i c h e d r e l a t i v e i n N i ( I I ) p o r p h y r i n s compared t o l e s s degraded o i l s . I t i s not c l e a r , however, whether t h i s enrichment i s a r e s u l t of s e l e c t i v e b i o l o g i c a l processes ( s e l e c t i v e degradation of N i ( I I ) p o r p h y r i n s ) , of s e l e c t i v e d i s s o l u t i o n b y a s s o c i a t e d w a t e r w a s h i n g , o r o f s e l e c t i v e o x i d a t i o n of N i ( I I ) p o r p h y r i n s r e l a t i v e to the VO(II) s p e c i e s . S t r o n g a n d F i l b y ( 2 4 ) h a v e a l s o c o n c l u d e d t h a t biodégradation h a d l i t t l e e f f e c t on p o r p h y r i n d i s t r i b u t i o n s i n t h e h i g h l y d e g r a d e d A l b e r t a o i l sands. I f biodégradation h a s l i t t l e e f f e c t o n p o r p h y r i n o r t r a c e m e t a l d i s t r i b u t i o n s , s u c h d i s t r i b u t i o n s may b e i m p o r t a n t c o r r e l a t i o n p a r a m e t e r s when o t h e r b i o s e n s i t i v e b i o m a r k e r s (ί·β_·, m o s t h y d r o c a r b o n s ) c a n n o t be u s e d . Summary The s t u d y o f p o r p h y r i n a n d t r a c e m e t a l s u i t e s i n c r u d e o i l s i s a promising t o o l of geochemical a n a l y s i s . In order to f u l f i l l t h i s p r o m i s e , i n v e s t i g a t i o n s i n a n u m b e r o f a r e a s w o u l d seem t o be n e c e s sary. R e l a t i o n s h i p s between o r g a n i c a l l y a s s o c i a t e d m e t a l s i n p e t r o l e u m and t h o s e i n s o u r c e r o c k s n e e d t o be a c c u r a t e l y d e t e r m i n e d . This r e q u i r e s i n v e s t i g a t i o n of the nature of minor p o r p h y r i n s u i t e s and any n o n - p o r p h y r i n c o m p l e x e s . Lack of a p p r o p r i a t e a n a l y t i c a l t e c h n i q u e s and t h e i n t r a c t a b i l i t y o f t h e s e m a t e r i a l s has caused r e s e a r c h e f f o r t s t o be f o c u s e d o n t h e m o r e e a s i l y s t u d i e d m a j o r p o r p h y r i n s and t h o s e m e t a l s f o u n d i n h i g h c o n c e n t r a t i o n s . I f t h e e t i o / D P E P r a t i o i s t o be u s e d a s a n y k i n d o f i n d i c a t o r , t h e n t h e o r i g i n o f e t i o - p o r p h y r i n s and t h e mechanisms o f e t i o and DPEP p o r p h y r i n d e g r a d a t i o n ( e . , d e a l k y l a t i o n , i s o c y c l i c r i n g s c i s s i o n ; d e m e t a l l a t i o n , e t c . ) m u s t be u n d e r s t o o d . Are the e t i o p o r p h y r i n s p r o d u c t s o f DPEP c o n v e r s i o n , o r a r e t h e y b e t t e r s u r v i v o r s in c e r t a i n environments than DPEP-porphyrins? Or do t h e y a r i s e i n some o t h e r m a n n e r ? Answers t o the above problems w i l l r e q u i r e a p p l i c a t i o n o f a n a l y t i c a l protocols for geoporphyrin analysis. As Q u i r k e h a s shown i n his overview a r t i c l e i n t h i s volume, s e p a r a t i o n techniques f o r geoporphyrins s t i l l lack standardization. Improvements i n our u n d e r s t a n d i n g of the g e o c h e m i s t r y of m e t a l chelates should r e s u l t i n a b e t t e r understanding of petroleum migration, which i n turn should a s s i s t i n p r o s p e c t i n g f o r petroleum. T h i s a c t i v i t y i s o f c o n s i d e r a b l y more t h a n a c a d e m i c i n t e r e s t . Acknowledgments J . F . B r a n t h a v e r t h a n k s t h e U.S. D e p a r t m e n t o f E n e r g y u n d e r C o n t r a c t Number D E - F C 2 1 - 8 3 F E 6 0 1 7 7 .

f o r support


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6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16. 17. 18. 19. 20. 21. 22. 23. 24. 25. 26. 27. 28. 29.

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Metal Complexes in Fossil Fuels - American Chemical Society

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