Generation of Nickel and Vanadyl Porphyrins from Kerogen During

Chapter 7

Generation of Nickel and Vanadyl Porphyrins from Kerogen During Simulated Catagenesis Gary J. Van Berkel and Royston H. Filby

Downloaded by UNIV OF CALIFORNIA SAN DIEGO on March 8, 2016 | http://pubs.acs.org Publication Date: July 6, 1987 | doi: 10.1021/bk-1987-0344.ch007

Department of Chemistry and Nuclear Radiation Center, Washington State University, Pullman, WA 99164-1300

The fate of the Ni and V complexes in Woodford and New Albany oil shale kerogens during simulated catagenesis was studied by laboratory pyrolysis at 100-450°C in toluene. Sequential pyrolysis of the same kerogen aliquot at increasing temperatures allowed a distinction to be made between metal complexes in the pyrolysate which were components of residual bitumen associated with the kerogen (low temperature pyrolysis) and those complexes generated from the kerogen matrix (high temperature pyrolysis). Both Ni(II) porphyrin (NiP) and VO(II) porphyrin (VOP) were generated from the kerogen matrix and in proportion to the amount of organically combined Ni and V in the kerogen. There is no indication that either type of porphyrin is chemically bound to the kerogen matrix, but the porphyrin compositions of the bitumen and pyrolysates are different. The pyrolysate VOP composition shifts to lower carbon number and increases in the amount of etio type porphyrins relative to DPEP type porphyrins as pyrolysis temperature increases. Results also indicate that release of Ni and V complexes from kerogen during catagenesis may substantially alter the Ni and V concentration, porphyrin content, and porphyrin composition of the bitumen accumulating in a source rock. There is increasing evidence that kerogen plays a major role in the geochemistry of biomarker compounds, particularly the porphyrins, in source rocks. Several experimental studies have shown that kerogen liberates a variety of biomarkers upon heating (_l-3), but no data on the porphyrins have been presented. Most of the evidence that indicates a kerogen-porphyrin association is indirect and is based on the analysis of porphyrins from sedimentary rocks, bitumens, and petroleums. For example, high molecular weight geoporphyrins (^33) are hypothesized to originate during catagenesis as thermal cracking 0097-6156/87/0344-0110$07.25/0 © 1987 American Chemical Society

Filby and Branthaver; Metal Complexes in Fossil Fuels ACS Symposium Series; American Chemical Society: Washington, DC, 1987.


7.

VAN B E R K E L A N D FU BY

Generation

of Nickel and Vanadyl

Porphyrins

111

o f C-C b o n d s r e l e a s e s p o r p h y r i n s c h e m i c a l l y b o u n d t o t h e k e r o g e n m a t r i x (_4,5) . S t u d i e s o f p o r p h y r i n d i s t r i b u t i o n s i n b i t u m e n s f r o m rocks at d i f f e r e n t degrees o f thermal maturation i n sedimentary b a s i n s (6,7_) h a v e b e e n i n t e r p r e t e d t o i n d i c a t e t h a t s u b s t a n t i a l q u a n t i t i e s o f VOP a r e g e n e r a t e d f r o m k e r o g e n d u r i n g c a t a g e n e s i s . A l s o , B a k e r a n d L o u d a ( 8 ) h a v e p o s t u l a t e d t h a t N i P a n d VOP f o r m v i a d i f f e r e n t pathways i n sediments. The N i P i s c o n s i d e r e d t o f o r m p r i m a r i l y a s f r e e o r s o l v e n t e x t r a c t a b l e s p e c i e s , w h e r e a s VOP f o r m s i n a bound, o r n o n - e x t r a c t a b l e , s t a t e l i n k e d t o kerogen and i s o n l y l i b e r a t e d when t h e t h e r m a l s t r e s s b r e a k s t h e k e r o g e n - V O P l i n k a g e . At t h e p r e s e n t t i m e , t h e r e i s no s a t i s f a c t o r y e x p l a n a t i o n f o r the apparent u n i q u e kerogen enhanced c h e l a t i o n and/or a s s o c i a t i o n o f VOP. I n f a c t , r e c e n t s t u d i e s ( 9 - 1 1 ) h a v e shown t h a t some k e r o g e n s may c o n t a i n s i g n i f i c a n t q u a n t i t i e s o f b o t h o r g a n i c a l l y b o u n d N i a n d V. M o r e o v e r , S p i r o et_ a l . ( 1 1 ) f o u n d t h a t t h e N i / V r a t i o i n t h e k e r o g e n o f some I s r a e l i o i l s h a l e s a n d t h e N i P / V O P r a t i o i n t h e a s s o c i a t e d bitumen were p r o p o r t i o n a l (but independent o f t h e N i and V contents of themineral phase), i n d i c a t i n g possible c o r r e l a t i o n between t h e p o r p h y r i n c o n t e n t s o f t h e bitumen and t h e N i and V concentrations i n the kerogen. The c h e m i c a l s t a t e s o f N i a n d V i n kerogen have n o t been d e t e r m i n e d , b u t a major f r a c t i o n o f b o t h metals i sp r o b a b l y present as s t a b l e t e t r a p y r r o l e complexes. Whether t h e s e complexes a r e c h e m i c a l l y bound t o t h e k e r o g e n m a t r i x ( a l k y l bonds, e s t e r bonds, e t c . ) , t r a p p e d i n a m o l e c u l a r s i e v e t y p e network, or s t r o n g l y adsorbed i s u n c e r t a i n . The m e c h a n i s m o f i n c o r p o r a t i o n o f t h e s e m e t a l i o n s and/or m e t a l complexes i n t o t h e k e r o g e n i s unknown, and t h e d i a g e n e t i c s t a g e d u r i n g w h i c h i n c o r p o r a t i o n t a k e s p l a c e a n d the f a t e o f t h e s e complexes d u r i n g c a t a g e n e s i s h a s n o t been i n v e s tigated. I n t h i s p a p e r , l a b o r a t o r y p y r o l y s i s was u s e d t o s t u d y t h e r e l e a s e o f N i and V complexes from o i l s h a l e kerogens d u r i n g simulated catagenesis. The o b j e c t i v e s o f t h i s s t u d y were: (1) t o d e t e r m i n e t h e amount a n d t y p e o f N i a n d V c o m p l e x e s r e l e a s e d f r o m a kerogen d u r i n g s i m u l a t e d c a t a g e n e s i s , and (2) t o determine t h e r e l a t i o n s h i p s among t h e N i a n d V c o m p l e x e s i n t h e k e r o g e n , t h e comp l e x e s r e l e a s e d f r o m t h e k e r o g e n d u r i n g p y r o l y s i s , a n d t h o s e complexes present i n t h e a s s o c i a t e d o i l shale bitumen. Sequential p y r o l y s i s o f t h e same k e r o g e n a l i q u o t a t i n c r e a s i n g t e m p e r a t u r e s w a s used t o d i s t i n g u i s h between m e t a l complexes i n t h e p y r o l y s a t e which were components o f r e s i d u a l bitumen a s s o c i a t e d w i t h t h e kerogen ( o r s o l u b l e o r g a n i c m a t t e r (OM) o r i g i n a l l y p r e s e n t o n t h e r o c k m a t r i x but w h i c h a s s o c i a t e d w i t h t h e kerogen a f t e r d e m i n e r a l i z a t i o n ) and those complexes g e n e r a t e d d u r i n g t h e r m a l breakdown o f t h e k e r o g e n . The c o n c e n t r a t i o n s o f N i a n d V w e r e d e t e r m i n e d b y i n s t r u m e n t a l neutron a c t i v a t i o n a n a l y s i s (INAA). The p o r p h y r i n c o n t e n t s o f t h e bitumen and kerogen p y r o l y s a t e s were determined by U V - v i s i b l e spectrometry and high-performance l i q u i d chromatography (HPLC). Experimental Samples S e l e c t i o n and P r e p a r a t i o n . M i s s i s s i p p i a n New A l b a n y S h a l e ( H e n r y v i l l e Bed O u t c r o p , C l a r k County, IN) and M i s s i s s i p p i a n D e v o n i a n W o o d f o r d S h a l e ( S p r i n g e r O u t c r o p , C a r t e r C o u n t y , OK) w e r e the sources o f t h e kerogens used i n t h i s study. D e t a i l e d g e o l o g i c a l



112

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

i n f o r m a t i o n o n t h e s e s h a l e s c a n be f o u n d e l s e w h e r e ( 1 2 , 1 3 ) . The s a m p l e p r e p a r a t i o n scheme i s o u t l i n e d i n F i g u r e 1. E a c h s h a l e was g r o u n d t o 200 m e s h a n d t h e n b i t u m e n - I was e x t r a c t e d b y s o n i c a t i o n w i t h t o l u e n e / m e t h a n o l ( 7 : 3 v / v ; 2 mL s o l v e n t / g s h a l e , 6 χ 45 m i n ) a t 40 C. The e x t r a c t s w e r e c o m b i n e d a n d f i l t e r e d ( 0 . 4 5 ym F l u o r o p o r e ) , and t h e s o l v e n t removed u s i n g a r o t a r y e v a p o r a t o r . B i t u m e n - I f r e e s h a l e (BF S h a l e ) was d r i e d i n v a c u o ( 8 0 C) a n d t h e n d e m i n e r a l i z e d u s i n g a p r o c e d u r e s i m i l a r t o t h a t o f D u r a n d and N i c a i s e (14). A f t e r n e u t r a l i z a t i o n o f r e s i d u a l HC1-HF o n t h e k e r o g e n w i t h d i l u t e ΝΉ3 f o l l o w e d b y s e v e r a l w a s h i n g s w i t h d o u b l e d i s t i l l e d H 2 O , t h e k e r o g e n c o n c e n t r a t e was d r i e d i n v a c u o (80°C). The k e r o g e n was t h e n e x t r a c t e d w i t h t o l u e n e / m e t h a n o l ( 7 : 3 v / v ; 2 mL solvent/g k e r o g e n , 6 χ 45 m i n ) t o r e m o v e b i t u m e n ( J L . £ . , b i t u m e n - I I ) l i b e r a t e d d u r i n g t h e a c i d d i g e s t i o n , a n d a g a i n v a c u u m d r i e d (80°C). Bitumen-II was i s o l a t e d u s i n g t h e same p r o c e d u r e a s f o r b i t u m e n - I . Kerogen P y r o l y s i s . The k e r o g e n s w e r e p y r o l y s e d a t c o n s t a n t t e m p e r a t u r e s w i t h i n t h e r a n g e o f 100-450°C i n a 1 L a u t o c l a v e (Autoclave E n g i n e e r s , E r i e , PA) a s shown i n F i g u r e 1. An a l i q u o t o f k e r o g e n t o g e t h e r w i t h 350 mL o f t o l u e n e was a d d e d t o t h e a u t o c l a v e a n d t h e system s e a l e d . The s y s t e m was p u r g e d w i t h n i t r o g e n f o r 5 m i n w i t h c o n s t a n t s t i r r i n g ( 1 0 0 0 r p m ) , p r e s s u r i z e d t o 250 p s i w i t h n i t r o g e n , then brought to the d e s i r e d temperature. The t e m p e r a t u r e o f t h e s y s t e m was a l l o w e d t o e q u i l i b r a t e (~1 h ) , m a i n t a i n e d f o r 5 h , a n d t h e n a l l o w e d t o c o o l t o b e l o w 80°C b e f o r e o p e n i n g t h e s y s t e m . P y r o l y s e d k e r o g e n was i s o l a t e d f r o m t h e p y r o l y s a t e b y c e n t r i f u g a t i o n a n d f i l t r a t i o n ( 0 . 4 5 ym F l u o r o p o r e ) a n d t h e n f u r t h e r e x t r a c t e d b y s o n i c a t i o n w i t h t o l u e n e ( 1 0 0 mL, 3 χ 20 m i n ) a t 40 C ( t o l u e n e / m e t h a n o l (7:3 v/v) i n t h e c a s e o f W o o d f o r d k e r o g e n ) . The filtered e x t r a c t s were c o m b i n e d and e v a p o r a t e d t o d r y n e s s t o y i e l d t h e pyrolysate. The p y r o l y s a t e i n t h i s c a s e i s d e f i n e d a s t h e s o l u b l e o r g a n i c m a t e r i a l l i b e r a t e d from the k e r o g e n w h i c h has a b o i l i n g point greater than that of toluene. The p y r o l y s e d k e r o g e n was vacuum d r i e d (80 C ) , s a m p l e d , and t r a n s f e r r e d t o t h e a u t o c l a v e f o r subsequent p y r o l y s i s at higher temperature. The p y r o l y s i s p r o c e d u r e was t h e n r e p e a t e d . Elemental A n a l y s i s . E l e m e n t a l a n a l y s i s (C,H,N,0) was c a r r i e d o u t C a n a d i a n M i c r o a n a l y t i c a l , LTD ( V a n c o u v e r , BC) u s i n g a C a r l o E r b a M o d e l 1106 E l e m e n t a l Analyzer. X-Ray D i f f r a c t i o n (XRD). XRD p a t t e r n s w e r e o b t a i n e d powder d e f r a c t o m e t e r u s i n g C u - K radiation.

with a

by

Norelco

a

Trace Element A n a l y s i s . C o n c e n t r a t i o n s o f N i and V w e r e d e t e r m i n e d by INAA. Sample a l i q u o t s and a p p r o p r i a t e s t a n d a r d s w e r e w e i g h e d i n t o c l e a n 1.5 mL p o l y v i a l s , r e - e n c a p s u l a t e d i n 7.5 mL p o l y v i a l s , b o t h o f w h i c h w e r e h e a t s e a l e d , and t h e n i r r a d i a t e d i n t h e W a s h i n g t o n S t a t e U n i v e r s i t y TRIGA I I I r e a c t o r . Gamma-ray s p e c t r a w e r e r e c o r d e d u s i n g t h e N u c l e a r D a t a ND 6 7 0 0 G e ( L i ) γ-ray s p e c t r o m e t e r system. The n u c l e a r r e a c t i o n s a n d m e t h o d s u s e d t o r e d u c e γ-ray s p e c t r a t o m e t a l c o n c e n t r a t i o n s were s i m i l a r t o t h o s e o f J a c o b s and F i l b y ( 1 5 ) . C o r r e c t i o n of the kerogen N i or V content to a m i n e r a l - f r e e b a s i s was c a r r i e d o u t i n a m a n n e r s i m i l a r t o t h a t o f V a n B e r k e l a n d F i l b y

(9).


Generation

VAN B E R K E L A N D FILBY


Porphyrins

SHALE 200

I

sonication

mesh toluene/MeOH (7:3v/v)

insoluble


BF

soluble

SHALE

BITUMEN-I

HCL/HF soluble

insoluble

WASTE

ORGANIC

sonication

RESIDUE

toluene/MeOH (7:3v/v)

insoluble

soluble

KEROGEN

Kerogen

BITUMEN-II

0

> t

v N

Autoclave

N

2

0 C H

2

0 C H

3

Pyrolysate

1

Pyrolysate

pyrolysis

insoluble

marcasite > covellite ~ rutile

68.22 6.71 2.24 4.83 1.17 0.05

a

-18 w t % pyrite > marcasite > ammonium c h l o r i d e

o f o r g a n i c n i t r o g e n content i s u n c e r t a i n because o f ammonium c h l o r i d e ( N H ^ C l ) i n t h e k e r o g e n m a t r i x .

M i n e r a l i m p u r i t y c o n t e n t u n c o r r e c t e d f o r o r g a n i c a l l y bound m e t a l contents. O r g a n i c a l l y combined N i and V a l o n e a c c o u n t f o r -0.3 w t % o f t h e apparent m i n e r a l component.


7. VAN B E R K E L A N D FILBY

Table I I .

Nickel

Generation

of Nickel and Vanadyl Porphyrins

a n d V a n a d i u m C o n t e n t o f New A l b a n y a n d W o o d f o r d Kerogen

Trace Element o r Ratio 3

[Ni]

K

[V] (Ni/V)

K

[Ni]

K


K

[v]

M

F

M F K

(Ni/V)

M F K

115

New

Element Content

Albany Shale Kerogen

(yg/g)

Woodford S h a l e Kerogen

2 5 0 0 ± 34 730 ± 16 3.42 + 0.09

505 ± 1 9 3 2 7 0 ± 62 0.154 ± 0.007

2128 ± 8 1 698 ± 26 3.05 ± 0.16

353 ± 3 3 3 2 6 2 ± 97 0.108 ± 0.01

C o n c e n t r a t i o n s ( y g / g ) o f N i a n d V i n t h e k e r o g e n ([Χ]χ) a n d m i n e r a l - f r e e k e r o g e n ([X]MFK)· M i n e r a l - f r e e kerogen v a l u e s were c a l c u l a t e d i n a manner s i m i l a r t o Van B e r k e l and F i l b y ( 9 ) . Ni/V r a t i o s a r eweight/weight r a t i o s .

polymorph, m a r c a s i t e . I n a d d i t i o n t o t h e s e m i n e r a l s , New A l b a n y kerogen a l s o c o n t a i n e d r u t i l e (T1O2) and c o v e l l i t e (CuS). Rutile was a n e x p e c t e d i m p u r i t y , b u t c o v e l l i t e , w h i c h i s s o l u b l e i n h o t HC1, w a s u n e x p e c t e d . However, because o f t h e h i g h c o n c e n t r a t i o n o f Cu i n t h e s h a l e ( 2 3 6 ppm, 1 3 ) a n d p o s s i b l e i n t e r g r o w t h s o f c o v e l l i t e and p y r i t e , t h e s u r v i v a l o f t h e f o r m e r i n t h e r i g o r o u s a c i d d i g e s tion i s probable. In a d d i t i o n t o p y r i t e and m a r c a s i t e , the Woodford kerogen a l s o c o n t a i n e d ammonium c h l o r i d e ( N H 4 C I ) , w h i c h f o r m e d o n t h e k e r o g e n b y r e a c t i o n o f a d s o r b e d HC1 w i t h d i l u t e N H 3 . The p r e s e n c e o f NH4CI i n the kerogen i m p l i e s t h a t t h e o r g a n i c n i t r o g e n content i n t h i s kerogen is overestimated. The N i a n d V c o n t e n t s o f t h e k e r o g e n s a r e g i v e n i n T a b l e I I . New A l b a n y k e r o g e n i s e n r i c h e d i n N i r e l a t i v e t o V, w h e r e a s f o r Woodford kerogen t h e r e v e r s e i s t r u e . Correction o f t h ekerogen N i o r V c o n t e n t s t o a m i n e r a l - f r e e b a s i s i s s m a l l ( b i t u m e n - I v e r s u s b i t u m e n I + I I ) . Bitumen composition i s a l s o a l t e r e d because o f the d i f f e r e n t compositions o f bitumen-I andbitumen-II , the N i and V concentrations are d i f f e r e n t ) . B i t u m e n - I I i s s o l u b l e OM w h i c h s t r o n g l y a s s o c i a t e s w i t h t h e mineral matrix and i s therefore d i f f i c u l t t o extract before acid digestion. J e o n g a n d K o b y l i n s k i ( 1 9 ) h a v e shown t h a t a s u b s t a n t i a l f r a c t i o n o f s o l u b l e OM i n a s h a l e f o r m s a k e r o g e n - m i n e r a l interf a c i a l l a y e r through chemical bonding o r p h y s i s o r p t i o n t o carbonate and, more s i g n i f i c a n t l y , s i l i c a t e m i n e r a l s . D i s s o l u t i o n o f the mineral matrix i n acid s o l u t i o n r e s u l t s i n i n t e r a c t i o n o f these s o l u b l e p o l a r organic s p e c i e s w i t h the kerogen. S p i r o (20) a l s o s h o w e d t h a t t h e s o l u b l e OM a s s o c i a t e d w i t h t h e m i n e r a l s w a s s y s t e m a t i c a l l y d i f f e r e n t i n composition from the bitumen. This difference was e x p l a i n e d b y t h e p h y s i c a l p r o p e r t i e s o f t h e c o m p o u n d s , a n d b y t h e c a t a l y s i s ( o r i n h i b i t i o n ) o f c e r t a i n r e a c t i o n s o f t h e s e compounds by t h e a s s o c i a t e d m i n e r a l p h a s e s . P y r o l y s i s a t l o w t e m p e r a t u r e (-100 C) r e s u l t s i n f u r t h e r r e m o v a l o f s o l u b l e OM a s s o c i a t e d w i t h t h e k e r o g e n . This m a t e r i a l i s probably s i m i l a r t o bitumen-II. A t t h i s p o i n t , the kerogen i s r e l a t i v e l y f r e e o f a n y s o l u b l e OM o r r e s i d u a l b i t u m e n ( p y r o l y s a t e 1 i s -3.5 w t % a n d -9.0 w t % o f t h e t o t a l s o l u b l e OM e x t r a c t e d f r o m New A l b a n y a n d Woodford s h a l e s , r e s p e c t i v e l y ) . P y r o l y s i s a t higher temperatures begins t o depolymerize the kerogen m a t r i x . T h e s o l u b l e OM p r o d u c e d i s e i t h e r c l e a v e d from t h e k e r o g e n m a t r i x b y bond r u p t u r e o r i s m a t e r i a l so s t r o n g l y adsorbed o r a s s o c i a t e d w i t h the kerogen m a t r i x to be d e f i n e d a s p a r t o f i t ( i n the c o n v e n t i o n a l sense o f s o l u b i l i t y ) , and i s o n l y s o l u b i l i z e d u n d e r t h e s e more d r a s t i c c o n d i t i o n s . Mckay ( 2 1 ) s u g g e s t e d t h a t t h e k e r o g e n o f some s h a l e s i s n o t a n i n s o l u b l e polymer, but m a t e r i a l o f s i m i l a r c o m p o s i t i o n t o the b i t u m e n , w h i c h can o n l y be s o l u b i l i z e d under c o n d i t i o n s d i f f e r e n t than those r e q u i r e d t o e x t r a c t the bitumen component. Neither kerogen produces s u b s t a n t i a l q u a n t i t i e s o f p y r o l y s a t e b e l o w 3 0 0 C. Y i e l d s o f p y r o l y s a t e become s u b s t a n t i a l a t 400°C a n d 4 5 0 C; h o w e v e r , t h e p r e s e n c e o f t o l u e n e p y r o l y s i s p r o d u c t s i n c r e a s e s the p y r o l y s a t e y i e l d . A l s o , a t 450 C the nature o f the p y r o l y s a t e changes from a d a r k , v i s c o u s b i t u m e n t o a n amber, n o n - v i s c o u s material. Other p y r o l y s i s s t u d i e s u s i n g t o l u e n e a s the s o l v e n t have shown l i t t l e e v i d e n c e o f t h e r m a l d e g r a d a t i o n o f t h e p y r o l y s a t e s p r o d u c e d a t 350 C may n o t b e e n t i r e l y


118



representative of the organic composed.

c o n s t i t u e n t s o f which the kerogen i s

E f f e c t o f P y r o l y s i s on t h e K e r o g e n C o m p o s i t i o n . The c h a n g e i n t h e elemental composition o f the kerogens a f t e r p y r o l y s i s i spresented i n T a b l e I V a n d shown g r a p h i c a l l y i n F i g u r e 2 b y p l o t t i n g t h e H/C v e r s u s 0/C r a t i o s o f t h e k e r o g e n a n d p y r o l y s e d k e r o g e n s . For both New A l b a n y a n d W o o d f o r d k e r o g e n s , t h e p y r o l y s i s - i n d u c e d m a t u r a t i o n f o l l o w s t h e t y p i c a l p a t t e r n o f d e c r e a s i n g H/C a n d 0/C r a t i o s a s thermal maturation increases. The anomalous b e h a v i o r o f Woodford k e r o g e n b e t w e e n 103°C a n d 200°C ( 0 / C r a t i o s g r e a t e r t h a n t h e o r i g i n a l k e r o g e n ) may b e t h e r e s u l t o f a d s o r b e d m e t h a n o l w h i c h w a s u s e d w i t h toluene t o e x t r a c t the p y r o l y s a t e s from t h i s kerogen. Pyrolysates f r o m New A l b a n y k e r o g e n w e r e e x t r a c t e d u s i n g o n l y t o l u e n e . Although t h e e l e m e n t a l c o m p o s i t i o n o f t h e kerogen changes a t each p y r o l y s i s t e m p e r a t u r e , t h e l a r g e s t changes o c c u r above 300 C which i s the point at which the kerogens begin t o generate substant i a l quantities of pyrolysate. E f f e c t o f P y r o l y s i s on t h e N i and V C o n t e n t s o f t h e Kerogen and Pyrolysates. T h e N i a n d V c o n t e n t s o f New A l b a n y a n d W o o d f o r d k e r o g e n a n d p y r o l y s e d k e r o g e n s a r e shown i n T a b l e V. B e l o w 4 5 0 C, the ( N i / V ) K r a t i o i s c o n s t a n t ( w i t h i n ± 3 s.d. o f o r i g i n a l k e r o g e n v a l u e ) , b u t d r a m a t i c a l l y i n c r e a s e s a t 450 C i n b o t h s h a l e s . M F

Table IV.

Elemental Composition o f Kerogens

Pyrolysis T e m p e r a t u r e (°C)

Sample

%C

and P y r o l y s e d

Kerogens

%H

%N

%0

5.74 5.82 5.71 5.47 5.29 4.51 3.32

2,.67 2..73 2..72 2..71 2,.75 2..93 3..01

6.87 6.79 5.98 5.64 5.57 5.34 4.45

6.71 6.59 6.12 6.13 6.00 5.07 3.15

2..24 2..04 1 97 2..02 2. ,12 2. ,34 2. ,81

4.83 5.08 5.16 4.46 4.09 3.92 3.07

New A l b a n y Kerogen Kerogen Kerogen Kerogen Kerogen Kerogen Kerogen

1 2 3 4 5 6

110 210 300 350 400 450

67.90 68.62 70.37 70.98 72.15 72.71 73.85 Woodford

Kerogen Kerogen Kerogen Kerogen Kerogen Kerogen Kerogen

0

_

1 2 3 4 5 6

103 200 300 351 400 450

68.22 67.42 64.64 68.17 69.72 69.11 70.87




New

Generation

Albany

(•)

Woodford

(•)


•

Porphyrins

103°C Ο 200°C

35 1°C •

1 1 0 ° C

300 C

/ 210 C 300°C B

/ À nn°r

^

A

e

a 300°c

450°C

0.0

I

«

3.0

«

1

4.0

5.0

O / C x 100

'

"

'

6.0

7.0

8.0

(atomic)

F i g u r e 2. V a r i a t i o n o f t h e e l e m e n t a l kerogens w i t h s e q u e n t i a l p y r o l y s i s .

composition of


120


T a b l e V.

Nickel

and Vanadium C o n c e n t r a t i o n s and N i / V R a t i o s f o r Kerogens and P y r o l y s e d Kerogens

Pyrolysis Temperature

(yg/g)

u

< c)

Sample


M i n e r a l - F r e e Kerogen Concentration

[ N i ]

( N i / V )

MFK

MFK

New A l b a n y Kerogen Kerogen Kerogen Kerogen Kerogen Kerogen Kerogen

0

_

1 2

110 210 300 350 400 450

3 4 5 6

2128 ± 81 2187 2209 2289 2297 2729 3132

6 9 8 ± 26 669 676 730 765 830 851

3.05 ± 0.16 3.27 3.27 3.14

3 2 6 2 ± 97 3357 3663 3609 3513 4541 5479

0.108 ± 0.01 0.115 0.103 0.100 0.115 0.120 0.163

3.00 3.29 3.68

Woodford Kerogen Kerogen Kerogen Kerogen Kerogen Kerogen Kerogen

0

-

1 2 3 4 5 6

103 200 300 350 400 450

353 + 33 385 378 362 403 543 892

C o n c e n t r a t i o n s (yg/g) o f N i and V i n t h e m i n e r a l - f r e e kerogen ([X]MFK)» M i n e r a l - f r e e k e r o g e n v a l u e s were c a l c u l a t e d i n a manner s i m i l a r t o Van B e r k e l and F i l b y ( 9 ) . M i n e r a l - f r e e N i and V c o n t e n t s o f t h e p y r o l y s e d k e r o g e n s were c a l c u l a t e d by m u l t i p l y i n g the measured m e t a l content by t h e percent o f t h e t o t a l m e t a l c o n t e n t w h i c h was o r g a n i c . The o r g a n i c f r a c t i o n o f t h e m e t a l was estimated by a d j u s t i n g t h e o r g a n i c f r a c t i o n o f t h e m e t a l i n k e r o g e n 0 t o a c c o u n t f o r t h e amount o f t h e e l e m e n t e x p e l l e d (organic) w i t h t h e p y r o l y s a t e a t each temperature. Percent r e l a t i v e s t a n d a r d d e v i a t i o n (% RSD) o f t h e p y r o l y s e d k e r o g e n v a l u e s i s .> t h e % RSD o f t h e o r i g i n a l k e r o g e n v a l u e s i n e a c h r e s p e c t i v e column.



7.


Generation


121

A f t e r t h e k e r o g e n s t a r t s t o t h e r m a l l y b r e a k down (~300°C), t h e c o n centration o f both metals i n the residue increases s i g n i f i c a n t l y above t h a t i n t h e o r i g i n a l kerogen. This i n d i c a t e s that as catagenes i s proceeds, themetals p r o g r e s s i v e l y concentrate i n t h e i n s o l u b l e kerogen f r a c t i o n . The p e r c e n t a g e o f t h e N i a n d V o r g a n i c a l l y b o u n d i n t h e k e r o g e n which i sexpelled with the pyrolysates (i-J^., expulsion y i e l d ) i s shown i n T a b l e V I . E x p u l s i o n y i e l d s f o r b o t h e l e m e n t s a r e l o w a t each temperature. T h e maximum e x p u l s i o n y i e l d f o r e a c h k e r o g e n w a s observed f o r t h e element i n h i g h e s t c o n c e n t r a t i o n i n t h a t kerogen ( N i f o r New A l b a n y ; V f o r W o o d f o r d ) . A s s e e n i n F i g u r e 3, t h e e x p u l s i o n y i e l d s o f b o t h e l e m e n t s show a p a r a l l e l b e h a v i o r . In fact, f o r New A l b a n y k e r o g e n t h e e x p u l s i o n y i e l d s f o r N i a n d V a t e a c h t e m p e r a t u r e a r e n o t s t a t i s t i c a l l y d i f f e r e n t (± 3 s . d . ) . F o r Woodford kerogen, however, t h e e x p u l s i o n y i e l d s a r e d i f f e r e n t w i t h g r e a t e r V e x p u l s i o n t h a n N i a t e a c h t e m p e r a t u r e , e x c e p t 4 5 0 C. H o w e v e r , a s p y r o l y s i s temperature i n c r e a s e s , t h e N i e x p u l s i o n y i e l d does i n c r e a s e r e l a t i v e t o t h e V e x p u l s i o n y i e l d (New A l b a n y k e r o g e n a p p e a r s t o show a s i m i l a r t r e n d ) . Since f o r both kerogens t h e e x p u l s i o n r a t e s o f N i and V (yg e l e m e n t / g TOC) a t e a c h t e m p e r a t u r e v a r y , t h e c o n c e n t r a t i o n s o f t h e elements i n t h e p y r o l y s a t e s vary. F o r p y r o l y s i s between 200 C and 4 0 0 C, t h e N i / V r a t i o s o f t h e New A l b a n y p y r o l y s a t e s a r e e q u a l t o t h e corresponding kerogen ( N i / V ) - ^ ^ r a t i o s w i t h i n t h e experimental e r r o r . However, t h e N i / V r a t i o s o f t h e bitumen ( I , I I , o r I + I I ) and t h e p y r o l y s a t e s produced a t these temperatures a r e n o t equal. In the case o f Woodford, t h e N i / Vr a t i o o f t h e p y r o l y s a t e s produced i n t h i s temperature range i s lower than t h e kerogen ( N i / V ) j ^ r a t i o , but equal t o t h e N i / V r a t i o o f bitumen-I. It i spossible that the organic Ni/V r a t i o o f the i n s i t u k e r o g e n i s a l t e r e d b y HC1-HF d e m i n e r a l i z a t i o n o f t h e s h a l e . This e f f e c t may e x p l a i n why t h e r e a p p e a r s t o b e n o s y s t e m a t i c c o r r e l a t i o n among t h e N i / V r a t i o s o f t h e b i t u m e n , p y r o l y s a t e s , a n d k e r o g e n c o n c e n t r a t e b e t w e e n t h e two s a m p l e s . However, i n t h e absence o f a documented model f o r t h e a s s o c i a t i o n o f m e t a l s p e c i e s w i t h t h e k e r o g e n , i t cannot be d e t e r m i n e d g e o c h e m i c a l l y whether t h e N i / V r a t i o o f t h e b i t u m e n , p y r o l y s a t e s , a n d k e r o g e n s h o u l d b e t h e same o r different. F K

Metalloporphyrins. UV-visible s p e c t r a l examination of the pyrolys a t e s r e v e a l e d t h e p r e s e n c e o f N i P a n d VOP. F i g u r e 4 s h o w s t h e s p e c t r a o f b i t u m e n - I a n d t h e p y r o l y s a t e s i n t o l u e n e a t t h e same concentrations. T h e New A l b a n y s a m p l e s c o n t a i n s i g n i f i c a n t q u a n t i t i e s o f b o t h N i P a n d VOP, b u t t h e N i P / V O P r a t i o i n c r e a s e s w i t h i n c r e a s i n g temperature from bitumen-I t o t h e p y r o l y s a t e s a s i n d i c a t e d by t h e a b s o r b a n c e a t t h e N i P a n d VOP S o r e t p e a k s ( 3 9 6 a n d 4 1 0 nm, r e s p e c tively). T h i s same t r e n d i s s e e n i n t h e N i / V r a t i o o f t h e p y r o l y s a t e s , w h i c h s u g g e s t s t h a t t h e NiP/VOP r a t i o and t h e N i / V r a t i o o f the p y r o l y s a t e s a r e p r o p o r t i o n a l . F u r t h e r support f o r t h i s c o n t e n t i o n i s shown i n F i g u r e 5 w h e r e t h e c o m b i n e d N i P a n d VOP Soret peak i n t e g r a t e d absorbance i sp l o t t e d v e r s u s t h e combined c o n c e n t r a t i o n o f N i and V i n the p y r o l y s a t e s . The e x c e l l e n t c o r r e l a t i o n o f S o r e t p e a k a b s o r b a n c e w i t h m e t a l c o n t e n t ( r = 0.98) i n d i c a t e s t h a t t h e NiP/VOP r a t i o o f t h e p y r o l y s a t e s i s p r o p o r t i o n a l



VI.

103 200 300 350 400 450

--

-

96.5

1.63 8.36 9.52 31.45 7.7

16.57 1.50 18.07 1.41

165.1 24.4

-

30.0 126.5 2.96 25.81 115.8

Expulsion yield defined i n the kerogen e x p e l l e d

-

5.19 0.633

0.810 3.69

0.272 0.286 1.43 1.79 5.44 0.98

-

3.34+0.20 7.16+0.33

1.15+0.06 1.69+0.31 1.24+0.07 1.62+0.06 3.20+0.08 3.63+0.19

Ni/V

0. 062+0.008 0. 040+0.003 0. 059+0.006 0.520 0. 057+0.002 0.603 0. 054+0.003 2.38 0. 062+0.004 2.91 0. 062+0.005 8.00 0. 078+0.003 0.95 0. 012+0.02

-

4.67 0.291

0.1774 0.828 3.32

V MFK

-

0.108+0.01 0.115 0.103 0.100 0.115 0.120 0.163

_

3.27 3.14 3.00 3.29 3.68

3.05+0.16 3.27

_

_

( N 1 / V )

i n the Bitumens,

a s w e i g h t p e r c e n t o f t h e o r g a n i c a l l y combined with the p y r o l y s a t e .

N i and V

TOC f o r t h e b i t u m e n s and p e r g k e r o g e n TOC

269 37.66 307 24.85 30.0 134.7 153.8 403.0 62.5

Woodford

-

49.5 3.32

8.08 31.9

0.0946

Albany

New 84.2 17.8 102.0 1.82

Ni

1 0 0

Yield

W

Expulsion (ug X/ug

V

Expulsion rate c a l c u l a t e d per g shale f o r the kerogen samples.

Bitumen-I Bitumen-II Bitumen-I+II Pyrolysate 1 Pyrolysate 2 Pyrolysate 3 Pyrolysate 4 Pyrolysate 5 Pyrolysate 6

400 450

210 300 350

110

Ni

E x p u l s i o n Rate (ug X/g TOC)

R a t e s and Y i e l d s f o r N i c k e l and Vanadium P y r o l y s a t e s , and R e s p e c t i v e Kerogens

Pyrolysis Temperature (°C)

Expulsion

Bitumen-I Bitumen-II Bitumen-I+II Pyrolysate 1 Pyrolysate 2 Pyrolysate 3 Pyrolysate 4 Pyrolysate 5 Pyrolysate 6

Sample

Table


7.


Generation of Nickel and Vanadyl Porphyrins

123


e.o

100

200 300 Pyrolysis Temperature ( C)

400

500

200 300 Pyrolysis Temperature ( C)

400

500

e

8.0

6.0

2.0

0.0

e

F i g u r e 3. W e i g h t p e r c e n t o f o r g a n i c N i a n d V i n New A l b a n y ( A ) and W o o d f o r d (B) k e r o g e n e x p e l l e d w i t h t h e p y r o l y s a t e ( E x p u l s i o n Y i e l d ) a t each p y r o l y s i s temperature ( E r r o r b a r s = ± 1 s.d.).




124



Generation



7.


125

126



t o t h e N i / V r a t i o ; h o w e v e r , t h e [ N i ] a n d [V] n e e d n o t be e q u a l t o t h e [ N i P ] and [VOP], r e s p e c t i v e l y (i.e_. , " n o n - p o r p h y r i n " N i and V may be p r e s e n t , b u t i n t h e same r e l a t i v e p r o p o r t i o n s t o N i P a n d VOP in each sample). The d e v i a t i o n o f t h e b i t u m e n - I p o i n t on t h i s p l o t i n d i c a t e s t h a t t h e f r a c t i o n o f N i and V i n t h e b i t u m e n p r e s e n t as p o r p h y r i n complexes i s l e s s than that i n the p y r o l y s a t e s . The U V - v i s i b l e s p e c t r a o f W o o d f o r d b i t u m e n - I a n d pyrolysates show t h e p r e s e n c e o f o n l y VOP. H o w e v e r , c o l u m n c h r o m a t o g r a p h y on S1O2 a l l o w s s e p a r a t i o n o f a N i P f r a c t i o n f r o m t h e s a m p l e s . Because the NiP Soret peak i s not d e t e c t a b l e i n the b u l k samples, a v i s u a l c o r r e l a t i o n o f N i P / V O P r a t i o w i t h N i / V r a t i o c a n n o t be made. However, p l o t t i n g Soret peak a b s o r b a n c e v e r s u s m e t a l content of the p y r o l y s a t e s , a s f o r t h e New A l b a n y s a m p l e s , g i v e s a s t r a i g h t l i n e p l o t ( r = 0.96) i n d i c a t i n g t h a t t h e NiP/VOP r a t i o o f the p y r o l y s a t e s i s p r o p o r t i o n a l to the Ni/V r a t i o . In t h i s case, the p l o t i n d i c a t e s t h a t t h e f r a c t i o n o f N i and V i n t h e b i t u m e n p r e s e n t a s p o r p h y r i n complexes i s g r e a t e r than that i n the p y r o l y s a t e s . F o r New A l b a n y k e r o g e n ^ t h e N i / V r a t i o o f t h e p y r o l y s a t e s p r o d u c e d b e t w e e n 200 C a n d 400 C i s a p p r o x i m a t e l y e q u a l t o t h e (Ni/V) ratio. S i n c e t h e N i / V r a t i o and NiP/VOP r a t i o i n t h i s t e m p e r a t u r e r a n g e a r e p r o p o r t i o n a l , t h e k e r o g e n m u s t be generating t h e N i P a n d VOP i n t h e same r a t i o a s t h e i r c o n t e n t s i n t h e k e r o g e n (ji.e:. , ( N I / V ) M F r a t i o ~ N i P / V O P r a t i o o f t h e k e r o g e n ) . Interest i n g l y , t h e s e r a t i o s a r e o v e r 2.5 t i m e s t h a t o f t h e b i t u m e n - I N i / V ratio. Over t h i s t e m p e r a t u r e range, however, the Ni/V r a t i o s of b i t u m e n - I and t h e p y r o l y s a t e s f o r W o o d f o r d a r e e q u a l and p r o p o r t i o n a l t o the NiP/VOP r a t i o o f the p y r o l y s a t e s , but d i f f e r e n t from the (Ni/V)j4pK r a t i o . The r e a s o n f o r t h e d i f f e r e n t b e h a v i o r o f t h e two k e r o g e n s i s n o t o b v i o u s , b u t may r e f l e c t d i f f e r e n c e s i n t h e s p e c i a t i o n a n d m o d e s o f a s s o c i a t i o n f o r t h e N i a n d V i n t h e New A l b a n y a n d Woodford kerogens. M F K

K

The p o r p h y r i n c o m p o s i t i o n s o f b i t u m e n - I a n d t h e p y r o l y s a t e s w e r e i n v e s t i g a t e d u s i n g HPLC ( 1 7 ) . R e l a t i v e abundances of f o u r v a n a d y l p o r p h y r i n s ( C 2 g t i o , C 2 9 e t i o , C 3 1 D P E P , and C 3 2 D P E P ) w e r e measured i n each sample (see T a b l e V I I ) . Porphyrin compositions of b i t u m e n - I and t h e p y r o l y s a t e s a r e d i f f e r e n t and c h a n g e w i t h p y r o l y s i s temperature. The n a t u r e o f t h e c o m p o s i t i o n a l c h a n g e i s s i m i l a r f o r t h e New A l b a n y a n d W o o d f o r d s a m p l e s . As p y r o l y s i s t e m p e r a t u r e i n c r e a s e s , two m a j o r c h a n g e s i n p o r p h y r i n d i s t r i b u t i o n are noted: (1) t h e r e l a t i v e a b u n d a n c e o f t h e l o w e r c a r b o n number p o r p h y r i n i n b o t h p o r p h y r i n s e r i e s i n c r e a s e s , and ( 2 ) t h e a b u n d a n c e o f e t i o p o r p h y r i n i n c r e a s e s r e l a t i v e t o DPEP. I n t e r p r e t a t i o n o f t h e s e changes must t a k e i n t o a c c o u n t not o n l y the p o s s i b l e g e n e r a t i o n of d i f f e r e n t p o r p h y r i n s from the kerogen at d i f f e r e n t t e m p e r a t u r e s , but a l s o t h e r m a l a l t e r a t i o n o f b o t h the s o l v e n t s o l u b l e and k e r o g e n - a s s o c i a t e d porphyrins. e

Discussion The e f f e c t o f HC1-HF d e m i n e r a l i z a t i o n o f t h e s h a l e o n t h e t r a c e element c o n t e n t o f t h e i s o l a t e d k e r o g e n c o n c e n t r a t e has not been assessed. However, b o t h k e r o g e n samples c o n t a i n h i g h concentrations o f o r g a n i c a l l y c o m b i n e d N i a n d V. V a r i a b l e amounts of m i n e r a l i m p u r i t y i n the kerogen samples w i l l cause the c a l c u l a t e d m i n e r a l -


7.

Generation


Table V I I .


R e l a t i v e Abundance of Four V a n a d y l P o r p h y r i n s i n B i t u m e n - I and t h e P y r o l y s a t e s a


R e l a t i v e Abundance C g.etio

Sample

2

C

2 9

etio

C DPEP 3 1

(%) C DPEP 3 2

New A l b a n y Bitumen-I Pyrolysate Pyrolysate Pyrolysate Pyrolysate Pyrolysate Pyrolysate

1 2 3 4 5 6

(110°C) (210°C) ( 3 0 0 C) (350°C) (400°C) ( 4 5 0 C)

13.6 25.0 24.5 40.2 93.2 100 100

21.1 23.7 23.1 43.3 100 68.2 56.5

40.4 62.9 66.4 82.0 83.2 50.9 60.1

100 100 100 100 87.4 34.7 56.5

Woodford Bitumen-I Pyrolysate Pyrolysate Pyrolysate Pyrolysate Pyrolysate Pyrolysate

a

1 2 3 4 5 6

(103°C) (200°C) (300°C) (350°C) (400°C) (450°C)

21.0 26.4 25.9 24.2 35.2 100 100

DPEP = d e o x o p h y l l o e r y t h r o e t i o

29.0 24.4 24.1 32.3 35.8 64.2 37.0

82.3 100 100 96.8 100 90.2

porphyrin; etio

= etio

100 91.4 92.0 100 97.4 57.5

porphyrin.


111

128



f r e e kerogen t r a c e element c o n t e n t s to d i f f e r because as the m i n e r a l i m p u r i t y content of the kerogen i n c r e a s e s , the t r a c e element content of the kerogen i s d i l u t e d . T h i s e f f e c t c a n be o v e r c o m e b y e x p r e s s i n g c o n c e n t r a t i o n s p e r g o f k e r o g e n TOC i n s t e a d o f p e r g o f kerogen. However, i f k e r o g e n t r a c e element d a t a a r e e x p r e s s e d as e l e m e n t a l r a t i o s ( e . j * . , N i / V ) t h e m i n e r a l d i l u t i o n e f f e c t i s o f no consequence. The e f f e c t o f v a r i o u s d e m i n e r a l i z a t i o n p r o c e d u r e s on the t r a c e element content of kerogen i s c u r r e n t l y under i n v e s t i g a t i o n in this laboratory. D u r i n g t h e s i m u l a t e d c a t a g e n e s i s N i P a n d VOP w e r e g e n e r a t e d from the kerogens i m p l y i n g t h a t the concept of s e l e c t i v e kerogen b i n d i n g o f VOP p r o p o s e d b y B a k e r a n d L o u d a (8) n e e d s t o be r e v i s e d . S i n c e b o t h N i P a n d VOP a r e s h o w n t o a s s o c i a t e w i t h t h e k e r o g e n , i t would a p p e a r t h a t t h e d e p o s i t i o n a l e n v i r o n m e n t o f t h e s e d i m e n t and t h e p o s t - d e p o s i t i o n a l e v o l u t i o n o f t h e k e r o g e n a r e more i m p o r t a n t f a c t o r s i n t h e k e r o g e n - p o r p h y r i n a s s o c i a t i o n t h a n any c h e m i c a l p r o p e r t y o f e i t h e r N i P o r VOP f a v o r i n g k e r o g e n e n h a n c e d c h e l a t i o n or association. The d a t a f r o m t h i s s t u d y s u g g e s t t h a t b o t h N i P a n d VOP a s s o c i a t e w i t h t h e k e r o g e n i n a s i m i l a r m a n n e r . The most l i k e l y modes o f a s s o c i a t i o n a r e : - Physisorption of discrete porphyrins - Chemisorption of discrete porphyrins - Molecular sieve trapping of discrete porphyrins - Chemical bonding of p o r p h y r i n s to the kerogen through a l k y l bonds, e s t e r l i n k a g e s , e t c . or t h r o u g h a x i a l bonding to the metal ion. Any " n o n - p o r p h y r i n " N i and V c o m p l e x e s g e n e r a t e d f r o m t h e kerogen are probably part of the asphaltene f r a c t i o n of the p y r o l y s a t e and, t h e r e f o r e , would bear a c l o s e resemblance t o the "nonp o r p h y r i n " complexes t h a t have been d e s c r i b e d i n a s p h a l t e n e s ( 2 4 ) . T h e s e a s p h a l t e n e m e t a l c o m p l e x e s h a v e b e e n c o n s i d e r e d t o be e i t h e r d i s c r e t e complexes ( a d s o r b e d , c h e m i s o r b e d , o r a c t u a l l y bound c h e m i c a l l y to the asphaltenes) or part of the asphaltene s t r u c t u r e . H o w e v e r , t h e y may be p o r p h y r i n s i n o n e o f t h e a s s o c i a t i o n m o d e s a b o v e ( o r y e t a n o t h e r ) w h i c h c a n n o t be l i b e r a t e d f r o m t h e k e r o g e n o r a s p h a l t e n e as a d i s c r e t e p o r p h y r i n s p e c i e s . T o o u l a k o u and F i l b y (25) h a v e shown t h a t t h i s i s t h e c a s e f o r a t l e a s t 2 5 % o f t h e V i n A t h a b a s c a o i l sand a s p h a l t e n e s . A c o m p a r i s o n o f t h e VOP c o m p o s i t i o n o f b i t u m e n - I a n d t h e p y r o l y s a t e s r e v e a l s a g e n e r a l s h i f t t o l o w e r c a r b o n number f o r e t i o and DPEP t y p e p o r p h y r i n s , a n d a n a p p a r e n t i n c r e a s e i n e t i o r e l a t i v e t o DPEP t y p e p o r p h y r i n s a s p y r o l y s i s t e m p e r a t u r e i n c r e a s e s . It is p o s s i b l e t h a t k e r o g e n g e n e r a t e s p o r p h y r i n s o f l o w e r c a r b o n number as p y r o l y s i s t e m p e r a t u r e i n c r e a s e s . Lower c a r b o n number f o r a g i v e n porphyrin type r e s u l t s i n increased p o l a r i t y . Thus, more p o l a r p o r p h y r i n s may be g e n e r a t e d p r e f e r e n t i a l l y a t h i g h e r p y r o l y s i s temperatures because of a s t r o n g e r a s s o c i a t i o n w i t h kerogen than h i g h e r c a r b o n number s p e c i e s . However, d e a l k y l a t i o n o f p o r p h y r i n s d u r i n g t h e r m a l m a t u r a t i o n has been demonstrated i n o t h e r l a b o r a t o r y s t u d i e s (26-29) and i s c o n s i s t e n t w i t h p o r p h y r i n d a t a o b t a i n e d from the a n a l y s i s o f bitumens from sample s u i t e s o f i n c r e a s i n g m a t u r a t i o n (6,7,28). T h e r e f o r e , t h e s h i f t t o l o w e r c a r b o n number p o r p h y r i n s a s p y r o l y s i s t e m p e r a t u r e i n c r e a s e s may be a s e c o n d a r y t h e r m a l e f f e c t which a l t e r s the p o r p h y r i n s as they are generated from the kerogen.



7. VAN B E R K E L A N D FILBY

Generation


129

The a p p a r e n t i n c r e a s e i n e t i o r e l a t i v e t o DPEP t y p e p o r p h y r i n s w i t h i n c r e a s i n g p y r o l y s i s t e m p e r a t u r e ( m a t u r a t i o n ) must be i n t e r p r e t e d w i t h c a u t i o n s i n c e t h i s t r e n d i s based on a n a l y s i s o f o n l y f o u r m e m b e r s o f t h e VOP s e r i e s i n t h e s a m p l e s . The EDPEP/Zetio r a t i o d e t e r m i n e d f r o m t h e DPEP a n d e t i o m a s s s p e c t r a l e n v e l o p e s i s a more r e l i a b l e i n d i c a t o r o f a c o m p o s i t i o n a l change a n d work i s i n progress t o determine t h i s r a t i o f o r both metalloporphyrins. The a p p a r e n t i n c r e a s e i n e t i o r e l a t i v e t o DPEP t y p e p o r p h y r i n s with increasing temperature has several possible explanations: (1) E t i o p o r p h y r i n s a r e p r e f e r e n t i a l l y a s s o c i a t e d w i t h k e r o g e n . Therefore, t h e kerogen p y r o l y s a t e i senriched i n e t i o type p o r p h y r i n s r e l a t i v e t o t h e bitumen. I t h a s been suggested t h a t o x i d a t i v e c l e a v a g e o f t h e DPEP i s o c y c l i c r i n g p r o d u c e s f u n c t i o n a l i z e d e t i o intermediates which could bind t o t h e kerogen m a t r i x (30). ( 2 ) DPEP a n d e t i o t y p e p o r p h y r i n s a r e g e n e r a t e d f r o m t h e k e r o g e n a t t h e same r a t e a t e a c h t e m p e r a t u r e , b u t : ( a ) DPEP p o r p h y r i n s a r e thermally converted t o e t i o porphyrins after being generated, o r ( b ) DPEP p o r p h y r i n s a r e t h e r m a l l y d e g r a d e d a t a f a s t e r r a t e t h a n e t i o porphyrins. Recent work (6,31) i n d i c a t e s t h a t t h e t h e r m a l c o n v e r s i o n o f DPEP t o e t i o i s o n l y a m i n o r s o u r c e o f e t i o t y p e p o r p h y r i n s . P r e f e r e n t i a l t h e r m a l d e g r a d a t i o n o f DPEP v e r s u s e t i o t y p e p o r p h y r i n s h a s b e e n shown i n t h e l a b o r a t o r y (31) a n d i s t h e more p l a u s i b l e e x p l a n a t i o n o f t h e two. ( 3 ) T h e s h i f t t o l o w e r c a r b o n n u m b e r (e._g. , d e a l k y l a t i o n ) o c c u r s m o r e r a p i d l y f o r t h e e t i o r e l a t i v e t o t h e DPEP t y p e p o r p h y r i n s . However, i f t h e e n t i r e homologous s e r i e s e n v e l o p e f o r b o t h p o r p h y r i n t y p e s s h i f t s t o l o w e r c a r b o n number t h e Z D P E P / E e t i o r a t i o w i l l n o t change. Of t h e e x p l a n a t i o n s a b o v e , p r e f e r e n t i a l d e g r a d a t i o n o f k e r o g e n g e n e r a t e d DPEP t y p e p o r p h y r i n s r e l a t i v e t o e t i o t y p e p o r p h y r i n s i s p r o b a b l y t h emajor mechanism p r o d u c i n g t h e changes i n c o m p o s i t i o n . The d a t a i n d i c a t e t h a t b o t h t y p e s o f p o r p h y r i n a r e p r e s e n t i n t h e s a m p l e s up t o a t l e a s t 400°C. N o t u n t i l 200-300°C d o e s t h e r a p i d change i n r e l a t i v e abundance o f t h e two p o r p h y r i n t y p e s a p p e a r . B u r k o v a e t a l . ( 3 1 ) showed t h a t s u b s t a n t i a l c h a n g e s i n D P E P / e t i o r a t i o s t a k e p l a c e w i t h t e m p e r a t u r e s a s l o w a s 200-250 C due t o p r e f e r e n t i a l d e g r a d a t i o n . Another i n d i c a t i o n t h a t t h i s change i s d u e t o t h e r m a l d e g r a d a t i o n comes f r o m t h e r e l a t i v e i n c r e a s e i n N i expulsion yield relative t o V expulsion yield with increasing p y r o l y s i s temperature. R o s s c u p a n d Bowman ( 3 2 ) s h o w e d t h a t VOP w a s more t h e r m a l l y l a b i l e t h a n N i P ; h e n c e , t h e d e c r e a s e i n V e x p u l s i o n y i e l d w i t h i n c r e a s i n g p y r o l y s i s t e m p e r a t u r e may b e d u e t o p r e f e r e n t i a l d e s t r u c t i o n o f l i b e r a t e d VOP r e s u l t i n g i n r e a s s o c i a t i o n o f the " i n o r g a n i c " V w i t h t h e kerogen. The r e l e a s e o f N i a n d V f r o m t h e k e r o g e n d u r i n g p y r o l y s i s o c c u r s a t a r a t e s u c h t h a t t h e t o t a l amount g e n e r a t e d p e r g o f k e r o g e n TOC i s m u c h l a r g e r t h a n t h e a m o u n t o f N i a n d V i n t h e b i t u m e n i s o l a t e d from an e q u i v a l e n t weight o f kerogen i n t h e shale. Theref o r e , t h e e x p u l s i o n o f t h e complexes from t h e kerogen c o u l d s u b s t a n t i a l l y a l t e r ( i g n o r i n g m i g r a t i o n and i n s i t u m a t u r a t i o n ) t h e N i and V c o n t e n t , p o r p h y r i n c o n t e n t , and p o r p h y r i n c o m p o s i t i o n o f t h e bitumen accumulating i n a source rock. Using t h e p y r o l y s a t e y i e l d s and m e t a l e x p u l s i o n r a t e s a t e a c h t e m p e r a t u r e , a n d a s s u m i n g : a) a c l o s e d s y s t e m , b ) a s a m p l e c o n t a i n i n g 1 g k e r o g e n TOC, a n d c ) n o



130


i n s i t u m a t u r a t i o n , t h e N i and V c o n t e n t s o f t h e a c c u m u l a t i n g b i t u mens w e r e e s t i m a t e d . The v a r i a t i o n o f t h e m e t a l c o n t e n t o f t h e accumulating bitumen i s p l o t t e d versus p y r o l y s i s temperature ( m a t u r a t i o n ) i n F i g u r e 6, a n d t h e N i / V r a t i o i s p l o t t e d i n F i g u r e 7. The d a t a a t 4 5 0 C w e r e n o t i n c l u d e d b e c a u s e o f p y r o l y t i c e f f e c t s w h i c h may h a v e s u b s t a n t i a l l y a l t e r e d t h e s a m p l e s . For Woodford, the e x p u l s i o n r a t e of the metals i s such that catagenesis reduces t h e i r c o n c e n t r a t i o n s i n the accumulating bitumen. H o w e v e r , t h e N i / V r a t i o r e m a i n s c o n s t a n t up t o 4 0 0 C, w h e r e i t i n c r e a s e s b y ~12% o v e r t h e o r i g i n a l b i t u m e n . The t r e n d f o r New Albany, however, i s d i f f e r e n t . The V c o n c e n t r a t i o n d e c r e a s e s a s t h e b i t u m e n a c c u m u l a t e s , b u t t h e N i c o n c e n t r a t i o n i n c r e a s e s up t o 300 C then decreases. Therefore, the Ni/V r a t i o of the accumulating b i t u men s h o w s a c o n s i s t e n t i n c r e a s e . The s u b s t a n t i a l q u a n t i t i e s o f p o r p h y r i n l i b e r a t e d f r o m k e r o g e n d u r i n g m a t u r a t i o n w i l l a l t e r t h e p o r p h y r i n c o n t e n t , and p o r p h y r i n c o m p o s i t i o n , of the accumulating bitumen. Although kerogen i s the source of the p o r p h y r i n s , i t i s probably thermal e f f e c t s which cause the c o m p o s i t i o n a l change i n the l i b e r a t e d p o r p h y r i n s r a t h e r than l i b e r a t i o n of c o m p o s i t i o n a l l y d i f f e r e n t porphyrins w i t h i n c r e a s i n g temperature. N o n e t h e l e s s , as m a t u r a t i o n (temperature) i n c r e a s e s , the VOP s e r i e s w i l l s h i f t t o l o w e r c a r b o n n u m b e r a n d e t i o t y p e p o r p h y r i n s w i l l i n c r e a s e r e l a t i v e t o DPEP t y p e p o r p h y r i n s . The b e h a v i o r f o r N i P i s e x p e c t e d t o be s i m i l a r , b u t d i f f e r e n c e s h a v e b e e n n o t i c e d b y o t h e r s ( 7 ) i n t h e r e l a t i v e o f r a t e s o f N i P a n d VOP d e a l k y l a t i o n d u r i n g m a t u r a t i o n , f o r example. Changes i n t h e p o r p h y r i n c o m p o s i t i o n and c o n t e n t o f t h e b i t u m e n s f r o m s a m p l e s u i t e s o f i n c r e a s i n g m a t u r i t y (e.g/? _»]) h a v e b e e n hypothesized to r e s u l t , at l e a s t i n p a r t , from the r e l e a s e of p o r p h y r i n s from the kerogen d u r i n g c a t a g e n e s i s . This study provides e x p e r i m e n t a l e v i d e n c e o f t h e g e n e r a t i o n o f N i P a n d VOP f r o m k e r o g e n . However, the e x a c t n a t u r e o f the changes i n the bitumen w i l l depend on t h e k e r o g e n a n d i t s t h e r m a l h i s t o r y a n d c a n n o t be g e n e r a l i z e d t o a l l sample s u i t e s . Conclusions S e v e r a l c o n c l u s i o n s a b o u t t h e g e o c h e m i s t r y o f N i and V c o m p l e x e s i n k e r o g e n c a n be d r a w n f r o m t h i s s t u d y . (1) The W o o d f o r d a n d New A l b a n y o i l s h a l e k e r o g e n s 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 c o m b i n e d N i a n d V. (2) K e r o g e n c a t a g e n e s i s s i m u l a t e d u s i n g l a b o r a t o r y p y r o l y s i s i s e f f e c t i v e i n l i b e r a t i n g o r g a n i c N i and V c o m p l e x e s f r o m k e r o g e n , i n c l u d i n g s u b s t a n t i a l a m o u n t s o f N i P a n d VOP. The r e s p e c t i v e a m o u n t s o f N i P a n d VOP g e n e r a t e d a r e d i r e c t l y p r o p o r t i o n a l t o t h e a m o u n t o f o r g a n i c a l l y combined N i and V i n t h e k e r o g e n . ( 3 ) The c o m p o s i t i o n o f t h e VOP g e n e r a t e d f r o m t h e k e r o g e n changes as a f u n c t i o n of p y r o l y s i s temperature. As p y r o l y s i s temp e r a t u r e i n c r e a s e s , the p o r p h y r i n s e r i e s s h i f t to lower carbon n u m b e r a n d t h e r e i s a n i n c r e a s e i n t h e a b u n d a n c e o f t h e C28 ^ C29 e t i o p o r p h y r i n s r e l a t i v e t o C32 a n d C32 DPEP p o r p h y r i n s . The a p p a r e n t i n c r e a s e i n g e n e r a t i o n o f e t i o r e l a t i v e t o DPEP t y p e p o r p h y r i n s w i t h i n c r e a s i n g p y r o l y s i s t e m p e r a t u r e c a n o n l y be c o n f i r m e d b y d e t e r m i n i n g t h e c a r b o n number d i s t r i b u t i o n s o f e a c h p o r p h y r i n t y p e for both metalloporphyrins. a n


Filby and Branthaver; Metal Complexes in Fossil Fuels ACS Symposium Series; American Chemical Society: Washington, DC, 1987. 1600

400

• ο = Accumulating Bitumen

£

>> ο ι_

Φ «»

1500

1

Β

1

ι 2500

• Ο

•

200

ι

Γ

400

ι

4500

1

h-- ο — I

(ppm)

3500

[V]

ι

ΚΗ

•

A

m

(ppm)

300

[Ni]

F i g u r e 6. C a l c u l a t e d e f f e c t o f k e r o g e n m a t u r a t i o n o n t h e N i a n d V c o n c e n t r a t i o n o f New A l b a n y ( A ) a n d W o o d f o r d ( B ) accumulating bitumen.

symbols) Α Δ = Bitumen-MI

2000

V (open

(ppm) • • = Bitumen-I

1200 and [ v ]

800

[Ni]

Ni ( s o l i d s y m b o l s )

400

α

Ε 300

200

2 φ

100 h -

ϋ

100


1

τ

1 5500

1

-ι

500

Γ"

3

I

•s,

r

D

>

w

m *> m r


Φ

ε

α

400

300

200

100

1.2

h

_l

I

1.6

I 2.0

Ratio

1.8 Ni/V

L 2.2

2.4

F i g u r e 7. Calculated Ni/V ratio (B) a c c u m u l a t i n g b i t u m e n .

1.4

I

Bitumen-

Ρ

h

h

Ni/V

0.062

0.064 Ratio

(A) and Woodford

0.060

o f New A l b a n y

0.058

400

300

200

ιοο h


0.066

m

G

x m

i

m r η

2

Κ)

7.


Generation


133

(4) G e n e r a t i o n o f N i a n d V c o m p l e x e s from k e r o g e n d u r i n g c a t a genesis can s u b s t a n t i a l l y a l t e r t h eN iand V contents, porphyrin c o n t e n t s , and p o r p h y r i n composition o f t h e bitumen accumulating i n a source rock. The e x a c t n a t u r e o f t h e changes w i l l be dependent o n the p a r t i c u l a r kerogen and i t s p o s t - d e p o s i t i o n a l h i s t o r y .


Acknowledgments The a u t h o r s t h a n k D r . P. S u n d a r a r a m a n ( C h e v r o n O i l F i e l d Research Co.) f o r t h e H P L C a n a l y s e s a n d D r . M.D. L e w a n (Amoco P r o d u c t i o n Company, R e s e a r c h C e n t e r ) a n d D r . R.K. L e i n i n g e r ( I n d i a n a G e o l o g i c a l S u r v e y ) f o r t h e s a m p l e s o f W o o d f o r d a n d New A l b a n y S h a l e , r e s p e c tively. The a s s i s t a n c e o f D r . F.F. F o i t , G e o l o g y Department, Washington State U n i v e r s i t y , i nperforming t h eX-ray d i f f r a c t i o n work i s acknowledged.

Literature Cited 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12.

13.

14. 15. 16. 17. 18.

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METAL COMPLEXES IN FOSSIL FUELS

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