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Geochemistry and Chemistry of Oil Shales Downloaded from pubs.acs.org by UNIV OF TEXAS AT EL PASO on 10/31/18. For personal use only.
G e o c h e m i s t r y of Israeli Oil S h a l e s M. SHIRAV (SCHWARTZ) and D. GINZBURG Geological Survey of Israel, 30 Malkhe Israel St., Jerusalem 95501, Israel
The Maastrichtian (latest Cretaceous) Israeli o i l shales consist of four main groups of components: organic matter; biogenic calcite and apatite; detrital clay minerals and quartz, with a l i t t l e amount of authigenic pyrite and feldspar. The main chemical characteristics of the o i l shales are reviewed,with an emphasis on those which may affect future utilization techniques. The o i l shales in Israel are widely distributed throughout the country (Figure 1). Outcrops are rare, and the information is based on borehole data. The o i l shales sequence is of UpperCampanian - Maastrichtian (latest Cretaceous) age and belongs to the Ghareb Formation (Figure 2). In places, part of the phosphorite layer below the o i l shales (Mishash Formation, Figure 2) is also rich in kerogen. The host rocks are biomicritic limestones and marls, in which the organic matter is generally homogeneously and finely dispersed. The occurrence of authigenic feldspar and the preservation of the organic matter (up to 26% of the total rock) indicate euxinic hypersaline conditions which prevailed in the relatively closed basins of deposition during the Maastrichtian ( 1). Current reserves of o i l shales in Israel are about 4,000 million tons (2),(3), located in the following deposits (Figure 1): Zin, Oron, Ef e, Hartuv and Nabi-Musa. The 'En Boqeq deposit, although thoroughly investigated, is of limited reserves and is not considered for future exploitation. Other potential areas, in the Northern Negev and along the Coastal Plain are under investigation. Future successful utilization of the Israeli o i l shales, either by fluidized-bed combustion or by retorting will contribute to the State's energy balance. f
0097-6156/ 83/0230-0085S06.00/0 © 1983 American Chemical Society
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GEOCHEMISTRY AND CHEMISTRY OF OIL SHALES
Figure I. Map showing location of oil shale deposits in Israel
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LEGEND
Clay minerals 3g Organic matter I
Apatite
I
,] Calcite
I
J Others (Pyrite, gypsum, dolomite)
Figure 2. Mineralogical log (Borehole T-l).
87
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GEOCHEMISTRY AND CHEMISTRY OF OIL SHALES
A n a l y t i c a l Methods I n d u c t i v e l y coupled plasma atomic emission spectrometry (ICP-AES) was used f o r the determination of most major and t r a c e elements. The samples are fused i n a C l a i s s e semi-automatic f u s i o n device i n Pt-Au c r u c i b l e s w i t h l i t h i u m metaborate (4_). The f u s i o n product i s d i s s o l v e d i n d i l u t e d HNO^ and brought to volume. For t r a c e elements d e t e r m i n a t i o n the sample i s decomposed by HF, HNO^ and HCIO^. Scandium serves as an i n t e r n a l standard and i s added to a l l samples and s o l u t i o n s . The instrument (product of J o b i n Yvon, F r a n c e ) i s c a l i b r a t e d u s i n g multi-element s y n t h e t i c standards. The aqueous s o l u t i o n s are n e b u l i z e d and i n j e c t e d i n t o the heart of a plasma f i r e b a l l . A computerized m u l t i - c h a n n e l vacuum spectrometer has been programmed f o r multi-element a n a l y s i s . A d d i t i o n a l methods used were: X-Ray f l u o r e s c e n c e spectrometry ( f o r t o t a l S d e t e r m i n a t i o n ) ; flame atomic a b s o r p t i o n (Hg and A s ) . Organic C was determined u s i n g Leco instrument, a f t e r decomposit i o n of the carbonate by HC1. C,H,N,S i n the kerogen were analysed using m i c r o a n a l y s i s techniques. Major Elements and Mineralogy T y p i c a l analyses of I s r a e l i o i l shales are shown i n Table I . Table I . Analyses of Composite Samples (wt.%) a. * b. c.
f
Ef e Bit-1 18-22m
Si0 16.9 A1 0 6.8 Ti0 0.32 Fe20 2.8 CaO 34.2 MgO 0.57 Na 0 0.27 K20 0.42 P 0 1.6 S0 2.3 S (Organ.) 1.4 Organ. Mat. 8.2 Loss on Ign. 33.5 2
2
3
2
3
2
2
5
3
*a.=location
f
Ef e Bit-1 60-70m
Hartuv HRB-1 62-82m
Hartuv HRB-1 130-150m
7.6 1.5 0.16 0.7 36.1 0.58 0.20 0.32 3.5 0.9 2.7 24.1 45.7
7.5 1.6 0.1 1.01 37.7 1.67 0.14 0.15 3.0 0.3 1.7 14.8 44.0
5.0 1.3 0.1 0.57 38.2 0.39 0.10 0.14 2.3 0.26 2.4 20.5 49.6
b.=borehole No. c.=depth i n t e r v a l of sample
f
One borehole i n the E f e d e p o s i t , T - l , coord. 1167/0544 ( I s r a e l G r i d ) was analysed meter by meter. The c o r r e l a t i o n f a c t o r s between the v a r i a b l e s are summed up i n F i g u r e 3.
5. SHIRAV AND GINZBURG
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Figure 3. Correlation factors for chemical analyses ofsamples from Borehole T-l, Ef'e Deposit. (O.M indicates organic matter.)
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GEOCHEMISTRY AND CHEMISTRY OF OIL SHALES
S1O2 content i s 2-17wt.%. The s i g n i f i c a n t c o r r e l a t i o n w i t h AI2O3 and Fe203 i n d i c a t e s i t s residence i n c l a y m i n e r a l s . D e t r i t a l quartz g r a i n s are present i n a very s m a l l amount. CaO (30-40wt.%) i s found l a r g e l y i n c a l c i t e (50-70% of the t o t a l r o c k ) . Small amounts of CaO are l o c a t e d i n a p a t i t e and gypsum. AI2O3 i s a main component i n c l a y m i n e r a l s . AI2O3 i s h i g h l y c o r r e l a t i v e w i t h S1O2, Fe2Û3 and T i 0 . The content of Α 1 0 along the o i l shale sequence i s l-8wt.%. Fe203 content i s 0.5-2.8wt.% and i t i s a s s o c i a t e d w i t h c l a y minerals and p y r i t e . S u l f u r i s shown on Figure 3 as SO3, which i n c l u d e s organic and i n o r g a n i c s u l f u r . D i r e c t observations and i s o t o p i c composition of s u l f u r (5) i n d i c a t e that kerogen-bound s u l f u r accounts f o r 60-80% of the t o t a l s u l f u r i n the rock w h i l e the remainder i s p y r i t i c and gypsum s u l f u r . P2O5 content w i t h i n the o i l shales i s l-5wt.%, w h i l e i n the phosphorous Mishash Formation i t may exceed 30%. Organic matter (kerogen) composes 5-26wt.% of the rock. The average content of organic matter i n I s r a e l i d e p o s i t s i s 14-16wt.%. Only rocks w i t h more than 10% organic matter are considered as "economic ' o i l s h a l e s . Depth shows s i g n i f i c a n t p o s i t i v e c o r r e l a t i o n w i t h the f o l l o w i n g v a r i a b l e s : organic matter, s u l f u r , phosphate; and negative c o r r e l a t i o n w i t h AI2O3, Fe203 and S1O2. Since A l , S i and Fe are dependent upon c l a y content, i t i s c l e a r that the amount of c l a y minerals decreases w i t h depth. Organic matter, s u l f u r and a p a t i t e contents i n c r e a s e w i t h depth. The carbonates content along the o i l shale sequence does not show any s i g n i f i c a n t change. Thus, these data represent a m i n e r a l o g i c a l system of four main v a r i a b l e s , changing w i t h g e o l o g i c a l time (=depth) (Figure 2 ) . The four main m i n e r a l o g i c a l phases a r e : a. organic matter - d e r i v e d mainly from marine algae and b a c t e r i a w i t h some c o n t r i b u t i o n of c o n t i n e n t a l p l a n t s . The kerogen i s very f i n e (0.05-0.1 micron), most of i t dispersed w i t h i n the m a t r i x or as a f i n e f i l m on the g r a i n s . Some of the preserved algae show d e f i n i t e s t r u c t u r e s . R e f l e c t a n c e measurements on v i t r i n i t e - t y p e g r a i n s i n d i c a t e a very low m a t u r i t y grade of the organic matter. b. c l a y minerals - mainly very f i n e d e t r i t a l k a o l i n i t e w i t h a s m a l l amount of m o n t m o r i l l o n i t e . c. c a l c i t e - most of i t i s of b i o g e n i c o r i g i n . The t e x t u r e i s of sparse b i o m i c r i t e made of p l a n k t o n i c f o r a m i n i f e r a skeletons w i t h c o c o l i t h o f o r i d e s i n the m a t r i x . d. b i o g e n i c a p a t i t e - l o c a t e d i n o v u l i t e s , bone fragments and f i s h s c a l e and t e e t h . Other minor c o n s t i t u e n t s a r e : a u t h i g e n i c p y r i t e which appears as framboides or separate c r y s t a l s ; secondary gypsum, mainly as v e i n f i l l i n g ; d e t r i t a l quartz g r a i n s and a u t h i g e n i c f e l d s p a r (microcline). 2
1
2
3
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Israeli Oil Shales
The m i n e r a l o g i c a l system described above i s one c l u e to the understanding of the paleogeographical set-up during the l a t e Cretaceous i n I s r a e l , as w e l l as a main f a c t o r f o r any assessment of o i l shale's q u a l i t y . E f f e c t of CaCO^ on Combustion F l u i d i z e d bed technology seems to be p r e f e r a b l e f o r o i l shale combustion ( 6 ) . S e r i e s of combustion t e s t s which were run i n d i f f e r e n t temperatures r e s u l t e d i n lower e f f e c t i v e c a l o r i f i c value w i t h the i n c r e a s e of o p e r a t i n g temperatures. F i g u r e 4 shows a DTA curve f o r a t y p i c a l I s r a e l i s h a l e . When o p e r a t i n g the f l u i d i z e d bed i n the range of 700-800^, endothermic r e a c t i o n s are only i n t h e i r b e g i n i n g , but i f the o p e r a t i n g temperature exceeds 800850 , the endothermic r e a c t i o n of c a l c i t e decomposition has a severe i n f l u e n c e on the e f f e c t i v e c a l o r i f i c v a l u e . F l u i d i z e d beds burning c o a l use a c e r t a i n c o n t r o l l e d amount of carbonate f o r S 0 t r a p p i n g , but i n t h i s case more than 60% of the m a t e r i a l which i s feeded i n t o the burner i s carbonate. Thus, the n e c e s s i t y of m a i n t a i n i n g d e l i c a t l y c o n t r o l l e d c o n d i t i o n s during combustion i s a d i r e c t outcome of the i n o r g a n i c composition of the o i l s h a l e . e
c
2
Calorific
Value
The High C a l o r i f i c Value of the o i l shales was determined by a "bomb" c a l o r i m e t e r on more than 90 composite samples from d i f f e r e n t d e p o s i t s and on one-meter samples along borehole s e c t i o n s . The average value i s 1000Kcal/Kg and the highest value measured was 1790Kcal/Kg. The c o r r e l a t i o n between organic matter content and the c a l o r i f i c value i s more than s i g n i f i c a n t (R=0.96). The equation f o r the E f e deposit i s : f
c a l o r i f i c value (Kcal/Kg) • 77.8+60.2(org. matter
wt.%)
and f o r the Hartuv d e p o s i t : c a l o r i f i c value (Kcal/Kg) = 52.0+71.3(org. matter
wt.%)
The l i n e f o r the Hartuv deposit i s steeper than that f o r the Ef'e deposit (Figure 5) i . e . : i n the range of 14wt.% organic matter (average f o r most d e p o s i t s ) the d i f f e r e n c e w i l l be 130Kcal/Kg i n favour of the Hartuv d e p o s i t . As the o v e r a l l i n o r g a n i c composition i s s i m i l l a r i n the two d e p o s i t s , we assume that the reason f o r t h i s d i f f e r e n c e i s due to c o m p o s i t i o n a l v a r i a t i o n s w i t h i n the organic matter.
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GEOCHEMISTRY AND CHEMISTRY OF OIL SHALES
Figure 4. Differential thermal analysis curve for Sample HRB-3a.
0
4
8
12
16
20
24
28
wt.% Organic matter Figure 5. Correlation between organic matter content and high calorific value (Ef'e and Hartuv Deposits).
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Israeli Oil Shales
F i s c h e r Assay F i s c h e r assay t e s t s were c a r r i e d out on s e v e r a l boreholes i n the E f e d e p o s i t ( 7 ) . The average o i l y i e l d was 15.6 G a l / t o n ; s e c t i o n s w i t h h i g h content of organic matter (20-26wt.%) y i e l d e d up t o 29 G a l / t o n . E v i d e n t l y , there i s a p o s i t i v e c o r r e l a t i o n between F i s c h e r assay r e s u l t s and the content o f organic matter; another i n t e r e s t i n g r e l a t i o n i s i l l u s t r a t e d i n F i g u r e 6: w i t h the i n c r e a s e o f depth, more o i l i s y i e l d e d per l w t . % o f o r g a n i c matter. The data i n Table I I suggest t h a t t h i s phenomenon may be r e l a t e d t o changes i n the elemental composition of the o i l s h a l e and/or t o the content of the bituminous f r a c t i o n w i t h i n the organic matter. f
Table I I . U l t i m a t e Analyses and O i l Y i e l d Sample No.
SRV 208
SRV 215
SRV 221
10.1
13.6
Org. C (wt.%)
7.8
H (wt.%)
1.28
1.56
1.76
Ν
(wt.%)
0.29
0.35
0.54
S (wt.%)
2.4
3.0
3.1
Oil
(Gal/Ton)
%Bitumen out o f t o t a l o r g . mat.
24.2
16.5
11.9 6.8
7.8
7.1
The average composition of kerogen from the Ef'e d e p o s i t i s : C-64.9%
H-8.0%
N-2.8%
S-9.1%
The average composition of r e t o r t e d o i l from the Ef'e deposit i s : C-79.8%
H-10.1%
N-l.1%
S-7.6%
Infra-Red Spectra of The Kerogen I n f r a - r e d s p e c t r a were used as " f i n g e r p r i n t s " of d i f f e r e n t kerogens, as they a l l o w a d i r e c t study of f u n c t i o n a l groups w i t h i n the kerogen's s t r u c t u r e . The main c h a r a c t e r i s t i c absorp t i o n s were as f o l l o w s : 2825-2960 1460 1380 720 1650 1710
cnT* cnT* cm~* cnT^ι cm cnT*
C-H C-CH2 C-CH3 C-CH3 C-H C=C C=0
aliphatic l i n e a r and c y c l i c l i n e a r and c y c l i c aliphatic aromatic; water a c i d ; ketones
Two t y p i c a l s p e c t r a a r e shown i n F i g u r e 7. The s p e c t r a a r e g e n e r a l l y s i m i l a r and i n d i c a t e the kerogen to be mainly a l i p h a t i c . Comparison of the two s p e c t r a suggests t h a t a l i f a t i c s t r u c t u r e s
GEOCHEMISTRY AND CHEMISTRY OF OIL SHALES
« 120 ε
i.iol
°
1.00
I
0.90|
···«
Φ
» 0.80 7
5 °-°l10
20
30 40 DEPTH (m)
60
50
70
Figure 6. Oil yieldper lwt%oforganic matter content as afunction ofdepth (Borehole Bit-1, Ef'e Deposit).
4000
3000
2000 1600 1200 WAVENUMBER (CM" )
800
400
1
Figure 7. IR spectra of Nabi-Musa (A) and Ef'e oil shale (B).
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Israeli Oil Shales
are more common i n the Ef'e kerogen. The s p e c t r a of I s r a e l i o i l shales are q u i t e s i m i l a r to those of the Estonian shales (8) and to the kerogen of the Green R i v e r Formation ( 9 ) . Trace Elements Table I I I summarizes t r a c e elements c o n c e n t r a t i o n data i n the o i l shales sequence of the Ef'e d e p o s i t , the phosphorite l a y e r from the same area (10) and the Green R i v e r o i l s h a l e (11).
Table I I I . Trace Elements Data (wt. Ef'e o i l shale Borehole T - l Ag As Ba Cr Co Cu Hg Li Mo Mn Ni V Pb Y Zn Zr U
1 34 250 280 5 112 0.2 17 26 41 138 110 10 39 310 38 27
Ef'e phosphorite n.d n.d 500 200 n.d 25 n.d n.d n.d 40 70 170 n.d 83 430 n.d 150
ppm) Green R i v e r o i l shale
