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O I L RESOURCE ESTIMATES-- HOW MUCH DO WE KNOW?
S u s a n A r t h u r
March 1982 WP-82-20
W o r k i n g P a p e r s a r e i n t e r i m r e p o r t s o n work o f t h e I n t e r n a t i o n a l I n s t i t u t e f o r A p p l i e d S y s t e m s A n a l y s i s a n d h a v e r e c e i v e d o n l y l i m i t e d r e v i e w . V i e w s o r o p i n i o n s e x p r e s s e d h e r e i n d o n o t n e c e s s a r i l y r e p r e - s e n t t h o s e o f t h e I n s t i t u t e o r o f i t s N a t i o n a l Member O r g a n i z a t i o n s .
INTERNATIONAL INSTITUTE FOR APPLIED SYSTEMS ANALYSIS A-2361 L a x e n b u r g , A u s t r i a
PREFACE
A key unknown i n e n e r g y s t u d i e s and f o r e c a s t s i s t h e u l t i - mate amount o f r e c o v e r a b l e o i l . Numerous e s t i m a t e s have been made o v e r t h e l a s t t h i r t y y e a r s . R e c e n t l y many r e s e a r c h e r s i n o i l r e s o u r c e s h a v e c l a i m e d t h a t e s t i m a t o r s have r e a c h e d a consen- s u s o f o p i n i o n a t a r o u n d 2 0 0 0 b i l l i o n b a r r e l s o f r e c o v e r a b l e o i l , i n c l u d i n g p a s t p r o d u c t i o n . O t h e r r e s e a r c h e r s c l a i m t h a t e s t i m a t e s h a v e r i s e n s t e a d i l y o v e r t h e l a s t 30 y e a r s and w i l l c o n t i n u e t o do s o . These two views n a t u r a l l y l e a d t o v e r y d i f f e r e n t o u t l o o k s
f o r a n o i l f u t u r e .
I n t h i s r e p o r t we t a k e a s h o r t , c r i t i c a l l o o k a t a l o n g s e r i e s of o i l r e s o u r c e e s t i m a t e s . W e c o n c l u d e t h a t n e i t h e r t h e c o n s e n s u s view n o r t h e s t e a d i l y r i s i n g view o f e s t i m a t e s c a n b e c o r r o b o r a t e d . I n s t e a d , o n e must a c c e p t a w i d e i n t e r v a l o f pos- s i b l e v a l u e s f o r t o t a l r e c o v e r a b l e w o r l d o i l r e s o u r c e s . I n ad- d i t i o n , w e i n d i c a t e some b i a s e s and s h o r t c o m i n g s o f o i l r e s o u r c e e s t i m a t e s i n g e n e r a l which s h o u l d b e k e p t i n mind when j u d g i n g any s u c h e s t i m a t e .
I I A S A h a s b e e n i n v o l v e d f o r s e v e r a l y e a r s , t h r o u g h t h e work o f Michel Grenon and h i s WELMM g r o u p , i n l o o k i n g a t w o r l d m i n e r a l r e s o u r c e s . T h i s r e p o r t g o e s hand-in-hand w i t h t h e e a r l i e r work.
I t i s b a s e d upon and a n a l y z e s t h e s u r v e y work o f t h e FJELMEil g r o u p w i t h r e s p e c t t o o i l r e s o u r c e s .
J a n u s z K i n d l e r Chairman
R e s o u r c e s & Environment Area
ACKNOWLEDGMENTS
The s t a t i s t i c a l i n t e r p r e t a t i o n p r e s e n t e d i n t h i s s h o r t e s s a y i s b a s e d a l m o s t e x c l u s i v e l y o n t h e i n f o r m a t i o n c o l l e c t e d by Michel Grenon and h i s g r o u p a t IIASA. The work would n o t h a v e been p o s s i b l e w i t h o u t G r e n o n ' s e x h a u s t i v e and i n f o r m a t i v e s u r v e y p a p e r on u l t i m a t e w o r l d o i l r e s o u r c e e s t i m a t e s , f o r t h - coming E P R I R e p o r t TPS80-763.
CONTENTS
WORLD O I L RESOURCE ESTIMATES, 1 9 4 6 - 1 9 8 0 INDEPENDENT WORLD ESTIMATES
REGIONAL ESTIblATES
SOURCES OF UNCERTAINTY AND B I A S CONCLUSION
APPENDIX REFERENCES
O I L RESOURCE ESTIMATES-- HOW MUCH DO WE KNOW?
Susan A r t h u r
A t t h e c o r e o f t h e e n e r g y problem i s t h e l i m i t e d n a t u r e o f t h e w o r l d ' s f o s s i l f u e l r e s o u r c e s , e s p e c i a l l y o i l r e s o u r c e s . But j u s t how l i m i t e d a r e o i l resources--how much o i l i s down t h e r e ? T h i s q u e s t i o n c a n , o f c o u r s e , n e v e r b e answered e x a c t l y and we a r e l e f t w i t h e s t i m a t e s . How good a r e t h e s e e s t i m a t e s ? How much c a n we t r u s t them?
Two views on r e s o u r c e e s t i m a t e s have begun t o emerge r e c e n t l y . The f i r s t , h e l d by a l a r g e number o f r e s e a r c h e r s , i s t h a t a con- s e n s u s o f o p i n i o n h a s b e e n reached--a c o n s e n s u s a t a b o u t 2 0 0 0 b i l l i o n b a r r e l s o f u l t i m a t e l y r e c o v e r a b l e o i l ( i n c l u d i n g p a s t p r o d u c t i o n and known r e s e r v e s ) . S t u d i e s o f p o s s i b l e e n e r g y f u t u r e s t e n d t o a c c e p t t h i s f i g u r e , e r e c t i n g l o n g - t e r m e n e r g y f o r e c a s t s and p o l i c i e s upon i t . But t h e c o n s e n s u s view h a s been v i g o r o u s l y c h a l l e n g e d by a n o p p o s i n g view. A few r e s e a r c h e r s ,
i n p a r t i c u l a r O d e l l ( 1 9 7 3 ) , O d e l l and Rosing (3975, 1980), and S c h u b e r t (1980) f e e l t h a t e s t i m a t e s have been i n c r e a s i n g s t e a d i l y , and w i l l c o n t i n u e t o do s o f o r some t i m e . T h i s s h o r t s t u d y t a k e s a c r i t i c a l l o o k a t b o t h t h e s e p o i n t s o f view, and a t o i l r e s o u r c e e s t i m a t e s i n g e n e r a l , a s k i n g i n e f f e c t : Low ~ u c h a o we r e a l l y know?
WORLD O I L RESOURCE ESTIIIATES, 1946-1980
There i s c e r t a i n l y no s h o r t a g e o f o i l r e s o u r c e e s t i m a t e s . Forty-two e s t i m a t e s made s i n c e 1946 a r e d e t a i l e d i n t h e Appendix.
F i g u r e 1 d i s p l a y s t h e s e e s t i m a t e s c h r o n o l o g i c a l l y , showing how t h e y have changed o v e r t i m e . * E s t i m a t e s a r e o f u l t i m a t e l y r e - c o v e r a b l e o i l , i n c l u d i n g p a s t p r o d u c t i o n and known r e s e r v e s .
What c a n o n e d i s c e r n from t h i s d e n s e c o l l e c t i o n o f f i g u r e s ? I t i s c l e a r t h a t u n c e r t a i n t y a b o u t u l t i m a t e o i l r e s o u r c e s h a s n o t d e c r e a s e d i n t h e l a s t t h i r t y y e a r s - - i n d e e d , t h e p r e s e n t r a n g e o f e s t i m a t e s i s l a r g e r t h a n e v e r . And c e r t a i n l y t h e upper l i m i t s t o s p e c u l a t i o n have d r a m a t i c a l l y i n c r e a s e d , e s p e c i a l l y i n t h e l a s t f i v e t o t e n y e a r s . A p a r t from t h e s e two o b s e r v a t i o n s , it i s d i f f i c u l t t o s e e what i n f e r e n c e s t o draw from a d i a g r a m such a s F i g u r e 1.
Evidence f o r a n i n c r e a s i n g t r e n d i s v e r y weak i n t h e d a t a o f F i g u r e 1 . Only i n c l u s i o n o f t h e low, pre-1950 e s t i m a t e s would g i v e s i g n i f i c a n c e t o t h e k i n d o f l i n e a r f i t p r o p o s e d by O d e l l and Rosing. E s t i m a t e s f o r t h e l a s t t w e n t y y e a r s would h a r d l y c o r r o b - o r a t e any r e g r e s s i o n l i n e e x c e p t o n e w i t h z e r o s l o p e . The jump
i n estimates between 1950 and 1958 was u n d o u b t e d l y d u e t o t h e i n t r o d u c t i o n o f o f f s h o r e s o u r c e s . I t i s c e r t a i n l y p o s s i b l e t h a t s i m i l a r jumps i n estimates may o c c u r a l o n g w i t h major improvements i n r e c o v e r y p r a c t i c e s o r major new f i n d s , b u t t h e r e i s no e v i d e n c e , among t h e e s t i m a t e s i n F i g u r e 1 , f o r a s t e a d i l y i n c r e a s i n g t r e n d . A d i f f e r e n t c o l l e c t i o n o f e s t i m a t e s m i g h t , o f c o u r s e , g i v e b e t t e r
s u p p o r t f o r a l i n e a r t r e n d . I t r y t o c o v e r t h i s p o s s i b i l i t y , i n t h e n e x t s e c t i o n , by l o o k i n g a t i n d e p e n d e n t e s t i m a t o r s o n l y .
What o f t h e view t h a t a c o n s e n s u s o f o p i n i o n h a s been r e a c h e d ? The i d e a o f a c o n s e n s u s o r c o n v e r g e n c e o f e s t i m a t e s h a s been prev- a l e n t i n t h e o i l l i t e r a t u r e s i n c e it was f i r s t mentioned by Warman
i n 1972 and Hubbert i n 1973. I t was c e r t a i n l y g i v m a d d i t i o n a l
*
These e s t i m a t e s a r e from a s t u d y by Michel Grenon ( f o r t h - coming EPRI-Report TPS80-763), w i t h t h e a d d i t i o n o f t h e e s t i m a t e by S t y r i k o v i c h (1976, 1 9 7 7 ) .Billions of barrels
600C
500(
4OOC
300C
200C
1 OOC
I 1 I I
1950 1960 1970 1980
Year of estimate
-+-
Separate estimates from same estimatorRange of estimate O+O Range with preferrt:d
(central) value
F i g u r e 1 . World o i l r e s o u r c e e s t i m a t e s , 1 9 4 6 - 1 9 8 0 .
i m p e t u s by t h e i n f l u e n t i a l 1975 e s t i m a t e s o f Moody and G e i g e r and o f Moody a n d E s s e r , a l l o f which w e r e c e n t e r e d n e a r 2000 b i l l i o n b a r r e l s , and i s now t h e most p r e v a l e n t view o f t h e s t a t e o f o i l r e s o u r c e e s t i m a t i o n .
A s shown i n F i g u r e 1 , v e r y many e s t i m a t e s s i n c e 1971 h a v e i n d e e d c l u s t e r e d a r o u n d 2000 b i l l i o n b a r r e l s . However, o n e must b e c a r e f u l i n j u d g i n g s u c h a c l u s t e r t o b e e v i d e n c e f o r a con- s e n s u s . The s i m i l a r i t y o f e s t i m a t e s f o r w o r l d t o t a l s h i d e s g r o s s u n d e r l y i n g d i f f e r e n c e s , i n r e g i o n a l estimates and i n t h e pro-
p o r t i o n o f u l t i m a t e l y r e c o v e r a b l e o i l assumed t o come f r o m a l r e a d y - d i s c o v e r e d a s o p p o s e d t o u n d i s c o v e r e d s o u r c e s . F o r e x a m p l e ,
N e h r i n g ( 1978) e s t i m a t e s t o t a l u l t i m a t e r e c o v e r a b l e o i l r e s o u r c e s a t 1700-2300 b i l l i o n barrel,^, o f w h i c h 263-555 b i l l i o n b a r r e l s a r e t o come from a s - y e t - u n d i s c o v e r e d s o u r c e s . Moody and E s s e r
( 1 9 7 5 ) e s t i m a t e a s i m i l a r e x p e c t e d t o t a l o f 2000 b i l l i o n b a r r e l s . But h e r e a n e x p e c t e d 963 b i l l i o n b a r r e l s a r e t o come f r o m a s - y e t - u n d i s c o v e r e d s o u r c e s . Such s m o o t h i n g o u t i n t h e g r a n d t o t a l o f m a j o r d i f f e r e n c e s i n s u b - t o t a l s l e a v e s room f o r d o u b t . Does a c o n s e n s u s a c t u a l l y e x i s t , o r i s it a s e l f - p e r p e t u a t i n g a r t i f a c t ?
I n j u d g i n g e v i d e n c e f o r e i t h e r t h e c o n s e n s u s view o f t h e i n c r e a s i n g t r e n d view f r o m l i s t s o f e s t i m a t e s s u c h a s t h o s e i n t h e Appendix, a m a j o r d i f f i c u l t y l i e s i n t h e i n t e r d e p e n d e n c e o f t h e e s t i m a t e s . Some estimates a r e u p d a t e s o f e a r l i e r e s t i m a t e s made by t h e same r e s e a r c h e r , some r e l y o n r e g i o n a l e s t i m a t e s
from a n a s s o r t m e n t o f s t u d i e s , some a r e r e w o r k i n g s o f e a r l i e r e s t i m a t e s u s i n g , f o r e x a m p l e , d i f f e r e n t r e c o v e r y r a t e s , a n d
some a r e , l i k e t h i s s t u d y , s i m p l y a n a l y s e s o f p r e v i o u s e s t i m a t e s . A s e c o n d d i f f i c u l t y i s t h a t e s t i m a t e s a r e n o t w h o l l y c o m p a r a b l e .
D i f f e r e n t r e s o u r c e d e f i n i t i o n s and d i f f e r e n t r e c o v e r y r a t e s a r e u s e d . Some e s t i m a t o r s i n c l u d e p o l a r and d e e p o f f s h o r e o i l , o t h e r s do n o t , a n d s o o n . The e f f e c t s o f d e p e n d e n c e and n o n - c o m p a r a b i l i t y c a n n o t b e e n t i r e l y removed, b u t t h e y c a n b e somewhat m i t i g a t e d . Once some o f t h e s e e f f e c t s a r e removed, w e w i l l see t h a t t h e r e i s l i t t l e e v i d e n c e f o r e i t h e r a c o n s e n s u s f i g u r e o r f o r a l i n - e a r l y i n c r e a s i n g t r e n d i n e s t i m a t e s .
INDEPENDENT WORLD ESTIMATES
Grenon ( f o r t h c o m i n g EPRI R e p o r t TPS80-763), who h a s a l s o p o i n t e d o u t t h e i m p o r t a n c e o f l o o k i n g a t i n d e p e n d e n t e s t i m a t e s , h a s i d e n t i f i e d s e v e n independ-ent e s t i m a t o r s ( g e o l o g i c a l o r
s t a t i s t i c a l / g e o l o g i c a l methods o n l y ) . They a r e H e n d r i c k s , Weeks, Moody, J o d r y , t h e West German G e o l o g i c a l S u r v e y ( B u n d e s a n s t a l t ffir G e o w i s s e n s c h a f t e n and R o h s t o f f e ) , G r o s s l i n g and N e h r i n g . For t h e p u r p o s e s o f t h i s s t u d y J o d r y was e x c l u d e d b e c a u s e t h e r e i s o n l y a second-hand r e f e r e n c e t o h i s method ( H u b b e r t 1 9 7 4 ) , a n d t h e West German G e o l o g i c a l Survey b e c a u s e it u s e s r e g i o n a l e s t i - m a t e s f r o m v a r i o u s o t h e r s o u r c e s . S t y r i k o v i c h was n o t i n c l u d e d b e c a u s e o f l a c k o f i n f o r m a t i o n on h i s method. T h i s l e a v e s f i v e e s t i m a t o r s s i n c e 1 9 5 8 - - a u t h o r s o f m a j o r , well-documented s t u d i e s , u s i n g w i d e l y v a r i e d methods o f e s t i m a t i o n . T h e i r e s t i m a t e s a r e r e a s o n a b l y , a l t h o u g h n o t t o t a l l y , i n d e p e n d e n t o f o t h e r w o r k e r s .
(Moody, f o r example, c r o s s - c h e c k e d h i s r e s u l t s u s i n g King H u b b e r t ' s method o f e x t r a p o l a t i n g from e x i s t i n g p r o d u c t i o n d a t a . ) Note
t h a t t h r e e o f t h e f i v e e s t i m a t o r s ( H e n d r i c k s , G r o s s l i n g , a n d N e h r i n g ) w e r e n o t a s s o c i a t e d w i t h a n y o i l company.
The g r o u p o f i n d e p e n d e n t e s t i m a t o r s i s l i s t e d i n T a b l e 1 and shown c h r o n o l o g i c a l l y i n F i g u r e 2 a . I n F i g u r e 2b w e have
a t t e m p t e d t o make t h e s e t o f i n d e p e n d e n t e s t i m a t e s more c o m p a r a b l e . Only t h e most r e c e n t e s t i m a t e f o r e a c h e s t i m a t o r i s shown. A
s i n g l e v a l u e was c h o s e n t o r e p r e s e n t e a c h r a n g e . I n c h o o s i n g t h e v a l u e we have t r i e d t o s t a n d a r d i z e , a s f a r a s p o s s i b l e , t o a
r e c o v e r y r a t e o f 40%. For G r o s s l i n g t h i s was n o t p o s s i b l e , and two v a l u e s were c h o s e n - - t h e m i d p o i n t o f e a c h o f h i s two r a n g e s o f v a l u e s . For Moody t h e e x p e c t e d v a l u e was t a k e n a s r e p r e s e n t a - t i v e , f o r Weeks t h e s e c o n d a r y r e c o v e r y v a l u e ( c o m p a t i b l e w i t h 40% r e c o v e r y ) , and f o r N e h r i n g t h e m i d p o i n t o f t h e r a n g e .
T h e r e i s l i t t l e e v i d e n c e i n F i g u r e s 2a and 2b o f t h e i n c r e a s i n g t r e n d h y p o t h e s i z e d by O d e l l a n d R o s i n g . One would e x p e c t s u c h a t r e n d t o b e p a r t i c u l a r l y a p p a r e n t i n u p d a t e d e s t i - m a t e s s u c h a s t h o s e from Weeks and Moody, b u t e v e n t h e s e two s e r i e s
show o n l y s m a l l i n c r e a s e s . (Two e s t i m a t e s made by Weeks i n 1948 a n d 1949 a r e much l o w e r t h a n t h e post-1958 e s t i m a t e s d u e t o l a c k o f knowledge o f o f f - s h o r e p o t e n t i a l . The f o u r l a t e r e s t i m a t e s ,
s p a n n i n g t h i r t e e n y e a r s , a r e s u r p r i s i n g l y s t a b l e . )
T a b l e 1 . I n d e p e n d e n t g e o l o g i c a l e s t i m a t o r s o f w o r l d o i l r e s o u r c e s , 3958-1980.
Estimator Estimate Comments
Weeks (Jersey, later consultant)
1958 1500/3000 Primary-recovery only/primary
and secondary
1959 2000/3500 11 II 11 II
1968 2200/3550 II II II II
1971 2290/3650 II I 1 II I 1
Hendricks (U.S.
Geological Survey)
1965 10,000/6200/(2480) Oil originally in place/
ultimately discoverable/
(if 40% recovery) Moody (Mobil, later
consultant) 1970
1975 ( & Geiger) 1975 ( 6 Esser) 1975 ( & Esser) 1979 ( 8 Halbouty) Grossling (U. S.
~ e o l o g i c a l survey) 1977
N e h r i n g (Rand) 1978
Probability range. Middle number is expected value.
40% recovery.
W separate ranges given.
bkthod based on giant f i e l d s . Ultimate recovery: 40-50% for U S ; for world maybe higher.
Revision with no explanation, so not included in following analysis. (If m j o r break- through in recovery technology)
Billions of barrels
6000i
-7-
( a ) A l l e s t i m a t e s
0 Weeks (Jersey) Hendricks (USGS) Moody (Mobil) Grossling (USGS) A Nehring (Rand)
Year of estimate
( b ) Summary' e s t i m a t e s ( 4 0 % r e c o v e r y )
Billions of barrels
'"I
0 Weeks (Jersey)Hendricks (USGS) Moody (Mobil) Grossling (USGS) A Nehring (Rand)
Year of estimate
F i g u r e 2 . I n d e p e n d e n t w o r l d o i l r e s o u r c e e s t i m a t e s , 1958-1980.
Figures 2a and 2b show very clearly the lack of any sort of "consensus" among the independent geological estimators of world oil resources, or even among the oil company estimators.
(It is interesting that Moody and Nehring, the two estimators who come closest to the 2000 billion barrel mark, show particu- larly large discrepancies in the sub-totals. These discrepancies show up in regional sub-totals as well as in the amounts of oil estimated to come from as-yet-undiscovered sources, as mentioned earlier.) Instead of a consensus, we find a very wide range of opinion, with the highest summary estimate (3800 billion barrels) nearly twice the so-called consensus figure. The spread of esti- mates is so wide that use of a single value such as 2000 billion barrels is clearly misguided--it implies a much higher level of certainty than actually exists. The best we can do is to offer an interval which includes the bulk of the independent estimates.
A suggested "central" interval, 2000-3800 billion barrels, is marked in Figure 2b. A wider interval, including upper and lower limits of the five independent estimators, and including almost all of the original forty-two estimates, is 1300-5600 billion barrels. It is important to note th.at the left-hand limits of these intervals are very much firmer than the right- hand limits. Speculation on upper limits has been as high as 7300 billion barrels (Desprairies' Delphi study 1978). The intervals are summarized in Table 2.
Table 2. Intervals for ultimate world oil resource estimates (in billions of barrels)
Firm Central Interval Upper Limits to Speculation Limit
1300 2000-3800 5500 Styrikovich 5600 Grossling 6000 Odell, Rosing
7300 Desprairies' Delphi Study
REGIONAL ESTIMATES
World o i l r e s o u r c e e s t i m a t e s a r e c l e a r l y i n a s t a t e o f d i s - a g r e e m e n t . V7hat a b o u t r e g i o n a l e s t i m a t e s ? One would e x p e c t t h a t f o r a t l e a s t some w e l l - e x p l o r e d a r e a s ( s u c h a s t h e U.S. and C a n a d a ) , w e would h a v e more p r e c i s e e s t i m a t e s . U n f o r t u n a t e l y , t h i s i s n o t t h e c a s e . A d e t a i l e d c o l l e c t i o n o f p a s t and p r e s e n t r e g i o n a l e s t i m a t e s w i l l n o t b e l i s t e d h e r e . But t o g i v e t h e r e a d e r a b r i e f i d e a o f t h e e x t e n t o f u n c e r t a i n t y i n r e g i o n a l e s t i m a t e s ,
w e p r e s e n t r e s u l t s o f t h e D e l p h i s t u d y made by D e s p r a i r i e s ( 1 9 7 8 )
.
The s t u d y c o n s i s t e d o f two q u e s t i o n n a i r e s s e n t t o f o r t y - t w o o i l e x p e r t s , a s k i n g f o r e s t i m a t e s o f w o r l d o i l r e s o u r c e s b r o k e n down by r e g i o n . The s e c o n d q u e s t i o n n a i r e a l l o w e d m o d i f i c a t i o n o f e s t i m a t e s i n l i g h t o f t h e a n s w e r s r e c e i v e d o n t h e f i r s t r o u n d . Twenty-nine a n s w e r s w e r e r e c e i v e d t o t h e f i r s t q u e s t i o n n a i r e , t w e n t y t o t h e s e c o n d .
T h e r e a r e some m a j o r d i s a d v a n t a g e s t o t h i s t y p e o f s t u d y . P a r t i c i p a n t s a r e anonymous, t h a t i s , t h e y a r e n o t l i n k e d t o t h e i r e s t i m a t e s . And t h e y a r e b u s y . F o r b o t h t h e s e r e a s o n s e s t i m a t e s a r e c e r t a i n l y much l e s s c a r e f u l l y t h o u g h t o u t t h a n when a r e s e a r c h e r s p e n d s a y e a r o r more o n a s t u d y t h a t w i l l b e a r h i s name. E s t i m a t e s may a l s o b e more l i k e l y t o t e n d t o a common v a l u e , a s p a r t i c i p a n t s r e a c h f o r t h e same well-known p a p e r s o n w o r l d o i l r e s o u r c e s a s
s t a r t i n g p o i n t s . I n d e e d , t h e o b j e c t o f D e l p h i s t u d i e s i s t o r e d u c e d i s a g r e e m e n t . However, d e s p i t e t h e s e d i s a d v a n t a g e s , s u c h a s t u d y d o e s o f f e r a l a r g e s e t o f r e a d i l y c o m p a r a b l e r e g i o n a l e s t i m a t e s .
The r e g i o n a l e s t i m a t e s f r o m t h e D e l p h i s t u d y ( i n t h i s c a s e e s t i m a t e s o f r e s o u r c e s r e m a i n i n g t o b e p r o d u c e d ) a r e shown i n T a b l e 3 . A l t h o u g h o n e would e x p e c t t h i s t y p e o f s t u d y t o u n d e r - s t a t e t h e t r u e u n c e r t a i n t y , n o t i c e t h a t t h e m a g n i t u d e o f u n c e r - t a i n t y s u g g e s t e d by t h e r a n g e o f v a l u e s i s e x t r e m e l y l a r g e . I t i s v e r y l a r g e e v e n f o r r e l a t i v e l y w e l l - e x p l o r e d a r e a s . W e c a n c o n c l u d e t h a t u n c e r t a i n t y i n w o r l d e s t i m a t e s c a n n o t b e a t t r i b u t e d t o l a c k o f knowledge i n a f e w u n e x p l o r e d a r e a s .
*
*
Note t h a t a d d i n g t h e minimum v a l u e s a n d maximum v a l u e s f o r e a c h r e g i o n i s n o t a n a p p r o p r i a t e way t o s u g g e s t a r a n g e f o r w o r l d estimates.Table 3. Regional breakdown of Delphi oil resource estimates (in billions of barrels).
Mininun* Maximum* Size of Range* Median Estimate Estimate ( m a x e ) Estimate USA & Canada
Latin America Western Europe
USSR, E. Europe & China East & South Asia
(incl. Japan, Australia, New Zealand)
Middle East & North Africa Africa South of Sahara Deep Offshore & Polar
*
Tabulations originally done by M. Grenon in gigatonnes (forthcaning EPEU Report TPS80-763).
SOURCES OF UNCERTAINTY AND BIAS
We have s o f a r t a k e n o i l r e s o u r c e e s t i m a t e s a t f a c e v a l u e , l o o k i n g a t t h e r a n g e o f e s t i m a t e s a s a n i n d e x o f u n c e r t a i n t y . I t i s t i m e t o l o o k a b i t more c r i t i c a l l y a t t h e e s t i m a t e s , i d e n - t i f y i n g some p o s s i b l e b i a s e s and o v e r l o o k e d s o u r c e s o f u n c e r t a i n t y .
I n e s t i m a t i n g w o r l d o i l r e s o u r c e s , two m a j o r s o u r c e s of un- c e r t a i n t y a r e :
--
t h e amount o f u n d i s c o v e r e d o i l ; and--
u l t i m a t e r e c o v e r y r a t e sThe s t u d i e s c o n s i d e r e d i n t h i s r e p o r t c o n c e n t r a t e e f f o r t on e s t i m a t i n g t h e f i r s t o f t h e s e , t h e amount o f u n d i s c o v e r e d o i l . The i m p o r t a n c e o f e s t i m a t i n g u l t i m a t e r e c o v e r y r a t e s h a s been l a r g e l y o v e r l o o k e d . S t u d i e s t e n d t o assume a v a l u e f o r u l t i m a t e r e c o v e r y r a t e s r a t h e r t h a n a d d r e s s i n g t h e problem d i r e c t l y . But r e c o v e r y r a t e s a r e t h e m s e l v e s u n c e r t a i n , and w i l l make a l a r g e d i f f e r e n c e t o t h e amounts o f o i l u l t i m a t e l y a v a i l a b l e f o r u s e . Each one p e r c e n t i n c r e a s e i n r e c o v e r y r a t e w i l l i n c r e a s e t o t a l r e c o v e r a b l e o i l r e s o u r c e s by one p e r c e n t .
A t t h e moment r e c o v e r y r a t e s a r e a b o u t 25-30% ( D e s p r a i r i e s 1 9 7 8 ) . F o r t y p e r c e n t r e p r e s e n t s a lower l i m i t t o most o p i n i o n s on u l t i m a t e r e c o v e r y r a t e s . Nehring (3978) f o r e s e e s p o s s i b l e r a t e s o f 50% o r more. One r e s e a r c h e r (Moore 3962) h a s e s t i m a t e d t h e u l t i m a t e r e c o v e r y r a t e f o r t h e U.S. a t 65-35%. To s e e how i n f l u e n t i a l t h e r e c o v e r y r a t e c a n b e , n o t e t h a t o u r c e n t r a l i n t e r v a l , 2000-3800 b i l l i o n b a r r e l s , b a s e d on 4 0 % u l t i m a t e r e - c o v e r y , becomes 2500-4750 b i l l i o n b a r r e l s i f u l t i m a t e r e c o v e r y r e a c h e s even 50%.
Both o i l d i s c o v e r y and r e c o v e r y r a t e s w i l l be h e a v i l y i n f l u e n c e d by w o r l d o i l p r i c e s . C e r t a i n l y t h i s p o i n t , i f n o t a p p r e c i a t e d b e f o r e , s h o u l d b e o b v i o u s s i n c e t h e a d v e n t o f OPEC.
However, t h e i m p o r t a n c e o f o i l p r i c e s h a s been a l m o s t t o t a l l y i g n o r e d by e s t i m a t o r s o f o i l r e s o u r c e s , e x c e p t i n t h e s t u d i e s by D e s p r a i r i e s (1978) and by w o r k e r s a t t h e West German G e o l o g i c a l Survey ( B a r t h e l e t a l . 3 9 7 6 ) . T h i s seems t o b e a c r i t i c a l o v e r - s i g h t o f a l m o s t a l l o i l r e s o u r c e e s t i m a t e s .
Oil, and oil expertise, is dominated by large international business organizations. The majority of world oil resource esti- mates are made by these companies, and some inevitable biases result. First, oil companies tend to have a short-term view and are far more interested in reserves than resources. Where
they are interested in resources, it is not the actual amounts that are of interest, but the relative quantities to be expected in various regions--that is, where the relatively best opportuni- ties for new discoveries lie. This purpose is openly acknowledged.
As the well-known consultant Weeks puts it, his estimates are
"primarily for quantitatively rating basins of the world" (1953), and are "aimed at efficiency in expenditure of the exploration dollar" (1968). Putting these relative regional estimates together to form a world estimate is often an afterthought.
Second, since estimates are aimed at exploration investments, oil companies are highly sensitive to political limitations.
There is a strong tendency to underestimate amounts of discoverable or recoverable oil in areas where companies have suffered under political restrictions, or have been nationalized. This seems to have been the case for Latin America, and a large part of the Third World. For a fuller discussion of this point, see Odell (1980).
Finally, oil company estimates are often presented without any details on the method or data used. This is at least partly due to the feeling that these are "company secrets", to be used in making exploration investments. As Warman (1971) says, "It is not...discrete as an employee of an actively exploring oil company to review in detail the prospects of oil discovery around the world." This attitude is understandable, but it does make judging the accuracy of estimates very difficult.
CONCLUSION
It is clear from this short, critical look at oil resource estimates that both world and regional estimates are very uncer- tain. Estimates cover a wide range of values--there is no
evidence for a consensus of opinion. Nor is there strong evidence for a steadily increasing upward trend. Factors such as ultimate
r e c o v e r y r a t e s and economic f e a s i b i l i t y a r e , i n g e n e r a l , i n a d e - q u a t e l y t a k e n a c c o u n t o f . And many b i a s e s r e m a i n . I n s h o r t , what w e know a b o u t u l t i m a t e o i l r e s o u r c e s i s s u r p r i s i n g l y l i t t l e .
Energy s t u d i e s m u s t , f o r now, a l l o w f o r t h e f a c t t h a t t h e b e s t w e c a n d o i s t a l k a b o u t a w i d e i n t e r v a l o f p o s s i b l e v a l u e s f o r t h e w o r l d ' s u l t i m a t e c o n v e n t i o n a l o i l r e s o u r c e s .
APPENDIX. World oil resource estimates (in billions of barrels)
,
1945-1 980.*
y e a r R e s e a r c h e r O r g a n i z a t i o n E s t i m a t e Comments
--- -
1946 Duce
1946 Pogue
1948 Weeks
1949 Levor s e n
1949 Weeks
1958 Weeks
Aramco 500
605
J e r s e y 610
S t a n f o r d Univ. 1625*
J e r s e y 1 0 1 5
J e r s e y 1500/3000
I n t r o d u c t i o n o f o f f - s h o r e s o u r c e s Comment o n Levorsen
P r i m a r y r e c o v e r y / p r i m a r y and s e c o n d a r y
1959 Weeks r e t i r e d 2000/3 500 P r i m a r y r e c o v e r y / p r i m a r y and s e c o n d a r y
1965 H e n d r i c k s U.S. G e o l o g i c a l S u r v e y 10,000/6200 (2480) O i l o r i g i n a l l y i n p l a c e / u l t i m a t e l y d i s c o v e r a b l e ( i f 40% r e c o v e r y )
1967 Ryman J e r s e y 2090 Not p u b l i s h e d ; r e f e r r e d t o by Hubbert (1969)
I 1968 Weeks
-.
1969
I Hubbert
C o n s u l t a n t 2200/3 550
U.S. G e o l o g i c a l Survey 1350-2100
P r i m a r y r e c o v e r y / p r i m a r y and s e c o n d a r y Based on Weeks and Ryman
1 9 7 0 Moody Mobil 1 8 0 0
1 9 7 1 Warman B r i t i s h P e t r o l e u m 1200-2000 I n c l u d e s a n a l y s i s o f o t h e r estimates 1 9 7 1 Weeks C o n s u l t a n t 2290/3650 P r i m a r y r e c o v e r y / p r i m a r y and s e c o n d a r y 1972 Warman B r i t i s h P e t r o l e u m 1 8 0 0 Anal. o t h e r e s t i m a t e s ; f i r s t m e n t i o n o f
c o n s e n s u s
1972 J o d r y s u n 1952 Not p u b l i s h e d ; r e f e r r e d t o by Hubbert (1974)
1973 Hubbert U.S. G e o l o g i c a l Survey 2000
1973 O d e l l Erasmus Univ. 4 000
Based o n Warman and p r o b a b l y J o d r y .
"Convergence o f e s t i m a t e s "
~ x t r a ~ o l a t i o n t o y e a r 2000 o f r e g r e s s i o n l i n e b a s e d o n s e r i e s o f e s t i m a t e s
1974 ( a ) P a r e n t , Linden I n s t . o f G a s Technology 3000 (4000) No i n f o . o n method ( i f r e c o v e r y > 45%) 1974 (b) P a r e n t , Linden I n s t . o f G a s Technology 3580 U s e s s e v e r a l d a t a s o u r c e s
*
E s t i m a t e s from M . Grenon, "A Review o f World Hydrocarbon Resource Assessment", EPRI r e p o r t TPS~O-763 ( f o r t h c o m i n g ) e x c e p t f o r e s t i m a t e by S t y r i k o v i c h .LI 3 a)
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