THE PETROLEUM GEOLOGY AND HYDROCARBON POTENTIAL OF NAVAL PETROLEUM … · 2006. 3. 15. · THE PETROLEUM GEOLOGY AND HYDROCARBON POTENTIAL OF , NAVAL PETROLEUM RESERVE NO. 4 NORTH

UNITED STATES

DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY

THE PETROLEUM GEOLOGY AND HYDROCARBON POTENTIAL OF

NAVAL PETROLEUM RESERVE NO. 4 NORTH SLOPE, ALASKA

PROPERN OF DGGS LIBRARY

OPEN-FILE REPORT 77-475

This report is preliminary and has not been edited or reviewed for conformity with Geological Survey standards and nomenclature

Menlo Park, California June 1977

UNITED STATES

DEPARTMENT OF THE INTERIOR

GEOLOGICAL SURVEY

Y

THE PETROLEUM GEOLOGY AND HYDROCARBON POTENTIAL OF

, NAVAL PETROLEUM RESERVE NO. 4 NORTH SLOPE, ALASKA

BY R. D. Carter, C. G . Mull, K. J. Bird, and R. B. Powers

OPEN-FILE REPORT 7747Ji

Thii report i s preliminary and has not been edited or reviewed for conformity with Geological Survey standards and nomendature

Figure 1. 2.

Index map, North Slope of Alaska. . . U.S.G.S. surface mapping coverage, North Slope of Alaska . . . . . . .

Pet-4 program seismic coverage,North Slope of Alaska . . . . . . . . . .

Tectonic elements of the North Slope of Alaska . . . . . . . . . . . . .

Structural-stratigraphic cross section,NPR-4 . . . . . . . . . . .

Stratigraphic sections, NPR-4 . . . . Reservoir-source rock relations and geochemical data, Prudhoe Bay area.

Approximate northern limits, Lisburne and Sadlerochit Groups. . . . . . .

Exploration trends, NPR-4 . . . . . .

TABLES

Table 1. Test and development wells, NPR-4. . . 2. Oil and gas fields, Alaska North

Slope . . . . . . . . . . . . . . . . 3. Geophysical data, NPR-4 Pet-4 program. 4. Petroleum geology and play analysis,

NPR-4. . . . . . . . . . . . . . . .

THE PETROLEUM GEOLOGY AND

HYDROCARBON POTENTIAL 0 F

NAVAL PETROLEUM RESERVE NO. 4 NORTH SLOPE, ALASKA

By R. D. Carter, C. G. Mul l , K. 3. Bird, and R. B. Powe 1 SUMMARY

The Naval Petroleum Reserves Production Act o f 1976 provide f o r the t ransfer of j u r i s d i c t i o n o f Naval Petroleum Reserve No. 4 f r o m he Depart- ment of the Navy t o the Department o f the I n t e r i o r on June 1, 1977. I n an t i c i pa t i on o f the enactment o f the law, the U.S. Geological Survey prepared an admin is t ra t ive repor t i n 1976 t o provide background in format i n, t o describe the s ta te o f knowledge o f the geology o f NPR-4, and t o recommend studies necessary f o r an evaluat ion o f the hydrocarbon po ten t ia l o f the Reserve.

I

This paper i s based on the above admin is t ra t ive repor t whic i n t u r n depended upon pub1 ished 1 i terature, unpublished U. S. Geological Survey data, and the background know1 edge o f Survey geologists w i t h extensive experience

p a t i b i 1 i t i e s of s ign i f icance were found.

I i n the regional geology and petroleum geology o f the North Slope of Alaska.

t I n addi t ion, resu l t s o f the ongoing Navy explorat ion o f NPR-4 we e made ava i lab le t o the Geological Survey fo l lowing the s ign ing o f the k c t by the President on A p r i l 5, 1976. These resu l t s were reviewed f o r posbible c o n f l i c t s w i t h in te rp re ta t ions and conclusions reached i n t h i s repor t and Po incom-

I

I Surface geology explorat ion by the USGS i n the NPR-4 area b gan i n 1904 and has continued sporad ica l ly t o the present. The PET-4 progra 1944-1953,

I

designed " to appraise the o i l p o s s i b i l i t i e s o f Naval Petroleum R 1 serve No. 4 and surrounding areas ," produced the f i r s t subsurface in format io i n the discovery o f several minor o i 1 and gas deposits. There exp lord t ion a c t i v i t y fo l l ow ing the terminat ion o f the PET-4 program when the Navy i n i t i a t e d a vigorous program o f geophysical and explorat ion.

1

and resu l ted was l i t t l e

u n t i 1 1974 d r i l l i n g

and the eastern boundary, they are very t h i n o r absent from NPR-4. Geo- chemical data ind ica te t ha t Cretaceous, Jurassic, and Upper T r iass ic shales have source-rock po ten t ia l . Mississippian and Lower Tr iass ic rocks are low i n source-rock po ten t ia l probably because o f low organic content and thermal over-maturi ty i n deeper parts o f the basin. The supergiant Prudhoe Bay f i e l d i s the r e s u l t o f r i ch , thermally mature Cretaceous source beds spperposed on the truncated edges of a ser ies o f good reservo i r beds. Unfortu ately, t h i s jux tapos i t ion w i l l probably not be found i n most o f NPR-4. WithFn the Reserve the unconfon i ty accounting f o r t h i s superposit ion i s apparently1 present on-

I n the Southern Foo th i l l s t rend gas may be found i n traps i n Mississippian allochthons, and i n T r iass ic and Estimated depths o f over 25,000 f e e t t o autochthonous c l ude them from explorat ion. Experience i n simi 1 a r t h a t t o t a l reserves are l i k e l y t o be smaller than i n A known prospect i n the Lisburne Group i n the Reserve exh ib i t s several hundred f e e t o f ta ins pyrobitumen. The rocks d ip d r i 1 l i n g object ive.

Current knowledge o f North plays t h a t might be considered Analysis o f the p l ays ind icates accumulations.

shore on ly i n very l i m i t e d areas along the nor th coast. Two of important Prudhoe Bay reservoirs, the Lisburne and Sadlerochit, i n a favorable s t r uc tu ra l - s t ra t ig raph ic pos i t i on on ly i n the eastern p a r t o f NPR-4. Regional dips would seem t o preclude o i l from the Prudhoe Bay area westward i n t o the Reserve. Known o i l occurrences i n NPR-4 are found i n Upper Tr iassic, Jurassic, and rocks whereas o lder beds have had no reported shows. Cretaceous rocks contain ing the r i c h e r source beds, o r reservo i r beds of any f l u i d migrat ion distance o f them, would appear t o be the major NPR-4.

Three broad exp lora t ion trends w i t h a number o f plays can be

the most nay be present

extreme north- I migrat ion

I and gas I Zretaceous o r Jurassic

age w i t h i n 03ject ives i n

predicted fo r NPR-4. The Coastal P la i n t rend i s prospective f o r o i l and g s t ruc tu ra l , s t ra t ig raph ic , and combination traps i n pre-Middle C rocks. The Northern Foo th i l l s t rend might f i n d o i l and gas i n s s t r uc tu ra l traps i n Middle Cretaceous and i n l i m i t e d Upper Creta Deeper s t r uc tu ra l and s t r a t i g raph i c traps i n Lower Cretaceous f o prospective f o r gas. A major p lay i n both the above trends i s t Group of Middle Cretaceous age, a coarse c l a s t i c wedge present o the northern Brooks Range Foo th i l l s and the southern coastal p l a i n St ra t igraph ic re la t ionsh ips are analogous t o the Cretaceous Mesa of the Rocky Mountains . Inter tongui ng o f marine and non-mari ne combined w i t h s t r uc tu ra l features may r e s u l t i n po ten t ia l traps. abundant and suggests a probable gas play. Many o f the sediments

area. Verde Group

sediments Coal i s are medium-

t o coarse-grained sandstones, bu t a c lay matr ix i n h i b i t s porosi a b i l i t y , and the p red ic t ion o f po ros i t y trends w i l l be a major

data gathered by the on-going Navy exploration program in- I

augurated in 1974 became available to the Geolog cal F Survey shortly after the transfer Act was signedl By no

means all of this considerable mass of informatibn has been

assimilated, but well and seismic results have b en reviewed.

No confidential or proprietaky Navy data are inc

this report. However, significant facts pertine t to a f description of the geology and an assessment of he hydro- f carbon potential of NPR-4 were carefully conside ed for 4 their effect on statements and conclusions put f rward in 0 this paper, and no inconsistencies were noted.

interpretations will undoubtedly be modified in

as more of this geophysical, geochemical, and wet1 infor-

mation is digested, and as additional material b comes e available.

and the Prudhoe Bay area. A discussion of the t

parent exploration trends is followed by a detai

This paper describes the history of explorad:ion

NPR-4 and documents the information base present1.y

able for hydrocarbon-resource assessment. From

base and first-hand knowledge the framework and

geology are described, and a comparison made

scription of the types of plays possible in NPR- . 4

of

avail- #

':his data

petroleum

between NPR-4

Tes t w e l l d r i l l i n g r e s u l t e d i n t h e d i scovery of an o i l

f i e l d a t Umiat; a gas f i e l d a t Gubik; a sma l l gqs f i e l d

a t Barrow; t h r e e p o s s i b l e gas f i e l d s a t Meade, quare Lake, 9 i and Wolf Creek; and two minor o i l d e p o s i t s a t S'mpson and

'

Fi sh Creek (Gryc, 1970, p . c3; f i g . 1 ) . The Pe -4 program

was r e c e s s e d i n March 1953.

S ince 1953 t h e A i r Force has d r i l l e d a we1 a t Barrow i t o r e p l a c e a Navy w e l l de s t royed by f i r e ( P o r t e f i e l d ,

1974) , and t h e Navy has d r i l l e d South Barrow we 1s Nos. 6 : through 1 3 i n o r d e r t o a s s u r e a con t inu ing supp y o f gas f o r 1 t h e n a t i v e s and t h e government f a c i l i t i e s a t Ba row. South

Barrow w e l l 1 2 (1974) was d r i l l e d 6 m i l e s e a s t f t h e f i e l d

and completed a s a marginal gas w e l l ( f i g . 1 ) . Recent Navy

e x p l o r a t o r y w e l l s i n c l u d e t h e Iko No. 1 (gas we 1?3 and t h e

Cape H a l k e t t No. 1 ( s t a n d i n g ) , bo th d r i l l e d i n 1975; t h e

Eas t Teshekpuk No. 1 (abandoned) d r i l l e d i n 197

w e l l s proposed f o r f i s c a l y e a r 1977. Of t h e l a

South Ha r r i son Bay No. 1 and t h e A t i g a r u Po in t

been d r i l l e d and plugged; t h e South Barrow No.

about 1 mi l e s o u t h e a s t o f South Barrow No. 1 2 , q a s been

completed a s a gas w e l l ; and t h e West F i sh Cree

t h e W . T. Foran No. 1, and t h e South Simpson No

p r e s e n t l y d r i l l i n g (March, 1977, f i g . 1 ) .

The i n c r e a s e i n f i s c a l y e a r 1974 funding f r NPR-4 0 al lowed t h e Navy t o embark on a v igorous e x p l o r d t i o n

program o f se i smic-and g r a v i t y - d a t a c o l l e c t i o n i n a d d i t i o n

1 28. Texaco W. Kurupa 2-2A 29. Arm Schrader

1 30. McCulloch Cdviile I McCulloch E. Umiat 1 Brit. Pet. E. Umiat 1 31. Arco ltkillik I 32. Union Kookpuk

1 33. Gulf Coiville Delta 1 1 34. Cape Halkett 1

1.2 35. East Teshekpuk 1 2 36. Iko 1

37. South Harrison Bay 1 1 38. Atigaru Point 1 1 39. West Fish Creek 1

40. W. T. Foran 41. South Simpson 42. Swth Barrow

- ----

EXISTING DATA BASE

P u b l i c a t i o n s

E a r l y geo log i c e x p l o r a t i o n o f NPR-4 through 1926 was

r e p o r t e d on by t h e U.S.G.S. (Schrader and P e t e r s , 1904;

Smith and Mer t i e , 1930) . The r e s u l t s o f t h e PET-4 program

were d i s cus sed a t l e n g t h i n U.S.G.S. P r o f e s s i o n a l Papers

301, 302 A-D, 303 A-H, 304 A, and 305 A - L . A comprehensive

r e p o r t on t h e subsu r f ace , s t r a t i g r a p h i c , s t r u c t u r a l , and

economic geology o f NPR-4 was pub l i shed by C o l l i n s and

Robinson (1967). Papers and r e p o r t s on NPR-4, and t h e North

Slope i n g e n e r a l , by t h e Geolog ica l Survey and o t h e r s a r e

l i s t e d i n two r e c e n t b i b l i o g r a p h i e s by Maher and Trollman

(1970) and by C a r t e r , Denman, and P i e r p o i n t (1975). Subse-

i quent s i g n i f i c a n t papers i nc lude t hose by Detterman and o t h e r s

(1975), Grantz , Holmes, and Kososki (1975), B i rd and Jordan

(1976), Blean (1976), and Jones and Speers (1976). Unpublished

d a t a i n March, 1977 i n c l u d e a f o l i o o f subsu r f ace mapping of

t h e e a s t e r n North S lope a r e a , g r a v i t y mapping and rock-

d e n s i t y t a b u l a t i o n i n t h e n o r t h e r n p o r t i o n of t h e Arctic

Nat iona l W i l d l i f e Range, and a n o r t h e r n Alaska paleomagnetism-

p l a t e t e c t o n i c s s t udy . Geologic mapping coverage i s shown on

f i g . 2 .

T e s t w e l l s

T e s t w e l l d a t a i n NPR-4 a r e shown i n f i g . 1 and i n t a b l e 1.

The 45 c o r e tests (page 10) a r e shown n e i t h e r on f i g . 1 no r

I i n t a b l e 1. A few were d r i l l e d i n wide ly s c a t t e r e d a r e a s ,

WELL Development Wells

N O . -

South Barrow

TOTAL DEPTH I N FEET

FORMATION AT TOTAL DEPTH

J u r a s s i c J u r a s s i c J u r a s s i c J u r a s s i c J u r a s s i c J u r a s s i c

? J u r a s s i c Pre-Dev. a r g i l l i t e J u r a s s i c

COMPLETED

Gas 6/55 Gas 3/64 Gas 4/68 Gas 5/69 Gas 4/70 Gas 31 73

? 31 74 Gas 5/74 Gas (Susp.) 1/77 Gas 2/ 77

Sources: U.S.G.S. Prof . Papers 301, 305-A-K; Alaska Div. of O i l and G a s ; The Alaska Scouting Serv ice , May 19, 1976; Navy p re s s r e l e a s e , Jan. 21, 1977; Petroleum Information, Feb. 16, 23, Mar. 23, 1977.

I 1 1

Table 1 (Cont): Test and development we l l s , NPR-4.

Table 2. O i l and gas f i e l d s , Alaska nor th slope.

Approximate Depth

of Production F ie ld - Production Producing Formation Reservoir Li thology i n f e e t

Umiat NPR-4 O i l h e r Cret. Nanushuk Group Sands tone 250-1,350

Gubik

South Barrow NPR-4

Meade NPR-4

Square Lake NPR-4

Wolf Creek NPR-4

Simpson NPR-4 F V

Fish Creek NPR-4

Prudhoe Bay

Gas

Gas

Gas

Gas

Gas

O i l

O i l

O i l

O i l & Gas

O i l & Gas

O i l & Gas

Upper Cret . Upper Cret .

J u r a s s i c

Lower Cret.

Upper Cret.

Lower Cret.

Upper Cret.

Lower Cret.

J u r a s s i c

J u r a s s i c

U. T r i a s s i c

L. Triassic-Perm.

Prince Creek Fm. Chandler-Ninuluk Fms. undiff .

Nanushuk Group

Seabee Fm.

Nanushuk Group

Nanushuk-Seabee Fms . Topagoruk Fm.

Kuparuk River

Sag River Fm.

Shublik Fm.

Sadlerochi t Grp.

Sandstone

Sandstone

Sandstone

Sands tone

Sandstone

Sandstone

Sandstone

Sandstone

Sandstone

Sandstone

Sandstone/Limestone

Sandstone

O i l & Gas Miss. & Penn. Lisburne Grp. Carbonates 11,500

Kavik Gas T r i a s s i c Sag River Fm. Sands tone 4,250

Gas T r i a s s i c Sadlerochi t Grp. Sandstone 4,600

Kemik Gas T r i a s s i c Shublik Fm. Limes tone 8,700

Sources: Harrison and o thers (1973); American Petroleum I n s t i t u t e and o t h e r s (1974); Morgridge and Smith (1972)

I d e n t i f i e d Resources (Econ. & Subecon.) Mil l ion bb l s . o i l

B i l l i o n c.f . gas

No e s t .

No e s t .

No e s t .

No e s t .

*9.6 b i l l . b b l s . o i l

26.5 t r i l l i o n c f g

No e s t .

No e s t .

No e s t .

No e s t .

*Measured Reserves

. -- - Naval Petroleum Reserve No.4 Boundary I

SEISMIC REFLECTION DATA

(S ing l e Fold Dynamite)

Source No. of P r o f i l e s Line Miles

U.S. Navy

U.S. Navy

U.S. Navy

U.S. Navy

U.S. Navy

U.S. Navy

U.S. Navy

U.S. Navy

U.S. Navy

Year Completed

1945

Tota ls : 13 ,431 3,357.75

Mileage based on s e i smic p r o f i l e spac ing o f 1,320 f t .

SEISMIC REFRACTION DATA

Source

U.S. Navy

U.S. Navy

U.S. Navy

>

No. o f P r o f i l e s Year Completed

U.S. Navy 15 1950

U.S. Navy 32 1952

T o t a l : 391 +

R e f r a c t i o n p r o f i l e s were u s u a l l y s h o t w i th 8 , 0 0 0 - f t sp read l e n g t h s .

Note: Does n o t i nc lude 5,000+ mi l e s o f s e i smic r e c o r d s r e c e n t l y acqu i r ed by t h e U. S r Navy.

Sources : Woolson and o t h e r s (1962) ;Kel le r and Henderson (1947).

Table 3 (Cont): Geophysical Data, PET-4 program, NPR-4 2 1

COASTAL PLAIN

SADE

a TOPAGORUK

Q BARROW

CONTINENTAL SHELF

oil show

O gas show

160 180 2 0 0 2 2 0 2 4 0 2 6 0 2 8 0 300 Miles I

I I

, I I I I

250 300 3 5 0 4 0 0 4 5 0 Kilometers

KINGAK SHALE KINGAK SHALE

CHERT, SILT 8 SH.

URNE GROUP

LST. (L OOL

NERUOKPUK GROUP?

AND QUARTZITE

Figure 6. Generalized stratigraphic sections, NPR-4

Brookian Sequence

The Brookian (Late J u r a s s i c , Cretaceous , T e r t i a r y )

sequence c o n s i s t s o f l a r g e amounts o f greywacke sands tone

and s h a l e d e r i v e d from an orogeny t h a t began i n La te

J u r a s s i c and con t inued i n t o La te Cretaceous and perhaps

E a r l y T e r t i a r y t ime i n t h e wes t e rn Brooks Range and a p p a r e n t l y

i n t o t h e Neogene i n t h e n o r t h e a s t e r n Brooks Range. Th i s

orogeny, a r e s u l t o f i n t e n s e compression, caused l a r g e - s c a l e

r e l a t i v e l y nor thward t h r u s t i n g o f Pa l eozo i c t o Cretaceous

age rocks . Aggregate s h o r t e n i n g i n t h e wes te rn Brooks Range

i s e s t i m a t e d t o be 100 km (62 mi) (Mart in , 1970) o r more

than 240 km (149 mi) (Snelson and T a i l l e u r , 1968) .

The orogeny d r a s t i c a l l y changed t h e paleogeography of

! A r c t i c Alaska . Northern sou rce s were r ep l aced by sou the rn

I

i s o u r c e s - - t h e Brooks Range. I n i t i a l l y , however, sediments

were s u p p l i e d from bo th n o r t h e r n (E l lesmer ian) and sou the rn

(Brookian) sou rce s . The n o r t h e r n sou rce subs ided and was

over lapped i n E a r l y Cretaceous (Neocomian) t i m e . Subsidence

o f t h i s sou rce a r e a i s recorded by t h e over lapp ing sediments

and subsequent northward downwarping and f a u l t i n g a long a i

l i n e a r zone approximate ly p a r a l l e l t o t h e p r e s e n t s h o r e l i n e .

The r e s u l t a n t s t r u c t u r e , t h e Barrow Arch, i s a l i n e a r basement

, r i d g e p lung ing t o t h e s o u t h e a s t ( f i g . 4 ) . The Prudhoe and @

I South Barrow f i e l d s a r e l o c a t e d on t h e c r e s t o f t h i s f e a t u r e .

Throughout t h e orogeny l a r g e volumes o f c l a s t i c d e b r i s

were shed northward i n t o a mig ra t i ng foredeep. The E a r l y

r

29

--

PETROLEUM GEOLOGY

In t roduc t ion

A petroleum province r e q u i r e s t h e r e l a t i v e l y c l o s e

a s s o c i a t i o n o f petroleum source rock, porous r e s e r v o i r rock,

I and s e a l i n g beds a d j a c e n t t o t h e r e s e r v o i r t o form t r a p s .

An a d d i t i o n a l and most c r i t i c a l requirement i s a favorab le

geo log ic h i s t o r y , g e n e r a l l y r e f e r r e d t o a s "timing". A

f avo rab le h i s t o r y r e q u i r e s t h e fol lowing events : 1 ) b u r i a l

I of source rocks s u f f i c i e n t l y deep f o r petroleum gene ra t ion ,

2 ) t h e presence of permeable rock t o provide a mig ra t ion p a t h

f o r t h e petroleum a s it i s genera ted and e x p e l l e d from t h e

source rock , and 3) t h e format ion o f t r a p s i n r e s e r v o i r s

updip from, o r a d j a c e n t t o , t h e source beds i n o rde r t o

e n t r a p t h e migra t ing petroleum and t o prevent i t s escape t o

t h e s u r f a c e .

The petroleum p o t e n t i a l o f a p rov ince , t h e r e f o r e , depends

on t h e q u a l i t y o f source and r e s e r v o i r rock, t h e s i z e a f t h e

t r a p s , and t h e geo log ic h i s t o r y of t h e bas in . The d i scovery

i n i t i a l l y o f s e v e r a l o i l and gas seeps and l a t e r s e v e r a l small

o i l and gas f i e l d s by t h e Navy confirmed t h e b e l i e f t h a t t h e

North Slope was an o i l p rov ince . However, t h e p o t e n t i a l of

t h i s p rov ince was no t f u l l y app rec i a t ed u n t i l t h e d i scovery

of t h e Prudhoe Bay f i e l d . This f i e l d i s an example of an

unusual combination of f avo rab le f e a t u r e s .

B r i e f l y t h e Prudhoe Bay f i e l d c o n s i s t s o f m u l t i p l e s t acked

r e s e r v o i r s , which reach t h e i r maximum development nea r t h e c r e s t

Diagrammatic cross-section B'- 8 of castem Arctic Slope; location is shown on Figure 4. Prudhoe Bay hydrocarbons are trapped beneath unconformity at base of Cretaceous on Barrow arch. Brooks Range thrusts are shown at left.

Reservoir-source rock relations in Prudhoe Bay field depicted on east-west diagrammatic cross section. Oil-source potential of finegrainid rock se- quences as determined hy amount of total organic catbon (expressed in percent and by size of circle) and amount of C,,, hydrocarbon content (expressed in parts per million and by size of pie slice). Basal Mississippian shale = 1.1% and 14 ppm; Mississip- pian redbeds = 0.04% and 10 ppm; Lisburne carbo- nate rocks = 0.3% and 35 ppm; basal Sadlerochit shale = 0.7% and 32 ppm; Jurassic marine shale = 1.9% and 660 ppm; Cretaceous marine shale = 5.4% and 3,000 ppm.

Figure 7. Diagrammatic cross-sections showing reservoir- source-rock relations and geochemical data in the Prudhoe Bay area (modified from Morgridge and Smith, 1972).

Reservoir Rocks

Both c l a s t i c and carbonate r e s e r v o i r rocks a r e present

on the North Slope. The b e s t r e s e r v o i r s a r e the pre-Middle

Cretaceous c l a s t i c and carbonate rocks along t h e Barrow

Arch. However, these r e s e r v o i r s a r e of l imi ted thickness

and a r e a l ex ten t . In c o n t r a s t , t h e Cretaceous rocks i n the

f o o t h i l l s region a r e genera l ly poorer q u a l i t y r e s e r v o i r s ,

but they a r e very t h i c k and a r e a l l y extenqive. Reservoir

data have been summarized f o r outcrop samples and Navy we l l s

(Brosge and T a i l l e u r , 1971), f o r t h e Sadlerochi t Group a t

Prudhoe Bay (van Poolen and Associates , Inc. , 1974; Jones

and Speers, 1976), and f o r the Lisburne Group (Bird and

Jordan, 1976) . The most a t t r a c t i v e r e s e r v o i r rocks a r e those r e l a t e d

t o a nor thern source a rea . Included a r e the Lisburne Group,

Sadlerochi t Group, Shublik Formation, Sag River Sandstone,

and Kuparuk River Sandstone. A l l a r e product ive a t Prudhoe

Bay and a r e b e s t developed i n the nor th . The Ellesmerian

sequence i n NPR-4 has been penet ra ted by t h e Topagoruk,

Simpson, and Barrow wel l s and probably by the r ecen t Navy

wel l s , Cape Halket t and East Teshekpuk ( t a b l e 1 ) . Data from

the a v a i l a b l e wel l s i n d i c a t e t h a t nea r ly a l l sandstone u n i t s

a t Prudhoe Bay a r e p resen t i n NPR-4. These da ta a r e i n -

s u f f i c i e n t t o determine the most favorable r e s e r v o i r f a c i e s

and t rends , but they do i n d i c a t e t h a t t h e b a s i c s t r a t i g r a p h i c

p a t t e r n i s progress ive northward onlap onto the Frankl inian

PETROLEUM

RESERVE \ !

NO. 4 / /'

0 J

I I ,ccc-\ I - /'

I L

Sadlerochit Group

a Lisburne Group

100 Miles Modified from Lowell, 1976

Wells I Simpson 2 Topagoruk 3 East Teshekpuk 4 Cape Halkett

Figure 8. Approximate northern limits, Lisburne and Saddlerochit Groups

Adequate s e a l s a r e expected t o be p r e s e n t i n most s t r u c t u r a l

1 and s t r a t i g r a p h i c t r app ing s i t u a t i o n s .

I The p o t e n t i a l f o r s t r u c t u r a l t r a p s i s g r e a t e s t i n t h e

1 f o o t h i l l s b e l t i n f o l d s a s s o c i a t e d wi th t h r u s t i n g . These

I t r a p s may be of l i m i t e d a r e a l e x t e n t and d i f f i c u l t t o

t exp lo re f o r , e s p e c i a l l y i n t h e more g e o l o g i c a l l y complex

I southern f o o t h i l l s . Accumulations i n s t r u c t u r a l t r a p s i nc lude

I t h e o i l f i e l d a t Umiat and t h e Gubik, Kemik, and Kavik gas

I f i e l d s . S t r u c t u r a l t r a p s r e l a t e d t o broad g e n t l e f o l d i n g

! and a s s o c i a t e d normal f a u l t i n g may a l s o be p r e s e n t on t h e

Barrow Arch. The South Barrow gas f i e l d may be an example

I of t h i s type o f t r a p .

S t r a t i g r a p h i c t r a p s may be r e l a t e d t o updip p'inch-outs

I and t r u n c a t i o n s i n t h e pre-Lower Cretaceous rocks a long t h e

Barrow Arch. However, t h e extremely f avo rab le s o u r c e - t o - I

r e s e r v o i r r e l a t i o n s h i p s a t Prudhoe Bay may no t be p r e s e n t .

An a d d i t i o n a l t r app ing mechanism may be updip s h a l i n g - o u t of

sands depos i t ed on t h e f o r e s e t and bot tomset beds i n Cretaceous

c l a s t i c wedges. Thin i s o l a t e d sands w i t h i n t h e t h i c k Torok

Sha le may be an example o f t h i s type .

Combination s t r u c t u r a l and s t r a t i g r a p h i c t r a p s such a s

Prudhoe Bay may be p r e s e n t . They may be sma l l , however,

compared t o Prudhoe Bay because of l e s s f avo rab le combinations

of r e s e r v o i r , source , and s t r u c t u r e .

Regionally in northern Alaska, hydrocarbon reservoir

horizons have been found in the Ellesmerian sequence,

consisting of Mississippian to Middle Pennsylvanian shallow

water carbonates (Lisburne Group), a major Early Triassic

sandstone and conglomerate horizon (Sadlerochit Group),

thin carbonates in the Late Triassic (Shublik Formation),

a thin late Triassic sandstone (Sag River Sandstone), and

Early Cretaceous and/or Jurassic sands tone (Kuparuk River

Sandstone) (fig. 6). All these horizons are related to the

northern platform area. In addition, Early Cretaceous

sandstones (Brookian sequence) derived from the south are

reservoir horizons in some areas. Late Cretaceous and

Tertiary beds are also potential reservoirs on the Arctic

Slope, but available information indicates that rocks of this

age are very thin or absent from most of the Reserve. With

the exception of limited areas along the northern coastline,

and the eastern boundary, Late Cretaceous and Tertiary rocks

may be precluded from consideration as exploration objectives

in NPR-4. I I

The Prudhoe Bay hydrocarbon accumulation is contained

in reservoirs of the Lisburne Group, the Sadlerochit Group,

the Shublik Formation, the Sag River Sandstone, and Kuparuk ,

River Sandstone. The major reservoir is the Lower Triassic

Ivishak Formation of the Sadlerochit Group. Published

geochemical data, in combination with the structural and

stratigraphic relationships (Morgridge and Smith, 1972)

oral commun., 1976; Gold and Lachenbruch, 1973). In either

case, regardless of the cause of the high gradient, the 8

result may be higher than average temperatures affecting

the sedimentary section and the organic matter contained

i within the sediments. Older rocks with longer burial I

histories may thus have had greater residence times at I

elevated temperatures and therefore may have been more I

greatly affected by eometamorphic processes while younger

beds may only be reaching the point of optimum oil generation

and migration. At Prudhoe Bay, the Sadlerochit reservoir

temperature ranges from 192" to 216°F at a depth of 8,650

feet, and an average of 200°F is being used in reservoir

calculations (van Poolen and others, 1974, p. 15). Calcu-

lations by Bird and Jordan (1976) on burial history and

geothermal gradient indicate that Mississippian coals in the

Prudhoe Bay area are probably within the gas generating

regime below 13,000 feet.

In summary, the supergiant Prudhoe Bay oil and gas

accumulation appears to be the result of the fortuituous

juxtaposition of organically rich, thermally mature,

Cretaceous source beds with older reservoir beds containing

good to excellent porosity and permeability. The importance

of these geological, geochemical, and thermal history relation-

ships cannot be overemphasized in an analysis of the hydro-

carbon potential of any part of northern Alaska.

4 . As a r e s u l t of the above f a c t o r s , the p r o b a b i l i t y

of juxtapos i t ion of Cretaceous source beds with

l a t e Paleozoic and e a r l y Mesozoic r e se rvo i r horizons

i n most of NPR-4 i s s l i g h t . Long d i s t ance hydro-

carbon migration from Cretaceous source beds i n t o

these horizons appears unl ike ly .

Subs tan t i a t ion of the Prudhoe Bay a rea geochemical da ta

seems t o be found i n the r e s u l t s of some of the Navy wel l da ta

from the PET-4 program of explora t ion , and from indus t ry

d r i l l i n g i n nor thern Alaska o the r than i n t h e Prudhoe Bay

area . Discoveries of gas and some o i l have been made from

t h i n J u r a s s i c and Upper T r i a s s i c beds i n t h e Barrow a rea .

An a c t i v e o i l seep and shows i n wel l s i n the Cape Simpson

a rea a r e probably derived from Upper Cretaceous beds.

Varying small amounts of o i l and gas were recovered from

Lower Cretaceous rocks a t var ious loca t ions i n NPR-4.

Almost every well t h a t has penet ra ted Cretaceous beds on t h e

Arc t i c Slope has had some hydrocarbon shows. I n c o n t r a s t ,

Permian and probable Lower T r i a s s i c and Mississ ippian beds

had no repor ted shows i n t h e only pub l i c ly a v a i l a b l e wel l

(Topagoruk #1) t h a t penet ra ted them i n NPR-4. East of

Prudhoe Bay, only gas has been recovered from T r i a s s i c

r e se rvo i r beds i n two a reas d i s t a n t l y removed from communi-

ca t ion with the r i c h Cretaceous source beds (Kemik and Kavik

f i e l d s , f i g . 1 ) .

I comparison with the similar Rocky Mountain Cretaceous

I section suggests that the play will be dominantly a gas

I play with small oil accumulations. This is somewhat

substantiated by the numerous gas shows in many of the Navy

wells in NPR-4. One of the main controlling factors in the

I play may be reservoir quality; although many of the sediments

I i are medium- to coarse-grained sandstones, a pervasive clay

1 matrix inhibits porosity and permeability. This clay probably I

I consists of primary depositional material plus clays from

1 diagenetic alteration of mafic igneous detritus derived from 1 an extensive source terrain in the Brooks Range. As a result, I

one of the major problems in the Albian play will be pre-

I diction of porosity trends. One of the major controls on

I distribution of clay matrix and therefore porosity may be

the environments of deposition. Winnowing of the clays may

t be much more efficient in some environments, whereas

diagenetic alterations of igneous detritus may have a greater

inhibiting effect in other environments. Only limited study

has been devoted to these relationships in northern Alaska.

The southernmost trend, the Southern Foothills sub-

province, is believed prospective for gas in complex structural

traps. Possible objectives are carbonate reservoirs in the

Mississippian (Lisburne Group) and Triassic (Shublik

Formation) and sandstone reservoirs in the Cretaceous

(Okpikruak, Fortress Mountain, and Ipewik Formations).

1966; Chapman and o t h e r s , 1964) , and on carbonate f a c i e s

s t u d i e s (Armstrong, 1970) . The Lisburne Group i n t h e a r e a

o f Lisburne Ridge, nea r t h e E t iv luk River a t t h e s o u t h e a s t e r n

corner o f NPR-4 ( f i g . 9), con ta ins approximately 500 f e e t of

dolomite w i t h observable i n t e r g r a n u l a r and vugular p o r o s i t y ,

some o f which con ta ins pyrobitwnen. Although a l loch thonous ,

and t i g h t l y fo lded , t h e rocks d i p northward i n t o t h e b a s i n .

The p o s s i b i l i t y o f a d r i l l i n g o b j e c t i v e t o t h i s a l loch thonous

hor izon should be s t u d i e d by a d d i t i o n a l f i e l d work and se i smic

s t u d i e s .

Hydrocarbon p l a y a n a l y s i s

Current exper ience on t h e A r c t i c Slope sugges t s t h a t

s e v e r a l types o f p l ays should be cons idered i n a s s e s s i n g t h e

hydrocarbon p o t e n t i a l o f NPR-4. These p l ays a r e summarized

i n t a b l e 4 i n approximate o r d e r o f r e l a t i v e importance. I t

should be emphasized, however, t h a t t h i s r e l a t i v e ranking i s

somewhat s u b j e c t i v e ; one o f t h e purposes o f an e v a l u a t i o n

program should be t o provide d a t a f o r a more a c c u r a t e

assessment o f t h e r e l a t i v e p o t e n t i a l o f t h e s e p l a y s . The

l i s t of p l ay types i s no t in tended t o be a l l - i n c l u s i v e ; it

inc ludes on ly those p l a y types and major c o n t r o l s t h a t have

been observed o r can be i n f e r r e d a s l i k e l y t o be p re sen t .

Eva lua t ion o f t h e t a b u l a t e d p l ay parameters ( t a b l e 4)

sugges t s t h a t t h e l i k e l i h o o d o f Prudhoe Bay type f i e l d s of

wide a r e a l e x t e n t i n NPR-4 i s s l i g h t . Seve ra l s tacked

r e s e r v o i r s on a s t r u c t u r e a r e n o t l i k e l y . S t r a t i g r a p h i c

Permian-Lower T r i a s s i c c l a s t i c s

Upper T r i a s s i c sandstones and d i r t y carbonates

Conventional J u r a s s i c and plays with Lower Cretaceous approximately sands from a coeval age northern source reservoi rs and source beds

do do Thick, possibly up t o Gas do 400', f a i r to excel- l e n t poros i ty and permeability

do S t r u c t u r a l Thin, l e s s than SO', Gas probably very f i n e grained sandstone with good t o exce l len t porosi ty and permea- b i l l t y , low r a t e o f l a t e r a l fac ies change

Lower Cretaceous do (Albian) sand- stones derived from a southern source (Nanushuk Group, Umiat type play

do Thin, probably l e s s Gas Traps could be than 100' n e t sand- possibly o i l e i t h e r l a rge stone with f a i r t o o r small, could good porosi ty and be f i l l e d t o permeability, f a i r s p i l l p o i n t l a t e r a l fac ies cont i - nuity

S t ra t ig raphic Thin, probably l e s s Gas Probably small and/or than 150' n e t porous possibly 0x1 f i e l d s ; i f gas, s t r u c t u r a l sandstone i n any one possibly f i l l e d

prospect, with f a i r to s p i l l po in t ; t o good poros i ty and i f o i l , probably permeability; thxck not f i l l e d t o s t r a t i g r a p h i c u n i t s p i l l po in t with numerous sand- stones t h a t could have l o c a l p o t e n t i a l

Possible play i n a narrow east-west band south of Barrow. Indigenous hydrocarbons probably q u i t e over- mature and l imi ted t o dry gas.

Probably presen t i n a broad band from the Barrow area t o the Colv i l le River. Indigenous hydrocarbons probably some what over-mature and somewhat gas prone, but with some o i l . This play probably represents the most prospec- t i v e o i l play i n NPR4. Other o i l p l q s have grea te r o i l po ten t ia l b u t a r e l i k e l y t o be present i n only a l i m i t e d a rea .

Present over a wide geographic a r e a of t h e e n t i r e cen t ra l por t ion Of NPR4. Sands a r e p a r t of a broad northward prograding coal-bearing c l a s t i c wedge. Dominantly a gas play because o f the abundant associ- a t e d coal . Some o i l p o t e n t i a l i n lower por t ion of sandstone i n t e r v a l i n zone of in te r f inger ing wlth under- ly ing marine sha les , and toward d i s t a l end of wedge where sands become marine. Total reserves may be l a r g e but l i k e l y to be i n numerous small s t r a t i g r a p h i c a l l y control led f i e l d s . Largest play on N P M i n terms of t o t a l hydrocarbon poten t ia l , second t o coas ta l p l a i n Jurassic-Lower Cretaceous play i n o i l p o t e n t i a l .

I c o n t r o l s a r e l i k e l y t o p l a y a major r o l e i n any hydrocarbon

I accumulation. P re sen t knowledge o f t h e p o t e n t i a l r e s e r v o i r

I hor izons sugges t t h a t f a c i e s v a r i a t i o n s may occur r a p i d l y .

F i e l d s may be of smal l a r e a l e x t e n t and e x p l o r a t i o n w i l l I I

r e q u i r e d e t a i l e d s e i smic f a c i e s i n t e r p r e t a t i o n s c l o s e l y

i i n t e g r a t e d w i t h micropa leon to log ic s t u d i e s , and wi th geo log i c

s t u d i e s t h a t i n c l u d e t h e l a t e s t concepts o f c l a s t i c and carbona te I I d e p o s i t i o n and t h e i r c o n t r o l on r e s e r v o i r p o r o s i t y and

I pe rmeab i l i t y .

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Brosge, W . P . , and T a i l l e u r , I . L . , 1971, Northern Alaska pet roleum p rov ince , i n Cram, I . H . , ed . , Fu ture Pet roleum Prov inces o f t h e Uni ted S t a t e s - - T h e i r Geology and P o t e n t i a l : Am. Assoc. Petroleum Geo log i s t s Mem. 15, p . 68-99.

Brosge, W. P . , and Whi t t ing ton , C . L . , 1966, Geology of t h e Umiat-Maybe Creek r eg ion , Alaska; P a r t 3, Area l geology (wi th a s e c t i o n on heavy-mineral s t u d i e s by R. H . Morr is ) : U.S. Geol. Survey P r o f . Paper 303-H, p . 501-638.

C a r t e r , R. D., Denman, J. M . , and P i e r p o i n t , J . G . , 1975, Geolog ica l l i t e r a t u r e on t h e North S lope of Alaska 1969-1974: U.S. Geol. Survey Open-File Rep. 75-384, 81 p . , 3 f i g s .

Chapman, R. M. , Detterman, R. L . , and Mangus, M. D . , 1964, Geology of t h e K i l l i k - E t i v l u k River r e g i o n , Alaska: U.S. Geol. Survey P r o f . Paper 303-F, p . 325-407.

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1,

1958b, T e s t w e l l s , Topagoruk a r e a , Alaska: U.S. Geol. Survey P r o f . Paper 305-D, p . 265-316, p l s . 17-18.

1958c, Tes t w e l l s , Meade and Kaolak a r e a s , Alaska: U.S. Geol. Survey P r o f . Paper 305-F, p . 341-376, p l s . 21-24.

1959, T e s t w e l l s , Square Lake and Wolf Creek a r e a s , Alaska: U.S. Geol. Survey P r o f . Paper 305-H, p . 423-484, p l s . 29-30.

1961, Core t e s t s and t e s t w e l l s , Barrow a r e a , Alaska: U.S. Geol. Survey P r o f . Paper 305-K, p . 569-644, p l s . 39-43.

Har r i son , C . R . , and o t h e r s , 1973, Developments i n Alaska i n 1972: Am. Assoc. Petroleum Geo log i s t s B u l l . , v . 57, no. 8 , p . 1406-1420.

Jones , H . P . , and Spee r s , R. G . , 1976, Permo-Tr iass ic r e s e r v o i r s o f Prudhoe Bay f i e l d , North S lope , Alaska i n Brauns t e in , J u l e s , ed. , 1976, North American o i l - and gas f i e l d s : Am. Assoc. Petroleum Geo log i s t s Mem. 24, p . 23-50.

K e l l e r , A . S . , Morr is , R. H . , and Detterman, R . L : , 1961, Geology o f t h e Shaviovik and Sagavanirktok Rivers r e g i o n , Alaska: U.S. Geol. Survey P ro f . Paper 303-D, p. 169-222, p l s . 21-26.

K e l l e r , F . , Jr., and Henderson, J. R . , 1947, Aeromagnetic Survey o f Naval Pet roleum Reserve No, 4 and a d j a c e n t a r e a s : U.S. Geol. Survey, Geological I n v e s t i g a t i o n s Naval Pet roleum Reserve No. 4, Alaska , Rep. No. 10, 16 p.

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