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Low-Permeability Gas Reservoirs in Marine Cretacetous Sandstones of Saskatchewan:

3. Lower Colorado (Middl e Albian to Cenomanian) Strata of East-Central Saskatchewan

by Frank Simpson l

The study area extends northwards f r om the nor thern l imi t of Township 20 to the

e r os i onal edge of Lower Colorado strata and is further delimited by the Third

Meridian and t he Mani toba border (Fi g. 1).

In this account, a lithologi c association referable t o the Viking Formation

(mi ddle Albian) is descri bed and compa red with other Cretaceous sandstones of eastern

Saskatch ewan . The Okla Sands tone, a unit within the Big River Formation (upper Albian

t o Cenomanian) is descri b ed f or the f irst time. It is restricted to the eastern shelf

of the area.

Stratigraphy

The Lower Colora do s uccession of east-central Saskatchewan ranges in thickness

from around 138 m i n the south to l ess than 82 rn in the nor th . ThP s equence is

divisible in to three main uni ts, listed in order of decreasin g age: the Joli Jou

Formation, th e Viking Formation and the Big Rive r Formation. All uni ts exhibi t a

generalized thickness decr ease i n a northerly direction, although it is noteworthy

tha t this trend is reversed in t he case of the Okla Sandstone . The main subdivisions

of the Lower Colo r a do strata of east- central Saskatchewan are shown in Figure 2 .

The con tac t be t ween the non-calcareous s hales of the Big River Formation and the

calcareous shale and shaly chalk of the overlying Second White-Speckled strata i s

f airly sharp . The dominant Big River lithology is dark gr ey (NJ) and medium dark

grey (N4), non-calcareous mudstone, which exhibits varying degrees of fissility.

The mudstone f r equentl y i ncorporates s ubordinate amounts of fine-grained sandstone

and silts tone, occurring as l ayers up to a few centimetres thick typically concentrated

t owards the base of the formation. Layers of nodular phosphorite and sideritic

concretions a lso occur. Benton ite layers, up to several centimetres thi ck, a re

widely distributed throughout the unit . Fish-skeletal debris is common throughout

the Big River sequence, b oth as single fragments and as concentrations a f ew

millimetres thick . The Fish- Scale Marker i s not s harply defined on geophysical well

l ogs and no attemp t was made to trace it across the study a r e a.

The Okla Sandstone is the name given to the yellowish grey (SY 8/1) and l igh t

1 Department of Ge ology , Unive rsity of Windsor, WINDSOR , Ontario N9B 3P4

MONTANA

* 11(Lt.,\ti.

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100 50 o 100 ;:,oo ...... __ __. ~ SC AI F IN MILES

• i g. l - Sketch map showing location of s tudy area .

ol i ve grey (SY 6/7) very fine- and fine- grained sandstone unit occurrin g from about

372 m to 380 min t he Imperial Okl a 1-29-35-8 well (Lsd l -29-35-8W2). The sandstone

is quartzose, micaceous and kaolinitic and occurs in l ayers ranging in t h ickne ss

from a few millimetres t o several centimetres and charact erized by gently i ncli ned

and horizontal lamination . There is a downward i ncrease in t he pr oport ion of dark

grey (N3) mudstone i ntercalations. Several thin bentonite layers are present and

fish- skeletal debris is concentrated in some sandstone layers . I t is poss ible that

the unit i ncorporates the Fish-Scale Marker . The uni t maintains a f airly constant

thickness and pinches out to t he south of the Sohio Baysel Foam Lake No. 3 we ll

(Ls d 4- 6-26-9W2).

The Viking Formation is a sandstone sequence, charac t erized by grada tional

:;:::",··,: t!A"~f I ,-{:AU l.!.K r 6 S.CC. W l't.( Pr( lfH.$'$ "lO I

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LSD 1-28 - 2.<& -·(; w 'l 11. e ? 1t:: 1M~ le~

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SC - •C ~-l f tl8[E · 5 .. N(.

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t)h'A.CQN[ S a..t0K1N(i T[t.,T r+,") G . 6

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\ 1 L _ \ ; ' ..... ~ > I < 1 . ::a - I ~ -<,_ :i_: . c·_ __ \ , L~~- -I • -

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' I' L \ ---~ < - , , ,-, , -- r I 7 l ' l ' -~=- ... __ ,- n , j_ l - ----- -- ,.. -'<::-1 ' ' ' "· . ' . --, - - - {,.__ I 1'1 ,,: .... ,. __ jT ___ ;_ - ._ , f f { l , ' ~ , ,. '- j· <,_

I 11 .----····.--- ~--< •• . .> <'. , ~-- --'- t- --- 1,1,:..,,, .• l ~ . ' ~ . ; ......_ . 1~ in ~--

Fi g. 2 - Sou th-north cros s-s ection from Soc . W Peepeekeesis No . l wel l (lsd 13- ll-22-llW2) to Bralome Smoki ng Tent No. 14-16 well (l sd 4-16-43-1 W2), showi ng l i thologic vari ation i n Lower Colorado (middl e Albian to Cenomanian) success ion of east- cent r al Saskatchewa n.

...... 00 00

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relations with t he overlying Big River Formation and a relatively sharp contac t

with the underlying Joli Fou Fonnation. The unit is of variable thickness,

a ttaining maximum values in the order of 23 m near the southern limi t of the area.

The i nves tigation by Price (1963) indicates that Viking sandstones do no t occur in

some parts of the area, notably in the vicinity of the Manitoba borde r. The sand­

stones of the Viking Formation are typi cally f ine-grained, quartzose, micaceous and

kaolinitic, with a light olive grey (SY 6/ 1) colour and occurring a s bioturbated

and cross-laminated or horizontally laminated layers up to several centimetres

thick, separated by thinne r frequently carbonaceous mudstone layers. Coalified

plant debri s is loca lly abundant. Sequence e lements of t ype-II and type-III

predominate and conunonly define f i ning-upward sequences.

These may be stacked as multistory units, as in the Imperial Leroy 7-20-34-19

well (Lsd 7-20-34-19W2), where three main s andstone bodies occur. The r e lative l y

sharp contact between the Viking Formation and the Joli Fou Formation is frequently

rendered the more striking by the occurrence of strongl y indurated sandstones,

cemented by calcite and siderite, a t the base of the Viking sequence. This is seen,

for example , in the Sohio Western Petroleum Tiny No. 1 well (Lsd l-14-31-5W2) at

288 m.

The Joli Fou Formation consis t s of dark grey (N3) non-calcareous mudstones

and shales. Sandstone interca lations up to several centimetres thick are collll\on and

frequently glauconitic. Less often encountered a re glauconitic sandstones occurring

as associated type-II and type-III elements forming sequences up to 2 m t hick, as in

t he SWP Bredenbury llA-36-22-1 well (Lsd 11-36-22-lWZ) from 385 m to 414 m. Some

gen e t i c association with part of the highly glauconitic Spinney Hill Sandstone of

central and wes t -central Saskatchewan seems probable . Phosphorite is common, both

as in-situ nodules and as reworked, relict deposits . The contact between the Joli

Fou Formation and underlying fine-grained, micaceous sandstones of the Pense

Formation (Mannville Group) is fairly sharp .

Discussion

The Okla Sandstone is petrologically similar to the sandstones of the Viking

Formation in east-central Saskatchewan and also to finer-gr a ined par ts of the St.

Walburg Sandstone in wes t -central Saskatchewan. The southerly pinch- out of t he

unit appears to indicate nort hern or eastern provenance . Mapping of the distribution

of the unit will provide useful, additional insight into t he geometry of the eastern

shelf of t he Colorado sea. The Okla Sandstone appears to subcrop beneath Quaternary

sediments and has minimal hydrocarbon prospects.

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The Viking Formation as a whole is somewha t more variable in lithology than

t he Okla Sandstone, notably on account of var ying de gr ees of shaliness o f the

Viking t ype-III elements. A notable s imilarity between Viking and Pense l i thologies

occurred in a number of wells, but nowhere more strikingly than in the Soc. W

Peepeekeesis No. 1 well (Lsd 13-11-22-llWZ) whe re both units consis t of light olive

grey (SY 6/1), fine grai ned, kaolini tic sandston e in horizontal laminae with lar ge

muscovite flakes and plant debris concentrated on bedding s urfaces .

In accordance with the ideas outlined by Simpson (1979) the most promising

hydrocarbon prospects appear to be i n the mul tis tory arrangement s of the Viking

sandstone bodies , s uch as the t wo cored in the Sohio Baysel Foam Lake No. 2 well

(Lsd 8-14-31-10W2), and the th ree penetrated by the Imperia l Ler oy 7-20-34-19 well

(Lsd 7-20-34-19W2) .

References

Price, L.L., 1963. Lower Cretaceous rocks of southeastern Saskatchewan: Geol. Survey Canada, Paper 62-29, 55 p.

Simpson, F., 1979. Low-permeability gas reservoirs in marine Cretaceous sandstones of Saskatchewan: 1. Proi ect outline and rationale, in Christopher, J.E., and Macdona ld , R.(Editors), Saskatchewan Geol. Surve~ Summary of Investigations , 1979.