- 127 -

Low Perrreability Gas Reservoirs in I-mine Sandstones of Saskatchewan : 6 . Bow Island Viking (Middle to Upper ) Correlations in Southwest ern Saskatchewan, Southeastern Alberta and North-Central Montana

by I" • Si. np..son

'rhe stlrly area i s that part of western Saskat­ l ithologic associations of the type area. chewan bounded by the northgm l im.i t of Also consi dered are cor~el ations with the Township 20 and La.ti tlrle 49 North and extend­ Bow Island sequence of nor th- centra.l J'

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Fi g. l - Sketch map s howing location o f s t udy a rea. - l.J.8 -

Stratigraphy unit that oontains the Viking Formation" (Price, 1963, p. 37 and Figs. 9-12). A A threefold subdivision of the LcMer Colorado different approadl was acbpted by SiJTpson sequence into the Joli Fou, Viking and Big (1975, Fig. 6, p. 570), who applied an arbi­ River Formations (in order of decreasing age) trary cut-off in his oorrel ations of geophy­ is applicable throughout the entire sttrly area. sical ~11-logs to define a wedge-shaped Price (1963) rerognized the gradational nature arrangerrent of shaly sandstone bOdies, marking of rontact relations between the Viking the northerly and northeasterly passage from Formation and the Joli Fou and Big River a relatively thick, proximal succession of Bew mudstones and in a sttrly of the LcMer Island Sarrls to a ItUdl thinner, distal Viking Cretaceous strata of southeastern Saskatchewan. sequence. Enploying the thickest Viking sequence in southwestern Saskatdlewan as a reference '!his generalized fonnat of lithologies is shaom section, he traced its upper and lower limits in Figure 2 as a stratigraphic cross-section, into the enveloping argillaceous strata and extending northeastwards across the study area was thus able to oorrelate "a marker-defined to the basinward pind¥:>ut of the sandstones.

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Fig . 2 - Southwest-northeast cross-section from Supertest et al Staynor 514-2-1-23 well (Lsd 14-~-)-23W3) to US Potash Jensen No. 1 well (Lsd 1-1 3-32-20W2), showing Bow Island-V1k1ng (Middle to Upper Albian) relations across southwestern Saskatchewan . - 129 -

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Fi g. 3 - West-east cross-section from Rio Prado Burdett No . 13-22 well (Lsd 13-22-10-12W4} to Amurex Albercan McC l oud 1-15 well (Lsd 1S-1 2-10-27W3), showing l ithologic variation of Bow Island Fo rmation (Middle to Upper Al bian ) east of type area. - 130 -

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Fi g. 4 - Southwest-northeast cross-section from True and Brown Mo l l No. 1 wel l (NE SW 20-32N-18E) to B.A. Cl imax Ross 8-31-4-16 well (Lsd 8-31-4-16W3), showi ng li t hologi c va riation in Bow Island Formation (Middle to Upper Albian) northeastward from Ti ger Ridge field, Montana . - 131 -

The distal Viking sequence, penetrated by inoorporate daninantly ooarsening-upward sand­ wells 7 through 10, is characterized by a stone bcxlies, in nany respects similar to the northeastward passage from a OOI'!pOsi te to Bow Island sandstone. The uppenrost nenber, single sandstone bodies; the c:uiposite sand­ the marine Bootlegger ~, aH;)ears to be stone bodies exhibit multistory stacking of equivalent to the upper Albian part of the single bodies, several tens of rretres thick, Big River Fonnation. Too Bootlegger sequence separated by breaks, of thickness on the overlies a non-marine succession of interbedded order of deciiretres and only exceptionally claystone, siltstone and sandstone, making up netres. The rrore proxiJnal Bow Island sucx:es­ the Vaughn Bentonitic M:mber, the upperrrost sion, penetrated by wells l through 6, oonpri­ strata of which include a red-speckled, ses rcostly conp:,site sandstone bcxlies, each bentonitic clay (Ped Speck zone), oontaining several tens of netres thick, separated by the mineral clinoptilolite. sequences, canposed mainly of rm.rlstones and shales, 'Which attain thicknesses of tens of rretre·s. Discussion

The Bow Island Formation takes its nane from The Bow Island-Viking wedge is interpreted as the Bow Island No. l well (Lsd 6-15-ll-11W4), marking a passage fran shoreline-nearshore to drilled to the northwest of Bow Island, deeper, marine-shelf environirents in a north­ Alberta. The mit is traced eastwards into easterly direction. No oontinental deposits southwestern Saskatchewan from the vicinity of have been recx:>gnized in southwestern the type section in Figure 3: a dominantly Saskatchewan; the closest non-narine strata sandy and silty ~ce, occupying the entire appear to be the Vaughn Bentonitic M?rrber of interval between the top of the Mannville the Bootlegger Formation. The Ped Speck zone Group and the base of the Fish-Scale Marker, at the top of this unit appears to lie between is replaced eastwards by a tripartite division the First and Seoond Bow Island sands. of the interval, $iroilar to that noted above. In addition, a persistent sandstone unit up In southwestern Saskatchewan, the Bow Island to 8 m thick, terned the Cessford Sand, is and Viking sequences are distinguishable on distinct from the Bow Island succession and the basis of the thickness of intemedded occurs near the base of the shale and the use of the term Bow Island is in the vicinity of the Fourth ~ridian. The recomt8lded for the thicker, dominantly sandy Bow Island Fonnation consist of relatively sequences of southwestern Saskatchewan, well washed and variably shaly, f ine- to hitherto terned Viking. '!he Bow Island strata ooarse-grained sandstone, with interbedded of southwestern Saskatchewan are lithologi­ siltstone and mudstone and with generally cally similar to those yielding hydrocarbon subordinate conglc:srerate and pel:±>ly sandstone. production in adjacent areas as is the Varicoloured chert and r~rked-relict, Cessford Sand. Both the Bow Island Sands nodular phosphorite are not~rthy coarse and the Cessford Sand are regarded as pros­ canponents of the conglonerates. COalified pective for hydrocarbons in southwestern plant fragmants are loca lly abundant. The Saskatchewan. main l::xxly occurs as up to three cx:rrposite sandstone units, te:nred First, Seoond and 'lhird Bow Island Sands in order of increasing References age, separated in vertical succession by mainly rnudstones and shales. Each of these Cannon, J.L. (1966): outcrop examination and sandstone l::xxlies and the lithologically interpretation of paleocurrent patterns similar Cessford Sand are largely made up of of the Blackleaf Forrration near Great coarsening-uµ,.,ard sandy sequences, consisting Falls, M:>ntana: Guidebook Billings Geol. of type -II, -III, -IV and -v sequence Soc., Seventeenth Ann. Field COnference, elerrents and characterized by an upward de­ and Cretaceous Stratigraphic crease in the proportion of intercalated shale. Traps, Sweetgrass Arch, August 17-20, 1966, Great Falls, Mt., p. 71-111. Bow Island strata are oorrelated northwards into Saskatchewan from the Bullhook-Tiger Price, L.L. (1963): Lawer Cretaceous rocks Ridge area of northern r.bntana in Figure 4. of southeastern Saskatchewan: Geol. Although detailed well-to-well correlation Survey Canada, Paper 62-29, 55 p. within the Bow Island Sands is selcbm possible, the strata traced into southwestern Saskat­ Sinpson, F. (1975) : Marine lithofacies and chewan from adjacent areas in Figures 3 and 4 biofacies of the COloraoo Group (middle appear to belong to the Seoond and Third Bow Albian to Santonian) in Saskatchewan: p. 553-588, in Caldwell, W.G .E. (F,ditor), Island Sands. Cannon (1966) has provided detailed lithologic descriptions for rrenbers The Cretaceous Systan in the Western of the Blackleaf Formation exp::>sed near Great Interior of North Arrerica, Geol. Assoc. Falls, M:mtana. 'lhree of the four rrerrbers Canada, Special Paper 13, 666 p. - 132 -

(1979) : I.o.r-pe:areability gas reservoirs in narine, Cre taceous sand­ stones of Saskatchewan: l. Project outline and rationale: p. 174-180, in Christopher, J.E. and Macrlonald, R. - (Editors), saskatchewan Geol. .survey, S1.1Trn1lry of Investigations, 1979, Saskat.chewan Mineral Resources, Misc. Rept. 79-10, 227 p.

(in press): Lithologic descrip­ tions of selected oored sections fran the Colorado and ~tana Groups (middle Albian to Carrpanian} of Saskatchewan: Saskatchewan Mineral Resources, Rept. no. 233.

Si.rrpson, F. and O'Connell, S. (1979): u:,w-­ penreability gas reservoirs in marine, Cretaceous sandstones of Saskatchewan: 2. ~r Col orado (middle Albian to Cenananian) strata of southern Saskat­ dlewan: p. 181-185, in Christopher, J .E. and Macdonald, R-:-(Editors), Saskatchewan Geol. Survey, Sunmary of Investigations, 1979, Saskatchewan Mineral Resources, Misc. Rept. 79-10, 227 p.