Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1937-05-29
REVEALS MAP OF GREAT ALTAMONT ANTICLINE

,v,y.n,an permian. Triassic and Lower Dur.
! assic time) this oil escaped into the atu1os-
! phere After the Madison was cosereo ~ ths
| Ellis shale, in Upper Jurassic time the o.
/ Generated ia the Devonian md rising throuet
| me Madison. accumulated In structures suef
4 as those OF the Alsamont Anticllne ana tbs
/ kelvin -Sunburst and Pondera oil fields.
! A very interesting feature OF the strait
,ra,bv ~ this bssgn from the economic stand
/ point Is the so-called cut Bank SAND This
sand lying on top Of the Ellis snaie, ana al
| the base Of the Blairmore, was oepositeo a
a delta. II lenses out completely on the east
ern and southeastern edges Of the gas area
Of the Cut Bank field (see cross sectionh
! s.AA'" and BIB - It thins down 20 six
feet in thickness on the crest OF tne De-
Bonita structure It undoubtedly is FED, OF
receives It's oil, from the synchne or axis Of
the basin, where faulting has placed tne TOP
Of the Madison lime IN luNtaPoslSlon with
this sand. thus allowing lateral migration Of
oil.
OH, FIELDS AND FAVORABLE STRUCTURES
KEyTN-sUNBURsT: This field produces
mainly from the Madison Limestone. Wntcn
yields an oil Of 80 gravity Ihe SanoeIst ssnu
a sand in the lower part OF the Blaifmore
formation Yields a sweet" oil Of a little
higher gravity in certain areas OF the Ileld.
As shown on Cross Section BIB = kevln-
spread out over a large area. The oil zone
in the lime is approximately 10 feet thick.
This makes for small wells and a low yiela
per acre. However, the producing area o.
CAPABLE Of an ultimate yield OF over 100000
600 barrels; particularly since the ADVENT OF
acidizing. -.
duces a So gravity sweet" oil from the so
called "Cutbank Sand" AS previously stated,
this sand lies at the base Of the Blairmore,
Immediately everything the Ellis snale II was
formed by q Delta coming out OF tine noun
tains to the west. 1t lenses out completely
on the eastern edge Of the gas area. II thick
ems TO the west. It varies IN thickness Dc
tween II and 30 feet in the oil area OF the
Cut Bank oil field It was shown to be 100
feet thick on the Dunbar structure cross
sections "A-A' " and BIB show TINS
lensing out and thickening Of the Cutbank
sand AS shown on the map and cross sec
tions the oil accumulation at Cut bank Is
spread out in q thin film, over large
area This makes for small wells ana low
yield per acre. However. the producing area
Of cut Bank is so large that the field IS
conceded to be capable Of an ultimate yield
in excess OF 200000.000 barrels.
THE ALTAMoNT ANTICLINE: This anti
clinal fold lies in an ideal location TO accunlu-
late the drainage Of oil from the geosyn-
cline. Every shred Of evidence shows that
this drainage is coming from the thick tense
Of the Devonian shale in the geosyncline and
from the Tow" Of the basin to the northwest
Of Spring Coulee The oil migrates up this
fold and. after the structures or the Alta
mont Anticline are filled, to the lowest clos
ing contour. the overflow migrates up into
Cut Bank Keyin-Sunburst and Pondera. These
Aitamont Anticline structures are Of the gen.
tie. mid-continent type Of folding Being Of
the CLOSED dome" type 1t would be reason
able to assume an equivalent production 70
that of Cut Bank and Kevin-Sunburst being
in a much smaller area, which
would make for large wells and a high yield
per acre. Ali Of these structures have an ex-
cellent possibility for large scale commercial
production in the Madison lime. However, the
Chalk Butte structure has peculiarly favor
able position for large production in the Gut
bank sand.
CHALK BUTTE STRUCTURE: This struc-
lure lies In the very center OF the delta which
Torms the Cutbank sand Therefore, a maxi
mum thickness Of this sand would be an
.icipated Structurally, Chalk Butte has ideal
conditions, due to the great offsetting between
his and the Dunbar structure. This offsetting
would give an unusual amount Of closure on
he southeast, or critical" end OF the struc-
lure. In fact, the writer anticipates q mini
mum Of 200 feet Of closure on the critical
of 100 feet for the Cutbank sand {
This would make for large wells and a very :
high yield per acre. Furthermore, cross sec
ion "A-A ." shows that practically the en-
ire source Of tine Oil OF the Cut Bank old .
leld is from drainage up the axis Of the .
Altamont Anticline. The oil enters the Cut
,ank overlap monocline' on the axis Of the
Altamont Anticline and then spreads in a
hin film over this monocline. Obviously,
owest closing contour, before any oil could
et into Cutbank. In addition to the Cut
'ank sand. this unusual closure on the crit
cal end Of the structure would make for
arge wells in the Madison limestone. Final
~ Chalk Butte lies in an ideal position In
he Basin for production from zones below
he Madison lime.