Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1933-12-09

above the Ellis, Is IN turn overlaiR
by the Colorado, which averages 1Tz5
feet on top Of the Arch and attains
a thickness OF 1850 feet on portions
OF the TANKS. Within this formation
OF consistent thickness and yielding
both commercial oil and gas is found
at the base OF the Colorado. This Is
the Dakota sand. II yields gas on
Bearsden and Reserve and also on
Flat Coulee and Reserve Above this
in the same locality approximately 500
feet is the Bow Island sand, which
yields comercial gas on Reserve and
North Devon and showed for COM
mercial gas on Flat Coulee and Grand
view. These two sands are not con-
sistently found along the Arch top.
The reason for the difference be-
tween the sands found on the flanks
and those found on the crest Of the
Arch, Of course, lies in the periods Of
emergenee and submergence OF the
Arch Island. During the periods Of
emergence the surface was subjected
TO atmospheric and other securing,
removing part OF the surface already
laid down. The TANKS being under
water were still having formations
deposited thereon while the island
was dry. These periods Of rising and
sinking we're slow and took long
periods of geologic time
As the Arch slowly rose above the
surface, the shoreline naturally re-
coded leaving sands exposed to be
washed or blown away AS the Island
again sank beneath Geologic seas
the water crept up It's shores, the
sands being protected by the water
from the effects of the elements.
Subsequently as the submergence be-
came complete, other formations we're
deposited on top OF the sands and
during long geologic cycles they be-
came compacted into sandstones and
shales, to be exposed later due to
continental emergence in places and
in other places to be uncovered by
the drflI. 1t can be seen from the
above why sands should be much
thicker down the TANKS than on the
crest and why they can he entirely
absent on the crest Of the Arch Tn
some cases.
The average sand is porous and
therefore makes good reservoir for
oil and gas, granted that structural
conditions are right In cases OF
shorelining the sand itself sometimes
fulfills the conditions which the struc-
ture does not. In other words II
a structural terrace or nose p1unges
in the direction of thickenfng of the
sand, with the sand having thfnned
out across the structurally open end
OF the nose. then ideal conditions
exist for accumulation OF oil and gas
in commercial quantities. This con-
ditfon Is more true than in the case
Of some d0mes where due to syphon-
ing or flushing, oil previously ac-
cumulated may have been dissipated.
The Cut Bank Nose on the Northwest
flank OF the Arch is the best example
of this. Here this structure, which
is really succession of noses, .pIunges
gene ally Northwestward, with the for
nations dipping Southwest, Northwest,
and Northeast AS said above IL.
involves several noses. which might
he termed the North Cut Bank Nose,
the Central Cut Bank Nose, and the
South Cut Bank Nose, all a part
of the same great Westward ter
racing The Sunburst Uplift on the
Arch axis or crest is to the East.
II shortening did not exist but the
same sands covered the Sunburst Up
lift then all OF the oil and gas which
Is now found in the Cut Bank Nose
would probably be found in the Sun
bursi Uplift. However. between the
Sunburst Uplift and the Cut Bank
Nose and across the open structural
end of the latter the sands wedge out
and disappear, giving perfect clos
ure against the Sunburst Upl7ft and
trapping the oil and gas in the Nose.
The North Cut Bank Nose was prov
en- for oil and gas this year. The
Central Cut Bank Nose, from which
the Montana Power draws it's gas
supply. has been proven for on and
gas for several years The South Cut
Bank Nose Is now being drilled by
combination of the Texas Company,
Montana Power, and Santa Rita on
its West end, and by the Producers
elopment-ImpeFial Natural Gas
Company in its central portion.
Other structural terraces or noses
exist along the Arch TANKS and by
studying wells drilled in these areas
and plotting the shorelihes OF the
sands from the data obtained, as
correctly as possible It Is probable
that several new oil fields can be
found. with, it is to be hoped. very
profitable yields.