The Hardin tribune-herald. [volume] (Hardin, Mont.) 1925-1973, 1937-02-05
Cut Bunk Oil Field Compared
With That of Eastern Texas
bu Tulsa Cos journal Writer

face near Great Falls are $500 feet
below the surface at Shelby and $500
or more feet deep at Lethbridge in
Canada. The average dips of the strata
are about SO feet to the mile. The Sweet
Grass arch lies east of the Rocky
mountains.
Late Cretaceous Age
Surface evidence indicates the arch
IS OF late Cretaceous age and the
Virgelle (Eagle) sandstone forms a
conspicuous eScarpment IL miles west
OF its crest. The Eagle sandstone is in
about the middle of the upper Creta.
ceous section and below this there are
the base OF the upper Cretaceous for
nations.
1.-The producing formations range
IN age from lower C]retaceous with the
Sunburst sand of the Kootenai for
nation productive in Kevin-Sunburst
and Cut Bank oil fields to the Ellis
Madison limestone of Mississippian
age: The Triassic, Permian and Pen
nsylvania formations are missing over
this arch which was apparently an an
Gent land surface during those geo.
logical periods.
THE geology of the Cut Bank field
ma not been worked out yet to the
satisfaction of all biologists. That is
to say they are not In accord on many
important features and until more evil
dence has been developed by drilling
1t Will be hard to make final decisions.
1t does seem apparent that in this
area the productive formations once
formed the shore line of ancient seas
n many of the sands are of the lent
icular type with photographic changes
in sedimentation playing an important
part in the trapping of the oil and gas.
One Causes Discussion
one well on the west edge of the
Cut Bank field has caused much dis
cusslon. It was drilled to a total depth
OF 1918 feet into the Ellis oil sand and
rels of water. The casing had been set
above this producing horizon and there
was about At feet of shale between the
Ellis shale and the Sunburst sand
which had been cased off. It was re-
called that a showing had been had in
the Sunburst when drilled so the well
a shot with 40 quarts of n%itroglyc-
erin through the casing at 1858 to 1850
feet and the largest well in the field
secured. It flowed as much as 1000
barrels of oil at n time and has
been capable of producing from 600
to 700 barrels of oil per day when the
market could take that much produc-
ton. Three other offset wells have been
drilled to the west partly because there
is no outlet for the oil if found. Opin-
ions differ as to whether this well is
producing from a highly permeable
sand section, a crevice or is influenced
by down-dip water.
1.-THE occurrence of water in this
field is peculiar. At the north end of
the structure there are three terraces.
One terrace has produced some gas
but in another terrace water was en-
countered at a point 700 feet higher
than the established water level at the
south end of the structure. This seems
to indicate lenticular sand bodies with
the general dip of the producing for
nations to the south and west.
Field Exceeds 140,O 900 Acres
While the area now proven for oil
and gas in the Cut Bank field exceeds
100000 acres the oil reserve is not
large compared with East Texas. The
production per acre is variously esti-
placed in sight about $50, 000, 900 bar
rels of oil. In the gas area it is esti-
mated at least 300 million feet OF gas
is in reserve and there is still a large
area between the north and south pro-
ducing fields to be drilled.
lone factor Of much Importance to
the practical oil man is the character
OF the producing formations. If it is
hard and tight 1t is usually assumed
the well will be of small capacity,
but If soft and highly permeable large
another way. II the producing forma-
tons is tight the oil will not rise very
high in the hole but If permeable win
come to o. nearly to the surface. Off,
set wells have varied widely in their
productivity and 1t seems apparent
| photographic conditions are largely re-
! sponsible Tor these differences" "@.