Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1938-06-11

migration of the oil, it would in part
account for the unequal distribution Of
the oil, it in the larger wells being To-
Gated near the more open assures, the
small wells being farther lateTally from
the assures and the barren areas rep
resenting places far removed from fis-
sures or fractures.
considerable quantity of black, heavy
dead oil is reported to have been found
near the base Of the Madison limestone
in the Dry Fork well, north of Conrad,
in Sec. 2-2S-3W. Showings of oil and
hydrocarbon gas as well as disseminated
oil are reported from the Devonian rocks
penetrated by the TToy-Sweetgrass and
Frazier wells, in the Kevin-Sunburst
field, and the Bearsden well, northeast
of East Butte The Athabaska tar sands,
400 miles north of the KeVin-Sunburst
oil field, which lies just above the Devon
ian, the oil found at points farther north
in Canada; and the oily odor found in
the Devonian limestone of the Little
Rocky Mountain all lead to the belief
that the Devonian contains a consider
able quantity of oil and may possibly be
the source of the oil of the Kevin-Sun-
burst field.
Considering the great thickness of the
Madison. the oil found in the Ellis for
nation, il derived from it, may have been
greatly concentrated If the oil was de-
rived from the Devonian rocks it must
have migrated upward at least 500 feet,
presumably through fractures in the mas
sive hard Madison limestone 1t is pos
sible that the Madison limestone does
not extend far north, on account of ero-
sion or nondeposition. and that the oil.
there migrated from the Devonian to the
base of the Ellis formation and thence
southwark along the unconformity for
many miles
After deposition, pressure would drive
the oil from the shale to the more OPP
en-textured rocks, where if water were
absent it would sink down and accumu-
late in the lowest places available. If
water were present under a hydrostat-
ic head the oil would rise into the high
est openings available, moving along
bedding planes to the tops of domes or
anticlines; or if the everything impervious
rocks were fissured or faulted it might
cross the bedding planes to higher sands.
The presence of artesian water in the
Madison limestone in many of the wells
in Kevin-Sunburst field makes it seem
improbable that the oil from the Koote-
mai or Colorado formations could have
migrated downward and accumulated in
the Ellis shale. the oil therefore appar
emily originated in the Ellis formation
or in the formations below it,
As disseminated oil is found in each
or the formations OF Jne Ilelus Ine Oll
under discussion probably originated in
the Ellis formation was forced by pres
sure into the more open-textured rocks
near at hand The unconformity at the
base of the Ellis offered the largest
cavities; the Sunburst sand, at the base
of the Kootenai was a thicker but less
porous rock Owing to the diverse ma
ture of the Ellis formation from place
to place and the carrying porosity of the
reservoir rocks, the quantities of oil held
a. these horizons would also vary. The
two distinct grades of oil may be due
to the fact that below the Ellds forma-
tion all the water contains some sui
phur and has a sulphur odor. whereas
above it most of the water is free from
sulphur The reaction of sulphur water
and oil probably affected the character of
the oil.
Possible Oil Sands in the Paleozoic Rocks
The drill core of the Troy-Sweet-
Fork we'll in Sec. 2-2SN-SW completed
in 1922 indicated a possibility of find
ing oil either in the Madison limestone
(Mississippian or in the Devonian rocks.
But it failed to show any sands In these
formations which could be expected to
serve as reservoirs. Attempts to find
commercial. quantities of oil in lower
formation unless you capital