Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1937-08-28

cIayey matter with thickness varying
from 40 to 40 feet, and the Jefferson
limestone is described as bIuish-black
or chOcOlate-browm limestone. In the
report on the Little Rocky Mountains the
jefferson limestone is described as
dark rock giving when struck with a
hammer an OdOr suggestive Of petroleum
1t carries a small but distinctive fauna
and is believed to be capable of prOduc-
oil I'm favorable localities. The forIna-
ton beneath the Sweetgrass Arch cOn-
sists mainly of limestone, but as shown
by well logs il carries some interbedded
black and greenish shaIe."
Information regarding lower fOrma-
tiOns was even less complete In the
basal Madison lime, MIR Collier reported
the Limestone contains small shOwings
of oil in vertical fractures" which tends
to prove to many that the oil found
at the top of the Madison lime actually
aCcumulates up from the lowest source
beds through faults or fractures in the
limestone. These fractures resulted from
the folding of the great Sweetgrass Arch
in which vast area of 5000 square
miles was bulged upward by noun
tain-building forces. The shaIes being
pliable, were bent into a great dome.
The lines below, being brittle, did not
bend but fractured and broke at the
points of greatest stress. This condition
collecting from below, and travelling up
word until it reaches some porous mat
terial, such as a weathered limestone or
a sandstone. Migration upward is halted
by plastic shales which form a seal.
Discussing the mcOnfOrmity at the top
OF the Madison lime, Collier says:.-"It
may be of great economic Importance
in Canada, for the Athabaska tar sands
are just above it and are thought to have
derived their petroleum from the Devon
ion rocks and the lowest production of
the Turner Valley field northwest OF the
Sweetgrass Arch is reported to be OBJ
tanned just below the uncomfortable con-
tact of a late PaleOzOic dOIOmite with
the Jurassic. 1t is Of great economic Inn
pOTtance in Montana, for the principal
oil sand of the Kevin-Sunburst oil field
lies just above it,"
Continuing, MIR. Collier said: ''The
presence of vertical fissure In the lime
stone suggests faulting, which, if it
could be demonstrated, would go far tow
ard proving that the source of the oil
is in the underlying rocks
1.-THE distribution of the oil may be
due in part 70 its source and method
Of migration. the small assures noted
In the Troy-Sweetgrass well may be parts
Of fracture zones or even faults which
reach down into the Devonian formation
and through which the oil reported in
that formation may have collected at
could be definitely proved to be the
source and method of migration of the
Oil, 1t would I'm part account for the un-
usual distribution of the oil Cat the top
Of the lime,) the larger wells being To-
Gated near the more open fissures, the
small wells being farther lateraIIy from
the assures, and the barren representing
places far removed from assures or frac-
lures"
To this we might add that the mod
ern science of acidization has gone a long
way toward uphOIding Golfers theory.
Bone dry holes have been drilled only
to turn into good wells when treated. Ac-
i'd, following minute cracks in the lime,
eats out channels to the nearest cracl
otherwise dry hole.
Mr.. Collier points out the presence OF
oil at the base of the Madison lime at
Dry Fork, north of Conrad, In a sym
cline where water was found In upper
beds; also in the Frazier deep test in
North kevtn-Sunburst and the Frazer
deep test ON Bears Den, northeast of the
East Butte. He continues, 1.-THE Athabas-
kar tar sands, 400 miles north of the
kevtn-Sunburst oil field, which lies Just
above the DevOntan, the oil found at
points farther north I'm Canada; and the
oily odor found in the DevOnian lime
stone of the Little Rocky Mountains all
ead to the belief that the Devonian con-
aims considerable quantity OF oil and
may possibly be the source of the oil of
he Kevin-Sunburst field.
Considering the great thickness OF the
the oil found in the Ellis for
nation If derived from It may hav, been
reatiy concentrated. II the oil was de-
lived from the uevOnian rocks IL rsx,af
nave migrated upward At least 500 feet,
presumably through fractures in the mas
i've hard Madison limestone. IL is pos
lble that the Madison limestone does not
xtend far north, on account of erosion