Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1938-06-11
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formations than the Ellis were made in
1925 near the top of the Kevin-Sun-
burst dome, in Sec. 21-34N-1W; Sec. IL
35N-1W and Sec. 20-33N-1W. The Dry
Fork well. On Sec. 22SN-3W completed
in 1923, which is reported to have found
a small quantity of oil in the Devonian
or perhaps in the Madison limestone,
also suggests the possibility that oil
may be found dn one of these lower for
nations, though the wells so far drill
ed to those formations have failed to
find more than traces of gas and oil.
Three wells drilled in 1925 and 1926
apparently 6ound commercial quantities
of oil in the Madison limestone less
than 100 feet below the Ellis formation
These wells-the Ohio-Johnson No.
and the Queen City No / in Section IT.
23N-1W and the O'Neil-Lashbaugh No.
in Sec. 7-35N-2W-struck oil at
IA, 29 and Sc feet respectively below
the Ellis, probably in parts Of the lime
stone made porous by solution. Pre-
sumably the oil is similar in origin to
that found in the Ellis. The discovery
of a 5000 barrel initial production at
a depth of SO feet below the top of the
Madison will undoubtedly lead to con-
siderable deeper drilling and may re-
suit in finding a lower oil horizon of
commercial importance, but it, would
probably not be found at uniform
depth in that formation, for the bedding
and structure of the Madison are prob
ably not conformable with those Of the
Ellis Five wells have been drilled thru
the Madison limestone on the Kelvin
Sunburst dome, and these wells have
been placed in unfavorable positions with
regard to the deeper structure. Not more
than 80 wells have been drilled as far
into the Madison as the O'Neil NO well,
which penetrated it for Sc feet.
The well was later drilled through
the Madison limestone to the Devonian
rocks at depth of 1920 feet, where, it
is reported, more gas and show OF Oil
were found Gas at several horizons is
ent1apped at this place, apparently on
the flank of a dome which has been
broken and sealed by a large mass OF
intrusive rock, probably a loccol1th. If
the Sweetgrass Hills were carefully
mapped in close detail other places
where similar conditions prevail might
be found where oil rather than gas
would be the more abundant hydrocar-
bon
The Dry Fork well in Sec 2-2SN-3W a
bout miles north of Conrad is report
ed to have reached the Madison Lime
stone at 2,14O feet, where sulphur water
was struck A strong flow of fresh wa
ter was reached at 1920 feet and
27-foot sand was reported to have been
reached at 2,62O feet, from which a
small quantity of free black sulphur-free
oil was obtained The oil rose from 40
to so feet in the hole during a night
The gravity of the oil is estimated at
2Oo to 250 Baume. This oil must be eth
err in a fissure in the Madison limestone,
or as seems more likely, in a Devonian
sandstone not found in the oil field. If
1t is in the Devonian the thickness Of
the Madison is not more than 600 feet
at this place The Dry Fork well is near
a Glow" area in the crest of the Sweet
grass arch, called by the writer the Con-
rad saddle The top of the Madison lime
stone at the well is about 1900 feet
above the sea, where as the summit of
the Kevin-Sunburst dome it is about
2,1OO feet.
In the light of this evidence it will
be necessary to drill many wildcat holes
before many parts of the Arch outside
of the Kevin-SunbuTst dome can be def
nitely declared to be barren There are
several townships in which no drilling
has yet been done in which some oil may
possibly be found. Experience on the
Kevin-Sunburst dome has shown that
even should one well be barren another
well a short distance away may be pro-
ductive. and also unfortunately. that the
contrary is equally true.
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