Montana oil and mining journal. [volume] (Great Falls, Mont.) 1931-1953, 1937-11-13

the contact" These acids dissolved
small amounts of limestone and as an
impervious bed was encountered, travelled
parallel to the bedding planes Thus the
largest amount of continuous porosity de-
Velops more or less parallel to the bed
ding planes where by virtue of the mode
or origin of the beds, resistance to migra-
ton is the least.
The Dowell people point out that many
wells have been drilled within a few feet
OF the depth at which it was almost GER
tain that water would be encountered
yet little or no bottom water entered the
wells for long period of time. This is
SAID to be proof that a majority of the
oil-bearing pores do extend horizantally
rather than vertically.
1t is a generally accepted theory that
vertical migration of oil in this field re-
suits in the accumulation at the top of
the Madison lime Oil coming up through
faults and cracks in the massive lime
encounters the impervious materials in
the Ellis formation which form a dam
and thus the oil accumulates in the soft
porous material at the top of the Madison
lime, migrating through horizontal por-
osity away from the faults or cracks in
the lime. The occasional well such as
the Ohio-Baker No. 3, has struck the
fault itself and has produced many times
as much oil as the porous formations of
contained. Where there is horizontal
porosity, there is better opportunity of
opening up new channels to these fault
sources. This theory is predicated on the
origin of oil in the Devonian or lower
formations and the further conclusion
that the Oil is forced upward through
faulting into the contact material by a
hydrostatic head which in due course Of
time invades the contact formation. as
in the Adams-Harte pool.
Discontinuous porosity, again, halts
the widespread encroachment of water
over the field In the Gladys Belle
group the old wells had turned to water,
yet the Rice we'll on the same farm in
undrilled territory a half mile distant
was one of the largest wells of the year,
after acidization, with no great amount
of water A second well on the farm,
quarter of a mile distant had no por-
osity, apparently, for it did not respond
to acid and was abandoned This may
proved evidence of discontinuous porosity
that may safeguard the Gunderson pool.
from water invasion from the Gladys
Belle pool.
Another problem has been pretty well
solved, in that many wells which seemed
to respond well to acid and were i'm
mediately shut in, were later opened up
and found to be virtually dry. It has
been determined that when a well is
acidized and the acid is not completely
removed by swabbing or hard pumping
that a chemical reaction occurs that re
suits in building up a gum or other sub
stance that actually dams the flow chan
nels. Operators have now learned that
they should produce their wells until
such time as all acid has been removed
The use of a tubing swab Is regarded
as excellent practice to remove all trace
of acid from the hole. In no case
should acid be allowed to remain in
the formation over a long period of time.
Samples from one well in the Sweetgrass
hills conclusively showed results of al
lowing the acid to stand on the forma-
ton In this instance the tubing parted
and it was impossible to pump the acid
off. When is was finally reamed out,
the cuttings of the side walls were found
to be glazed over as if burned. Whereas
the well had appeared to be greatly inn
proved by the acid Immediately after
treatment it was in fact damaged when
the acid was allowed to stand on the
formation. gum formed which ac-
tually held the production back.
Biologists now carefully examine the
formation which is believed to be a
subject for acid treatment, to determine