Petroleum

3695

Petroleum

over cable tools in speed, in reduced casing
costs, in drilling soft cavey formations, and
in confining the contents of each stratum
within that formation. The greatest objec-
tion to the rotary system is the impossibility
of recognizing with certainty the various
formations penetrated and their contents.
This can be remedied by coring at the points
in question, but is expensive. The cable tool
system is more suitable for drilling new ter-
ritory where oil, gas and water horizons are
unknown and for drilling hard rock which
rotary tools will not penetrate.

The pressure of the accompanying natural
gas often forces oil from wells in their early
life, such wells being known as gushers or
flowing wells. Later, as the gas pressure is
reduced, oil from the wells of the United
States and some other countries is lifted by
specially designed reciprocating plunger
pumps. A central power plant may pump as
many as thirty or forty wells, or a single
plant may be provided at each well. In some
districts oil is bailed from the hole with the
ordinary bailer; it is also swabbed from the
hole. A swab both lifts oil and reduces the
pressure in the well and thus induces flowing.
The air-lift or gas-lift method of pumping
has been known for many years but did not
come into general use until 1926. Another
factor in production methods is the main-
tenance of the pressure in the producing
strata by returning to them the gas that is
recovered from the well.

Crude petroleum varies in color from very
light yellow to black, frequently with a
preen fluorescence when viewed by reflected
light. The viscosity varies over a wide range,
some oils being little more viscous than kero-
sene, while others are practically solid at or-
dinary temperatures. The petroleums of the
United States are frequently classified as
paraffin base, naphthene (or asphaltic) base,
and intermediate base crudes. The paraffin
base crudes are those containing relatively
high percentages of aliphatic hydrocarbons.
Naphthene base crudes contain relatively
high percentages of cyclic hydrocarbons. In-
termediate base crudes, as the name indi-
cates, are intermediate in properties, between
the two former classes. The Pennsylvania
petroleums are typical paraffin base crudes;
California and Gulf petroleums are typical
naphthene base crudes. Russian petroleum
contains considerable proportions of naph-
thenes, whereas petroleum from the East In-
dies frequently contains notable percentages
of aromatic hydrocarbons.

In the process of conversion into useful
products, crude petroleum is usually sub-
jected to fractional distillation, each fraction
being further purified by distillation and fre-
quently by chemical treatment. The first frac-
tion recovered is known technically as 'crude
naphtha' or 'crude benzine,' which must not
be confused with benzene, or benzol derived
from coal tar. This fraction is usually re-
distilled in a steam still and the final prod-
uct is used as gasoline in internal combustion
engines. The same crude naphtha fraction
can also be refined to produce naphtha, which
is used as a solvent in the arts.

The second fraction recovered from the
crude oil is known as 'kerosene distillate' or
'burning oil' distillate. This is steam stilled to
remove naphtha and purified by successive
treatments with sulphuric acid and caustic
soda solution. Several different grades of
kerosene are marketed, the highest quality is
water-white in color. Other grades of kero-
sene are used for fuel in stoves and to some
extent as a solvent and for export. The frac-
tion of crude oil distilling at a temperature
just above kerosene is known as 'gas oil' and
is used for enriching water-gas. In recent
years it has also served as a base material for
the manufacture of gasoline by the so-called
'cracking' processes. A third use is as fuel for
Diesel and semi-Diesel engines and in oil-
burners for domestic or commercial heating.

The fourth fraction derived from the crude
oil is known as 'wax distillate* or 'lubricating
oil distillate.' It contains most of the paraffin
wax originally carried by the crude. Paraffin
wax is used for water-proofing paper and
wooden containers for various products, also
for manufacturing candles, coating matches,
etc. The oil drained from the wax in the
filter presses and sweating pans is refined by
distillation, chemical treatment, and yields a
large number of lubricating oils, varying
from the light-colored, non-viscous oil used
for lubricating typewriters and clocks to the
viscous oils used in internal combustion en-
gines and for lubricating heavy machinery.

Oil is usually transported to the refinery
and, in some cases, to the seaboard by pipe
line; it is then loaded into tank steamers,
which carry it to refineries at distant ports.
Refined products are carried principally by
tank cars while trans-oceanic shipments are
made in tank steamers built for the purpose.
The oil pipe line has become a fundamental
part of the oil industry and is by far the
most satisfactory method of transporting
petroleum on land. The net-work of pipe