92 PETROLEUM TECHNOLOGY, ECONOMICS, AND POLITICS
before it can be carried considerable distances through the pipelines or in the tankers. Railroad cars and motor vehicles are also
used to a large extent for the transportation of petroleum products.
Fluids produced from a well are seldom pure crude oil. In fact,
the oil often contains quantities of gas, saltwater, or even sand.
Separation must be achieved before transportation. Separation and
cleaning usually take place at a central facility that collects the oil
produced from several wells. Gas can be separated conveniently
at the wellhead. When the pressure of the gas in the crude oil as it
comes out at the surface is not too great, a simple flow tank fitted
with baffles can be used to separate the gas from the oil at atmospheric pressure. If a considerable amount of gas is present, particularly if the crude oil is under considerable pressure, a series
of flow tanks is necessary. The natural gas itself may contain as
impurities one or more non-hydrocarbon substances. The most
abundant of these impurities is hydrogen sulfide, which imparts a
noticeable odor to the gas. A small amount of this compound, or an
equally odiferous derivative, is considered advantageous as it gives
an indication of leaks and where they occur, (Mokhatab et al., 2006).
Another step that needs to be taken in the preparation of crude
oil for transportation is the removal of excessive quantities of water.
Crude oil at the wellhead usually contains emulsified water in proportions that may reach amounts approaching 80 to 90%. It is generally required that crude oil to be transported by pipeline contain
substantially less water than may appear in the crude at the wellhead. In fact, water contents from 0.5 to 2.0% have been specified
as the maximum tolerable amount in a crude oil to be moved by
pipeline. It is therefore necessary to remove the excess water from
the crude oil before transportation.
In an emulsion, the globules of one phase are usually surrounded
by a thin film of an emulsifying agent that prevents them from congregating into large droplets. In the case of an oil-water emulsion,
the emulsifying agent may be part of the heavier (asphaltic) more
polar constituents. The film may be broken mechanically, electrically, or by the use of demulsifying agents and the proportion of
water in the oil reduced to the specified amounts, thereby tendering the crude oil suitable for transportation.
The transportation of crude oil may be further simplified by
blending crude oils from several wells, thereby homogenizing
the feedstock to the refinery. It is usual practice, however, to
blend crude oils of similar characteristics although fluctuations in
before it can be carried considerable distances through the pipelines or in the tankers. Railroad cars and motor vehicles are also
used to a large extent for the transportation of petroleum products.
Fluids produced from a well are seldom pure crude oil. In fact,
the oil often contains quantities of gas, saltwater, or even sand.
Separation must be achieved before transportation. Separation and
cleaning usually take place at a central facility that collects the oil
produced from several wells. Gas can be separated conveniently
at the wellhead. When the pressure of the gas in the crude oil as it
comes out at the surface is not too great, a simple flow tank fitted
with baffles can be used to separate the gas from the oil at atmospheric pressure. If a considerable amount of gas is present, particularly if the crude oil is under considerable pressure, a series
of flow tanks is necessary. The natural gas itself may contain as
impurities one or more non-hydrocarbon substances. The most
abundant of these impurities is hydrogen sulfide, which imparts a
noticeable odor to the gas. A small amount of this compound, or an
equally odiferous derivative, is considered advantageous as it gives
an indication of leaks and where they occur, (Mokhatab et al., 2006).
Another step that needs to be taken in the preparation of crude
oil for transportation is the removal of excessive quantities of water.
Crude oil at the wellhead usually contains emulsified water in proportions that may reach amounts approaching 80 to 90%. It is generally required that crude oil to be transported by pipeline contain
substantially less water than may appear in the crude at the wellhead. In fact, water contents from 0.5 to 2.0% have been specified
as the maximum tolerable amount in a crude oil to be moved by
pipeline. It is therefore necessary to remove the excess water from
the crude oil before transportation.
In an emulsion, the globules of one phase are usually surrounded
by a thin film of an emulsifying agent that prevents them from congregating into large droplets. In the case of an oil-water emulsion,
the emulsifying agent may be part of the heavier (asphaltic) more
polar constituents. The film may be broken mechanically, electrically, or by the use of demulsifying agents and the proportion of
water in the oil reduced to the specified amounts, thereby tendering the crude oil suitable for transportation.
The transportation of crude oil may be further simplified by
blending crude oils from several wells, thereby homogenizing
the feedstock to the refinery. It is usual practice, however, to
blend crude oils of similar characteristics although fluctuations in