Oil and Gas at Your Door? (2005 Edition) - Earthworks

STAGES OF OIL & GAS DEVELOPMENT
Gathering is the movement of bulk oil or gas from a production well to the
treatment facility.
Below is a general overview of some of the processes involved in preparing
the oil and gas for sale.
If crude oil is being recovered: Some separation of associated natural gas
from the raw crude oil may occur at the wellhead. The most basic type of separator
is known as a conventional separator. It consists of a simple closed
tank, where the force of gravity serves to separate the heavier liquids like oil,
and the lighter gases, like natural gas. The natural gas may be captured and
sold, but often it is simply flared or vented to the atmosphere. Flowlines or
gathering lines move the raw crude oil to an oil battery, for additional conditioning
before sending the oil to a refinery. At the oil battery, the fluids pass
through a production separator, which separates gases from the oil and
water. The oil and water then go to a heater treater, where the oil is separated
from the water and any solids that are present. The crude oil is at least
98% free of solids after it passes through this treatment. 106 The oil is then
piped to a storage facility, where it remains until it is transported offsite by
either trucks or by pipeline.
If a gas pipeline or gas transportation vehicles are present, the gases may be
transported to a gas plant for processing into products such as methane,
ethane, propane, and butane. Alternatively, the gases may be treated as a
waste product, and be vented or flared. 107 The water and solids removed may
be piped to a pit, a tank, or into a flowline leading to an underground disposal
well. 108
If natural gas is being recovered: Natural gas conditioning methods will be
used to remove impurities from the gas so that it meets the quality required
to be accepted by gas transportation systems. This is not always necessary,
as some natural gas is pure enough to pass directly into the pipeline. Often,
the most significant impurity is hydrogen sulfide (H 2 S). Other impurities that
may have to be removed include: water vapor, natural gas liquids, sand, nitrogen,
and aromatic compounds such as benzene, toluene, ethylbenzene, and
xylene.
FIGURE I-12. NATURAL GAS
DEHYDRATOR. Source of benzene.
Sweetening removes H 2 S from the gas. The most common method of sweetening
involves exposing the gas to an amine solution, which reacts with H 2 S
and separates it from the natural gas. The H 2 S may be disposed of by flaring,
incineration, or, if a market exists, by sending it to a sulfur-recovery facility.
Another sweetening method uses an iron sponge, which reacts with H 2 S to
form iron sulfide. The iron sulfide is oxidized, then buried or incinerated. 109
Dehydration removes water from the gas. The most common dehydration
method used at the wellhead is glycol dehydration. In this method, gas is
exposed to glycol, which absorbs the water. The water can be evaporated
from the glycol so that the glycol can be reused. If the gas is sent to a natural
gas plant for processing, solid desiccants are more commonly used to
remove the water. Solid desiccants are crystals that have large surface areas
that attract water molecules. Like glycol, these desiccants can be reused
after water has been removed from them. If gas is extracted from deep, hot
wells, simply cooling the gas to a low enough temperature can remove
enough water to allow it to be transported. 110
FIGURE I-13. GAS PROCESSING
PLANT. Source of NO X .
Photo by Dan Randolph
I-21