Page 43 - Synthetic Fuels Handbook

NATURAL GAS 31

are removed and sold separately, including propane and butane. Other impurities are also
removed, like hydrogen sulfide (the refining of which can produce sulfur, which is then
also sold separately). After refining, the clean natural gas is transmitted through a network
of pipelines that deliver natural gas to its point of use.
In terms of reserves, natural gas is produced on all continents except Antarctica
(BP, 2006). The world’s largest producer is Russia. The United States, Canada, and the
Netherlands are also important producers. The proven reserves of natural gas are of the
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order of in excess of 3600 trillion cubic feet (1 Tcf = 1 × 10 ). Approximately 300 Tcf exist
in the United States and Canada. It should also be remembered that the total gas resource
base (like any fossil fuel or mineral resource base) is dictated by economics. Therefore,
when resource data are quoted some attention must be given to the cost of recovering those
resources. Most important, the economics must also include a cost factor that reflects the
willingness to secure total, or a specific degree of, energy independence.
Natural gas is produced in many countries around the world and most of those countries
produce both oil and natural gas; a few produce only natural gas. The ten largest natural
gas-producing countries are: United States, Canada, Russia, United Kingdom, Algeria,
Netherlands, Iran, Indonesia, Norway, and Uzbekistan (EIA, 2004; 2006). Because trans-
portation costs add to the cost of natural gas, in most countries natural gas is consumed
within the country or exported to a neighboring country by pipeline. Technology for
liquefying natural gas so that it can be transported in tankers is improving (Mokhatab et al.,
2006). As technology continues to expand the options for gas transportation, demand for
natural gas is expected to grow.
A common misconception about natural gas is that resources are being depleted at an
alarming rate and the supplies are quickly running out. In fact, there is a vast amount of
natural gas estimated still to be retrieved from a variety of reservoirs. However, many
proponents of the rapid-depletion theory believe that price spikes indicate that natural gas
resources are depleted beyond the point of no return. However, price spikes of any com-
modity are not always caused by waning resources but can be the outcome of other forces
at work in the marketplace.

2.3 CONVENTIONAL GAS

2.3.1 Associated Gas
Associated or dissolved natural gas occurs either as free gas in a petroleum reservoir or as
gas in solution in the petroleum. Gas that occurs as a solution in the petroleum is dissolved
gas whereas the gas that exists in contact with the petroleum (gas cap) is associated gas.
Crude oil cannot be produced without producing some of its associated gas, which
comes out of solution as the pressure is reduced on the way to and on the surface.
Properly designed well completions and reservoir management are used to minimize
the production of associated gas so as to retain the maximum energy in the reservoir and
thus increase ultimate recovery. Crude oil in the reservoir with minimal or no dissolved
associated gas is rare and dead crude oil is often difficult to produce as there is little
energy to drive it.
After the production fluids are brought to the surface, they are separated at a tank battery
at or near the production lease into a hydrocarbon liquid stream (crude oil or gas condensate),
a produced water stream (brine or salty water), and a gaseous stream. The gaseous stream is
traditionally very rich (rich gas) in natural gas liquids (NGLs). Natural gas liquids include
ethane, propane, butanes, and pentane (C H ) and higher molecular weight hydrocarbons.
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The higher molecular weight hydrocarbon product, which may also contain some pentane,
is commonly referred to as natural gasoline.