Unit 5 Notes.docx - 13.1 Natural Gas Geology and Generation...

13.1 Natural Gas Geology and Generation
- Natural gas is primarily methane, or CH
4
, with smaller quantities of other hydrocarbons.
- It was formed millions of years ago when dead organisms sunk to the bottom of the
ocean and were buried under deposits of sedimentary rock
o Subject to intense heat and pressure, these organisms underwent a
transformation in which they were converted to gas, over millions of years.
- Natural gas is found in underground rocks called reservoirs
o The rocks have tiny spaces called pores, that allow them to hold water, natural
gas, and sometimes oil
o The natural gas is trapped underground by impermeable rock called a cap rock,
and stays there until it is extracted
- Natural gas can be categorized as dry or wet
o Dry gas is essentially gas that contains mostly methane
o Wet gas, on the other hand, contains compounds such as ethane and butane, in
addition to methane
 These natural gas liquids, or NGLs for short, can be separated and sold
individually for various uses such as in refrigerants and to produce
products like plastics
- Conventional natural gas can be extracted by drilling wells
- Unconventional forms of natural gas like shale gas, tight gas, sour gas, and coal bed
methane, have specific extraction techniques
- Natural gas can also be found in reservoirs with oil and is sometimes extracted alongside
oi
o This type of natural gas is called associated gas
o In the past, associated gas was commonly flared or burned as a waste product,
but in most places today, it is captured and used
- Once extracted, natural gas is sent through small pipelines called gathering lines, to
processing plants, which separate the various hydrocarbons and fluids from the pure
natural gas, to produce what is known as pipeline-quality dry natural gas, before it can
be transported
- Processing involves four main steps to remove the various impurities:
o Oil and condensate removal, water removal, separation of natural gas liquids,
sulfur and carbon dioxide removal
- Gas is then transported through pipelines called feeders to distribution centers, or
stored in underground reservoirs for later use
o In some cases, gas is liquefied for shipping in large tankers across oceans
o This type of gas is called liquefied natural gas, or LNG
- Natural gas is mostly used for domestic or industrial heating and to generate electricity.
It can also be compressed and used to fuel vehicles and as a feedstock for fertilizers
hydrogen fuel cells and other chemical processes

- Natural gas development, especially in the United States, has increased as a result of
technological advances in horizontal drilling and hydraulic fracturing
- When natural gas is burned, there are fewer greenhouse gas emissions and air
pollutants when compared to other fossil fuels
o In fact, when used to produce electricity, natural gas emits approximately half
the carbon emissions of coal
- Despite fewer emissions, natural gas is still a source of CO2
- In addition, methane is a potent greenhouse gas itself, having nearly 24 times the impact
of CO2
o During the extraction and transportation process, natural gas can escape into the
atmosphere and contribute to climate change
- Natural gas leaks are also dangerous to nearby communities because it is a colorless,
odorless, highly toxic, and highly explosive gas
- As discussed in Unit 4 on petroleum, natural gas is generated alongside oil
o The main difference is that natural gas is comprised of the shorter-chained