Page 105 - Hydrocarbon

92 Current Environmental Concerns

5.4.2. Gas venting and flaring
Gas venting has historically been used in many operations as a means of disposal for
excess associated gas. Alternatively, gas was flared, a process that emits carbon
dioxide and water vapour into the air, another contributor to global warming.
Much effort is now being spent on gathering excess gas and to make commercial
use of it where possible, or otherwise to re-inject it into reservoirs. Some countries,
such as Norway, have introduced a carbon tax, which penalises companies for
venting or flaring gas.

5.4.3. CO 2 sequestration
New large-scale gas projects, such as the Gorgon development on the Australian
North West shelf and the Sleipner field in Norway have dedicated CO 2
sequestration schemes whereby carbon dioxide separated from natural gas or flue
gases from combustion are injected into suitable formations in the subsurface. The
benefits are increased oil recovery and the ultimate capture of CO 2 known as
sequestration. Seismic surveys and pressure measurements are employed to monitor
the integrity of the storage.

5.4.4. Oil-in-water emissions
When water is produced along with oil, the separation of water from oil invariably
leaves some water in the oil. The current oil-in-water emission limit into the sea is
commonly 40 ppm. Oily water disposal occurs on processing platforms, some
drilling platforms and at oil terminals. The quality of water disposed from terminals
remains an area of scrutiny, especially since the terminals are often near to local
habitation and leisure resorts. If the engineer can find a means of reducing the
produced water at source (e.g. water shut-off or re-injection of produced water into
reservoirs) then the surface handling problem is much reduced. Recent trends are
for governments to disallow oil-in-water emissions entirely, forcing operators to
install produced water re-injection schemes (PWRI).

5.4.5. Ozone-depleting substances
The ‘Montreal Protocol on Substances that Deplete the Ozone Layer’ is an
international agreement designed to protect the stratospheric ozone layer. It
stipulates that the production and consumption of compounds that deplete ozone in
the stratosphere, including chlorofluorocarbons (CFCs), halons, carbon tetrachlor-
ide and methyl chloroform have to be phased out. Scientific theory and evidence
suggest that, once emitted to the atmosphere, these compounds could significantly
deplete the stratospheric ozone layer that shields the planet from damaging UV
radiation. Some of these substances are used in fire-suppression equipment or in gas
refrigeration processes.