OIL AND GAS DIPLOMA COURSES 03214278510 IN SIALKOT

3 Reservoir and wellheads
There are three main types of conventional wells. The most common is an oil
well with associated gas. Natural gas wells are drilled specifically for natural
gas, and contain little or no oil. Condensate wells contain natural gas, as well
as a liquid condensate. This condensate is a liquid hydrocarbon mixture that
is often separated from the natural gas either at the wellhead, or during the
processing of the natural gas. Depending on the well type, completion may
differ slightly. It is important to remember that natural gas, being lighter than
air, will naturally rise to the surface of a well. Consequently, lifting equipment
and well treatment are not necessary in many natural gas and condensate
wells, while for oil wells, many types of artificial lift may be installed,
particularly as the reservoir pressure falls during years of production.
There is no distinct transition from conventional to unconventional oil and
gas production. Lower porosity (tighter reservoirs) and varying maturity
create a range of shale oil and gas, tight gas, heavy oil, etc., that is simply
an extension of the conventional domain.
3.1 Crude oil and natural gas
3.1.1 Crude oil
Crude oil is a complex mixture consisting of 200 or more different organic
compounds, mostly alkanes (single bond hydrocarbons on the form CnH2n+2)
and smaller fraction aromatics (six-ring molecules such as benzene C6H6)
Figure 4. Basic hydrocarbons
Different crude contains different combinations and concentrations of these
various compounds. The API (American Petroleum Institute) gravity of a
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particular crude is merely a measure of its specific gravity or density. The
higher the API number expressed as degrees API, the less dense (lighter,
thinner) the crude. Simply put, this means that the lower the degrees API,