Page 308 - Hydrocarbon Exploration and Production Second Edition

Surface Facilities 295

production
wellhand

to gathering
cellar to contain station
small spills

cement
casing
production tubing
Figure 11.26 Single wellhead arrangement.

11.2.2.1. Wellsites
The first function of a wellsite is to accommodate drilling operations. However,
a wellsite must be designed to allow access for future operations and maintenance
activity, and in many cases provide containment in the event of accidental emission.
Production from a single wellhead or wellhead cluster is routed by pipeline to a
gathering station, often without any treatment. In this case, the pipeline effectively
becomes an extension of the production tubing. If a well is producing naturally or
with assistance from a downhole pump, there may be little equipment on site during
normal operations, apart from a wellhead and associated pipework (Figure 11.26).

11.2.2.2. Gathering stations
The term ‘gathering station’ may describe anything from a very simple gathering
and pumping station to a complex processing centre in which produced fluids are
treated and separated into gas, NGLs and stabilised crude.
If several widely spaced fields are feeding a single gathering and treatment centre,
it is common to perform primary separation of gas and oil (and possibly water) in
the field. A field station may include a simple slug catcher, temporary storage tanks
and pumps for getting the separated fluids to the main gathering and treatment
centre (Figure 11.27).
A complex gathering station may include facilities to separate produced fluids,
stabilise crude for storage, dehydrate and treat sales gas, and recover and fractionate
NGLs. Such a plant would also handle the treatment of waste products for disposal
(Figure 11.28).
On a land site where space and weight are not normally constraints, advantage can
be taken of tank type separation equipment such as wash tanks and settling tanks, and