Page 309 - Hydrocarbon Exploration and Production Second Edition

296 Facilities

gas

produced oil
fluids
slug catcher
pump
tank
Figure 11.27 A simple gathering station.

single wellhead sales gas pipe line

NGL
gathering
station

tank storage

stabilised
wellhead cluster
crude
Figure 11.28 Land-based production facilities.

batch processing methods. Such equipment is generally cheaper to maintain than
continuous throughput vessels, though a combination of both may be required.

11.2.2.3. Evacuation and storage
Once oil and gas have been processed the products have to be evacuated from the
site. Stabilised crude is normally stored in tank farms at a distribution terminal
which may involve an extended journey by pipeline. At a distribution terminal,
crude is stored prior to further pipeline distribution or loading for shipment by sea
(Figure 11.29).
Sales gas is piped directly into the national gas distribution network (assuming
one exists) and NGL products such as propane and butane can be stored locally in
pressurised tanks. NGL products are often distributed by road or rail directly from
the gathering station, although if ethane is recovered it is normally delivered by
pipeline.
Two basic types of oil storage tank are in common use: fixed roof tanks and
floating roof tanks. Floating roof tanks are generally used when large diameters are
required and there are no restrictions on vapour venting. Such tanks only operate at
atmospheric pressures, and the roof floats up and down as the volume of crude