Page 77 - Petroleum and Gas Field Processing

Figure 6 Classification of hydrocarbons found in wellhead fluids.

assumed that such mixtures contain essentially three main groups of
hydrocarbon, as illustrated in Figure 6:
1. Light group, which consists of CH 4 (methane) and C 2 H 6 (ethane)
2. Intermediate group, which consists of two subgroups: the
propane/butane (C 3 H 8 /C 4 H 10 ) group and the pentane/hexane
(C 5 H 12 /C 6 H 14 ) group.
3. Heavy group, which is the bulk of crude oil and is identified as
C 7 H 16 .

In carrying out the gas–oil separation process, the main target is to
try to achieve the following objectives:
1. Separate the C 1 and C 2 light gases from oil
2. Maximize the recovery of heavy components of the intermediate
group in crude oil
3. Save the heavy group components in liquid product
To accomplish these objectives, some hydrocarbons of the
intermediate group are unavoidably lost in the gas stream. In order to
minimize this loss and maximize liquid recovery, two methods for the
mechanics of separation are compared:
1. Differential or enhanced separation
2. Flash or equilibrium separation
In differential separation, light gases (light group) are gradually and
almost completely separated from oil in a series of stages, as the total
pressure on the well-effluent mixture is reduced. Differential separation is

Copyright 2003 by Marcel Dekker, Inc. All Rights Reserved.