Page 279 - Hydrocarbon

266 Oil and Gas Processing

11.1. Oil and Gas Processing

This section will consider the physical processes which oil and gas (and
unwanted fluids) from the wellhead must go through to reach product specifications.
These processes will include gas–liquid separation, liquid–liquid separation, drying of
gas, treatment of produced water, and others. The process engineer is typically con-
cerned with determining the sequence of processes required, and will work largely
with chemical engineering principles, and the phase envelopes for hydrocarbons
presented in Section 6.2, Chapter 6. The design of the hardware to achieve the
processes is the concern of the facilities engineer, and will be covered in Section 11.2.

11.1.1. Process design
Before designing a process scheme, it is necessary to know the specification of the
raw material input (or feedstock)and thespecificationof the end product desired.
Designing a process to convert fluids produced at a wellhead into oil and gas products
fit for evacuation and storage is no different. The characteristics of the well stream or
streams must be known and specifications for the products agreed. At the simplest
level the majority of process facilities are designed to split commingled wellhead
fluids into three streams of mainly gas, oil and water, as soon as possible (Figure 11.1).
Thereafter, each of these streams is further treated to achieve a defined product
specification by passing through one or more processes arranged in series. The
process streams are described in more detail in Sections 11.1.2 and 11.1.3.

11.1.1.1. Description of wellhead fluids
The quality and quantity of fluids produced at the wellhead is determined by
hydrocarbon composition, reservoir character and the field development scheme.
Whilst the first two are dictated by nature, the last can be manipulated within
technological and market constraints.
The main hydrocarbon properties which will influence process design are

PVT characteristics: which describe whether a production stream will be in the gas
or liquid phase at a particular temperature and pressure

gas

Production seperation
from and oil
wells treatment

water
contaminants
Figure 11.1 Oil and gas process schematic.