Page 11 - Petroleum and Gas Field Processing

Introduction

Fluids produced from oil and gas wells genrerally constitute mixtures of
crude oil, natural gas, and salt water. These mixtures are very difficult to
handle, meter, or transport. In addition to the difficulty, it is also unsafe and
uneconomical to ship or to transport these mixtures to refineries and gas
plants for processing. Further, hydrocarbon shipping tankers, oil refineries,
and gas plants require certain specifications for the fluids that each receive.
Also, environmental constraints exist for the safe and acceptable handling of
hydrocarbon fluids and disposal of produced salt water. It is therfore
necessary to process the produced fluids in the field to yield products that
meet the specifications set by the customer and are safe to handle.

I. CRUDE OIL PROCESSING
Crude oil–gas–water mixtures produced from wells are generally directed,
through flow lines and mainfold system, to a central processing and treatment
facility normally called the gas–oil separation plant (GOSP). The first step in
processing of the produced stream is the separation of the phases (oil, gas, and
water) into separte streams. This takes place in mechanical devices known as
two-phase gas–oil separators when the produced stream contains no water or
three-phase separators when the produced stream contains water. Gas–oil
separation carried out in these separators is recognized as the backbone
process in a train of field processing units of oil and gas operations. The
separators are used to relieve the excess pressure due to the gas associated
with the produced crude and, consequently, separating it from the oil. When
water exists in the produced stream, separators are also used to separate the
free water from the oil. Once separation is done, each stream undergoes the
proper processing for further field treatment, as shown in Fig. 1.
Oil leaving the separator does not generally meet the purchaser’s
specifications. Oil may still contain between 10% and 15% water that exists

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