Page 205 - Petroleum and Gas Field Processing

7

Crude Oil Stabilization
and Sweetening

7.1 INTRODUCTION

Once degassed and dehydrated–desalted, crude oil is pumped to gathering
facilities to be stored in storage tanks. However, if there are any dissolved
gases that belong to the light or the intermediate hydrocarbon groups
(as was explained in Chap. 3), it will be necessary to remove these gases
along with hydrogen sulfide (if present in the crude) before oil can be
stored. This process is described as a ‘‘dual process’’ of both stabilizing
and sweetening a crude oil.
In stabilization, adjusting the pentanes and lighter fractions retained
in the stock tank liquid can change the crude oil gravity. The economic
value of the crude oil is accordingly influenced by stabilization. First,
liquids can be stored and transported to the market more profitably than
gas. Second, it is advantageous to minimize gas losses from light crude
oil when stored.
This chapter deals with methods for stabilizing the crude oil to
maximize the volume of production as well as its API gravity, against two
important constraints imposed by its vapor pressure and the allowable
hydrogen sulfide content.
To illustrate the impact of stabilization and sweetening on the
quality of crude oil, the properties of oil before and after treatment
are compared as follows:

(a) Before treatment
Water content: up to 3% of crude in the form of emulsions and
from 3% to 30% of crude as free water
Salt content: 50,000–250,000 mg/L formation water

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