Page 13 - Fundamentals of Enhanced Oil and Gas Recovery

CHAPTER ONE

An Introduction to Enhanced

Oil Recovery

Amirhossein Mohammadi Alamooti and Farzan Karimi Malekabadi
Department of Chemical and Petroleum Engineering, Sharif University of Technology, Tehran, Iran

1.1 OVERVIEW

In the early stages of oil field development, reservoirs are mainly planned to
produce oil naturally by intrinsic energy. The recoverable oil by the natural forces,
including all various mechanisms (gas cap drive, water drive, solution gas drive, rock
and fluid expansion, and gravity drainage), can be extracted up to 50% of original oil
in place (OIP) (averagely 19%), and most of the oil will remain untouched in the res-
ervoir. For extracting more oil, other methods are chronologically utilized after the
first natural flow mechanisms. Thus the first and second actions for enhancing oil
recovery (EOR) after primary recovery are called secondary and tertiary recovery,
respectively.
In the secondary recovery period most focuses are on the reservoir energy mainte-
nance. This aim is performed by waterflooding or gas injection. In gas injection, gas
is injected to the gas cap to prepare the required energy of oil drive. The process of
gas injection to the gas cap is not as effective as waterflooding. This fact and the vast
usage of waterflooding as the most common reservoir energy-saving method have
made many references consider waterflooding equivalent to the secondary recovery
method.
Tertiary recovery processes include all methods conducted to extract irrecoverable
oil by the two first production stages. Also it should be noted that many reservoirs,
such as high viscous oil reservoirs or very tight reservoirs, are not capable of produc-
ing oil without the tertiary action. Thus in many cases the chronological-based classi-
fication of EOR methods fails, especially when the oil is not producible by natural
forces or energizing methods. Therefore considering the tertiary actions as exclusive
EOR methods is not out of mind. Almost all procedures classified in this category can
be categorized to thermal, chemical, microbial, miscible, and immiscible gas injection
actions. The mechanism of increasing the oil recovery varies along these methods.

Fundamentals of Enhanced Oil and Gas Recovery from Conventional and Unconventional Reservoirs. © 2018 Elsevier Inc.
DOI: https://doi.org/10.1016/B978-0-12-813027-8.00001-1 All rights reserved. 1