Page 199 - Fundamentals of Enhanced Oil and Gas Recovery

CHAPTER SIX

Chemical Flooding

Mohammad Ali Ahmadi
Department of Chemical and Petroleum Engineering, University of Calgary, Calgary, AB, Canada

6.1 INTRODUCTION

Historically, oil production from oil reservoirs has been divided into three
phases. Initially, oil is produced by the native energy of the reservoir (such as the dis-
solved gas drive, or the natural water-drive aquifer), and this period is called primary
production. Primary production results in 5% 30% original oil in place (OOIP)
recovery [1]. Since water is the cheapest fluid available, water flooding is carried out
to increase the oil production beyond that of primary production and this stage is
called secondary production. The water pushes the oil in front of it toward the pro-
duction wells and helps to increase the total recovery to 40% 60% OOIP. The pro-
cess continues until the water oil ratio at the production wells becomes very high
and reaches the economic level at which the oil production is not cost-effective any-
more. At this stage, there is a significant amount of oil (40% 60% OOIP) still left in
the reservoir due to many factors including unfavorable wettability conditions,
heterogeneity of reservoir rock, and capillary-trapped oil. In order to recover this
residual oil and increase the ultimate oil recovery of the reservoir, enhanced oil recov-
ery (EOR) methods are utilized. Since these methods often follow the secondary pro-
duction, they are sometimes called tertiary oil recovery methods. The EOR processes
can be divided into three main categories [2 6]:
• Chemical methods
• Miscible methods
• Thermal methods

6.2 CHEMICAL-BASED ENHANCED OIL RECOVERY METHOD

In chemical EOR methods, an agent that is not normally present in the reser-
voir is injected to enhance the oil displacement. Examples of the chemical processes
are gel polymer and polymer flooding aimed to shutoff the high-permeability areas of

Fundamentals of Enhanced Oil and Gas Recovery from Conventional and Unconventional Reservoirs. © 2018 Elsevier Inc.
DOI: https://doi.org/10.1016/B978-0-12-813027-8.00006-0 All rights reserved. 187