Page 61 - Fundamentals of Enhanced Oil and Gas Recovery

Screening Criteria of Enhanced Oil Recovery Methods 49

the projects have been carried out in reservoirs with oil viscosity over the range of
9 75 cp [14].
In addition to Daqing project and many polymer flooding projects in China, some
pilot and large-scale polymer flooding projects have been reported worldwide. North
Burbank in the United States, Pelican Lake in Canada, El Tordillo field in Argentina,
Jhalora field in India, Buracica and Canto do Amaro fields in Brazil, and Marmul field
in Oman are some examples of polymer flooding in Sandstone reservoirs [17,37,38].

2.3.2 Surfactant Flooding
Surfactants are amphiphilic organic molecules that possess hydrophilic and hydropho-
bic regions [39]. They have a long hydrocarbon tail and an ionic or polar head group.
The surfactant molecules form an interface between two immiscible liquids, and larger
quantities of surfactant lead to more interfacial area between two liquids until eventu-
ally they are considered miscible. Also, oil and water emulsion produced by surfactant
flooding increases the displacement efficiency of the process. The main mechanisms
for enhancing the displacement efficiency are interfacial tension (IFT) reduction, wet-
tability alteration, and as a result reducing capillary force in porous media.
There are four types of surfactant categorized based on the ionic type of the head
group as anionic, cationic, nonionic, and zwitterionic. The most used types in the
chemical EOR are anionics while they do not adsorb on the negative charged clays of
sandstone reservoirs (surface of the rock). In contrast, cationic surfactants are more
expensive than anionics, and they are only used in carbonate reservoirs to change rock
wettability, while ability of nonionic surfactants to reduce the IFT is less than anionic
surfactants; therefore, they are mostly used as cosurfactant in chemical flooding.
Sometimes, surfactant flooding in sandstone reservoirs is combined with polymer,
alkali, or even the both chemicals. Although surfactant flooding is more popular in
sandstone reservoirs, recently few field studies were carried out in carbonate reservoirs
[40,41]. Detailed screening criteria for the existing combinations are discussed further
in details.

2.3.3 Alkaline Flooding

Alkaline flooding is the cheapest chemical EOR method, and the main alkali used in
oil field is sodium hydroxide. Alkali (NaOH) interacts with the pseudo acid compo-
nent (HA) of crude oil and creates the sodium salt of the organic acid (NaA) on the
interface between the oleic and aqueous phases. In other words, in situ anionic surfac-
tant is produced to decrease the IFT of the system (Fig. 2.1). This mechanism requires
high pH condition; therefore, no promising result was noticed in waterflooding pro-
jects. Moreover, high viscosity crude oils are recommended for alkaline flooding since
they contain high organic acid content.