Page 230 - Enhanced Oil Recovery in Shale and Tight Reservoirs

CHAPTER NINE

EOR mechanisms of wettability
alteration and its comparison

with IFT

Abstract

A surfactant has two functions: interfacial tension (IFT) reduction and wettability alter-
ation. The function of wettability (alteration) may be more important in shale and tight
formations. This chapter focuses on the discussions related to wettability alteration and
a brief discussion of IFT related to wettability alteration. The discussions include the EOR
mechanisms of wettability alteration and IFT, formulation of these two functions, IFT
reduction versus wettability alteration, surfactants used to alter wettability, determina-
tion of wettability, and conversion of wetting angles.

Keywords: Conversion of wetting angles; Determination of wetting angles; Formulation;
IFT; Wettability alteration; Wetting angles.

9.1 Introduction

Although chemical methods like surfactant injection are important
methods to enhance oil recovery in conventional reservoirs (Samanta et al.,
2012; Rai et al., 2015; Mandal, 2015), very limited applications were reported
in shale and tight reservoirs. More often, surfactants are added as an additive in
the fracturing fluid or completion fluid to improve oil and gas production.
When surfactants are added for the EOR purpose, water-oil interfacial ten-
sion reduction results in the increase in capillary number so that residual oil
saturation is reduced. This mechanism related to IFT reduction has dominated
the literature. Sheng (2013b) explicitly explained that a surfactant has two
functions: interfacial tension (IFT) reduction and wettability alteration, and
he quantified the two mechanisms using simulation. Chen and Mohanty
(2015) subsequently experimentally studied the two functions. As the func-
tion of wettability (alteration) becomes more important in EOR in shale
and tight formations, more research has been focusing on this mechanism
recently. This chapter focusses on the discussions related to wettability and
brief discussion of IFT related to wettability alteration. The discussions

Enhanced Oil Recovery in Shale and Tight Reservoirs © 2020 James Sheng.
ISBN: 978-0-12-815905-7 Published by Elsevier Inc.
https://doi.org/10.1016/B978-0-12-815905-7.00009-8 All rights reserved. 213 j