Page 306 - Enhanced Oil Recovery in Shale and Tight Reservoirs

CHAPTER TEN

Spontaneous imbibition

Abstract
In shale and tight formations, imbibition, especially water imbibition, plays a very
important role during fracturing and in enhancing oil and gas recovery. In this chapter,
fundamentals of spontaneous imbibition and upscaling theories are first reviewed.
Then the main factors which affect spontaneous imbibition are discussed. These factors
include permeability and porosity, initial wettability, wettability alteration, interfacial
tension diffusion, gravity, viscosity ratio, and initial water content. Countercurrent
flow is compared with cocurrent flow. Finally, behaviors of different surfactants are
discussed.

Keywords: Cocurrent flow; Countercurrent flow; Diffusion; Gravity; Initial wettability;
Spontaneous imbibition; Surfactants; Upscaling; Viscosity ratio.

10.1 Introduction

Spontaneous imbibition is defined as the process in which a wetting
phase imbibes into the rock (matrix). During the spontaneous imbibition,
one fluid displaces another in a porous medium by capillary pressure. In shale
and tight formations, imbibition, especially water imbibition, plays a very
important role during fracturing and in enhancing oil and gas recovery. In
this chapter, imbibition fundamentals and upscaling theories are first
reviewed. Then the main factors which affect imbibition are discussed.
These factors include permeability and porosity, initial wettability, wetta-
bility alteration, interfacial tension (IFT), diffusion, gravity, viscosity ratio,
and initial water content. Countercurrent flow is compared with cocurrent
flow. Finally, behaviors of different surfactants are discussed.

10.2 Discussion of some theoretical equations on
spontaneous imbibition
McWhorter and Sunada (1990) derived a general two-phase Darcy
equation for countercurrent imbibition. Schmid and Geiger (2013) demon-
strated that the solution can be viewed as the capillary analog to the

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/B978-0-12-815905-7.00010-4 All rights reserved. 279 j