Page 190 - Enhanced Oil Recovery in Shale and Tight Reservoirs

CHAPTER EIGHT

Fluid-rock interactions

Abstract
This chapter discusses the research results on the interactions between an aqueous so-
lution and a clay-bearing rock. The effects of confining stress, bedding, existing natural
fractures, low-pH and carbonated water, high-pH water and surfactants on the perme-
ability changes from water-rock interactions are discussed. The effects of some of those
factors on rock mechanical properties are also discussed. Some reactions which induce
fractures are introduced.

Keywords: Confining stress; Fluid-rock interactions; Mechanical properties; Natural
fractures; Permeability changes; pH; Reaction-induced fractures; Surfactants.

8.1 Introduction

The fluid-rock interactions to be discussed in this chapter are the
interactions between an aqueous solution and a clay-bearing rock. There
are three reasons we need to study the interactions in shale and tight reser-
voirs: (1) most of fracturing fluids are aqueous fluids; (2) most of chemicals
are injected through aqueous fluids; (3) water injection may still be a practical
EOR method. In conventional reservoirs, it is generally accepted that water-
rock swelling may cause formation damagedreducing formation perme-
ability. However, there are some discrepancies in shale reservoirs regarding
the results of water-rock interactions. Some believe water-rock interactions
also cause formation damage. Some argue that water-rock interactions, espe-
cially the interactions between water and shale, may generate microfractures
or reopen existing natural fractures; therefore, formation may not be
damaged, instead, it may be stimulated. This chapter is to discuss the research
results on the interactions between water and a clay-bearing rock.

8.2 Evidences of microfractures generated or existing
natural fractures reopened

Many papers have been published on water-rock interaction. It is
commonly accepted that water-rock interaction causes formation damage

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/B978-0-12-815905-7.00008-6 All rights reserved. 173 j