Page 367 - Enhanced Oil Recovery in Shale and Tight Reservoirs

CHAPTER TWELVE

Fracturing fluid flow back

Abstract
In this chapter, the flow back and production performance from common shale
reservoirs and experimental results are summarized. Mechanisms of low flow back
are proposed. The effects of shut-in, initial rock wettability, invasion depth and surfac-
tant additives on flow back are discussed. Finally, some solutions to deal with flow back
are summarized.

Keywords: Delay; Flow back; Invasion; Invasion depth; Permeability recovery; Shut in;
Surfactant additives; Water blockage.

12.1 Introduction
After hydraulic fracturing, a well can be put in production immedi-
ately or after some time. Several terms have been used anonymously to
describe the time to defer well production: soak, shut-in, resting, and delay.
Strictly speaking, shut-in or resting means a time lapse between two flowing
periods, while the delay means the time before the first flowing period. We
try to explicitly use the different terms of “shut in” and “delay.” The shut-in
is sometimes called the first shut-in which is from the end of fracturing stim-
ulation to the start of the first fluid flow back. The shut-in after the first flow
back is the second shut-in or subsequent shut-in, which is an intentional or
unintentional event in operation.
Generally, fracturing treatments are designed with good fluid stability
during the pump time. It is desired to break the fluid as quickly and
completely as possible to facilitate rapid cleanup of the well and minimize
conductivity damage. It is commonly believed that if the shut-in in the
reservoir is too long, fracture conductivity damage may increase. For a
multistage fracturing job, it is desirable to flow the treatment fluid back after
each stage to recover the fluid, because the shut-in time for the preceding
stages will be too long, if the flow back is executed after the fracturing
work at the last stage is completed. Then a problem is that offshore and
geographically remote well operations often require the use of the drilling
rig for completion operations. The time consumed on the completion phase

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/B978-0-12-815905-7.00012-8 All rights reserved. 339 j