Page 94 - Enhanced Oil Recovery in Shale and Tight Reservoirs

CHAPTER FOUR

Huff-n-puff injection in shale gas
condensate reservoirs

Abstract

This chapter discusses huff-n-puff gas injection in shale and tight gas condensate oil
reservoirs. Huff-n-puff gas injection is compared with gas flooding in terms of their po-
tential to enhance liquid recovery and remove liquid blockage. Huff-n-puff gas injection
is also compared with huff-n-puff solvent injection in core scale and field scale. The sol-
vents are methanol and isopropanol. The capacity of surfactants to remove liquid
blockage is also studied. Factors that affect huff-n-puff gas injection performance are
discussed. Mechanisms of huff-n-puff injection are discussed. Optimization of huff-n-
puff injection is proposed.

Keywords: Gas condensate; Gas flooding; Huff-n-puff; Liquid blockage; Liquid recovery;
Solvents; Surfactants.

4.1 Introduction
To understand the problem and solution of a gas condensate reservoir,
first look at the phase diagram of a gas condensate (Fig. 4.1). When a gas
condensate reservoir is produced, the pressure near the production well is
depleted along the path 1 to 5 at the initial reservoir temperature. The
pressure initially is at point 1 at the initial reservoir pressure. When the
pressure is decreased at point 2 (dew point), some heavy components in
the gas phase start to condense. From point 2 to point 3, more condensation
occurs, and at point 3, the liquid condensate reaches the maximum between
15 and 20 shown in the figure. From point 3 to point 4, the liquid
condensate starts to vaporize, and the vaporization is completed at point 5
(back to the dew point). At this point, the fluid becomes gas again. Because
some pressure is needed to produce the well, the pressure near the bottom of
the well cannot be as low as the pressure at point 5. Thus, some liquid
condensate forms from the bottom of wellbore to some distance deep
into the reservoir, as shown in Fig. 4.2. From this figure, it is obvious that
the liquid condensate blocks the gas flow into the wellbore. As liquid is
more difficult to flow than gas, the wellbore productivity is reduced.

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/B978-0-12-815905-7.00004-9 All rights reserved. 81 j