Page 116 - Enhanced Oil Recovery in Shale and Tight Reservoirs

Huff-n-puff injection in shale gas condensate reservoirs 103

1.5e2.5 (Bang et al., 2008). When a surfactant was used to treat reservoir
and outcrop sandstone rocks, the relative permeability of the gas condensate
at a connate water saturation was improved by a factor of 2 (Bang et al.,
2009, 2010). The improvement remained after a large pore volume of the
gas-condensate flood. However, Ahmadi et al. (2011) found that a
polyamine primer preflush was necessary to make fluorinated chemicals
durable. Karandish et al. (2015) used an anionic fluorosurfactant mixture
to have altered the Sarkhun carbonate cores from water-wet to intermediate
gas-wet. Their gas relative permeability was improved by 1.7 times.
Li et al. (2011) treated tight cores with the permeability less than 0.1 mD
using a fluorocarbon surfactant. Water and decane imbibition tests were
conducted to demonstrate wettability alteration from water wet to gas wet.
Sharma et al. (2018) treated Eagle Ford outcrop cores using a fluoro-
carbon surfactant. The porosity ranged from 8% to 9% and the permeability
ranged between 700 nD to 900 nD. A gas-condensate mixture of 0.85 mol
fraction methane and 0.15 mol fraction n-butane was used as a reservoir
fluid. Its phase properties are presented earlier in this chapter. In this section,
the experiments were carried at the room temperature of 74 F at which the

dew point pressure of the fluid was 1870 psi. The maximum liquid dropout
was 6.5% at 1500 psi. The nonionic fluorinated surfactant with 95%
additives was used in experiments. Its fluoroalkyl group provided the oil-
and water-repelling characteristics, resulting in gas wetting, while the
alkylene oxide head group associated with the rock surface by hydrogen
bonding caused by adsorption. The solution was prepared by diluting the
2 wt.% surfactant, 94 wt.% methanol, and 4 wt.% deionized water.
The contact angle measurements for the treated cores showed significant
wettability alteration to preferentially gas wetting. The water/air/rock con-

tact angle increased from 60 to 80 , and the n-decane/air/rock contact

angle increased from 0 to 60 .The experimental setup is shown in Fig. 4.3.

To perform a huff-n-puff experiment to remove condensate blockage, a
condensate banking needed to be established. The core was first saturated
with the single-phase gas-condensate mixture. Then the outlet A was set
at 1500 psi at which the maximum liquid dropout occurred. The gas
mixture was continuously flooded through the other end of the core B, until
the average CT number did not change, indicating a steady flow through
the core. Then the condensate saturation gradually decreased from the
maximum at the outlet B to zero at some distance from the inlet B. Such
condensate saturation represented a real liquid saturation profile from a
well to some point in the reservoir.