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336 Enhanced Oil Recovery in Shale and Tight Reservoirs

Figure 11.25 Spontaneous imbibition, forced imbibition and cyclic injection for the
high-IFT surfactant solution.
imbibition was higher than that from the spontaneous imbibition; the oil
recovery from cyclic injection was highest because extra oil was obtained
by depleting the core pressure. Those results also show that the forced imbi-
bition had higher oil recovery for the high-IFT solution than that for the
low-IFT solution.

11.8 Field tests of surfactant EOR

Surfactants are often added in the fracturing fluid for different reasons,
but not necessarily for enhancing oil recovery. There have been few field
tests where surfactants were added for the direct EOR purpose.
It is well known that surfactants can change wettability and enhance
water imbibition. For conventional oil-wet fractured carbonate reservoirs,
many laboratory studies have been conducted using surfactants to stimulate
spontaneous imbibition, for example, Chen et al. (2001), Olson et al. (1990),
and Hirasaki and Zhang (2004). Some surfactant stimulation tests (injection,
soak and flush back) have been tried in the Yates field in Texas (Yang and
Wadleigh, 2000), the Mauddud carbonate in Bahrain (Zubari and Sivaku-
mar, 2003), in the Cottonwood Creek field, Wyoming (Xie et al., 2005;
Weiss et al., 2006), and in the Baturaja formation in the Semoga field in
Indonesia (Rilian et al., 2010). Field results in general showed positive
responses to surfactant stimulation (Sheng, 2013a).