Page 229 - Enhanced Oil Recovery in Shale and Tight Reservoirs

212 Enhanced Oil Recovery in Shale and Tight Reservoirs

8.13 Surfactant effects
Surfactants are typically added in fracturing fluids to assist flowback,
enhance water imbibition, and enhance oil and gas recovery through other
mechanisms such as wettability alteration and IFT reduction. Kim et al.
(2009) studied the effects of surfactants on the crack growth rate in nanoporous
organosilicate thin films. They found that the C m E n surfactant significantly
retarded crack growth rates, whereas dimeric surfactants accelerated the crack
growth process. The dimeric surfactants were shown to accelerate growth
rates by lowering the surface energy of the fracture surface. The C m E n surfac-
tant is polyoxyethylene alkyl ether, CH 3 (CH 2 ) m 1 (OCH 2 CH 2 ) n OH, with
various hydrophobic alkyl tail lengths, m, and hydrophilic ethylene oxide
(EO) head lengths, n. The suppression of crack growth rates in C m E n surfac-
tant solutions was attributed to bridging of the crack surfaces by surfactant
molecules or the formation of nanobubbles in the surfactant-containing
solution. Their work indicates that surfactants may affect crack growth.
Aderibigbe and Lane (2013) conducted unconfined compression and
Brazilian tests after Mancos shale samples were exposed to water and surfac-
tant solutions. In their uniaxial compressive strength tests and the Brazilian
tests, the strength of the samples was the weakest when exposed to water,
a similar (slightly lower) reduction was observed with the samples exposed
to 0.1% w/v DTAB (dodecyl trimethylammonium bromide) and 0.1%
w/v SDBS (sodium dodecyl benzenesulfonate) solutions. In other words,
the surfactant addition did not significantly change the rock strength
compared with water. The rock strength in 4% KCl solutions was higher
than in water or in surfactant-only solutions.