Surface Energy of North American Shales and its Role in Interaction of Shale with Surfactants and Microemulsions

Abstract

In recent years a number of laboratory studies on the use of surfactants and microemulsions in hydraulic fracturing of shale formations have been reported. These studies mainly focused on such metrics as improvement in permeability regain and enhancement of fluid recovery from packed columns upon the use of surfactant-containing chemicals. Laboratory studies have also been backed by the documented observations from the field illustrating benefits of using microemulsions for the increase in gas production from shale formations. It is a commonly accepted view that these additives benefit gas production by lowering capillary pressure and altering wetability of shale formation. Although it is recognized that the interaction of surfactants and microemulsions with shale is governed by the energetics of solid/liquid, liquid/gas and solid/gas interfaces, there are practically no studies in which surface energies have been determined for different shales. The surface energy, as well as dispersive, non-dispersive, Lifshitz-van der Waals, and Lewis Acid-Lewis Base components of surface energy of several North American shales have been determined from contact angle measurements. It has been discovered that the surface energy of all shale rocks is rather low, typically in the range of 40-50 mJ/m 2 a contribution from non-dispersion ("polar") component of about 8-11 dyn/cm. Consequently, shales are capable of interacting with liquids predominantly via dispersion and Lifshitz-van der Waals molecular interactions, which should substantially influence the orientation of surfactant molecules and microemulsion moieties at the shale surface. Furthermore, there was no significant variation in surface energy of shales from different basins, which suggests that individuality of shale surface chemistry should play only a secondary role in the development of shale-specific chemical treatments, and factors other than surface chemistry should be considered first.

Dynamic Interfacial Tensions and Contact Angles of Surfactant-in-Brine/Oil/Shale Systems: Implications to Enhanced Oil Recovery in Shale Oil Reservoirs

“…This was attributed to increase in the adsorption of surfactant with hydrophobic tail facing the shale rock surface. 30 Similarly, another investigation on wettability of Bakken shale using both anionic and nonionic surfactant solutions found that wettability of the upper Bakken shale shifted from oil wet to neutral wet at 60 to 90 ℃ and for the middle Bakken it altered from weakly oil wet to neutral wet at 23 ℃. 3 The discrepancy between the above mentioned studies and the results in this study might be due differences in the mineralogy, pore types, the composition of crude oil, and measurement techniques.…”

Dynamic interfacial tension and wettability of shale in the presence of surfactants at reservoir conditions

“…Therefore, we expect low 499 surfactant losses due to adsorption on shale during hydraulic frac-500 turing with this surfactant. There are a number of experimental 501 studies that report a reduction in contact angle when using non-502 ionic surfactants with negatively charged surfaces such as quartz503 and shale[20,39,40]. The reduction in CA was attributed to (/g in[20]), which is three to four times smaller than the 510 adsorption of nonionic surfactant in these studies.…”

“…Although the effect of some surfactants on the interfacial 38 properties of shale oil systems has been investigated in the past, the limited data available in the litera-39 ture were mainly obtained at ambient conditions and thus may not be representative of fluid-rock inter- 40 actions at actual reservoir conditions. 41 In this study, a new framework is proposed to investigate the effect of surfactants on fundamental 42 parameters governing fluid displacement in two brine/oil/shale systems (A and B) at reservoir conditions.…”

Forced and Spontaneous Imbibition Experiments for Quantifying Surfactant Efficiency in Tight Shales

“…Furthermore, we observed an increase in the contact angle for higher surfactant concentrations (up to 60 ppm): Shale surfaces treated with the surfactant are characterized by a high contact angles for deionized (DI) water (Figure 1), while spontaneous imbibition tests on neighboring samples demonstrate a reduced uptake of the surfactant solutions relative to pure water. Surface energy values obtained from contact angle measurements have been found to be similar for most shale types (Zelenev, 2011), which makes those measurements relatively ineffective in determining an optimal and field-specific treatment (surfactant). These observations are usually obtained from small samples, and due to the heterogeneous nature of shales, a good deal of variability (uncertainty) is associated with such measurements: Contact angle observations, as a result, can vary significantly even for samples that are located in close proximity.…”