Kristine Spildo

Uniform and mixed wetting in square capillaries

Square capillaries provide a better model of the pore space in rocks than do capillary tubes of circular cross-section because they have corners where wetting fluid can be retained. We report experimental observations of imbibition of an aqueous phase into square capillary tubes with uniform and mixed wetting. Each capillary had an oil-wet end to ensure that water imbibed in one direction only. Swelling of arc menisci in the corners of the square tubes and formation and movement of main terminal menisci were observed during water imbibition. Clean, strongly water-wet capillaries were studied with water displacing decane or air. Wetting was altered by exposing clean capillaries to crude oil or to decane with polar additives. Uniform changes in wetting were effected by filling the capillary with a single phase. Capillaries exposed first to brine, then drained with crude oil, became mixed-wet. The rates and amounts of oil produced are reported. For crude oil-treated capillaries, a consistent trend of decreased rate and extent of oil production with increased aging time emerged. Wetting alteration by polar and acid/base interactions was consistent with previously proposed interaction mechanisms based on contact angle observations.

Salinity Selection for a Low Salinity Water-Low Salinity Surfactant Process

A laboratory selection of salinity for a low salinity water-low salinity surfactant (LS-LSS) process is presented in this paper with systematical investigation on surfactant phase behavior, interfacial tension (IFT), and dynamic retention in porous media with IOS2024 and isoamyl alcohol (IAA) as surfactant system. The results show that 0.4 wt% IOS2024 with 1 wt% IAA can provide ultra-low IFT of 10−3 mN/m at around 3000–4000 mg/L total dissolved solids, but at that salinity range the surfactant retention is very high. The search for an optimum surfactant formulation has to consider solution properties and retention in addition to the low IFT. The salinity for a LS-LSS process should thus not be focused on either optimal salinity or ultra-low IFT, but instead the best choice could be a compromise between the properties in question. The three-phase region, where ultra-low IFT are found, is also associated with high retention values. However, we show that as salinity is increased from a two-phase region with oil solubilized in a water continuous microemulsion, there is a region close to the three-phase boundary which has potential. This region does not give ultra-low, but fairly low (10−2 mN/m in this case) interfacial tensions, and also significantly lower retention.