Yongfu Wu

An experimental study of wetting behavior and surfactant EOR in carbonates with model compounds

This study focuses on the mechanisms responsible for enhanced oil recovery (EOR) from fractured carbonate reservoirs by surfactant solutions, and methods to screen for effective chemical formulations quickly. One key to this EOR process is the surfactant solution reversing the wettability of the carbonate surfaces from less water-wet to more water-wet conditions. This effect allows the aqueous phase to imbibe into the matrix spontaneously and expel oil bypassed by a waterflood. This study used different naphthenic acids (NA) dissolved in decane as a model oil to render calcite surfaces less water-wet. Because pure compounds are used, trends in wetting behavior can be related to NA molecular structure as measured by solid adsorption; contact angle; and a novel, simple flotation test with calcite powder. Experiments with different surfactants and NA-treated calcite powder provide information about mechanisms responsible for sought-after reversal to a more water-wet state. Results indicate this flotation test is a useful rapid screening tool to identify better EOR surfactants for carbonates. The study considers the application of surfactants for EOR from carbonate reservoirs. This technology provides a new opportunity for EOR, especially for fractured carbonate, where waterflood response typically is poor and the matrix is a high oil-saturation target.

Branched Alkyl Alcohol Propoxylated Sulfate Surfactants for Improved Oil Recovery

Abstract This investigation considers branched alkyl alcohol propoxylated sulfate surfactants as candidates for chemcial enhanced oil recovery (EOR) applications. Results show that these anionic surfactants may be preferred candidates for EOR as they can be effective at creating low interfacial tension (IFT) at dilute concentrations, without requiring an alkaline agent or cosurfactant. In addition, some of the formulations exhibit a low IFT at high salinity, and hence may be suitable for use in more saline reservoirs. Adsorption tests onto kaolinite clay indicate that the loss of these surfactants can be comparable to or greater than other types of anionic surfactants. Surfactant performance was evaluated in oil recovery core flood tests. Selected formulations recovered 35–50% waterflood residual oil even with dilute 0.2 wt% surfactant concentrations from Berea sandstone cores.

Alkyl Polyglycoside-Sorbitan Ester Formulations for Improved Oil Recovery

Abstract We measured interfacial tensions (IFT) of aqueous alkyl polyglucoside (APG) systems formulated with sorbitan ester-type cosurfactants against n-octane. The study focused on low to ultra-low IFT systems which are relevant for enhanced oil recovery (EOR). In addition, we measured equilibrium adsorption concentrations of these surfactants and cosurfactants onto kaolinite clay, commonly found in oil reservoirs. We present one surfactant EOR laboratory flood experiment with one selected APG-sorbitan ester formulation with which we recovered 94% of initial oil in place (IOIP).

Analysis of the Influence of Alkyl Polyglycoside Surfactant and Cosolvent Structure on Interfacial Tension in Aqueous Formulations versus n-Octane

Abstract We studied the influence of molecular structural elements of alkyl polyglycoside (APG) surfactants on the interfacial tension (IFT) in aqueous formulations against n-octane. This included the analysis of alkyl and aryl chain length, type and number of sugar-ring head, anomers, addition of cosolvents and effect of salt addition. We found that longer alkyl or aryl chains lead to lower IFT, consistent with data recorded for commercial (mixed) APGs. APGs with only one sugar-ring head had lower IFT than their analog maltose derivates (two-ring head). Intriguingly the stereochemistry of the sugar head (i.e. galactose versus glucose) and the type of anomer showed a significant influence on IFT. The n-octyl-α-D-glucopyranoside anomer had a lower IFT than the corresponding β-anomer. 1-octanol and 1-hexanol were efficient cosolvents consistent with the datasets observed for commercial APGs. Salt addition reduced IFT. Functional groups (aldehyde, amide-methoxy) integrated into the molecular architecture of the APG skeleton were efficient in terms of significantly reducing IFT, suggesting a strategy for the molecular design of advanced APG surfactants. We discuss the results in the context of the hydrophilic-lipophilic deviation (HLD) concept, which we modified so that IFT values are discussed instead of phase behavior.

Experimental Study of Surfactant Retention on Kaolinite Clay

Abstract We measured equilibrium surfactant retention on kaolinite clay for a large array of surfactants. We demonstrate that the mass balance measurements we used are a rapid way to screen surfactants in terms of their potential to be used in enhanced oil recovery applications. Surfactant classes investigated include: alkyl(aryl) sulfonates, ethylene oxide-propylene oxide copolymers, ethoxylated alkylphenols, alkyl polyglucosides, sorbitan ester ethoxylates, alkyl alcohol propoxylated sulfate sodium salts, gemini surfactants, sulfosuccinates and organo silicone-ethylene oxide-propylene oxide terpolymers. We identified several surfactants which had zero retention under the test conditions and which may therefore be suitable as enhanced oil recovery chemicals in surfactant flooding schemes. We discuss surfactant retention mechanisms on kaolinite clay and analyze surfactant structure-retention relationships for several surfactant classes.

Alkyl Polyglycoside/1-Naphthol Formulations: A Case Study of Surfactant Enhanced Oil Recovery

Abstract We present a case study of surfactant enhanced oil recovery using Alkyl polyglucoside/1-naphthol formulations. Alkyl polyglucosides are a green, non-toxic and renewable surfactant class synthesized out of agricultural raw materials. We measured interfacial tensions versus n-octane and viscosities of these formulations and conducted one coreflood enhanced oil recovery (EOR) experiment where we recovered 82.6 % of initial oil in place demonstrating that these formulations are efficient EOR agents.