Equivalent Alkane Carbon Number Of Oil Research Articles

Coupled Interfacial Tension and Phase Behavior Model Based on Micellar Curvatures.

This article introduces a consistent and robust model that predicts interfacial tensions for all microemulsion Winsor types and overall compositions. The model incorporates film bending arguments and Huh's equation and is coupled to phase behavior so that simultaneous tuning of both interfacial tension (IFT) and phase behavior is possible. The oil-water interfacial tension and characteristic length are shown to be related to each other through the hydrophilic-lipophilic deviation (HLD). The phase behavior is tied to the micelle curvatures, without the need for using the net average curvature (NAC). The interfacial tension model is related to solubilization ratios in order to introduce a coupled interfacial tension-phase behavior model for all phase environments. The approach predicts two- and three-phase interfacial tensions and phase behavior (i.e., tie lines and tie triangles) for changes in composition and HLD input parameters, such as temperature, pressure, surfactant structure, and oil equivalent alkane carbon number. Comparisons to experimental data show excellent fits and predictive capability.

An Equation-of-State Model To Predict Surfactant/Oil/Brine-Phase Behavior

Summary Surfactant/polymer (SP) floods have significant potential to recover waterflood residual oil in shallow oil reservoirs. A thorough understanding of surfactant/oil/brine-phase behavior is critical to design SP-flood processes. Current practices involve repetitive laboratory experiments of dead crude at atmospheric pressure in a salinity scan that aims at finding an “optimum formulation” of chemicals for targeted oil reservoirs. Although considerable progress has been made in developing surfactants and polymers that increase the potential of a chemical enhanced-oil-recovery (EOR) project, very little progress has been made to predict phase behavior as a function of formulation variables such as pressure, temperature, and oil equivalent alkane carbon number (EACN). The empirical Hand (1930) plot is still used today to model the microemulsion-phase behavior with little predictive capability because these and other formulation variables change. Such models could lead to incorrect recovery predictions and improper SP-flood designs. In this research, we develop a new predictive-phase-behavior model and introduce a new factor β to account for pressure changes in the HLD equation. This new HLD equation is coupled with the net-average-curvature (NAC) model to predict phase volumes, solubilization ratios, and microemulsion-phase transitions (Winsor II–, Winsor III, and Winsor II+). The predictions of key parameters are compared with experimental data and are within relative errors of 4% (average 2.35%) for measured optimum salinities and 17% (average 10.55%) for optimum solubilization ratios. This paper is the first to use the HLD/NAC model to predict microemulsion-phase behavior for live crudes, including optimal solubilization ratio and the salinity width of the three-phase Winsor III region at different temperatures and pressures. Although the effect of pressure variations on microemulsion-phase behavior is generally thought to be small compared with temperature-induced changes, we show here that this is not necessarily the case. The predictive approach relies on tuning the model to limited experimental data (such as at atmospheric pressure) similar to what is performed for equation-of-state (EOS) modeling of miscible gasfloods. This new EOS-like model could significantly aid the design of chemical floods where key variables change dynamically, and in screening of potential candidate reservoirs for chemical EOR.

Characterization of Crude Oil Equivalent Alkane Carbon Number (EACN) for Surfactant Flooding Design

Equivalent alkane carbon number (EACN) of crude oil reflects the hydrophobicity of the crude oils, thus it would be helpful to estimate the EACN of crude oil before fine tuning the surfactant selection for enhanced oil recovery field application. In this study, we used the titration methodology to quantify the EACN values for several crude oil samples retrieved from the targeted mature oil fields. The results showed that the method of using extended surfactant was simpler but reliable to determine the EACN of crude oils. The resulting EACN for these crude oils was found to be in the range of 6.0–11.3.

Retrograde transition in the phase behaviour of surfactant-oil-water systems produced by an oil equivalent alkane carbon number scan

The phase behaviour of surfactant-oil-water systems is affected by the so-called formulation variables, i.e. by the nature of the components or their physicochemical characteristics. One of the formulation variables is the nature of the oil, often rendered through the alkane carbon number (ACN), or the equivalent alkane carbon number (EACN) when the oil phase is not an alkane. In most cases the decrease in the oil ACN contributes to the increase in the interfacial interaction between the surfactant and the oil, which results in a WI→WIII→WII transition, similar to that observed when the water salinity is increased. However, in some cases the Winsor II phase behaviour is never reached with the EACN decrease, and a WI→WIII→WI so-called retrograde transition is exhibited instead. Such an anomalous case is analysed here for a system containing a commercial non-ionic polyethoxylated surfactant, a mixture of n-heptane (ACN 7) and benzene (EACN 0), and water. The high performance liquid chromatography analysis of the different phases indicates that the surfactant oligomer partitioning between phases is affected by the alkane benzene mixture. The retrograde transition due to the increase in benzene is shown to arise from the strong increase in the partitioning of lipophilic and balanced oligomers into the more aromatic oil phase, with the remaining surfactant, in particular the interfacial mixture, becoming more hydrophilic. A phase diagram bidimensional (EACN-water-to-oil ratio) mapping indicates that this phenomenon occurs in very limited situations.