EACN

The assessment of surfactant structures and optimal mixtures for potential use in tertiary flooding strategies in North Sea fields has been examined from fundamental investigations using pure oils. The present study furthermore addresses the physico-chemical problems associated with reservoir oils and how the phase performance of these systems may be correlated with model oils, including the use of toluene and cyclohexane in stock tank oils to produce synthetic live reservoir crudes. Any dependence of surfactant molecular structure on the observed phase properties of proposed oils of equivalent alkane carbon number (EACN) would render simulated live oils as unrepresentative. 

Ehase Inversion Temperatures It was possible to determine the Phase Inversion Temperature (PIT) for the system under study by reference to the conductivity/temperature profile obtained (Figure 2). Rapid declines were indicative of phase preference changes and mid-points were conveniently identified as the inversion point. The alkane series tended to yield PIT values within several degrees of each other but the estimation of the PIT for toluene occasionally proved difficult. Mole fraction mixing rules were employed to assist in the prediction of such PIT values. Toluene/decane blends were evaluated routinely for convenience, as shown in Figure 3. The construction of PIT/EACN profiles has yielded linear relationships, as did the mole fraction oil blends (Figures 4 and 5). The compilation and assessment of all experimental data enabled the significant parameters, attributable to such surfactant formulations, to be tabulated as in Table II. 

Optimal Salinities Because the EACN values ascribed to oil systems are usually derived from salinity scanning, it was considered appropriate to evaluate the salinity tolerance of ICI NP6, and to determine the EACN value for toluene so that a comparison could be made between the two experimental techniques employed in this study. Inspection of Table III reveals an EACN value for toluene of -10.3 which can be compared to the value of -16 determined from PIT data. Such large negative values... 

Optimal Salinities Phase inversions at optimal salinity were assessed routinely by salt titrations into systems maintained at constant temperature. For the Leonox IOS surfactant system, increasing levels of salinity were necessary to cause the emulsion state to phase invert as the alkane molecular weight increased (Figure 11). Ihe initial conductivity value at the condition where zero salt had been added may in part reflect the salt contamination naturally present within the supplied formulation. Ihe internal olefin sulphonate species again revealed a linear relationship between EACN and optimal salinity as did all ionic formulations under test (see Figures 12 and 13, plus Table III). Ihe estimation of EACN values for both toluene... 

SURFACTANT TEST TEMPERATURE /or d S H FA PM S AT EACN=0 /g dm-3 S VALUE FOR OILS/g cbf3 (MEASURED OR EXTRAPOLATED) OIL EACN FROM S ... 

In the absence of alcohol the salinity/alkane sensitivity will be dominated by the nature of the surfactant hydrophile. A linear response was observed between optimal salinity and alkane chain length for the ICI NP6 surfactant with a recorded coefficient of ds /d EACN = 17.Sgdm "3/1 EACN. This high salt tolerance was expected for nonionics and can reflect an... 

The EACN values for toluene were found to vary depending upon the nature of the surfactant molecular structure, but sulphonate systems confirm an EACN equivalence of 0. 

Deuterium-labelled Tetralin and deuterium were used to determine incorporation of hydrogen by structural position in the Tetralin and coal products. Approximately two-thirds of the protium incorporated into the Tetralin-di2 was found in the a-alkyl position, indicating that hydrogen exchange between the coal and tetralin involves the a-Tetralinyl radical. In the case of the coal products, the terms 2H >yFy and 1HX (1-Fy) were used to calculate the deuterium and protium contents or eacn structural position. Preferential incorporation was found in the a-aliphatic position of the soluble coal products, indicating that these positions participated preferentially in hydrogen exchange and addition. The... 

It is worth noting here that this difference between the interface and in the bulk is not specific to surfactant mixtures. While oil mixtures of very similar substances, such as n-alkanes, exhibit a linear mixing rule written in terms of equivalent alkane carbon number or EACN [62-64], mixtures of oils containing substances with very different polarities behave in a non-ideal way and exhibit a segregation near the interface, which results in an accumulation most polar oil components close to the interface [65]. 

Ysambertt F, Anton RE, Salager JL (1997) Retrograde Transition in the phase behavior of surfactant-oil-water systems produced by an oil EACN scan. Colloid Surf A 125 131-136... 

Queste S, Salager JL, Strey R, Aubry JM (2007) The EACN scale for oil classification revisited thanks to fish diagrams. J Colloid Interface Sci 312 98-107 Cayias JL, Schechter RS, Wade WH (1976) Modeling Crude Oils for Low Interfacial tension. Soc Petrol Eng J 16 351-357... 

Our approach is vo establish eacn unit then comoine the units by utilizing molecular aggregates. Our progress towards this goal is described in Sections 19.3 (catalysts), 19.4 (photoexcited state electron transfer in a heterogeneous phase), and 19.5 (sensitization of Ti02 in water). 

Key words hydrophobic oils equivalent alkane carbon number (EACN) surfactant-enhanced remediation... 

Oil contaminants can range in both viscosity and molecular weight. The purpose of this work was to find optimal surfactant formulations to extract low viscosity ( ( 100 cp), high molecular weight (hydrophobic) oils. In surfactant formulation it is common to define the oil molecular weight (hydrophobicity) by virtue of its equivalent alkane carbon number (EACN) aka, how many carbons would there be in an alkane oil of equivalent behavior. Thus, since some crude oils behave similarly to hexane, and since hexane has an alkane carbon number of 6, these crude oils also have an... 

EACN of six. We thus define high molecular weight (hydrophobic) oils as having EACN values >10 and low molecular weight oils (hydrophilic oils) as having an EACN of < 6. 

Thus, given the optimal salinity for an unknown oil, it is possible to back-calculate the oil EACN. However, this is not helpful in designing the surfactant system in the first place. It is desirable to characterize the oil EACN using an alternate approach. One such approach uses alcohol partitioning as an indicator of an unknown oil EACN. The partition coefficient(ky) for low concentrations of alcohol between water and NAPL is dependent upon the NAPL EACN where kjj is defined as the concentration of the alcohol in the NAPL (mg/L) divided by the concentration of the alcohol in the water. The subscripts i and j refer to the NAPL and... 

Recent work evaluated the partition coefficients between 22 different alcohols and nine NAPLs ranging in EACN from chloroform (-15.13) to decane (10) (Dwarakanath 1998). Both plots ofLn (s ) vs. EACN and Ln(kij) vs. EACN provided good agreement for the EACN of each of the nine NAPLs. We have extended these results by measuring ky for four alcohols and 5 neat normal alkanes having EACN from 6 (hexane) to 16 (hexadecane). Next, we measured ky for each alcohol with diesel, and from calibration curves determined the EACN of diesel. 

Since the oil EACN is so critical to formulating surfactant middle phase microemulsions (MPMs), we will begin by discussing a method for characterizing the EACN of unknown NAPLs. The relation between the oil-water partitioning of alcohols (k,j) and NAPL EACN is dependent upon the hydrophobicity of the alcohol, as given by ... 

Where the partitioning coefficient (ky) was previously defined and Nj is the NAPL EACN. C and B are the slope and intercept, respectively, for each alcohol obtained from regression of the experimental data. Figure 2 plots Ln k against EACN for the four partitioning alcohols, and Table II... 

Figure 2. Plots of LnCk,j) versus EACN and best fit lines for each of the partitioning alcohols described in text.

The bilinear relation between k,j and EACNs of both NAPL and alcohol can be shown as follows ... 

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