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Glover, C.J.,* SPE-AIME, Exxon Production Research Puerto, M.C., SPE-AIME, Puerto, M.C., SPE-AIME, Exxon Production Research Co. Maerker, J.M., SPE-AIME, Exxon Production Research Co. Sandvik, E.L., SPE-AIME, Exxon Production Research Co. Abstract Surfactant retention in reservoir rock is a major factor limiting effectiveness of oil recovery using microemulsion flooding processes. Effects of salinity and surfactant concentration on microemulsion phase behavior have a significant impact on relative phase behavior have a significant impact on relative magnitudes of retention attributed to adsorption vs entrapment of immiscible microemulsion phases.Surfactant retention levels were determined by effluent sample analyses from microemulsion flow tests in Berea cores. Data for single surfactant systems containing NaCl only and multicomponent surfactant systems containing monovalent and divalent cations are included. Retention is shown to increase linearly with salinity at low salt concentrations and depart from linearity with higher retentions above a critical salinity. This departure from linearity is shown to correlate with formation of upper-phase microemulsions. The linear trend, therefore, is attributed to surfactant adsorption, and retention levels in excess of this trend are attributed to phase trapping.Divalent cations are shown to influence microemulsion phase behavior strongly through formation of divalent-cation sulfonate species. A useful method for predicting phase behavior in systems containing divalent cations is described. This method combines equilibrium expressions with a relationship defining the contribution of each surfactant component to optimal salinity. Observed experimental data are compared with predicted data. Introduction Two essential criteria that must be met for successful recovery of residual oil by chemical flooding arevery low interfacial tensions between the chemical bank and residual oil and between the chemical bank and drive fluid andsmall surfactant retention losses to reservoir rock. If retention is excessive, interfacial tensions eventually will become high enough to retrap residual oil in the remainder of the reservoir.Previous studies have described several mechanisms responsible for surfactant retention in porous media. These include adsorption, porous media. These include adsorption, precipitation, partitioning into a residual oil phase, precipitation, partitioning into a residual oil phase, and entrapment of immiscible microemulsion phases. Of particular interest is Trushenski's discussion of microemulsion phase trapping as a consequence of surfactant-polymer interaction, and a supporting statement that similar behavior often was observed when microemulsions were diluted with polymer-free brine. Here, we attempt to provide some understanding of this surfactant dilution phenomenon by examining phase behavior as a function of salinity, divalent-ion content, and surfactant concentration. Experimental Procedures Surfactant Systems Two surfactant systems were used in this study. (Specific microemulsion compositions are discussed later.) One system was the 63:37 volumetric mixture of the monoethanol amine salt of dodecylorthoxylene sulfonic acid and tertiary amyl alcohol (MEAC12OXS/TAA) described by Healy et al. The oil component for these microemulsions was a mixture of 90% Isopar M TM and 10% Heavy Aromatic Naptha.(TM)** The brine contained NaCl only. SPEJ P. 183

6.0 5.0 4.0 . , . . AAA-1 Original AAG-1 Original --AAA-l Aged --AAG-1 Aged --The oxidation of asphalt is a major cause of pavement failure. The low-temperature oxidation kinetics of 14 asphalts are presented. A t constant temperature and oxygen pressure, asphalt oxidation occurs in two stages: (1) a relatively rapid-rate period, followed by (2) a long period of constant rate. Activation energies for the constant-rate region vary ji-om 64 to 109 kJ/mol, and reaction orders relative to oxygen pressure vary from 0.25 to 0.61. This variation in activation energy and reaction order leads to skepticism regarding the present practices of eualuating road-condition asphalt-hardening rates at a single elevated temperature and perhaps at an elevatedpressure. The asphalts occur in essentially two groups, one at high values of both activation energy and reaction order and the other at low values of each. The data indicate the existence of an isokinetic temperature near 100°C. The degree of oxidation that occurs during the initial rapid-rate region varies inversely with the oxygen reaction order of the constant-rate region.Aging temperatures 170", 180", and 190°F; aging pressures 0.2 atm and 20 atm.

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Ten asphalts, including seven Strategic Highway Research Program (SHRP) asphalts and three Texas asphalts, plus naphthene and polar aromatic Corbett fractions for five of the seven SHRP asphalts were aged at laboratory conditions. The oxygen content by direct measurement and the FTIR carbonyl content were obtained for samples which were aged to varying degrees. It was found that, for each material, the oxygen content correlates linearly with the carbonyl content. The correlation is independent of aging temperature and aging pressure over the ranges studied. Furthermore, each material has a unique correlation coefficient, and the correlation slope for a whole asphalt is smaller than those of its fractions, except for asphalt AAM-1. Since the major oxidation products, including ketones, carboxylic acids, and anhydrides, have different oxygen content−carbonyl content ratios, the correlation coefficients provide qualitative information about the distribution of oxidation products. Relations between oxygen, carbonyl, and asphaltene production are deduced from these and earlier results.