Generation of Ultralow Tensions Over a Wide EACN Range Using Pennsylvania State U. Surfactants

Klaus, E.E., Pennsylvania State U. Jones, J.H., Pennsylvania State U. Nagarajan, R., Pennsylvania State U. Ertekin, T., SPE. Pennsylvania State U. Chung, Y.M., Pennsylvania State U. Arf, G., Pennsylvania State U. Yarzumbeck, A.J., Pennsylvania State U. Dudenas, P., Pennsylvania State U. Abstract Saturated paraffinic and naphthenic hydrocarbons without aromatics have been vapor-phase oxidized to produce cyclic ethers and lesser amounts of olefins. These cyclic ethers appear to be effective cosurfactants for the preparation of slugs containing petroleum sulfonate surfactants. The cyclic-ether/olefin mixture has been reacted with SO from oleum or liquid SO to form sulfonates comprising a mixture of mono-, di-, and polysulfonates. The reaction products consisting of the sulfonates, unreacted oxidized products, and residual hydrocarbons have been extracted with isopropanol (IPA) to give two sulfonate fractions. The first fraction is predominantly monosulfonate with lesser quantities of disulfonates. The second fraction consists primarily of di-, tri-, and polysulfonates. The monosulfonate fraction in a low-concentration slug exhibits ultralow interfacial tension (IFT) against hydrocarbons of low equivalent alkane carbon number (EACN). The behavior of this fraction is similar to that of the commercial sulfonates in that its ability to generate low IFT is confined to a narrow range of EACN. To achieve low IFT's at higher EACN in the range of a Pennsylvania crude oil, it is necessary to raise the equivalent weight of the Pennsylvania State U. monosulfonate fraction by blending with a commercial sulfonate of higher equivalent weight. Recent studies show that by mixing, the two IPA fractions of the sulfonation products. a remarkably new surfactant behavior is obtained. In contrast to the behavior of other surfactants that yield ultralow tensions over only a narrow range of values of EACN, this mixture of mono- and polysulfonates generates low IFT's over a wide range of EACN extending from C5 to C12. The salt tolerance of monosulfonates and polysulfonates, either alone or in mixtures. is rather high and even at about 4 wt% NaC1, the surfactant solutions remain stable and yield low IFT's against crude oil. Introduction Chemical flooding processes for terliary oil recovery based on both low-concentration surfactant solutions (typically 2 to 3 wt% or less) and high-concentration surfactant solutions (about 10 wt%) are being investigated in a number of laboratory and field studies. In both types of processes, the ability of surfactant solutions to lower the IFT against crude oil is a major factor determining the oil displacement efficiency. A variety of surfactants, primarily sulfonates synthesized from aromatics present in petroleum fractions, have been identified as those possessing the physical and chemical properties required for the flooding process. The surfactant slug formulations typically consist of the sulfonates, electrolytes, and cosurfactants such as alcohols. The slug, when contacted with oil, can generate a microemulsion phase coexisting with oil and water phases. Low IFT's are found to occur at those conditions that favor the formation of the preceding three phases. Several investigations have focused on determining the conditions for the three- phase formation and IFT lowering in terms of the molecular structure and the molecular weight of the surfactant, the characteristics of the oil (namely, its EACN), salinity, surfactant concentration, and the type and amount of cosurfactant, if used. SPEJ P. 73^