Arf, T.G., Pennsylvania State U. LaBelle, G., Pennsylvania State U. Klaus, E.E., Pennsylvania State U. Duda, J.L., Pennsylvania State U. Nagarajan, R., Pennsylvania State U. Biterge, M.B., SPE, Pennsylvania State U. Ertekin, T., SPE, Pennsylvania State U.
Summary
Petroleum sulfonate surfactants were synthesized from C19, C22, and C26 feedstocks and evaluated in core tests for their ability to enhance oil recovery. All three feedstocks are composed predominantly of saturated paraffinic and naphthenic hydrocarbons. The C19 feedstock includes about 12% aromatics. The hydrocarbons were vapor-phase oxidized at low temperatures to provide cyclic ethers, which subsequently were sulfonated to form a product mixture of mono-, di-, and trisulfonates. Corefloods were conducted with both sulfonates developed at Pennsylvania State U. and commercial sulfonates in Berea sandstone cores. Production performances have been related to recovery and performances have been related to recovery and interfacial activity of the sulfonates. The core tests show that the optimum use of Penn State sulfonates for oil recovery is in the form of dilute slugs. High oil recovery efficiencies are realized when the Penn State sulfonates are used without cosurfactants to form dilute chemical slugs. Specifically, the enhanced oil recoveries obtained with C22 sulfonates are significantly larger than those obtained with the C19 and C26 sulfonates. This is consistent with the oil/water interfacial tension (IFT) and phase behavior of the three types of sulfonates. Furthermore, EOR results and core-effluent analysis studies indicate that sodium carbonate (Na2CO3) in low concentrations is an effective sacrificial agent for Penn State sulfonates.
Introduction
Conventional petroleum sulfonates are produced from aromatic crude oil fractions of suitable boiling-point range. These have been the most frequently considered surfactants for EOR by chemical flooding. Because they are also in demand as lubricant additives and for other uses, their supply is not adequate for large-scale EOR projects. Consequently, paraffinic and naphthenic crude oil fraction that normally cannot be sulfonated have been sulfonated at Penn State by use of a novel two-step process. In the first step, reactive sites are introduced by carefully controlled low-temperature vapor-phase oxidation. The main products are cyclic ethers, predominantly tetrahydrofurans, which are sulfonated in the second step to form surfactants suitable for EOR. One of the possible reaction paths is shown in Fig. 1. Unlike sulfonation of aromatics, the sulfonation reaction of oxidized paraffinic and naphthenic hydrocarbons is not limited to a specific site. The cyclic ether initially forms a sulfate zwitterion, which undergoes elimination to form a diene. Sulfonation of this diolefin is assumed to follow the same scheme as alkene sulfonation. The diene sulfonates to form a mixture of dienesulfonic acids, hydroxyolefin sulfonic acids, and sultones. Relative yields of these products may vary with reaction conditions. Further reaction to form polysulfonate occurs readily; therefore, reactions polysulfonate occurs readily; therefore, reactions must be carefully controlled. Numerous methods have been presented for formulating surfactant systems from petroleum sulfonates, cosurfactants, and electrolytes, usually by optimizing IFT or phase behavior with the oil to be displaced. phase behavior with the oil to be displaced. The average equivalent weight (EW) of the surfactants and the type and concentration of cosurfactants and electrolytes are varied to minimize IFT or to maximize the amounts of oil and water solubilized in a middle-phase microemulsion. In this study, a procedure based on these methods has been applied to nonaromatic Penn State sulfonates and conventional aromatic sulfonates. The connection between the molecular structures of the Penn State sulfonates, their interfacial activity, and their ability to displace oil in corefloods is explored.
Surfactant Synthesis
Three feedstocks were chosen for vapor-phase oxidation and sulfonation: a C19 narrow boiling fraction, a C22 white oil, and a C26 oil. Table 1 lists some properties of the oils. The oxidation and sulfonation have been described in a previous paper, and hence only a brief description will be given.
Oxidation
The oxidation reaction was carried out in a single-pass tubular reactor 4.25 ft [1.3 m] long by 0.17 ft [0.05 m] in diameter with some 10 oxygen and 3 steam inlets along the reactor. The schematic of the reactor is shown in Fig.
The feed is diluted with sufficient steam and/or N2 to keep all the hydrocarbons in the vapor phase and to moderate the heat of reaction. Low-temperature oxidation (570 to 750F [300 to 400C]) favors the production of oxygenated compounds, while high-temperature oxidation (930F [500C] and above) favors the production of olefins.
SPERE
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