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Abstract

One of the most severe limitations of surfactant waterflooding is the instability of the commonly employed surfactants in the usual ionic environments of oil reservoirs. A specific modification to the usual structure of sulfonate surfactants not only makes them immune to high concentrations of monovalent and divalent cations, but also enables them to act as stabilizers of the common surfactants and to displace tertiary oil in brines of high salinity and divalent ion content.

Introduction

The surface active agents employed in surfactant waterflooding processes are usually of the alkylaromatic type and most commonly petroleum sulfonates. They are utilized either alone or in the presence of co-surfactants, such as alcohols. These presence of co-surfactants, such as alcohols. These surfactants, under appropriate conditions, are capable of lowering the oil-water interfacial tension and of mobilizing tertiary oil; their chief drawback is their sensitivity towards saline waters in general and divalent cations in particular.

This paper describes a modification to the structure of common sulfonate surfactants, which involves the insertion of the succinimide moiety (or the analogous succinamic acid) between the hydrophobic alkyl side chain and the hydrophilic aromatic sulfonate group, thus producing a new class of surfactants, the imidosulfonates (Fig. 1). The brine tolerance of imidosulfonates, and in particular their tolerance towards calcium and magnesium ions, is dramatically improved and is about one hundred times higher than that of common sulfonate surfactants Additional features of the imidosulfonates that are described in the paper include their ability to act as stabilizers of other sulfonate surfactants, their lowering of oil-water interfacial tensions to the millidyne region, their adsorptive behavior, and their ability to mobilize tertiary oil in highly saline environments.

EXPERIMENTAL PART

All of the brine solutions that were employed contained sodium, calcium, and magnesium ions as the chlorides. Even though the total salt concentration varied, the relative concentration of the three metallic cations was kept constant at the ratio

Na + : Ca ++ = mg 10:2:1

Interfacial tensions were measured by the sessile drop technique after varying times of phase equilibration. The oil phase was Arabian Medium crude oil and the petroleum sulfonate was Witco's TRS-1080, employed without purification.

Aqueous surfactant concentrations were determined by ultraviolet absorption measurements at 45000 cm-1 and/or 38500 cm-1.

The oil displacement experiments were done in plexiglass columns, having a length of 1 m and an plexiglass columns, having a length of 1 m and an ID of 1.5 cm. They were packed with crushed sandstone (40-325 mesh) and they typically displayed an effective porosity of about 35% and a permeability to brine of about 3 darcies. The procedure involved the following steps:

  • Saturation of the sandpack with brine under vacuum and evaluation of porosity and pore volume.

  • Oil flooding until water production ceased, followed by waterflooding until the end of oil production. This point corresponded to the conclusion production. This point corresponded to the conclusion of a conventional waterflood.

  • Injection of surfactant solution and determination of the efficiency of the recovery of tertiary oil. Flow rates were about 1.5 meters/day so as to approximate usual field conditions. Figure 2 shows a schematic diagram of the experimental set-up.

SURFACTANT PREPARATION AND STRUCTURE

The preparation of the imidosulfonate surfactants is relatively straightforward and the overall process involves essentially two condensation steps. process involves essentially two condensation steps. P. 45

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