The Effect of Sulfonate/Polymer Interaction on Mobility Buffer Design

Abstract

A study was made of the movement of 1-PV slugs of polymer solutions in cores that had been treated previously with sulfonate and then flushed with previously with sulfonate and then flushed with brine. The data revealed premature polymer breakthrough. These results were attributed to low polymer retention and an inaccessible pore volume polymer retention and an inaccessible pore volume to polymer flow. The shapes and absolute values of the polymer breakthrough curves depended on the type of polymer and sulfonate used. When no brine flush followed the sulfonate solution, an even earlier polymer breakthrough was observed. This phenomenon was thought to be related mainly to a phenomenon was thought to be related mainly to a polymer/sulfonate interaction. polymer/sulfonate interaction. Solutions of 10 chemically different polymers were blended with solutions of four sulfonates. After standing, these mixtures separated into two layers - a top layer highly concentrated in polymer and a bottom layer containing a higher sulfonate concentration. Viscosities, fractional volumes, and interfacial tensions to oil of the separated layers depended on the particular polymer/sulfonate system. These layers were found to be separate phases with a measurable, but very low, interfacial phases with a measurable, but very low, interfacial tension at the phase boundary. The effect of salinity and polymer concentration on phase separation also was studied. Phase separation of polymer/sulfonate systems also occurred in Berea core flow tests, resulting in differing mobilities of the separated phases. This phenomenon can result in a low recovery efficiency in low-tension surfactant flooding. An improvement in tertiary oil recovery efficiency was achieved, however by using low salinity in the mobility bank. Introduction This study discusses low-tension oil displacement, wherein an aqueous surfactant slug is driven by a polymer solution. Many papers have dealt with such systems, particularly as they relate to tertiary oil recovery; however, little attention has been devoted to polymer behavior in the polymer/sulfonate mixing zone. Recently, Trushenski et al. reported that high mobility had developed in the polymer/sulfonate mixing zone. The mechanism for this phenomenon was not proposed. They also showed that because of polymer/sulfonate incompatibility, phase separation can occur, which can lead to excessive sulfonate retention through "phase entrapment." This study investigates this phase-separation phenomenon and its effect on flow behavior in the phenomenon and its effect on flow behavior in the polymer/sulfonate mixing zone. polymer/sulfonate mixing zone. POLYMER INJECTION INTO POLYMER INJECTION INTO SULFONATE-TREATED BEREA CORES PROCEDURE PROCEDURE In one set of experiments, two sulfonate solutions [Witco TRS-18/40, (1/1) and Amoco H-4344-1 Tm] were injected into separate Berea cores. Concentrations were 2 wt % (0.02 kg/kg) in 2%. NaCl brine, volume was 2 PV, and the injection rate was 14 ft/D (4.27 m/d). Thereafter, 3 PV of 2% NaCl brine was injected at the same rate. This was followed by 1 PV of 600-ppm polymer solution in 2% NaCl brine, then by 2% NaCl brine. During the last two cycles, the injection rate was 4 ft/D (1.22 m/d). During both polymer injection and the subsequent brine flush, the inlet pressure was recorded and effluent samples were taken to analyze polymer concentration. Polymer concentrations were determined by radioactivity in the case of C14-tagged polymers (Polymers 454 and 340 trade mark) and by the viscosity measurement technique when Kelzan MF (trade mark) was used. In the second set of experiments, a polymer solution directly followed the sulfonate solution. Injection rates were the same as in the first set of experiments. Both sets of experiments used Berea cores, 5.08 cm in diameter and 14.2 cm in length. Each polymer solution was filtered through a separate Berea core disk with about 500 md permeability and with diameter and length of 5.08 and 1.4 cm, respectively. SPEJ P. 4