Chemical Stability of Polyacrylamide Polymers

Abstract

Summary A comprehensive study of the chemical stability of polyacrylamide (PAA) polymers was conducted. The primary emphasis of the study was to determine the stability of Dow Pusher TM 500 PAA in Sundance brine a 115 deg. 17 (46 deg. C). Experiments were completed which show the effect of biocides, metals, ferrous and ferric iron salts, pH, surfactants, alcohols, antioxidants, sodium hydrosulfite, thiourea, plastic pipe, formaldehyde concentration, free radical scavengers, hydrazine, oxygen, and temperature on the chemical stability of PAA. Stability tests were conducted at temperatures ranging from room temperature to 221 deg. F (105 deg. C). The results showed that many substances caused substantial chemical degradation of PAA polymers in the presence of oxygen; however, in many cases, the adverse effects of these substances could be reduced or eliminated by the proper selection of chemical stabilizers or the nearly complete removal of oxygen from the solutions. Introduction During the mid-1970's, Conoco Inc. completed a successful tertiary recovery pilot flood in the Second Wall Creek sand of the Big Muddy field, located near Glenrock, WY. A sodium sulfonate surfactant was used to lower the interfacial tension between the crude oil and the reservoir brine, while a polysaccharide polymer was used to reduce the mobility of the injected fluids.An expanded pilot project consisting of nine 10-acre five-spots is scheduled for the 1980's, and a joint contract between Conoco Inc. and the U.S. DOE has been consummated. 2 This project will require about 2.6 million lbm (1.18 x 10 kg) of polymer and, although a polysaccharide was used successfully in the previous Big Muddy pilot project, the price differential between polysaccharide [$2.50/lbm ($2.50/0.45 kg)] and PAA polymers [$1.50/lbm ($1.50/0.45 kg)] was sufficient to warrant a substantial laboratory effort to determine if the cheaper PAA polymers could be used in the low permeability reservoir at Big Muddy. Therefore, it was a major objective of this study to determine the long-range chemical stability of PAA polymers, as well as to determine the effect of selected additives and solution variables on the stability of PAA polymers.The stabilizing effect of formaldehyde on PAA polymers was reported by Knight; however, the maximum temperature used was 140 deg. F (60 deg. C), while the heating time usually did not exceed 50 days and in no case exceeded 320 days.Additional PAA stability experiments were conducted by Foshee et al., who reported the stability of PAA polymers in the presence of sodium hydrosulfite, formaldehyde, and selected metals. While the results of this study were informative and interesting, the temperatures [122 deg. F (50 deg. C)] were not high enough nor the time (30 days) long enough to address satisfactorily the problem of long-term stability of PAA polymers.In our study, some solutions have been held at 115 deg. F (46 deg. C) for more than I year. However, these experiments should continue for many years and, in addition, several solutions are being aged at 187 deg. F (86 deg. C) and 221 deg. F (105 deg. C). Studies also have been completed which show the effect of pH, metals, biocides, surfactants, alcohols, thiourea, antioxidants, oxygen scavengers, and other additives on the chemical stability of PAA polymers. Dow Pusher 500 PAA polymer was used exclusively in the experiments described in this paper and for convenience is called P-500. JPT P. 1513^