A High-Pyruvate Xanthan for EOR

Abstract

Abstract High-pyruvate xanthan (HP xanthan) is produced by a proprietary strain of the Xanthomonas campestris organism and is available in the form of a 3 to 5 % broth or a 12 to 15% concentrate. The liquid product is supplied commercially (FLOCON 4800 or 4800C™ from Pfizer Inc.) for use as a mobility control and permeability reduction agent for micellar, water-thickened, and waterflood diversion projects. This paper deals with use of the product for mobility control. The biopolymer is similar in structure to other commercial xanthans but contains a significantly higher level of ketal-bound pyruvic acid. Assay methods, including those applicable to field waters, are discussed. While dilute HP xanthan exhibits viscosity/concentration profiles and pH sensitivities that are similar to other xanthans, it has superior tolerance to high levels of salinity and hardness. Injectivity, as measured by Millipore™ filtration, is not adversely affected by high levels of monovalent cations and magnesium ion. The presence of ferric ion produces severe filterability deterioration, while problems with calcium and ferrous ions are less serious. Good filterability in the presence of iron or hardness cations is restored by use of certain chelating agents and surfactants. Sequential filtrations of HP xanthan and other xanthans have been carried out with various-size Millipore membranes. On this basis, the effective size of the HP-xanthan molecule was shown to be no larger than 0.2 µm. Compatibilities of HP xanthan with biocides, oxygen scavengers, and surfactants are discussed, as is information demonstrating control of microbiological problems and field propagation of the biopolymer.