Molecular Size Studies of Degraded Fracturing Fluid Polymers

Abstract

ABSTRACT Effective degradation of fracturing fluid polymers is necessary to minimize fracture and formation damage to allow rapid fluid return and economic production of gas (and/or oil). In this study, size exclusion chromatography (SEC) was used to investigate degradation of water-soluble polymers, such as modified guar and cellulose polymers. SEC was used to monitor the decrease in molecular size of the polymer degradation products using oxidant breakers in the temperature range 343 K to 370 K (158°F to 205°F). SEC, however, was capable of monitoring the effects of polymer type and concentration, breaker type and concentration, break time and temperature. The SEC results were then correlated with solution fluid loss characteristics and residue production to define the molecular size reduction needed to minimize damage to a propped fracture. Results were compared to sandpack damage studies reported in the literature. Greater insoluble residue production required greater molecular weight reduction to minimize damage. SEC results were also correlated with solution viscosity. Measured viscosities depended on polymer concentration and degree of polymer degradation. Low solution viscosity did not guarantee reduction of polymer molecules to a non-damaging size. SEC analysis should also be useful for evaluating new or improved breaker and polymer systems. Presently available breaker systems (in the temperature range of this study) did not provide both high initial solution viscosity and efficient molecular size reduction to minimize damage.