Successful Field Application of High-Temperature Rheology of CO2 Foam Fracturing Fluids

Abstract

ABSTRACT High temperature rheology of carbon dioxide foam fracturing fluids has been developed in the laboratory and successfully applied to improve the design of foam fracturing treatments of tight gas sands. In the laboratory phase of the project, carbon dioxide foam properties were measured to 250°F (121°C) in a high temperature, high pressure pipe viscometer. The effects of foamer type and concentration on high temperature carbon dioxide foam rheology were determined. It was found that, above a certain level, further increases in foamer concentration provide little corresponding increase in foam stability or rheology. Carbon dioxide foam stability can be improved by the use of higher concentrations of gelling agent. Test data indicates that higher concentrations of foamer and gellant are required to produce stable carbon dioxide foams, as compared to nitrogen foams. It was found that rheological data generated for nitrogen foams will not be sufficient to describe the same system when pumped as a carbon dioxide foam, as had been previously assumed. Historically, foam fracturing design and fluid composition (gellant and foamer) have been based on rules of thumb and common area practice. The laboratory generated foam rheology and stability data were used to modify fracturing design and fluid composition. These design changes have resulted in more successful carbon dioxide foam stimulation treatments and have drastically reduced screen-outs. Examples of successful treatments utilizing the new design data will be compared and contrasted with historic treatments in several tight gas sands.