The Utility of CO2 as an Energizing Component for Fracturing Fluids

Abstract

Summary: The use of CO2 as an energizer in hydraulic fracturing fluids has increased dramatically in the past few years. The history of CO2 usage for this application is discussed briefly, and CO2 is compared with the other commonly used energizer, N2. The design considerations for using CO2 in a fracturing treatment, both as a minor (energizer) and a major (foam) component, are presented. Special consideration is devoted to CO2 foam because CO2 is pumped as a compressible liquid that changes to a gas downhole. This paper presents the calculations required to estimate the surface liquid CO2 volumes and injection rates needed to obtain the desired downhole foam properties. Also, the instrumentation required to meter the liquid CO2 safely and accurately is discussed. Field results further evidence CO2's utility in hydraulic fracturing. This discussion includes a comparison of fracture stimulation with and without CO2 as an energizer as well as treatments that compare CO2 -energized fluids with N2-energized fluids. Economic considerations of pumping CO2 vs. N2 vs. no energizer are discussed. Conclusions suggest what further study is required to help improve design techniques and when CO2 should be considered as a component of a fracture stimulation treatment.