Revealing the effects of thermal properties of supercritical CO2 on proppant migration in supercritical CO2 fracturing

Abstract

In supercritical CO2 (Sc-CO2) fracturing, the temperature variation along the fracture significantly impacts Sc-CO2's density and viscosity. Furthermore, alterations in Sc-CO2's density induce volumetric changes, affecting the flow velocity in fractures. In pursuit of a comprehensive investigation, this study integrates the heat transfer and fluid leak-off models within the Eulerian-Eulerian two-fluid framework. This integration facilitates a systematic exploration of the combined effects of Sc-CO2's thermal properties, including density, viscosity, and density-induced volumetric changes, on proppant migration under different injection temperatures, formation temperatures, and formation pressures. To accurately capture Sc-CO2's thermal properties, its density, viscosity, isobaric heat capacity, and thermal conductivity are all temperature and pressure-dependent. The results showed that the temperature field in the fracture could be classified into four distinct zones, with Zones A and B recognized as primary flow regions, largely impacting the proppant migration process. Furthermore, the outcomes underscored the intricate interplay between Sc-CO2's volumetric expansion or shrinkage and its concurrent density and viscosity alterations. The dominance of either of these effects and the directions of their influence were contingent upon the injection and formation conditions. In aggregate, a longer proppant bed was achieved through elevated formation pressure, increased formation temperature, and reduced injection temperature. These findings enhance the temperature field's comprehension and provide valuable insights for designing and optimizing Sc-CO2 fracturing processes.