Analysis of flow process of CO2 in wellbore and prediction of fracture initiation pressure during SC-CO2 fracturing

Abstract

Numerical simulation of the behavior of supercritical CO₂ during the entire fracturing operations is performed to investigate the pressurization features and flow characteristics before and after rock breakdown. To achieve these goals, a numerical model coupling fluid convective heat transfer and conduction heat from the formation is developed. Results indicate that the accumulation of CO₂ density can slow the growth of frictional pressure drop to promote pressurization, and that a higher injection temperature is not conducive to pressurization. After the rock breakdown, the injection temperature is above 263.15 K, and the CO₂ at the bottomhole can maintain a supercritical phase. The change of bottomhole pressure has no significant effect on the variation of CO₂ temperature. A higher bottomhole temperature can elevate the rock fracture initiation pressure, and in-situ stress difference σ_H/σ_h increases from 1 to 3, with a 93 % decrease in initiation pressure due to increased temperature.