Abstract: Aiming at the serious channeling during CO₂ flooding and the lack of a mechanical mechanism explanation for channeling formation,by analyzing the energy evolution law of CO₂ channeling fracture network formation in tight sandstone during CO₂ flooding in ultra-low permeability reservoirs,the critical energy law for the simultaneous diversion of both ends of natural fracture-type channeling pathways with accumulated injection energy was studied.Furthermore, an energy criterion for the formation of channeling fracture networks was established.The applicability and accuracy of this criterion were verified by tracer dynamic monitoring results of field CO₂ channeling.The study results show that critical energy is positively correlated with natural fracture size,stress intensity factor,etc.,negatively correlated with elastic modulus, and exhibits a trigonometric function relationship with its own dip angle and wellbore angle;the energy required for channeling fracture network connectivity increases with increasing injection pressure and injection rate;by comparing with tracer monitoring of channeling in two well groups,it was found that this energy criterion is applicable to inter-well distances of about 300 m.This energy criterion can avoid complex fluid-solid coupling calculations at the front of the channeling pathway and compensate for the defect of classical stress criteria in reflecting the effect of action time,providing mechanical mechanism support for CO₂ channeling in ultra-low permeability reservoirs.

Key words: ultra-low permeability reservoir, CO₂ flooding, channeling fracture network, energy criterion