Mechanism and development of CO2 pre–pad fracturing stimulation for tight conglomerate low–permeability condensate gas reservoirs

Tight conglomerate condensate gas reservoirs in the Permian Jiamuhe Formation respond poorly to conventional hydraulic fracturing because of low permeability, clay sensitivity and water blocking. Although CO 2 pre-pad fracturing has been reported to mitigate these issues, the magnitudes of its physical, chemical and carrier-fluid contributions have not been quantitatively separated. We therefore developed a mechanism-partitioning workflow that couples a dedicated pure-CO 2 true-triaxial baseline with paired mortar–outcrop testing and an EDFM surrogate. A four-hydroxyl CO 2 -responsive viscoelastic surfactant (S-4; 3 wt%, 60,000 mg/L brine) was developed as the carrier fluid; it retained 68 mPa·s at 70 °C, broke within 1 h and caused post-break permeability damage within SY/T 7627 limits. In true-triaxial tests ( n = 3 per scheme), the pre-pad scheme lowered breakdown pressure by 36.0% relative to hydraulic fracturing, of which 26.8 pp arise from CO 2 physical effects and 9.2 pp from VES viscosification plus temporal pre-conditioning; outcrop validation on Jiamuhe glutenite further isolated a 4.4 pp chemical-weakening contribution (bootstrap 95% CI 2.6–6.3 pp). The pre-pad scheme was also the only mode to raise fracture complexity ( D f = 2.31 vs. 2.14 for hydraulic, p = 0.002). An XGBoost–MOPSO surrogate (held-out R2 = 0.93) identified an operational window of CO 2 volume 200–300 m 3 /stage, injection rate ~ 8 m 3 /min and cluster spacing 15–20 m, projected to deliver a 16.8% SRV gain over un-optimised pre-pad parameters.