Investigating rock properties and fracture propagation pattern during supercritical CO₂ pre-fracturing in conglomerate reservoir

Abstract

Carbon dioxide pre-fracturing has shown high application potential in improving oil recovery in conglomerate reservoirs. However, the influence of CO₂ on the physical properties of reservoir rock and its diffusion behavior within the reservoir matrix have not been systematically studied. This paper integrates CO₂-saturated water soaking experiments, true triaxial fracturing experiments and field-scale tests to demonstrate that CO₂ soaking induces quartz reduction and clay mineral increase, leading to a decrease in porosity and mechanical strength. Clay-cemented conglomerates experience a greater loss in compressive strength and a higher reduction in permeability compared to calcareous-cemented counterparts under identical CO₂ soaking. In the horizontal principal stress direction, CO₂ fracturing achieves a greater fracture penetration depth than slickwater fracturing or CO₂ pre-injection followed by slickwater fracturing. CO₂ pre-fracturing reduces breakdown pressure by 15%-5% and increases fracture complexity. Field tests confirm a reduction in injection pressure and improved effective stimulation. However, dnarrower fracture width and higher tortuosity may limit proppant transportation.Document Type: Original articleCited as: Zhou, H., Yan, T., Trivedi, J., Wang, B., Zhou, F. Investigating rock properties and fracture propagation pattern during supercritical CO₂ pre-fracturing in conglomerate reservoir. Advances in Geo-Energy Research, 2025, 17(2): 95-106. https://doi.org/10.46690/ager.2025.08.0