A 3D coupled numerical simulation of energised fracturing with CO2: Impact of CO2 phase on fracturing process

Feng Xiao, Saeed Salimzadeh, Qian Bing Zhang

Research output: Contribution to journalArticleResearchpeer-review

Abstract

Engineered fractures play a critical role in enhancing energy extraction efficiency. In this study, energised fracturing with CO2, as an alternative approach to conventional water-based hydraulic fracturing, is investigated via numerical simulations. We validated the CO2 finite element-based fracturing model against analytical as well as CO2-fracturing laboratory experiments, then utilised the model to investigate the effects of pressure-temperature dependent properties of CO2 on energised fracturing process. To account for the temperatures expected in a real field, four cases with injection temperatures of CO2 varying between 250 K and 350K, under both isothermal and adiabatic conditions have been considered. In the adiabatic conditions, the temperature variation during compression of CO2 is captured using the Joule-Thompson coefficient, assuming no thermal exchange between the CO2 and the surrounding medium. The results highlight the significant influence of CO2 phase on the fracturing process, during the pressurisation stage, as well as post-breakdown, the speed of fracture growth after the breakdown and subsequent depressurisation and associated cooling of CO2. In the designed cases, the phase-change from gas to liquid or supercritical occurs during the pressurisation and prior to breakdown, while the phase remains unchanged post breakdown and during fracture propagation. Liquid CO2 presents a fast-pressurising process while gaseous CO2 undergoes a lengthy compression stage. Supercritical CO2 is the best performing as the pressurisation is not too lengthy, while the instantaneous post breakdown fracturing is significant. Results show that higher temperature of supercritical CO2 is causing larger instantaneous fracture propagation as it has lower viscosity for the given in situ stresses (>10 MPa).

Original languageEnglish
Article number105863
Number of pages12
JournalInternational Journal of Rock Mechanics and Mining Sciences
Volume182
DOIs
Publication statusPublished - Oct 2024

Keywords

  • CO energised fracturing
  • Phase transition
  • Supercritical CO
  • Thermo-hydro-mechanical coupled simulation
  • Thermodynamic properties of CO

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