Simulation of Supercritical Carbon Dioxide Fracturing in Shale Gas Reservoir

In order to fracture shale gas reservoir with carbon dioxide as the working fluid, laboratory experiments were firstly conducted to measure the influence of carbon dioxide immersion on shale rock's properties, and then the coupling mechanism between stress and seepage during hydraulic fracturing was simulated based on cohesive zone model. The fracturing ability of carbon dioxide and water was also compared under the same working conditions, and finally sensitivity analysis (including elastic modulus of shale, filtration coefficient, pump rate and viscosity of carbon dioxide) were conducted based on field application. The results show that, the elastic modulus of shale increased by 32.2%, the Poisson's ratio decreased by 40.3% and the compressive strength decreases by 22.9% after geothermal reaction with carbon dioxide under 30 MPa and 335.15 K for 2 hours. Compared with water fracturing, carbon dioxide fracturing induces longer fracture (increased by 25.3%) and narrower fracture (decreased to 40.8%). The fracture tends to get longer and narrower with increasing elastic modulus of shale. As filtration coefficient increases, the maximum width of fracture decreases significantly, whereas the length changes little. Both the length and maximum width of fracture increase with increasing pump rate, however the changing rate of length tends to decrease. The influence of viscosity of carbon dioxide on both fracture width and length is negligible, which validates the stable feasibility of carbon dioxide fracturing in different formation conditions.

Automated summary

Laboratory experiments were conducted to measure the influence of carbon dioxide immersion on shale rock's properties, and the coupling mechanism between stress and seepage during hydraulic fracturing was simulated based on cohesive zone model. The results showed that the elastic modulus of shale increased, Poisson's ratio decreased, and compressive strength decreased after geothermal reaction with carbon dioxide. Compared with water fracturing, carbon dioxide fracturing induces longer and narrower fractures. The influence of viscosity of carbon dioxide on fracture width and length is negligible, validating the stable feasibility of carbon dioxide fracturing.