Fracture propagation and induced strain response during supercritical CO2 jet fracturing

Abstract

To investigate fracture generation and strain variation during SC-CO2 (supercritical carbon dioxide) jet fracturing, the model of induced strain is established and the experiments are comprehensively studied. The influence factors are comprehensively explored, such as jet pressure, ambient pressure, etc. With the increasing jet pressure, the fracture morphology changes from parallel cracks to oblique cracks. Both the mass loss of specimen and CO2 absorption increase significantly, and the growth rate and minimum value of strain also rise exponentially. Under a high ambient pressure of 8.0 MPa, the main fractures mostly propagated from the surface to the bottom surface of the specimen. The maximum strain and the stable duration under higher ambient pressure are 1.5 times and 10 times, respectively, of the case under the ambient pressure of 5.0 MPa. The comparison shows that the optimal jet distance is 5–7 times the nozzle diameter, resulting in massive mass loss, large CO2 absorption, and peak strain. Moreover, the nonlinear variation of strain curve during jet pressurization is related to the type of rock and ambient pressure. These studies clearly show the relationship between the fracture morphology and induced strain, which are crucial for SC-CO2 fracturing in shale gas reservoirs.