Hydraulic Crack Growth Dynamics from Ultrasound Transmission Monitoring in Laboratory Experiments

• Published in: Izvestiya. Physics of the solid earth 2021-09, Vol.57 (5), p.671-685
• Main Authors: Turuntaev, S. B., Zenchenko, E. V., Zenchenko, P. E., Trimonova, M. A., Baryshnikov, N. A., Novikova, E. V.
• Format: Article
• Language: English
• Subjects: Compressive properties; Crack initiation; Crack propagation; Earth and Environmental Science; Earth Sciences; Fracture mechanics; Geophysics/Geodesy; Gypsum; Hydraulic fracturing; Hydraulics; Injection; Laboratories; Laboratory experiments; Pressure; Sound transmission; Stresses; Vertical loads; Viscous fluids
• ISSN: 1069-3513; 1555-6506
• DOI: 10.1134/S1069351321050207

—Acoustic transmission data obtained in the laboratory experiment are used to identify stages of hydraulic fracture initiation, growth, and filling with a fracturing fluid. The laboratory setup allows for performing experiments with porous saturated samples made of artificial materials, with a diameter of 430 mm and height 70 mm. The model material was a mixture of gypsum and cement; the sample was saturated with water solution of gypsum and loaded by vertical and two independent horizontal stresses. Fracture was created by constant-rate injection of a viscous fluid through a cased hole in the center of the sample. Hydraulic fracture (HF) was monitored using ultrasonic pulses transmitted through the sample. The comparison of amplitude variations of ultrasonic pulses and injection pressure indicates that HF crack propagation initiates at lower pressure than maximum; HF crack grows faster than is filled with a fluid; after the crack volume is filled up with a fluid, fracture aperture expands. Once the injection stops, the crack closes when pressure in the wellbore decreases due to fluid leakage into the sample. It is shown that if the principal compressive stresses reorient, a secondary hydraulic fracture can appear provided that the primary fracture is perpendicular and secondary parallel to the well axis.