Ultrasonic Detection of Fracture Propagation and Complexity in Hydraulic Fracturing Experiments
Hydraulic fracturing is a proven method used to enable the recovery of hydrocarbons from tight reservoirs and source-rock plays. More complex fractures have larger surface areas, which is thought to help maximize recovery. However, measuring the degree of complexity and interconnectedness of fractures is a challenging problem, even with microseismic data. Here, we use laboratory-scale hydraulic fracturing experiments in conjunction with active and passive source compressional waves to evaluate how seismic waveform responses can be used to better constrain fracture development. Piezoelectric transducers were used to send waveforms through a confined, isotropic acrylic block as it fractured within a biaxial testing apparatus. Acoustic emissions were passively recorded during the fracturing process in certain experiments. Fracking fluids are delivered to the sample at a constant stress rate in all cases. Initial results show that detection of propagating fracture fronts is possible by analyzing the relative attenuation differences in active compressional wave amplitudes as a function of time. Further experiments test whether there is an observable difference in attenuation values based upon the compositions of fracking fluids or gasses used, and how variable compositions influence the complexity of the resultant fracture surface. In order to apply these methods at the field scale, deconvolving multiple seismic signals would be necessary to back out attenuation changes. Our experimental results suggest that fracture development can be observed by analyzing the relative attenuation changes in compressional waveforms.
AAPG Datapages/Search and Discovery Article #90335 © 2018 AAPG 47th Annual AAPG-SPE Eastern Section Joint Meeting, Pittsburgh, Pennsylvania, October 7-11, 2018