Abstract
We combine active and passive acoustic measurements to improve the spatio-temporal imaging of hydraulic fracture growth performed under true triaxial confinement in the laboratory. 64 active piezo-electric transducers (54 P waves, 10 S waves) work in source (32) - receivers (32) mode to perform an acoustic survey at repetitive intervals (every 10 seconds) during a hydraulic fracture growth experiment. The analysis of the evolution of the active acoustic monitoring changes allow to image the evolution of the fracture front (via an inversion of the active acoustic waves diffracted by the fracture front). An additional 16 piezoelectric transducers are pre-amplified and work in passive mode continuously recording at 10MHz. We present a nearly-automatic passive signal processing, acoustic emission detection, and location algorithm. This allows to record, detect and to locate acoustic emissions associated with fracture initiation and growth in between the active acoustic measurement sequences. Using a hydraulic fracturing test performed in gabbro, we discuss how active and passive acoustic monitoring complements one another and bring different type of information on hydraulic fracture growth.
Highlights
Hydraulic fractures are a class of tensile fractures that propagate in a material as a result of fluid pressurization
We combine active and passive acoustic measurements to improve the spatiotemporal imaging of hydraulic fracture growth performed under true triaxial confinement in the laboratory. 64 active piezo-electric transducers (54 P waves, 10 S waves) work in source (32) - receivers (32) mode to perform an acoustic survey at repetitive intervals during a hydraulic fracture growth experiment
Active acoustic imaging is based on a 4D seismic survey at the laboratory scale in the ultrasonic range: an acoustic survey is repeated at regular intervals during the experiment
Summary
Hydraulic fractures are a class of tensile fractures that propagate in a material as a result of fluid pressurization. AE observations do not provide the entire story behind a hydraulic fracturing treatment and are limited to energies released in a specified frequenc rangey, they provide significant numbers of located events which help in imaging the fracture zone and understanding mechanisms of their source ruptures They are one of the most used markers to estimate the fracture initiation phase ([20, 21, 22]). For all source-receiver pairs, the recorded signal at given time during the experiment is subtracted from the one of an initial survey recorded at the beginning of the experiment prior to fracture initiation The evolution of these active acoustic changes for each source-receiver pair are sorted with respect to their acquisition times, and the evolution of the arrival time of the diffracted wave by the fracture are manually picked (see Figure 2b). Than for the active sensors, each passive sensor is pushed to the specimen by a spring set behind
Sign-in/Register to view highlights & summary 
Published Version (
Free)
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call