Time-Lapse Ultrasonic Measurements of Laboratory Hydraulic-Fracture Growth: Tip Behavior and Width Profile

Abstract

Summary We performed acoustic measurements in a time-lapse sequence in scaled laboratory tests. The advantage of time-lapse measurements is that the fracture response can be separated from the background signal. As a consequence, not only can the hydraulic fracture be detected, but its shape and geometry can be measured during its growth. This application requires the combined information of both compressional- and shear-wave measurements. We apply this technique to propagation, flowback tests, and reopening of hydraulic fractures. Acoustic waves excite diffractions at the fracture tip. These diffractions are used to locate and to characterize the fracture tip. The acoustic measurements indicate that we can distinguish between a dry tip and the fluid front of the fracture. Shadowing of shear-wave transmissions allows estimation of the moment of fracture initiation. The width profile of the fracture is determined with compressional-transmission measurements. This application is based on the fact that the attenuation and time delay of compressional transmissions are proportional to the fracture width. Analysis of a flowback test shows that the fracture closed at the wellbore but remained open farther away from the wellbore.