Hydraulic-fracture geometry characterization using low-frequency DAS signal

Abstract
Monitoring and diagnosing completion during hydraulic-fracturing operations provides insight into the fracture geometry, interwell frac hits, and connectivity. Conventional monitoring methods (microseismic, pressure gauges, tracers, etc.) can provide a range of information about the stimulated rock volume but may often be limited in detail or clouded by uncertainty. Utilization of distributed acoustic sensing (DAS) as a fracture monitoring tool is growing; however, most of the applications have been limited to acoustic frequency bands of the DAS recorded signal. In this paper, we demonstrate some examples of using the low-frequency band of DAS signal to constrain hydraulic-fracture geometry. DAS data were acquired in both offset horizontal and vertical monitor wells. In horizontal wells, DAS data record formation strain perturbation due to fracture propagation. Events like fracture opening and closing, stress shadow creation and relaxation, ball seat, and plug isolation can be clearly identified. In vertical wells, DAS response agrees well with colocated pressure and temperature gauges, and illuminates the vertical extent of hydraulic fractures. We show that DAS data in the low-frequency band is a powerful attribute to monitor small strain and temperature perturbation in or near the monitor wells. With different fibered monitor well design, we can measure the far-field fracture length, height, width, and density using crosswell DAS observations.