Gas Driven Fracturing of Deformable Porous Media

Abstract:

Flows in fractured and deformable media are difficult to characterize and predict, and this is especially so for multiphase flows where interactions at interfaces between gas, liquid and granular phases contribute to the fluid dynamics. Here we study gas driven (pneumatic) fracturing of a wet unconsolidated granular packing confined in a Hele-Shaw cell, and present an in-depth analysis of both pore-scale phenomena and large scale pattern formation. The fracture growth process is governed by a complex interplay between pressure, capillary, frictional and viscous forces. Fractures are observed to grow in an intermittent, stick slip fashion, punctuated by stationary periods. Growth is impeded by friction from local compaction fronts forming around the growing fracture branches, and new fractures are triggered by initial pore invasion followed by fluidization of the compaction front. We study the influence of granular properties (size/shape) as well as gas injection rate, and find that the system undergoes a series of transitions in terms of observed dynamics and pattern formation. We propose simple mathematical models that predict fracture density from basic properties of the deformable granular packing, and also a transition from fracturing to fluidization and viscous fingering beyond a critical injection rate.