Enhancing hydraulic fracturing for in-situ remediation in low-permeability soils: A comprehensive investigation of fracture propagation

Abstract

Enhancing the complexity of the hydraulic fractures to provide a wide channel for the injection of the agent is crucial for remediating low-permeability contaminated sites. This study involved a physical simulation experiment of large-scale true triaxial hydraulic fracturing in undisturbed soil, as well as field fracturing tests, to investigate fracture initiation mechanisms and the influence of different factors on fracture propagation. The study revealed a unique failure mode for low-permeability soils characterized by impact splitting, involving simultaneous tensile and shear failure. Three typical fracture propagation patterns emerged: (1) horizontal fracture, (2) parallel fracture, and (3) complex fracture. Silty clay predominantly exhibited horizontal fractures, while mucky clay facilitated the formation of complex fractures dominated by multiple transverse fractures. As the vertical stress difference coefficient increased from 1.0 to 1.5, the pressure on the fracture surface enhanced the connection between hydraulic fractures and natural fractures. Hydraulic fracturing in low-permeability soils necessitated large displacements and high-viscosity fracturing fluids to sustain fracture propagation. The field fracturing test results underscored that soil type and in-situ stress were the primary factors governing hydraulic fracture initiation and propagation. Identifying the optimal fracturing location was critical for achieving the maximum stimulated formation volume (SFV).

Potassium permanganate oxidation of low-permeability phenanthrene contaminated soil under fracturing conditions

“…Laboratory experimental studies that can realistically consider initial conditions such as the water content and stress state of low-permeability contaminated soils and provide guidance parameters such as oxidant concentration and total oxidant demand (TOD) for remediation sites under fracking conditions are still scarce. Previous studies have shown that hydraulic fracturing can create horizontal fractures, which may appear as flat-lying circular disks filled with coarse-grained proppant in the field [31,32,35]. These disks can be reduced to circular fracture layers with a certain thickness and high permeability; thus, the oxidant transport between two parallel fracture layers can be considered a one-dimensional transport.…”