Pilot Test Evaluation of High-Pressure Jet Injection for In situ Remediation of Low-Permeability Zones

In situ remediation of chlorinated solvents in clay till and saprolite is challenging because low-permeability constrains reagent delivery, and solvent diffusion into the matrix substantially limits the rate of treatment. Pneumatic and hydraulic fracturing can enhance delivery of treatment agents; however, their radius of influence (ROI) is limited and primarily controlled by the natural fracture networks. Here we present the results of two pilot studies using jet injection, a novel 10,000 psi hydraulic fracturing method to create large hydraulic fractures in in clay till and saprolite. Pilot test results showed greater  ROI than conventional fracturing methods, the potential to bypass natural fractures, and feasibility of implementation on a rapid and flexible drilling platform.

A pilot test was completed using jet injection to deliver zero-valent iron from two wells into clay till at a test site in Taastrup, Denmark. The resulting fracture network was mapped by excavating the 18m x 24m x 8m test plot. The injection achieved an ROI of 6 to 7m, farther than previous hydraulic fracturing in similar clay tills. However, the loss of kinetic energy caused by jetting through the well casing and surrounding grout resulted in short circuiting into the natural fracture system rather than creation of new fractures. To improve performance, a second pilot test combining direct push technology (DPT) and jet injection was implemented in South Carolina saprolite. Customized tooling was fabricated for DPT rods that distributed all of the kinetic energy of the water jet into the formation. The DPT injection of water and dye at 10,000 psi resulted in the formation of fracture cavities up to 2.1 m long and 90 cm wide. The innovative combination of DPT and jet injection provides a flexible, rapid, and promising method to achieve a large injection ROI that bypasses natural fractures in low-permeability zones.