Controlled Hydraulic Fracturing
While hydraulic fracturing was initially used in the petroleum industry for increasing recovery of oil from tight formations, the technology expanded in the 1980’s to the environmental industry to enhance contaminant recovery. Almost four decades later, hydraulic fracturing has been used in a combination with a variety of scenarios:
- Enhancement of existing recovery systems, i.e., dual phase, SVE, pump & treat, etc.
- Addition of higher volumes of remedial amendments due to increased porosity and/or conductivity
- Potable water well enhancement
- Increasing efficiency of thermal systems
- Extraction of product recovery in tight formations
- Emplacement of passive treatment systems
GeoSierra Environmental employs the vertical hydraulic fracturing method (also known as vertical inclusion propagation or VIP) for both single and multi-azimuth installations in addition to horizontal fracture emplacement. Below is a description of each method.
Single-azimuth VIP “IS” the Trenchless PRB method. Instead of iron filings, sand or ceramic beads are injected creating a continuous conductive zone or PRTZ – Permeable Reactive Treatment Zone. The PRTZ is then used for injection of remedial amendments: ISCO, ISCR, bioaugmentation, etc., either by new injection wells installed within the PRTZ or via GeoSierra Environmental’s specialized casings, which can be reused for injections. Either way the objective of the design is a means for homogenous and continuous treatment which may be in a mid-plume location, as a cutoff treatment barrier, or for upgradient nitrate reduction prior to a downgradient PRB. The design considerations are endless.
Adapted from the single azimuth PRB installation technology, GeoSierra Environmental has commercialized a state-of-the-art multi-azimuth vertical inclusion propagation process. Originally tested as an oil field well enhancement technology, the multi-azimuth approach has been modified and adapted to allow installation in a variety of lithologic environments for source area remediation, as well as permeability enhancement for existing injection/extraction and potable water supply wells.
Primarily used for injection of coarse, high permeability sand, ceramic beads or other permeability enhancing materials like iron filings, injection field tests of a 6-wing configuration resulted in a 100x increase in permeability during enhancement of source area extraction wells. The multi-azimuth technology utilizes a similar vertical inclusion propagation technology to control injections in 4, 6 or 8 wing configurations. GeoSierra Environmental has implemented the multi-azimuth VIP technology for enhancement of extraction wells, injection of iron filings in a source area, and for immediate and future injections for bioremediation.
Horizontal Inclusion Propagation
GeoSierra Environmental uses the horizontal fracturing method to emplace proppants such as sands or ceramic beads or even oxidants when thin clay lenses exist, interception of vertical pathways or a greater lateral distribution is required, or treatment is required under a building. Temporary injection wells are typically installed using direct push technology and fractures are completed from the bottom up, depending on the project objectives and lithology. A horizontal notch is cut at the initiation depth followed by the injection of the highly viscous cross linked guar gum gel. An enzyme is added to the gel prior to injection so the gel’s starches biodegrade to sugars and water within a couple hours. Vertical spacing is typically two feet, and lateral inclusions may extend upwards of 50 feet in diameter.
GeoSierra Environmental pioneered the use of horizontal hydraulic fracturing to enhance soil vapor extraction (SVE) systems as tight soils are not amenable to conventional SVE due to their low permeability. Installing horizontal sand filled fractures in these soils significantly increases the soil mass permeability and greatly enhances the radius of influence of the SVE extraction wells. Fracture enhanced SVE significantly reduces the cost and time to remediate tight soil formations.
GeoSierra Environmental has completed numerous fracture enhanced SVE projects at sites throughout North America. Many of the projects are operating chemical or manufacturing facilities requiring horizontal fractures to be installed beneath and around existing buildings and utilities. The buildings are monitored by a high precision biaxial tilt meter and the fracture geometry is recorded during injection by the active resistivity method.
The fracture enhanced SVE system typically consists of a high vacuum, high flow system to maximize removal of contaminants. A high vacuum stress toward the fractures is applied to permeable contaminants in the soil. Such a system typically results in planned levels of soil remediation within 1 to 2 years.