Fluid Delivery & Recovery / Well Enhancement
The creation of a sand lens or sheet adjacent to a well effectively increases the area of contact between the well and the earth. A portion of the sand face is considerable distance from the well, so the effective radius of the well also increases. These two phenomena enhance the flow rate out of (or into) the well for a given fluid head. Indeed, hydraulic fracturing was first developed by the petroleum industry to enhance the flow of oil and gas wells (click here for more information about the history of hydraulic fracturing). Research and development work by the US EPA showed that soil vapor extraction wells enhanced with hydraulic fractures discharged at ten fold greater rate than conventional wells in low permeability soil. This project is featured in the EPA SITE report, subsequent guidance documents, and publications.
More recently, the most popular environmental use of hydraulic fractures as flow enhancements has been to deliver nutrient solutions – typically vegetable oil emulsions and the like – on a periodic basis to sustain in situ bioremediation. Both aerobic and anaerobic processes can be maintained in this fashion. Sand-filled hydraulic fractures also have been used to distribute chemical agents such as sodium persulfate or Fentons Reagent throughout target formations.
The distribution of fluid delivered through hydraulic fractures is subject to laws of hydrology. Two subtle effects may have significant impact as discussed in the following additional notes.
First, multiple hydraulic fractures at different elevations often are created at a well location. If all fractures are operated at the same fluid head or flow potential, dead spots of no-flow can develop between adjacent fractures. The remedy is to maintain separate access to each fracture and operate the system strategically. Click here for more information.
Second, if small batches of fluid are delivered to the formation through a fracture, the distribution around the fracture might not be uniform, and substantially more than the pore volume of the fracture may need to be injected to ensure reagent floods the fracture all the way to the tip. Click here for more information.