In spite of the recent oil price declines the shale oil production is recovering at a rapid rate. With it, the amount of water used in hydraulic fracturing grows as well, including the water used both at the front end of this process, in fracking liquid, and at the back end, the flowback and produced water. The front-end water has to meet specific environmental standards before it can be pumped into the well, especially with regard to microorganism and mineral contents. Similarly, flowback and produced water must meet certain standards before it can be re-used or discarded. Additionally, fouling caused by high mineral content in water shortens the life of pumps and heat exchanges used in oil and gas production and increases capital and maintenance costs. As a result, water purification requirements increase the cost of oil and natural gas production, thus creating an increasing need for more cost-effective methods water disinfection and demineralization.

To address this need, Drexel engineers have developed a new system and method for fracking and produced water treatment using a combination of high-voltage high-current plasma spark discharge and electric field oscillating at radio frequencies (RF). Spark discharges with short pulse duration (10-100 ns) are to generate highly localized, focal regions of heat (stochastic heating) and other active species such as OH-, O2-, O3, H2O2, UV light and electric fields. The UV and other reactive species generated by the spark discharge kill or neutralize microorganisms in water, whereas the stochastic heating dissociates bicarbonate ions, which are essential building blocks of mineral fouling and scale.  Superimposing the RF electric field provides additional heating to the bicarbonate ions for more efficient dissociation and anti-fouling effect.  In order to further stimulate the RF heating of water, a scaffold or grid structure is positioned in the water between the two electrodes used for RF electric field generation.  This grid structure can be constructed of a polymer lattice with higher conductivity material at grid intersections such as metal beads. As a result of the synergistic effect of the spark discharge and RF electric field, both disinfection and water softening in the form of mineral fouling prevention are achieved.

This method of water treatment does not require addition of chemicals traditionally used for disinfecting and softening water, which, in addition to cost savings, makes it a clean technology. This is also an energy-efficient method for both disinfection and water softening: the spark discharge can be produced at an energy consumption rate of 100 J/L and RF electric field can also be generated at less than 100 J/L.