“In electromagnetism, absolute permittivity is the measure of the resistance that is encountered when forming an electric field in a medium.” (Wikipedia)
Permittivity describes the degree to which electromagnetic waves (e.g. microwaves) are absorbed by a material. Shales, sandstones, marlstones, and many other type of rocks have a very low permittivity, meaning that microwaves can travel through them without losing much energy. If these rocks contain water and hydrocarbon compounds such as kerogen, the permittivity increases, microwave energy is absorbed which results in an increase in temperature and liquification or pyrolysis of the hydrocarbons.
Because water is present in the rock, microwave energy rapidly heats the water causing the rock to fracture. Once the hydrocarbons are heated to sufficient temperatures, these fractures provide a pathway for the liquid or gas hydrocarbons to flow toward the collection wells.
After the water and hydrocarbons have been removed from the rock, the permittivity decreases allowing the microwave power to penetrate deeper into the rock. This process produces a migrating phase boundary that removes 99 plus percent of the hydrocarbons.
