How so? Sounds logical to me. It costs a lot more to extract oil from shale than to just drill a hole. If the selling cost of a barrel drops below the production cost....then it makes sense there will be less drilling. Operating at a loss is not real good business sense.
That ignores the shale plays for natural gas, which also produces propane, benzene, pentane, ethane, etc along with ... some oil. The EPA actions forcing some coal fired power plants to close will increase the demand for natural gas.