fracturing as a method to stimulate shallow, hard rock oil wells dates back to the 1860s. dynamite or nitroglycerin detonations were used to increase oil and natural gas production from petroleum bearing formations. on 24 april 1865, us civil war veteran col. edward a. l. roberts received a patent for an "exploding torpedo". it was employed in pennsylvania, new york, kentucky, and west virginia using liquid and also, later, solidified nitroglycerin. later still the same method was applied to water and gas wells. stimulation of wells with acid, instead of explosive fluids, was introduced in the 1930s. due to acid etching, fractures would not close completely resulting in further productivity increase.