Generation of oil in rocks by shearing pressures; II, Effect of shearing pressures on oil shales and oil-bearing rocks

This paper, the second of a series on the generation of oil in rocks by shearing pressures, gives details regarding experiments performed with oil shales from Colorado, Australia, Kentucky, and Cleveland, Ohio. The shales were subjected to high shearing pressures of varying intensity and under different conditions, so that they yielded by either fracture or flow. Nearly all the tests were conducted at room temperature. In no case was any oil generated, and the shearing appears to have had little effect on the solubility of the organic matter. One effect noticed is the occurrence of more volatile matter in extracts from sheared shales than in extracts from shales not sheared. This, however, is explained by oxidation and is not applied to natural occurrences. Other experiments include the shearing of Colorado oil shale with various catalysts present and of a California shale containing oil. By the latter it is demonstrated that high shearing pressures will squeeze out practically no oil from a highly saturated shale. A general conclusion, based on the experiments, is that high shearing pressures on oil shales at low temperatures and throughout relatively short periods of time are quantitatively not important in the generation of oil from such rocks. It is also pointed out that where the deformation of oil shales occurs even partly by fracture and under considerable containing pressures, an increase in volume is brought about which will cause a reduction of fluid pressures. Should pressure be proved to influence the change of organic matter in oil shales towards oil, this reduction of fluid pressures may be important in explaining any actual changes brought about in nature.