An Investigation Into the Effects and Implications of Gamma Radiation on Organic Matter, Crude Oil and Hydrocarbon Generation

Abstract

Black shales are known widely for their ability to produce hydrocarbons from their rich organic makeup. This high TOC (total organic carbon) makeup brings a large amount of radioactive elements such as Uranium (U), Thorium (Th), and Potassium-40 (40K). As these radioactive elements decay, they all release energy in the form of gamma rays. The energy supplied from the gamma radiation can lead to radiolysis in organic materials, as shown with oleic acid in previous experiments (Howton et. al 1966). By breaking specific bonds with the use of radiation, it can be said that radioactive decay promotes mechanics that lead to the production of hydrocarbons. This was further investigated by using gamma rays produced by a cesium-137 core to break molecular bonds in oil samples also containing brine and clay minerals in the systems. By using fourier transform infrared spectroscopy (FTIR), the composition of the oil before and after irradiation was determined and the changes of the crude oil compositions were evaluated. The FTIR results signify that there are multiple changes in the oil samples. The samples containing both brine and clay minerals seem to have formed both a lighter oil fraction along with a heavier, more viscous oil fraction. The samples containing only brine and crude oil seem to have only formed a heavier, more viscous oil fraction based on an increase in the CH2 groups along with a decrease in CH3 groups. This increase in CH2 groups and decrease in CH3 groups would also be accompanied with the production of H2(g). When introduced to gamma radiation, this additional H2(g) in combination with H2(g) already present in source rocks may serve as a source of kinetic energy in these source rocks. The collision of the gases with various organic bonds may also help facilitate the generation of hydrocarbons. Organic material from the Woodford Shale was also irradiated with various amounts of gamma radiation then evaluated using a Rock-Eval pyrolysis. Differences in the control and irradiated samples of kerogens were then determined. These experiments may lead to answers about radiogenic maturation processes in hydrocarbons.

AAPG Datapages/Search and Discovery Article #90216 ©2015 AAPG Annual Convention and Exhibition, Denver, CO., May 31 - June 3, 2015