In-situ conversion of low-to medium-mature organic-rich shales by nuclear irradiation

Abstract

Organic-rich shale is an important potential energy resource in the world. In situ organic-rich shale conversion has been discovery highly efficient to convert kerogen to oil through electric heating. However, the heating method is highly energy-consuming and less economically feasible. Finding other replaceable technique becomes an urgent task. Low-to medium-mature shale samples from continental freshwater and saline lake were irradiated by a cobalt-60-source with energy doses of 0.5 kGy, 1 kGy, 10 kGy, 100 kGy, and 1000 kGy. The changes of minerals and organic matters in shale were thoroughly monitored using various analysis including rock thin section, X-ray diffraction, scanning electron microscope, TOC, pyrolysis test, gas chromatography, and infrared spectrum. The results show that the TOCs of shale samples decrease gradually as irradiation doses increase and their organic matter functional group compositions change greatly. Irradiation reduces the content of long-chain hydrocarbons (especially C30+) in shale and generates short-chain hydrocarbons and gaseous substances. M-1 (Santanghu shale) and ZK-1 (Ordos shale) shows largest yields after irradiation, amount to 62 kg and 130 kg per ton shale respectively. Those two samples are S-rich shale which may have low activation energy for petroleum transformation from kerogen and thus benefit for hydrocarbon generation after irradiation. Therefore, we infer that the irradiation method can provide a new idea for the effective development of medium-to low-mature shale oil in the future, especially for those shales depositing at S-rich, saline, deep to semi-deep lacustrine environments.