Optimising the Use of Spent Oil Shale

Abstract

Worldwide deposits of oil shales are thought to represent ~3 trillion barrels of oil. Jordanian oil shale deposits are extensive and high quality, and could represent 100 billion barrels of oil, leading to much interest in the development of deposits. The exploitation of oil shales has raised a number of environmental concerns including: land use, water consumption, gaseous emissions and spent oil shale disposal.
To understand the environmental impact of spent oil shale, a study was conducted in Lothian, Scotland, providing a unique opportunity to examine the weathering process on aged deposits. Sequential extraction studies were conducted to determine the partitioning of trace elements within spent oil shale, soil and vegetation, with results demonstrating the stability of spent oil shale deposits.
The sequestration of CO2 within spent oil shale has the potential to reduce CO2 emissions associated with the retorting of oil shale. Jordanian spent oil shale was found to sequester up to 5 wt % CO2, on reacting under supercritical conditions, which is 68 % of the theoretical carbonation. Results show that the duration of reaction; gas temperature; CO2 pressure; and the interactions between these factors significantly affect the extent of carbonation.
The magnitude of the CO2 sequestration achieved was sufficient that it could lower CO2 emissions by up to 29 kg CO2/bbl, thereby bringing the emissions from oil shale processing in line with those from conventional oil extraction methods. Modification of the processing conditions was also considered: to reduce CO2 emissions, maximise oil recovery, and produce valuable by-products. Pyrolysis at 500 °C, combustion at 750 °C, and accelerated carbonation methods, may offer the greatest benefits for the processing of Jordanian oil shale.