One recurring question that geologists face is that of oil shale. Specifically, what potential does it have to solve the energy and economic problems that we face? Much research has been done on this material, and much of the work is well summarized by Munther Bseiso and by the late Yousef Hamarneh (updated by Jamal Alali and Suzane Sawaqed). A very short summery is available here. Herein, I will try to shed some light on this. First, I need to give some geological and geochemical background.
In oceans, most primary productivity (plant growth) is related to micro-organisms such as algae (like diatoms). When these microscopic plants die, they usually decompose though reaction with oxygen in the water column. If there is not enough oxygen to decompose all of the plants, then the available oxygen is used up and the environment becomes anoxic. Under this condition, organic material is preserved, and sediments deposited in such an environment become organic-rich sediments.
Because sediments rich in fine grained clay materials have low permeability (i.e. they don’t let water move through them), often such sediments are organic-rich because dissolved oxygen in the overlying water column can not reach the organic materials in the sediment to decompose them. When clay-rich sediments turn into rocks (or lithify), they are called shale. When organic-rich clay rich sediments lithify, they become oil shale.
Through time and changes in physical conditions, the organic material changes it’s molecular composition, changing into complex mixtures of materials that are broadly classified as being kerogen, bitumen, or hydrocarbons. Bitumen is defined to be all the organic material that can be dissolved in organic solvents, whereas kerogen is all of the organic material that can not. Both kerogen and bitumen are solid, whereas hydrocarbon is either liquid or gas. Subjecting kerogen or bitumen to heat can lead to the release of liquid petroleum or natural gas. This can be a natural process (petroleum generation) or a synthetic one (retorting).
In Jordan, the term “oil shale” has been applied to both organic rich shale-like materials called marls as well as to organic-rich limestones. All “oil shale” in Jordan is Upper Cretaceous to Paleocene in age (80 to 60 million years old), and belongs to the Muwaqqar Chalk Marl (MCM) Formation. The MCM is exposed over large areas of Jordan, and organic-rich sections of it are found in the north and center of the country. It has been estimated that the oil shale reserves in the country amount to about 50 billion tons, with an average organic content of about 10%. This reserve is enough to meet Jordan’s energy needs for hundreds of years.
Most of the organic component in the oil shale consists of kerogen, making the chemical separation of the oil from the rock virtually impossible. Options for exploitation are either direct burning of the rock for electricity generation or retorting to extract the oil from the rock by heat. In future posts, I will discuss these options.