At present oil is the most important source of energy and for some applications it is irreplaceable, but till when will it be able to satisfy the growing demand of energy? The day will come when the production of oil shall reach a peak, after which it shall inexorably decrease with a consequent increase in prices. The distribution of the main oil basins around the world is not uniform, however it is not even random. In fact it depends on the geological conditions that are necessary for the formation of large deposits and the difficulty encountered to explore and search for oil in isolated scarcely known areas, as for example areas characterized by environmental conditions that are particularly severe (vast areas in Siberia, the rain forest area in South America and deep offshore areas). The geological history of our country is very complex and has given the peninsula a complicated and not very “tranquil” structural and sedimentary order. This has not favoured the formation of large extensive oil basins but has created local situations that are favourable for the formation of a number of oil provinces that are quite important, even though their extension is not great.
The non conventional hydrocarbon family includes compounds that differ greatly from one another, however they are all characterized by a high density and viscosity. The “heavy raw materials” are those oils whose density, according to the API (American Petroleum Institute) scale, is less than 25°, while the definition of viscous oils is a viscosity >50 cP (centiPoise; 10 Poise = 1 Pascal/s). Hydrocarbons with viscosity >10,000 cP and density <10° API (and therefore denser than water) are defined “extra heavy”. This latter category also includes tar extracted from sand and clay or oil shale.
Heavy hydrocarbons are also characterized by a significant content of foreign elements, such as sulphur (present in percentages up to 6-8%), nitrogen and heavy metals, in particular nickel and vanadium : all these components can create problems in the refining and manufacturing processes and can cause environmental pollution.
Non conventional hydrocarbons are generally found at modest depths (<1,000 m), and rarely below 3,000 m, because high temperatures decrease the viscosity; often the reservoirs are found in very porous sandstone. Heavy hydrocarbons are always on the bottom of the reservoirs, and they account for an important part of the reserves, however they can also be found in concentrations when the hydrocarbons migrate from the mother rock where they were produced (in the so called “oil window” at depths from 3,500 to 4,500 m), and undergo degradation and alteration processes (for example due to bacteria) or evaporation and dissolving processes of the lighter more precious fractions. Very often these can be found in large quantities in the basins of rivers that flow on the Earth’s surface (as for example in the Orinoco river basin in Venezuela), and it is in these areas that research is now concentrated.
The terms bituminous sand, tar sand and oil sand refer to sand deposits that are not cemented together, and are very porous, and contain non mobile viscous oils. The largest known accumulation is in the region of Alberta (Canada), with an accumulation of oil that is over 60 m thick, at depths ranging from 0 to 600 m, in porous sand. The oil that is produced has a high content of sulphur and a very high viscosity level (2 x106 cP).
Clays that are rich in organic substance are the most common mother rocks and many clays (oil shale) can contain large amounts of organic substance that has still not been completely transformed into hydrocarbons (kerogen), dispersed in small particles or concentrated in thin lenses or laminas: kerogen is typical in mother rocks that were never buried deep enough to generate hydrocarbons.
Where in the world
Exploiting non conventional hydrocarbons on a large scale began in the Eighties. These new fossil fuels initially contributed only small percentage amounts, but today they account for approximately 10-12% of the world production.
Research began (actually even before the Eighties) in California, Venezuela and Canada, which are considered the pioneer countries for this kind of research.
Non conventional reserves
It is not easy to estimate what lies underground, however it is believed that in the sedimentary rocks worldwide, there are probably 1.8 x 1012 cubic metres (approximately 12 x 1012 barrels) of liquid oil. Liquid hydrocarbons, even though they all belong to the same family, differ from one another. They are made up of compounds with different chemical and physical characteristics: oils, heavy oils, tar and very heavy oils.
Asphalts, tar and heavy oils are not a recent discovery, on the contrary, it may be said that these were the first hydrocarbons to be used by man. Since the dawn of human civilization, in fact, these were used for the most varied purposes: as a sealing and waterproofing material for boats and the roofs of houses, as a glue, as fuel for oil lamps and lights, and as a medication for wounds
The productivity of an oilfield depends on different factors, such as the permeability of the rocks of the reservoir, the pressure inside the oilfield, or the viscosity and density of the hydrocarbons that it contains: because of these limiting factors it is not possible to extract all the hydrocarbons in a reservoir, but only a percentage of the same. The “recovery factor” is an important index that makes it possible to evaluate the percentage of hydrocarbons that can be extracted in an economically profitable manner. Maybe not many people know that with the most well known and economical technologies that are currently in use, the percentage of recovery is surprisingly low: it rarely exceeds 50%. This means that in the known fields there is more or less the same amount of hydrocarbons as the amount extracted in the history of oil exploitation: an enormous quantity that, if made available in some way, would enable us to shift further the dreaded moment in which the reserves of fossil fuels shall inevitably finish.
Furthermore, till date, hydrocarbons have been available in sufficient amounts to cater to the demand, and only the best quality hydrocarbons, which are lighter and more liquid, have been extracted and utilized: a very large part of the hydrocarbons does not have characteristics that are suited for the refining process, as they are too dense, too heavy, too viscous or rich in unwelcome impurities, such as sulphur or heavy metals. However our economy and our energy production are necessarily still based on fossil fuels, and the need to dispose of this (for the time being) essential source of energy has intensified research and development programmes, thus leading research institutes and the principal oil companies to pay attention to what some already define (light-heartedly, but not seriously...) the “bottom of the barrel”.
Technologies for extraction
The basic concept for the recovery of non conventional oils is that the dense not very mobile hydrocarbons must be moved towards the extraction well. This is obtained in different ways: by increasing the permeability of the rock of the reservoir, by artificially creating pressure gradients in the oilfield, or by increasing the mobility of the oils by decreasing their viscosity.
Treatments for special hydrocarbons
In Estonia, oil shale is burnt directly in thermoelectric power plants, however this is one of the few examples of direct utilization of non conventional oils. Normally, heavy hydrocarbons cannot be utilized in conventional refinery plants: they are too dense and viscous and contain large quantities of substances such as sulphur or heavy metals. These require a prior treatment, known as upgrading, that transforms them into lighter hydrocarbons, which also purifies them from the more harmful substances.
The cost of extracting and treating non conventional hydrocarbons is about 10-20$ per barrel more than for conventional hydrocarbons: of these costs, approximately half are for improving the quality of the hydrocarbons (upgrading). Therefore this is not an economically profitable source, and its utilization will not make the price of oil drop.